CA1131959A - High yield fiber sheets - Google Patents
High yield fiber sheetsInfo
- Publication number
- CA1131959A CA1131959A CA352,254A CA352254A CA1131959A CA 1131959 A CA1131959 A CA 1131959A CA 352254 A CA352254 A CA 352254A CA 1131959 A CA1131959 A CA 1131959A
- Authority
- CA
- Canada
- Prior art keywords
- hardwood
- high yield
- fibers
- softwood
- yield fibers
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H5/00—Special paper or cardboard not otherwise provided for
- D21H5/26—Special paper or cardboard manufactured by dry method; Apparatus or processes for forming webs by dry method from mainly short-fibre or particle material, e.g. paper pulp
- D21H5/2607—Pretreatment and individualisation of the fibres, formation of the mixture fibres-gas and laying the fibres on a forming surface
- D21H5/2628—Formation of a product from several constituents, e.g. blends of various types of fibres, fillers and/or binders or formation from various sources and/or streams or fibres
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
- A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
- A61L15/22—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons containing macromolecular materials
- A61L15/28—Polysaccharides or their derivatives
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
- A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
- A61L15/40—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons containing ingredients of undetermined constitution or reaction products thereof, e.g. plant or animal extracts
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
- D21H17/71—Mixtures of material ; Pulp or paper comprising several different materials not incorporated by special processes
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
- D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
- D21H23/04—Addition to the pulp; After-treatment of added substances in the pulp
- D21H23/06—Controlling the addition
- D21H23/08—Controlling the addition by measuring pulp properties, e.g. zeta potential, pH
- D21H23/10—Controlling the addition by measuring pulp properties, e.g. zeta potential, pH at least two kinds of compounds being added
Abstract
HIGH YIELD FIBER SHEETS
James C. Williams ABSTRACT
Wet-laid sheets of softwood high yield fibers in combination with hardwood high yield fibers. The sheets, which are strong enough to be handled by commercial equipment, are formed on conventional papermaking machines using a furnish comprising a major proportion of softwood high yield fibers in admixture with a minor proportion of hardwood high yield fibers. The hardwood high yield fibers are specially prepared by a procedure comprising treating hardwood with relatively high levels of chemicals under relative stringent conditions and defibrating the treated hardwood with relatively high levels of power input. Airfelts made from these sheets exhibit low wet densities. Processes for making the sheets and the airfelts are also pro-vided.
James C. Williams ABSTRACT
Wet-laid sheets of softwood high yield fibers in combination with hardwood high yield fibers. The sheets, which are strong enough to be handled by commercial equipment, are formed on conventional papermaking machines using a furnish comprising a major proportion of softwood high yield fibers in admixture with a minor proportion of hardwood high yield fibers. The hardwood high yield fibers are specially prepared by a procedure comprising treating hardwood with relatively high levels of chemicals under relative stringent conditions and defibrating the treated hardwood with relatively high levels of power input. Airfelts made from these sheets exhibit low wet densities. Processes for making the sheets and the airfelts are also pro-vided.
Description
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HIGH YIELD FIBER SHEETS
James C. Williams TECHNICAL FIELD OF THE INVENTION
This invention relates to wet laid sheets of high yield wood pulp fibers, which sheets are prepared : on conventional paper-making mac~ines, and to air-`: 5 laid, non-woven webs which are subsequently made ` from these shee~s of high ~ield wood pulp fibers.
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1131~59 , BACKGROUND ART
Absorbent articles such as disposable diapers, sanitary napkins, and the like, manufactured from wood pulp have become staple items of commerce.
Heretofore, these items have been primarily made from chemical pulp (e.g. wood pulp made by the sulfite process or by the kraft process).. While these absorbent articles have been of good quality, the use of chemical pulp offers certain disadvantages. One major disadvantage is inherent in the chemical pulping process itself.
Only about 50% of the wood entering the chemical pulping process is recovered as pulp. The remaining fraction of the wood, as well as the concentrated chemicals used in the pulping process, contribute to both atmospheric and ground water pollution unless expensive steps are taken to control plant emissions.
Ano~her disadvantage of the use of chemical pulp in absorbenL articles is the relatively low bulk of the chemical pulp. (Bulk, the reciprocal of density, is a measure of the ability of wood pulp to make a pro-;~ duct of low inherent density.) Wood pulps having high bulks make products with low densities. Since absorbency is inversely related to density, products with low densities are more absorbent on a weig~lt basisthan are products with high densities. The use of a wood pulp with higher bulk allows the manufacture of a product having relatively greater absorptive cap-acity on an equal weight basis than a similar product made from wood pulp with lower bulk. Alternatively, on an equal absorptive capacity basis, products made from a wood pulp with higher bulk will contain a smaller quantity ~`.` -. .
of fiber than a product made from wood pulp with lower bulk.) In more recent times, these two described dis~dv~n-ta~es have been at least ~artially overcome throu~h the u~e of high yield fiber~ As used herein, the term "~igh yield fiber" denotes a wood pulp which is made by a process which allows significantly more of the entering wood to be recovered as wood pulp fiber than do the conventional sulfite or kraft pulping processes. High yield fibers are classified into numerous different types.
One of the oldest and most widespread nigh yield fibers is known as groundwood. It is produced by mech-anically reducing the wood to fibers as by pressing th~ wood against a rotating stone. Groundwood, which is sometimes known by the generic term mechanical pulp, has found little application in absorbent articles such as diapers - because this method of fiber~separation leads to significant fiber shortening~and dama~e before a reasonably low level of~fiber bundles, i.e. shives, is obtained.
Another form of mechanical pulp which has found somewhat greater use in absorbent products is broadly kno,wn as thermomechanical pulp. Thermomechanical pulp, which is generally attributed to the work o Asplund and his coworkers as described in U.S. Patent
HIGH YIELD FIBER SHEETS
James C. Williams TECHNICAL FIELD OF THE INVENTION
This invention relates to wet laid sheets of high yield wood pulp fibers, which sheets are prepared : on conventional paper-making mac~ines, and to air-`: 5 laid, non-woven webs which are subsequently made ` from these shee~s of high ~ield wood pulp fibers.
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1131~59 , BACKGROUND ART
Absorbent articles such as disposable diapers, sanitary napkins, and the like, manufactured from wood pulp have become staple items of commerce.
Heretofore, these items have been primarily made from chemical pulp (e.g. wood pulp made by the sulfite process or by the kraft process).. While these absorbent articles have been of good quality, the use of chemical pulp offers certain disadvantages. One major disadvantage is inherent in the chemical pulping process itself.
Only about 50% of the wood entering the chemical pulping process is recovered as pulp. The remaining fraction of the wood, as well as the concentrated chemicals used in the pulping process, contribute to both atmospheric and ground water pollution unless expensive steps are taken to control plant emissions.
Ano~her disadvantage of the use of chemical pulp in absorbenL articles is the relatively low bulk of the chemical pulp. (Bulk, the reciprocal of density, is a measure of the ability of wood pulp to make a pro-;~ duct of low inherent density.) Wood pulps having high bulks make products with low densities. Since absorbency is inversely related to density, products with low densities are more absorbent on a weig~lt basisthan are products with high densities. The use of a wood pulp with higher bulk allows the manufacture of a product having relatively greater absorptive cap-acity on an equal weight basis than a similar product made from wood pulp with lower bulk. Alternatively, on an equal absorptive capacity basis, products made from a wood pulp with higher bulk will contain a smaller quantity ~`.` -. .
of fiber than a product made from wood pulp with lower bulk.) In more recent times, these two described dis~dv~n-ta~es have been at least ~artially overcome throu~h the u~e of high yield fiber~ As used herein, the term "~igh yield fiber" denotes a wood pulp which is made by a process which allows significantly more of the entering wood to be recovered as wood pulp fiber than do the conventional sulfite or kraft pulping processes. High yield fibers are classified into numerous different types.
One of the oldest and most widespread nigh yield fibers is known as groundwood. It is produced by mech-anically reducing the wood to fibers as by pressing th~ wood against a rotating stone. Groundwood, which is sometimes known by the generic term mechanical pulp, has found little application in absorbent articles such as diapers - because this method of fiber~separation leads to significant fiber shortening~and dama~e before a reasonably low level of~fiber bundles, i.e. shives, is obtained.
Another form of mechanical pulp which has found somewhat greater use in absorbent products is broadly kno,wn as thermomechanical pulp. Thermomechanical pulp, which is generally attributed to the work o Asplund and his coworkers as described in U.S. Patent
2,008,892 (July 23, }935) and its progeny, involves the mechanical defibration of wood after the lignin has been softened by steaming.
Semi-chemical pulp, sometimes known as chemi-mechanical pulp, or semi-mechanical pulpl is a refinement of the basic thermomechanical process. Here, wood chips are given a mild che~ical treatment during a heating step prior to mechanical defibration in a device ..
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such as a rotating disc defibrator. The chemical treat-ment is limited so as to merely sorten the lignin rather t~an completely remove it as in conventional chemical pulping processes. Workers such as Beverage and Keough S in U.S. Patent 2,422.522 (June 17, 1947), Beverage, Keough and Surino in U.S. Patent 2,425,024 (August 5, 1947) and Asplund, Cederquist and Reinhall in U.S. Patent
Semi-chemical pulp, sometimes known as chemi-mechanical pulp, or semi-mechanical pulpl is a refinement of the basic thermomechanical process. Here, wood chips are given a mild che~ical treatment during a heating step prior to mechanical defibration in a device ..
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such as a rotating disc defibrator. The chemical treat-ment is limited so as to merely sorten the lignin rather t~an completely remove it as in conventional chemical pulping processes. Workers such as Beverage and Keough S in U.S. Patent 2,422.522 (June 17, 1947), Beverage, Keough and Surino in U.S. Patent 2,425,024 (August 5, 1947) and Asplund, Cederquist and Reinhall in U.S. Patent
3,338,525 (August 29, 1967) have described semi- --chemical ~igh yield fiber processes.
Also within the prior art is a semi-chemical high yield fiber process which yields a product having relatively high bulk and a relatively low shive content.
This particular process comprises the steps of preheating wood chips, treating the heated chips with a chemical solution which comprises sodium sulfite and, optionally, basic chemicals, at such a concentration as to yield pulp having a pH greater than 5.7. The chips are then mechanically defibrated to pulp with an energy con-sumption of less than about 600 kilowatt hours per metric ton of pulp produced. (Anonymous, Research Disclosures, March, 1978, p. 20.) Generally speaking, following the pulping operation high yield fibers are formed into sheets by any of several well kno~m wet forming processes typified by the conventional Fourdrinier process. (The operation of forming the wood pulp fibers into sheets is sometimes known as lapping.) The sheets are then usually dried with conventional equipment. For use in absorbent products such as tiapers, the sheets are comminuted and the hi~h 3U yleld fibers are formed into absorbent products known as alrfelts.
The high yield fibers most preferred for use in absorbent products such as diapers are generally derived from softwoods ~gyl~#æ~so). One of the problems ~ '~' , ,, . :
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associated with the use of these softwood high yield fibers in absorbent products heretofore has been the weakness of the sheets of pulp fibers. These . sheets must be strong enough to be handled by commercial - equipment during the airfelt making process, but sheets of the preferred softwood high yield fibèrs are generally too wea~ to be used as is. In fact, it is impossible to form sheets at all from some of the most preferred softwood high yield fibers.
One way the strength of the sheets has been improved has been by mechanically refining the fibers. This operation, which is kno~m to increase strength in almost all papermaking areas, suffers from the disadvantages of increased cost and those effects which flow from the mechanical damage to fibers caused by the refining process, e.g. increased fines, lowered drainage rate, increased density, lowered absorbency. Refining is not, however, necessarily effective with all softwood high yield fibers.
Sheet strength has also been improved by adding a~quantity of chemical pulp to the softwood high yield fibers. Chemical pulp,which may comprise up to 25% or more of the total pulp mixture, can optionally be refined in the wet state prior to its addition to the pulp blend. While tbe addition of chemical pulp does increase the strength of the wet laid sheets of softwood high yield fibers, certain adverse effects do occur. One of the most readily apparent, of course, is the increased cost of the total fiber mixture which re~ult~ fro~ the repla~ement of relatively low cost high yield fiber with relativel~J high cost chemical fiber. A second, more subtle adverse effect is the increase in wet density of the airfelt which results when chemical fibers are blended with the softwood high yield fibers.
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Sg High yield fibers are essentially non-delignified;
that is, m~st of the lignin remains with the cellulosic fiber. This lignin contributes to the stiffness of the fiber. It has been found that these stiff fibers form air-felts having lower wet density than do conventional chem-ical pulp fibers. That is, if equivalent airfelts are formed from chemical pulp fibers and from stiff, non-deligniied, high yield fibers, and the airfelts are compressed dry to the same initial density, the high yield fiber airfelts exhibit lower density when wet and under load than do the chemical pulp fiber airfelts.
~lthough Scott, in U.S. Patent ~,642,359 (June 16, 1953) has suggested that the strength of a pulp sheet can be enhanced by incorporating into the fiber furnish from which the sheet is made a quantity of short fibers which tend to bind together long fibers, it is well-kno~m in the art that hardwood high yield fibers (which are generally shorter than softwood fibers) contribute to the~weakness~of~sheets of fibers.
There are basic~anatomical differences between ftwoods and hardwoods. The arbitrary term softwood and hardwood designate~,~respectively, trees having needle or~scalelike leaves and~trees having broad leaves~which are deciduous in temperate zones.
The hardness or density of the wood is not involved.
While there are diferences between the chemical structures o~ hardwood and softwoods, the important difference,for this invention, lies in the variation ~ ~ in cell structure. Softwoods for the most part ;~ 30 are made up of cells whose len~th is several hundred times their dia~eter. That is, even though barely visible to the eye, they are threadlike. Hardwoo~s, on the other hand, are made up of a wider variety of cell types characterized by a length to diameter , .
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~ 1131959 ratio which may run from 1:1 to 20:1. Hardwood fiber is generally considered to be inferior to softwood fiber for certain applications. Because its ratio of length to diameter is so much smaller, the bonding between fibers is poorer because -the inter-fiber crossings per fiber are fewer and the bond area of each is smaller. Consequently, a sheet is generally weaker when it contains hardwood fibers. Grandis commented on the lower strength properties of nardwood sheets relative to softwood sheets in a paper entitled "Poplar Groundwood in Different Grades of Paper" delivered the EU~EPA Symposium on Mechanical Pulp held in Oslo, Norway during June, 1970, as reported in the Abstract Bulletin of the Institute of Paper Chemistry, Vol. 42, No. 3, Abstract No. 2647 (September, 1971).
DISCLOSURE OF THE INVENTION
This invention concerns sheets of softwood high yield fibers which have adequate strength for commercial usage and which have been formed by wet-laying tech-niques. Adequate strength is obtained by blending with the softwood high yield fibers a quantity of hardwood high yield fibers which have been specially prepared. The special preparation comprises treating hardwood chips with relatively high levels of chemicals for relatively long periods of time and defibrating the chips with rçlatively hi~h power input. The blended fibers are formed into sheets by conventional processes. The sheets are then used in the m~nufacture of airfelts made by other conventional processes.
Accordingly, it is an object of this invention to provide dry sheets of wood pulp fibers, said sheets having adequate strengt'n for commercial processin&.
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It is an object of ehis invention to prov~de sheets comprised of relatively undamaged, substantially non-delignified, softwood high yield fibers, said sheets having adequate strength for commercial usage.
It is an object of this invention to provide airfelts having improved wet density properties.
It is a further object of this invention to provide a process for preparing the above-mentioned sheets of fibers.
It is a still further ob~ect of this invention to provide a process for preparing the above-mentioned airfelts~
These and other ob~ects will become readily apparent from a reading of the Detailed De~cr~ption of the Invention which follows~
The present invention,in one aspect, resides in a wet formed sheet comprising a major proportion of 6ubstantially non-delignified and relatively undamaged softwood high yield fiber6 having a Canadian standard freeness value greater than about 700 ml and a minor porportion of hardwood high yield fibers, said hardwood high yield fibers having a Canadian standard freeness value of ~rom ~bout 50 ml to about 400 ml wherein said hardwood fibers have been prepared separately from said ~oftwood fibers and with ~ignificantly more stringent pretreating and defibrating conditions than have been used to prepare 6aid softwood fibers.
In another aspect, this invention resides in a process for preparing sheets of high yield wood pulp fibers comprising the stops of:
~ a) providing substantlally non-dellgnifiod and rolatively undamaged softwood high yield fibers having a Canadian standard freeness value greatex than about 700 ml;
(b) providing hardwood high yield fibers having a Canadian standard freeness value of from about 50 ml to about 400 ml;
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(c) preparing a papermaking ~urnish from said softwood high yield fibers and said hardwood high yield fibers; and (d) wet forming 6aid sheet6 from said papermaking furnish wherein said 60ftwood high yield fibers are provided in a major proportion compared to 6aid hardwood high yield fibers and said hardwood fibers are provided in a minor proportion compared to said so$twood high yield fibers and wherein said hardwood fibers have been prepared separately from said softwood fibers and with significantly more stringent pretreating ~nd defibrating conditions than have been used to prepare said ~oftwood f~bers.
In a ~u-thcr aspect, the prc30nt invention residcs in a process for preparing airfelts comprising the steps of:
(a) comminuting sheets of high yield wood pulp fibers; and (b) airlaying sa$d comminuted high yield wood pulp fibers wherein said sheets of high yield wood pulp fibers comprise a major proportion of substantially non-delignified and relatively undamaged softwood high yield fibers having a Canadian standard freeness value greater than about 700ml and a minor proportion of hardwood high yield fibers,-6aid hard-wood high fibers having a anadian standard freeness value of from about 50 ml to a~out 400 ml and wherein ~aid hardwood fibers have been prepared separately from said 60ftwood fiber6 and with significantly more ~tringent pretreating and defibrating conditions than have been used to prepare said oftwood iibers.
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- 8b-1131959 etailed Description of the Tnvention While this specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as the invention, it is believed that the invention will be better understood through a reading of the followin detailed description of it and of the non-limiting example appended thereto.
This invention is directed not only to the pro-duction of dried sheets comprised totally or substantially of high yield fibers and to the production of airfelts from such sheets, but also to the dried sheets of fibers and to the airfelts per se. The invention can best be described, however, in terms of several distinct process operations.
The improved sheets of this invention are comprised primarily of high yield fibers derived from softwoods (gpl~sp~s~). Any of the softwood species com~only used for making paper ~,.
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_~ 1 31 9 5 9 pulp can be used. Suitable species include Picea ~lauca (white sprucej, Picea mariana (black spruce), Picea rubra (red spruce), Pinus strobus (white pine), Pinus caribeau (slash pine), and Pinus tadea (loblolly pine). The last named species is a preferred one for use in this invention.
Processes for convereing softwoods to high yield fiber pulps are relatively well known in the art.
The one described in the following paragraphs can be used advantageously in the practice of this invention, but this invention is not to be considered limited to the use of this process.
Softwood trees are reduced to chips and the - chips are optionally washed using~equipment ant processes c~mon in the pulp industry. The washed chips are held in storage bins until they are needed in the pulping process.
The pulping process begins when the washed wood chips are removed fro~ the chip storage bin and are conveyed by any suitable neans to a presteamer.
In the presteamer, the te~perature of the chips is raised from ambient up to any desired level below about 99C by the introduction of steam. The purpose of the presteamer, which can be any suitable vessel, is to raise the temperature of the chips and expel much of the air associated with them.
From the presteamer, the chips are conveyed to a treatment unit. A suitable conveying device is a screw conveyor, optionally tapered, which tends to compress the chips. Not only does such a device move the chips and seal the treatment unlt against pressure 1088, but it also materially aids in the impregnation of chips during the treating step.
The chips which have been compressed in the screw conveyor are discharged in that compressed condition .
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into the treatment unit below the surface of the treat-ment liquor contained therein. When the mechanical pressure on the chips is reduced as the chips are introduced into the treatment unit, the chips expand - 5 and absorb treatment liquor.
During the treating step performed in the treatment unit, the chips are impregnated wit~ treatment liquor and are maintained at elevated temperature and pressure for a prescribed length of time.
A suitable treatment unit comprises two elements: an impregnator and a retention chamber.
The impregnator preferably comprises a cylindrical vessel oriented with its axis vertical. This cylindrical vessel is provided~with a first means adapted for the introduction of treatment liquor into the impregnator and with a second means adapted~for the moving of chips vertically through the cylindrical vessel to a point where they are allowed to exit the~vessel. The first means can be any arrangement of valves and piping the specification of which is well within the ability of one~skilled in the~art. Provision of a region equivalent to a pool of treatment liquor within the impregnator is desirable. The second means can be a vertically oriented screw conveyor.
Preferably, the impregnator is contained within a larger pressurized outer vessel wherein elevated pressure and temperature are maintained by the introduction of steam. The impregnator is preferably situated in the upper regions of this pressurized outer vessel and a portion of the lower regions provides a retention chamber. After exiting the impregnator, the chips and the treatment liquor associated therewith are allowed to fall ~ 31959 by gravity through the atmosphere of the pressurized outer vessel into the :retention chamber where they are held for a prescribed time.
The treatment liquor is an aqueous solution which facilitates,-without removing substantial quantities of lignin, the defibration of wood chips into substantially undamaged fibers in the subsequent defibration step. It can be water or any suitable chem-ical solution commonly used to prepare thermomechanical, I0 semi-chemical or chemi-mechanical high yield fibers.
A preferred treatment liquor is one comprising as treatin~
agents sodium sulfite and sodium bisulfite, each pre-~; sent at about from about 2% to about 6% by weight of-dry pulp. Other suitable treatment liquors can contain as lS treating agents alkali ~etal sulfite, alkali metal bisulfite, sulfur~dioxide in combination with alkali metal hydroxide, or mixtures thereof. The treatment liquor can optionally contain minor amounts of materials for~penetration and mineral control.
~;20 Suitable treatment temperatures fall within the range of about 124~C~to about l9QC, preferably from about 125C to~about~160~C. ~The pressure within the~treatment unit~is that~stream pressure which corresponds~to the~temperature chosen.
25~ T~e average~res~idence time of a chip at elevated temperature~in~the retention c~amber is ~rom about l to about 60 minutes, preferabIy fro~ about 1 to about 6 minutes.
When loblolly pine is used in this invention, the treatment liquor~preferably comprises about 3% sodium sulfite and about 3% s~odiu~ bisulfite. The chips are preferably treated at a temperature of about 158C for about 5 minutes.
As indicated above, there is maintained in the impregnator an amount of treatment liquor ., -;' ' ' ,, , ~: , ..
~13~59 sufficient to provide an excess of liquit when the ch~ps are fully impregnated. The quantity of treatment liquor absorbed by the chips is dependent upon the species~ the previous history of the chips, and the exact equipment and operating parameters used.
Typically> for the equipment described above, the chips are impregnated with from about 30% to about 70% by weight treatment liquor based on the bone dry weight of the wood, From the treatment unit, the treated wood chips pass to the defibration unit through the use of any suitable device such as a screw conveyor.
The defibrator can be any of the well known units used in the manufacture of thermomechanical or Asplund pulp. Specific examples are the Defibrator L-42 and the Asplund defibrators types 0VP-20, ~LP-SOS, and PT-P-54S. All of these units comprise one stationary disc and one rotating disc. Optionally, the defibration units can h~ve two rotating disks.
Disc designs can be any of those commonly used in the manufacture of ther mechanical or Asplund pulp .
Defibration is usually accomplished at from about 124 to about 160C at a consistency of about 25+ ~" by weight. Water or chemicals can be added to the treated chips im~ediately prior to their entry into or after their exit from the defibrator to adjust the consistency and to serve other purposes such as bleac~.ing.
3n Power input to the defibrator is controlled, as b~ ad~usting the clearance between the dlscs, so that t:~e treated chips are defibrated to a pulp of acceptably high bulk while the level of shives is ma;ntained at acceptably low levels. It is preferred that t'ne fibers be left essentially intact and undamaged.
t~en loblolly pine is used, and is treated as described hereinjefore~ a power input of approximately 140 to aboue 450 kilowatt hours per metric ton is suitable.
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~-- 113~959 From the defibrator, the pulp passes to a bleac~ing unit wherein it is bleached. Optionally, the bleaching step can be omitted at this point in the processing scheme, but it is then performed later after the softwood high yield fibers are ~e~--with the hard~ood high yield fibers.
Any of the con~entional bleaching processes well known to those skilled in the pulp art can be used.
For example, hydrogen perox~de, sodiu~ peroxide, or hydsosulfite can be used. Various bleaching systems are describet in t~e BleachinR of Pulp, W. H. Rapson, Editor, TAPPI Monograph Series No. 27, (New York, 1963).
The fibers at this point in the process are presented as an aqueous slurry. They can either be directly incorporated in the form of this aqueous slurry into the furnish from which the dry sheets of this invention are mate, or they may be dried by conventional bulk drying metnods. In the latter sit~ation they are redispersed i.- wa-~er as 2art of the sheet maki,lg process.
The softwood high yield fibers are relatively undamaged and substantially non-delignified. Relatively unda~aged means that at least the majority of the indi~îdual fibers are rendered into pulp while retaining the length at ~hich tney were present in the raw wood and that at least the majority of the fibers do not present the typical appearance of fibers which have been mec~anically refined. Subatantially non-teli~nified means that associated with the flbers i9 a quantity . of lignin substantially greater than that associated with those fibers from the same wood source which ha~e been rendered into pulp by the conventional sulfite or kraft processes.
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h 1131959 The Canadian standard freeness value (CSF) of the softwood high fibers useful in this invention is greater than about 700 ml. as determined according to T.A.P.P.I. Method.T-227 OS-58. -The second component of the sheets of this invention are high yield fibers prepared from hardwoods (angiosperms). ~uitable~hardwoods include, for example, a}der, aspen, oak, and gum~
The high yieId fibers prepared from hardwood are prepared in a manner analogous to that used for the softwood high yield fibers, but with significantly more stringent pretreating and defibrating conditions.
~ The treatment liquor can contain as a treating agent ; alkali metal sulfite, alkali metal bisulfite, sulfur 15~ dioxide in combination wit~h alkali metal hydroxide, or mixtures thereof. Sodium-is the preferred alkali metal.
The levéls of~treating;agent in~the treatment liquor can be from about 2% to~about 40% by~weight.~ The treatnent liquor can optionally contain minor amounts of materials for~penetra;tlon and~mlneral~control. For example, when mixed hardwoods~, predominately gum, are used, the treatment liquor~preferably ~comprises from about 2% to about 20% by weight sodium sulfite and from about 2 to about 20% by weight sodium bisulfite. A5 above, the quantity o~ treatme~t liquor abs~rbed by the c~ips i9 `dependent on ~any factors. Absorption levels of 100%
or greater by ~eight of treatment liquor are possible.
The chips are treated at about 130 to about 190C
for from about~l to about 60 minutes and are defibrated ~ 30 with a power input during defibration of from about 155 ;- to about 500 kilowat~t hours per metric ton of treated hardwood.
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-15- 1131~59 The hardwood high yield fibers can then be bleached in a bleaching unit as described above for softwood high yield fibers. Optionally, the bleaching step is omitted at this point in the processing scheme, but it is then performed later after the ~wo types of high yield fibers are blended.
Canadian standard freeness (CSF) values of the hardwood high yield fibers are determined according to T.~.P.P.I. Method T-227 OS-58, Preferably, the CSF of the hardwoot high yield fibers used in this invention ~s between about ~ ml.
and about 400 ~i.
The softwood high yield fibers and the hardwood high yield fibers described above, bleached or optionally unbleached, are mixed in the wet state to prepare the papermaking furnish which will be used to form the sheets of this invention. ~ile no special techniques or precautions are required in the mixing opera~ion, ~.~hich can be performed using equipment and techniques well known in the art, techniques which tend to retain any fines associated with the hardwood high vield fibers are preferred. There should be present in the furnish a major proportion of softwood high yield fibers and a minor proportion of hardwood high yield fibers.
The weight ratio of softwood to hardwood high yield fibers should be from about 2.33:1 to about 19:1, preferably from about 5.67:1 to about 15:1.
If the two types of high yield fibers have not been bleached earlier in the processin~ scheme, they can be , bleached after mixing. Any of the ~leachin~ techniques described above can be used.
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The slurry comprising the mixture of bleached softwood high yield fibers and bleached specially prepared hard-wood high yield fibers is used as the furnish to form the sheets of this invention. Any of the various wet-forming techniques well known in the art for forming sheets of fibers can be used. Of particular usefulness are the various mod~fications of the well known Fourdrinier process. In general, this process involves adjusting the~
furnish to the appropriate consistency, applying the furnish to a moving foraminous surface such as a Fourdrinier wire, allowing excess water to drain from the fiber mat 80 formed through the foraminous surface, and sub~ecting the drained fiber mat to various pressing operat~ons so as to expel more water.
The coherent fibrous web is then dried by any convenient means such as a drying tunnel or rotating drum dryer. The dried sheet of fibers, which has significantly improved strength over an all-softwood high yield fiber sheet, is then cut into convenient sections or is wound upon a core to form a convenient sized roll.
Bursting Strength of the dried sheet is measured by T.A.P.P.I. Method T-403 OS-76, Tensile Strength by T.A.'P.P.I. method T-404 OS-76, and Tnternal Tearing 2~ Resistance (Tear) by T.A.P.P.I. method T-44 TS-65.
The thic~ness of a dried sheet is measured using a motorized micrometer which applies a load of 0.50 kg. per square centimeter using an anvil having a diameter o~ 1.60 centimeters.
The airfelts of this invention ase prepared f,,rom the hereinbefore described sheets by a process comprising the steps of comminution, airlayin~, and, optionally, compaction.
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Comminution (i.e. the mechanical separatiDn of the sheets into essentially individual fibers) is accomplished by any of the equipment and processes - well known in the art. Examples are found in U.S. Patent 3,750,962 which was issued to Morgan on August 7, 1973 and in U.S, Patent 3,519,219 which was issued to Sakulich et al. on July 7, 1970.
Following comminution, the separated high yield fibers are formed 10 into a fibrous web by airlaying with equipment and processes common in the art. U.S. Patent 3,772,739 ~which issued to Lovegrin on November 20, 1973, ~illustrates a suitable 2airlaying process and provides a thorough discussion 15 of airlaying technology. The airlaid web is optionally compressed by means well known in the art.
The apparent wet density of an airfelt is determined :on a pad which has been compressed to a uniform ~ density and which has been loaded witn synthetic urine.
The airfelt to be tested is prepared by airlaying 42 gr~s (dry basis) fiber as a 35.6 centim~ter square pad.
This pad is then cut into 10.2 centimeter square sections for testing. Any tissues on the sections are carefully + re~oved. The section is co~pressed to such a thickness 3 25 which will result, when the compressing load is ~, renoved, in an airfelt having a density of 0.10+ 0.01 ~ gra~ per cubic centimeter. (Unless otherwise specified, when thethickness of an airfelt must be determined, as when densities are determined, the thickness is ~easured under a load of 1~.4 grams per square centimeter.) The densified section is placed on a planar surface and sprayed uniformly with a quantity of synthetic urine equal to three times the dry weight of the airfelt section. The wetted section is subjected --, -.
, ` -18- 1 1 31 ~ 59 to a loading of 2~2 grams per square centimeter The load is removed and the section is subjected to a load-ing of 12.4 grams per square centimeter. The load is removed and the section is subjected to a loading of 35.2 grams per square centimeter~ The load is removed and the section is allowed to recover for 60 seconds. The section is then subjected to a loading i of 2.2 grams per square centimeter. The load is removed and the section is then subjected to a loading of 12.4 grams per square centimeter and the thickness of the section under this loading is recorded.
The apparent wet density of the section is determined by dividing the dry weight of the section (in grams) by 104 times the last above measured thickness (in l~ centimeters) of the section.
As used herein, synthetic urine is a 1%
(weight) aqueous solution of sodium chloride which also contains 0.0025% octylphenoxy polyethoxy ethanol nonionic surfactant.
2~ The wet burst strength of the airfelt is i measured by deter~ining the force required to rupture the sample used in the apparent wet density ' test with a rod provided with a 1.~ centimeter diameter ! spherical end, traveling at.the rate of 1~.7 centimeters per minute, while the sample is secured bet~7een plates having superi~posed 6.35 centimeter-diameter ~ orifices.
i . ~hen intended f^r use in products such as - disposable diapers, the airfelt has 8 basis wcight of from about 240 to about 420 grams per square meter and a ~, dry tensity of ~rom about 0.08 ~o ~hout 0.~8 ~rams per cubic centimeter. Those skilled in the art can readil~y adjust these parameters to suit the particular end product ¦ use. Diapers can be made from the airfelt according . .
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1131~S9 .
~ -19-to the teachings of U.S. Patent Re. 26,151 which was ;
issued to Duncan and Baker on January 3l~l962~
Other absorbent products, such as sanitary napkins, - 5 incontinent pads, surgical bandages, and the like, ; can be prepared from the airfelts of this invention by means well known in the art.
As shown by the following example, one of the prominent features of the airfelt of this invention 10 is its improved wet density property.
The follow~ng example ~s presented to more fully describe the invention disclosed herein " and not by way of limitation.
Chips having a nominal length of 1.6 centimeters -~ were prepared by standard techniques fro~ debarked ~ loblolly pine logs. These chips were used to make ;~ softwood high yield fibers by the techniques and with the equipment hereinbefore described.
The cnips were heated in the presteamer to ~; a temperature of 93 by the use of steam. From ~~ the presteamer, the heated chips were conveyed by a screw conveyor to the impregnator of the treatment 25 unit where they were impregnated with a treatment liquor co~prising 4.5% (weight) sodium sulfite, 4.5~ sodium bi-sulfite and ~inor amounts of chemicals for mineral and penetration control, The chips retained 3%
- sodium sulfite and 3% sodium bisulfite, (The latter v 30 percentages are in terms of weight on the basis o oven dry wood,~ The impregnated chips were re~oYed from -.
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the i~pregnator by a screw conveyor and were allowed to fall through the atmosphere of the pressurized outer vessel to the retention chamber where they were retained for 5 minutes at 158C. The impregnated, heated chips were conveyed by screw conveyor to an L-42 defibrator fitted with type 10782 plates. The chips were ,, defibrated with a power input of 177 kilowatt hours ' per metric,ton of pulp. `Defibration was accomplished ¦ at 27% b~ wei'g~t cons~stenc~ The pH of t~e pulp 1~ ex~ting t~e def~brator was controlled, The softwood high yield fibers were washed with softened water and were bleached with sodium peroxide using standard bleaching techniques. The bleaching solution comprised 6% (by weight) hydrogen peroxide, 5% 41 Be sodium silicate, ~%
sodium hydroxide, 0.5C/o magnesium sulfate, and 0.15VZ DTPA. The bleaching was accomplished at a consistency of lz~r in two hours at 82C. The ,~, resulting pulp slurry was neutralized by the addition ', 20 of sulfur dioxide. A second bleaching operation using 1% sodium hydrosulfite and 0.2% sodium tripolyphosphate was conducted at ~% consistency ~,' ' for 1 hour at 50C. The resulting pulp had a I CSF of about 750 milliliters.
; 25 Chips having a nominal length of 1.6 centimeters were prepared from debarked gu~ logs. Hardwood 1' high yield fibers were prepared in the same equipment using the same techniques as were used to-prepare the softwood high yield fibers with the exception that 0 the chips were impregnated with a sufficient quantity of a treatment liquor comprising 7.8% (weig'nt) sodium sulfite, 7.8% sodium ~isulfite and a mlnor amount o~
mineral control agent to provide 10% sodium sulfite and ,, ~ ~o 11319S9 sodium bisulfite, (The latter percentages are in terms of weig~t on the basis of oven dry wood.~ T~e ~m-pregnated chîps ~ere held in the retention c~amber - for 3Q minutes at 177C, During defibrating, the power input was 296 ~ilowatt hours per metric ton.
Following bleaching as immediately hereinbefore described, the hardwood high yield fibers had a CSF of about 230 ~ milliliters.
- Blends of 10~/~ (by weight), 15%, and 20% hardwood -~, 10 high yield fiber and, respectively, 90%, 85%, and 80%
a softwood high yield fiber were prepared and sheets were made on a conventional wet forming papermaking machine. It should be noted that skilled artisans - were unable to prepare a sheet from a furnish comprising 100% of the softwood high yield fibers of this example.
For comparison purposes, a control sheet was made from a blend of 90% of the above-described softwood high yield fiber and 10% northern kraft pulp refined to a CSF of approximateIy 270 milliliters. Also for comparison purposes, sheets were made from 10070 chemical co~mirution grade pulp prepared from un-refined southern pine fibers.
The tests described above were conducted on the finished sheets. In ~ddition, airelts were prepared by standard techniques from the sheets of fibers.
The above described tests were used to evaluate the wet properties of these airfelts.
While the sheets having 10% and 15% hardwood high yield fiber were strong enough t-o be handled on commercial equipment, they exhibited slightly lower tensile strengths than the control sample.
At the same time, they exhibited somewhat greater tear strength than did the control. The sheet con-'~' ~i~195~
taining 20% hardwood high yield fiber had grea~er tensile and tear strengths than did the control sheet.
Airfelts made from the sheets containing 10%
and 15% hardwood high yield fiber had lower wet 5 densities than did the airfelt made from the control sheet while the airfelt made from the sheet containing 20% hardwood high yield fiber had a slightly higher wet density than did the airfelt made from the control sheet. All three airfelts containing 10 hardwood high yield f ber had wet burst strengths equivalent to the airfelt made from the control sheet.
I As expected, sheets and airfelts made from ; conventional chemical comminution grade commercial pulp.
were stronger than any of those made from the soft-s 15 wood high yield fiber, but the airfelt made with . the conventional pulp had a significantly higher = wet density than did those made from the softwood high yield fiber.
It is contemplated that the sheets and airfelts 20 of this invention will be comprised essentially or primarily of high yield fibers. It is within the ` scope of the invention, however, to incorporate quantities of chemical pulp into the sheets and ' into the airfelts. Quantities of chemical pulp -~ 25 up to about 25'~o by weight of total fiber can be incorporated into the sheets and into the airfelts. Fibers other than ~oo~ pulp fibers can al50 be incorporated into the sheets and airfelts of this invention, but such incorporation i8, in 30 general, not preferred.
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Also within the prior art is a semi-chemical high yield fiber process which yields a product having relatively high bulk and a relatively low shive content.
This particular process comprises the steps of preheating wood chips, treating the heated chips with a chemical solution which comprises sodium sulfite and, optionally, basic chemicals, at such a concentration as to yield pulp having a pH greater than 5.7. The chips are then mechanically defibrated to pulp with an energy con-sumption of less than about 600 kilowatt hours per metric ton of pulp produced. (Anonymous, Research Disclosures, March, 1978, p. 20.) Generally speaking, following the pulping operation high yield fibers are formed into sheets by any of several well kno~m wet forming processes typified by the conventional Fourdrinier process. (The operation of forming the wood pulp fibers into sheets is sometimes known as lapping.) The sheets are then usually dried with conventional equipment. For use in absorbent products such as tiapers, the sheets are comminuted and the hi~h 3U yleld fibers are formed into absorbent products known as alrfelts.
The high yield fibers most preferred for use in absorbent products such as diapers are generally derived from softwoods ~gyl~#æ~so). One of the problems ~ '~' , ,, . :
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associated with the use of these softwood high yield fibers in absorbent products heretofore has been the weakness of the sheets of pulp fibers. These . sheets must be strong enough to be handled by commercial - equipment during the airfelt making process, but sheets of the preferred softwood high yield fibèrs are generally too wea~ to be used as is. In fact, it is impossible to form sheets at all from some of the most preferred softwood high yield fibers.
One way the strength of the sheets has been improved has been by mechanically refining the fibers. This operation, which is kno~m to increase strength in almost all papermaking areas, suffers from the disadvantages of increased cost and those effects which flow from the mechanical damage to fibers caused by the refining process, e.g. increased fines, lowered drainage rate, increased density, lowered absorbency. Refining is not, however, necessarily effective with all softwood high yield fibers.
Sheet strength has also been improved by adding a~quantity of chemical pulp to the softwood high yield fibers. Chemical pulp,which may comprise up to 25% or more of the total pulp mixture, can optionally be refined in the wet state prior to its addition to the pulp blend. While tbe addition of chemical pulp does increase the strength of the wet laid sheets of softwood high yield fibers, certain adverse effects do occur. One of the most readily apparent, of course, is the increased cost of the total fiber mixture which re~ult~ fro~ the repla~ement of relatively low cost high yield fiber with relativel~J high cost chemical fiber. A second, more subtle adverse effect is the increase in wet density of the airfelt which results when chemical fibers are blended with the softwood high yield fibers.
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Sg High yield fibers are essentially non-delignified;
that is, m~st of the lignin remains with the cellulosic fiber. This lignin contributes to the stiffness of the fiber. It has been found that these stiff fibers form air-felts having lower wet density than do conventional chem-ical pulp fibers. That is, if equivalent airfelts are formed from chemical pulp fibers and from stiff, non-deligniied, high yield fibers, and the airfelts are compressed dry to the same initial density, the high yield fiber airfelts exhibit lower density when wet and under load than do the chemical pulp fiber airfelts.
~lthough Scott, in U.S. Patent ~,642,359 (June 16, 1953) has suggested that the strength of a pulp sheet can be enhanced by incorporating into the fiber furnish from which the sheet is made a quantity of short fibers which tend to bind together long fibers, it is well-kno~m in the art that hardwood high yield fibers (which are generally shorter than softwood fibers) contribute to the~weakness~of~sheets of fibers.
There are basic~anatomical differences between ftwoods and hardwoods. The arbitrary term softwood and hardwood designate~,~respectively, trees having needle or~scalelike leaves and~trees having broad leaves~which are deciduous in temperate zones.
The hardness or density of the wood is not involved.
While there are diferences between the chemical structures o~ hardwood and softwoods, the important difference,for this invention, lies in the variation ~ ~ in cell structure. Softwoods for the most part ;~ 30 are made up of cells whose len~th is several hundred times their dia~eter. That is, even though barely visible to the eye, they are threadlike. Hardwoo~s, on the other hand, are made up of a wider variety of cell types characterized by a length to diameter , .
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~ 1131959 ratio which may run from 1:1 to 20:1. Hardwood fiber is generally considered to be inferior to softwood fiber for certain applications. Because its ratio of length to diameter is so much smaller, the bonding between fibers is poorer because -the inter-fiber crossings per fiber are fewer and the bond area of each is smaller. Consequently, a sheet is generally weaker when it contains hardwood fibers. Grandis commented on the lower strength properties of nardwood sheets relative to softwood sheets in a paper entitled "Poplar Groundwood in Different Grades of Paper" delivered the EU~EPA Symposium on Mechanical Pulp held in Oslo, Norway during June, 1970, as reported in the Abstract Bulletin of the Institute of Paper Chemistry, Vol. 42, No. 3, Abstract No. 2647 (September, 1971).
DISCLOSURE OF THE INVENTION
This invention concerns sheets of softwood high yield fibers which have adequate strength for commercial usage and which have been formed by wet-laying tech-niques. Adequate strength is obtained by blending with the softwood high yield fibers a quantity of hardwood high yield fibers which have been specially prepared. The special preparation comprises treating hardwood chips with relatively high levels of chemicals for relatively long periods of time and defibrating the chips with rçlatively hi~h power input. The blended fibers are formed into sheets by conventional processes. The sheets are then used in the m~nufacture of airfelts made by other conventional processes.
Accordingly, it is an object of this invention to provide dry sheets of wood pulp fibers, said sheets having adequate strengt'n for commercial processin&.
-8- ~13~959 .
It is an object of ehis invention to prov~de sheets comprised of relatively undamaged, substantially non-delignified, softwood high yield fibers, said sheets having adequate strength for commercial usage.
It is an object of this invention to provide airfelts having improved wet density properties.
It is a further object of this invention to provide a process for preparing the above-mentioned sheets of fibers.
It is a still further ob~ect of this invention to provide a process for preparing the above-mentioned airfelts~
These and other ob~ects will become readily apparent from a reading of the Detailed De~cr~ption of the Invention which follows~
The present invention,in one aspect, resides in a wet formed sheet comprising a major proportion of 6ubstantially non-delignified and relatively undamaged softwood high yield fiber6 having a Canadian standard freeness value greater than about 700 ml and a minor porportion of hardwood high yield fibers, said hardwood high yield fibers having a Canadian standard freeness value of ~rom ~bout 50 ml to about 400 ml wherein said hardwood fibers have been prepared separately from said ~oftwood fibers and with ~ignificantly more stringent pretreating and defibrating conditions than have been used to prepare 6aid softwood fibers.
In another aspect, this invention resides in a process for preparing sheets of high yield wood pulp fibers comprising the stops of:
~ a) providing substantlally non-dellgnifiod and rolatively undamaged softwood high yield fibers having a Canadian standard freeness value greatex than about 700 ml;
(b) providing hardwood high yield fibers having a Canadian standard freeness value of from about 50 ml to about 400 ml;
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(c) preparing a papermaking ~urnish from said softwood high yield fibers and said hardwood high yield fibers; and (d) wet forming 6aid sheet6 from said papermaking furnish wherein said 60ftwood high yield fibers are provided in a major proportion compared to 6aid hardwood high yield fibers and said hardwood fibers are provided in a minor proportion compared to said so$twood high yield fibers and wherein said hardwood fibers have been prepared separately from said softwood fibers and with significantly more stringent pretreating ~nd defibrating conditions than have been used to prepare said ~oftwood f~bers.
In a ~u-thcr aspect, the prc30nt invention residcs in a process for preparing airfelts comprising the steps of:
(a) comminuting sheets of high yield wood pulp fibers; and (b) airlaying sa$d comminuted high yield wood pulp fibers wherein said sheets of high yield wood pulp fibers comprise a major proportion of substantially non-delignified and relatively undamaged softwood high yield fibers having a Canadian standard freeness value greater than about 700ml and a minor proportion of hardwood high yield fibers,-6aid hard-wood high fibers having a anadian standard freeness value of from about 50 ml to a~out 400 ml and wherein ~aid hardwood fibers have been prepared separately from said 60ftwood fiber6 and with significantly more ~tringent pretreating and defibrating conditions than have been used to prepare said oftwood iibers.
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- 8b-1131959 etailed Description of the Tnvention While this specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as the invention, it is believed that the invention will be better understood through a reading of the followin detailed description of it and of the non-limiting example appended thereto.
This invention is directed not only to the pro-duction of dried sheets comprised totally or substantially of high yield fibers and to the production of airfelts from such sheets, but also to the dried sheets of fibers and to the airfelts per se. The invention can best be described, however, in terms of several distinct process operations.
The improved sheets of this invention are comprised primarily of high yield fibers derived from softwoods (gpl~sp~s~). Any of the softwood species com~only used for making paper ~,.
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_~ 1 31 9 5 9 pulp can be used. Suitable species include Picea ~lauca (white sprucej, Picea mariana (black spruce), Picea rubra (red spruce), Pinus strobus (white pine), Pinus caribeau (slash pine), and Pinus tadea (loblolly pine). The last named species is a preferred one for use in this invention.
Processes for convereing softwoods to high yield fiber pulps are relatively well known in the art.
The one described in the following paragraphs can be used advantageously in the practice of this invention, but this invention is not to be considered limited to the use of this process.
Softwood trees are reduced to chips and the - chips are optionally washed using~equipment ant processes c~mon in the pulp industry. The washed chips are held in storage bins until they are needed in the pulping process.
The pulping process begins when the washed wood chips are removed fro~ the chip storage bin and are conveyed by any suitable neans to a presteamer.
In the presteamer, the te~perature of the chips is raised from ambient up to any desired level below about 99C by the introduction of steam. The purpose of the presteamer, which can be any suitable vessel, is to raise the temperature of the chips and expel much of the air associated with them.
From the presteamer, the chips are conveyed to a treatment unit. A suitable conveying device is a screw conveyor, optionally tapered, which tends to compress the chips. Not only does such a device move the chips and seal the treatment unlt against pressure 1088, but it also materially aids in the impregnation of chips during the treating step.
The chips which have been compressed in the screw conveyor are discharged in that compressed condition .
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into the treatment unit below the surface of the treat-ment liquor contained therein. When the mechanical pressure on the chips is reduced as the chips are introduced into the treatment unit, the chips expand - 5 and absorb treatment liquor.
During the treating step performed in the treatment unit, the chips are impregnated wit~ treatment liquor and are maintained at elevated temperature and pressure for a prescribed length of time.
A suitable treatment unit comprises two elements: an impregnator and a retention chamber.
The impregnator preferably comprises a cylindrical vessel oriented with its axis vertical. This cylindrical vessel is provided~with a first means adapted for the introduction of treatment liquor into the impregnator and with a second means adapted~for the moving of chips vertically through the cylindrical vessel to a point where they are allowed to exit the~vessel. The first means can be any arrangement of valves and piping the specification of which is well within the ability of one~skilled in the~art. Provision of a region equivalent to a pool of treatment liquor within the impregnator is desirable. The second means can be a vertically oriented screw conveyor.
Preferably, the impregnator is contained within a larger pressurized outer vessel wherein elevated pressure and temperature are maintained by the introduction of steam. The impregnator is preferably situated in the upper regions of this pressurized outer vessel and a portion of the lower regions provides a retention chamber. After exiting the impregnator, the chips and the treatment liquor associated therewith are allowed to fall ~ 31959 by gravity through the atmosphere of the pressurized outer vessel into the :retention chamber where they are held for a prescribed time.
The treatment liquor is an aqueous solution which facilitates,-without removing substantial quantities of lignin, the defibration of wood chips into substantially undamaged fibers in the subsequent defibration step. It can be water or any suitable chem-ical solution commonly used to prepare thermomechanical, I0 semi-chemical or chemi-mechanical high yield fibers.
A preferred treatment liquor is one comprising as treatin~
agents sodium sulfite and sodium bisulfite, each pre-~; sent at about from about 2% to about 6% by weight of-dry pulp. Other suitable treatment liquors can contain as lS treating agents alkali ~etal sulfite, alkali metal bisulfite, sulfur~dioxide in combination with alkali metal hydroxide, or mixtures thereof. The treatment liquor can optionally contain minor amounts of materials for~penetration and mineral control.
~;20 Suitable treatment temperatures fall within the range of about 124~C~to about l9QC, preferably from about 125C to~about~160~C. ~The pressure within the~treatment unit~is that~stream pressure which corresponds~to the~temperature chosen.
25~ T~e average~res~idence time of a chip at elevated temperature~in~the retention c~amber is ~rom about l to about 60 minutes, preferabIy fro~ about 1 to about 6 minutes.
When loblolly pine is used in this invention, the treatment liquor~preferably comprises about 3% sodium sulfite and about 3% s~odiu~ bisulfite. The chips are preferably treated at a temperature of about 158C for about 5 minutes.
As indicated above, there is maintained in the impregnator an amount of treatment liquor ., -;' ' ' ,, , ~: , ..
~13~59 sufficient to provide an excess of liquit when the ch~ps are fully impregnated. The quantity of treatment liquor absorbed by the chips is dependent upon the species~ the previous history of the chips, and the exact equipment and operating parameters used.
Typically> for the equipment described above, the chips are impregnated with from about 30% to about 70% by weight treatment liquor based on the bone dry weight of the wood, From the treatment unit, the treated wood chips pass to the defibration unit through the use of any suitable device such as a screw conveyor.
The defibrator can be any of the well known units used in the manufacture of thermomechanical or Asplund pulp. Specific examples are the Defibrator L-42 and the Asplund defibrators types 0VP-20, ~LP-SOS, and PT-P-54S. All of these units comprise one stationary disc and one rotating disc. Optionally, the defibration units can h~ve two rotating disks.
Disc designs can be any of those commonly used in the manufacture of ther mechanical or Asplund pulp .
Defibration is usually accomplished at from about 124 to about 160C at a consistency of about 25+ ~" by weight. Water or chemicals can be added to the treated chips im~ediately prior to their entry into or after their exit from the defibrator to adjust the consistency and to serve other purposes such as bleac~.ing.
3n Power input to the defibrator is controlled, as b~ ad~usting the clearance between the dlscs, so that t:~e treated chips are defibrated to a pulp of acceptably high bulk while the level of shives is ma;ntained at acceptably low levels. It is preferred that t'ne fibers be left essentially intact and undamaged.
t~en loblolly pine is used, and is treated as described hereinjefore~ a power input of approximately 140 to aboue 450 kilowatt hours per metric ton is suitable.
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~-- 113~959 From the defibrator, the pulp passes to a bleac~ing unit wherein it is bleached. Optionally, the bleaching step can be omitted at this point in the processing scheme, but it is then performed later after the softwood high yield fibers are ~e~--with the hard~ood high yield fibers.
Any of the con~entional bleaching processes well known to those skilled in the pulp art can be used.
For example, hydrogen perox~de, sodiu~ peroxide, or hydsosulfite can be used. Various bleaching systems are describet in t~e BleachinR of Pulp, W. H. Rapson, Editor, TAPPI Monograph Series No. 27, (New York, 1963).
The fibers at this point in the process are presented as an aqueous slurry. They can either be directly incorporated in the form of this aqueous slurry into the furnish from which the dry sheets of this invention are mate, or they may be dried by conventional bulk drying metnods. In the latter sit~ation they are redispersed i.- wa-~er as 2art of the sheet maki,lg process.
The softwood high yield fibers are relatively undamaged and substantially non-delignified. Relatively unda~aged means that at least the majority of the indi~îdual fibers are rendered into pulp while retaining the length at ~hich tney were present in the raw wood and that at least the majority of the fibers do not present the typical appearance of fibers which have been mec~anically refined. Subatantially non-teli~nified means that associated with the flbers i9 a quantity . of lignin substantially greater than that associated with those fibers from the same wood source which ha~e been rendered into pulp by the conventional sulfite or kraft processes.
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h 1131959 The Canadian standard freeness value (CSF) of the softwood high fibers useful in this invention is greater than about 700 ml. as determined according to T.A.P.P.I. Method.T-227 OS-58. -The second component of the sheets of this invention are high yield fibers prepared from hardwoods (angiosperms). ~uitable~hardwoods include, for example, a}der, aspen, oak, and gum~
The high yieId fibers prepared from hardwood are prepared in a manner analogous to that used for the softwood high yield fibers, but with significantly more stringent pretreating and defibrating conditions.
~ The treatment liquor can contain as a treating agent ; alkali metal sulfite, alkali metal bisulfite, sulfur 15~ dioxide in combination wit~h alkali metal hydroxide, or mixtures thereof. Sodium-is the preferred alkali metal.
The levéls of~treating;agent in~the treatment liquor can be from about 2% to~about 40% by~weight.~ The treatnent liquor can optionally contain minor amounts of materials for~penetra;tlon and~mlneral~control. For example, when mixed hardwoods~, predominately gum, are used, the treatment liquor~preferably ~comprises from about 2% to about 20% by weight sodium sulfite and from about 2 to about 20% by weight sodium bisulfite. A5 above, the quantity o~ treatme~t liquor abs~rbed by the c~ips i9 `dependent on ~any factors. Absorption levels of 100%
or greater by ~eight of treatment liquor are possible.
The chips are treated at about 130 to about 190C
for from about~l to about 60 minutes and are defibrated ~ 30 with a power input during defibration of from about 155 ;- to about 500 kilowat~t hours per metric ton of treated hardwood.
;
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-15- 1131~59 The hardwood high yield fibers can then be bleached in a bleaching unit as described above for softwood high yield fibers. Optionally, the bleaching step is omitted at this point in the processing scheme, but it is then performed later after the ~wo types of high yield fibers are blended.
Canadian standard freeness (CSF) values of the hardwood high yield fibers are determined according to T.~.P.P.I. Method T-227 OS-58, Preferably, the CSF of the hardwoot high yield fibers used in this invention ~s between about ~ ml.
and about 400 ~i.
The softwood high yield fibers and the hardwood high yield fibers described above, bleached or optionally unbleached, are mixed in the wet state to prepare the papermaking furnish which will be used to form the sheets of this invention. ~ile no special techniques or precautions are required in the mixing opera~ion, ~.~hich can be performed using equipment and techniques well known in the art, techniques which tend to retain any fines associated with the hardwood high vield fibers are preferred. There should be present in the furnish a major proportion of softwood high yield fibers and a minor proportion of hardwood high yield fibers.
The weight ratio of softwood to hardwood high yield fibers should be from about 2.33:1 to about 19:1, preferably from about 5.67:1 to about 15:1.
If the two types of high yield fibers have not been bleached earlier in the processin~ scheme, they can be , bleached after mixing. Any of the ~leachin~ techniques described above can be used.
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The slurry comprising the mixture of bleached softwood high yield fibers and bleached specially prepared hard-wood high yield fibers is used as the furnish to form the sheets of this invention. Any of the various wet-forming techniques well known in the art for forming sheets of fibers can be used. Of particular usefulness are the various mod~fications of the well known Fourdrinier process. In general, this process involves adjusting the~
furnish to the appropriate consistency, applying the furnish to a moving foraminous surface such as a Fourdrinier wire, allowing excess water to drain from the fiber mat 80 formed through the foraminous surface, and sub~ecting the drained fiber mat to various pressing operat~ons so as to expel more water.
The coherent fibrous web is then dried by any convenient means such as a drying tunnel or rotating drum dryer. The dried sheet of fibers, which has significantly improved strength over an all-softwood high yield fiber sheet, is then cut into convenient sections or is wound upon a core to form a convenient sized roll.
Bursting Strength of the dried sheet is measured by T.A.P.P.I. Method T-403 OS-76, Tensile Strength by T.A.'P.P.I. method T-404 OS-76, and Tnternal Tearing 2~ Resistance (Tear) by T.A.P.P.I. method T-44 TS-65.
The thic~ness of a dried sheet is measured using a motorized micrometer which applies a load of 0.50 kg. per square centimeter using an anvil having a diameter o~ 1.60 centimeters.
The airfelts of this invention ase prepared f,,rom the hereinbefore described sheets by a process comprising the steps of comminution, airlayin~, and, optionally, compaction.
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Comminution (i.e. the mechanical separatiDn of the sheets into essentially individual fibers) is accomplished by any of the equipment and processes - well known in the art. Examples are found in U.S. Patent 3,750,962 which was issued to Morgan on August 7, 1973 and in U.S, Patent 3,519,219 which was issued to Sakulich et al. on July 7, 1970.
Following comminution, the separated high yield fibers are formed 10 into a fibrous web by airlaying with equipment and processes common in the art. U.S. Patent 3,772,739 ~which issued to Lovegrin on November 20, 1973, ~illustrates a suitable 2airlaying process and provides a thorough discussion 15 of airlaying technology. The airlaid web is optionally compressed by means well known in the art.
The apparent wet density of an airfelt is determined :on a pad which has been compressed to a uniform ~ density and which has been loaded witn synthetic urine.
The airfelt to be tested is prepared by airlaying 42 gr~s (dry basis) fiber as a 35.6 centim~ter square pad.
This pad is then cut into 10.2 centimeter square sections for testing. Any tissues on the sections are carefully + re~oved. The section is co~pressed to such a thickness 3 25 which will result, when the compressing load is ~, renoved, in an airfelt having a density of 0.10+ 0.01 ~ gra~ per cubic centimeter. (Unless otherwise specified, when thethickness of an airfelt must be determined, as when densities are determined, the thickness is ~easured under a load of 1~.4 grams per square centimeter.) The densified section is placed on a planar surface and sprayed uniformly with a quantity of synthetic urine equal to three times the dry weight of the airfelt section. The wetted section is subjected --, -.
, ` -18- 1 1 31 ~ 59 to a loading of 2~2 grams per square centimeter The load is removed and the section is subjected to a load-ing of 12.4 grams per square centimeter. The load is removed and the section is subjected to a loading of 35.2 grams per square centimeter~ The load is removed and the section is allowed to recover for 60 seconds. The section is then subjected to a loading i of 2.2 grams per square centimeter. The load is removed and the section is then subjected to a loading of 12.4 grams per square centimeter and the thickness of the section under this loading is recorded.
The apparent wet density of the section is determined by dividing the dry weight of the section (in grams) by 104 times the last above measured thickness (in l~ centimeters) of the section.
As used herein, synthetic urine is a 1%
(weight) aqueous solution of sodium chloride which also contains 0.0025% octylphenoxy polyethoxy ethanol nonionic surfactant.
2~ The wet burst strength of the airfelt is i measured by deter~ining the force required to rupture the sample used in the apparent wet density ' test with a rod provided with a 1.~ centimeter diameter ! spherical end, traveling at.the rate of 1~.7 centimeters per minute, while the sample is secured bet~7een plates having superi~posed 6.35 centimeter-diameter ~ orifices.
i . ~hen intended f^r use in products such as - disposable diapers, the airfelt has 8 basis wcight of from about 240 to about 420 grams per square meter and a ~, dry tensity of ~rom about 0.08 ~o ~hout 0.~8 ~rams per cubic centimeter. Those skilled in the art can readil~y adjust these parameters to suit the particular end product ¦ use. Diapers can be made from the airfelt according . .
I
1131~S9 .
~ -19-to the teachings of U.S. Patent Re. 26,151 which was ;
issued to Duncan and Baker on January 3l~l962~
Other absorbent products, such as sanitary napkins, - 5 incontinent pads, surgical bandages, and the like, ; can be prepared from the airfelts of this invention by means well known in the art.
As shown by the following example, one of the prominent features of the airfelt of this invention 10 is its improved wet density property.
The follow~ng example ~s presented to more fully describe the invention disclosed herein " and not by way of limitation.
Chips having a nominal length of 1.6 centimeters -~ were prepared by standard techniques fro~ debarked ~ loblolly pine logs. These chips were used to make ;~ softwood high yield fibers by the techniques and with the equipment hereinbefore described.
The cnips were heated in the presteamer to ~; a temperature of 93 by the use of steam. From ~~ the presteamer, the heated chips were conveyed by a screw conveyor to the impregnator of the treatment 25 unit where they were impregnated with a treatment liquor co~prising 4.5% (weight) sodium sulfite, 4.5~ sodium bi-sulfite and ~inor amounts of chemicals for mineral and penetration control, The chips retained 3%
- sodium sulfite and 3% sodium bisulfite, (The latter v 30 percentages are in terms of weight on the basis o oven dry wood,~ The impregnated chips were re~oYed from -.
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the i~pregnator by a screw conveyor and were allowed to fall through the atmosphere of the pressurized outer vessel to the retention chamber where they were retained for 5 minutes at 158C. The impregnated, heated chips were conveyed by screw conveyor to an L-42 defibrator fitted with type 10782 plates. The chips were ,, defibrated with a power input of 177 kilowatt hours ' per metric,ton of pulp. `Defibration was accomplished ¦ at 27% b~ wei'g~t cons~stenc~ The pH of t~e pulp 1~ ex~ting t~e def~brator was controlled, The softwood high yield fibers were washed with softened water and were bleached with sodium peroxide using standard bleaching techniques. The bleaching solution comprised 6% (by weight) hydrogen peroxide, 5% 41 Be sodium silicate, ~%
sodium hydroxide, 0.5C/o magnesium sulfate, and 0.15VZ DTPA. The bleaching was accomplished at a consistency of lz~r in two hours at 82C. The ,~, resulting pulp slurry was neutralized by the addition ', 20 of sulfur dioxide. A second bleaching operation using 1% sodium hydrosulfite and 0.2% sodium tripolyphosphate was conducted at ~% consistency ~,' ' for 1 hour at 50C. The resulting pulp had a I CSF of about 750 milliliters.
; 25 Chips having a nominal length of 1.6 centimeters were prepared from debarked gu~ logs. Hardwood 1' high yield fibers were prepared in the same equipment using the same techniques as were used to-prepare the softwood high yield fibers with the exception that 0 the chips were impregnated with a sufficient quantity of a treatment liquor comprising 7.8% (weig'nt) sodium sulfite, 7.8% sodium ~isulfite and a mlnor amount o~
mineral control agent to provide 10% sodium sulfite and ,, ~ ~o 11319S9 sodium bisulfite, (The latter percentages are in terms of weig~t on the basis of oven dry wood.~ T~e ~m-pregnated chîps ~ere held in the retention c~amber - for 3Q minutes at 177C, During defibrating, the power input was 296 ~ilowatt hours per metric ton.
Following bleaching as immediately hereinbefore described, the hardwood high yield fibers had a CSF of about 230 ~ milliliters.
- Blends of 10~/~ (by weight), 15%, and 20% hardwood -~, 10 high yield fiber and, respectively, 90%, 85%, and 80%
a softwood high yield fiber were prepared and sheets were made on a conventional wet forming papermaking machine. It should be noted that skilled artisans - were unable to prepare a sheet from a furnish comprising 100% of the softwood high yield fibers of this example.
For comparison purposes, a control sheet was made from a blend of 90% of the above-described softwood high yield fiber and 10% northern kraft pulp refined to a CSF of approximateIy 270 milliliters. Also for comparison purposes, sheets were made from 10070 chemical co~mirution grade pulp prepared from un-refined southern pine fibers.
The tests described above were conducted on the finished sheets. In ~ddition, airelts were prepared by standard techniques from the sheets of fibers.
The above described tests were used to evaluate the wet properties of these airfelts.
While the sheets having 10% and 15% hardwood high yield fiber were strong enough t-o be handled on commercial equipment, they exhibited slightly lower tensile strengths than the control sample.
At the same time, they exhibited somewhat greater tear strength than did the control. The sheet con-'~' ~i~195~
taining 20% hardwood high yield fiber had grea~er tensile and tear strengths than did the control sheet.
Airfelts made from the sheets containing 10%
and 15% hardwood high yield fiber had lower wet 5 densities than did the airfelt made from the control sheet while the airfelt made from the sheet containing 20% hardwood high yield fiber had a slightly higher wet density than did the airfelt made from the control sheet. All three airfelts containing 10 hardwood high yield f ber had wet burst strengths equivalent to the airfelt made from the control sheet.
I As expected, sheets and airfelts made from ; conventional chemical comminution grade commercial pulp.
were stronger than any of those made from the soft-s 15 wood high yield fiber, but the airfelt made with . the conventional pulp had a significantly higher = wet density than did those made from the softwood high yield fiber.
It is contemplated that the sheets and airfelts 20 of this invention will be comprised essentially or primarily of high yield fibers. It is within the ` scope of the invention, however, to incorporate quantities of chemical pulp into the sheets and ' into the airfelts. Quantities of chemical pulp -~ 25 up to about 25'~o by weight of total fiber can be incorporated into the sheets and into the airfelts. Fibers other than ~oo~ pulp fibers can al50 be incorporated into the sheets and airfelts of this invention, but such incorporation i8, in 30 general, not preferred.
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Claims (29)
1. A wet formed sheet comprising a major proportion of substantially non-delignified and relatively undamaged softwood high yield fibers having a Canadian standard freeness value greater than about 700 ml and a minor porportion of hardwood high yield fibers, said hardwood high yield fibers having a Canadian standard freeness value of from about 50 ml to about 400 ml wherein said hardwood fibers have been prepared separately from said softwood fibers and with significantly more stringent pretreating and defibrating conditions than have been used to prepare said softwood fibers.
2. The sheet of Claim 1 wherein the weight ratio of said softwood high yield fibers to said hardwood high yield fibers is from about 2.33:1 to about 19:1.
3. The sheet of Claim 1 wherein the weight ratio of said softwood high yield fibers to said hardwood high yield fibers is from about 5.67:1 to about 19:1.
4. The sheet of Claim 1 wherein said hardwood high yield fibers are prepared by a process comprising the steps of (a) treating hardwood with an aqueous solution comprising from about 2% to about 40% of weight of a treating agent selected from the group consisting of alkali metal sulfite, alkali metal bi-sulfite, sulfur dioxide with alkali metal hydroxide, and mixtures thereof, at a tem-perature of from about 130°C to about 190°C for about 1 to about 60 minutes;
and (b) defibrating said treated hardwood.
and (b) defibrating said treated hardwood.
5. The sheet of Claim 4 wherein the power input during the defibrating step is from about 155 to about 500 kilowatt hours per metric ton of treated hardwood.
6. The sheet of Claim 1 wherein said hardwood high yield fibers are prepared by a process comprising the steps of:
(a) treating hardwood with an aqueous solution comprising from about 2% to about 20% sodium sulfite and from about 2% to about 20% sodium bisulfite at a temperature of from about 130°C
to about 190°C for from about 1 to about 60 minutes; and (b) defibrating said treated hardwood.
(a) treating hardwood with an aqueous solution comprising from about 2% to about 20% sodium sulfite and from about 2% to about 20% sodium bisulfite at a temperature of from about 130°C
to about 190°C for from about 1 to about 60 minutes; and (b) defibrating said treated hardwood.
7. The sheet of Claim 6 wherein the power input during the defibrating step is from about 155 to about 500 kilowatt hours per metric ton of treated hardwood.
8. An airfelt comprising a major proportion of substantially non-delignified and relatively undamaged softwood high yield fibers having a Canadian standard freeness value greater than about 700 ml and a minor proportion of hardwood high yield fibers, said hardwood high yield fibers having a Canadian standard freeness value of from about 50 ml to about 400 ml wherein said hardwood fibers have been prepared separately from said softwood fibers and with significantly more stringent pretreating and defibrating conditions than have been used to prepare said softwood fibers.
9. The airfelt of Claim 8 wherein said airfelt is prepared by a process comprising the comminution of a dried sheet comprises of said softwood high yield fibers and said hardwood high yield fibers.
10. The air felt of Claim 9 wherein the weight ratio of said softwood high yield fibers to said hardwood high yield fibers is from about 2.33:1 to about 19:1.
11. The airfelt of Claim 9 wherein the weight ratio of said softwood high yield fibers to said hardwood high yield fibers is from about 5.67:1 to about 19:1.
12. The airfelt of Claim 9, wherein said hardwood high yield fibers are prepared by a process comprising the steps of (a) treating harawood with an aqueous solution comprising from about 2% to about 40% by weight of a treating agent selected from the group consisting of alkali metal sulfite, alkali metal bisulfite, sulfur dioxide with alkali metal hydroxide, and mixtures thereof, at a temperature of from about 130°C to about 190°C for about 1 to about 60 minutes; and (b) defibrating said treated hardwood,
13. The airfelt of Claim 12 wherein the power input during the defibrating step is from about 155 to about 500 kilowatt hours per metric ton of treated hardwood.
14. The airfelt of Claim 9 wherein said hardwood high yield fibers are prepared by a process comprising the-steps of:
(a) treatlng hardwood with an aqueous solution comprising from about 2% to about 2b% sodium sulfite and from about 2% to about 20z sodium bisulfite at a temperature of from about 130°C
to about 190°C for from sbout 1 to about 60 minutes; and (b) defibrating said treated hardwood,
(a) treatlng hardwood with an aqueous solution comprising from about 2% to about 2b% sodium sulfite and from about 2% to about 20z sodium bisulfite at a temperature of from about 130°C
to about 190°C for from sbout 1 to about 60 minutes; and (b) defibrating said treated hardwood,
15. The airfelt of Claim 14 wherein the power input turing the defibrating step is from about 155 to about 500 kilowatt hours per metric ton of treated hardwood.
16. A process for preparing sheets of high yield wood pulp fibers comprising the steps of:
(a) providing substantially non-delignified and relatively undamaged softwood high yield fibers having a Canadian standard freeness value greater than about 700 ml;
(b) providing hardwood high yield fibers having a Canadian standard freeness value of from about 50 ml to about 400 ml;
(c) preparing a papermaking furnish from said softwood high yield fibers and said hardwood high yield fibers; and (d) wet forming said sheets from said papermaking furnish wherein said softwood high yield fibers are provided in a major proportion compared to said hardwood high yield fibers and said hardwood fibers are provided in a minor proportion compared to said softwood high yield fibers and wherein said hardwood fibers have been prepared separately from said softwood fibers and with significantly more stringent pretreating and defibrating conditions than have been used to prepare said softwood fibers.
(a) providing substantially non-delignified and relatively undamaged softwood high yield fibers having a Canadian standard freeness value greater than about 700 ml;
(b) providing hardwood high yield fibers having a Canadian standard freeness value of from about 50 ml to about 400 ml;
(c) preparing a papermaking furnish from said softwood high yield fibers and said hardwood high yield fibers; and (d) wet forming said sheets from said papermaking furnish wherein said softwood high yield fibers are provided in a major proportion compared to said hardwood high yield fibers and said hardwood fibers are provided in a minor proportion compared to said softwood high yield fibers and wherein said hardwood fibers have been prepared separately from said softwood fibers and with significantly more stringent pretreating and defibrating conditions than have been used to prepare said softwood fibers.
17. The process of Claim 16 wherein the weight ratio of said softwood high yield fibers to said hardwood high yield fibers is from about 2.33:1 to about 19:1.
18. The process of Claim 16 wherein the weight ratio of said softwood high yield fibers to said hardwood high yield fibers is from about 5.67:1 to about 19:1.
19. The process of Claim 16 wherein said hardwood high yield fibers are prepared by a process comprising the steps of (a) treating hardwood with an aqueous solution comprising from about 2% to about 40% by weight of a treating agent selected from the group consisting of alkali metal sulfite, alkali metal bisulfite, sulfur dioxide with alkali metal hydroxide, and mixtures thereof, at a temperature of from about 130°C to about 190°C for about 1 to about 60 minutes; and (b) defibrating said treated hardwood.
20. The process of Claim 19 wherein the power input during the defibrating step is from about 155 to about 500 kilowatt hours per metric ton of treated hardwood.
21. The process of Claim 16, wherein said hardwood fibers are prepared by a process comprising the steps of (a) treating hardwood with an aqueous solution comprising from about 2% to about 20% sodium sulfite and from about 2% to about 20% sodium bisulfite at a temperature of from about 130°C
to about 190°C for from about 1 to about 60 minutes; and (b) defibrating said treated hardwood.
to about 190°C for from about 1 to about 60 minutes; and (b) defibrating said treated hardwood.
22. The Process of Claim 21 wherein the power input during the defibrating step is from about 155 to about 500 kilowatt hours per metric ton of treated hardwood.
23. A process for preparing airfelts comprising the steps of:
(a) comminuting sheets of high yield wood pulp fibers; and (b) airlaying said comminuted high yield wood pulp fibers wherein said sheets of high yield wood pulp fibers comprise a major proportion of substantially non-delignified and relatively undamaged softwood high yield fibers having a Canadian standard freeness value greater than about 700 ml and a minor proportion of hardwood high yield fibers, said hard-wood high fibers having a Canadian standard freeness value of from about 50 ml to about 400 ml and wherein said hardwood fibers have been prepared separately from said softwood fibers and with significantly more stringent pretreating and defibrating conditions than have been used to prepare said softwood fibers,
(a) comminuting sheets of high yield wood pulp fibers; and (b) airlaying said comminuted high yield wood pulp fibers wherein said sheets of high yield wood pulp fibers comprise a major proportion of substantially non-delignified and relatively undamaged softwood high yield fibers having a Canadian standard freeness value greater than about 700 ml and a minor proportion of hardwood high yield fibers, said hard-wood high fibers having a Canadian standard freeness value of from about 50 ml to about 400 ml and wherein said hardwood fibers have been prepared separately from said softwood fibers and with significantly more stringent pretreating and defibrating conditions than have been used to prepare said softwood fibers,
24. The process of Claim 23 wherein the weight ratio of said softwood high yield fibers to said hard-wood high yield fibers is from about 2.33:1 to about 19:1.
25. The process of Claim 23 wherein the weight ratio of said softwood high yield fibers to said hardwood high yield fibers is from about 5.67:1 to about 19:1.
26. The process of Claims 23, wherein said hardwood high yield fibers are prepare by a process comprising the steps of (a) treating hardwood with an aqueous solution comprising from about 2% to about 40% by weight of a treating agent selected from the group consisting of alkali metal sulfite, alkali metal bisulfite, sulfur dioxide with alkali metal hydroxide, and mixtures thereof, at a temperature of from about 130°C to about 190°C for about 1 to about 60 minutes; and (b) defibrating said treated hardwood.
27. The process of Claim 26 wherein the power input during the defibrating step is from about 155 to about 500 kilowatt hours per metric ton of treated hardwood.
28. The process of Claims 23, wherein said hardwood high yield fibers-are prepared by a process comprising the steps of:
(a) treating hardwood with an aqueous solution comprising from about 2% to about 20% sodium sulfite and from about 2% to about 20% sodium bisulfite at a temperature of from about 130°C
to about 190°C for from about 1 to about 60 minutes; and (b) defibrating said treated hardwood-.
(a) treating hardwood with an aqueous solution comprising from about 2% to about 20% sodium sulfite and from about 2% to about 20% sodium bisulfite at a temperature of from about 130°C
to about 190°C for from about 1 to about 60 minutes; and (b) defibrating said treated hardwood-.
29. The process of Claim 28 wherein the power input during the defibrating step is from about 155 to about 500 kilowatt hours per metric ton of treated hardwood.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/041,043 US4247362A (en) | 1979-05-21 | 1979-05-21 | High yield fiber sheets |
| US041,043 | 1979-05-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1131959A true CA1131959A (en) | 1982-09-21 |
Family
ID=21914418
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA352,254A Expired CA1131959A (en) | 1979-05-21 | 1980-05-20 | High yield fiber sheets |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4247362A (en) |
| CA (1) | CA1131959A (en) |
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| US9879361B2 (en) * | 2012-08-24 | 2018-01-30 | Domtar Paper Company, Llc | Surface enhanced pulp fibers, methods of making surface enhanced pulp fibers, products incorporating surface enhanced pulp fibers, and methods of making products incorporating surface enhanced pulp fibers |
| JP6461181B2 (en) | 2014-02-21 | 2019-01-30 | ドムター ペーパー カンパニー， エルエルシー | Fiber-reinforced cement composite material and manufacturing method thereof |
| KR101863620B1 (en) | 2014-02-21 | 2018-07-05 | 돔타르 페이퍼 컴퍼니 엘엘씨 | Surface enhanced pulp fibers at a substrate surface |
| US11473245B2 (en) | 2016-08-01 | 2022-10-18 | Domtar Paper Company Llc | Surface enhanced pulp fibers at a substrate surface |
| WO2018075627A1 (en) | 2016-10-18 | 2018-04-26 | Domtar Paper Company, Llc | Method for production of filler loaded surface enhanced pulp fibers |
| CA3088962A1 (en) | 2018-02-05 | 2019-08-08 | Harshad PANDE | Paper products and pulps with surface enhanced pulp fibers and increased absorbency, and methods of making same |
| WO2020198516A1 (en) | 2019-03-26 | 2020-10-01 | Domtar Paper Company, Llc | Paper products subjected to a surface treatment comprising enzyme-treated surface enhanced pulp fibers and methods of making the same |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2131097A (en) * | 1926-02-04 | 1938-09-27 | Barrett Co | Impregnated felt |
| US1920496A (en) * | 1928-08-23 | 1933-08-01 | United States Gypsum Co | Insulating or wall board product |
| US2325055A (en) * | 1940-05-22 | 1943-07-27 | Wood Conversion Co | Thermal insulation |
| SE303088B (en) * | 1963-05-31 | 1968-08-12 | Defibrator Ab | |
| US3591450A (en) * | 1967-08-30 | 1971-07-06 | Int Paper Co | Method and apparatus for conditioning and defibrating a web of paper pulp prior to air laying |
| US4152197A (en) * | 1974-09-23 | 1979-05-01 | Mo Och Domsjo Ab | Process for preparing high-yield cellulose pulps by vapor phase pulping an unpulped portion of lignocellulosic material and a partially chemically pulped portion |
| SE432118B (en) * | 1975-02-26 | 1984-03-19 | Moelnlycke Ab | MECHANICAL FLUFF MASS AND SET FOR PREPARATION THEREOF |
| SE7602750L (en) * | 1975-03-03 | 1976-09-06 | Procter & Gamble | USE OF THERMOMECHANICAL PULP FOR THE MANUFACTURE OF HIGH BULK TISSUE |
| US4116758A (en) * | 1976-05-14 | 1978-09-26 | Canadian International Paper Co. | Method of producing high yield chemimechanical pulps |
| US4145246A (en) * | 1976-07-19 | 1979-03-20 | Crown Zellerbach Corporation | Process for making high-strength, high-yield sulfite-modified thermomechanical pulp and a linerboard composition produced therefrom |
-
1979
- 1979-05-21 US US06/041,043 patent/US4247362A/en not_active Expired - Lifetime
-
1980
- 1980-05-20 CA CA352,254A patent/CA1131959A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4247362A (en) | 1981-01-27 |
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