US 3203850 A
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Description (OCR text may contain errors)
Aug. 31, 1965 F. MCCARTY 3,203,850
METHOD OF FORMING CREPED AND EMBOSSED EXTENSIBLE PAPER Filed Jan. 12, 1965 4 Sheets-Sheet 1 f L w k I Q M Q u l l W: m 9, D [D k G) g E N "n '0 s O 6 m A a a D 6 t 5 a Q Q 35 It x Q Q 'E \I t b INVENTOR ATTORNEYS Aug. 31, 1965 F. M CARTY 3,203,850
METHOD OF FORMING CREPED AND EMBOSSED EXTENSIBLE PAPER Filed Jan. 12, 1965 4 Sheets-Sheet 4 COMP/PE 88/ VE LY SHRU/VK K/MF T WET ans/=50 KRAFT N07 EMBOSSED rDRY CREPED K RAF T M. D. STRETCH 9'0 000/ /Sd HIS/V3815 37/SIV31 INVENTOR. EUGENE E M: CARTI' .ATTOR A/EKS United States Patent 3,203,850 METHOD OF FORMING 'CREPED AND EMBOSSED EXTENSIBLE PAPER Eugene F. McCarty, Newburgh, N.Y., assignor to St.
Regis Paper Company, New York, N.Y., a corporation of New York 7 Filed Jan. '12, 1965, 'Ser, No. 424,940
2 Claims. (CL 162-413) This application is a continuation-in-part of my copending application Serial No. 216,658, filed August 13, 1962 (now abandoned).
This invention pertains to improvements in extensible paper, more particularly of the creped and embossed, bilaterallyextensible type, and to the continuous production thereof in paper-making machines.
An object of the invention is to provide such a paper having in the machine direction, a relatively high'stifin'ess, on the order of 260290 Gurley, and a relatively high elastic modulus, on the order of 175,000-200,000 p.s.i., said stiffness and modulus being substantially uniform across a web width of said paper of at least 30 inches, and varying not more than about 15% each across said width, said paper also having excellent properties in other respects, such as high tensile energy absorption, tear resistance, instantaneous recoverable extensibility, anti-skid characteristics, etc., thereby adapting the same for the high speed mass production of bags on conventional bag tubing and forming apparatus, including bags of the multi-walled, stepped end types.
A further object of the invention is to produce such a paper having a preselected and controlled combination of properties as aforesaid together with novel methods and means for so producing the same as to impart such properties. 7
Still another object is to provide methods and apparatus for producing such paper of uniform grade and quality throughout its length and width, as a continuous and uninterrupted operation and in the widestof web widths and at the highest mill speed of modern paper-making machines. h
These and other features and objects of the invention will become apparent as the description proceeds.
Bilaterally extensible, creped and embossed paper has heretofore been produced by modifications of conventional paper-making techniques consisting in, feeding the wet paper web as formed on the Fourdrinier wire and after Wet pressing, directly onto a crepin-g roll, wherein a minimum amount of creping is imparted, on the order of about 8.5 to 15%. The so-creped web is then fed over a series of dryer rolls, and thence through an embossing unit comprising a metal embossing roll and a cooperating resilient roll, which embosses the so-creped web substantially longitudinally thereof and at spaced intervals'transversely thereof in the form of substantially longitudinally extending grooves. The so-creped and embossed web is thereupon 'fed through a series of additional dryer rolls, operating at asufiiciently higher speed than the embossing press, to pull out about one-quarter to one-half of the previously induced extensibility, and also to demoisturize the web substantially to the dry state.
This, however, is inherently a relatively slow procedure, since the wet crepe as thus produced and containing about 6075% moisture content, is difficult to dry on the drying rolls owing to the thermally insulating air pockets formed between these rolls and the creped paper owing to the creping effect. Also the web containing such a high moisture content, has extremely low resistance against permanent extension and thus tends to stretch out and permanently reduce the creping effect in passing over the dryer rolls to the embosser. These objectionable eifects are eliminated in accordance with one aspect 3,203,850 Patented Au a1, 1965 of the invention by passing the wet-pressed web, in the flat state onto the first series of dryer rolls to remove the excess moisture prior to crepingto a low moisture content and thereby permit a speeding up of the rate of web feed oommensurate'ly with the resulting increased drying rate.
I have further found in this connection that the moisture content of the web at which the creping and embossing operations are effected, is of critical importance as regards the physical properties of the ultimate creped and embossed product. -I have found that if these operations are conducted on the web at too high a moisture level, for example at 60% or above, that the resultant product is too stiff and lacking in requisite degree of extensibility, and in fact approaches the properties of ordinary, flat finished paper. On the other hand, if the paper is creped and embossed at too low a moisture level, i.e., at less than about 40%, the bonding action of the embossing step is relatively ineffective, so that the product partake's increasingly of the properties of ordinary creped .but uneinbossed paper.
I have accordingly discovered in accordance with the basic concept of my invention, that the magnitude of the moisture content of'the web at the creping and embossing stages, determines the properties of the final product as regards such controlling factors as machine direction stiffness, elastic modulus, and instantaneous recoverable ex-v tensibility, and also bilateral tensile energy absorption and tear resistance. My experiments have shown that for the optimum overall combination of such properties for most applications, the moisture content at the point of compacting should be broadly on the order of about 4059%, the preferred range, particularly for hag-forming applications, being somewhat narrower and preferably about 50 55%, in order to impart the high machine direction stiifness and elastic modulus properties above stated.
-I have additionally discovered as a further generic 'aspoet of my invention, that the moisture profile across the Web at the creping and embossing stages is likewiseof critical importance in determining the properties of the end product. If the moisture content in this cross direction of the web varies appreciably, i.e., more than about a percent or so plus or minus, not only is there a corresponding variation across the web of the properties of the finished product, but in addition operational difliculties are encountered in production on the paper machine and also subsequently in bag tubing and forming operations.
During production on the paper machine, if the moisture content varies appreciably across the web at the creping stag the degree of its adherence to the creping roll will vary correspondingly across its width, with resultant varying degrees of ease of separation of the web from the roll by the creping knife. This results in flapping, buckling and flaring or blowing of the web as it passes into the embossing press, and also in permanent wrinkling therein. These effects become increasingly exaggerated with increasing speed of the machine, because the velocity of the web increases the amplitude of flapping, etc., and also the magnitude of wrinkling.
In addition, if the final product does not have adequate machine direction elastic modulus uniformly across the web, it will not feed uniformly through the bag tuber and printing apparatus in subsequent bag tubing and printing operations. If, for example, the machine direction, elastic modulus of the paper, is less along one edge than in the remainder, that edge will tend to extend more during these operations and produce skewed effects, as well as wrinkling, both of which are serious and productive of much scrap loss as well as down time.
Also if the machine direction stifiness is not adequately uniform across the web when the bag lengths are cut ofi prior to delivery from the bag tu'ber, they will tend to fold or buckle and jam the equipment. Likewise in the production of stepped end bags, if the machine direction stiffness of a bag ply or portion thereof is too low, it will tend to buckle in coming against the register stop for a bottoming operation, for example, and will thus curl up and not form a proper bottom of the bag.
It is accordingly of controlling importance that the moisture profile of the web at the compacting stage, be not only held as to magnitude within the moisture limits above stated, but in addition that the moisture profile be substantially constant across the web and not vary more than about plus or minus 1% in this direction, or not more than 2% in total amount.
The moisture profile may be controlled in various ways, as by imparting appropriate crowns to the rolls of the wet press in conjunction with the drying action of the subsequent dryer rolls. For example the rolls of the Wet press may be so crowned that the web issues wetter along the edges than along the center, thus to offset the higher drying rate normally occurring along the edges than at the center on subsequent passage of the web about the drying rolls prior to creping.
The moisture profile across the web is not a problem in making ordinary flat paper, because by the time the paper reaches the end of the machine, it is adequately dried across the entire width thereof. Nor is it a problem in the manufacture of ordinary creped paper for the same reason, but becomes a problem only in the case of creped and embossed paper for reasons above stated. For these reasons the significance of this factor has not heretofore been appreciated or understood in the production of creped and embossed paper insofar as I am aware,
despite the difliculties heretofore encountered in the production thereof, and in subsequent bag tubing and forming operations owing to improper moisture content and moisture profile of the web at the creping and embossing stages. Nor has the source of these difficulties been recognized, nor have method or means for eliminating the same heretofore been devised, to the best of my knowledge.
As explained above, for producing the creped and embossed paper, the web should be creped as dry as possible in order to remove the maximum moisture permissible by drying the web in the flat before creping, but the retained moisture at the creping stage must be sufficient to adhere the web to the creping roll, and also such as to assure that there will be no serious loss in strength of the final product due to insufiicient bonding as a result of the subsequent embossing operation. 011 the other hand, the web should be embossed at as high a moisture content as possible because as above pointed out, the higher the moisture content at the embossing stage the higher the ultimate stiffness and modulus elasticity of the creped and embossed product. These two rather antithetical considerations logically require that the embossing operation immediately follow the creping operation, and that both occur in the paper-making sequence following sufiicient drying of the web in the flat to reduce the moisture content to a value within the broad and preferred ranges above stated.
Referring now to the annexed drawings for a further description of the invention;
FIG. 1 is a more or less schematic or diagrammatic representation of a preferred embodiment of apparatus for practicing the invention.
FIG. 2 is a graphical showing of the manner in which the machine stiffness and elastic modulus of the creped and embossed product varies with the moisture content of the web at the creping and embossing stages.
FIG. 3a is a graphical showing of the moisture profiles across the web and certain properties of the resulting extensible paper, obtained on the apparatus of FIG. 1 when constructed and adjusted in accordance with the present invention to provide a substantially constant, cross direction moisture profile at the creping and embossing stages, this series of graphs showing the moisture profiles at the first and second wet pressing stages, respectively, and also at the creping and embossing stages, and also showing for .the resulting creped and embossed extensible paper thus produced, the cross web profiles for the machine direction elastic modulus and stiffness, and also the basis weight thereof.
FIG. 3b is a graphical showing similar to that of FIG. 311, but showing the corresponding moisture profiles obtained in accordance with prior art practices at the first and second wet pressing stages, respectively, and also after dryer roll demoi-sturizing as at 13, FIG. 1, prior to creping, and also showing for the resulting creped and embossed paper, the cross web profiles for the machine direction elastic modulus and stiffness, and also the unsatisfactory basis weight profile which contributes to the poor moisture distribution.
FIG. 4 is a diagrammatic showing in side elevation of the wet press rolls illustrating in exaggerated degree the manner in which the rolls are crowned for producing the moisture profiles of the web shown in FIG. 311.
FIG. 5 is a graphical showing of typical machine direction stress-strain diagrams for, respectively, a fiat kraft, a dry creped kraft, a conventional, wet creped kraft, a compressively shrunk kraft, and a wet creped and embossed kraft, the latter in accordance with the present invention.
FIGS. 6 and 7 are plan views on a greatly enlarged scale of the front and reverse sides, respectively, of a creped and embossed paper in accordance with the present invention; While FIGS. 8 and 9 are sectional views thereof as taken at 88 and 99 of FIG. 6.
Referring to FIG. 1, a web W of kraft paper is formed in conventional fashion on a Fourdrinier wire 10 of a paper-making machine, and is fed successively thence between the pairs of pinch rolls 11a, 11b and 12, 12b, comprising the first and second wet presses, respectively, wherein excess moisture is squeezed out down to the level of about 67-70% moisture content. The web is fed thence about the sequence of dryer rolls 13, wherein the moisture content is further reduced to the level of about 40-59% and preferably about 50-55%, as above explained, and is fed thence onto the creping roll 14, provided with cooperating pressure roll 15, for adhering the web to the creping roll. Bearing against the creping roll is the knife blade 17 for stripping the web from the creping roll in creped manner, from whence the web is fed optionally about the series of rolls 18, for suitably handling the wet creped web in passing from the creping roll directly to the embossing press rolls 20a, 20b, wherein the creped web is preferably embossed longitudinally at spaced intervals transversely thereof.
Owing to the machine direction shrinkage of the web at the creping roll 14 due to the creping effect, the embossing rolls 20a, 2011, must be run at a lower peripheral speed than the creping roll and the preceding rolls of the machine, this lineal speed differential being proportional to the shrinkage effect and thereby constituting a measure of the amount of creping. For example, if the creping and preceding rolls are run at a lineal speed of 700 feet per minute and the embossing rolls at a speed of 600 feet per minute, the difference would be feet per minute or approximately 15% of the lineal speed of the creping roll, so that the creping effect would also be approximately 15%. A preferred percentage range as thus determined for the creping effect is about 620%, preferably about 10-15%.
The so-creped and embossed web passes out of the embossing rolls 20a, 20b, under the guide roll 21 and thence about the series of drying rolls 22 operating at such increased lineal speed as compared to that of the embossing rolls, as to remove a substantial portion of previously induced stretch imparted by the creping, for example, about one-fourth to one-half thereof, and also to complete demoisturizing the web substantially to the dry state. The web passes thence about the rolls of the calender stack 23 to the Winder 24, to produce the final creped and embossed product, as illustrated in FIGS. 6 to 9, inc.
Referring to FIGS. 3a and 4, the rolls 11a, 11b, of the first wet press, are crowned as in FIG. 4, and as indicated at 30, 31, to provide a cross direction moisture profile for the web issuing therefrom, substantially in accordance with graph 32 of FIG. 3a, as obtained in a typical test run in accordance with the invention. Likewise the rolls 12a, 12b, of the second wet press are similarly crowned to impart a moisture profile to the issuing web substantially as shown by graph 33 of FIG. 3a, also as obtained in said test run. During subsequent passage of the web about the drying rolls 13, FIG. 1, the marginal edges thereof dry at a faster rate than the central portion of the web, to give a resulting moisture profile of the web as it passes onto the creping roll 14, FIG. 1, substantially as shown by graph 34 of FIG. 3a; also obtained in said test run, from which it will be seen that the moisture profile is substantially constant at this stage, having an average value of about 54%, and a variation of not over about plus or minus 1% or a total variation of not over 2%. The web as thus both creped and embossed at this moisture level, imparts to the final creped, embossed and fully dried extensible paper, cross direction profiles, for the machine direction modulus of elasticity and stiffness and for the basis weight, as shown by graphs 35, 36 and 37, respectively, of FIG. 30, from which it will be seen that each of these profiles is substantially constant across the width of the web, the ma chine direction elastic modulus having a high average value of about 202,000 p.s.i., the machine direction stilfness a high average value of about 285 Gurley, and the basis weight having an average value of about 49.9 pounds.
Referring now to FIG. 3b, representative of prior art practices in the production of creped and embossed paper, graphs 40-45, inc., correspond, respectively, to graphs 32-37, inc., of FIG. 3a. It will be seen from the graphs of FIG. 3b, that the moisture profile across the web is substantially greater at the center than along the edges at all stages of demoisturizing, and that this effect hecomes increasingly more pronounced as the demoisturizing proceeds through the first and second wet pressing stages and the first dryer section, as evidenced by graphs 40, 41 and 42, respectively. From graph 43, it will be seen that at the creping stage there is roughly an eight percent variation in moisture content across the web, productive in the final creped and embossed paper, of a variation in the cross direction profile for the machine direction elastic modulus from about 100,000 p.s.i. at the web edges to about 200,000 p.s.i. at the center, or a variation of approximately 100%. From graph 44 showing the cross direction profile for the machine direction stiffness, it will be seen that it ranges from about 225 Gurley at the web edges to about 300 Gurley near the center, or approximately 35%. Similarly for the basis weight profile 45 the variation over the profile is about 7%. As compared to these variations, the graphs of FIG. 3a typifying the present invention show that at the creping stage of graph 34 the variation of moisture content across the web is less than 2%. From graph 35 it will be seen that the variation in machine direction modulus across the web is confined within limits of about 180,- 000 and 200,000 or a total variation of about 30,000 which as compared to the average value of 202,000, is about 10%. Likewise the stiffness variation is confined within limits of about 280-290 which as compared to the average value of about 285, is less than The test results of FIGS. 3a and 3b were obtained by modifying a standard paper machine, installed for the production of flat kraft paper at a web width of about 125 inches and at a web speed of about 400-800 feet per minute. Referring to FIG. 1, this machine was initially modified by installing the creping and embossing sequences 14-21, inc., between the first and second dryer sections 13 and 22. The crowns on the wet press rolls of the machine as installed, and previously operated in the standard, conventional manner, were measured and found to be as follows: On the top roll of the first press the circumference at the center of the roll was greater than at the outer ends of the roll, the roll being 20" in diameter at the ends. For the bottom roll of the first press, the circumference at the center of the roll was greater than at the ends, this roll being 24" in diameter at the ends. The same dimensions were employed for the top and bottom rolls, respectively, of the second press. Creped and embossed paper as produced on the machine as thus modified gave the cross direction profile graphs 40-45, inc., of FIG. 3b. The roll crowns were then modified experimentally until until the cross direction moisture profiles at the first and second wet press stages were as shown by graphs 32 and 33 of FIG. 3a to produce the cross direction profile at the creping stage as shown by graph 34 of FIG. 3a. As thus modified the circumference of the top roll for the first press, was made A" greater at the center of the roll than at the ends, the diameter at the ends being 20". No change was made in the bottom roll. For the second press, the circumference of the top roll was made greater at the center than at the ends. The bottom roll was left unchanged from that above stated. The machine as thus modified was again operated to produce creped and embossed paper, and the resulting cross direction profiles for the machine direction modulus and stiffness and for the basis weight were then found to be as shown in graphs 35, 35 and 37 of FIG. 3a. I
It is to be understood, of course, that alternative expedients may be employed 7 for imparting a substantially constant moisture profile at the creping stage, as for example, by so contouring the crowns of the wet press rolls as to impart a substantially uniform moisture profile to the issuing web, followed by substantially uniform drying across the width of the web as it passes about the first se'riesof dryer rolls, which can be obtained by the installation of hot air blowers medially of the Web, etc.
Referring to FIG. 5, there is shown at gnaph A, the average moisture content of the web at the creping and embossing stages, is progressively increased, the machine direction stiffness and modulus values of the resulting creped and embossed paper will increase in substantially linear proportion thereto, in the manner illustrated by the graphs 36a and 36b, respectively.
Referring to FIG. 5, there is shown at graph A, the machine direction stress-strain diagram for a typical Wet creped and embossed kraft paper as produced in accordance with the present invention, as compared on the same basis weight to that of a dry creped paper, graph B, a Wet creped and unembossed paper, graph C, a compressively shrunk and unembossed paper, graph D, and a natural kraft flat paper, graph E. Graph F shows the machine direction modulus of elasticity for the wet creped and embossed paper, while graphs G and H show the elastic moduli for the fiat kraft and for the compressively shrunk kraft paper, respectively.
It will be seen from a comparison of the graphs F, G and H, that the creped and embossed paper of the present invention, graph A, has "a substantially higher machine direction high modulus of elasticity than that of the compressively shrunk paper, graph D, and one which although lower than the machine direction elastic modulus of the flat kraft, graph G, is nevertheless approaching the order of magnitude of the latter.
The moisture content of the paper at any stage of production, is defined as the wet weight minus the dry weight divided by the wet weight, which ratio times one hundred gives the moisture content in percent.
Reverting to FIGS. 1 and 6-9, inc., the embossing roll 20a of the embossing press 20, is provided with axially spaced peripheral ribs and interposed slots for impanting the grooves 46 extending longitudinally of the web and having disposed therebetween the creped lands '47. It is to be understood, however, that other embossing patterns may be employed, such as zig-zag or sinuous grooves as well as other patterns. Also the creped web may for some applications advantageously be flat pressed rather than embossed by employing cylindrical press rolls in the embosser.
The present invention thus provides methods and means for producing a new article of manufacture, namely, creped and embossed extensible paper, having throughout the width of the paper web as produced, and irrespective of web width, high and substantially uniform values for machine direction stiffness, on the order of 260-290 Gurley, and for the elastic modulus, on the order of 175,000200,000 p.s.i., together with excellent and uniform properties in other respects such as bilateral tear resistance, machine direction instantaneously recoverable extensibility, and bilateral energy absorption. Such extensible paper having such properties may be produced in the Widest web widths of modern paper machines which extend up to 25 feet or more, and at the highest web speeds of such machines ranging up to 2000 ft./min. or more. The web so produced may be slit to any desired width for producing bags of correspondingly high and uniform machine direction stiffness, elastic modulus, etc., in the bag plies, such bags ordinarily being made from such web stock slit to widths of about 30-55 inches.
What is claimed is:
1. The method of producing on a Fourdrinier wire paper machine, a continuous web of extensible paper, of high and uniform machine direction stiffness and elastic modulus, which comprises: progressively forming raw paper stock on said wire into a continuous wet web of substantial width; progressively removing excess moisture from said web to a greater extent along the medial portion thereof than along the outer edges; thereafter progressively drying said web to a greater extent along the outer edges thereof than along said medial portion and to a substantially uniform moisture content throughout its width and to a value within the range of about 4059% and varying not more than about 2% in total amount across the Width of the Web, thereafter creping said Web transversely of its length; thereafter embossing the so-creped web substantially longitudinally thereof and at spaced intervals transversely thereof; thereupon pulling out a portion of said oreping; and thereupon progressively further demoisturizing said web to substantial dryness.
2. The method of producing on a paper machine, a continuous web of extensible paper, of high and uniform machine direction stiffness and elastic modulus, which comprises: progressively forming raw paper stock into a continuous Wet web of substantial Width; progressively feeding said web between opposed pressure rolls, contoured to demoisturize the median portion of said web to a greater degree than the marginal portions thereof; thereafter progressively drying said Web at a higher rate along the marginal portions thereof than along said median portions thereof until the moisture content of said web is substantially constant across the width thereof and has a value within the range of about 4055 and varying not more than about 2% in total amount across the Width of the web, thereafter creping said web transversely of its length; there-after embossing the so-creped web substantially longitudinally thereof and at spaced intervals transversely thereof; thereupon pulling out a portion of said creping; and thereupon progressively further demoisturizing said web to substantial dryness.
References Cited by the Examiner UNITED STATES PATENTS Re. 25,335 2/63 Hamilton 162-413 2,996,425 8/61 Hamilton 162--113 3,104,197 9/63 Back et a1 162-113 OTHER REFERENCES Calkin: Modern Pulp and Paper, 3rd edition, 1957, Reinhold Publishing Corp., N.Y., page 340.
DONALL H. SYLVESTER, Primary Examiner.