CA2128015A1 - Method and apparatus for crosslinking individualized cellulose fibers - Google Patents

Abstract

An apparatus is disclosed for preparing a quantity of individual treated fibers from one or more fiber mats. The apparatus comprises a fiber treatment zone, and a conveyor for conveying each mat through the fiber treatment zone. In the treatment zone each mat is impregnated by an applicator with a treatment material, such as a crosslinking substance, and conveyed directly to an attrition device. The attrition device fiberizes the mats to form a fiber output having a low nit level, such as no more than about three, and a dryer both dries the fiber output and cures the crosslinking substance. The fiberizer is configured to minimize the accumulation of fiber at locations therein. Fiber is transported from the attrition device to the dryer at a high velocity under reduced pressure to promote drying. A heated retention bin is provided after drying to increase curing time in the system. A thermobonding agent may be added to the dried and cured fibers to enhance the wet strength of webs made from the fiber.

Description

WO 93/14264 P~us93~00280 212~01~

ME~OD AND APPAl~TIJS FOR CROSSLI~NC;
INDIVIDIJALIZF.l- CELLULOSE FIBERS ~`
`~
SCROSS-REPERENCE TO RELATED CASES
This is a conhnuation-in-part of pending IJnited States~Patent Applications Serial No. 07/665,761, filed March 7, 1991; and Serial No.
071607,268, file~ Oc~ber 31, 1990, which is a continua~on-in-part of Serial No.
07/3~,208, filed August 179 19899 which is a continùa~ion-in-part of ApplicationSerial No. 07/284,~85, filed December 15, 19889 which ls a continuation-in-part of Application Senal No. 07/140,922~ filed December 28, 1987, which is a con~inua~ion-in-part of Application Serial No~ 071004,72g, filed 3anuary 20, 1987.
....
BACKGROUND OP TB INVEN~ON
1. Field of the Invention This invention rdates t~ a fiber t~eatment apparatus and m~e par~icularly to the apparatus of the :type which utilizes sp~ayers or other applicators to treat a fiber mat and mechanisms for subsequently fibenzing the mat followingsuch treatment.

2. Gene~al Discussion of the Background Various ~eYices are known in the ~ for treating fibers with crosslin~ng agents in; mat form and thereaft brea~ng the mats into indh~idual fibers. ~or example, U.S. Patent No. 3,440,135 to Chung discloses a mecha-~ism 2~ for applying a crosslinking agent to a cellulosic fiber mat, then passing the mat while still wet and following ~aging" th~ough a fibeI~zer, sueh as a hammermill to fibe~
~he mat, and drying ~he resulting loose fibers in a two stage dryer. The first drye~
stage is at a tempera~ure sufficient to flash water vapor f~m the fibers and the seeond drye~ stagc is at a tempe~ture that effeets cu~g of the crosslirlldng a~gent.
30 A cyclone separator is then illustrated separatillg the fihrs from the gas and for subsequent collection. Chung mentions the need for the "aging" step, of many hour~

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duration, in order to reduce the level of nits in the resulting fiber product. Asdescribed below, nits are typically interbonded fibers which can inter~ere withproduct quality. Therefore, the Chung apparatus suffers from the drawback of requiring the inconvenient and ~s~ly storage of wet fiber mats ~e.g. in roll form) for S a substan~al pe~iod of time in order to minimize nit forma~on.
Unfor~unately, fiberization process~ known in the art which employ currently available fiberizing or comminution machinery yield crosslinked fibers that have too many nits and hlots to be acceptable for many uses. A pr~bable reason is that such machinery has excess dead space where fibers are excessively pressed 10 together and/or has localized regiolls of elevated temperature hot enough to cause ~-~ premature curing of the crosslinl~ng agent while fibers are in intimate con~act with each other. Since fibenzation is per~ormed on a mat that Is still wet with the uncured crosslin~ng agent, dead spa~s and hot spots in the fiberizer would encou~age the fo~n~on of interfiber bondx, which form ni~s, that v~ y ~ot be broken by downstream ~quipment.
Interfiber bonding in a conventional fiberizer apparatus can also lead to produc~on of e~ccessive ~nounts of "fines," which are undesirably short fibers due ~ncipally to ffber breakage. Crosslinl~ng imparts substan~al bnttleness to cellulose fibers, which thereby exhibit limited compliance to mechanical stresses. Nits are especially susc~ptible to mechanical stresses becau~ of their density which is much g}eater than the density of individual fibers. Excess fiber breakage and fisles not only deg~de abso~ncy but can substandally reduce the loft and resiliency of a product made from crosslinlced fibers.
One approach to reducing fines is to diminish interfiber crosslinl~ng, as in published Ew~n Patent Application Nos. 427,316 A2; 429,112 A2; 427,317 A2; and 4409472 A1, as well as in copending United States Patent Applica~on Serial No. 07/~7,268, filed Oetober 31, 1990. A drawback to this approach is thae the substan~al elimina~on of interfiber bonds p~oduces a we~ ha~g low ~ensile st~eng~h. Wet laid sheets made ~rom such fibers tend to ~all apart, ~d are unsuitable f~r many indus~rial applica~ons.

SUBSTITUTE SHEET

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Yet another problem ~th prior pr~esses is that output from the system is so r~pid that fibers ~eated with the crosslillldng agent do not haYe sufficient ~me to cure after they are fiberized and dried. Curing time ean be increased by lengthening the conduit through whieh fiberized and d~ied mate~ial S passes, but such a solu~on is expensive. Lengthening conduits requires a lar~e capital investment that reduces cost efficiency.
Hence, there is a need for an apparahls that will produce ~eated fibers, such as in~fiber crosslink~d cellulose, having a nit level lower than levels obtainable with exis~ng ~uipment. There is also a need for such an apparatus 2hat will produce fibers from a mat compnsed of cross!inked ~11ulose while not causing ~r significant breakage of individual fibers of the mat.
It is an object of this invention to provide such an individualized, in~afiber ~osslinl~ed cellulose web ~at has improved wet tensile s~rength.
It is another object of the inven~on to pr~de a pr~cess for produciog an individuaiized, isl~afiber crosslinked~product that provides increased cu~ing time ~or cr~sslinking to progress after the fibers are dried.
l[t is yet another object of the invention to pr~vide such a process that has improved flash drying of moisture from the fibers prior to cunng.
It is ano~her object of the invenbon to enhance the uniformity of crosslinlcing agent applicabon to a fibrous mat.
Another object of the present invendon is to provide ~ apparatus and method for produGing treated fibers, such as crosslinked cellulose fibers9 with a low nit leYel and preferably a nit l~vel no greater than about three.
Another obj~t is to provide such an apparatu~ and meth~ that comminutes one or more mats of non~Iosslillked cellulose fibers whieh have been impregnated with a erosslinldng substanee, where the comminution is perfonned before the cr~sslinl~ng substance is dried and cured.
Another object is to provide such an appa~atus and me~od that minimizes the b~eal~ge of individual fibe~
Another object is to provide such an appar~tus and method that ~elds crosslinked fibers having substan~ally no krlots.

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It is yet another object to provide a crosslinking process th~t o~rates at a pH that is compatible with siandard unmodified papermaking equipment.
Finally, it is an object of the pre~nt invention to provide a shæt having high bulk, wet resilience and good porosity in~ which liquid impregnants can .
S be ef~lciently introduced. - ~
These and other obJects of the inven~ion will be understood rnore ~-:
clearly by reference to the ~ollowing detailed desc~tion and drawings. `
',':
SUMMARY OP ~IE INYENTION
The apparatus of the present invention is par~cularly adapted ~for preparing a quantity of individual crQsslinked cellulose fibers from one or more mats Gomprised of non~rosslinked cellulose fibers. The apparatus comprises~
applicator that applies a crosslir~ng substa~ce to a mat of cellulose fibers at a fiber treatment zone; a fiberizer having a fiberizer inlet;~ a conveyor that convey~ the ma~
through the fiber treatment zone and dir~ctly to the fibenzer iniet without s~Lng ~ i for cum~g. Ihe fibe~izer provides sufficien~ hammering fo~e to r~e the ;.
cellulose fibers of the mat into a fib~ ou~put of substantially unbroken individual cellulose fi~rs. A drye~ coupled to the fibenzer receives the fiber ~utput, dries the fiber OUtpUIt, and cu~ the crosslinking subs~ance, thereby ~orming dned and cured 20 fibers. The fiberizer prefe~ably fiberizes the treated mat to foml a fiber ouq)ut having a low nit level, such as a nit level of no :more tlhan: about 3.
The apparatus also includes a reduced pressure conduit betw~n the fibe izer and dryer in which the indiv~dual cellulose fibers are heated and the veloc~
of their flow is incsea~ed after they l~ve the fib~rizer. This conduit ope~s into an ~:
25 expansion chamber that allows the fiber flow to expand and increase fiber sepaIa~on.
The flow velociqr of dle fibe~s in the conduit is preferably inc~d by reducing the dia~neter of the condwt betw~en the fiberizer an~ dryer. A downs~n connec~ion between the conduit and drya g~ually increases in diameter to provide an e~cpansion ~ne bct~vecn the c~nduit and e~cpansion chamber. The reduced dia~eter30 conduit pr~vides an area of r~duced pressure that promotes evaporadon of m~isture from the fibers o~ the conduit. The expansion chamber subsequently p~vides SUE~5TlTUTE SHEEl-w~ g~/14264 2 1 2 ~ O 1 ~ P~/USg3/~0280 another evapora~on ~ne in which moisture is quickly and explosiYely released from the fibers, ~hereby further enhaulcing their separation and productioD of individualized fibers.
l~e apparatus further includes a ho~ air blower that blows hot air in~
S the conduit toward the expansion chamber. ~ibers are introduc~d into the conduit between the blower and expansion chamber through a fiber introduction inlet. Theblower preferably introduces hot air at a temperature of about 260C into the conduit to ~ansport the fibers and reduce their moistur~ content in the r~duced pressureenvironment of the necked down conduit. -The appa~atus also preferably includes a heated ~eten~nn cha~ into -- which dried, ~eated fiber output is inaoduced for a preselected period of time to allow curing ~f the crosslinl~ng substance. In some embodiment3, the reten$ion chamber is posi~oned between ehe flash d~ing and curing chambers of the dryer.
In other embodimellts, the reten~on chamber is do~stre~m from ~e ~ing ch~nb~r, for example9 aft~r a cyclone s~ra~or that sepalates fibers ~ecei~red fr~m the curing chamber. In especial~y pref~red embodiments, the:reten~n chamber has the sh~pe of an mverted pyramid with an open ba3e through which ~he fibets are introduced. The apex of the py~amidal chamber can selectively be open~ and closed to control the movement ~ cured fibers out of the bottom of tlae re~ on chamber.Representa~ve conveyors include, but are not lin~ited to, conveyor bel~s and ~oller mechanisms. In the fiber treatment zone, the crosslinking substance can be applied to the mat via any suitable means including, but not limited to, spraying, roller coa~ng, and a combina~on of spraying and roller coa~g. ~e applicator that applies the crosslin~g agent is prefe~ably a shower sp~ay ~ollow~
by an impregna~on r~ller that p~sses the crosslinking substance into the mat. Inespecially prefe~red embodiments, the shower spray indudes a ~ of opposing shower spray applic~tors that direct droplets of the crosslinl~ng agent toward the two oppos~g face of the mat. The impregna~on roller is preferably a pair OI ~osing rollers ~hat coo~vely e~cert l-50 psi, preferably 1-2 psi, impregnadon pressure on t} e mat. In par~cularly disclosed embodiments, ~e shower spray applicators are positioned vertically ove~ a fiberiær inlet, and the impregna~on rollers abut the mat 5UBSTITUTE 5HE~T

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between the spray applicators and the fiberi~er outlet. The area be~ n the rollers can form a flooded nip that diminishes flow of excess erosslinl~ng agents into the fiberizer outlet. .
The dryer of the apparatus pre~erabl~ includes a drying zone ~or 5 ~orming dned fibers, and a curing zone for curing ~ crosslinking substances on the dried fibers. The drying zone preferably includes the expansion chamber, which has an inlet for receiving the individ~ cellulose fibers from the restricted diameter conduit. The dryer inlet has a temperature within the range of about 2~315C so as to fl2sh evaporate moistur~ from and expand the cellulose fibers. The subsequent 10 cunng zone has an outlet through which the dned and cured fibers are delivered ~' from the dryer. The outlet of the curing zone preferably has a temper~ture within a ~ange of about 14~180C~
The drying ~nd curing zones preferably compIise a first and a second tower, respectively, in which the fibers are lo~ed to ensure thorough flber 15 ~ separa~on. In the d~er, flash d~ng of the fibers occurs which microscopically e~plosively separates fiber~ loosely adhering tog~er in the form of a fiber lalot.
The fiberizer apparatus comprises at least an attri~on device which produces a low nit level fiber output. The fiberizer may also optionally include a disk refiner of conventional design coupled to the attrition device and a fluff 20 generator of novel: design coupled to the disk refiner.
A preferred embodiment of the ~t~ition device compIises a substan~ally cylindrical rotor rotatable about a longitudinal a~is ~nd a housingsurTounding the rotor. The housing may include up to six ma~ feeder assemblies each capable of simultan~ously urging a wet or dry treated mat ~to engagement with 25 ~he rota~ing rotor. The rotor includes groups or stacks of }~ntners e~ctending longitudinally and radially oYer the surfa~ of the rotor, such as in an alterna~g fashion. In a specifie arIangement, any hammer group is longitudinally and ra~y adjzcent an empq~ space large enough to accept a hammer gr~up, arld any said emp~
s~ace is adjacent a hammer group. Air flow mly be di~cted wi~in ~he attrition 30 de~ice away from the ends and toward the center of the rotor thereill to minimi~ the possible accumulation of fibers at such end locations. Also, the attrition device may SUBSTlTUTE SHEET

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7 - ~
include a fluid, and preferably a liquid, flushing mechanism for use in cl~ing any ~;
accumulated fiber from the a~i~on device. The att~i~on device substantially la~
internal hot spots and dead spaees, there~y inhibi~ng ~ormation of nit~, in the fibers produced by said device. Also, the a~i~on device inhibits fiber breakage.
S A preferred embodiment of the fluff generator comprises three ro~o~s having coplanar parallel longi~udinal axes ea~h su~ounded by a cylindrical housing.
The rotor housings are con~guous and par~ally intersecting. All three rotors rotate synchronously in the same direction abou~ their axes. ~ach rotor compriscs mul~ple lon~itudinally ex~ended groups of multiple radially pr~ecting pins which, dunng ro~a~on of ~he rotor, ~avel past multiple~ longitudinally ~tended groups of mul~ple shoner pins projecting from the inside of the corre~nding rotor housing toward the rotor axis. The fluff generator is effec~e ~or providing a~ditional comminution, if requiled, of the fibers~ pardcularly of residual hlc3ts in the comminu~ fibers produ~d by the attrition device. ~ ;
The present inven~don also includes a method of pr~ucing crosslinbxi celluh~se fibels by applying a crosslinking substance to a mat of cellulos~ fibers at a fi~er treatment zone, then conv~ring the mat from the fiber ~ tment zone dir~c~y into a fiberi~er without stopping to cure the crosslinking substance.: The ~es the fibers by hammering :them into substantially unbroken individual :~
~ellulose fibers, pre~erably having a ~t level of no more than about 3. The `~;
~ted fibers are then dried at a tempe~e of about:200 315C so as to flash evaporate water ifr~m the fiber output7 and then cure~ at a temperature of about l~ i 180~
In par~cularly prefelTed embodiments, a thermobonding a8ent is added to the dried and cured cellulose fibe~s produced by ~e foregoing p~. The mix~ure ~ thermobonding agent and cellulose fibers forms a mi~ture that is made ;nto a web, and ~e web is ~en hea~ to a sufficient tempe~ature to thennobond ~e `
fibers: t~gether ~nd increase the wet strength of the web. l~e thermobonding agent can, for ~xample, be a bicomponent fiber having a core cornponent in a sheath, wherein the core component (for e~c~nple, polyprop~lene) has a higher melting point than the sheath eomponent (for example, polyethylene). The ther nobonding agent ~.

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comprises 5-50% by weight, more preferably 20 40% of the mixture. The ~ermobonded crosslinked fibers have been found to produce a bulky, crosslinked product having good absorbent properties.
When the eore of the bicomponent fiber Is rnade of polypropylene and 5 the sheath is made of polyethylene, the mixture is heated to about 13~1$0~C to melt ~he polyeehylene sheath, while allowing the polypropylene core to maintai~ i~s s~ruc~u~al integnty. The intact core provides a ma~c in ~e mat that enhan~s the wet strength of ~he resulting web. ~e enhanced wet s~ngth of the web pennits formation of cellulose products using a wet laid pr~ess. These products may be 10 impregna~dwithbinders,suchascarboxymethylcellulose. Soft,flexiblepac~aging ~-~ materials can be made by impregnating the product with a binder such as acrylic or vinyl acetate latex. Flame-retardant cellulose materials can be made by impregnating the mat wi~ polyvinyl c~oride or poly~inylidine chloride, fos use as insulation material in build~ngs. Rigid paclcaging or soundpr~ofing material~ :an similarly be 15 made by impregna~ng the wet laid mat with acrylic or polyvinylacet~t~ bind~s.In yet another embodiment, the dried and cured fibers of the present inven~on can be collected and introduced into a pulp furnish to increase bulk and subsequent imp~egna~on of che~cals into a sheet made fr~m the pulp furnish. The high bulk fibers of the present invention increase the porosity and absorbance of a 20 sheet made from the ~rnish. Compared to a standard fiber made without addih~nof high b~ fibers, the pulp fun~ish of the present i~r en~on produces a sheet haviog an increased sa~ on ~ate~ incre~sed bulk, and under cer~ condi~ons enhanc~d s~ngth at higher bulk~ Enhanced absorbency of *e resul~ng sheet~d product increases impregna~on efficiency and r~duces waste dwing subsequent impregna~on ~5 of the fibrous material with binders such as late~. In ~cularly preferred embodim~ts, the high bulk fibers of the present inven~on can be added to a pulp fu~ish, which is then used to make fibers that a~e subjected to the crosslinl~ngpr~ss ~ the present inven~on.
The crosslîr~ng agents of the present inven~on ~n include 30 p~ly~bo~ylic acids and urea derivatives consis~ng of methylolated urea, methylolated cyclic ureas, lower all~l subs~tut~d cyclic ureas, dihydroxy cyclic SUBSTlTlJTE SHE~T

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ureas, lower alkyl substituted cyclic ureas, and methylolated dihydroxy cyclic ureas;
acid anhydrides fr~m the group consis~ing of maleic anhydride~ phthalic anhydride, 4 carboxyphthalic anhydride, pyromelli~c anhydride, and melliti~ anhydride, ~yromelli~e anhydride, and mellitic anhydride; polycarboxylic acids; dialdehydes;
Sand mi~ctures thereof. The crosslinlcing agent i more preferably a polycarboxylic acid, for example a tricarboxylic or tetraca~Dxylic aeid, such as citric acid (2-hydroscy-l ,2,3-p~opane~carboxylic acid) or 1 ,2,3,4-butanecarboxylic acid.
The pH of the cellulose fibers remains above about 2 a~ter the - crosslinking agent is applied to the mat, and is preferably no more than about 4.
10llle most preferred pH range is 3-4. A pH below 2 may damage the cellulose fibers .~by acid hydrolysi~ whereas a pH above 4 may reduce the efficiency of the crosslinl~ng reac~on.

BRIE~ D~SCRIPI~ON OF THE DRAW~GS
15FIG. 1 is a schemadc de~ic~ion of the components of the appa~atus of thepresentinvention.
PIG. 2 is an isometric external view of a ~erred embodiment of an a~i~on d~vice, where certain details of the mat feeder ~semblies have been omitted for el~ty.
20FIG. 3 is a ~ sverse sec~ional ~r~ew of a mat fe~der assembly of the pre~err~d em~iment of the at~i~on device.
~:IG. 4 is an isometric view of the rotor of the attrition device o~
FIG. 2.
PIG. S is a plan view of aL hammer plate used in the rotor of ~IGc 4 25FIG. 6 is an isometric view of a stack of hamme~ plates used in ~e rvtor of ~IG. 4.
PIG. 7 is an isometric ~iew of the e~cterior of a p}efer~ed embodiment of a fluff geneIator included as an option in the apparatus of the present invention.
~;IG. 8 is a transverse sec~onal view ~hrough a hou~ing por~on alad 30rotor of the fluff gene~ator of FIG. 7.
FIG. 9 is a plan sechonal view of the fluff generator of FIG. 7.

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FIG. 10 is an enlarged view of the crosslinking applicator portion of the diagrarn of ~IG. 1, only olle feeder roll being shown for sinnplicity.
PIG. 11 is an alt~rna~ve view of the system showing a retal~on bin that allows curin~ of the crosslinking agent afeer the fiber is dried.
S FIGS. 12 and 13 a~e cross-s~ctional view~ of concen~ic and acen~ic bicomponent fibers for incorp~ratio~ to fibrous mats containing the individ~
fibers produc~d by the method of the present invention.
FIG. 14 shows the fibrous mat of the pre~ent invention con~ning lon~
bicomponent fibers (prio~ to thermobonding).
FIG. 15 shows a matrix s~ructure f~rmed by the bicomponent s~uctu~es ~-~ in the mat after th~rmobonding.
PIG. 16 is a schem~tic view of air laid equipment for produeing the ~hennobonded absorbent matenal of ~:~e present invention.

DErAI~ DESCRlPrlON
Overall System The apparatus 10 (~;IG. 1) of the present inven~on eomprises a ~:~ conveying device 12 for ~sporting a mat 14 of cellul3se fibers or other fibers through a fiber treatmerlt zone 16; an applicator 18 for applying a treatment substan~ such as a crosslinhng substance from a sou~ce 19 thereof to the mat 14 at the fiber treatment zone 16; a novel q3pe of fibe~iær 20 for completely separa~g the individu~l cellNlose fibers comprising ~e mat 14 to form a fiber vutpu~
` comprising subseantially unbroken ~ellulose f~ substan~ally without nits or l~nots;
and a dryer æ couple~ tO the fiberizer for flash~.rapora~ing residual moistu~ m the fiber output and ~or cu~ing the crosslinl~ng substance, thereby fonning dried and cured oellulose fibe~s. The apparatus 10 of the p~nt inverl~ion has been observed nsist~tly p~oduce fibers with a nit level of less than three, which is subs~ally lower than obtainable using any ~tus p~iy Icnown in the art.

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Raw Matenals As used herein, a "mat~ denotes any non-woven sheetlike structure eomprising cellulose fibers or other fibers that are not covalently bonded together.
The fibers may be obtained ~om wood pulp or other source including cotton llragn~
S hemp, grasses, cane, husks, cornstalks, or any other suitable source of cellulose fiber that can be laid into a sh~t.
Preferably, the m~t 14 includes a debonding agen~ whieh cas~ be applied a~ter ~ormation oiF the mat 14 or ~dded to cellulose fibers be~ore fonT~ing the mat therefrom. For exals~ple, with mats comprising pulp fibers, the debon~ing agent can be added to wet pulp before the rnat is laid using convetltional p~permaking~-~ machinery. D~nding agents tend to minimi~e interfiber bonds be~ween fibers Qf the mat. A fair, but none~haustive, sampling of debonding agents is disclosed in~J.S. Paten~ Nos. 3,395,708 and 3,544,862 to Hervey, ee aL; 4,144,1;!2 ~D
Emanuelssl~n7 e~ al.; 3,677~886 tc~ Forssblad, ee al.; 4,351,699 to Osbome I[I;
4,476,323 to HeDsten, et al.; and 4,303,471 to Laursen, all of which ~ herein incorporated by re~erence. Any suitable debonding agents may be used, such as preferably Berocell 584 ~m 13erol Chemicals, Incorporated of Metairie, Louisianain a 0.25% weight of debonder to weight of fiber. However, use of a debonding agent is not re~uir~d for complete fibenzation USillg the present apparatus.
The mat 14 of cellulose fibers is pre~erably in an ~xtended sheet form : stor¢d in the fiorm of a roll 24 un~l use. While the mat 14 can al~ be one of a number of baled sheets (not shown) of discrete size, rolls 24 are generally m~reeconomically adaptable ~o a con~nuous process. The cellulose fi~ in the mat 14 should be in a non-wo~en configuration produced by a pulping process or ~e liloe, such as in a p~per mill, and can be bleached or unbleached. The mat 14 ca~ haYe any of a wide va~iety of ba is weights. For simplicity, FIG. 1 shows a roll 24 as . the sour~e of each mat 14, but it is to be understood that the mat 14 can be supplied in any foml amenable for stonng sheet-l;ke st~uctures. Also, the mat ma~ be obtained dir0ctly from the headbox of pa~er making equipment or othe~wise ~ormedin any suitable manner.

SlJ~STlTUTE St~EET

WO 93/1"2~4 P~r/USg3/00280 . -It is nonnally not necessary that the cellulose fibers comprising the mat14 be completely dry. Since cellulose is a hydrophilic substance, molecules thereof will typieally have a certain level of residual mois~re, even a~ter air drying. The level of residual moisture is gene~lly 10% w/w or less9 which is not detætable as S "wetness.'' - :
E:IQ. 1 also shows that more than one supply, such as multiple r~lls ~4, of the mat 14 of cellulosic fibers can be simultaneously pr~sed USi-lg the present invention. For simplicity, FIG. 1 shows two rolls 24 being processed~ but it is to be underst~ that even more supplies of cellulosie fibers can be 10 simultaneously processed, depending upon ~he capacity of the equipment, particularly the fiberiær 20. As discussed her~in below, the preferred embodiment of the fiberizer 20 can fiberize up to six mats at one ~me.
At ~rne fiber ~eatment zone 16, sprayers or oth~r appli~tors 18 apply chemicals such as ~rosslinldng agents to the mat. Typically, chemicals are applied 15 uni~ormly to bo~ sides of the mat. PIG. lO shows one pa~cular em~diment of the applic~tor in which a ~r of opposing sprayers 18 are posi'doned adjacent each face of mat 14 to spray crosslinking agent at the mat and saturate it ~nth the crosslinldng agent. The wetted mat ~s between a pair of impregnation rollers 28 which assist in distribu~ng ~e chemicals uniformly through the mat. Rollers 28 coopera~vely 20 apply light presswe on the mat (for example, 1-2 psi) to force crosslinking agents uniformly in~ ~he interior of the mat acr~s~ its width. The roller~ 28 form a seal with the ma~ such th~t the crosslinl~ng agent can form a puddle at the nip. This seal helps pr~vene the liquid c~osslinl~ng agen~ iFrom f~g into the inlet 34a of the fib~rizer 32 that is posi~oned ver~cally ~elow the flooded nip. Other applicators 25 may also, of coursel be used. Examples of other applicators include si~e presses, nip p~esses, blade a~plicator systems and ~oam applicators.
Each mat 14 is urged by the first and s~cond pair of ~ollers 26, 28 ~ough ~e fiber trea~nent wne 16 whe~e the mat 14 is impregn~ted wi~h a liquid ~sslinki;lg substance. The c~osslinldng subs~nce is pre~e~ly applied to one or 30 both su~faces of the mat using any of a varie~r of me~ods known in ~e art useful for such a purpose, such as spraying, rolling, dipping, or an analogous method.

SUBSTITUTE SHEET

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;~O 93/1426~ 2 1 ~ 8 0 1 !; PCI/U~93/0028~

Spraying has the advantage of consistent and rapid full coverage of a planar sufface such as a mat at a controllable rate, esp~cially when the sp~ay is applie~ to a surface moving past a spray s~ozzle or analogous applicator at a fix~d rate. Roller applicators have also proven to be reliable and ef~ec~e in such applications as paper S coa~ng and the like and would ~erefore be e~fective ~or applying the crosslin~ng substance in the present instance. Combina~ons of spray and roller ~pplicat~rs can also be employ~d.
The crosslinl~ng substance is typically appli~d in an amount rang~g from about 2 kg to about 200 kg chemical per ton of celllllose fiber and preferably about 20 kg to about 100 lcg chemical per ton of cellulose fiber.
~-~ The rollers 28 ean ~ posi~oned relative to each other to have a defined gap therebetween so as to enable them to impart a controlled squeeze action to the impregnated mat as it de~; the fiber treatment zone 16. As men~oned above, such squee~ng action ~acilita~es complete and w~iform penetra~on of ~e 15 crosslin~ng substance throughout the ~ichless dimension of *e mat. The squeezing action also helps to regulate the degr~e of satura~on (~loading level") of the mat 14 with the crosslinl~ng substance.
l~he crosslinking substance is a liquid solution containing any of a variety of crosslinl~ng solutes known in the art. If r~quired, ~he crosslinl~ng 20 substance can include a catalyst to a~celerate the bonding reac~ons behYeen : mol~ules of the c~osslinldng substance and cellulose molecules. Howe~er, many if not most c~osslinl~ng substances do no~ require a ca~yst.
Preferg~d types of crosslinldng substances a~e selected from the group cs~nsisting of urea de~iva~ves such as methylolated urea, methylolated cyclic ureas, 25 methylolated lower alkyl subs~d~uted cyclic ureas, dih~roxy cyclic ureas, low~ allyl subs~tuted dihydroxy cyclic ureas, and methylola~d dihydro~y cyclic u~eas; a~d anhydrides from the group consisting of male;c anhyd~ide, phthalic anhydride, 4-~hthalic anhydride, pyromelli~c anhydride, and mellitic anhydnde;
poly~bo~ylic acids; dialdehydes; and mixtures thereof. A ~fically prefe~ed 30 crosslinldng substance would be dimethylsldihydroxyethylene urea (DMDHE~U). In addi~on, another prefe~ed crosslin~ng agent is a polycarboxylic acid, such as citric SUBSTlTUTE 5HEET

WO ~3/14264 PCr/US93/00280 ~l2'S~

acid ~2-hydroxy-1 ~2,3-pro~etricarbo~ylicacid) orthe 1 ,2,3,4-butanecar~cylicacid disclosed in co pending United States Pat~nt Applicahon Senal No. 07l395,208 filed August 17, 19~9, which is a continua~on^in part of S~rial No. 07/284,8857 filed December 15, 198~, which is a con~nuation~ part of Serial No. 07/140,922, filed December 28, 1987, which is a u)n~nuation~ part of Senal No. 07/004,729, filed January 20, 19~7. Other cro~slinking materials are known in the art, such as de~ribed in tbe previously mentioned Chung ~tent; U.S. Patent No. 4,935,022 to Lash et al.; U.S. Patent No. 4,889,595, to Herron et al.9 U.S. Patent No. 3,819,470 to Shaw et al.; U.S. P~tent No. 3,658~613 to Steiger et al.; U.S. Paten~ No.
4,822,4S3 to Dean et al.; and U.S. Pa~ent No. 4~8~3,086 to Graef et al., all of ~- which are hereby incorporated herein by reference.
Suitable catalysts include acidic salts which can be use~ul when urea-based crosslinking substances are used. Such sales include ammonium chlonde, ammonium sulfate, aluminum chlonde, magnesiun~ chloride, or mi~tures of these or15 other similar compounds. ~ metal salts of phosphor~us containing acids may al30 be used.
In FIG. 1, the crosslir~ng substance applied to the mat 14 is obtainea from a supply 19 ther~f, such as a tank or analogous vessel. It is also possible for the supply 19 of crosslinl~ng substance to be con~inuously produced on-line to 20 prevent pre~un of the crosslinking substance that may occur over ~me if it were stored in a large vessel. On-line produc~on of the crossli~ng substance is par~cularly advan~eous when it contains a catalyst. Alte~natively, for e~cample,a ba~ch of the crosslinldng subs~nce ~ be pre~ared ~resh each day, so long as nosignificant deterio~ation of the solution will occur during the period in which the 25 batch is consum~.
Crosslinked cellulose fibers are individual fibers e~ch compnsing mul~ple cellulose molecules whe~e at least a portiun of the hydro~cyl groups on the cellulose molecules have been covalently bonded to hydroxyl gro~ps on neighboring cellulose molecules in the same fiber via crosslin~ng reac~ons wi~ ac~ sly 30 added chemical reagents termed "crosslifll~ng SUbS~UlCeSff or ~crosslinldng agents".

SUB5TlTUTE S~EET

~0 93/1~264 Pc~r/uss3/oo~8o .
212~

Suitable crosslinking agents are gene~ally of the bifunc~onal type which cre~te covalently bond~ "bridges" between said neighboring hyd~xyl groups.
Crosslink~ cellulose fibers have particular applicability not only in wrinkle-resistant fabric~ but also in mate~ials d~nved from wood pulp having one or S more desirable cha~acte~istics such as high loft, ls~w density, high water absorbency, resiliency, and light weight. As a result, cr~ssiinked cellulose fibers are candidates for use in absorbent s~uctures ~ound: in disposable pr~uc~ such as diapers and pads.
lhey are also useful for paper towelling, wiping cloths, filters, and other similar uses.
Despite thdr desiMble quali~es~ crosslinked celluloæ fib~rs have ~r previously enjoyed limited success as a raw matenal. A principal reason for this is because the most con~enient way for a manufacturer to crosslinlc cellulose fibers is by applicadon of the c~ossliPJdng agent ta a cellulosic fibrous sheet or mae which must be sub~equently fibenzed (all~ thc constituent fibers of the sheet or ma~
separated ~rom one ano~her) before the fibe~ ~ be subjected to a s~ in which thecrossiirldng agent is cured. If any curing occurs before the fibers are completely :~ separated, interfiber bonding can occur which would make any subsequen~ attempt ~: at c~mplete fibe~iza~ion virtually impossible.
Crosslinked cellulose fibers when used in many products cannot have excessive asnounts of ce~n de~ts hnown in the art as~ "~aots" or "ni~si'. Knots are agglom;lbons of fibers rem~ning ~r an incomplete fibenza~on of a cellulosi~fibrous sheet. Nits may be defined as hard, dense agglome~ations of fi~ held togetber by the cr~sslin~ng subs~ce due to the ability of crosslinl~ng agents ~
:~ covalently bond individual fi~s together (interfiber bonding). Nits are generally regarded in ~he ~ as ha~g a surf~ce area of abaut 0.04 mm2 to about 2.00 mm2.
A nit usually has a density greater than 0.8 g/cm3, where a den~ of a~out 1,1 g/cm3 is typic~l. The fib~s compnsing a nit virtually cannot be sepa~ om one another in a conventional fibai;cing device. As a result, these rec~lat~ant par~cles b~ome inco~ ted into the final pr~duct where they can cause subs~al degradation of product aesthetie or func~onal quality. Por example, ni~s can substan~y reduce the absorbency, resiliency, and lot of al~ absorbent product. Por SUBSTlTUTE SH~T

WO 93/14264 PCr/lJS93~0Q2~0 ~.

aesthetically sensi~e products, such as high quali~ paper, a "nit level" of three or less (two or fewer nits per ~inch diameter test "handsheetn; see l~xample 1) is generally regarded as a ma~imally accep~ble number of nits. Knots can also seriously degrade product appearance. Also, as an e%ample of the effect of theseS par~cles on product performance, filters n~ade using cro~slinked fibers containing any nits and ~ots would in many cases be incapable of performing t~ s~ificatiops.

C: onveying Device Referring further to ~;IG. 1, each mat 14-of cellulosic fibers is 10 conv~yed by a conveying device 12, which can comprise, for example, a conveyor ~-~ belt or a series ~ driven rollers with the mat posi~oned therebetween. The conveying dlevice 12 carries ~he mats through the fiber treatment zone 16. FIG. 1 . also show~ a further portion of olle type of conve~g device compnsed of a first pair of rollers 26 and a second pair of rollers 28 for ea~h mat 140 The first and second pair of rollers 26, 28 are par~eularly effective for urging the corresponding mat at a substantially constant and con~olled rate of spe~d.

Fibenzer The subsystem following ~e. fiber treatment zone is a fiberizer 20 which serves to comminute one or mo~e mats 30 impregnated with the crosslinldng subs~ance into individual substantially unbroken cellulose fib~rs comprising a fiber output. The fib~ 20 performs its task on one or more mats, which a~e pre~eirably s~ll moist ~but which may be ~ om application of the crosslinldng agen~. In this case, the wet sheets are delivered ~tly and immediately to the fiberizer by the oonveyor 12 without aging ~r other sigs~ificant delays. As detailed beloYv, the preferr~d embodiment of the fib~ 2Q is designed to ~mize inte~fiber bonding and the ~ormation of nits th~. Also, the preferred esnbodiment of the fiberizer 20 thoroughly ffbenzes e~ch impregnated mat 30, thereby ~irtually elimina~ng residual knots.
The prefe~ed embodiment of the fiberizer 20 comprises an attridon device 32 as detailed hereinbelow and in copending U.S. Patent Application Serial SUBSmUTE 5HEET

.. ~0 93/14264 PCrJUS93/00280 212~01~

No. 07/607,312 en~tled "Fibe~izing ApparatusH, filed on October 31, 1990, which is incc~rporated herein by reference. The attri~on device 32 preferably can simultaneDusly fiberiæ a plu~ality sf imp~egnated ma1:s 30 and has a separate mat inlet 34a, 34b for receiving each corresponding impregnated mat.
The exterior of a pr~fe~ embodiment of the at~ition d~Yice S0 is shown in FIG. 2, which compnses an elongat~d cylinder-sha~ housing 52 having an e~ ior surface 54. A firs~ end panel 56 is located orl one end of the housing S2 and a second end panel ~8 is loca~ed at the other end of the housing 52. Multiple - ma~ inlets (~vo of which 60a, 60b are shown) defined by the housing are located radially ill an ar~ compnsing a portioll of ~e circumference of the housing 52,- whe~e ch mat inlet is dedicat~d to feeding a s~a~ate mat in~ the attrition device 50. An outlet chute 62 extends from the housing 52. Each end panel 56, 58 defines a central onfice 64 through which coa~;ially extends a cor~onding ~tor sha~t end 66 ~otatable relative to ~he housing 52. ~e ~otor shaft ~nd 66 is coupled to a dnve motor 68 serving to impart rotational mo~on ~ereto.
An:air flow port 69 is pro~rided through each end panel 56, 5~. As a : ~ downs~eam blower l60 ~discuss~d below) coupled to outlet 62 is operated, air is : drawn in through openings 69, and around the ends of the rotor 100 (discus~ below in connec~ with FIG. 4) tQ assist in minimizing the accumulations of fiber at such locations. ~Ithough valiable, air typically flows at a rate of about 50 m3lmin through each of the openings 69. Also, a sonduit (not shown) is typieally included and ~oupled to wall 52 delivering water or other cl~ing fluid to the interior of the housing th~ough plural nozzle openings to slean any fiber accumulations f~om theattri~on device. A liquid cleaning operatiotl is typically accomplished by diree~ng water t~ward the rotors ~ a d~on somewhat counter to the direc~on of the normal ~otor rota~on as the roto~ is roeated in t&is ~on. Cl~g may be peIiodically peffonned, such as once e~ry sixteen hours of ope~a~on of ~e at~ition de~ce, depe~ding in part up~n the volume of fibe~ ~g p~ssed, 13y cleaning fiber aGcumula~on~ in this manner, the accumuhtions do not end up in the fini~hed product where they may compnse bonded nits.

SlJBSTlTUTE St~EET

WO 93/14264 P~/US93/00~0 lB
Eaeh mat inlet includes a ~er assembly, such as assemblies 70a-70f shown par~ally in FIG. 2, each mounted e~ iorly relative to the cylindrical housing 52 at a l~ation adjacent the corresp~nding mat inlet. A representative fe~der assembly (such as 70d in FIG. 2~ is shown in more de~ail ~n the transverse sectional S ~riew of FIG. 3. 13ach feeder assembly 70 is comprised of a first feed ~r seal roller 72 and a second feed or seal roller 74 extellding longitudinally between the first and s~cond end panels 56, 68 ~IG. 2). Also extending longitudinally ~tween the firstand second end panels ~6, 58 are corresponding support angles or bracket~ (such as 76a and 76b in PI(3. 3) and wedg~shap~d alignment or moun~ng bars (such as 78a and 78b in FIG. 3). Since PIG. 3 only depicts one ~er assembly 70d, angles 76a . -~ and 76b correspond to the fieeder a~sembly 70d. The first and second seal rollers 72, 74 ex~nd longitudinally in a direction substan~ally parallel to, and haYe a length substan~ally equal to, ~e corresponding mat inlet 6~ situa~ between a leg ~0 of the angle b~ack 76a an~ a leg 82 of the angle bracket 76b. The seal rollers 72, 74 15 are rotatably mounted for rota~on about their respes~ve longihldinal a~ces 84, 86 at locations equidistant from the mat inlet 6~a. The distance D, f~m a plane through the axes of seal rollers 72, 74 to the effec~ve rotor surface l44 swept by the hammers of the rot~r 100 (:PIG. 4? is preferably ~rom about one-half ~ch to no more than abou~ four inches when wet shee~s are being fed to the roto~ lO0. This 20 minimizes the possibili~ of plugging of the opening 6()a as the sheets are being delivered thereto.
Ln one ~fiGllly preferred design, each seal roller has a central shaft and an outer roll. The ends of the een~al shaft of ea~h seal roller 74 are coupled by a ~ive bearing to the end pl~tes 56, 58. In addi~on, ~e e~ds of ~e ~ntral 25 shaft of ~e seal rolle~s 72 are support~d for rot~on by a bra~et (one being shown as 87 ~n FIG. 33. Typi~y the s~l rollers are of a ~igid material, such as steel,he seal roller 74 being mounted at a fixed location. The ends of the shaf~ of the seal ~olle~ 72 ar~ posi~oned within res~ ve ~esses 85 in the res~ e b~cbets 87. The bIacloet 87 may be pivotally coupl~d ~o the housing ~or pivoting30 in the diroc~on of alTow 9l upon removal of a bolt or other stop 89. When bracke~
87 is shifted upwardly in FIG. 3, the seal roller 72 may be Pmo~ed for repair and SUBSTITUTE StlE~T

~IO g3/14264 P~r/US93/0~280 212~0~

or cleaning and to provide access to seal rolle~ 74. Pneuma~c cylinders, not shown, typically apply a load of from 5 psi to 80 psi to the ~espective ends of the shaft of the seal roller 72 to bias the seal rollers together. This pressure is typically ~elieved to allow ~he feeding of a sheet be~ween ehe seal rollers and is then reinstated du~ing S normal operation of the attri~on device. At least one of ~e ~ rollers~ SUC~
roller 74, is rot~tably driven via a motor ~not shown) at a ~ntr~lled angular velocity to advance a mat (not shown) situated betw~n ~he first and second rollers 72, 74.
Roller 74 may, i~or example, be driven in the direc~on of arrow 93 at a predetenTIined mat feed rate t~rough the mat-inle~ 60a.
A first guide %8 and a ses~ond guide 9() are also mounted to the ~- corre~onding moun~ng bra~ke~s 76a and 76b, lespec~vely. Ea~h of the guides 88, 90 ~xtend longitudinally in a direc~iol~ substan~ally parallel to the cor~esponding seal r~llers 72, 74, ~vely. Each guide 88, 90 i~ typically construc~ OI a rigid matenal and includes arl Quter edge 92, 94, especdvely" adjacent to, but ~
from the sur~ace of tbe corresponding seal roller 72, 74, respec~vely, along ~he ~ull length of the roller. The guides 889 90 there~y s~rve to substantially pre~ent air from passing past the guides and to the eorresponding mat il~let 60a~ Therefore,substarltially all of the air drawn into the at~on device passes through the openings 69 (as p~eviously e~plained3.
The fib~r mat passing through inlet 60a passes an op~onal nose bar 95 d is delivered against the ro~or 100 traversing the e~fective rotor surface 144 (FIG.

3). The gap between the inlet 60a and ~he effec~ve rotor su~face is typi~ally nom~re than about one-fourth to one inch.
PIG. 4 shows a rotor 100 of ~he type ~a~ially mounted ~side the att~i~on de~ice housing 52 (PIG. 1?. The rotor 100 ~omp~ises a plurality of subsgaJI~ally annular spacer or hammer moun~ng plates 102 mounted to the rot~r shaft 104. The plates lOQ e~tend ladially ou~dly f~om the longi~dinal axis ~A"
OI ~c Totor ~ 104 and are parallel t~ one another. The rot~r 100 also has a first ~otor end plate 106 and a se~ond rotor end plate 1089 ea~h substan~lly annular in shape and oiente~ parallel to the moun~ng plates lOQ. The first and second rotor end plates 106, 108 are mounted coaxially to the rotsr shaft 104 and have a diarneter SUBSTITUTE SHEET

W(:~ 93/14264 Pcr/u~s3/oo28o 2 ll~28ols sufficiently large such that only a narrow gap (e.g. one-six~nth ~o one-half inch) is left between the inner surface of the cylindrieal housing (no~ shown in FIGo 4) and the perimeter of the f;rst and second end plates 106, 108. The illus~ated plates 106, 108 extend radially ouh rardly beyond the distal ends of hammers 116 to minimizeS the possible accumula~on of fibers adjacent to the end plates.
Attached to and extending between the first and second end plates ~re plu~al inner moun~ng rods 110 and an identical number of outer mounting rods 112oIien~d parallel to the longitudinal ~s "A" of the r~tor sh~ft 104. The inner and outer mour~ g rods 110, 112 are secured to the first and second rotor end plates10106, 108. As shown clearly in FIG. 4, the moun~ng rods 110, 112 are ar~anged as ~-~ plural equiangularly spaced ~rs. Each pair comp~ises a single inner mounting rod 110 and a radi~ly ou~wardly posi~oned single outer mounting rod 112. A typical rotor 100 has sLsteen such ~s of rods arTanged radially about the rotor a~cis "Ar.
Ea~h pair of moun~ng r~ds 110, 112 has m~unted ~here~ plu~ groups 15of ha~s~mer plates, each group comp~ising a hammer assembly 116. ~ach such hammer assembly 116 is located either between adjacent moun~slg plates 102 or bet~veen a spacing plate 102 and an adjacent rotor end plase 106~ 108. However, each hamme~ assembly 116 is spaced from an adjacent hammer assembly 116, by an empty space 118 large enough to accommodate ano~her hammer assembly. As a 20result, on a rotor 100 with twenty-seven moun~ng plate~ 10~ and h~O rotor end plates 106, 108, for example, the m~mal number of hammer assemblies 116 held by a gi~en ~ of moun~ng rods 110, 112 is fou~teen.
A re:presenta~ve fht hammer plate 130 of assembly 116 is depicted in :E;IG. 5, wherein each hammer plate 130 has a pro~cimal end 132 posi~oned toward25the rotor axis (not shown) and a distal end 134 posi~oned radially outward relative to the ro~or a~is. The hammer plate 130 also defines two moun~ng holes 136a, 136b for atta~hing the hammer 130 to an ~atetl pair of moun~ng rods 110, 112 (not shown in FIG. 5). I~e distal end su~ace 134 of the lummer plate l~si a ~ailing edge 138 and a l~ding odge 140, whaein the l~ding edge 140 e~tends radiialliy 30outward rela~ve to the rotor axis beyond the trailing edge 138. The distal end 134 SUE~STlTUT~ SHEET

~0 93/14264 2 1 2 ~ ~ 1 5 Pcr/usg3/oo28~

is cut at a five degree angle rela~ve to a line 142 parallel to the pro~mal edge 132.
The direc~on of rota~on of the rotor is indicated by an arrow 145 in FIG~ 5.
As shown in FIG. 6, each illustrated hammer assembly 116 comprises plural planar plate-like hammers 130 (~hree being shown in this figure). ~ese plates are typically spac~d apart by spacers (not shown). Each of said hammer assemblies 116 located between adjacent n ounting plates 102 (only one plate ~02 being sh~wn in this figure) also includes a le~t-angled hammer 146 and a right-angled hammer 148 e~ch having a lip lSOa, 150b, re~tively, extending transversely in an opposing direction relative to each other. The width dimension 152 of the lip of each angled lû hammer is typically equal to or slightly less than half the thichless dimension of a ~-' mounting plate 102. Also, each of the hammer assemblies 116 located between a plate 102 and a ro~or end plate replaces one of the L-sha~ hammers with a flat hammer pla~e adjacent to the end plate. Other hammer configu~ations ~d ~gements may be used. HoweYer, a prefelTed hamme~ ar~gement minill~izes any gaps in the wr~ace swept by hasnmer elements to ~prefaably no mo~o than onerfourth of an inch.
The illus~ated embodiment 50 of the attri~on device is operated by driving the rotor 100 at a high angular vdocity while feeding one or more impregnat~d mats through one or more ~nding mat inputs. The mat is urged ~ ~ 20 at a contr~led linear veloci~y into the corresponding mat input slot 60 by the :~ eontrolled ~a~on of thc fe~d roller~ 727 74. As the impregnated mat enters a mat ~ ~ :
inlet, it is ~ledly impacted by the distal end surface and~in paltiCUIar9 the leading edge of tbe hammer pla~es, wh}ch ef~ ~ely and completely comminutes the mat into its individual constîtuent fiber~, subs~n~ally ~ree of Itnots and l~its.
l~e prefe~ embodimen~ 50 of the a~on device as described hereinabove is par~ularly ~ dve in simultaneously fiberizing o~ or mor~
se~a~te ~nat~ (up tt3 si~) to form a volume of indh~id~ cellulose fibers h~ving a nit level substantially lower than levels achievablc Ynth ~usting attri~on devices such as hamm~mills. This is be~icved to be due to the fact tha~ the present attridon : 30 de~ice lacks hot spots and dead sp~ces, when~in fibers can accumulate, fowld in convendonal hammeTmills or other at~ition de~,rices culTently used in the art.

SUBSTlTUTE 5HEET

W(~ 93/14264 212S6J~S PCr/US93/0028 Referring further to FIG. l, a first conveyor fan 160 of conventional design can be u~ for prc~pellirlg the fibers ~rom ~he outlet 62 of the a~ on device 32 through a condui~ 16~.
An optional component of ~e fiberizer 20 is a first cyclone l64 or 5 similar apparanls imown in the art, u~ d in a conventional manner to concentrate the fibers passing out of the outlet 62 of the attrition device 32. The first cyclone 164 receiYe~; the fibers ~rough the conduit 162 coupled thereto.
Excess air can be rec~vered at ~he top 166 of the firs~ cyclone 164 and recycled as required t~Wgtl a conduit to a location upstream of the first conveyor 10 fan 1~1 (îf used3. Such additional air ~ be berleScial ~or easing the ~sfer of the ~-~ fibers th~ough the hrst con~reyor fan 160.
A disk refiner 168 is another op~ional component of the fibenzer 20 which can be employed to effect addi~donal ~eparation of fibers (removal of h~ots) if required. The disk ~er 168 is of a typ~ Imowra in the art and comprises a disk refiner inlet 170 and a disk refiner outlet 172. A representative disl~ refiner 168 is type DM36 manufactured by Sprout-Bauer, Incorporated of Muncie, Pennsylvania.
If the disk refiner 168 is used, the inlet 170 thereof is coupled via a conduit 174 to an outlet 176 of ~c f;rst cyclone 164.
A second conveyor fan 178 may optionally be u~liæd to urge ~0 pr~paga~on of the fibers through a conduit 180 downs~am of the disk ref;ner 168.
~cess air can be reoovered from the top 166 of the first cyclone 164 and routed via a ~Dnduit 181 ~ a tee 182 just upstream of ~he ~nd conveyor fan 178.
Another op~onal ~ompon~nt of the fiberizer 2Q is a fluff generator 190 which receiYes the fibers f~m the op~onal s~cond conveyor fan 17~ through a 25 conduit 184. The flu~f generator is descnbed in detail below and in copending U.S.
P~tent Applica~on Serial No. 07/607,157 en~tled "Mul~ Rotor Fiber ~:luff Generator~, filed on C)ctober 31, 1990, inco~porat~ herein by refe~ence.
~ efemng now to ~;IG. 7, aprefe~red embodimentof ~e fluffgene~ator 190 compri~es a housing 192 sh~ped in the form of three contiguous, p~ally 30 in~rsec~g cylinders, including a first housing portion 194 opening into a second (or middle) housing portion 196, which-~pens into a third housing portion 198. Each SUBSTlTUTE 5HEET

. ~093/14264 PCI/US93/00280 ` 212~01~

housing portion 194, 196, 198 has a longitudinal coplanar axis A1, A2, A3, respectively. The housing 192 has an inlet 200 pe~itting delivery (arrow 202) offibers to the first housing portion 194, and an outlet 204 conduc~ing fluffed fibers away (arrow 206) from the thir~ housing por~on 1~8.
As shown in FIG. 8, sho~g a transverse sectional view of the first housing portion 194, the interior surfa~s 212 of each of the first, sscond, and third housing por~ions have affixed thereto multiple stator pins 214 radially poin~ng tcrward the respective axis of the housillg pol~ion. The pins 214 are grou~ in longitudinally extended rows along l~es ~el to the respective housing por~o 10 axis.
~-~' Each of the ISrst, second, and third housing portions 194, 196, 198, respec~vely7 is in surrounding rela~onship to a first rotor 216, a sesond rotor 218, and a ~ird rotor 220, resp~vely, as shown in PIG. 9. Each ~otor 216, 218, 220 has a co~Dnding rotor shaft 2æ, 224, 226, coæ~al with the axi5 Al, A2, A3 of 15 the re~ective housing por~i~n. ~s shc~ in FIG. 8 ~sho~nng a transverse sec~onal view of ~he first housing ponion 194 only, but applicable to illus~a~e similar det~ils inside tlle second housing portiorl lg6 and third housing por~on 198) and PIG. 9, t~
~he shaft 222 of the rotor 216 are mounted four longitudinally ex~ended rows of : plural r~tor pins 2289 where each row of r~ or pins 228 is equiangularly spaced in a ~dial manne~ ~round the co~onding rotor shaft 222. The rotor pins 228 radially extend from the shah æ2 n~ly to the iDside su~ 212 of the : ~ITe~ondiDg housing portion 194 but are positioned on the rotor shaft 222 such that : tlhey will pass bgtween lon~dinally adjacen~ stator pins 214 when the rotor 216 is rota~ng a~ut its a~is. Rotor sha~s n4 and 226 are similarly equipp~d with rotor ~5 pins ~28.
As shown in PIG. 9, each rotor shaICt 222, 2~, 226 has a fir~t end 230, 232, 234, respec~vely, and a second end, ~36, 238, 240, re~ectively, each e~tendir~g t~ough and journaled in the co~e~onding h~using por~on 194, 196, 198,~vdy. The first and second ends of each rotor shaf~ e~tend ou~ e the ~onding housing portion. A pulley 242a, 242b is attached to each of the Srst ends 230, 232, re~vely, of the f~st and second rotor shafts 222, 224, SUBSTITUTE SHEET

WO 93/142S4 PCI`/US93/0~280 . .

res~pectively~ Iikewie, a pulley 244a, 244b is ~ttached to the secoDd ends 238, 240, re~ec~vely, of the se~nd and ~ird roto~ shaf~s 224, 226, ~e~Y~ly. The fir~t end 234 of the third rotor shaft is r~tatably cwpl~d dir~ctly or indirect~y to a drive motor 250~ Each set of pulleys is coupled by a d~ive belt ~2a, 252b ens~g that, when the dfive mo~r 250 rotates ~e ~i~d r~or 2~, the ~econd and first roto~s 218, 216, re~ec~ely, synchronously ~t~e in ~e same ~otational direc~on as the ~ir~
rotor 220.
The fluff gene~ator 190 is operated by synehr~nously dri~g the rotors 216, 218, 220 at a high rota~onal speed and conducting fibe~s 202 (PIG. 7) fr~m their disk refiner 168 (PIG. 1), where the velocity of said fi~ is increased via the ~-~second conveyor fan 178, into the inlet 200 of the fluff gene~ator 190. The fibers are conducted sequen~ally through the first, second, and third housing po~ons 194, 196, 198, re~ec~vely, and e~it 206 ~he fluff generator 190 thrwgh the outlet 204.
As the fi~rs pass through the h~using 192 of ~e fluff gene~ator 190, they encounter s~aong agitation and turbuience gene~ated by ~e groups of ~tor pins 228 on each of ~e three ~pidly ~ta~ng rotors 216, 218, no passing by the sta~onary stator pins 214. By encountering such turbulence and agitation, any hlots remaining in the fibers are comminuted to fonn a fiber ou~tput containing v~rtually no hlots.
As used herein, the "fiber output" is the mass of tho~oughly individualized fibers exiting the fiberize~ 20 and passing to the dryer 22.
As discussed hereinabove, the disk refiner 168 and fluff generator 190 are op~onal compollents of the presenl apparatus 10. In most cases, the attrition device 32 alone is adequate for completely fiberizing plural mats. However, in cases where ~he mats are unusually bulky, the disk refiner 168 and fluff generator 190 can be employed, particularly to ensure the absence of h~ots in the fiber output.

Dsyer Referring fur~her to FIG. 1, a preferred embodiment of the present apparat:us 10 includes a dryer 22 which is utili~ed to perform two sequential fimctions: remove residual moisture from the fibers and cure the crosslinking agent.
Preferably, the dver 22 compnses a drying introduction zone 273 for receiving SUB5TlTUTE SHEET

WO 93/1426~ 2 1 2 8 0 1 ~ Pcr/US93/00280 fibers e.g. from ~ f gen~rato~ ou~ 204 and for ~m~ving n~sidual mois~e f~m the fibers via a Uflash drying~ me~hod a~d anothe~ dryiJlg wne 260, 262 for curing the ~osslilll~g agentO In ~IG. 1, ~e cunng s~s in zone 260 and con~u~
~rough zone 262.
The FIG. 1 em~e~t shows that zone X73 is coupl~d ~ the fluff generator ou~et by a conduit 272 and ~ a source 274 of hea~ ~, typically pr~duced by combus~on of a ~upply of n~ al ga~ 276 and fresh air 278. The temp~rature of heated air is regul~ted to maintain the tempe~ e of ~e drying zone 273 within a range of about 200C to about 315~C. To achieve ~is tempe~ature in zone 273, a~r is bl~wn f~om source 274 at a tempera~ur~, ~or ~ample, of ~u~
~-~ 260C. The drying ZODe 273 is a J-shaped conduit ~hat includes a necked down or reduc~d diame~er cDnduit having an ini~al por~on 273a, and a righ~ angle por~on 273b th~t flares to increase th¢ di~neter of the conduit as it co~ s wi~ the inlet 268 of the expansio~ chambe~ defined by body ~66 of drying z~ne 260. The diame~er of the reduced di~neter por~on conduit is ~educed comp~d to the diameter of the conduit 272 thr~ugh wl~ich the fibers flow from the fiberizer. The diameter reduction increases the velocity of the flow of filbers and causes a decrease in pressure that promotes rapid evaporation and drying of the fibers in portion 273a.
The fiber output in ~nduit 272 is in~oduced int~ the reduced diarneter por~on 273b of conduit 273 at inlet 275 immediately downst~ rom where portion 273a necks begins.
As the fiber output passes into the drying zone 273 at inlet 275, the wet fibers compnsing the fiber output are substantially instantaneously exposed to the high temperature in this zone. Such rapid exposure to high temperature impares a "flash drying" effect to the fibers, thereby causing rapid and thorough dryingSuch ~flash drying" also tends to separate, in a microscopically explosive manner, fibers that are touching one another, thereby ensllring thorough separation of the fibers. lhe passage time through the drying zone 273 is preferably less than onesecond, which is deliberately kept shon to avoid overhea~ng and scorching the fibers, which become highly susceptible to scorching after the residual moisture has been driven therefrom.

SU8STlTUTE SltEET

4 , PCI/U~93100280 ~ .
2~,2~0~ :

As the fib~rs ente% ~e expanding thr~t of s~on 2 73b and en~er fir~t drying zone 260, pressure cha~ges enhance ~e mic~osco~ic fi~ explosions as wate~vapor is ~api~ly releas~d ~rom the fibe~ d pushes ~e fiber ~art. This ~ding thr~at 273b mates with an e~ding inlet 268 to an e~pan~ion chambe~ def;ned by S first d~ying zone 260. The FIG. 1 em~>odiment shows that ~he first dr~g zone 2~
eomprises a first tow~ 2~ ring a b~dy por~on 266, an inle$ 2689 and a first t~wer outlet 270. ~e dryer zone 273 is ooupled via condl~it 272 to ~he outlet of ~e fluff generat:or 190. Since the fluff gene~ator 190 is an optional component, it is also possible to couple the dryer introduc~don zone 273 d~tly to the ou~et 62 of the attrition de~rice 32 if neither the fluff ge~e~ator l90 nor the ~isk refiner 168 are ' -~ mcluded. -In ~I(i. 1, the first tower ou~et 270 is shown preferably coupled via a conduit 280 to a d~wn tube 282, which i~ coupled via a conduit 284 to a third conveyor fan 286 located at an inlet 288 of a s~ond tower 290. The third conveyor ~an 286 performs the fi~nc~on of transpor~ng the fibe~s ~rough the dryer which the~by pass through the inlet ~88 of the s~conld tower 290.
The second towe~ 290 is shown which includes the inlet 2889 a s~cond tower body 292, and an outlet 294 serving as an outlet of ~he dryer 22. Dri~d fi~rs .
are propelled through the inle~ 288 of the second tower 290 via the third conveyor ~an 286. As the fibers are lo~ted through the second tower body 292, they are still exposed to a curing tempe~ature within a range of about 140C to about 180~C, which is sufficient to effect euring of the crosslinldng agent without scorching the ' dry fibers. The lof~ng keeps the fibers separated until the crosslinl~ng reaction is complete. The curing temperature depends upon the type of crosslin~ng material 2S used t~ ~eat the fibers and also is set at a level so as not to scorch ~he fibers during curing. I~ should be noted that single stage d~yers may also be used.
The dried and cured fibers exiting the dryer outlet 294 have an ex~emely low level of nits and v~ y no hlots. Further, they are not discolored from scorching and the like, and have a median fiber length substantially unchanged from the median length of the fibers compnsing the mat 14.

SUBSTlTUTE 5~1EET

~o 93/14264 P~r/US93~002~0 21280~ `

~IG. 1 als~ shows a s~cond cyclone 300 of c~ven~onal design ~upled ~na a collduit 302 to the ~yer ou~e~ 294t serving ~ co~ b ae ~e fib~
passing therethro~gh in p~ara~on for collec~on. E~ce~s air 3W is vent~d ~rough the top 3~ of ~e sewnd cy~lone 300. The resul~ng ~oncen~a~ed fibers can lbe collect~d using any of a number 4f c~lle~on d~ces 308 known in the art, ~uch a$
fiber bagging de~
It is possible to add re~n~on bins ~ the ~ystem of FIG. 1 ~
curing time of ~e crosslin~ng agent. Such a bin 310 is shovvn betweell cyclone 300 and collec~on device 308. Bin 310 has ~e shape of an in~er~di py~an~id~ and is large enough to hold the output from cyclone 300 ~or a period of l-S minutes when ~-~ the system is ~ ng. The bin is preferably heaeed to a tempera~e of about 175~
190(: to p~omote curing of ~e er~sslinker. The most preferred temperature within ehis range may vary ~nth the capaci~ of ~e bin, because larger retaining bins will allow longer residence ~mes at lower tempeIatures. A bin with a sufflcient ~cityto collect 5 minutes of output from cyclone 300 could, for ~ample, be heated to a temperatu~e of 175C. A smaller bin with only a th~ee n~inute capa~ity, however,may r~quire a ~sidence tempe~ature of l~O~C. Very small reten~on bins, for eacample bins with a one minute capaci~, rnay have a bin temperature of 190C topromote curing of the crosslinldng agent in the sho~ter period of tisne.
An alterna~ve c~osslin~g system having a reten~on bin is shown m FIG. 11, in which an air heater 400 propels fibers through a conduit 402. The fibers which enter conduit 402 have already been saturated with ~e crosslinking agent, and the fibers begin to dry as they are moved through heated corlduit 402 by a ~nveyor fan 404 into a conduit 405. Fibers are then introduced tangentially frcm conduit 405 inio a top cylindrical area of a first dryer 406, and then fall downwardly. The bottom por~ion of dryer 406 tapers at 408 tv an outlet 410 such that partially d~ied fibers are withdrawn through a conduit 412 and propelled by a second heated air blower 414 through a conduit 416. Movement of partially dried Sbers through conduit 416 is assiste~ by a second conveyor fan 418, which helps propel the partially dried fibers tangentially into a top cylindrical zone of a second dryer 420.
Dryer 420 tapers at 422 to a restricted outlet 424 through which fibers are withdrawn WO 93/14264 PCr/US93/00280 2~ LS

through a conduit 426 and emp~ed ~ a reten~on bin 428. Bin 428 has a ta~g bo~m po~on 430 with a selec~Yely closed outlet 432 through which c~ed fibers m~y be withdrawn ~ n ~e re~ on bin at preselect~d intemls when ~e bin is filled to capa~:i~. When outlet 432 is open~ s are int~oduced into a condwt 434, whence they are c~nveyed by a s~onveyor fan 436. 1Hea~ ~ is not in~uc~d into a3rlduit 434, he~ce cuoling of the fib~rs occurs as they travel t}~ough conduit 434 and are coll~t~d in a eollection bin 438.

- EXAMPLE I
19 In onç specific embodiment of the inven~on, the fibers are moved ~through conduits 4029 405 at a temperature of about 250C. Firs~ dryer 406 is appro~imately 50 feet tall, and has a largest diameter of 14 feet ~ i~s cylindrical upper po~on. The heated fibers undergo a flash evaporation as th~y enter the relativelg low pressur~ en~nment of large diameter tank 406. The par~ally dried fibers then e~it through conduut 412 at a temperature of about 60C, and are once again heated to about ~50~C by hot air from air heater 414 blowing through sonduit 416. Flash evaporation of ~e fibers once again occurs in dryer 42û, which in ~isexample is approximately 60 feet tall and has a largest diameter of about 16 feet in its cylindrical upper portion. The flash dried fibers exit dryer 420 through outlet 424 and are ~ollected in retention bin 428. The bin has a su~ficient capacity to collect fiber output from dryer 420 for a peIiod of 60 seconds. The retention bin is maintained at ~ sufficient temperatu~e, for example 1~0C, to allow the crosslinking agent to cure during the 60 s0cond period of retention in bin 438. At the end of a 60 s~nd retention period, the fibers are withdrawn through outlet 432 and conveyed through conduit 434 to holding tank 436.

EXAMPLE II
In this example, non-wov~n fibrous mats were impregnated with a crosslinking agent, fiberized, dried, and cured using the apparatus as diagrammed 30 schematically in ~IG. 1.

. ~ j SUBSTITIJTE 5HE~T

. ~0~3/14264 PCI~/US93/002~0 ~
2 1 2 ~

29 ~;
Two 52-inch wide mats of sDu~ern pine lm~Ft wood pulp fibers (~
NB316 from Weyerhaeus~r Compally) and ha~ing a basis wei~ht OI 680 g/m2 were `
fed to the appara~s. The mats w~e impre~sd using dimethyl~ld;hydroxy~
ethylene urea a~ a concentration of about 5%, a~li~ ~ver both sides of each mat using a combina'don of spr~y n~zzles and imp~ ~ollers. The l~adirJg level ~ -of crosslin~ng age~t was ab~ut 4.~% w/w.
rne ~t~ fiber r~ w~ fed at the ~ate of g meee~s/minute to the :
a~i~on device 32. The sp~cific attritioD device us~ is e~ample was equipped i~;
wi~ six m~t inlets and a rotor having 16 rows of hamme~ as desc~ibed~ above around the circumference of the rotor. The rotor had a diamet~r of 30 inches and :
~-~ was rotated at an angular velocity of 1200 Ipm by an electric motor. Other Ipm rates ha~e also been tested and have proven sa~s~actory, inclùding e%tremely high rpm ra~es.
RalldQm samples of fibers were obtained f~om the output a~don ~:
device and observed for nits. These samples were 2.6 grams and were ~nsis~ently observed ~o have fewer than three nits on the average with most samples having no `~
nits. The attridon device was flushed with water once eve~y sLsteen hours for c~ g purposes ~ ~ ,!
A disk refiner was employed downstream of the at~ition device. This sp~ifie disk refiller was a DM36 refiner as previously mentioned.
A fluff generator as deseribed in FIGS. 7-9 was also employed in this downs~eam of the disk re~er.
The temperature at the dryer input 273 in this example was within the range of 200C to 315C, and conduit 273a had a diameter of 3'~ feet. The tower body 266 that fonned zone 260 had a diameter of 7 f~et, hence the diameter ratio of conduit 273a to tower 266 was 1:2. The tempe~ature at the second tower outlet 294 was within the range of 140C to 180C.
Crosslinked fiber at the output of the dryer was produced at a rate of about 5~0 ~unds per hour and had a nit level on an average of from 1 to 3 and a maximum bulk of greater than 22. Bulk and nit l~vels were determined by the SUBSmUTE 5HEE~

WO 93/t4264 PCl'~US93/al0280 ~ollowing proc~dure, involving ~he production of test "handsheets" with a diamete~
of a~ut 6 Lnches:
A "Bri~sh handshee~ mold~ was filled wi~ 3 to 4 inches of water. To appro~cimately 750 mL of water w2~e add~ 1.2 g:rams of pulp, av~le from S Weyerha~ Comp~ny, follc~wed by agi~on usang a Waring bllender for 20 s~onds to yieJd a pulp slurry. A 2.4 g~m sample o~ the abo~e olbtained sros~link~
fiber was added to the pulp slurry ~ ~he ble~de~ followed by ~lation ~:ereqn ~oranotheF 10 seconds. The ~esulting slurry was add~ to ~e handsheet mold up to a fill mark. The slurry in the mold was gendy mi~c0d using a spa~ for 3 seconds9 then d~ained, leaving ~e pulp wet laid on the scr~en ~ the mold. The wet pulp ~-~ layer was blotted to removc ~ much mois~ure as possible, then ~em~ved from the sc~n. The resulting handsheet was dned between two blotters orl a drum dryer, then weighed tn the nearest 0.01 g~am immediately after drying.
Bulk was de~ermined using a ca~ r, performed immediately after drying. Mean ~ickness was de~ermined using five thichless dete~ a~ons of various locations on the handsheet. Bulk was ~culated in units of cm3/g as follows:

(mean thichless) cm (20.38) cm2 = Bulk (Handsheet weight) grams Nit level was detennined by examination of the handsheet and simple determina~on of ~e number of nits present on the handsheet. If no nits were obseNed a nit level of 1 was assigned to the test sheet; if 1 nit was observed, a nit 25 level of 2 was æsigned to the sheet; if 2 nits were observed, a nit level of 3 was assigned to the sheet; and so forth for higher nit levels~
Therefore, the appa~atus of the present inven~on effectively produces a low nit level product, and one of high bulk even when erosslin~ng agents are used.

SUBSTlTlJTE SHEET

.~O~3~t426~ 212 ~ i PCr/US93/00280 Pibe~ Thermobonding One problem with the fiber ~sslir~g m~od of the pres~nt invention is that it may pr~duoe a wet 12id sh~et having r~duced tensile strEngth.
The intlafiber cro~g in t}ae cellulosc chen~ically Lnhibits interfiber bonds tha~
give in~egri~ to a web. As a result, it is sametimes dif~cult tD ma~e a wet laidsh~et wi~h the dried and cu~d crosslin~d fib~ou~ output of ~he present inven~on ~he present invs~tors have overcome this problem by adding a the~nobonding agentto the d~ied and cur~d individual eellulose fibers to form a mi~tture that is made into a wet laid we~. The web is then hea~ to a sufficient ~lemp~ re to ac~rate the thermobonding matenal and in~ase the wet strength o~ the web by providing a ~-~ thermoplas~c matri~c within the web. Addi~on of a thermobonder can also be used to increase the t~nsil~ s~ength of an air laid web.
A nurnber of s~mthe~c fibers have been developed in recent years which are heat-adhesive (~e~obondable) synthe~c fibers. These ~nobondable synthe~dc fibers can be used to bond fib~rs together, thereby providing all abxorbent matf~il Ynt~h impr~ved strength ~at allows thinner and lighter weight products to be pr~duced. Examples of patenes deseIibing such fibetS, or their use or p~du~on, are U.S. Patent Nos. 4,1899338 (non-woven fabric con~prising side-by-side bicomponent fibers); 49234,655 (heat adhesive composite fibers); 4,269,888 (heatadhesive com~sosite fibers); 4,425,126 (fibrous material using thermoplastic synthe~c fibers); 4,458,0~2 (absorbent matenal containing polyolefin pulp treated with a wet:~ng agent); 4,655,877 (absorbent web structure containing short hydrophilic thermoplasdc fibers); and European Patent Application No. 248,598 ~olyolefin~
nonwoven fabric). Thermobonding agents are commercially available~ for example Celbond~ dual-polymer (bicomponent) fibers from Hoechst Celanese Corporation of Somerville, N.J. Examples of other commercially availa~le thermobonding agents include Vinyon~ monocomponent fiber made by Hoechst Celanese from a copolymer of polyvinyl ohloride and polyvinyl acetate, and Kodel0 100% polyester monoeomponent fiber from the Eastman Kodak Company of Rochester, New York.
The manufacture and use of thermobondable bicomponent synthetic fibers is fully disclosed in European Patent Application publication number 340,763, WO 93/14264 Pcr/u~93/0~280 ~ ~
7~

filed Mar~h 5, 1989, the disclosure of which is incorpo~ated by reference. Briefly summariz~d, the bicompone~t fiber comp~ an inne~ core cornponent and an outer sheath component in which the core component is a p~lyolefi~ or polyester, ~e sheath comps~nent is a polyolefin, and the c~re component has a highe~ mel~ng point S ~an the sheath cs~mponent. The core is pr~e~ly su~unded by a coa~ial sheath, in which the core componsnt typically has a mel~g ~t of at least about l5GC, while the sheath coznponent typically }~s a mel~ng point of about 140~C or lower.
The sheath eomponent is preferably selected from ~e g~oup consis~ng of polye~hylene; polypropylene, poly(l-butene), and copolymers and ~tures ~er~of, 10 while the core component is selected from the group consis~ng of polypropylene, ~ly(1~4~yclohexylene dimethylen~ htala~e), poly(~me~yl-l-pentene), polyester and copolymers and n~LY~ture~ of ~e foregoing. The weight ra~do of the she~th and core components in the bicomponent fiber is pre~erably in the range of 10:90 to 90:10, more preferably f~om about 30:70 to 70:30, and most prefe~ably from about40:60 to 65:35. The cross-section of ~e fiber is prefe~ably cir~ular and has a fin~ess of about 1-7 decitex. The fiber is cut to a length of ~ut 3-~4 millimete~s, typically about 5-20 millimeters, p~eferably about ~18 millimeters.
The wet strength of a crosslinked cellulose material in accordance with the present inven~ion c~ be increased with the thermobondable bicomponent fibersby subjecting the bicomponent fibers and crosslinked fibers to blending. The bicomponent fibers and non-bicomponent fibers can be blend~ or example~ by dispersion in water in a wet-laid nonwoven production process, so as to obtain anonwoven web in which ~e bicomponent fibers are dis~ibuted in a substan~ally random and homogenous manner.
The percentage weight of bicomponent fibers in ~he fluf~ is preferably in the range of about S-50%, more preferably 20 40%. The nonwoven web should contain a certain minimum amount of the ~icomponent fibers in order that the improved cha~acteris~cs due to the suppor~ng stmcture of the thermobonded bieompotlent fibers can be aehieYed. Thus, a bicomponellt fiber content of about 5 %
is regarded as being the usual minimum. On the other hand, the bicomponent fibers of the present invention need not nff~ssarily constitute a large portion of the fluff.

SUE~SmUTE 501EET

wo 93/14264 Pc~ 93/002~0 212~0~5 II a large amount of bicomponent fiber is add~d ~ the mi~c~ure, the physical properties ~f the bicomponent fiber will begin to pr~do~Rate ~ver the desired cha~tens~s of ~e crossli7~d fib~, xuch as high bulk and absorbency. One of the advan~ages of the bicomponent fi~e~s of ~e prese~t irlven~on is that ~ey can be S us~d in low amoun~s. Ihe weight ~a~o of the bicomponen~ fibe~s to tAe non-bicomponent fibers in the fluff can the~efore be about ~:95-10:95.
FIG. 12 shows a cross~ on ~ a bicomp~nent fiber 8 with a concentric configula~on. A core component 10 is su~Tounded by a sheath comporlent 12 with subs~ally uniform thickness, resul~ng in a bicomponent fiber in which 10 the core component 12 is substantially cen~lly loca~d. PIC;~ 13 shows a cross~
.~ s~ion of another bicomponent fiber 14 with an acen~nc configuration. A core componellt 16 in this configuration is substan~ially surrounded by a sheath component 18 with a varying thicla~ess, resul~g in a bicomps~nen~ fiber in which the core componen~ 16 is not cenhally located.
1~ PIG. 14 shows the struct~lre of a nonwoven web pr~or to ~hermobonding. Bicomponent fibers 20~ a,cording to the present inven~on, are arranged in a substalltially random and homogenous manner among non-bicomponent fibers 22 in the flu~f. FIG. 15 shows ~he same structure as illus~ated in FIG. 14, but after thermobonding. The sheath component of the bicornponent fibers has been melted by the thermobonding process, fusing the intact core components together (as at 24~, thus forming ~ supporting three~imension~l matrix. The non-bicomponent fibers 22 are randomly arranged in the spa~s defined between the bicomponent fibers, and some of ~he non-bicomponent fibers 22 have been fused (as at 26) to the bicomponent fibers.
FIG. 16 illustrates an air laid metho~ by which tbe mixture of bi~mponent and non-bicomponent fibers is fused to achieYe the transition shown between PIG. 14 and FIG. 15. The mixture of cellulose fibers and thermobonding agents is introduced through an inlet 60 to a fluff mat forming hood 62, wher~ a fluf~
mat 63 is formed by suction of the fibers onto a wire mesh 64. A layer of superabsorbent polymer (SAP) may be sprinkled on top of mat 63 to form a top SAPlayer or introduced about halfway through formation of mat 63 to form a middle SUBSTlTUTE 5HEET

WO g3J14264 PCr/~93/00~80 ~.

SAP layer. The fluff mat 63 typically passes through a series of rollers 669 in whieh :
the mat 63 is eolldensed or embossed prior to the thermobotlding process. The 63 is then led via a second wi~e me~h 72 past a through air oven 68, which thennobonds the material, thus p~oducing the su~ ng structure ~ormed by the coreS componen~ of the bicomponellt fibers, as shown in ~;IG. 15. The thermo~onded mate~ial is then led to a converting ma~hine 74, in whîch the productîon of hygiene absor~ent products, such as diapers~ es place.
The follo~g e~amples will illustrate use of CelbondD K-56 bicomponent fiber with ~he intrafiber cros~linked fibers of the present invention.
-~-~ EXAMPLE III
A slurry was prepared con~ing 20% weight percent of 0.4 inch long Celbond0 K-56 type bicomponent fiber, and 80% of high buLk additive (HBA~ fibers~
prepare(l as in Example II. 1 he bicomponent and HBA fibers were n~i~ed in water15 at a consistency of appro~cimately 0.01%. This slurry was dewatered on the forming wire of an inclined wire Fodrinier-type wet-laid nonwoven machine, and subsequently transferred, while s~ll containing approximately 50% water, to a r~through~ryer, which served to both fully dry the web and partially fuse the bicomponent Celbond~ portion of ~e web. The basls weight of the dried web was 275 gsm, with a bulk density of approximately 0.03 g/cc. A control web, formed using conventional woodpulp at the 80% level in place of the HBA, resulted in a web with a bulk density of 0.1 g/cc. The resulting HBA/Celbon~D dried and fused web possesses sufficient integnty to allow handling in further conversion steps, e.g., slitting/winding. :`
EXAMPLE IV
The bonded web of Example III is treated with a secondary binder treatment in order to de~relop specific properties in the web while mai~taining its desirable low-density cha}ac~e~istics. A saturant is prepared by diluting a suitable binder product (such as Airflex 120 latex, manufactured by Air Products and Chemicals, lnc. of Allentown, Pennsylvania) with water to a solids content of S~ ~

SUBSmUTE SHEET .

YVO 93/142M Pcr/uss3/oo28o 2f 2~0~5 from its o~iginal solids content of 52%~ Airfle~c 120 is a sel~osslin~g ~inyl acetate~thylene polymer, possessing low Tg (-20C) which Iesults in the combina~on of tensile st~ h, abra~on resistance and fl~ubility in substrates to which it is applied. The bonded we~ of E~ple m is satura~d in a bath of ~e S diluted la~x, then pas~ ~hrough a ~ of nip r~llers which ~squee~e out e~ccess late~c, resulting in a web con~g a~ro~mate~y 100% of sat~aJIt based on the weight of the dry web. The highly ~silieDt = of the HBA fibers in the web causes the web ~xihng the nip of ehe sque~e ~ollers to regain appr~imately ehe s~une ~ickn~s as ~at ente~g the nip, ~nd thus allow xetention of ~e low density nature of the web. This satura~d product is ~hen dned without compression in a suitable ~-~ appa~atus such as an oven at a temperature below 127C, the mel~ng point of the Celbondq~ sheath polymer. This heating ste~ dries the web and crosslinks the Airfle~
120 polymer without aff~c~ng ~he integ~i~ of the web which might be reduced by re-mel~ng the Celbond~ sheath polymer. The low compression drying is required to ~void crosslinking thc binder while the web is in a d~nsified configura~on. The $nal product is a str~ng, flexible, resilient, abrasion-resistant web suitable for packaging delicate or abrasive ar~cIes.
~ .
EXAMPLE V
Lightweight (5~100 g) thermobonded HBA pads, eitber as-is or with subsequent binder treatment, are suitable for use as a "cushion layer" ~ a diaper or similar absorbent construc~ons, providing a m~s to rapidly wicl~ moisture away from the ~op surface of tlhe c~nstruct to a lower, relatively heavy, absorbent eo~
The thermobonded pad provides re~istance to flow back to the upper surface because of relatively high thichless of the cushion layer.
Having illustrated and descnbed the principles of the present inven~ion in a preferred embodiment and variations thereof, it should be apparent to thoseskilled in the art ~at the inven~on can be modified in arrangement and detail without dq~arting from such principles. We claim all modifications coming within the spirit and scope of the following claims.

Sl.J ~STITlJT~ S~ EET

Claims (56)

We Claim:

1. An apparatus comprising:
an applicator that applies a crosslinking substance to a mat of cellulose fibers at a fiber treatment zone;
a fiberizer having a fiberizer inlet;
a conveyor that conveys the mat through the fiber treatment zone and directly to the fiberizer inlet without stopping for curing;
the fiberizer providing sufficient hammering force to separate the cellulose fibers of the mat into a fiber output of substantially unbroken individual cellulose fibers; and a dryer coupled to the fiberizer and which receives the fiber output, dries the fiber output, and cures the crosslinking substance, thereby forming dried and cured fibers.

2. The apparatus of claim 1 wherein the fiberizer provides sufficient fiberizing force to separate the cellulose fibers into individual fibers having a nit level of no more than about three.

3. The apparatus of claim 1 wherein the fiberizer comprises an attrition device.

4. The apparatus of claim 1 wherein the fiberizer comprises an attrition device, a disk refiner coupled to the attrition device, and a fluff generator coupled to the disk refiner.

5. The apparatus of claim 1 wherein the dyer defines a drying zone for forming dried fibers, and a curing zone for curing the crosslinking substance in the dried fibers, thereby forming dried and cured fibers.

6. The apparatus of claim 5 wherein the drying zone has a dryer inlet for receiving the fiber output, where the dryer inlet has a temperature within a range of about 200°C to about 315°C so as to flash evaporate water from the fiber output and form the dried fibers, and in which the curing zone has an outlet through which the dried and cured fibers are delivered from the dryer, where the dried and cured fibers passing through the outlet of the curing zone have a conveyance temperature within a range of about 140°C to about 180°C so as not to scorch the cellulose fibers.

7. The apparatus of claim 1 further comprising:
a reduced diameter conduit between the fiberizer and dryer in which the individual cellulose fibers are heated and the velocity of the flow is increased after they leave the fiberizer; and an expansion chamber after the necked down conduit that allows the fiber flow to expand and increase fiber separation.

8. The apparatus of claim 1 further comprising means for increasing a flow velocity of the fibers between the fiberizer and expansion chamber.

9. The apparatus of claim 7 wherein the reduced diameter conduit comprises a venturi that opens into the expansion chamber.

10. The apparatus of claim 7 in which the dryer comprises a drying zone for forming dried fibers and a curing zone for curing the crosslinking substances in the dried fibers, wherein the drying zone comprises the expansion chamber.

11. The apparatus of claim 10 wherein the drying zone has an inlet for receiving the individual cellulose fibers, where the drying zone inlet has atemperature within the range of about 200°C to about 315°C so as to flash evaporate water from and expand the cellulose fibers.

12. The apparatus of claim 11 wherein the curing zone has an outlet through which the dried and cured fibers are delivered from the dryer, where thedried and cured fibers passing through the outlet have a temperature with a range of about 140°C to about 180°C.

13. The apparatus of claim 7 wherein the reduced diameter conduit increases the transport velocity of the individual cellulose fibers from the fiberizer as the fibers enter the dryer.

14. The apparatus of claim 7 further comprising a hot air blower that blows hot air into the conduit toward the expansion chamber, and a fiber introduction inlet intermediate the blower and expansion chamber through which the fibers are introduced into the conduit.

15. The apparatus of claim 14 wherein the blower blows hot air at a temperature of about 200-315°C.

16. A cellulose fiber treatment apparatus comprising:
an applicator that applies a crosslinking substance to a mat of cellulose fibers as. a fiber treatment zone;
a mechanical fiberizer having a fiberizer inlet for the mat of cellulose fibers;
a conveyor that conveys the mat through the fiber treatment zone and directly to the fiberizer inlet without stopping for curing;
the mechanical fiberizer providing a sufficient hammering force to separate the cellulose fibers of the mat into a fiber output of substantially unbroken individual cellulose fibers with a nit level of no more than about three;
a dryer coupled to the mechanical fiberizer for receiving the fiber output, the dryer comprising an expansion chamber for drying the fiber output and a curing chamber for curing the crosslinking substance, thereby forming dried and cured fibers, the expansion chamber further defining an inlet for receiving the fiber output, where the dryer has a temperature within a range of about 200°C to about 315°C so as to flash evaporate water from the fiber output during drying, and in which the curing chamber has an outlet from which the dried and cured fibers aredelivered from the dryer, where the dried and cured fibers at the outlet of the curing chamber have a conveyance temperature within a range of about 140°C to about 180°C so as not to scorch the cellulose fibers;
a necked down conduit between the fiberizer and expansion chamber in which the fibers are heated and the velocity of their flow is increased after they leave the fiberizer;
a hot air blower that blows hot air at about 260°C into the conduit toward the expansion chamber; and an inlet into the conduit, intermediate the blower and expansion chamber, through which the fibers are introduced into the conduit.

17. The apparatus of claim 1 further comprising a heated retention chamber into which the fiber output is introduced for a preselected period of time to allow curing of the crosslinking substance after the fiber output is dried.

18. The apparatus of claim 17 wherein the dryer comprises a flash drying chamber and the curing chamber, and the retention chamber is positioned between the flash drying and curing chambers.

19. The apparatus of claim 17 wherein the dryer comprises a flash drying chamber and the curing chamber, and the retention chamber is downstream from the curing chamber.

20. The apparatus of claim 19 further comprising a cyclone separator downstream from the curing chamber, wherein the retention chamber is downstream from the cyclone.

21. The apparatus of claim 17 wherein the retention chamber is inverted pyramid.

22. The apparatus of claim 1 wherein the applicator comprises a shower spray that sprays the crosslinking substance on the mat, and an impregnation roller that presses the crosslinking substance into the mat.

23. The apparatus of claim 22 wherein the shower spray comprises a pair of opposing, shower spray applicators.

24. The apparatus of claim 22 wherein the impregnation roller comprises a pair of opposing rollers that cooperatively exert 1-2 psi impregnation pressure on the mat.

25. The method of claim 24 wherein the pair of shower spray applicators are positioned vertically over the fiberizer inlet, and the impregnation rollers are positioned for abutting the mat between the spray applicators and the fiberizer inlet.

26. A method of producing crosslinked cellulose fibers, comprising the steps of:
applying a crosslinking substance to a mat of cellulose fibers at a fiber treatment zone;

conveying the mat through the fiber treatment zone and directly into a fiberizer without stopping to cure the crosslinking substance, the fiberizer having a fiberizer inlet;
separating the fibers in the fiberizer by hammering them into substantially unbroken individual cellulose fibers; and drying and then curing the individual cellulose fibers.

27. The method of claim 26 wherein separating step comprises separating the cellulose fibers into individual fibers having a nit level of no more than about 3.

28. The method of claim 26 wherein the drying step comprises drying the fibers at a temperature of about 200-315°C so as to flash evaporate water from the fiber output and form the dried fibers.

29. The method of claim 26 further comprising curing the fibers at a temperature of about 140-180°C.

30. The method of claim 26 further comprising the step of adding a thermobonding agent to the dried and cured individual cellulose fibers, to form a mixture that is made into a web, then heating the web to a sufficient temperature to increase the wet strength of the web.

31. The method of claim 30 wherein the thermobonding agent is a bicomponent fiber comprising a core component and a sheath, wherein the core component has a higher melting point than the sheath component.

32. The method of claim 31 wherein the sheath component is selected from the group consisting of polyethylene, polypropylene, poly(1-butene), and copolymers and mixtures thereof, and the core component is selected from thegroup consisting of polypropylene, poly(1,4-cyclohexylene-dimethylene-terephtalate), poly(4-methyl-1-pentene), polyester and copolymers and mixtures of the foregoing.

33. The method of claim 30 wherein the mixture comprises the cellulose fibers and thermobonding agent in ratios by weight of 90:5 to 50:50.

34. The method of claim 33 wherein the mixture comprises 20-40%
by weight of thermobonding agent.

35. The method of claim 31 wherein the core is polypropylene and the sheet is polyethylene, and the heating step comprises heating the mixture out 130-150°C.

36. The method of claim 30 further comprising the step of applying a binder to the web.

37. The method of claim 36 wherein the step of applying a binder to the web comprises saturating the web with the binder and impregnating the binderinto the web with pressure on the web.

38. The method of claim 36 wherein the binder is selected from the group consisting of carboxymethyl cellulose, acrylic, styrene butadiene rubber, polyvinyl chloride, polyvinylidine chloride, polyvinyl alcohol and polyvinyl acetate.

39. The method of claim 26 further comprising the step of adding the dried and cured individual cellulose fibers to a pulp furnish to increase porosity and impregnation of a sheet made from the pulp furnish.

40. The method of claim 39 further comprising the step of forming a sheet from the pulp furnish and applying a liquid impregnant to the sheet.

41. The method of claim 40 wherein the applying step comprises applying the crosslinking agent to the sheet.

42. The method of claim 26 further comprising the step of holding the fibers in a retaining station for a selected period of time after drying them.

43. The method of claim 42 wherein the holding step comprises holding the fibers in a retaining station after curing them.

44. The method of claim 26 wherein the drying step comprises flash drying the separated fibers then introducing them into an expansion chamber.

45. The method of claim 44 wherein the drying step comprises introducing the fibers into the expansion chamber through a venturi.

46. The method of claim 44 wherein the flash drying step comprises conveying the individual cellulose fibers are conveyed from the fiberizer to theexpansion chamber by a conduit that decreases in diameter downstream from the fiberizer to increase a flow velocity of the fibers before they enter the expansion chamber.

47. The method of claim 26 wherein the applying step comprises applying a crosslinking substance selected from the group consisting of polycarboxylic acids; urea derivatives consisting of methylolated urea, methylolated cyclic ureas, lower alkyl substituted cyclic ureas, dihydroxy cyclic ureas, lower alkyl substituted cyclic ureas, and methylolated dihydroxy cyclic ureas; acid anhydrides from the group consisting of maleic anhydride, phthalic anhydride, 4-carboxyphthalic anhydride, pyromellitic anhydride, and mellitic anhydride; dialdehydes; and mixtures thereof.

48. The method of claim 47 in which the crosslinking agent is selected from the group consisting of methylolated urea, methylolated cyclic ureas, lower alkyl substituted cyclic ureas, dihydroxy cyclic ureas, lower alkyl substituted dihydroxy cyclic ureas, methylolated dihydroxy cyclic ureas, and mixtures thereof.

49. The method of claim 47 wherein the applying step comprises applying a polycarboxylic acid crosslinker.

50. The method of claim 49 wherein the crosslinking agent is selected from the group consisting of 1,2,3,4-butanecarboxylic acid and 2-hydroxy-1,2,3-propanetricarboxylic acid.

51. The method of claim 26 wherein the pH of the cellulose fibers remains above about 2 after the crosslinking agent is applied to the mat.

52. The method of claim 51 wherein the pH is within the range of 2-4.

53. The method of claim 52 wherein the pH is within the range of 3-4.

54. A method of making individualized crosslinking fibers, comprising the steps of:
contacting the fibers with a crosslinking agent comprising a polycarboxylic acid;
separating the fibers into substantially individual form; and drying the fibers and reacting the crosslinking agent with the individualized fibers to form intrafiber crosslink bonds.

55. The method of claim 54 wherein the polycarboxylic acid is citric acid.

56. The method of claim 26 wherein the separating step comprises separating the fibers in a hammermill comprising:
a housing;
an elongated rotor within the housing and having a longitudinal axis of rotation, the rotor including a plurality of hammers having distal end surfaces sweeping out an effective rotor surface upon rotation of the rotor about the axis of rotation, the distal end surfaces of the individual hammers upon such rotation sweeping separate cylindrical paths with gaps between the paths, the gaps between the paths not exceeding about one-quarter of an inch;
a rotator that rotates the rotor about the axis of rotation to thereby rotate the hammers to provide the effective rotor surface; and the hammermill including at least one inlet through which a fiber mat is delivered to the effective rotor surface for fiberization by the rotating hammers, the housing defining an outlet located at an intermediate position corresponding to an intermediate portion of the effective rotor surface between the ends of the rotor, the outlet extending substantially the entire length of the housing.