CA2249331A1 - Nonwoven fabric having a pore size gradient and method of making same - Google Patents
Nonwoven fabric having a pore size gradient and method of making same Download PDFInfo
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- CA2249331A1 CA2249331A1 CA 2249331 CA2249331A CA2249331A1 CA 2249331 A1 CA2249331 A1 CA 2249331A1 CA 2249331 CA2249331 CA 2249331 CA 2249331 A CA2249331 A CA 2249331A CA 2249331 A1 CA2249331 A1 CA 2249331A1
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- fibers
- web
- pore size
- group
- average pore
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- LLLVZDVNHNWSDS-UHFFFAOYSA-N 4-methylidene-3,5-dioxabicyclo[5.2.2]undeca-1(9),7,10-triene-2,6-dione Chemical compound C1(C2=CC=C(C(=O)OC(=C)O1)C=C2)=O LLLVZDVNHNWSDS-UHFFFAOYSA-N 0.000 claims 1
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- NLZUEZXRPGMBCV-UHFFFAOYSA-N Butylhydroxytoluene Chemical compound CC1=CC(C(C)(C)C)=C(O)C(C(C)(C)C)=C1 NLZUEZXRPGMBCV-UHFFFAOYSA-N 0.000 description 1
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Landscapes
- Nonwoven Fabrics (AREA)
Abstract
Methods and apparatus for forming a nonwoven fiber web containing a pore size gradient resulting in enhanced wicking properties. A first method utilizes a conventionally formed web having an average pore size and comprises selectively contacting the web with a heat source to shrink the fibers in selected areas. The smaller pore sizes have greater wicking ability. A second method utilizes a novel apparatus and comprises forming a nonwoven fiber web having zones of fibers, each zone having generally an average set of fiber structure and/or composition, the zones preferably overlapping. The zones of fibers are exposed to a heat source, which shrinks the fibers according to their denier and composition. The apparatus uses a conventional meltblown or spunbond system and provides a plurality of resin sources which feed resin to a plurality of meltblowing dies. Each die produces fibers of a particular denier and/or composition which forms zones in a web collected on a collecting belt. The web moves underneath a manifold which blows heated air or sprays boiling water onto the fibers. The fibers shrink according to their structure and composition to form a web having a pore gradient.
Description
W 097140223 PCTrUS97/05788 NONWOVEN FABRIC HAVING A PORE SIZE GRADIENT
AND METHOD OF MAKING SAME
FIELD OF THE INVENTION
The present invention relates generally to a fibrous nonwoven web having a pore size gradient and methods for forming such a web. The method of the present inventionuses in one e",boJi",ent a formed web having an average pore size and selectively subjecting it to heat in order to shrink po,lions of the fibers thus fG",~;ng smaller pores in the sele~ed areas. In a second embodiment a web is formed of dirre,~ nt fiberdian~et~rs or fiber cGmposilions. Subjecting the web to heat ur,ifo""ly shrinks the ~liffer~nt diar"et~r fibers or co"~posilion to difrerent degrees thus f~""i"g a pore size gradient across the web.
BACKGROUND OF THE ART
The manufacture of nonwoven fabrics is a highly developed art. In general nonwoven webs or webs and their manufacture involve fG""ing fila",ents Ot fibers and depositing them on a carrier in such a manner so as to cause the fila",enls or fibers to overlap or entangle as a web of a desired basis weight. The bonding of such a web may be a~ aved simply by entanglement or by other means such as adhesive application ofheat and pressure to thermally responsive fibers or in some cases by pressure alone.
While many variations within this general description are known two cGrr""only used prucesses are defined as spunbonding and meltblowing. Spunbonded nonwoven structures and their manufacture are defined in numerous patents including for exd",r e U.S. Pat. Nos. 3,565 729 to Ha,l",ann dated FebnJary 23 1971 No.
4 405 297 to Appel et al. dated September 20 1983 and No. 3 692 618 to Dorschner et al. dated September 19 1972. DisuJssi~n of the meltblowing process may also be found in a wide variety of sources including for example an article entitled "Superfine The~ opl~slic Fibers" by Wendt in Industnal and Engineering Chemistry, Volume 48No. 8 (1956) pp. 1342-1346 aswell as U.S. Pat. Nos. 3 978 185 to Buntin et al. dated August 31 1976 No. 3 795 571 to P~enlice dated March 5 1974 and No. 3 811 957 toButin dated May 21 1974.
For the purposes of the present ~isclQsure the term Ucomposition" shall mean thechelll -~' makeup of a fiber. The term "structure" shall mean the physical characle,iatics of the fiber including, but not limited to denier tength crimping kinking number of co."ponents (such as bi- or multi-cG",ponent fibers disçussed in more debil hereinbelow) and sl, enyll ,.
Among the charc.c~erialics of the fiber web produced by either a meltblown or a sp~"bonded process are the fiber cJia",e~er also known as the "denier" of the fiber and the wicking power of the fabric which relates to the ability of the web to pull moisture from an area of ~pplication. The ability to wick moisture is related to the denier of the fiber and the density of the web which deflnes the pore size in the ",alerial. Wicking is caused by the capillary action of the fibers in contact with one another. The pulling or capillary action is inversely related to the pore size or capillaries in the web. Therefore the smaller the capillary the higher the pressure and the greater the pulling or wicking power.
It has been found useful to create a fabric having a co",posiLiGn conlaill,ng a pore size gradient over a given area of the fabric. An advantage of this is greater control over fluid wicking in target areas. Several patents have alle",pted to address methods of ~ ,~aling nonwoven fabrics of variable pore size.
U.S. Pat. No. 4 375 446 to Fujii et al. disr~oses a meltblown process in which fibers are blown into a valley created bet~,veen two drum plates having pores. One drum is a co"ection plate and the other drum is a press plate; the fibers are pressed between the two dnJms. The angle at which the fibers are shot into the valley is ~liscussed as creating webs of varying chara~lerislics.
U.S. Pat. No. 4 999 232 to LeVan disclQses a sl,et~.l)able batting cor"posed of differe,ltially-shn~ l.rble b.~.c."ponent fibers which form cross-lapping webs at detemlined angles. The angle determines the degree of stretch in the machine di~c~on and cross dir~ction. A helical crimp is induced into the material by thedif,e,t:ntial shrinking.
U.S. Pat. No. 2 952.260 to Burgeni discloses an absG,bent product such as a sanitary napkin having three layers of webs folded over each other; each layer has dirre,cnl shaped bands of porous zones of compacted or u"cG."pacted fibers.
U.S. Pat. No. 4 112 167 to Dake et al. ~li5~ ~oses a web including a wiping zone having a low density and high void volume. The low density zone is heated with a lipophilic cleansing emollient. The web is made by drying two layers of slurry formed webs.
U.S. Pat. No. 4 713,069 to Wang et al. disclQses a baffle having a central zone having a water vapor l,.-ns"~ission rate less than that of non-central zones of the baffle. The baffle can be fomned by melt t ~;.,9 or a la",ir,ate of spun bonded web layers or by coaffng the central zone with a cGmrositicn.
U.S. Pat. No. 4 738,675 to Buckley et al. disclQses a multiple layer d sposAhle diaper having cG"~p,t7ssed and uncGr"p,~ssed regions. The cG,n,ur~ssed regions can be created by en~bossi"g by rollers.
U.S. Pat. Nos. 4 921 659 and 4 931 357 to Marshall et al. ~isclose a ",ell,od of forming a web using a variable transverse webber. Two independent fiber sources (one short fiber one long fiber) are rolled and fed by feed rolls to a central mixing zone. The relative feed rates of the feed rolls is conl~ ~~le to alter the fiber co",posilion of the web formed U,er~f,c,-U.S. Pat. No. 4 927582 to Bryson diselQses a gradu~t~d distribution of granule ",alenals in a fiber web which is formed by introducing a high-abso,L,er,cy i"aleiial whose flow is reg~ ted into a flow of fibrous material which intem,ix in a f~"";ng ~ cha",ber. The cG"l,- ~le flow velocity permits selective distribution of high-absG,L.ency material within the fibrous material deposited onto the fomning layer.
U.S. Pat. No. 5.227107 to Dickenson et al. disrloses a multi-component nonwoven made by directing fibers from a first and a second fiber source throughout a forming chamber such that they mix to form a relatively uniform fibrous precursor which is then deposiled from the fo""i,-g cl ,~,nber onto a forming surface such that a fibrous nonwoven web is made which is a mixture of the first and second fibers.
U.S. Pat. No. 5 330 456 to R~bi.)son ~Jis~oses an absorbent panel having a fibrous absG,L ent panel layer of super absG,Lent polymer (SAP) and a liquid l,a,~srer layer the latter of which is positioned above the SAP layer.
Fabrics c,eat~d by multilayer processes can have t,~narer difficulties between layers I0 due to the inter-layer barrier caused by i",pe~rect wicking between the layers. Fabrics ceated by dirrertntial co",p~ssion of various areas are also undesirable bec~se altemating areas of high and low density slows down liquid lla"sport.
It would be desirable to have a method of c,~aling a variable pore size material that could utilize existing IlleLllods of c,eati"g the web. Such a web would have improved flow and wicking cl-a,~- ler,~lics that would enhance a fluid absorbing product s ability to absorb fluid in a target area and wick the fluid rapidly away to distant areas. Such a web would have enhanced vicl~i"g rates and cap~rities.
SUMMARY OF THE INVENTION
The present invention provides methods of fo""ing a nonwoven web having a pore size gradient created from thermally responsive fibers.
In a first pre:fe,.ed embodiment the present invention provides a web made in a conventional manner having an average pore size. The web can be formed using conventional meltblown Sp~ll ,bor,ding ai, rOl,, ,ing, wetro" "ing or other processes known to those skilled in the art. The web can be cut into a wedge or other shape and the malenal is selectively eYposed to heat so as to selectively shrink certain areas of the web. The heat source can be heated water oil or other liquid such as in the form of a spray a solid such as a heated roller or gear a radiated heat source such as incandescent (incoherent) or laser (coherent) light ultraviolet light microwave energy or other electromagnetic .~dialion. The wider areas of the web are exposed to more heat than the narrower areas resulting in a rectangular-shaped web having a poregradient. Various shaped webs can be e~ oyed prior to heating depending on the shape of the end product desired.
In a second prt,f~ d e",bGdi,nenl the present invention provides a ",ell,od and S appa,~ s for fomming a nonwoven web having over;app.ng or dis~re~e zones of Jifr~r~nl structure and/or co-.,posiliGn of fiber. In a meltblown p,ucess after the fibers are fommed and deposited onto a c~l'e~t:~n belt. the fibers are ~tl~oS~d to a generally ur,if~l-l,ly apptied heat source such as hot air. heabd solid or liquid blown or sprayed across the width of the fommed web. The fibers shrink accordi"g to the c h8~dCI~:ristics of the fiber structure and co",position fo"-,;.)g a web having a pore size gradient.
An appa,d~us for acl,.eving the Ill~tllod of the second prere"ed e",bodil.,ent using a meltblown process coi,lpnses at least one reservoir capable of containing a supply of at least one polymer resin (co"",lonly provided in pellet form) each reservoir being in commu,l -7tion with a meltblowing die. A foraminous conveyor belt disposed below the die re~ives attenuated fiber sl.l:allls exiting the die tip. A heat source such as a hot air blower or liquid pump is in commun-cation with a ",anif, i disposed across at least a portion of the width of the conveyor belt. The "~anif~ld has at least one aperture located on the bottom portion that can blow hot air or spray liquid on the fiber web as it passes undemeath the manifold while on the conveyor belt. An air fllter can optionally be ~isposed between the hot air source and the manifold or at the hot air source for filtering conla",i"anla. Optionally a reservoir containing fibers or other particles can be in communication with the manifo!d for blowing the fibers or particles onto the fiber web with the hot air which can provide additional control over structural and functional prupe"ies by changing the composition of the material prior to shrinking. In the case of a fluid heat source the fluid such as water is removed from the web using convenlional means, such as a vacuum source.
In a third embodiment the second pr~fe"ed e",bodi",ent method can be used e",r'~y"~g a spunbonding apparatus as is convenlionally known and adding the ",anifc'd and heat source as previously described.
W O 97140223 PCT~US97/OS788 In a fourth e~"bodiment, meltblown and spunbond processes are used in conjunction to aeate a cG",posile layered web, such as spunbond-meltblown-spunbond webs, which are known in the art and produced by the assignee of the present invention.
It is also possible to use multi-cGi~ponenl fibers, such as, but not limited to sheathlcore, eccenl,ic sheath/core, side by side (bi-co",ponent), side by side by side (tri-cGn,ponenl) or other known multi-cG",ponenl stnuctures and composilions.
Accord,n~ly, it is an object of the present invention to provide a rllt:lhod and appa,atus for fo""ing a nonwoven web having a variable pore size gradient.
It is another object of the present invention to provide a method for fo""ing a fiber web having a pore size gradient by conldcling a fiber web having an average pore size with a heat source to selectively shrink the fibers.
It is still ano~l,er object of the pr~se"l invention to provide a method for forming a fiber web having a pore size gradient by contacling a fiber web co",posed of cl;r~erer,l fiber denier or other stnuctural cha,d~.lerislics with a heat source to selectively shrink the 1 5 fibers.
It is still ano~l ,er object of the pr~sehl invenffon to provide a method for forming a fiber web having a pore size gradient by co"tacling a fiber web cor ,posed of zones of fibers, each zone containing a fiber of a distinct composition or structure, the zones possibly ove,i~FF:ng, with a heat source to selectively shrink the fibers.
It is yet another object of the present invention to provide a method for forming a fiber web of a difrt:r~nl web cGInrosilion or structure, using fiber and particle introduction to control cG"~rosilion and stnucture.
Other objects, features, and adva,llages of the present invention will become apparent upon reading the r~'lov ing detailed desc(ip(ion of el"bodil"ents of the invention, when bken in conjunction with the accol"panying drawings and the appended claims.
W 097/40223 PCTnUS97/05788 BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated in the drawings in which like reference characters designate the same or similar parts throughout the figures of which:
FIG. 1 shows a perapecli~e view of a section of web having an initial ho"~ogenous pore size according to a first prefe~ d e",bodi",ent of the present invention.
FIG. 2 shows a perspective view of the web of FIG. 2 after eYr~osure to heat.
FIG. 3 is a chart showing pore radius distribution of meltblown PET fibers prior to shrinking acco,d;ng to the first prefe"ed e,.,bodi",e,~l.
FIG. 4 is a chart shu~ing pore radius distribution of meltblown PET fibers aftershrinking accordil-g to the first pr~fel,ed embocli",enl.
FIG. 5 shows a perape~ e view of a meltblown appa~alus used to form a variable co",l)ositiGn fiber web according to a second pr~e"ed el"bocJi",el,l of the present i"~ nlion.
FIG. 6 shows a pictorial view of an appa,alus wherein one row of meltblown dies form a first layer of fibers and a second row of meltblown dies produce fibers which overlay the first layer of fibers producing a laminate structure.
FIG. 7 shows a side view of a spunbond appa,dlus used to form a variable composition fiber web accorJing to a second preferred embodiment of the present invention using three spunbond dies.
FIG. 8 shows a side view of an appa,alus accordi"g to an altemative embodiment in which a layer of fibers is first deposited by a row of spunbond die assen,'l.es folla~/ed by deposition of a second layer of fibers produced by a row of ",ellblol,vn dies.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
- The present invention can be employed to produce nonwoven fiber webs having conl,ulled pore gradient distribution created using thermally responsive fibers. The pr~fe" ~d embodiments of the invention set forth methods of and apparal.ls for applying heat or other force which selectively causes fibers to shrink.
With all the e",bcdi",ell~s of the present invention the polymer used can be anysuitable thermopl~stic maLenal such as, but not limited to, polymers and copolymers of S ethylene, propylene, ethylene ter~phll ,alate, mixtures thereof and the like. The polymer should exhibit the prop~ily of being shrinkable. Such malenals are known to those skilled in the art and need not be rEviewed in detail. The~r~tically, any ~I,e""opl~s~ic polymer known to those skilled in the art will exhibit heat-s~"i"!~ ility prope,lies if it is first oriented (as in a fiber spinning process) and then solidified so as to "freez~in~ the G~ientaliGn. Subsequent app'.~~tion of heat will cause the material to shrink to relieve the stresses induced in the orien~dlion process. Additionally, the fibers formed can be standa(~ monorilar"ent, mono-co",ponent fibers, or, can be multi-co",ponent fibers, such as, but not limited to sheathlcore, eccen~(ic sheath/core, side-by-side (bi-componenl), islands-in-the-sea (tri-cG",ponen~), or the like. For a desc.,i~,tion of these and other multi-cG",ponen1 fibers, see U.S. Pat. No. 5,382,400, issued to Pike et al.
(which is incG"~ordted by reference herein) and assigned to the assignee of the present in~en~on.
In a first prefe"t:d embo:Ji",ent of the invention, shown in FIGS. 1-4, a portion of a nonwoven fiber web 10 has a su~slanlially uniform pore size distribution defined by fibers or rila",ehls 12. The terms fiber and filament are synonymous, as are the terms web and web, and may be used inter~,hangeably herein. The web 10 is created using standard meltblown or spunbond technic, ~es known in the art, which need not be rcvie~/ed in detail. Briefly, however, in a meltblown process, an amount of polymer resin pellets is passed through an extruder by a screw conveyor and then through a meltblown die having multiple fine apertures. The molten resin is forced through the apertures to form fibers. The fibers are attenuated and broken up by being contacted by heated dl~JI;ng air and are co"ect~d as an enta"glEd web on a moving surface,such as a foraminous vacuum belt. The fibers are co"ected from the belt after setting.
In this first embodiment the meltblown die forms a web of fibers having an average pore size across the width of the web because the die apertures are the same diameter, resulting in the fibers being generally of the same diameter. A sample pore size distribution chart for unshrunk PET fibers formed using a meltblown process is shown in FIG. 3. The pore size can be in the range of about 5~u to about 1000~u in equivalent pore radius, ~r~fer~bly in a range of from about 20~u to about 500~ . Other pore size ranges, prior to and after shrinking, are conle",plated as being within the S scope of the present invention. Flt:ferably the coerr,ciant of vanation is not greater than about ~0%. A descri~ulion of pore size appears in U.S. Pat. No. 5,039,431, issued to John30n et al., assigned to the assignee of the pr zsent invention and inco".,Grdtad by rbf~r~nce herein. FIG. 4 shows a pore size distribution chart for shnunk PET fibers formed using a meltblown process.
F~fe,ably, heated air may be blown at the fibers in 5el~1ed areas to shrink the fibers.
FIG. 2, for e~atr,~le, shows the effect of selectively healing zone 14 of the web 10.
Fibers or fila,nenls 12 are shrunk and more highly enLanglcd in zone 14 resulting in reduced pore sizes in that zone co",pared with the remainder of web 10. Factors influencing the amount of shrinlkaae inciude, but are not limited to, tel"peral,Jre of the heated air, velocity of the air, dislance of the no7~1e from the fibers, duration of heat application, makeup of the air itself (e.g., humidity, pH, co",poailion of other vapori~ed or non-vapo,i~ed co"-ponents) and the like.
Selective shrinkage of the fibers is accG".F'ished by appl.~-tion of heat to the fibers.
Albmatively, steam, oil, or other sult~~le liquid, is contacted with the fibers in selected areas for specific periods of time to shrink the fibers more in some areas and less in other areas. Shri,.kt3e can be conl,olled by several factors, including, but not limited to, temperature of the heat source applied, composition of the heat source, dislance of the heat source ~Fploc~t~r from the web, and duration of eYpos~re.
Other factors which may influence sh"in'.cge that may be used with the present invention include, but are not limited to, water, light (UV, laser), pressure, magnetism or other ele_llomoti~r~ foree, and the like, depending on the fiber and mat composition. It is possible to use fib~ having a pH sensitive col,lposilion and use acid or alkaline adjusted fluid to control shrinkage.
It is also possible to use microwave energy to heat the fibers. An example of this method can be fG""ing fibers using metal particles as a co-forming material. The W O 97140223 PCTrUS97/05788 i...pr~gnaled ps,licles will heat upon ~xros~re to microwave or other energy and thus shrink the fibers. Dirrer~nt concenl,dtions of particies within areas of the web can be ach ~v0d by a plurality of different sized die tips or by a plurality of dis..~ete dies or by other techniques known to those skilled in the art. As an alle."alive to microwave energy one or more heat rolls can be used to apply heat to the web. Several pairs of heat rolls between which the web is pressed can provide a controlled amount of heating and also set the web such as in the case of a composite web stnucture.
In a second pr~rentd embodiment shown in FIG. 5 a variable cG"-rosition web 100 having zones of ~Jifrt ~-~nt fiber clia,.,ele,~ is preferably formed by a meltblown prucess.
It is to be under~lood that other processes can be used such as spu"bond;ng scussed in more detail herei.~below) airforming wel~u""ing or the like. A meltblown appardl.ls and process are described in detail in U.S. Pat. No. 5 039 431 issued to Johnson et al which uses a number of dies to form a layered web. FIG. 5 shows anappdlc~LUS 105 has a number of hoppe~ 110 each containi. ,9 lI ,e, lllop!~slic pellets 112 l 5 (not shown) of potymer resin. Each hopper 110 can have a distinct polymer ~r.~ro~itiGn or various hoppers can have the same comrosilion. The following d~~c,i~Jtion takes place for each die asse,nbly 111. The pellets 112 are transported to an extruder 114 which conlc.;,,s an intemal screw conveyor 116 The screw conveyor 116 (not shown)is driven by a motor 118. The extruders 114 are heated along their length to the melting temperature of the the""oplasl,c resin pellets 112 to form a melt.
The screw conveyors 116 driven by the motors 118 force the molten resin materialthrough the extruder 114 into an aKached delivery pipe 120 each of which is connected to a die head 122 124 and 126. Each die head has a die width. P~eferably the die heads 122 124 and 126 are spaced close to each other so that the fibers formed thert:fro", will become entangled. Fibers are produced at the die head tip in a convenlio~al manner i.e. using high pressure air to attenuate and break up the polymer stream to form fibers at each die head which fibers are deposited in layers on a moving foraminous belt 128 to form the web 100. A vacuum box 129 is positionedbeneath the belt 128 to draw the fibers onto the belt 128 during the meltblowingprocess. It is possible that one hopper 110 can supply polymer to a plurality of die heads 122 124 and 126. Altematively each hopper 10 can supply a different polymer to each die.
wo 97/40223 PCT/US97/0S788 The web 100 thus formed is heated by a manifold 130, which distributes heated air uniforrnly across the web 100 assisted by a vacuum box 131 improve ullifullllily of heating through the web thickness. The heated air enters the l"anifoid 130 by a conduit 132, which is in commun.c~tion with a heated air source 134. Optionally, an air filter 136 can be inse,led downstream from the heat source 134 to reduce contamination of the web 100. In an alle"~dli~e embodiment, the r"ar~ir~'d 130 can have a plurality of di5_1etê areas, each area being sn~p' ed by a dirre,ent heated air source, each source ~en~r~ting heat of a dirrerent te",perature. In an altemaffve embodiment, a manifold 130 is positioned beneath the belt 116 and the web 100 and the posilion of vacuum box 131 is, likewise, reversed.
The web 100 can be quenched to stop the action of heat on the fibers. Once the shrunk fiber web 100 has been created the web 100 can be withdrawn from the belt128 by conver,lional withdrawal rolls (not shown). Optionally, conven~ional calendar rolls (not shown) can engage the web 100 after the withdrawal rolls to emboss or bond the web 100 with a pattem thereby providing a desired degree of sli~rness and/orallerl~J~I, to the web 100.
At least one of the zones A, B and C of the web 100 shrink upon ~pos~re to the heat.
Rec~use the fibers are intertwined, the shrinl.i"g produces a gradient effect. The extent of shrinkage is dependenl on a number of factors, including, but not limited to, the fiber cGIllposi~iQn, fiber dis,lleter, fiber density, the overlap in zones, time of expos~re to heat after web formation and setting, heated air temperature, duration of ~xpos~re to the heated air, distance of the manifold 130 from the web 100, and the lilce.
Additionally, the heated air itself may have dir~erenl van~'es assoc,~led therewith, such as but not limited to, te,llperalure, humidity, acidity, and the like. The air source can contain vapGli~-~d water or other fluid. Such fluids may alter the chemical makeup of the fiber web and increase or decl~ase pore size or other characleristics. Moreover, the air source can also contain fibers, such as wood pulp, or panicles, such as superdbso, ben~ polymer ~"SAPn), which when blown into the web 100 become enb~pped either on the surface, or within the pores. In the case where the fibers or panicles are partially melted, they can adhere and solidify on or in the web 100.
W O 97/40223 PCT~US97/05788 The resulting web 100 has a gradient of pore sizes across the width of the web. For example, if the die head 122 produces fibers of large (relative) denier, die head 124, produces fibers of medium denier, and die head 126 produces fibers of fine denier, then the resulting gradient will have fibers in zone A having the largest pore size, the fibers in zone B having smaller pore size, and the fibers in zone C having the smallest relative pore size.
In an ~ ,ali~/e embodiment, the three die heads 122, 124, and 126 are replaced by a single die head 150 (not shown) having apertures of difrerenl diameters. By controlling the aperture size aaoss the width of the die head 150, the denier of fiber created can be cor,l~.lled.
Altematively, it is possitl~ to use an apparalus 200, shown in FIG. 6, in which a layer of fibers 210, cG",posed of a polymer A, is deposited on a conveyor belt 212 by a first row of meltblown lor spunbond) dies (partially shown and noted collectively as 214), which are fed molten resin polymer A, as described herai.-above with ~espect to the assembly 111. A second layer of fibers 216, co,nposed of a polymer B, is deposited on theconveyor belt 212 by a second row of meltblown dies noted collectively as 218, which are similarly fed molten resin polymer B. Vacuum boxes 219 and 219A positioned benedtl, the belt 212 draw the fibers formed onto the belt 212 during the process.
resulting laminate web 220 is subjected to heat in the manner described above using a "-anife~ 230, which is connecled by a conduit 232 to a heated air source 234. Optional boxes 236 can be inserted in the conduit 234. A vacuum box 237 assists in improving ur,ifo""ily of hea~ing through the web thickness. The advantage of using two or more polymers is that the l-eat sh,in!~?ge chara~la,islics of each polymer can permit greater control over the pore size gradient fommed thereby. Using polymers with very different heat shrinking charac~nstics may provide greater Z direction shrinking, which may produce a web having greater or less abso, ~tion or wicking properties.
A meltblown p,c cass may be advantageous where a smaller relative pore size range of the pre-shrunk web is to be created and a spunbonded process may be advantageouswhere a larger pore size range is to be achieved.
W O 97/40223 PCTrUSg7/OS788 As an alt~",aLi~e web-forming process to the second prefe~.ed e",bod;ment the pr~senl invention can be prac liced with a spunbond process and apparatus. Spunbond web fo""a~ion is known in the art and need not be rcvicwcd in detail here. Briefly l~o~evcr FIG. 7 shows a perspective view of an appa.al.ls 300 in which hoppers 310 feed polymer into extruders 312, which is then fed by pipes 314 into a spi.,ne.t:t 316.
The s~:nne.~t draws the resin into fibers which are quenched by a quench btower 318 positioned below each spinneret (one of which is shown in the drawing). A fiber draw unit or asp"d~or 320 is positioned below the spinneret 316 and receives the quenched r~ld.~6nLs. It is to be ul1der~tood that any number of spunbond extruder-spinneret asse.. ,blies can be used according to the present invention.
The fiber draw unit 320 includes an elongate vertical p~esage through which the rila..,enls are drawn by aspirating air entc,i"g from the dies of the p~ss~ge and flowing downwardly through the passAge. A heater 322 (one of which is shown in the drawing) sl~r.~. es hot aspirating air to the fiber draw unit 320. The hot aspi-dling air draws the rll~.. ,en~s and ambient air through the unit 320. A foraminous collecting belt 324 re~i~res the continuous rild",enls from the outlet openings of the fiber draw unit 320 assisled by a vacuum box 325 to form a web 328. Optionally calender rolls (not shown) can be em,~'~yed in a convenlionally known manner to apply pattern or overall bonding to the web 328.
After the web 328 has been formed a heating manifold 330 as described hereinabove is used to apply heat to the web 328 and a vacuum box 329 is used ad described hereinabove. A pore gradient is thus formed in the web.
In further altemative embodiment to the second embodi",ent a colr,~:nalion meltblown and spunbond process can be used to create co",posiLe web that is shrunk using the heat source appara~.ls and method of the second e",bodi",ent. A composite of spunbond-meltblown-spunbond fibers known as SMS can be created and heat shrunk using the present invention. In such a process a layer of meltblown fibers is formed on top of a layer of spunbond fibers and combined with a second spunbond iayer to form a three layer la",i.laLe which laminate is then pressed between a pair of cale,-der rolls to form a unitary web. FIG. 8 shows an apparatus 400, which can form a spunbond-meltblown web 410. Hopper 412 feeds polymer pellets into an extruder 414. Extruded resin in fed by a pipe 416 into a spinneret 418 which forrns filaments from the resin. A
quench btower 420 is positioned adjacent the filament stream and quenches the fila",ents. The rila",enls are received into a fiber draw unit 422 which is supplied with hot air by a heater 424.
The f;la",enls formed are drawn onto a foraminous collecting belt 426 by a vacuum box 428 posilioned below the belt 426. A meltblowing die head 430 s~-rFl ed with polymer resin from a hopper 432 via an extruder 434 and pipe 436 assembly produces a layer of meltblown fila",ents which is deposited on the collecting belt 426 onto the spunbond layer of filaments. A heating manifold asse~bly 440 and vacuum box 44~ as descril~ed in detail hereinaboYe selectively heat shrinks the laminate web 410 to foml a pore size gradient neck stretching roller assembly 442 and/or calender rolls 443 and 444 can be used as is known to those skilled in the art. A collecting roller 450 can remove and collect the ri"ished product.
An advantage of the first e",bodi",ent of the present invention is that a con~/en~ionally formed web can be treated after f~""ation to differentially create a pore size gradient.
This method can reduce the necessity of creating new appaldlus for fG""i"g the web. A
pore gradient is advant~geous in that the smaller the pore size the greater the wicking power of the web. A pore gradient structure is the most erril ;ent structure fort(anspG,ting liquid against gravity. Where smaller areas are to have a pore gradient selective heat arFli-~tion to a hG"~ogenous pore size web can have a high degree of control over the s~"i"k73e. A further advantage of this Illt:~hod is that addilion of ~co-forming particles provides additional control over web characteristics.
An advantage of the second e",bGdi",ent is that control over the range of pore sizes achievable is much greater because there are two degrees of freedom with respect to control i.e. web density and heat arpl;c~lion.
E)CAMPLES
The invention will be further described in connection with the following examples which are set forth for purposes of illu~ lion only. Parts and percentages appea,i"g in such e,.d",~ es are by weight unless ~J~I,erv.~,se stir~ te~
HOMOGENOUS COMPOSITION
A meltblown web (sample #5214~ was made from PET in a conve,ltiGnal manner to form a suL~larltially ho",ogenous pore size distribution. For a detailed description of a method of fomming a meltblown web see Butin et al. U.S. Pat. No. 3849241. A
sample of material was cut in the form of a truncated inverted triangle. Sections of the web sample were dipped in boiling water (100~ C) for 30 seconds to shrink selectively po, lions of the web. Altematively a spray head~ "anifold extending subsldnlially across the belt and the width of the web is used to spray boiling water onto the web.
The speed of the fiber on the belt passing below the manifold and the length of the manifold determine the length of expos~re of the web to heat.
The ",ell,od c~alecJ a unitary structure with a pore size gradient.
SAMPLES OF E)(AMPLE 1 The pore radius distribution chart of the formed unshrunk web is illustrated in FIG. 3 in which the x-axis shows pore radius in ",i._rons and the y-axis shows absorLence in ml/g, as detemmined by using an appa~alus based on the porous plate method firstrepG,ted by Burgeni and Kapur in The Textile and Research Journal Volume 37 (1967) p. 356. The system is a modified version of the porous plate method and consbl~ of a movable Velmex stage inte,faced with a pruy,a"""able stepper motor and an electronic balance cor,~, ed by a r";~.,oco~"puter. A control prugld~ll aulon,dLically moves the stage to the desired height collects data at a specified sampling rate until e~uilibrium is reached and then moves to the next calculated height. Controllable pa,a",eter~ of the method include sampling rates criteria for equilibrium and the number of absorption/desorption cycles.
Wo 97/40223 pcTruss7tos788 Data for this analysis were collected in an oil medium. Readings were taken every fifteen seconds; if, after four consecutive readings, the average change was less than 0.005 g/min, equilibrium was assumed to have been reached. One complete abs~,~tio,,/desG,,l,tion cycle was used to obtain the reported data. The sample used was a 2.75 in. in di~,neter die cut sheet.
The pore radius distribution for the unshrunk sample peaked at 170,u. The pore radius distribution for the shrunk sample is shown in FIG. 4.
A vertical wicking techn ~le involves partially sub,.,e,~i.,g a long piece of sample fabric in a basin of fluid, and allowing it to hang vertically from above for a certain period of time. The depth of fabric in the fluid is not critical. The vertical wicking height is the height the fluid travels ve.licall~ up the fabric (measured from the fluid level of the fabric) after equilibrium has been reached. The equilibrium height is considered to be the maximum wicking height possible (reached after about one to two hours). The equilibrium times of the samples compared in this experiment were not necess~rily 1 5 equivalent.
An experiment was done using mineral oil 9 = 27 dyneslcm, ~ = 6 cps, where 9 is surface tension and tl is viscosity. The equilibrium vertical wicking heights for the pore ~(ad;ent sample and the hGmogenous, unshrunk sample were as follows:
Sample ID Wicking d;slar,ce CGIIt:SPOndjn9 radius Shrunk sample ~15cm c45,u Unshrunk sample 7cm 95,u The values were consistent with the pore size distribution measured in the absor~,tion mode.
EXAMPLE 3--METHOD OF HEAT TREATING THE HOMOGENOUS web STRUCTURE
The homogenous composition sample of Example 1 is subjected to a hot air stream across the surface of the web from a hot air source for a period of between about 5 seconds and 2 minutes at a temperature range of between about 100~ C to about 200~
W O 97/40223 PCT~US97/OS788 C. The stream is di,ecled to selective portions of the web for dirrertnt lengths of time. A
smooth movement of the hot air source creates a smooth t,ansilion between portions.
STRUCTURE FROM VARIABLE COMPOSITION
S A variable cGmposiliol1 web having different fiber dia" leter~ is made using polypropylene by a meltblowing process using three dies, each die extnuding a dirrerent fiber dia"leter to form three zones. Altematively, a single die having different aperture sizes across the die can be used. Zone fiber contenl, relstive shrinkage, and pore size is as follows:
Unit Composition Shrin'-~gs/pore sizeDenier Zone No.
Large fiber PET or 50150 PET/ Low shrinkagellarge 20-3û~J
polypropylene pore size 2 Medium fiber PET or 75/25 PETI Medium 1 0-20,u polypropylene shl il Ik:~g~'/medium pore size 3 Fine fiber PET High shlinl:~ge/ small 2-5~U
pore size A sample of the web obtained is cut into an inverted truncated triangle. The sample is f~l~osed ulli~Olrllly to a heat source, such as hot air having a temperature preferably in the range of from about 150~ - 200~ C or boiling water for approxilllately 30 seconds. It is to be unders~ood that these ranges are appro3 i~llale and ~ iations, e)~pansion and narrowing of the ranges are usable and conle,llplaled as being within the scope of this invention. The resulting product has the greatest shrinkage and therefore slll~"~st pore size in Zone 3"lloderd~e shrinkage and medium pore size in Zone 2 and lowest shnn':age and largest pore size in Zone 1.
EXAMPLE ~--ALTERNATIVE METHOD OF CENTRAL AND SIDE ZONES CREATION
For ,llatelial that can be manufactured into a diaper or the like, along a length of the web to be formed Zone 1, the central zone, is made of large fiber PET; Zones 2 and 3, W O 97/40223 PCT~US97/05788 on either side of Zone 1, are made of medium or fine fiber PET or PET/polypropylene mixture. After app' ~tion of the heat source, the central Zone 1, where fluid contact and absorption flux is greatest, has a large pore size. The side Zones 2 and 3, which wick fluid away from the central Zone 1, have smaller pore sizes.
STRUCTURE FROM A MIXTURE OF FIBERS USING MELTBLOWN PROCESS
An apparatus as shown in FIG. 6 is used in which fibers meltblov~m from one polymer A
are fommed by three dies and deposiled across and onto a belt. While the A poly."er fibers are stitl molten, fibers meltblown from a polymer B are de~osited by sepa~dle dies on top of the A polymer such that the fibers mix and become entrained. After the mixed A and B fibers web is formed, it is subjected to a heat source, as des~.,ibed in the previous ~dmr'es. The multi-co",pGnent web thus formed has a pore size gradient that can be co"l.."ed by the structure and composition of each fiber A and fiber B
used.
1 S While the invention has been described in connection with certain preferred e,.,bodi."enls, it is not intended to limit the scope of the invention to the particular forms set forth, but, on the corlt~d,y, it is intended to cover such alternatives, "~od;ricdlions, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
AND METHOD OF MAKING SAME
FIELD OF THE INVENTION
The present invention relates generally to a fibrous nonwoven web having a pore size gradient and methods for forming such a web. The method of the present inventionuses in one e",boJi",ent a formed web having an average pore size and selectively subjecting it to heat in order to shrink po,lions of the fibers thus fG",~;ng smaller pores in the sele~ed areas. In a second embodiment a web is formed of dirre,~ nt fiberdian~et~rs or fiber cGmposilions. Subjecting the web to heat ur,ifo""ly shrinks the ~liffer~nt diar"et~r fibers or co"~posilion to difrerent degrees thus f~""i"g a pore size gradient across the web.
BACKGROUND OF THE ART
The manufacture of nonwoven fabrics is a highly developed art. In general nonwoven webs or webs and their manufacture involve fG""ing fila",ents Ot fibers and depositing them on a carrier in such a manner so as to cause the fila",enls or fibers to overlap or entangle as a web of a desired basis weight. The bonding of such a web may be a~ aved simply by entanglement or by other means such as adhesive application ofheat and pressure to thermally responsive fibers or in some cases by pressure alone.
While many variations within this general description are known two cGrr""only used prucesses are defined as spunbonding and meltblowing. Spunbonded nonwoven structures and their manufacture are defined in numerous patents including for exd",r e U.S. Pat. Nos. 3,565 729 to Ha,l",ann dated FebnJary 23 1971 No.
4 405 297 to Appel et al. dated September 20 1983 and No. 3 692 618 to Dorschner et al. dated September 19 1972. DisuJssi~n of the meltblowing process may also be found in a wide variety of sources including for example an article entitled "Superfine The~ opl~slic Fibers" by Wendt in Industnal and Engineering Chemistry, Volume 48No. 8 (1956) pp. 1342-1346 aswell as U.S. Pat. Nos. 3 978 185 to Buntin et al. dated August 31 1976 No. 3 795 571 to P~enlice dated March 5 1974 and No. 3 811 957 toButin dated May 21 1974.
For the purposes of the present ~isclQsure the term Ucomposition" shall mean thechelll -~' makeup of a fiber. The term "structure" shall mean the physical characle,iatics of the fiber including, but not limited to denier tength crimping kinking number of co."ponents (such as bi- or multi-cG",ponent fibers disçussed in more debil hereinbelow) and sl, enyll ,.
Among the charc.c~erialics of the fiber web produced by either a meltblown or a sp~"bonded process are the fiber cJia",e~er also known as the "denier" of the fiber and the wicking power of the fabric which relates to the ability of the web to pull moisture from an area of ~pplication. The ability to wick moisture is related to the denier of the fiber and the density of the web which deflnes the pore size in the ",alerial. Wicking is caused by the capillary action of the fibers in contact with one another. The pulling or capillary action is inversely related to the pore size or capillaries in the web. Therefore the smaller the capillary the higher the pressure and the greater the pulling or wicking power.
It has been found useful to create a fabric having a co",posiLiGn conlaill,ng a pore size gradient over a given area of the fabric. An advantage of this is greater control over fluid wicking in target areas. Several patents have alle",pted to address methods of ~ ,~aling nonwoven fabrics of variable pore size.
U.S. Pat. No. 4 375 446 to Fujii et al. disr~oses a meltblown process in which fibers are blown into a valley created bet~,veen two drum plates having pores. One drum is a co"ection plate and the other drum is a press plate; the fibers are pressed between the two dnJms. The angle at which the fibers are shot into the valley is ~liscussed as creating webs of varying chara~lerislics.
U.S. Pat. No. 4 999 232 to LeVan disclQses a sl,et~.l)able batting cor"posed of differe,ltially-shn~ l.rble b.~.c."ponent fibers which form cross-lapping webs at detemlined angles. The angle determines the degree of stretch in the machine di~c~on and cross dir~ction. A helical crimp is induced into the material by thedif,e,t:ntial shrinking.
U.S. Pat. No. 2 952.260 to Burgeni discloses an absG,bent product such as a sanitary napkin having three layers of webs folded over each other; each layer has dirre,cnl shaped bands of porous zones of compacted or u"cG."pacted fibers.
U.S. Pat. No. 4 112 167 to Dake et al. ~li5~ ~oses a web including a wiping zone having a low density and high void volume. The low density zone is heated with a lipophilic cleansing emollient. The web is made by drying two layers of slurry formed webs.
U.S. Pat. No. 4 713,069 to Wang et al. disclQses a baffle having a central zone having a water vapor l,.-ns"~ission rate less than that of non-central zones of the baffle. The baffle can be fomned by melt t ~;.,9 or a la",ir,ate of spun bonded web layers or by coaffng the central zone with a cGmrositicn.
U.S. Pat. No. 4 738,675 to Buckley et al. disclQses a multiple layer d sposAhle diaper having cG"~p,t7ssed and uncGr"p,~ssed regions. The cG,n,ur~ssed regions can be created by en~bossi"g by rollers.
U.S. Pat. Nos. 4 921 659 and 4 931 357 to Marshall et al. ~isclose a ",ell,od of forming a web using a variable transverse webber. Two independent fiber sources (one short fiber one long fiber) are rolled and fed by feed rolls to a central mixing zone. The relative feed rates of the feed rolls is conl~ ~~le to alter the fiber co",posilion of the web formed U,er~f,c,-U.S. Pat. No. 4 927582 to Bryson diselQses a gradu~t~d distribution of granule ",alenals in a fiber web which is formed by introducing a high-abso,L,er,cy i"aleiial whose flow is reg~ ted into a flow of fibrous material which intem,ix in a f~"";ng ~ cha",ber. The cG"l,- ~le flow velocity permits selective distribution of high-absG,L.ency material within the fibrous material deposited onto the fomning layer.
U.S. Pat. No. 5.227107 to Dickenson et al. disrloses a multi-component nonwoven made by directing fibers from a first and a second fiber source throughout a forming chamber such that they mix to form a relatively uniform fibrous precursor which is then deposiled from the fo""i,-g cl ,~,nber onto a forming surface such that a fibrous nonwoven web is made which is a mixture of the first and second fibers.
U.S. Pat. No. 5 330 456 to R~bi.)son ~Jis~oses an absorbent panel having a fibrous absG,L ent panel layer of super absG,Lent polymer (SAP) and a liquid l,a,~srer layer the latter of which is positioned above the SAP layer.
Fabrics c,eat~d by multilayer processes can have t,~narer difficulties between layers I0 due to the inter-layer barrier caused by i",pe~rect wicking between the layers. Fabrics ceated by dirrertntial co",p~ssion of various areas are also undesirable bec~se altemating areas of high and low density slows down liquid lla"sport.
It would be desirable to have a method of c,~aling a variable pore size material that could utilize existing IlleLllods of c,eati"g the web. Such a web would have improved flow and wicking cl-a,~- ler,~lics that would enhance a fluid absorbing product s ability to absorb fluid in a target area and wick the fluid rapidly away to distant areas. Such a web would have enhanced vicl~i"g rates and cap~rities.
SUMMARY OF THE INVENTION
The present invention provides methods of fo""ing a nonwoven web having a pore size gradient created from thermally responsive fibers.
In a first pre:fe,.ed embodiment the present invention provides a web made in a conventional manner having an average pore size. The web can be formed using conventional meltblown Sp~ll ,bor,ding ai, rOl,, ,ing, wetro" "ing or other processes known to those skilled in the art. The web can be cut into a wedge or other shape and the malenal is selectively eYposed to heat so as to selectively shrink certain areas of the web. The heat source can be heated water oil or other liquid such as in the form of a spray a solid such as a heated roller or gear a radiated heat source such as incandescent (incoherent) or laser (coherent) light ultraviolet light microwave energy or other electromagnetic .~dialion. The wider areas of the web are exposed to more heat than the narrower areas resulting in a rectangular-shaped web having a poregradient. Various shaped webs can be e~ oyed prior to heating depending on the shape of the end product desired.
In a second prt,f~ d e",bGdi,nenl the present invention provides a ",ell,od and S appa,~ s for fomming a nonwoven web having over;app.ng or dis~re~e zones of Jifr~r~nl structure and/or co-.,posiliGn of fiber. In a meltblown p,ucess after the fibers are fommed and deposited onto a c~l'e~t:~n belt. the fibers are ~tl~oS~d to a generally ur,if~l-l,ly apptied heat source such as hot air. heabd solid or liquid blown or sprayed across the width of the fommed web. The fibers shrink accordi"g to the c h8~dCI~:ristics of the fiber structure and co",position fo"-,;.)g a web having a pore size gradient.
An appa,d~us for acl,.eving the Ill~tllod of the second prere"ed e",bodil.,ent using a meltblown process coi,lpnses at least one reservoir capable of containing a supply of at least one polymer resin (co"",lonly provided in pellet form) each reservoir being in commu,l -7tion with a meltblowing die. A foraminous conveyor belt disposed below the die re~ives attenuated fiber sl.l:allls exiting the die tip. A heat source such as a hot air blower or liquid pump is in commun-cation with a ",anif, i disposed across at least a portion of the width of the conveyor belt. The "~anif~ld has at least one aperture located on the bottom portion that can blow hot air or spray liquid on the fiber web as it passes undemeath the manifold while on the conveyor belt. An air fllter can optionally be ~isposed between the hot air source and the manifold or at the hot air source for filtering conla",i"anla. Optionally a reservoir containing fibers or other particles can be in communication with the manifo!d for blowing the fibers or particles onto the fiber web with the hot air which can provide additional control over structural and functional prupe"ies by changing the composition of the material prior to shrinking. In the case of a fluid heat source the fluid such as water is removed from the web using convenlional means, such as a vacuum source.
In a third embodiment the second pr~fe"ed e",bodi",ent method can be used e",r'~y"~g a spunbonding apparatus as is convenlionally known and adding the ",anifc'd and heat source as previously described.
W O 97140223 PCT~US97/OS788 In a fourth e~"bodiment, meltblown and spunbond processes are used in conjunction to aeate a cG",posile layered web, such as spunbond-meltblown-spunbond webs, which are known in the art and produced by the assignee of the present invention.
It is also possible to use multi-cGi~ponenl fibers, such as, but not limited to sheathlcore, eccenl,ic sheath/core, side by side (bi-co",ponent), side by side by side (tri-cGn,ponenl) or other known multi-cG",ponenl stnuctures and composilions.
Accord,n~ly, it is an object of the present invention to provide a rllt:lhod and appa,atus for fo""ing a nonwoven web having a variable pore size gradient.
It is another object of the present invention to provide a method for fo""ing a fiber web having a pore size gradient by conldcling a fiber web having an average pore size with a heat source to selectively shrink the fibers.
It is still ano~l,er object of the pr~se"l invention to provide a method for forming a fiber web having a pore size gradient by contacling a fiber web co",posed of cl;r~erer,l fiber denier or other stnuctural cha,d~.lerislics with a heat source to selectively shrink the 1 5 fibers.
It is still ano~l ,er object of the pr~sehl invenffon to provide a method for forming a fiber web having a pore size gradient by co"tacling a fiber web cor ,posed of zones of fibers, each zone containing a fiber of a distinct composition or structure, the zones possibly ove,i~FF:ng, with a heat source to selectively shrink the fibers.
It is yet another object of the present invention to provide a method for forming a fiber web of a difrt:r~nl web cGInrosilion or structure, using fiber and particle introduction to control cG"~rosilion and stnucture.
Other objects, features, and adva,llages of the present invention will become apparent upon reading the r~'lov ing detailed desc(ip(ion of el"bodil"ents of the invention, when bken in conjunction with the accol"panying drawings and the appended claims.
W 097/40223 PCTnUS97/05788 BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated in the drawings in which like reference characters designate the same or similar parts throughout the figures of which:
FIG. 1 shows a perapecli~e view of a section of web having an initial ho"~ogenous pore size according to a first prefe~ d e",bodi",ent of the present invention.
FIG. 2 shows a perspective view of the web of FIG. 2 after eYr~osure to heat.
FIG. 3 is a chart showing pore radius distribution of meltblown PET fibers prior to shrinking acco,d;ng to the first prefe"ed e,.,bodi",e,~l.
FIG. 4 is a chart shu~ing pore radius distribution of meltblown PET fibers aftershrinking accordil-g to the first pr~fel,ed embocli",enl.
FIG. 5 shows a perape~ e view of a meltblown appa~alus used to form a variable co",l)ositiGn fiber web according to a second pr~e"ed el"bocJi",el,l of the present i"~ nlion.
FIG. 6 shows a pictorial view of an appa,alus wherein one row of meltblown dies form a first layer of fibers and a second row of meltblown dies produce fibers which overlay the first layer of fibers producing a laminate structure.
FIG. 7 shows a side view of a spunbond appa,dlus used to form a variable composition fiber web accorJing to a second preferred embodiment of the present invention using three spunbond dies.
FIG. 8 shows a side view of an appa,alus accordi"g to an altemative embodiment in which a layer of fibers is first deposited by a row of spunbond die assen,'l.es folla~/ed by deposition of a second layer of fibers produced by a row of ",ellblol,vn dies.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
- The present invention can be employed to produce nonwoven fiber webs having conl,ulled pore gradient distribution created using thermally responsive fibers. The pr~fe" ~d embodiments of the invention set forth methods of and apparal.ls for applying heat or other force which selectively causes fibers to shrink.
With all the e",bcdi",ell~s of the present invention the polymer used can be anysuitable thermopl~stic maLenal such as, but not limited to, polymers and copolymers of S ethylene, propylene, ethylene ter~phll ,alate, mixtures thereof and the like. The polymer should exhibit the prop~ily of being shrinkable. Such malenals are known to those skilled in the art and need not be rEviewed in detail. The~r~tically, any ~I,e""opl~s~ic polymer known to those skilled in the art will exhibit heat-s~"i"!~ ility prope,lies if it is first oriented (as in a fiber spinning process) and then solidified so as to "freez~in~ the G~ientaliGn. Subsequent app'.~~tion of heat will cause the material to shrink to relieve the stresses induced in the orien~dlion process. Additionally, the fibers formed can be standa(~ monorilar"ent, mono-co",ponent fibers, or, can be multi-co",ponent fibers, such as, but not limited to sheathlcore, eccen~(ic sheath/core, side-by-side (bi-componenl), islands-in-the-sea (tri-cG",ponen~), or the like. For a desc.,i~,tion of these and other multi-cG",ponen1 fibers, see U.S. Pat. No. 5,382,400, issued to Pike et al.
(which is incG"~ordted by reference herein) and assigned to the assignee of the present in~en~on.
In a first prefe"t:d embo:Ji",ent of the invention, shown in FIGS. 1-4, a portion of a nonwoven fiber web 10 has a su~slanlially uniform pore size distribution defined by fibers or rila",ehls 12. The terms fiber and filament are synonymous, as are the terms web and web, and may be used inter~,hangeably herein. The web 10 is created using standard meltblown or spunbond technic, ~es known in the art, which need not be rcvie~/ed in detail. Briefly, however, in a meltblown process, an amount of polymer resin pellets is passed through an extruder by a screw conveyor and then through a meltblown die having multiple fine apertures. The molten resin is forced through the apertures to form fibers. The fibers are attenuated and broken up by being contacted by heated dl~JI;ng air and are co"ect~d as an enta"glEd web on a moving surface,such as a foraminous vacuum belt. The fibers are co"ected from the belt after setting.
In this first embodiment the meltblown die forms a web of fibers having an average pore size across the width of the web because the die apertures are the same diameter, resulting in the fibers being generally of the same diameter. A sample pore size distribution chart for unshrunk PET fibers formed using a meltblown process is shown in FIG. 3. The pore size can be in the range of about 5~u to about 1000~u in equivalent pore radius, ~r~fer~bly in a range of from about 20~u to about 500~ . Other pore size ranges, prior to and after shrinking, are conle",plated as being within the S scope of the present invention. Flt:ferably the coerr,ciant of vanation is not greater than about ~0%. A descri~ulion of pore size appears in U.S. Pat. No. 5,039,431, issued to John30n et al., assigned to the assignee of the pr zsent invention and inco".,Grdtad by rbf~r~nce herein. FIG. 4 shows a pore size distribution chart for shnunk PET fibers formed using a meltblown process.
F~fe,ably, heated air may be blown at the fibers in 5el~1ed areas to shrink the fibers.
FIG. 2, for e~atr,~le, shows the effect of selectively healing zone 14 of the web 10.
Fibers or fila,nenls 12 are shrunk and more highly enLanglcd in zone 14 resulting in reduced pore sizes in that zone co",pared with the remainder of web 10. Factors influencing the amount of shrinlkaae inciude, but are not limited to, tel"peral,Jre of the heated air, velocity of the air, dislance of the no7~1e from the fibers, duration of heat application, makeup of the air itself (e.g., humidity, pH, co",poailion of other vapori~ed or non-vapo,i~ed co"-ponents) and the like.
Selective shrinkage of the fibers is accG".F'ished by appl.~-tion of heat to the fibers.
Albmatively, steam, oil, or other sult~~le liquid, is contacted with the fibers in selected areas for specific periods of time to shrink the fibers more in some areas and less in other areas. Shri,.kt3e can be conl,olled by several factors, including, but not limited to, temperature of the heat source applied, composition of the heat source, dislance of the heat source ~Fploc~t~r from the web, and duration of eYpos~re.
Other factors which may influence sh"in'.cge that may be used with the present invention include, but are not limited to, water, light (UV, laser), pressure, magnetism or other ele_llomoti~r~ foree, and the like, depending on the fiber and mat composition. It is possible to use fib~ having a pH sensitive col,lposilion and use acid or alkaline adjusted fluid to control shrinkage.
It is also possible to use microwave energy to heat the fibers. An example of this method can be fG""ing fibers using metal particles as a co-forming material. The W O 97140223 PCTrUS97/05788 i...pr~gnaled ps,licles will heat upon ~xros~re to microwave or other energy and thus shrink the fibers. Dirrer~nt concenl,dtions of particies within areas of the web can be ach ~v0d by a plurality of different sized die tips or by a plurality of dis..~ete dies or by other techniques known to those skilled in the art. As an alle."alive to microwave energy one or more heat rolls can be used to apply heat to the web. Several pairs of heat rolls between which the web is pressed can provide a controlled amount of heating and also set the web such as in the case of a composite web stnucture.
In a second pr~rentd embodiment shown in FIG. 5 a variable cG"-rosition web 100 having zones of ~Jifrt ~-~nt fiber clia,.,ele,~ is preferably formed by a meltblown prucess.
It is to be under~lood that other processes can be used such as spu"bond;ng scussed in more detail herei.~below) airforming wel~u""ing or the like. A meltblown appardl.ls and process are described in detail in U.S. Pat. No. 5 039 431 issued to Johnson et al which uses a number of dies to form a layered web. FIG. 5 shows anappdlc~LUS 105 has a number of hoppe~ 110 each containi. ,9 lI ,e, lllop!~slic pellets 112 l 5 (not shown) of potymer resin. Each hopper 110 can have a distinct polymer ~r.~ro~itiGn or various hoppers can have the same comrosilion. The following d~~c,i~Jtion takes place for each die asse,nbly 111. The pellets 112 are transported to an extruder 114 which conlc.;,,s an intemal screw conveyor 116 The screw conveyor 116 (not shown)is driven by a motor 118. The extruders 114 are heated along their length to the melting temperature of the the""oplasl,c resin pellets 112 to form a melt.
The screw conveyors 116 driven by the motors 118 force the molten resin materialthrough the extruder 114 into an aKached delivery pipe 120 each of which is connected to a die head 122 124 and 126. Each die head has a die width. P~eferably the die heads 122 124 and 126 are spaced close to each other so that the fibers formed thert:fro", will become entangled. Fibers are produced at the die head tip in a convenlio~al manner i.e. using high pressure air to attenuate and break up the polymer stream to form fibers at each die head which fibers are deposited in layers on a moving foraminous belt 128 to form the web 100. A vacuum box 129 is positionedbeneath the belt 128 to draw the fibers onto the belt 128 during the meltblowingprocess. It is possible that one hopper 110 can supply polymer to a plurality of die heads 122 124 and 126. Altematively each hopper 10 can supply a different polymer to each die.
wo 97/40223 PCT/US97/0S788 The web 100 thus formed is heated by a manifold 130, which distributes heated air uniforrnly across the web 100 assisted by a vacuum box 131 improve ullifullllily of heating through the web thickness. The heated air enters the l"anifoid 130 by a conduit 132, which is in commun.c~tion with a heated air source 134. Optionally, an air filter 136 can be inse,led downstream from the heat source 134 to reduce contamination of the web 100. In an alle"~dli~e embodiment, the r"ar~ir~'d 130 can have a plurality of di5_1etê areas, each area being sn~p' ed by a dirre,ent heated air source, each source ~en~r~ting heat of a dirrerent te",perature. In an altemaffve embodiment, a manifold 130 is positioned beneath the belt 116 and the web 100 and the posilion of vacuum box 131 is, likewise, reversed.
The web 100 can be quenched to stop the action of heat on the fibers. Once the shrunk fiber web 100 has been created the web 100 can be withdrawn from the belt128 by conver,lional withdrawal rolls (not shown). Optionally, conven~ional calendar rolls (not shown) can engage the web 100 after the withdrawal rolls to emboss or bond the web 100 with a pattem thereby providing a desired degree of sli~rness and/orallerl~J~I, to the web 100.
At least one of the zones A, B and C of the web 100 shrink upon ~pos~re to the heat.
Rec~use the fibers are intertwined, the shrinl.i"g produces a gradient effect. The extent of shrinkage is dependenl on a number of factors, including, but not limited to, the fiber cGIllposi~iQn, fiber dis,lleter, fiber density, the overlap in zones, time of expos~re to heat after web formation and setting, heated air temperature, duration of ~xpos~re to the heated air, distance of the manifold 130 from the web 100, and the lilce.
Additionally, the heated air itself may have dir~erenl van~'es assoc,~led therewith, such as but not limited to, te,llperalure, humidity, acidity, and the like. The air source can contain vapGli~-~d water or other fluid. Such fluids may alter the chemical makeup of the fiber web and increase or decl~ase pore size or other characleristics. Moreover, the air source can also contain fibers, such as wood pulp, or panicles, such as superdbso, ben~ polymer ~"SAPn), which when blown into the web 100 become enb~pped either on the surface, or within the pores. In the case where the fibers or panicles are partially melted, they can adhere and solidify on or in the web 100.
W O 97/40223 PCT~US97/05788 The resulting web 100 has a gradient of pore sizes across the width of the web. For example, if the die head 122 produces fibers of large (relative) denier, die head 124, produces fibers of medium denier, and die head 126 produces fibers of fine denier, then the resulting gradient will have fibers in zone A having the largest pore size, the fibers in zone B having smaller pore size, and the fibers in zone C having the smallest relative pore size.
In an ~ ,ali~/e embodiment, the three die heads 122, 124, and 126 are replaced by a single die head 150 (not shown) having apertures of difrerenl diameters. By controlling the aperture size aaoss the width of the die head 150, the denier of fiber created can be cor,l~.lled.
Altematively, it is possitl~ to use an apparalus 200, shown in FIG. 6, in which a layer of fibers 210, cG",posed of a polymer A, is deposited on a conveyor belt 212 by a first row of meltblown lor spunbond) dies (partially shown and noted collectively as 214), which are fed molten resin polymer A, as described herai.-above with ~espect to the assembly 111. A second layer of fibers 216, co,nposed of a polymer B, is deposited on theconveyor belt 212 by a second row of meltblown dies noted collectively as 218, which are similarly fed molten resin polymer B. Vacuum boxes 219 and 219A positioned benedtl, the belt 212 draw the fibers formed onto the belt 212 during the process.
resulting laminate web 220 is subjected to heat in the manner described above using a "-anife~ 230, which is connecled by a conduit 232 to a heated air source 234. Optional boxes 236 can be inserted in the conduit 234. A vacuum box 237 assists in improving ur,ifo""ily of hea~ing through the web thickness. The advantage of using two or more polymers is that the l-eat sh,in!~?ge chara~la,islics of each polymer can permit greater control over the pore size gradient fommed thereby. Using polymers with very different heat shrinking charac~nstics may provide greater Z direction shrinking, which may produce a web having greater or less abso, ~tion or wicking properties.
A meltblown p,c cass may be advantageous where a smaller relative pore size range of the pre-shrunk web is to be created and a spunbonded process may be advantageouswhere a larger pore size range is to be achieved.
W O 97/40223 PCTrUSg7/OS788 As an alt~",aLi~e web-forming process to the second prefe~.ed e",bod;ment the pr~senl invention can be prac liced with a spunbond process and apparatus. Spunbond web fo""a~ion is known in the art and need not be rcvicwcd in detail here. Briefly l~o~evcr FIG. 7 shows a perspective view of an appa.al.ls 300 in which hoppers 310 feed polymer into extruders 312, which is then fed by pipes 314 into a spi.,ne.t:t 316.
The s~:nne.~t draws the resin into fibers which are quenched by a quench btower 318 positioned below each spinneret (one of which is shown in the drawing). A fiber draw unit or asp"d~or 320 is positioned below the spinneret 316 and receives the quenched r~ld.~6nLs. It is to be ul1der~tood that any number of spunbond extruder-spinneret asse.. ,blies can be used according to the present invention.
The fiber draw unit 320 includes an elongate vertical p~esage through which the rila..,enls are drawn by aspirating air entc,i"g from the dies of the p~ss~ge and flowing downwardly through the passAge. A heater 322 (one of which is shown in the drawing) sl~r.~. es hot aspirating air to the fiber draw unit 320. The hot aspi-dling air draws the rll~.. ,en~s and ambient air through the unit 320. A foraminous collecting belt 324 re~i~res the continuous rild",enls from the outlet openings of the fiber draw unit 320 assisled by a vacuum box 325 to form a web 328. Optionally calender rolls (not shown) can be em,~'~yed in a convenlionally known manner to apply pattern or overall bonding to the web 328.
After the web 328 has been formed a heating manifold 330 as described hereinabove is used to apply heat to the web 328 and a vacuum box 329 is used ad described hereinabove. A pore gradient is thus formed in the web.
In further altemative embodiment to the second embodi",ent a colr,~:nalion meltblown and spunbond process can be used to create co",posiLe web that is shrunk using the heat source appara~.ls and method of the second e",bodi",ent. A composite of spunbond-meltblown-spunbond fibers known as SMS can be created and heat shrunk using the present invention. In such a process a layer of meltblown fibers is formed on top of a layer of spunbond fibers and combined with a second spunbond iayer to form a three layer la",i.laLe which laminate is then pressed between a pair of cale,-der rolls to form a unitary web. FIG. 8 shows an apparatus 400, which can form a spunbond-meltblown web 410. Hopper 412 feeds polymer pellets into an extruder 414. Extruded resin in fed by a pipe 416 into a spinneret 418 which forrns filaments from the resin. A
quench btower 420 is positioned adjacent the filament stream and quenches the fila",ents. The rila",enls are received into a fiber draw unit 422 which is supplied with hot air by a heater 424.
The f;la",enls formed are drawn onto a foraminous collecting belt 426 by a vacuum box 428 posilioned below the belt 426. A meltblowing die head 430 s~-rFl ed with polymer resin from a hopper 432 via an extruder 434 and pipe 436 assembly produces a layer of meltblown fila",ents which is deposited on the collecting belt 426 onto the spunbond layer of filaments. A heating manifold asse~bly 440 and vacuum box 44~ as descril~ed in detail hereinaboYe selectively heat shrinks the laminate web 410 to foml a pore size gradient neck stretching roller assembly 442 and/or calender rolls 443 and 444 can be used as is known to those skilled in the art. A collecting roller 450 can remove and collect the ri"ished product.
An advantage of the first e",bodi",ent of the present invention is that a con~/en~ionally formed web can be treated after f~""ation to differentially create a pore size gradient.
This method can reduce the necessity of creating new appaldlus for fG""i"g the web. A
pore gradient is advant~geous in that the smaller the pore size the greater the wicking power of the web. A pore gradient structure is the most erril ;ent structure fort(anspG,ting liquid against gravity. Where smaller areas are to have a pore gradient selective heat arFli-~tion to a hG"~ogenous pore size web can have a high degree of control over the s~"i"k73e. A further advantage of this Illt:~hod is that addilion of ~co-forming particles provides additional control over web characteristics.
An advantage of the second e",bGdi",ent is that control over the range of pore sizes achievable is much greater because there are two degrees of freedom with respect to control i.e. web density and heat arpl;c~lion.
E)CAMPLES
The invention will be further described in connection with the following examples which are set forth for purposes of illu~ lion only. Parts and percentages appea,i"g in such e,.d",~ es are by weight unless ~J~I,erv.~,se stir~ te~
HOMOGENOUS COMPOSITION
A meltblown web (sample #5214~ was made from PET in a conve,ltiGnal manner to form a suL~larltially ho",ogenous pore size distribution. For a detailed description of a method of fomming a meltblown web see Butin et al. U.S. Pat. No. 3849241. A
sample of material was cut in the form of a truncated inverted triangle. Sections of the web sample were dipped in boiling water (100~ C) for 30 seconds to shrink selectively po, lions of the web. Altematively a spray head~ "anifold extending subsldnlially across the belt and the width of the web is used to spray boiling water onto the web.
The speed of the fiber on the belt passing below the manifold and the length of the manifold determine the length of expos~re of the web to heat.
The ",ell,od c~alecJ a unitary structure with a pore size gradient.
SAMPLES OF E)(AMPLE 1 The pore radius distribution chart of the formed unshrunk web is illustrated in FIG. 3 in which the x-axis shows pore radius in ",i._rons and the y-axis shows absorLence in ml/g, as detemmined by using an appa~alus based on the porous plate method firstrepG,ted by Burgeni and Kapur in The Textile and Research Journal Volume 37 (1967) p. 356. The system is a modified version of the porous plate method and consbl~ of a movable Velmex stage inte,faced with a pruy,a"""able stepper motor and an electronic balance cor,~, ed by a r";~.,oco~"puter. A control prugld~ll aulon,dLically moves the stage to the desired height collects data at a specified sampling rate until e~uilibrium is reached and then moves to the next calculated height. Controllable pa,a",eter~ of the method include sampling rates criteria for equilibrium and the number of absorption/desorption cycles.
Wo 97/40223 pcTruss7tos788 Data for this analysis were collected in an oil medium. Readings were taken every fifteen seconds; if, after four consecutive readings, the average change was less than 0.005 g/min, equilibrium was assumed to have been reached. One complete abs~,~tio,,/desG,,l,tion cycle was used to obtain the reported data. The sample used was a 2.75 in. in di~,neter die cut sheet.
The pore radius distribution for the unshrunk sample peaked at 170,u. The pore radius distribution for the shrunk sample is shown in FIG. 4.
A vertical wicking techn ~le involves partially sub,.,e,~i.,g a long piece of sample fabric in a basin of fluid, and allowing it to hang vertically from above for a certain period of time. The depth of fabric in the fluid is not critical. The vertical wicking height is the height the fluid travels ve.licall~ up the fabric (measured from the fluid level of the fabric) after equilibrium has been reached. The equilibrium height is considered to be the maximum wicking height possible (reached after about one to two hours). The equilibrium times of the samples compared in this experiment were not necess~rily 1 5 equivalent.
An experiment was done using mineral oil 9 = 27 dyneslcm, ~ = 6 cps, where 9 is surface tension and tl is viscosity. The equilibrium vertical wicking heights for the pore ~(ad;ent sample and the hGmogenous, unshrunk sample were as follows:
Sample ID Wicking d;slar,ce CGIIt:SPOndjn9 radius Shrunk sample ~15cm c45,u Unshrunk sample 7cm 95,u The values were consistent with the pore size distribution measured in the absor~,tion mode.
EXAMPLE 3--METHOD OF HEAT TREATING THE HOMOGENOUS web STRUCTURE
The homogenous composition sample of Example 1 is subjected to a hot air stream across the surface of the web from a hot air source for a period of between about 5 seconds and 2 minutes at a temperature range of between about 100~ C to about 200~
W O 97/40223 PCT~US97/OS788 C. The stream is di,ecled to selective portions of the web for dirrertnt lengths of time. A
smooth movement of the hot air source creates a smooth t,ansilion between portions.
STRUCTURE FROM VARIABLE COMPOSITION
S A variable cGmposiliol1 web having different fiber dia" leter~ is made using polypropylene by a meltblowing process using three dies, each die extnuding a dirrerent fiber dia"leter to form three zones. Altematively, a single die having different aperture sizes across the die can be used. Zone fiber contenl, relstive shrinkage, and pore size is as follows:
Unit Composition Shrin'-~gs/pore sizeDenier Zone No.
Large fiber PET or 50150 PET/ Low shrinkagellarge 20-3û~J
polypropylene pore size 2 Medium fiber PET or 75/25 PETI Medium 1 0-20,u polypropylene shl il Ik:~g~'/medium pore size 3 Fine fiber PET High shlinl:~ge/ small 2-5~U
pore size A sample of the web obtained is cut into an inverted truncated triangle. The sample is f~l~osed ulli~Olrllly to a heat source, such as hot air having a temperature preferably in the range of from about 150~ - 200~ C or boiling water for approxilllately 30 seconds. It is to be unders~ood that these ranges are appro3 i~llale and ~ iations, e)~pansion and narrowing of the ranges are usable and conle,llplaled as being within the scope of this invention. The resulting product has the greatest shrinkage and therefore slll~"~st pore size in Zone 3"lloderd~e shrinkage and medium pore size in Zone 2 and lowest shnn':age and largest pore size in Zone 1.
EXAMPLE ~--ALTERNATIVE METHOD OF CENTRAL AND SIDE ZONES CREATION
For ,llatelial that can be manufactured into a diaper or the like, along a length of the web to be formed Zone 1, the central zone, is made of large fiber PET; Zones 2 and 3, W O 97/40223 PCT~US97/05788 on either side of Zone 1, are made of medium or fine fiber PET or PET/polypropylene mixture. After app' ~tion of the heat source, the central Zone 1, where fluid contact and absorption flux is greatest, has a large pore size. The side Zones 2 and 3, which wick fluid away from the central Zone 1, have smaller pore sizes.
STRUCTURE FROM A MIXTURE OF FIBERS USING MELTBLOWN PROCESS
An apparatus as shown in FIG. 6 is used in which fibers meltblov~m from one polymer A
are fommed by three dies and deposiled across and onto a belt. While the A poly."er fibers are stitl molten, fibers meltblown from a polymer B are de~osited by sepa~dle dies on top of the A polymer such that the fibers mix and become entrained. After the mixed A and B fibers web is formed, it is subjected to a heat source, as des~.,ibed in the previous ~dmr'es. The multi-co",pGnent web thus formed has a pore size gradient that can be co"l.."ed by the structure and composition of each fiber A and fiber B
used.
1 S While the invention has been described in connection with certain preferred e,.,bodi."enls, it is not intended to limit the scope of the invention to the particular forms set forth, but, on the corlt~d,y, it is intended to cover such alternatives, "~od;ricdlions, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
Claims (45)
1. A method of forming a nonwoven fiber structure having a pore size gradient comprising.
(a) providing at least one polymer resin capable of forming thermally responsive fibers;
(b) forming a plurality of fibers from said resin;
(c) forming a nonwoven fiber web from said fibers said web having an average pore size;
(d) selectively applying a heat source to said web such that a portion of said fibers shrink to form an average pore size smaller than that of said average pore size in step (c).
(a) providing at least one polymer resin capable of forming thermally responsive fibers;
(b) forming a plurality of fibers from said resin;
(c) forming a nonwoven fiber web from said fibers said web having an average pore size;
(d) selectively applying a heat source to said web such that a portion of said fibers shrink to form an average pore size smaller than that of said average pore size in step (c).
2. The method of Claim 1 wherein said polymer is a thermoplastic polymer.
3. The method of Claim 2 wherein said polymer is selected from the group consisting of polymers and copolymers of ethylene propylene ethylene terephthalate and mixtures thereof.
4. The method of Claim 1 wherein said fibers are formed in step (b) by a meltblown process.
5. The method of Claim 1 wherein said fibers are formed in step (b) by a spunbond process.
6. The method of Claim 1 wherein said fibers are selected from the group consisting of mono-component and multi-component fibers.
7. The method of Claim 6 wherein said multi-component fibers are selected from the group consisting of sheath/core eccentric sheath/core side by side and islands-in-the-sea arrangements.
8. The method of Claim 1 wherein said fibers formed have an average diameter of from about 0.1µ to about 100µ.
9. The method of Claim 1, wherein said fibers formed have an average diameter offrom about 1.0µ to about 5.0µ
10. The method of Claim 1, wherein said web formed in step (c) has an average pore size of from about 5µ to about 1000µ.
11. The method of Claim 4, wherein said web formed in step (c) has an average pore size of from about 5µ to about 20µ.
12. The method of Claim 5, wherein said web formed in step (c) has an average pore size of from about 200µ to about 700µ.
13. The method of Claim 1, wherein in said web formed in step (c) has an averagepore size of less than about 50% variation.
14. The method of Claim 1, wherein said fibers are co-formed with a material selected from the group consisting of fibers wood pulp particulate matter and superabsorbent polymer (SAP).
15. The method of Claim 1, wherein said heat source is selected from the group consisting of a fluid, air, solid and particulate material.
16. The method of Claim 15, wherein said fluid is selected from the group consisting of water and oil.
17. The method of Claim 1, further comprising step (e) quenching said web.
18. The method of Claim 1, wherein said web is produced by a combination of meltblown and spunbond processes.
19. A nonwoven fiber structure having a pore size gradient produced according the method of Claim 1.
20. A method of forming a nonwoven fiber structure having a pore size gradient, comprising:
(a) providing at least one polymer resin capable of forming thermally responsive fibers;
(b) forming a plurality of fibers from said resin;
(c) forming a nonwoven fiber web from said fibers, said web having an average pore size and having a variable structure of at least two fiber characteristics each of said at least two fibers being in a zone; and, (d) selectively applying a heat source to said web such that at least a portion of said fibers shrink to produce zones having different average pore sizes.
(a) providing at least one polymer resin capable of forming thermally responsive fibers;
(b) forming a plurality of fibers from said resin;
(c) forming a nonwoven fiber web from said fibers, said web having an average pore size and having a variable structure of at least two fiber characteristics each of said at least two fibers being in a zone; and, (d) selectively applying a heat source to said web such that at least a portion of said fibers shrink to produce zones having different average pore sizes.
21. The method of Claim 20, wherein said polymer is a thermoplastic polymer.
22. The method of Claim 21, wherein said polymer is selected from the group consisting of polymers and copolymers of ethylene, propylene and ethylene terephthalate and mixtures thereof.
23. The method of Claim 20, wherein said fibers are formed in step (b) by a meltblown process.
24. The method of Claim 20, wherein said fibers are formed in step (b) by a spunbond process.
25. The method of Claim 20, wherein said fibers are selected from the group consisting of mono-component and multi-component fibers.
26. The method of Claim 25, wherein said multi-component fibers are selected from the group consisting of sheath/core, eccentric sheath/core, side by side and islands in the sea arrangements.
27. The method of Claim 20, wherein said fibers formed have an average diameter of from about 0.1µ to about 100µ.
28. The method of Claim 20, wherein said fibers formed have an average diameter of from about 1.0µ to about 5.0µ
29. The method of Claim 20, wherein said web formed in step (c) has an average pore size of from about 5µ to about 1000µ.
30. The method of Claim 23, wherein said web formed in step (c) has an average pore size of from about 5µ to about 20µ.
31. The method of Claim 24, wherein said web formed in step (c) has an average pore size of from about 200µ to about 700µ.
32. The method of Claim 20, wherein said web formed in step (c) has an average pore size of less than about 50% variation.
33. The method of Claim 20, wherein said fibers are co-formed with a material selected from the group consisting of fibers, wood pulp, particulate matter and superabsorbent polymer (SAP).
34. The method of Claim 20, wherein said heat source is selected from the group consisting of a fluid, air, solid and particulate material.
35. The method of Claim 20, wherein said fluid is selected from the group consisting of water and oil.
36. The method of Claim 20, wherein said web is made of at least one shrinkable fiber and at least one non-shrinkable fiber.
37. The method of Claim 20, further comprising step (e) quenching said web.
38. The method of Claim 20, wherein said at least two zones have a smooth transition.
39. The method of Claim 20, wherein said heat is applied in a uniform manner.
40. The method of Claim 20, wherein said heat is applied to selective portions of the web.
41. The method of Claim 20, wherein said web is produced by a combination of meltblown and spunbond processes.
42. The method of Claim 20, wherein a plurality of polymer resin compositions capable of forming thermally responsive fibers are each extended through a discrete meltblown die so as to form a plurality of fibers having an average pore size and having a variable structure of at least two fiber characteristics each of said at least two fibers being in a discrete zone.
43. A nonwoven fiber structure having a pore size gradient formed by the process of Claim 20.
44. A nonwoven fiber structure having a pore size gradient formed by the process of Claim 42.
45. An apparatus for forming a nonwoven fiber web of varying fiber structure having a pore gradient, comprising;
(a) at least two hoppers each capable of containing an amount of a resin material;
(b) at least two dies, each die having at least one aperture;
(c) means for placing said hoppers in communication with said dies, each reservoir being in communication with at least one die;
(d) means for forming thermally responsive fibers from said dies;
(e) means for collecting said fibers as a web comprising a moving foraminous belt; and (f) a heat source means associated with said apparatus for applying heat to said web such that said fibers selectively shrink, with a portion of said fibers having a smaller pore size than said unshrunk fibers.
(a) at least two hoppers each capable of containing an amount of a resin material;
(b) at least two dies, each die having at least one aperture;
(c) means for placing said hoppers in communication with said dies, each reservoir being in communication with at least one die;
(d) means for forming thermally responsive fibers from said dies;
(e) means for collecting said fibers as a web comprising a moving foraminous belt; and (f) a heat source means associated with said apparatus for applying heat to said web such that said fibers selectively shrink, with a portion of said fibers having a smaller pore size than said unshrunk fibers.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/637,998 | 1996-04-25 | ||
| US08/637,998 US5679042A (en) | 1996-04-25 | 1996-04-25 | Nonwoven fabric having a pore size gradient and method of making same |
| PCT/US1997/005788 WO1997040223A1 (en) | 1996-04-25 | 1997-04-08 | Nonwoven fabric having a pore size gradient and method of making same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2249331A1 true CA2249331A1 (en) | 1997-10-30 |
Family
ID=29422958
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2249331 Abandoned CA2249331A1 (en) | 1996-04-25 | 1997-04-08 | Nonwoven fabric having a pore size gradient and method of making same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2249331A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112176526A (en) * | 2020-09-15 | 2021-01-05 | 浙江优全护理用品科技股份有限公司 | Green antibacterial cleaning and nursing dry towel and preparation method thereof |
-
1997
- 1997-04-08 CA CA 2249331 patent/CA2249331A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112176526A (en) * | 2020-09-15 | 2021-01-05 | 浙江优全护理用品科技股份有限公司 | Green antibacterial cleaning and nursing dry towel and preparation method thereof |
| CN112176526B (en) * | 2020-09-15 | 2023-01-13 | 浙江优全护理用品科技股份有限公司 | Green antibacterial cleaning and nursing dry towel and preparation method thereof |
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