wo 98/04397 PCT/USg7/13579 PROC~SS OF ADJUSTING WVTR OF POLYOLEFIN FILM
This invention relates generally a process of adjusting the water vapor S tr~ncmi~cion/porosity of films and film composites, while ~ g general recict~nce to liquid trancmi~sion (strikethrough). More specifically this invention is directed towards a process for producing films, film composites, and articles made therefrom, that are made permeable to water vapor, by passing them through interdigit~ting grooved rollers.
Polyolefin films which are rendered more permeable to water vapor using filler loading and orientation are known.
Such films or film composites are said to be more breathable, that is to have improved, increased permeability to water vapors, while Ill~ A;~ g a reci~t~nce to liquid strikethrough (defined herein). Uses of such films or film composites include on a diaper the permeability of which may permit the passage of moisture vapor and air, while substantially preventing the passage of liquid. The advantages ofsuch a film used in a diaper are that after the wearer voids, the liquid is generally ret~ine-l, while much of the liquid vapor can escape decreasing the "wet feeling", and lowering the possibility of uncol.,fo, lable diaper rash.
U.S. Patent No. 4,472,328, ~signed to Mitsubishi Chemical Industries, Ltd., suggests a breathable polyolefin film pl cpared from a polyolefin/filler composition having from 20 percent to 80 percent by weight of a filler such as asurface treated calcium carbonate. A liquid or waxy hydrocarbon polymer elastomer such as a hydroxyl-termin~ted liquid polyb~lt~liçne was purported to produce a precursor film that could be mono-axially or biaxially sLlclched to make a film l)reall-~le. The breathable film desc,il,ed by Mitsubishi is also described in Great Britain Patent No. 2,115,702, ~c.~ ed to Kao Col~ol~lion. The Kao patent further describes a disposable diaper prepared with a breathable film as disclosed by the Mitsubishi patent. The breathable film is used as a backing for the diaper to contain liquid.
96~0l~.pcr ~ - 2 -U.S ~ate~t i!~o. 4,350,655, lc~igned to ~ x Fiber Film, describes a porouspalyolefin f~ ln col~t~inin8 at least 50 percent by weight of a coated inor~anic filler.
The precursor film is formed without the ~dditi~n of an elastomer by ~mploying ainOr~aTnC filler surfae~ coated w~th a fatty acid ester of only silicon or titarlium.
The precur; or fi~n is then rolled between h~onzontal~y sroo~,ed rollers~ Cold stretching o ~the precursor fi~m at 1 tetnperature below 70~ C, produces a porous film. Some of the resulting films were stated to be both vapor and liquid perme~ble, ! owever, at least one film ~E;~a~ple 3) was stated to be perrneable to ai~.
US ~777,073 su~gests a breathable film produced by stretching ~f prec~rsor f lrn prepared from ~ pclyolefin/filler composit;on. The doc~ment su~gests that the penneability ~nd strength, especislly te~r stren~th are purportedly improved by melt ern~ossing th~ preeursor ~Slm w~th a patterned m~ltembo~s~ng .oller and stretching the film to impar~, a pattern of different film 15 thickness h Iving greater per~T~e~bility ~.thin the areas of reduced t~iCl~ness c~mpared t~: the areas of greater thi~l~nPce US 4,289,832, the nearest art, suggests a process for co~t~ng or rcgn~fin;7, a film of a blend of thermop]astic o~ien~able polyrner ~th an incu~ ibl second pha~e, followed by selecti~e stretching ~n a st~tion prsvi~ed 20 with a set of ~roo~red rollers to form an opaque, low den~ity, porous film.
Hawever, a~sent the coating or impre~tin~, the film even when stretched by the grooved rol'ero" is not rendered water pe~néable.
EP l 352 802 su~,çsts a method for making s~ exible, microporous film~ haviny high bre~t~ility leve~s in whdch a film is ~I-ricAted by blending a25 milcture of a polymer or a copolymer of an aJpha-olefin with 60 to 75~~o by wei~,ht of an inorga.n~c filler. The film is then bia~ially stretched from about 1.5 to about 7 time~o, in eac!l direction.
The shc;lcl~ll~ i5 a~con~rli~h~d by "well known techniques", ~n~ in~
hyd~aulics, ?inch rolls, or t~t~rin~ No dic~ ure exists in this ~0¢~1m~t to 30 grcoved rollers.
3680 11 .PCT
~ - 2(a) -~ , 48-0~0774 sug~est~ a polyalefin resin mL~ed with ~-laO parts nlbber ~nd less th~,n 1200 palts of an inorganic fine particles, molded irto film or sheet fonn a~.d st-etche~ to give porous films or sheets. The 'ilm is said to have ~ood wri~ing a~ld pnnt~ng properties. No disclo3ur~3 or suggestion to use or grooYed 5 roller to strl tch the film ex~sts.
n~ 01-256l50 suggest3 a watar vapour perrn~able film comprising a film made from ~ composition blended 50-200 w~ight parts of inorganic filler, ~ith 100 p~s of p~ mer blend. 11.~ blend comprises 20-80% Of cr~st~llir,e polyrne~ c~nd 8û-20% of thermoplastic el~stomer. ~he film i5 onented. ~o disclosure to 1~ stretching vLa grooved rollers s ~ound.
Moc ~ of these techniques require that a fism c~r films composite be rendered breatha~le, regardless of the technique but general'.y through tentenng (for trarlsverse ~ ecrion or TD oieMation, and ~ ial speeds of two rol]s f~r ~ hin~ dL-~ction or MD onentation~, in ~ separate operatiGn, prior to final lS con~tructiol of the end-use article, for instance the di~per, !eading to expensive double pro~ ~ sing or more expensive transpart of the film rendered less d~nse by the te~terinl~, operation.
The efore, a commercial need ~sts for a pr~c~ss that can be used to improve (in rease3 the film or film composite water vapor trancm~ on rate 20 ~IR) at ~ co3~merci~1ly acceptable r.3te with exi~ting col~s~lt,.cial equip~nent, such that thl: disposable article will have relatively high water vapor l~ ;s~ ;~n rate~ in all e ~ part ~f the ~rticle, with good resist~nce to liquid permeability, while ;..g .3 sufficient level of physic~l strength to fonn a u~efill disposa~le article. A process for ~tt~inin~ such an article at relatively rapid, econorn~cal rate 25 would be a~lvanta~eou~.
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WO 98/04397 PCT/US97tl3579 SUMMARY
We have discovered that certain polyolefin films and film composites can be processed to have greater water vapor transmis.eion rates, relatively low liquidstrikethrough, while m~int~ining film integrity, by using certain film forming formulations and techniques and passing the film, the film composite and/or the fini.ched fabricated disposable article, through a nip of at least one interrligit~ting grooved roller, or at least one pair of such rollers.
In certain embodiments of our invention a polyolefin film or film composite comprises at least one layer of a disposable article and is rendered breathable by passing the film, film composite or fabricated article through interdigitating grooved rollers. The film, film composite or fabricated article will have either a single layer or multilayer construction and the polyolefin/filler combination can be co-extruded, l~min~ted or blended with other polyrners or polymer based fabricated articles.
In an embodiment of our invention, a film ("precursor film") is made, utili7:ing a polyolefin or a polyolefin blend with a relatively higher filler loading, generally inclllrling embossing a pattern thereupon, such that its subsequent manipulation, either by itself, in a film composite or as a part of a disposablearticle, will render the film breathable (hereinafter defined as water vapor permeable, within certain limits of water vapor tran~mi~ion rates (WVTR), while m~int~ining a certain level of liquid i~l.pe~l..eability) while ...~ g a miniml~m level of physical p.op~;.lies, elongation/tensile strength being of most importance.
The manipulation of the film, film composite, and/or fabricated disposable article includes passing all or parts of the film, film composite, and/or fabricated disposable article through a grooved roller and/or inter ligis~ting grooved rollers, at a rate sllffici~nt to develop a minimllm level of breathability to the film or film portion of the article, at a commercial and economical rate.
The tear ~l-englll~ elasticity, and softness of a film prepared from the polyolefin/filler composition may be improved by addition of small amounts of anolefinic elastomer ~ , , .
The WVTR desired is above 100 glm21day ~ 38~ C, 90% RH plere.~bly above 200 g, and can be easily greater than 1000 glm2/day.
BR~EF DESCRIPTION OF THE DRAWINGS
The foregoing aspects, features and advantages of the present invention will become clearer and more fully understood when the following det~iled description, and appended claims are read in conjunction with the accoll.pallying drawings, in which is a sçh~m~-iG drawing of an embodiment of our invention for hlll)alling breathability to a film or film composite:
Figure I is a schematic view of a process for converting a precursor film (and optionally other layers) into a film with greater WVTR.
Figure II illustrates a cross-sectional view of the inter~ligit~ting grooved rolls of Figure I, taken along the lines 2-2.
Figure III illustrates an enlarged view of area 3 from Figure II showing several inter~igit~ting teeth from the grooved rolls.
Introduction High WVTR films, high WVTR film composites, and disposable articles made thelerlo-ll of our invention, are produced from a precursor film that is prepared from a polymer composition that complises at least one polyolefin component, at least one filler component, and optionally an elastomeric component. The polyolefin colllponent may be any polyolefin which is suitable for film formation such as homo or co-polymer polypropylene, homo or co-polymer polyethylenes or blends thereof. A preferred polyolefin is a copolymer of propylene and low density polyethylene, particularly prt;relled is linear low density polyethylene. The linear low density polyethylene may be a polymer made from either traditional Ziegler-Natta or metallocene catalysts, or con-l)illalions thereo~
In an embodiment of our invention the films, film composites, and articles made thelt;fiulll based on polyolefin filler col.lbinalions, when passed through a nip of interdigitating grooved rollers (helehlaner used interchangeably with "ring rolling") would surprisingly and unexpectedly have improved water vapor tr~ncmicsion rates while m~ inil~g rçcist~nce to liquid permeability; and ret~ining film integrity. Following is a detailed description of certain prefelred, films, film composites, and/or fabricated disposable articles made therefrom, within the scope of the present invention. Also disclosed are preferred methods of producing these films, film composites, and fabricated disposable articles made thererrolll as well as preferred applications thereof. Those skilled in the art will appreciate that numerous modifications to these prefelled embodiments can be made without departing from the scope of the invention. For example: Though the properties ofcertain films, film composites, and fabricated articles such as diapers are exemplified, especially after ring-rolling, the films and composites will have numerous other uses. To the extent our description is specific, it is solely for the purpose of illustrating ple~lled embodiments of our invention and should not be taken as limiting the present invention to these specific embodim~nts.
It will be appreciated by those of ordinary skill in the art that the films and film composites of certain embodiments of the present invention, can be combinedwith other polymers or polymer based fabricated articles such as films, fibers7 fabrics (incl~1~ing non-woven fabrics) and the like, depending on the intended function of the resnlting film or, or structure.
As an example of such combinations, by extrusion co~tine coextrusion coating, or by coextrusion or ~ lA~ g of the film with other polymer films, e.g polyolefin. Other properties may be achieved. For in~t~nc~ after ring-rolling anentire film cross-section, certain (machine direction) sections could be extrusion coated to ~.limin~te breathability in those selecte(l portions so coated. Also cont~n pl~ted are varying col~lbh~alions of the precursor film, or the film after ring-rolling, with other films, or non-woven fabrics, generally made from one or morepolyolefins. Such combinations, while in~ ing the precursor or the post ring rolled film, can include several conll)il,dlions, such as film, non-woven/film, film/non-woven, film/non-woven/film, film/film, and the like.
Other methods of improving WVTR of a film or article fabricated from the film, may be used in addition to use of the filled polyolefin and process of passing the filled polyolefin film through the nip of interdi~it~ting grooved rollers described herein, without departing from the int~n-led scope of my invention. For example, including microporous voids through pin-point punctures (also known as "aperatured film") to improve the WVTR, in addition to ringrolling is not excluded by the present invention. Also, it is well known that manipulation of a film by ~h~n~in~ quench conditions during melt processing, and/or by irr~ ting the film will have an effect on WVTR and/or physical properties Such me~h~nical or other trç~tment or manipulation is not excluded by this invention.
Films or film composites employing the polyolefintfiller blends of certain embodim~nt~ of the present invention can be oriented, annealed, or crosslinked Additionally, polyolefin/filler colllbhlalions of the present invention can be made into film by processes including blown or cast film m~m~f~ctnring techniques. The blend components can function to modify barrier, opacity, sealing, cost, or other functions that will be known to those of ordinary skill in the art.
The films or composite structures are often used in infant diapers, toddler training pants, adult inContin~nce devices, medical drapes and apparel, such as surgical gowns, feminine hygiene articles, and the like. Use of the term "film composites" may include one or more film and/or non-woven layers bonded mechanically, thermally, or adhesively to the film. Such non-woven materials include spun-bonded-meltblown (SM), SMS, each individually. Such non-woven materials are most often made from polyolefins, such as homopolymer polyethylene, copolymer polyethylene (including one or more of a-olefins of 4-10carbon atoms, vinyl acetate, ethylincally unsaturated acrylic acid esters, ac~lic acid, meth~cryclic acid, ionomers, polypropylene homopolymers, polypropylene copolymers in~.ludin~ one or more of ethylene and a-olefins of 4-10 carbon atoms, homopolymer and copolymer polypropylene).
ComPonents of A Precursor Film Film Formin~ Polyolefin Most film follllillg polyolefins and cGIllbinalions of film follnillg polyolefins may be used in embo~lim~nt~ of our invention.
Polyethylenes Linear low density polyethylenes are among the materials favored in embo-lim~nts of our invention. Linear low density polyethylene (LLDPE), generally that having density between 0.910 to 0.935 g/cc and a melt index from 0.01 to 10 dg/min. Another polyolefin that may be considered in such composites is very low density polyethylene (VLDPE, also plastomer) which will have densities in the range of from 0.860 to 0.910 g/cc. High density polyethylene (HDPE) having densities in the range of from 0.935 to 0.970 g/cc may also be considered. Such polyethylenes may be produced by copolymerizing ethylene with one or more C4 to C20 a-olefin. Generally the p~rel.ed a-olefins include those selected from the group consisl;l.g of butene-1, pentene-1, 4-methyl-1-pentene, hexene-1, octene-1, decene-1 and combinations thereof. Most pler~lled are ethylene copolymers of butene-1, hexene-1, octene-1 and combinations thereof.
The comonomers may be present in amounts up to 20 mole percent. The amount of comonomer or comonomers will generally determine density, for instance HDPE
will have from 0 to 1 mole percent comonomer, while plastomers with densities lower than 0.900g/cc will have up to 15 or even 20 mole percent conlonolner (s).Such polyethylenes may be made utili7ing traditional Ziegler-Natta, chromium based, metallocene (both alumoxane and ionic activators). Processes useful for plepalillg such polyethylenes include gas phase, slurry, solution and the like. The density of polyethylenes such as these, in prefel.ed embodiments, will generally be in the range of from 0.900 and 0.935 g/cm3, preferably in the range of from 0.910 to 0.925 g/cm3, most preferably from 0.915 to 0.920 gm/cm3. The polyethylenes will have a melt index in the range offrom 0.1 to 10 g/~0 min, preferably 0.5 to 5 g/10 min., generally consistent with film follning conditions.
Polypropylene Component Polypropylene may be used in conjunction with one or more polyethylenes, or by itself as the polyolefin component of the precursor film. Polypropylene may be made from many of the catalysts and processes di~cu~sed supra, inclu~in~
optional inclusion of one or more a-olefins.
Elastomeric Colll~onelll One or more elastomers may be in~luded in the polyolefin component. Such elastomers include, but are not limited to natural rubber, ethylene alpha olefinrubber (EPM), ethylene, alpha olefin diene monomer rubber (EPDM), styrene-isoprene-styrene (SIS), styrene, butadiene, styrene (SBS), butyl and the like. Of these SIS and SBS are prerelled, with SBS more particularly prefelled. The rangeof elastomer inclusion are generally between 5-40, preferably 5-3 0, more preferably 5-25 parts per hundred parts polyolefin.
Amounts of each component can vary with the desired properties for the precursor film or film composite. For in.ct~r~ce, a nominal 0.917 g/cc density LLDPE may be combined with 15 parts of an elastomer per hundred parts of LLDPE. Such a co~bh~ation might provide improved elastlc behavior.
Other components in a film forming polyolefin are not excl~ded Such components may include additives such as anti-oxidants, anti-static agents, colors and the like, well known to those of ordinary skill. Further, blending of polyolefins with polymers is also contemplated. For example, blending of traditional Z-N
catalyzed, chromium catalyzed (CR), metallocene catalyzed (MCN) and free radical initi~ted (FR) polyolefins using one or all in a blend as the film forming component is contemplated. For in~t~nce inclll~in~, but not limited to MCN/ZN, MCN/CR, MCN/FR, MCN/ZN/FR, combinations and the like are contemplated.
Other free radical initi~ted polyethylenes, high pressure polyethylene, ethylenehomopolymers as well as ethylene copolymers may be inr.~ ie(l Both in the case of other polyolefins and the elastomeric polymers, the combinations should be generally formable into a film.
As used in this application, the term "polyolefin" will mean the polyolefin, anycombination of polyolefins, elastomers, additives, and the like.
Filler Materials To impart breathability to polyolefin films, addition of fillers and subsequent straining is known.
To form the precursor film, fillers may be incorporated at relatively high levels, limited only by the ability of the con~hlation (polyolefin/filler) to be formed into a film. Further, it is believed that useful films may not be made with an amount of the filler in excess of 250 parts filler per hundred parts polyolefin (pphp) (or polyolefin blend of the film forming composition. While at lower than 20 pphp of filler, the polyolefin/filler composition may not have sufficient breathability.
WO 98104397 PCT/US97tl3~;79 Higher amounts of filler may cause difficulty in compounding and losses in ~11 engl of the final breathable film. Generally, the range of filler may be in the range of from 35 to 200, preferably from in the range of from 50 to 150. The minimum amount of filler is needed to insure the interconnection within the film of voids created at the situs of the filler, particularly by the stretching operation to be subsequently performed Fillers useful in certain embodiments of our invention may be any inorganic or organic material or combinations thereof having a low affinity for and a significantly lower elasticity than the polyolefin component or the optional elastomeric component. Preferably the filler should be a rigid material having anon-smooth surface, or a material which is treated to render its surface hydrophobic. The mean average particle size of the filler is between 0.5 to 7 microns, preferably between 1 to 5, more preferably from 2 to 3.5 microns. It should be understood that smaller particle sizes, such as 0.75 to 2, will provide the best balance of compoundability and eventual breathability, but there relative economics makes them generally less useful than particle sizes of 3 microns and above. Such particle sizes are p~efelled for films having a thickness of between0.5-6 mils. Examples of the inorganic fillers include calcium carbonate, talc, clay, kaolin, silica diatomaceous earth, m~gne~ m carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, ~lnminum hydroxide, zinc oxide, magnesium oxide, calcium oxide, m~gnçcium oxide, i ~a:lium oxide, alumin~mica, glass powder, zeolite, silica clay, and combinations thereof, and the like.
ri~lm carbonate is particularly p~ere,.c;d. The inorganic fillers such as calcium carbonate are pler~lably surface treated to be hydrophobic so that the filler can repel water to reduce agglomeration of the filler. Also, the surface coating should improve binding of the filler to the polymer while allowing the filler to be pulled away from the polyolefin when the film formed from the polyolefin/filler co.llbh~aLion is stretched or oriented. ~lere.led coatings are stearates, such as calcium stearate, which are generally compliant with FDA regulations. Organic fillers such as wood powder, pulp powder, and other cellulose type powders may . .
be used. Polymer powders such as Teflon(~) powder and Kevlar(~) powder may also be included. Combinations of these fillers are also contemplated.
Compounding of the Polyolefin/Filler Composition Polyolefin/ffller compositions usable in this invention may be compounded in several di~renl ways. The components may be brought into intim~te contact by, for example, dry blending these materials and then passing the overall composition through a compounding extruder. Alternatively, the polyolefin and filler components may be fed directly to a mixing device such as a compounding extruder, higher shear continuous mixer, two roll mill or an internal mixer such as a Banbury mixer. Overall, the objective is to obtain a uniform dispersion of the filler in the polymer without agglomeration, and this is readily achieved by in~ul~ing sufficient shear and heat to cause the polyolefin component to melt. However, time and temperature of mixing should be controlled as is normally done to avoidmolecular weight degradation.
Film Extrusion and/or Embossing The film forming composition (polyolefin/polyolefin blends and filler or fillers) may be m~mlf~ctllred into a precursor film by conventional tubular extrusion (blown bubble process) or by cast extrusion. Film formation by cast extrusion may be more convenient, as the film can be immedi~fely melt embossed as described below.
In the cast extrusion process, the molten resin is extruded from an elongate die in the form of a web. The web may be pulled over at least one patterned embossing roller to chill and solidify the film with an embossed pattern for reasons diccussecl further below. The precursor film is may be produced to a gauge of between 0.5 to 6 mils, preferably from 0.75 to 5 mils, more preferably from I to 4 mils, most preferably from 1.5 to 3 mils, which allows for further stretching asdescribed below. However, those of oldinaly skill in the art will understand that many factors affect the response of the precursor film to the ring rolling process. It is our intent that the film or film part of a film composite will have bleaLllability, and at least a minimllm of physical properties to ~ its function, that is the film after ring rolling (either as part of a composite or by itself) should have the .
WO 98/04397 ~ PCT/US97/13579 ability to perform its function. For inst~nce in the side panel of a diaper, the film might even have substantial voids, providing excellent breathability, but havingenough strength to m~int~in the physical form of the diaper or other article during its use.
The extrusion tel"pelal-lres, die telllpelal~lres, and embossing roll (if used) temperatures will depend on the composition employed, but generally will be in the following ranges for compositions of the present invention prepared by cast extrusion:
Melt Temperature (~F.) 350 550 Die Temperature (~F.) 350-550 Embossing Roll Temperature (~F.) 50-130 Embossing may be used on the surface of polyolefin films to reduce gloss, although such will not be the films primary function in a ring rolling process.
Embossing can be imposed on the precursor film surface at the time of the film fabrication for cast extrusion, or at a subsequent time for cast or tubular extrusion by procedures well known in the art. For the present invention, embossing may impose a pattern of dirrelenl film thicl~n~sses within the precursor film, and can be con~lucted with an micro/macro pattern, e.g. cross-h~hing, dots, lines, circles,diamonds, hexagons, etc. The pattern can be either in line and/or off line and the rolls can be engraved with either pin up and/or pin down type configurations.
Use of the Precursor Film Traditionally, breathable film has been made using such film precursors as described above, and then orienting the film by a variety of techniques, such astentering in one or both of the machine direction(MD) or cross or transverse direction (TD). The oriented and breathable film could then be used for a variety of end use articles, such as diapers (usually back sheets, but also top sheets),fell~ill;lle hygiene items, ~nd~ei, c~ l pads, panty liners, incol~ l briefs, and the like. However, use of certain embodiments of the present invention will include the precursor film either by itself or a film composite in an interdigitating grooved roller process. By film composite, we intend that one or more additionallayers or materials are added or l~min~ted to the film. Such additional materials WO 98/04397 - 12 - PCT/US97/1357g and layers include synthetic woven, synthetic non-woven, synthetic knit, non-woven, apertured film, macroscopically exr~nded three-dimensional formed film, filled compositions or l~min~tes and/or a con,bina~ion of these items. The non-wovens may be made by processes inrh~ling~ but not limited to spunlace, spunbond, meltblown, carded and or air-through or calendar bonded. The materials or layers of the composite can be combined by many method known to those of ordh-al y skill. For inet~nc~, adhesives (incl~ ing spray adhesives, hot melt adhesives, latex based adhesives and the like), thermal bonding, ultra-sonic bonding, extrusion l~min~tion, needle punching, and the like. For inst~nce, in the m~nllf~cture of infant diapers, toddler training pants, adult incontinence devices, feminine hygiene items, medical gowns, medical drapes, and house wrap, parts or all of the final product may be assembled (by for instance heat or adhesive l~min~tion) then the partial or finished construction is passed through one or more interdigit~ting pairs of rollers to render the precursor film high in WVTR.
1 5 Stretching High WVTR film, film composites or fabricated articles made therefrom may achieved by stretching the precursor film to form interconnected voids prior to ring rolling. Stretching or "orientation" of the film may be carried out monoaxially in the m~r.hine direction (MD) or the transverse direction (TD) or in both directions (biaxially) either simult~neously or sequentially using conventional equipment and processes following cooling of the precursor film.
Blown films are prere,~bly stretched in the m~rhine direction or in both directions whereas cast films are prerelably stretched in the transverse direction.
For orientation in the MD, the precursor film is passed around two rollers driven at dirrelenl surface speeds and finally to a take up roller. The second driven roller which is closest to the take up roll is driven faster than the first driven roller. As a consequence the film is stretched between the driven rollers.
Stretching of melt embossed precursor films either using both a tentering device and a directly in a ring rolling device or just the ring rolling device produces breathable films having the desired water vapor permeability. The resulting films had greater permeability in the areas of reduced thickness in comparison to the areas of greater thickness.
Although not thoroughly investig~ted controlling of the strain on the film during stretching is believed to be important to controlling the WVTR. For stretching in the transverse direction, strain is controlled for a given stretch ratio by adjusting the film speed and the stretching r~i~t~nce. The stretching ~list~nce is measured, between the point where the film starts to increase in width to the closest point where the film is fully stretched. For stretching in the m~chinl direction, strain is controlled for a given stretch ratio by controlling film speed and the gap between the first and second driven rollers A range of stretching ratios from 1:2 to 1:5 prove s~tief~ctory for MD
stretching with a ratio of 1:4 being plerel.ed. A range of stretching ratios of 1:2 to 1:5 prove s~ti~f~ctory for TD stretching with a ratio of 1:4 being prefe~ed.
It is a further object of this invention to provide such a process for producing a barrier layer having high liquid strikethrough resistance.
The process of ring rolling also may activate the elasticity of the web (dependent upon specific ring rolling pattern used), in addition to imparting breathability to the web. Precursor webs cont~inin~ elastomeric components add to the elasticity developed during the ring rolling process.
Ring Rolling Process To illustrate the process the term web or webs are used. As used herein, the term web will include a precursor film and optionally one or more additional webs or layers, as ~iccusced above, for in.ct~nce one or more non-woven webs and/or one or more film webs. Such web components can be pre-assembled or l~min~te~l Prior to ring rolling, at least one additional web may be added. Web 10 and alternatively 11 may be webs of a precursor film with either another film or fabric (11) the ~orecw~or film will have a thickness from 0.5 to 6 mils. For example, the second (11) web may be melt-blown webs of the type taught in the article entitled "Superfine Thermoplastic Fibers" by Van A. Wente, appearing in Ind21strial Engineering Chemis~ry, August, 1956, Vol. 48, No. 8 (pages 1342-1346). While melt-blown material may be nylon, polyester, or any polymer or polymer blend capable of being melt-blown, a melt-blown polypropylene web is preferred. A
melt-blown web could comprise two or more zones of dirrelel" melt-blown polymers. Melt-blown webs having a basis weight of up to 30 g/m2 or greater can be used in the present invention, but lower weight webs are generally plerel,cd in order to minimi7e the cost of the barrier layer produced the~tLunl. Technology provides for the production of melt-blown webs with a miniml~m basis weight of 3g/m2, but available commercial melt-blown webs generally have a basis weight of 10 g/m2 or more. The preferred basis weight for optional web 11 is from 10 g/m2 to 30 g/m2; most preferably from 10 g/m2 to 20 g/m2. The density of melt-blown web 1 1 is preferably up to 0.15 g/cc and most preferably up to 0.1 g/cc. Webs 10 and 11 may be the same or different.
Web 10 and (when present) 11 have preferably been rolled up together as plies with adjacent surfaces on feed roll 20. They are unrolled from feed roll 20 ret~ining their contiguous relationship and passed into the nip of inter~igit~tin~
grooved rolls 24 and 25. Grooved rolls 24 and 25 have grooves perpendicular to the axis of the rolls (parallel to the m~rhine direction) as shown in FIG. 2 which is a sectional view of grooved rolls 24 and 25 taken along line 2-2 of FIG. 1.
It has been found that the web or webs (10 and optionally 11) will be stretched more uniformly with less tendency to tear the webs when inter-iigit~tinf~
grooved rolls 24 and 25 are heated. The rolls are preferably heated such that their surface temperature are within the range of 160~ F. to 220~ F.; more preferably within the range of 180~ F. to 200~ F. FIG 1 shows a pl~re.,ed arr~ngçm~nt of inter-ligit~ting grooved rolls 24 and 25 being located with their centers in a horizontal plane and webs 10 and 11 cont~cting the surface of roll 24 for one-fourth of a revolution before entering the nip between rolls 24 and 25; this provides an opportunity for the web or webs 10 and 11 to be heated prior to entering the nip. However, inter~igit~tinp grooved rolls 24 and 25 could be positioned with their centers in a vertical plan or at any other angle and webs 10 and 11 could be fed directly into the nip of the rûlls. ~Içhe~ p of webs 10 and 11 if found to be necessa.y in order to avûid tearing ûf the webs, could be accomplished in any conventional manner.
. ~ . _ , The webs where two or more webs are fed is stretched and enmeshed while passing between the inter~ t~ting grooved rolls 24 and 25 and are thus lightly bonded together producing final product 12. Where final improved WVTR
composite film 12 has been stretched in the cross-m~Ghine direction by the grooved rolls 24 and 25 of FIGS. I and 2, a device such as a curved Mount Hope roll 26 or tenter clamps is needed to extend the now high WVTR film or film composite to its fullest width. The extended and smoothed film 12 is then rolled up on a takeup roll 27.
The amount of lateral stretch imparted to web plies by the grooved rolls 24 and 25 will depend on the shape and depth of the grooves of the rolls, and on the gap spacing between the rolls.
U.S. Pat. No. 4,223,059, issued to Eckhard C.A. Schwarz on Sept. 16, 1980 discloses inter~ it~tinf~ rolls having grooves of generally sine-wave shapecross-section which may be used for the present invention. U.S. Pat. No.
4,153,664 issued to Rinehardt N. Sabee on May 8, 1979, discloses the stretching of polymeric webs by ring-rolling with rolls having grooves with a variety of shapes. The shape of the grooves of the rolls will generally determine whether the web is stretched uniformly or at inc~ e~ l, spaced portions of the web.
Incremental stretching of the web is more likely to cause some local tearing of film or film composites which would damage the liquid strikethrough reci~t~nce of thefilm and, therefore, is not prel~ ~ ed for the present invention.
A prere"ed groove pattern for inter-ligit~ting rolls 24 and 25 iS shown in FIG. 3 which is an enlarged view of area 3 of FIG. 2. FIG. 3 shows a partial cutaway view of interdigitating rolls 24 and 25. Teeth 54 and 55 of grooved roll24 intermesh with teeth 51, 52 and 53 of grooved roll 25. The length 60 of the teeth is 3.81 mm., and the distance 61 between the centerlines of adjacent teeth on each roll is 2.54 mm. The teeth have generally straight sides which are at an angle 62 from a plane perpen~icul~r to the axis of rolls 24 and 25 of 9' 17". The land at the base of the teeth has a radius 63 of 0.51 mm. Sharp corners 66 at the ends of the teeth are removed.
WO 98/04397 PCT~US97/13S79 It is pre~.led that the interdigit~ting grooves of rolls 24 and 25 be perpendicular to the axis of the rolls. In this way, the maximum number of grooves of a given size will engage the web 10 and 11 at the same time and impact stretch to the webs. By having the maximum number of teeth engage the web at a given time, a more uniform stretching of the webs is achieved so that local tearing of the film or film composite is ...;~-;.n;~d. The stretched film 12 can be easily smoothed in the cross-m~chine direction.
A reproducible gap setting between grooved rolls 24 and 25 can be achieved by having the bearing of one of the grooved rolls, e.g. 24, stationary while those of the other grooved roll 25 can be moved in the horizontal direction.
Groove roll 25 iS moved in the horizontal direction. Groove roll 25 is moved toward roll 24 until its teeth are intermeshed with those of grooved roll 25 and it will move no further. The bearings of grooved roll 25 are then moved away from grooved roll 24 a measured di~tAnce, the gap setting. The preîelled gap setting for practicing the present invention are from 0.76 mm. to 1.65 mm. With grooved rolls 24 and 25 having a tooth configuration as shown in FIG. 3 and described above, the maximum width of film or film composite layer 12 which can be 4 achieved for a single pass is 2l/2 to 3 times the width of starting webs 10 and 11.
By incising the gap between grooved rolls 24 and 25, the amount of lateral stretch imparted to webs 10 and 11 is decreased. Therefore, the width of film or film composite 12 CGn.pal ed to the width of starting web can be varied for a single pass between grooved rolls 24 and 25 from a maximum increase of 2l/2 to 3 times to noincrease by the app-.~pliale gap setting.
If it is desired to stretch the web more than can be achieved by a single pass between the grooved rolls, multiple passes between grooved rolls 24 and 25 can be used.
Basis weight is generally an ill-pG,lanl plopelly desired to be controlled for film or film co"-posile layer (total ring rolled web) 12. For cost reasons, the lightest film or film composite that will provide sufficient breathability is desired.
A basis weight of the film produced by itself will be generally above 20 g/cm2.
The desired basis weight can be obtained by controlling the amount of stretch W O 98/04397 - 17 - PCT~US97/13579 imparted to web 10 and optional web 11 by grooved rolls 24 and 25 as described above, and by the selection of the basis weights of the starting webs 10 and 11.For the present invention, starting webs 10 and 11 have a c..n~ tive basis weight in the range of 1.1 to 4 times the ultimate desired basis weight, p.c;l~,ably in the range of 1.5 to 3 times the desired basis weight, most preferably 2 times the desired basis weight. Correspondingly, the desired width of breathable film or film composite 12 can be achieved by selecting a proper coml)illalion of stretch imparted by the grooved rolls 24 and 25 and initial width of starting webs 10 and 1 1 ~or the present invention, the initial width of starting webs 10 and 1 1 before passing between grooved rolls 24 and 25is within the range of 0.9 to 0.25 times the desired width, preferably within the range of 0.7 to 0.3 times the desired width, most preferably 0. 5 times the desired width Test Procedures The test procedures used to determine the unique pl-ope. Iies of the layers of the present invention and to provide the test results in the examples below are as follows:
Gurley Porosity Teleyn Gurley Model 4190 Porosity Tester with sensitivity ~tt~chm~tt is used With the procedure as follows a) Cutting a strip of film (~2't wide) across the entire web width, b) Inserting a film sample to be tested between orifice plates, c) Setting the sensitivity adjustment on "5", d) Turning the inner cylinder so that the timer eye is vertically cellleled below the 1 Occ silver step on the cylinder, e) Resetting the timer to zero, f) Pulling the spring clear of the top flange and rele~cinE the cylinder, When the timer stops counting, the test is completed The number of counts is multiplied by 10 and the res -ltin~ number is "Gurley seconds per 100 cc".
It will be appreciated by those of ordinary skill in the art that the films of m-polyethylene resins of certain embodiments of the present invention, can be combined with other materials, depending on the intçn~led function of the resulting film.
Other methods of improving and/or controlling WVTR properties of the film or container may be used in addition to the methods described herein without departing from the int~nrled scope of my invention. Por example, meçh~nical treatment such as micro pores.
Liquid Column Strikethrou~h R~sict~nr.e Test The liquid strikethrough r~ci~t~nce test is a method for determining the water pressure in millimeters of water at which water penetrates a repellent barrier layer at a specified fill rate and with the water and barrier layer at a specified temperature. Such a test is described in INDA Journal, Vol. 5, No. 2, Karen K.
Leon as; the strikethrough resistance of embodiments of our invention are from 50 - 500 cm.
Example 1-12 LLDPE/CaCO3 films are made utili7.in~ the following conditions, materials and equipment shown in Table 1.
Examples 1-12 used LL3003.09 (a 3 melt index 0.917 g/cc polyethylene (Z-N) available from Exxon Chemical Co., Houston, TX.) examples: co.
levels of CaCO3 as shown in Table 1, blended with 100 parts of LL-3003.
Examples 13-16 Example 13-16 were made under the conditions shown in Table 1, eA~Illple~ 1-12, but with Exceed~ ECD-112 a 3.4 MI, 0.917 glcc density m-LLDPE from Exxon Chemical Co., Houston, TX with filler, master batch (MB) and elastomer levels as shown in Table 2.
Examples 1-4, 9, 10, I l, 12, 13, 14 and 15 were run on a Davis Standard cast line. EA~Il,.)le~ 9, 10, 11, 12, 14, and 15 were oriented in the TD, Example 9, 10, 11, 12, and 15 were further MD drawn. Excall~,lcs 5, 6, 7, 8, and 16 were run on a blown film extruder.
Each film sample was run through various ring rolling appalallls as shown in Tables 2, 3, and 4, with the results for basis weight shown in Table 2, the results for WVTR in Table 3, the results for air porosity shown in Table 4.
While the present invention has been described and illustrated by reference to particular embodim~nts thereof, it will be appreciated by those of ordinary skill in the art that the invention lends itself to variations not necessarily illustrated herein. For ~ ple, it is not beyond the scope of this invention to include additives with the claimed improved, high WVTR film process. For this reason, then, reference should be made to the appended claims and the r~m~incler of the specification for purposes of determining the true scope of the present invention.
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