MXPA99006060A - Stable and breathable films of improved toughness and method of making the same - Google Patents

Abstract

The present invention relates to uniaxially oriented microporous breathable films of exceptional toughness transverse to the direction of orientation. Such films include a particulate filler and a nonelastic material including a copolymer of ethylene with at least one C4-C8&agr;-olefin monomer, such copolymers being described in the trade as"super tough","next generation", etc., and being prepared with"new"or"improved"catalyst systems or with metallocene or similar single-site catalysts. A method of manufacture is also disclosed.

Description

MOVIES WITH ABILITY TO BREATHE AND STABLE OF RESISTANCE IMPROVED AND METHOD TO MAKE THEMSELVES FIELD OF THE INVENTION The present invention is directed to breathable thermoplastic films using copolymers of ethylene and at least one C4-C8 olefin < ? In addition, the present invention is directed to a method for making such films.

BACKGROUND OF THE INVENTION The present invention is directed to breathable thermoplastic films. Such materials have a wide variety of uses, especially in areas of limited use and disposable items.

Films have traditionally been used to provide barrier properties in limited use or disposable articles. By limited or disposable use, it is meant that the product and / or the component is used only a small number of times or possibly only once before being discarded. Examples of such products include, but are not limited to, health-care and surgical products, such as surgical drapes and gowns, disposable workwear such as gowns and lab coats, and absorbent products. for personal care such as diapers, training pants, incontinence garments, sanitary napkins, bandages, cloths and the like. In absorbent personal care products such as infant diapers and adult incontinence products, films are used as outer covers for the purpose of preventing body waste from contaminating clothes, bed sheets and other aspects of the surrounding environment of use. In the area of protective clothing including hospital gowns, the films are used to prevent the cross-exchange of microorganisms between the user and the patient.

Even though these films can be effective barriers, they are not aesthetically pleasing, because their surfaces are smooth and are either sticky or slippery. These are also visually flat and "plastic" making them less desirable in costume applications and other uses where they are in contact with human skin. It would be more preferable if these items were more of a cloth type in both tactile and visual aspects. For example, infant diapers that have the feel and appearance of traditional cloth undergarments are perceived as premium products and may, in some cases, overcome the tendency to believe that they require covering for other garments for aesthetic reasons. Adult incontinence products of the garment type can improve the self-image of the incontinent individual. In addition, more than a garment-type isolation gowns will help to feel the less strange and threatening hospital environment to the patient and increase user comfort. It is also preferable to have films that can make an outer cover material with more elastic performance and recovery to provide better fit and comfort.

The lamination of the films has been used to create materials which are both liquid impervious and some type of cloth in appearance and texture. The outer covers on the disposable diapers are just one example. In this regard, reference may be made to United States of America Patent No. 4,818,600 dated April 4, 1989 and United States Patent No. 4,725,473 dated February 6, 1988. Surgical gowns and drapes are other examples. See in this regard, United States of America Patent No. 4,379,102 dated April 5, 1983.

A primary purpose of the film in such laminations is to provide the barrier properties.

A need is also used for such laminates to be breathable so that they have the ability to transmit moisture vapor. The laundry made from laminates of these breathable or microporous films is more comfortable to use by reducing the concentration of moisture vapor and the consequent hydration of the skin underneath the article of clothing. As well, the pore size in breathable films can not be too large, especially in protective clothing applications where the penetration of chemical vapor presents a risk of contamination to the user.

The conventional process for obtaining a breathable microporous film has been to stretch the thermoplastic film containing the filler. The microvoids are created by the filler particles during the stretching process. The film is usually heated before these pulling processes to make the film more plastic or more malleable. This pulling or stretching also orients the molecular structure within the film which increases its strength and durability. Molecular orientation caused by stretching is desired to improve durability.

A film can be stretched in the direction of the machine or in the direction transverse to the machine. The stretching of the film in the transverse direction is particularly challenging because the forces applied to the edges of the film cause it to stretch in the width direction. Stretching frames are commonly used. In contrast, the stretching of the film in the machine direction is relatively easy. It is only necessary to increase the pulling, or the speed ratio between the two rollers while the film is in the plastic or heated state. There is a problem of durability, however, with the films uni-directionally stretched, be it in the direction of the machine or in the transverse direction. Unidirectional stretching causes a molecular orientation only in the stretched direction. This results in movies that are easily torn or torn along that dimension. For example, a film oriented in the machine direction has a propensity to tear or break along the direction of the machine. Also, the tension characteristics of the film (stretched in the machine direction) are dramatically increased in the machine direction, but the tensile strength in the transverse direction is significantly lower than that of the machine direction. For example, therefore, if at the same time that the CD strength of the film decreases, the elongation to CD breaking is also reduced, the film can be very easily divided in use, and an article made with it, such as a diaper, it can squeeze out, which is obviously an undesirable effect.

These durability problems with uni-directionally oriented or stretched films are well known. Two approaches have been commonly used to make obvious the durability problems of the product resulting from these characteristics of highly isotropic resistance. The first is to orientate-stretch the film in both the direction of the machine the transverse. Films that have been biaxially stretched have more balanced strength properties. The second approach is to combine in a laminate a layer of a film oriented in the direction of the machine with a layer of the film oriented in the transverse direction.

Another aspect of manufacture is the stretching of the "aged" films. In commercial manufacturing operations, "fresh" films such as recently extruded films are not generally available for orientation. The extruded films are often set aside or stored for later orientation, usually at room temperature. During this storage period, a change in polymer morphology may occur, the change of which may cause the property of the film to change. The orientation of such aged film often results in products with characteristics of lower durability such as a lower peak DC voltage (or an elongation to breaking in the transverse direction). A critical property, for example, for the durability of an outer diaper cover made of this film.

Therefore, there is a need for an elastic breathable film and a process that provides a film with both the cloth type aesthetics and the durability and comfort that are desired.

SYNTHESIS OF THE INVENTION The present invention relates to a breathable thermoplastic film that includes a linear low density polyethylene resin material including copolymers of ethylene and a C4-C8 olefin monomer and a filler present in an amount that is at least 40 % by weight of the filled resin, wherein the filler has a particle size that contributes to pore formation Preferably, the film includes from about 40 to about 65% filler by weight of the filled resin. an application, where the minimum desired water vapor transmission rate is around 1,500 g / m2 / 24 hours, the amount of filler present is around 48% by weight.

The present invention is also directed to a process for preparing a breathable film of the present invention, including providing a polymeric resin including a linear low density polyethylene resin material; adding to the resin at least 40% by weight of a filler having a particle size that contributes to the formation of pore to form a filled resin; forming a film having a first length of the resin filled; and stretch the film to form a microporous film. The process of the invention is applicable to films formed by various processes, for example, cured or blown films. In one embodiment of the invention, the microporous film is stretched to a second length that is from about 160 to about 400% of the first length. In another embodiment, the film is tempered after stretching.

The preferred film of the present invention has a water vapor transmission rate of from about 300 to about 4,500 grams per square meter per 24 hours (measured by a Standard Test ASTM E 96-80 with ® Celgard 2500 as control).

Such films have a wide variety of uses including, but not limited to, applications for absorbent articles for personal care, including diapers, training pants, sanitary napkins, incontinence devices, bandages and the like. These same films can also be used in articles such as drapes and surgical gowns as well as various articles of clothing either as the entire article or simply as a component thereof.

Having thus described the invention in detail, it will be appreciated that various changes and modifications may be made to the present invention without departing from the spirit and scope of the claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic side view of a process for forming a film according to the present invention.

Figure 2 is a cross-sectional side view of a nonwoven laminate / film according to the present invention.

Figure 3 is a top plan view partially cut away of an absorbent personal care item for example, in this case a diaper, which may use a film made in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY The present invention is directed to breathable thermoplastic films including copolymers of ethylene and a C4-C8 α-olefin monomer.

A particularly useful example is known as "super-octene". The term "super-octene" as used herein includes those linear low density polyethylene (LLDPE) materials that are produced by the polymerization of ethylene and 1-octene comonomer and designated Dowlex NG brand.

("NG resin") available from Dow Chemical Corporation of Midland, Michigan. The "super-octene" resin is made with an improved ® catalyst system other than the "metallocene" or Insite. Suitable "super-octene" resins useful in the present ® invention include, for example, Dowlex NG 3347A and Dowlex NG 3310, both of which contain about 7% octene (nominal weight%), 93% ethylene. While not wishing to be bound by the following theory, it is postulated that the improved catalyst regulates the molecular weight / molecular weight distribution as well as the placement of the comonomer and the branching on the polymer molecule more precisely than conventional catalysts. It is possible, for example, that as a result of the improved technology, the NG resins have a narrower molecular weight distribution, a more homogeneous branching distribution as well as a smaller highly branched low density and unbranched high density fractions. The physical characteristics of the unfilled films made of super-octene resins are indistinguishable from this resin of conventional LLDPE resins, as illustrated in Table A. Table A lists the physical data of Dowlex NG 3347A and, by comparison , the data of certain "conventional" LLDPE resins, ® Dowlex 2045 and 2244A.

As can be seen from Table A given above, the typical properties ((a) to (d)) of films not filled with these various resins are not remarkably different. Minor variations can be explained by variations in the melt index and in the density or crystallinity of the olefins.

Other copolymers of ethylene base with C4-C8 α-olefins are also useful in the present invention including, for example, materials commercially available from Exxon Corporation under the trade name ExactMrca. These materials are all prepared with a "new" or "improved" catalyst system with respect to the metallocene or similar single site catalysts.

Other suitable ethylene-based copolymers with C4-C8 c-olefin monomers of the present invention include non-elastic metallocene-catalyzed polymers. The term "metallocene catalyzed polymers" as used herein includes those polymer materials that are produced by the polymerization of at least one ethylene using metallocenes or constricted geometry catalysts, a class of organometallic complexes as catalysts. For example, a common metallocene is ferrocene, a complex with a metal in the form of a sandwich between two cyclopentadienyl ligands (Cp). Metallocene process catalysts include bis (n-butylcyclopentadienyl) titanium dichloride, bis (n-but i lcyclopent adieni 1) zirconium dichloride, bis (cyclopentadienyl) scandium chloride, bis (indenyl) zirconium dichloride, bis (methylcyclopentadienyl) titanium dichloride, bis (metailcyclopentadienyl) zirconium dichloride, cobaltocene, cyclopentadienyltitanium trichloride, ferrocene, hafnocene dichloride, isopropyl (cyclopentadienyl, -1-fluoroenyl) zirconium dichloride, molybdocene dichloride, niquelocene, niobocene dichloride, retenocene, titanocene dichloride, hydride circonocene chloride, zirconocene dichloride, among others. A more exhaustive list of such compounds is included in United States Patent No. 5,374,696 issued to Rosen et al. And assigned to the Dow Chemical Company. Such compounds are also discussed in U.S. Patent No. 5,064,802 issued to Stevens et al. And also assigned to Dow. The aforementioned complete patents are incorporated herein by reference.

The metallocene process and particularly the catalyst support systems and the catalysts are an object of a number of patents. U.S. Patent No. 4,542,199 issued to Kaminisky et al. Describes a process wherein MAO is added to toluene, the metallocene catalyst of the general formula (cyclopentadienyl) 2MeRHal wherein Me is a transition metal, Hai is a halogen and R is cyclopentadienol or an alkyl radical Cl to Cd or a halogen, is added, and ethylene is then added to form a polyethylene. U.S. Patent No. 5,189,192 issued to LaPointe et al. And assigned to Dow Chemical discloses a process for preparing addition polymerization catalysts through metal center oxidation. United States Patent No. 5,352,749 issued to Exxon Chemical Patents, Inc., describes a method for polymerizing monomers in fluidized beds. U.S. Patent No. 5,349,100 discloses chiral metallocene compounds and the preparation thereof by creating a chiral center by enantioselective hydride transfer. The co-catalysts are materials such as methylaluminoxane (MAO) which is the most common, other alkylaluminiums and boron-containing compounds such as tris- (pentafluorophenyl) boron, lithium tetrakis (pentafluorophenyl) boron. Research is continuing on other co-catalytic systems or the possibility of minimizing or even eliminating alkylaluminiums due to problems of product contamination and handling. The important point is that the metallocene catalyst is activated or ionized to a cationic form for reaction with the monomer (s) to be polymerized.

The metallocene-catalyzed ethylene-base polymers used in the present invention impart stretch and recovery properties to the film. Preferably, the metallocene-catalyzed ethylene-based polymer is selected from copolymers of ethylene and l-butene, copolymers of ethylene and 1-hexene, copolymers of ethylene and 1-octene and combinations thereof. In particular, preferred materials include Affinity brand metallocene-derived copolymers of ethylene and 1-octene, both available from Dow Plastics of Freeport, Tex. Copolymers derived from metallocene of ExactMark brand of ethylene and are also preferred. -butene and the copolymers of ethylene and 1-hexane, available from Exxon Chemical Company of Houston, Texas In general, the metallocene-derived ethylene-based polymers of the present invention have a density of at least 0.900 g / cc .

At least one ethylene copolymer and a C4-C8 α-olefin monomer is the main polymer component of the film of the present invention. Preferably, the film of the present invention contains at least 30 percent, more preferably about 40-50 percent by weight of the filled film composition. Other polymeric components may also be present as long as they do not adversely affect the desired characteristics of the film.

In addition to the polymeric material, the film layer also includes a filler which allows the development of micropores during the orientation of the film. As used herein, a "filler" is intended to include particulates and other forms of materials which can be added to the polymer and which do not interfere chemically or adversely affect the extruded film but are capable of dispersing uniformly throughout the film . Generally, the fillers will be in a particulate form and will usually have something of a hemispherical shape with the average particle sizes in the range of about 0.5 to about 8 microns. In addition, the film will usually contain a filler in an amount of at least 40 percent (%), preferably around 45 to about 65 percent, based on the total weight of the film layer. More preferably, from about 45 to about 55 percent of the filler is present in the film. Both organic and inorganic fillers are contemplated to be within the scope of the present invention as long as they do not interfere with the process of film formation, the breathability of the resulting film or its ability to bind to another layer such as a non-woven fabric. of fibrous polyolefin.

Examples of fillers include calcium carbonate (CaC02), various kinds of clay, silica (Si02), alumina, barium sulfate, sodium carbonate, talc, magnesium sulfate, titanium dioxide, zeolites, aluminum sulfate, powders cellulose type, diatomaceous earth, magnesium sulfate, magnesium carbonate, barium carbonate, kaolin, mica, carbon, calcium oxide, magnesium oxide, aluminum hydroxide, pulp powder, wood powder, cellulose derivative, polymer particles, chitin and chitin derivatives. The filler particles may optionally be coated with a fatty acid, such as a stearic acid or a behenic acid which can facilitate the free flow of the particles (in bulk) and their ease of dispersion into the polymer matrix.

Generally, it has been possible to produce films with a water vapor transmission rate (WVTR) of at least about 300 grams per square meter per 24 ® hours, as measured by the ASTM E-96-80 test (using Celgard 2500 as the control). In general, the factors that affect the amount of respirability include the amount of filler, the conditions of stretch of the film, (for example? , if performed at ambient or elevated temperatures), the orientation ratio, and the film thickness. Generally, the WVTR of the film of the present invention that can be used as a component in a disposable or limited use article is from about 300 to 4,500, and, in one application, preferably from at least about 1,500 g. / m2 / 24 hours. In addition, the preferred films of the present invention, when stretched in the machine direction, have superior extensibility and increased resistance to failure with respect to film defects.

These properties can be obtained by first preparing a polymer resin from a super-octene LLDPE resin, filling the resin with filler, extruding a film from the filled resin and then stretching or orienting the filled film in at least one direction, usually the address of the machine. As explained in more detail below, the resulting film is microporous and has improved strength properties in the orientation direction.

The processes for forming filled films and guiding them are well known to those skilled in the art. In general, a process for forming an oriented filled film 10 is shown in Figure 1 of the drawings. The film 10 is unwound and directed to a film stretching unit 44 such as an orienter in the machine direction, which is a device commercially available from vendors such as Marshall and Williams Company of Providence, Rhode Island. Such an apparatus 44 has a plurality of stretching rollers 46 moving at progressively faster speeds relative to the pair disposed in front of them. These rollers 46 apply an amount of stress and therefore progressively stretch the filled film 10 to a stretch length in the machine direction of the film which is the direction of travel of the filled film 10 through the process as shown. in Figure 1. The stretching rollers 46 can be heated for better processing. Preferably, the unit 44 has also included the rollers (not shown) up and / or downward of the stretching rollers 46 which can be used to preheat the film 10 before orienting and / or quenching (or cooling) after stretching. The purpose of tempering is to stabilize the film so that it will shrink less or not shrink when exposed to elevated temperatures during subsequent processing, storage, transportation or product use.

The uniaxial orientation is well known in the art in the plastic film industry. Films are frequently oriented to improve their strength and other physical properties. The most common and the simplest kind of uniaxial orientation is in the machine direction (MD) on a computer frequently called a machine direction oriented, or short MDO. Several MDO designs are used in the industry, all of which use temperature controlled rollers for heating or cooling and transport of the film that is being processed. Stretching is achieved between slow clamping and quick clamping, slow clamping retaining the film backing and quick clamping by accelerating the film making it longer and thinner and somewhat narrower. In practical terms the degree of orientation is usually described as in the stretch ratio, such as 3X or 4X which is the ratio of the surface velocity of the rapid clamping point to the surface velocity of the slow clamping point. The slow clamping point is generally preceded by the preheated rollers which can heat the film to the desired stretching temperature, and the quick clamping point is followed by rollers to heat the film to some of the tempering temperature. The cooling roll (s) can be used to cool the drawn film before further processing.

The polymer films are oriented above the glass transition temperature and below the melting temperature of the polymers used. Good film properties can be obtained at relatively low shrinkage temperatures, such as room temperature. However, the higher temperature can be used for ease of processing and to allow for practical processing speeds. For example, the preheat and slow clamping point may be at I6O0F, the rapid clamping point and the first tempering roller may be varied from the ambient temperature to about 215oF, and the last tempering roll may be around 200 , 210, or 215oF. Processing speeds can be about 80-100 feet per minute (fpm) over the slow clamping point, and about 320-425 (fpm) over the quick clamping point.

The useful degree of stretch for breathable films is somewhat different for the different polymers used. To avoid unstretched segments or points in the film, this is to make the film fully oriented, the lower stretch ratio is preferably around 3X. Good results can be obtained at around 4X-4.25X. If a movie is "overstretched" (usually above around 5X), it could become excessively breakable. At the stretched length, a plurality of micropores are formed in the film 10. If desired, the film 10 is directed out of the apparatus 44 so that the tension is removed to allow the stretched film 10 to relax.

Sometimes it may be desirable to laminate the filled film 10 to one or more support layers or substrates 20 as shown in Figure 2. The lamination of the film can improve the strength and hence the durability of the film. If desired, the filled film 10 can be fastened to one or more support layers 30 to form a laminate 32. Referring again to Figure 1, a conventional fibrous nonwoven fabric forming apparatus 48, such as a pair of machines joined by spinning, it is used to form the support layer 30. The essentially continuous fibers 50 are deposited on the forming wire 52 as an unbonded fabric 54 and the unbonded fabric 54 is then sent through a pair of bonding rollers. 56 to join the fibers together and increase the tear strength of the resultant fabric support layer 30. One or both of the rolls are frequently heated to aid bonding. Typically, one of the rollers 56 also has a pattern such as to impart a discrete bonding pattern with a binding surface area prescribed to the fabric 30. The other roller is usually a soft anvil roller, but this roller can also be patterned if desired Once the filled film 10 has been sufficiently stretched and the supporting layer 30 is formed, the two layers are put together and laminated to one another using a pair of laminated rolls or other means 58. As with the bonding rolls 56, the rolling rollers 58 can be heated. Also, at least one of the rollers can be patterned to create a discrete bond pattern with a prescribed bonding surface area for the resulting laminate 32. Generally, the maximum bond point surface area for a given area of The surface on one side of laminate 32 will not exceed about 50 percent of the total surface area. There are a number of discrete union patterns which can be used. See, for example, Brock et al., United States Patent No. 4,041,203 which is incorporated herein by reference in its entirety. Once the laminate 32 leaves the rolling rollers 58, it can be wound onto a roll 60 for subsequent processing. Alternatively, the laminate 32 can continue online for further processing or additional conversion.

While the support layers 30 and the film 10 shown in Figure 1 were joined together through the thermal point joint, other joining means can also be used. Suitable alternatives include, for example, adhesive bonding and the use of glutinizing agents. In the adhesive bond, an adhesive such as a hot-melt adhesive is applied between the film and the fiber to bond the film and the fiber together. The adhesive can be applied by, for example, melt spraying, printing or melt blowing. Various types of adhesives are available including those produced from amorphous, hot melted polyalphaolefins to ethylene vinyl acetate base and Kraton brand adhesives available from Shell Chemical of Houston, Texas and Rexene Brand adhesives from Odessa, Texas. Rextac brand When the film and the supporting layer (s) are bonded with glutinizers, the adhesive resin can be incorporated into the film itself. The glutinizer essentially serves to increase the adhesion between the film and fiber layers. The film and fiber laminate can be thermally bonded, even though very little heat is usually required, since the glutinizer tends to increase the pressure sensitivity of the film and a bond similar to an adhesive bond can be formed. Examples of the useful glutinizers include WingtackMarca ,,.,, 95, available from Goodyear Tire & Rubber Co., of Akron, Ohio, and EscorezMarc 5300, available from Exxon Chemical Company of Houston, Texas.

The support layers 30 as shown in Figure 2 are nonwoven fibrous fabrics. The manufacture of such fibrous non-woven fabrics is known. Such non-woven fibrous fabrics can add additional properties to fill the film 10, such as a softer cloth-like feel. This is particularly advantageous when the filled film 10 is being used as a barrier layer for liquids in such applications as outer covers for absorbent articles for personal care and as barrier materials for hospitals, surgical and clean room applications such as, for example, surgical drapes, gowns and other forms of clothing. The fastening of the support layers 30 to the filled film 10 can be by the use of a separate adhesive such as solvent-based and hot-melt adhesives or through the use of heat and / or pressure (also known as thermal bonding), as with heated bonding rollers.

The backing layer in a laminate containing the film layer of the present invention can be of spun-bonded polypropylene spunbonded, crimped polypropylene spunbonded, bonded and bonded fabrics, meltblown or spunbond fabrics elastomers produced from elastomeric resins. A particularly advantageous support layer is a nonwoven fibrous fabric. Such fabrics can be formed from a number of processes including, but not limited to, carded and bonded tissue processes, formed by meltblowing and formed by spinning. The melt-blown fibers are formed by extruding the melted thermoplastic material through a plurality of capillaries, usually circular and fine, such as filaments or melted yarns into a gas stream heated at a high speed usually such as air, which has had the filaments of melted thermoplastic material to reduce their diameters. Then, the melt-blown fibers are carried by the gas stream usually heated at high speed and are deposited on a collecting surface to form a randomly dispersed melt-blown fabric of fibers. The meltblown process is well known and is described in several patents and publications, including the Report of the Naval Research Laboratory 4364, "Manufacture of Superfine Organic Fibers" from B.A. Wendt, E. L. Boone and D. D. Fluharty; the Report of the Naval Research Laboratory 5265, "An Improved Device for the Formation of Superfine Thermoplastic Fibers" by K. D. Lawrence, R. T. Lukas, J.A. Young; U.S. Patent No. 3,676,242, issued July 11, 1972 to Prentice; and U.S. Patent No. 3,849,241 issued November 19, 1974 to Buntin et al. The above references are incorporated herein by reference in their entirety.

Spunbonded fibers are formed by extruding a melted thermoplastic material such as filaments of a plurality of usually circular and fine capillaries into a spinning organ with the diameter of the extruded filaments then being rapidly reduced, for example, by pulling in eductive fluid or non-eductive or other well-known splicing mechanisms. The production of non-woven fabrics bonded by spinning is illustrated in patents such as from Appel et al., US Pat. No. 4,340,563; that granted to Matsuki et al., United States of America Patent No. 3,802,817; U.S. Patent No. 3,692,618 issued to Dorschner et al .; U.S. Patent Nos. 3,338,992 and 3,341,394 issued to Kinney, U.S. Patent No. 3,276,944 issued to Levy; U.S. Patent No. 3,502,538 issued to Peterson; the patent of the United States of America? 3,502,763 granted to Hartman, US Pat. No. 3,542,615 issued to Dobo et al .; and Canadian Patent No. 803,714 issued to Harmon. All of the above references are incorporated herein by reference in their entirety.

A plurality of support layers 30 can also be used. Examples of such materials can include, for example, laminated spunbond / formed by blowing melted and laminated spunbond / formed by blowing molten / spunbonded as shown in the patent to Brock et al in United States of America No. 4,041,203 which is incorporated herein by reference in its entirety.

The woven carded and united are made of short fibers which are usually bought in bales. The bales are placed in a collector which separates the fibers. The fibers are then sent through a carding or combing unit which breaks in separation and in line the short fibers in the machine direction so as to form a fibrous nonwoven fabric oriented in the direction of the machine. Once the tissue has been formed, it is then joined by one or more joining methods. A bonding method is a bond with powder wherein the powder adhesive is distributed through the fabric and then activated, usually by heating the fabric and the adhesive with hot air. Another bonding method is pattern bonding where heated calendering rolls or ultrasonic bonding equipment is joined to join the fibers together; usually in a localized bonding pattern even when the weave can be bonded through its entire surface if desired. When short bicomponent fibers are used, air-binding equipment is especially advantageous for many applications.

The process shown in Figure 1 can also be used to create a three layer laminate. The only modification to the previously described process is to feed a supply 62 of a second support layer tej gone unframed fibrous 30a inside the rolling rolls 58 on a side of filled film 10 opposite that of the other layer fibrous non-woven fabric support 30. As shown in Figure 1, one or both of the support layers can be formed directly in line, as the support layer 30. Alternatively, the delivery of one or both of the support layers can be to be in the form of a preformed roller 62, as is the support dandruff 30a. In the event that, the second support layer 30a is fed into the lamination rolls 58 and is laminated to the filled film 10 in the same manner as the first support layer 30.

As previously stated, the filled film 10 and the breathable laminate 32 can be used in a wide variety of applications the least of which includes absorbent articles for personal care products such as diapers, training pants, devices incontinence , products for feminine hygiene such as sanitary napkins. An example article 80, in this case a diaper, is shown in Figure 3 of the drawings. Referring to Figure 3, most personal care absorbent articles 80 include a liner or liquid permeable topsheet 82, an outer cover or backsheet 84 and an absorbent core 86 positioned between and contained by the top sheet 82 and the backsheet 84. articles 80 such as diapers may also include some type of fastening means 88 such as adhesive fastening tapes or hook type fasteners and mechanical loop to keep the garment in place about the user. The clamping system can contain the stretched material to form the "stretch ears" for greater comfort.

Filled film 10 by itself or in other forms such as the support / film layer laminate 32 can be used to form various parts of the article including, but not limited to, the stretched ears, the top sheet and the back sheet 84. If the film or laminate to be used, the liner 82, this will have to be perforated or otherwise made permeable to the liquid. When a nonwoven laminate / film is used as the outer cover 84, it is usually advantageous to place the nonwoven side facing away from the wearer. Furthermore, in such embodiments it is possible to use the non-woven part of the laminate as the loop part of the hook-and-loop combination.

Other uses for the filled film and the support layer / breathable film laminates according to the present invention include, but are not limited to, medical protective articles such as drapes and surgical gowns, as well as drapes, barrier materials and articles. of clothing or parts thereof including such items as work clothes and laboratory coats.

The advantages and other features of the present invention are best illustrated by the following examples: EXAMPLE Eight resin compositions listed in Table 1 given below were composed. The films were formed and stretched in an orienter in the machine direction according to the condition listed in Table 1 given below.

TABLE I The elongation characteristics at the break in the transverse direction to the WVTR machine of each stretched film were measured according to the procedures listed below. The results of these measurements are listed in Table II given below.

Stress Test The peak film load ("DC tensile strength") and elongation at the peak load (elongation at critical break 90o to the direction of orientation in this case, "elongation at critical CD break") were determined in accordance with the Federal Test Methods Method 5102 Number 191A. The sample sizes were three inches by six inches (2.54cm x 15.24 cm) with the cross-machine direction of the sample running parallel to the six-inch length of the sample. Three samples were run for each material and the values were averaged. The jaws of the tension tester were three inches wide, the initial separation or measurement length was three inches (7.62 cm) and the crosshead speed was 12 inches per minute (305mm / min).

Water Vapor Transmission Data The proportion of water vapor transmission (WVTR) for the sample materials was calculated in accordance with ASTM Standard E96-80. The circular samples measured three inches in diameter and each of the test materials was cut and a control which was a piece of film ® CELGARD 2500 from Hoechst Celanese Corporation of Sommerville, New Jersey. The CELGARD 2500 film is a microporous polypropylene film. Three samples were prepared for each material. The test dish was a Vapometer tray No. 60-1 distributed by Thwing-Albert Instrument Company, of Philadelphia, Pennsylvania. About one hundred milliliters of water was poured into each Vapometer tray and individual samples of the test materials and control material were placed through the open top portions of the individual trays. The bolted flanges were tightened to form a seal along the edges of the tray, leaving the associated test material or control material exposed to the ambient atmosphere over a circle of 6.5 centimeters in diameter having an exposed area of approximately 33.17 square centimeters. The trays were placed in a forced air oven at 100 ° F (32 ° C) for one hour to balance. The oven was at a constant temperature with an external air circulating through it to prevent the accumulation of water vapor inside. A suitable forced air furnace is, for example, a Blue M Power-0-Matic 60 furnace distributed by Blue M Electric Company of Blue Island, Illinois. When the balance was complete, the trays were removed from the oven, weighed and immediately returned to the oven. After 24 hours, the trays were removed from the oven and weighed again. The preliminary test water vapor transmission rate values were calculated with Equation (I) given below: (I) Test WVTR = (weight loss grams over 24 hrs.) X 315.5 g / m2 / 24 hours) The relative humidity inside the oven was not specifically controlled.

Under predetermined placed conditions of lOOoF (32 oc) and a relative ambient humidity, the WVTR for the CELGARD ® 2500 control has been defined as being 5000 grams per square meter per 24 hours. Therefore, the control sample was run with each test and the preliminary test values were corrected to the conditions established using Equation II given below: (II) WVTR = (WVTR test / WVTR control) x (5000 g / m2 / 24 hours) TABLE II As shown in Table II, a film of the present invention (films A) has an elongation to break in the cross-machine direction (a measure of stiffness) when comparing film B which contains the same amount of filler and has a WVTR value similar to film A. Furthermore, even when films G and H have increased stiffness at the same filler content, their WVTR value values were lower than those of the film of the present invention (film A) . The data relating to the films C, D, E, F listed in Table II given above, show that these films of the present invention have a good controllable WVTR and excellent stiffness with a lower filler content.

EXAMPLE 2 The films A, G and H listed in Table 1 given above were each used to prepare laminations. A sheet of absorbent material comprising polypropylene melt blown fibers mixed with pulp fibers, also known as coform, was directed under a spray head where it was sprayed with a hot melt adhesive, such as NS-5610 available of National Starch & Chemical Co. of Bridgewater, NJ, at a temperature of 350OF at a rate of about 2 grams per square meter. One of the films given above was unrolled from a roll and was carried to a pair of fastening point rolls where the film and the spray absorber was contacted to form a laminate which was then rolled into a roll. Subsequently, a spin-bonded layer of 0.8 ounces per square yard of basis weight was attached to the film side of the laminate by the identical hot-melt lamination process. The WVTR of the three-layer laminates with each of the films was measured and compared to that of the films. The WVTR of the laminate with the film A decreased to 4220 g / m2-24 hours of the 4735 films, a drop of 10.9%.

The laminate fall of film G was 33.4% (to 2143 of 3220), and the laminate fall of film H was 28% (to 2278 of 3163). As is evident from the example given above, the WVTR of the films containing CatalloyMarca (G) of a polypropylene copolymer (H) already starting from the lowest values, essentially declined more than the WVTR with the film A, the subject of this invention.

This illustrates the stability of the film of the present invention. Films C, D, E and F not containing the unstable and undesirable components were not found to be unstable or otherwise thermally sensitive to decreases in respirability.

Thus, the films of the present invention have a high water vapor transmission rate and roughness imparting a wide variety of functionalities including vapor permeability, liquid impermeability and comfort. In addition, such films can be attached to the support layers to form laminates.

Of course, it should be understood that a wide range of changes and modifications can be made to the modalities described above. Therefore, the above description is intended to illustrate rather than limit this invention and that the following claims include all equivalents which define this invention.

Claims (38)

R E I V I N D I C A C I O N S

1. An oriented-stretched thermoplastic film comprising: a filled resin comprising at least one copolymer of ethylene with at least one C4-C8 c-olefin monomer and from about 40 to about 65% by weight of said resin material filled with at least one filler that contributes to pore formation; wherein said film has a water vapor transmission rate of from about 300 to about 4,500 g / m2-24 hours; wherein said film has an elongation at critical break of 90o to the orientation direction of more than about 100%.

2. The film as claimed in clause 1, characterized in that the elongation of 90o at critical breakage to the direction of orientation is greater than about 150%.

3. The film as claimed in clause 1, characterized in that the water vapor transmission rate remains essentially constant after exposure to the film at elevated temperatures.

4. The film as claimed in clause 1, characterized in that said filler is calcium carbonate.

5. The film as claimed in clause 1, characterized in that said filler includes a plurality of particles having a fatty acid coating.

6. The film as claimed in clause 1, characterized in that: said filler is present in an amount of about 48% by weight of said resin material; Y said water vapor transmission rate is around 1,500 g / m2 / 24 hours.

7. The film as claimed in clause 1, characterized in that said film is uniaxially oriented.

8. An absorbent article for personal care comprising a liquid permeable topsheet and a backsheet with an absorbent core positioned therebetween, at least one of said backsheet and said topsheet includes the film of clause 1 .

9. The article as claimed in clause 8, characterized in that said article is a diaper.

10. The article as claimed in clause 8, characterized in that said article is a training brief.

11. The article as claimed in clause 8, characterized in that said article is selected from a sanitary napkin or a menstrual pantyhose.

12. The article as claimed in clause 8, characterized in that said article is an incontinence device.

13. A process for making a microporous film comprising the steps of: providing a resin including a non-elastic material comprising at least one copolymer of ethylene with at least one C4-C8 α-olefin monomer; adding to said resin material from about 40 to about 65% by weight of said resin material filled with at least one filler that contributes to pore formation to form a filled resin; extruding said filled resin to form a film; stretching said film to form a microporous film; wherein said film has an elongation at critical break of 90o to the orientation direction of more than about 100%.

14. The process as claimed in clause 13, characterized in that said non-elastic material is provided in an amount of at least about 30% by weight of said filled resin.

15. The process as claimed in clause 13, characterized in that said film is stretched uniaxially.

16. The process as claimed in clause 13, characterized in that: said filler is present in an amount of about 48% by weight of said filled resin; Y said water vapor transmission rate is around 1,500 g / m2 / 24 hours.

17. The process as claimed in clause 13, characterized in that said filler is calcium carbonate.

18. The process as claimed in clause 13, characterized in that said water vapor transmission rate of said microporous film remains essentially constant after exposing said film to high temperatures.

19. A microporous film prepared by the process of clause 13.

20. A uniaxially oriented thermoplastic film comprising: a filled resin including a non-elastic material comprising at least one copolymer of ethylene with at least one C4-C8 ce-olefin monomer, said filled resin further comprising from about 40 to about 65% by weight of said resin material filled with at least one particulate filler having a particle size of from about 0.5 to about 8 microns; wherein said film has a water vapor transmission rate of from about 300 to about 4,500 g / m2 / 24 hours; wherein said film has an elongation at critical break of 90 ° to the orientation direction of more than about 100%.

21. The film as claimed in clause 20, characterized in that said filled resin includes at least 30 percent by weight of said non-elastic material.

22. The film as claimed in clause 20, characterized in that said non-elastic material includes metallocene-catalyzed ethylene-based copolymer with a density of at least about 0.900 g / cc.

23. A breathable laminate comprising: a thermoplastic film including a filled resin comprising at least one copolymer of ethylene and with at least one C4-C8 α-olefin monomer and from about 40 to about 65% by weight of said resin material filled with at least one filler that contributes to pore formation; and at least one support layer bonded to said film layer wherein said film has an elongation at critical break of 90o to the orientation direction is greater than about 100%.

24. The laminate as claimed in clause 23, characterized in that said elongation at critical break of 90o to the direction of orientation is greater than about 150%.

25. The laminate as claimed in clause 23, characterized in that: said filler is present in an amount of about 48% by weight of said resin material; and said film has a water vapor transmission rate of about 1,500 g / m2 / 24 hours.

26. The laminate as claimed in clause 23, characterized in that said support layer is a nonwoven fibrous fabric.

27. An absorbent article for personal care comprising a liquid permeable topsheet and a backsheet with an absorbent core positioned therebetween, at least one of said backsheet and said topsheet including the laminate of clause 23 .

28. The article as claimed in clause 27, characterized in that said article is a diaper.

29. The article as claimed in clause 27, characterized in that said article is a training brief.

30. The article as claimed in clause 27, characterized in that said article is selected from a sanitary napkin and from a menstrual pantyhose.

31. The article as claimed in clause 27, characterized in that said article is an incontinence device.

32. The article as claimed in clause 27, characterized in that said article is a bandage,

33. A process for forming a breathable laminate comprising: providing a filled film layer comprising from about 40 to about 65% by weight of a filler having a particle size that contributes to pore formation and a linear low density polyethylene polymeric material that includes at least an ethylene copolymer with at least one C4-C8 α-olefin monomer; stretching said filled film to produce a microporous film, - joining at least one support layer to said microporous film to form a laminate.

34. The process as claimed in clause 33, characterized in that said support layer is thermally bonded to said microporous film.

35. The process as claimed in clause 33, characterized in that said support layer is bonded to said microporous film with a hot-melt adhesive.

36. The process as claimed in clause 33, characterized in that said filled film is stretched uniaxially.

37. A medical garment comprising: a thermoplastic film including a filled resin comprising at least one copolymer of ethylene with at least one C4-C8 at-olefin monomer and from about 40 to about 65% by weight of said resin material filled with at least one filler that contributes to pore formation; Y at least one support layer attached to said film layer; wherein said film has an elongation at critical break of 90o to the orientation direction of more than about 100%.

38. The laminate as claimed in clause 38, characterized in that said elongation at critical break of 90o to the orientation direction of more than about 150%. SUMMARY The present invention relates to uniaxially oriented microporous breathable films of exceptional resistance transverse to the direction of orientation. Such films include a particulate filler and a non-elastic material that includes a copolymer of ethylene with at least one C4-C8 α-olefin monomer, such copolymers being commercially described as "super hard", "the next generation", etc., and being prepared with "new" or "improved" catalyst systems or with metallocene similar single site catalysts. A manufacturing method is also described.