FIELD OF THE INVENTION The present invention relates to a multilayered film having a layer of polyolefin and a layer formed from a polyolefin and one or more polyolefin oxides selected from polyethylene oxide and polypropylene oxide. The polyethylene oxide particul.arly is polyethylene glycol (PEG), .and the polypropylene oxide particularly is polypropylene glycol (PPG), or combinations of the two. The layer formed from a polyolefin and a polyethylene oxide particularly PEG, or a polypropylene oxide particularly PPG of the invention CM also be adhered to or coated onto a subweb of paper, aluminum, plastics such as nylon and polyester, or other subwebs suitable for coating. This multilayered film demonstrates modified surface tension properties and modified protein adhesion properties which, when formed on a polyolefin layer, make it useful in films used in liquid-absorbing products such as feminine hygiene pads, baby diapers and adult incontinence products. BACKGROUND OF THE INVENTION

In the field of feminine hygiene pads, baby diapers, adult incontinence products and the like, perforated polyolefin films have been used to allow passage of fluid from the user to an adjacent absorbent material. The most commonly used polyolefin is low density polyethylene (LDPE) which as a surface tension of approximately 32 dynes/cm. This value of surface tension is high enough for some protein-containing discharge products such as menstrual blood and feces to adhere somewhat to the surface of the film, partially blocking the holes and inhibiting drainage, resulting in an increase in discomfort for the wearer.

Polyolefin film containing a thin layer of PEG and/or PPG on the surface has a surface tension of approximately 45 dyne^cm. As surface tension increases, fluid drainage rate through the holes in a perforated film also increases. Normally as surface tension increases, the tendency for protein products to adhere to the film also increases. However, it has been found that PEG and/or PPG resists protein adhesion. So the product of the present invention has the advantages of both increasing fluid drainage and reducing soiling, thus greatly enhancing the comfort of the wearer.

The incorporation of PEG and PPG into polyolefin films has been practiced for some time. For example, U.S. Pat. No. 4,327,009, incorporated herein by reference, teaches the use of PEG in LDPE to reduce the blocking tendencies of the film. European Patent Application Publication Number

0 217 585, which is incorporated herein by reference, teaches the incorporation of PEG in linear low density polyethylene (LLDPE) to reduce extruder horsepower.

The perforation of polyolefin films to enhance fluid absorptive characteristics is described in U.S. Pat. No. 3,929,135, incorporated herein by reference.

SUMMARY OF THE INVENTION

The present invention provides a film formed from (i) a polyolefin and (ii) one or more polyolefin oxides selected from polyethylene oxide and polypropylene oxide. This film preferably is formed into a layer (b) coated or laminated onto a layer (a) of polyolefin or other suitable subweb.

In addition, layer (b) may be surface treated, such as by corona discharge, to improve the adhesion of the polyethylene oxide, particularly PEG, and/or the polypropylene oxide, particularly PPG, to the .surface of the film.

The present invention further encompasses the use of the films hereindescribed in the aforementioned absorbent products.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the following terms have the meanings given below.

"Polyolefin", whether used in layer (a) or layer (b) of the film of the present invention, ews homopolymers .and copolymers of unsaturated hydrocarbons having 2 - 20 carbon atoms. They can be made by processes well known in the art, including metallocene processes. In particular, the polymers .are homopolymers of ethylene or propylene or copolymers of ethylene with one or more alpha-olefin hydrocarbons having 3 - 10 carbon atoms, especially propylene, butene-1, hexene-1 and octene-1 and styrene. Suitable alpha-olefins also include dienes, that is, monomers with more than 1 site of unsaturation, especially 1,3 butadiene, 1,5 hexadiene and norbornadiene. In particularly preferred embodiments, the Polyolefins .are copolymers of ethylene with a hydrocarbon alpha-olefin having from 4 - 8 carbon atoms and having a density in the range of about 0.850 to about 0.970 griuns per cubic centimeter (g/cm-*) .and especially in the range of 0.920 to 0.930 g/cm^. Preferably, the polymers have a melt index (MI) in the range of 0.05 to 120 dg min, especiidly 0.1 to 75 dg min .and in particular 1 to 10 dg min. (as measured per ASTM D-1238, condition E).

In alternative embodiments, direct copolymers or blends of copolymers of ethylene and a polar monomer, e.g., α,β-ethylenically-unsaturated C3- Cg carboxylic acid ("ethylene-acid copolymers"), or ester thereof, or an ethylenically unsaturated ester of a carboxylic acid may be employed as the Polyolefins or may

be blended with the Polyolefins. By "direct copolymer", it is meant that the copolymer is made by polymerization of monomers together at the same time, as distinct from a "graft copolymer" where a monomer is attached or polymerized onto an existing polymer chain. Preparation of the direct ethylene-acid copolymers is described in U.S. Pat. No. 4,351,931.

The ethylene-acid copolymers can be E X/Y copolymers where E is ethylene; X is a modifying comonomer and Y is the ot,β-ethylenically-unsaturated C3- Ce carboxylic acid, particularly acrylic or metliacrylic acid, or ester thereof. Preferably, however, the ethylene-acid copolymer is a dipolymer (no modifying comonomer). The preferred acid moieties are methacrylic acid and acrylic acid. . Suitable modifying comonomers (X) are selected from alkyl acrylate and alkyl methacrylate, the alkyl groups having from 1 - 12 carbon atoms, which, when present, may be up to 30 (preferably up to 25, most preferably up to 15) wt.% of the ethylene-acid copolymer. X may also be vinyl acetate or carbon monoxide. A wide range of percent acid moiety in the ethylene-acid copolymer may be used. The acid moiety may be present in a range of about 1 to 30 weight percent of the acid copolymer, preferably in a range of about 5 to 25, alternatively about 10 to about 20. The ethylene-acid copolymers with high levels of acid are difficult to prepare in continuous polymerizers because of monomer-polymer phase separation. This difficulty can be avoided however by use of "cosolvent technology" as described in U.S. Pat. No. 5,028,674 or by employing somewhat higher pressures than those at which copolymers with lower acid can be prepared.

Examples of such copolymers include ethylene acrylic acid copolymers, ethylene/methacrylic acid copolymers, ethylene/itaconic acid copolymers, ethylene/alkyl acrylate copolymers .and ethylene/ kyl methacrylate copolymers especially where the alkyl group is methyl, ethyl, propyl or butyl, and ethylene/vinyl acetate copolymers.

Specific other copolymers include ethylene/alkyl acrylate/acrylic acid, ethylene alkyl acrylate/methacryiic acid, ethylene alkyl acrylate maleic anhydride, and ethylene/alkyl methacrylate/maleic anhydride, wherein the alkyl group can have 1-10 carbon atoms, preferably n-butyl, iso butyl, or methyl, ethylene/vinyl acetate/methacryiic acid, ethylene/vinyl acetate/maleic .anhydride, ethylene/vinyl acetate/carbon monoxide, ethylene/alkyl acrylate/carbon monoxide, ethylene/alkyl methacryiate carbon monoxide, ethylene/carbon monoxide/acrylic acid, ethylene/vinyl tri-alkoxy silane, ethylene/vinyl acetate/tri-alkoxy sil.ane, ethylene/ kyl acrylat^vinyl tri-alkoxy silane, ethylene/vinyl acetate/glycidyl methacrylate, ethylene/glycidyl methacrylate, ethylene/alkyl acrylate/glycidyl

methacrylate and ethylene/alkyl methacryiate glycidyl methacrylate where the alkyl or alkoxy group can have 1-10 carbon atoms.

In the alternate embodiments, ionomeric copolymers may be employed as the Polyolefins or may be blended therewith. These ionomers are derived from direct copolymers of ethylene and ethylene-acid copolymers by neutralization with metal ions. Methods of preparing such ionomers are well known and are described in U.S. Pat. No. 3,264,272. The ethylene-acid copolymers are partially neutralized (15 to 75 percent) with metal cations, particularly monovalent .and/or bivalent metal cations. Preferώly about 25 to about 60 of the acid is neutralized. Preferred metal cations include lithium, sodium, and zinc, or a combination of such cations. Zinc is most preferred.

Further, gr.aft copolymers or blends of graft copolymers of polyolefins may be used as the Polyolefin, either by themselves or blended with the Polyolefins, ethylene/polar-monomer dir-ect copolymers, or inomeric copolymers. These graft copolymers are made by means well known in the art with one or more graft monomers. The graft monomers CM be selected from the group consisting of ethylenically unsaturated acidic monomers and their derivatives including acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, 5- norbornene-2,3-dicarboxylic acid, maleic anhydride, monosodium maleate, disodium maleate, itaconic anhydride, citraconic anhydride, monomethyl fυmarate and monomethyl maleate. Also, the graft monomers can be selected from ethylenically unsaturated monomers containing amino or hydroxy functional groups including vinyl pyridines, vinyl silanes, 4-vinyl pyridine, vinyltriethoxysilane, and hydroxy ethyl methacrylate. The graft monomers can also include styrene and glycidyl methacrylate. The grafting monomers, and mixtures thereof, can be present in the graft polymer in an amount of about 0.05 to about 5 weight percent. Preferred polyolefins for grafting include polyethylene, polypropylene, ethylene propylene diene terpolymer .and copolymers of ethylene with vinyl acetate, carbon monoxide, or ethylenically unsaturated carboxylic acids or esters thereof. Mixtures .and blends of the Polyolefins may be used. In general, the polymers are of the type that may be extruded in the form of film.

The Polyolefin may contain additives, for example antioxidants and other stabilizers, anti-block and slip agents and the like. The Polyolefin may also contain fillers, e.g., talc, mica, calcium carbonate, and the like and/or pigments, e.g., titanium dioxide. In addition, the Polyolefin may contain modifying polymers, e.g., rubber-like modifying polymers such as ethylene/propylene/diene .and other

elastomers. It is to be understood that any additive must not cause undue adverse effects on the surface tension properties of the film.

Polyethylene oxide has the general formula:

-[CH ₂ — CH ₂ -O] _n -

.and polypropylene oxide has the general formula:

wherein n, in each case, is sufficiently large to result in a molecular weight in the range of 200 to 10,000, preferably 400 to 2000.

At the molecular weights contemplated in the present invention, the polymer is typically hydroxyl-group terminated at each end and, in the case of polyethylene oxide has the general formula:

HO— .CH ₂ — CH ₂ — O] _n — H

and, in the case of polypropylene oxide has the general formula:

In this hydroxyl-group-terminated form, the polyethylene oxide is also referred to as poly(ethylene glycol) or PEG and the polypropylene oxide is also referred to as poly(propylene glycol) or PPG. The polyethylene oxides and polypropylene oxides can also have a terminal hydroxyl and an alkoxy, preferably a methoxy, terminal group. They can also be derivatized and transformed into esters, amines and acetals.

It should also be noted that polypropylene oxides such as PPG have similar surface tension and protein inhibition characteristics as polyethylene oxides such as PEG and can be used in the present invention, either alone or in combination with the polyethylene oxide such as PEG. PEG and PPG are sold by Union Carbide under the tradename

"Carbowax".

Layer (b) will typically contain, by weight of Polyolefin, about 0.5 to about 12% polyolefin oxide, particularly PEG and/or PPG, preferably about 2 to about 5%.

When the present invention comprises a subweb as layer (a) to which layer (b) will not effectively adhere, a suitable tie layer may be required between layer (a) and layer (b).

"Tie Layer" means an extrudable adhesive layer well known in the art selected for its capability to bond a core layer to outer layers. Examples of such adhesive, tie layer polymer are based on either polyethylene or ethylene vinyl acetate copolymers. Ethylene-based and propylene-based homopolymers .and copolymers, modified to enhance adhesion, are marketed by E. I. du Pont de Nemours and Company under the tradename, BYNEL®. They are typically modified with carboxyl groups such as anhydride.

Layer (a), the subweb, may be any subweb known in the art suitable for coating or being laminated with polyolefins. In particular, the subweb may be paper particularly kraft paper, non-wovens, metal foil such as steel or aluminum, plastics such as nylon and polyesters particularly polyethylene terephthalate, or other subwebs suitable for coating. Preferably, the subweb is a Polyolefin, particul.arly the same Polyolefin used in the film of layer (b).

Processes for the manufacture of films of the type described above are known, such as by coextrusion of layer (a) and layer (b). In such coextrusions, polyolefin is fed to one extruder to form layer (a) and polyolefin and polyolefin oxides, particularly PEG and or PPG are fed to a second extruder to form layer (b). The second extruder should be capable of forming a uniform mixture of the components .and of extruding a uniform mixture in the form of a molten web so as to form a film, which may be in the form of a sheet or coating on a substrate.

The components that form the layer (b) may be fed to the extruder in a number of ways. For instance, all components may be fed to the hopper of the extruder as is described in greater detail below. In alternative procedures, some of the components may be fed through the hopper of the extruder and the remainder fed directly into the extruder. For example, the polyolefin may be fed to the hopper and heated in the extruder until in a molten condition. Subsequently, the remaining ingredients may be introduced into the extruder by means of suitable feed ports on the extruder. For instance, the remaining ingredients may be fed into a cavity transfer mixer located in the extruder after the barrel of the extruder containing the extruder screw and prior to the extrusion die or other orifice through which the polymer is extruded. Cavity transfer mixers are known and are used for admixing of two or more materials in an extruder immediately prior to extrusion. Alternatively, the remaining ingredients may be introduced into the

extruder through a gear pump, which is .also known for the introduction of ingredients into .an extruder.

A suitable procedure for extruding a film according to the present invention is as follows: a first Polyolefin is fed to a first extruder; simultaneously, a second Polyolefin is fed to a second extruder through the hopper of the extruder. The Polyolefin is heated in the extruder to form molten polymer, which is then admixed with the remaining components of the composition, for example, using a cavity transfer mixer. Thus, the polyolefin oxides such .as PEG and/or PPG are each fed into the molten polymer. This may be done simultaneously or the components may be fed into the molten polymer in two or more stages. It is important that the introduction of the components of the composition .and the mixing capabilities of the apparatus being used be such that a uniform mixture is formed in the extruder .and extruded therefrom.

In addition, the aforementioned composition for forming layer (b) may be blended with low density polyethylene (LDPE) or a Polyolefin of the types described above and which is compatible with the polyolefin layer containing the polyolefin oxides, particularly PEG and or PPG without adversely effecting the properties of the resulting film. Such blending can range from about 0.1 parts to about 1.5 parts LDPE or Polyolefin to 1 part layer (b) composition. If the components are fed in p.art directly into the extruder, e.g., using a cavity transfer mixer, then higher levels of polyolefin oxides, particularly PEG and/or PPG up to about 20% may be used, which may be advantageous to the properties of the product that is obtained.

Layer (a) of the present invention will typically have a thickness of about 10 to about 100 microns (micrometers), preferably from about 15 to about 25 microns. Layer (b) of the present invention will typically have a thickness of about 1 to about 10 microns, preferably from about 2 to about 6 microns.

In a further embodiment of the present invention, layer (b) may be subjected to surface treatment such as by corona discharge. The corona discharge is applied to layer (b) after formation of the film, preferably shortly after formation of the film, e.g., prior to the film being wound up.

In preferred embodiments, the corona discharge is formed between two elongated electrodes, using techniques that are known to those skilled in the art. The film is passed between the electrodes while the corona discharge is formed between the electrodes. Subjecting the film to a corona discharge results in a film having superior characteristics compared with film that has not been so treated. The film may conveniently be treated at the speeds at which film is extruded from

an extruder in the manufacture thereof. Other techniques for chemically activating the surface of the film, such as flame treatment and plasma discharge, may be used in place of corona discharge. Such techniques and the associated equipment are known to those skilled in the art. The .corona discharge treated films of the present invention may be perforated using known techniques and employed in the aforementioned feminine hygiene pads, baby diapers and incontinence products.

EXAMPLES Example 1

A two-layer coextrusion was made by the blown film process using a 200 mm diameter coextrusion die and two 50 mm single screw extruders. Layer (a) was a 20-micron film of 5 MI LDPE. Layer (b) was a 5 micron film formed from a previously compounded blend of 10 MI LLDPE .and 3% PEG with a molecular weight of 400. Surface tension on the (b) layer was 45 dynes/cm. Infra-red analysis showed that some of the PEG had migrated through layer (a) of the film to the surface of the (a) layer.

Example 2

A two-layer blown film coextrusion was made under the same conditions as Example 1. Layer (a) was 23 microns thick .and layer (b) was 2 microns thick. The film was corona treated on the (b) side. After 48 hours, the surface tension on the (b) side was 45 dynes/cm. No PEG had migrated through layer (a) of the film to the (a) side.