Multilayer chlorine-free film with barrier layer of a polyamide blend and ostomy pouches formed therefrom

Films for ostomy applications should have good odor barrier properties and produce minimal noise when flexed or wrinkled to avoid embarrassment to users. Typically, films currently in use for ostomy applications utilize polyvinylidene chloride (PVDC) or copolymers of vinylidene chloride with a comonomer such as methylacrylate or vinylchloride as the gas barrier layer of a multilayer film. Such multilayer films have good resistance to odor transmission and are also relatively quiet; however, they are also believed to be hazardous to the environment when disposed of by incineration, a common practice in numerous countries. Chlorinated polymers generate hydrochloric acid as a byproduct of incineration and are believed to be a significant contributor to hydrochloric acid release from incinerator flue gases. Furthermore, chlorinated polymers are believed to form toxic dioxin derivatives as byproducts of incineration which are retained in the ashes and may possibly cause solid waste disposal problems.

Unfortunately, films formed of chlorine-free barrier resins tend to be stiffer and noisier than films utilizing conventional PVDC-based resins and do not match the quality of conventional chlorinated films for use in ostomy appliances. Thus, a need exists for a multilayer film which is chlorine-free, can be manufactured by coextrusion from readily available raw materials, is heat sealable, has high softness and low noise when flexed or wrinkled, and is impermeable to fecal odors.

U.S. patent 5,567,489 discloses a multilayer barrier film in which a chlorine-free barrier layer is composed of amorphous nylon, crystalline nylon, copolymers of ethylene and vinyl alcohol, or blends thereof. Although data presented in the patent indicate the multilayer films to be comparable in quietness to some chlorinated films in general commercial use, experience has revealed that such chlorine-free films are nevertheless significantly noisier than the chlorine-containing films commonly employed for the fabrication of ostomy pouches. The general observation is that chlorine-free barrier resins are high modulus, stiff materials that do not lend themselves to the production of low noise ostomy films. This is true of all nylon (polyamide) barrier resins, both crystalline and amorphous. It is true also of other known chlorine-free barrier resins such as hydrolyzed ethylene-vinylacetate copolymers, commonly known as ethylene-vinylalcohol copolymers, and copolymers of acrylonitrile or methacrylonitrile of high nitrile content, commonly known as nitrile resins.

Other references illustrating the current state of the art relating to chlorine-free multilayer films are U.S. patents 5,496,295, 5,643,375, 5,407,713, and 5,895,694.

EP-A2-1101605 discloses a multilayer chlorine-free film comprising an odor barrier layer of an amorphous polyamide resin blended with about 10 to 30% per total weight barrier layer of an anhydride-modified olefinic polymer or copolymer having a density of 0.89 g/cc or lower, at least one heat-sealable skin laser of an ethylene polymer or copolymer, or blends thereof, and an adhesive tie layer of an anhydride-modified ethylene polymer or copolymer interposed between said skin layer and said barrier layer.

US 5,985,390 relates to a multilayer film, which is useful for making flexible satchets, comprising (i) a barrier film of a mixture of polyamide and of polyolefin, and (ii) on at least one of its faces, a film of a copolymer of ethylene and of an unsaturated ester, which is high frequency weldable.

EP-A2-0622182 relates to a multilayer recyclable sealable film formed from at least one scrap-layer and one sealing layer, wherein the scrap-layer consists of a polyamide/polyolefin recycled material and a tackifier, wherein the amount of the recycled material is from 60 to 98 wt% of the scrap-layer, wherein the recycled material has a polyamide content of from 3 to 45 wt%, wherein the sealable layer is a single layer or multilayer structure and consists of a polyolefin polymer or copolymer, and wherein the layers my be the same or different.

An important aspect of this invention lies in the discovery that the noise properties of a multilayer film in which amorphous nylon (polyamide) is utilized for the odor barrier layer may be significantly reduced, without appreciably affecting the barrier properties, by blending the nylon with an anhydride-modified olefinic copolymer having a density of 0.95 g/cc or lower. The anhydride-modified olefinic copolymer comprises a copolymer of ethylene with at least one ester containing comonomer and 0.1 to 2% maleic anhydride and should be present in the range of about 10% to 30%, preferably 15% to 25%, per total weight of the barrier layer.

The multilayer film includes at least one skin layer, preferably two such skin layers, consisting essentially of an ethylene polymer or copolymer, and an adhesive tie layer interposed between each skin layer and the blended amorphous nylon barrier layer. Each adhesive tie layer is primarily composed of an anhydride-modified ethylenic polymer, such as polyethylene or copolymer of ethylene and vinylacetate, containing anhydride groups capable of promoting interfacial adhesion with the polyamide-containing barrier layer.

The result is a heat-sealable multilayer film that is particularly useful for ostomy appliances because of its exceptional odor barrier properties while at the same time being relatively soft (low modulus) and quiet in relation to known chlorine-free films in which the odor barrier layer is formed entirely of nylon, ethylene-vinylalcohol copolymers, or nitrile resins. With regard to the generation of noise upon flexing, the chlorine-free multilayer films of this invention compare favorably with prior art ostomy films having chlorinated barrier layers. A pouch formed of the multilayer film of this invention therefore has properties comparable to those exhibited by high-quality pouches formed of chlorine-containing compositions but without the environmental shortcomings described above.

Other features, advantages and objects of the invention will become apparent from the specification and drawings.

<u style="single">DRAWINGS</u>

<ul id="ul0001" list-style="none"><li>Figure 1 is a schematic cross-sectional view of an embodiment of the multilayer barrier film of this invention.</li><li>Figure 2 is an elevational view of an ostomy pouch formed from the multilayer barrier film of Figure 1.</li></ul>

<u style="single">DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS</u>

The multilayer chlorine-free film of the present invention may be produced using standard coextrusion techniques involving either casting or blowing. Preferably, the multilayer film has five layers--a chlorine-free barrier layer sandwiched between two heat-sealable skin layers with tie layers interposed between the skin and barrier layers--but the advantages of the invention may be at least partially achieved in a three-layer structure having a barrier layer and single skin and tie layers, or barrier layer and two skin layers without tie layers. The film may have more than five layers, for example, a seven-layer structure ABCDCBA could be made where D is the barrier layer, C is a tie layer, A is a skin layer, and B is an additional layer interposed between skin and tie layers. Asymmetric structures with different skin materials are possible and may provide different surface characteristics if so required.

Figure 1 schematically illustrates a multilayer chlorine-free film 10 having an odor barrier layer 11 sandwiched between tie layers 12 and 13 and skin layers 14 and 15. The chlorine-free barrier layer 11 is essentially composed of a blend of amorphous polyamide (nylon) resin and an anhydride-modified olefinic copolymer. Unlike crystalline polyamides which are entirely aliphatic, amorphous polyamides have a partially aromatic structure and are typically produced by the condensation of an aliphatic diamine with an aromatic diacid, or combination of diacids, in molar amounts equivalent to the diamine used. While it is believed that any amorphous polyamide resin may be used, effective results have been obtained with a polyamide resin marketed as Selar PA3426 by DuPont Company. Selar PA3426 is understood to be substantially amorphous with a density of about 1.19 grams per cubic centimeter (g/cc). It has high melt strength and can be used under a broader range of processing conditions than conventional crystalline nylons. Selar PA3426 is produced by the condensation of hexamethylenediamine, terephthalic acid, and isophthalic acid such that 65% to 80% of the polymer units are derived from hexamethylene isophthalamide. For further information, reference may be had to 52 Fed. Reg. 26,667 (1987). A similar polyamide is marketed as Grivory 21 by EMS-Chemie of Switzerland.

The amorphous polyamide resin is the major constituent of the blend, comprising about 70% to 90% by weight of that blend. The anhydride-modified olefinic copolymer comprises about 10% to 30%, preferably 15% to 25% of the total weight of the barrier layer. The density of the anhydride-modified olefinic copolymer should be no greater than 0.95 g/cc. Anhydride-modified olefinic copolymers with densities higher than 0.95 g/cc might still be effective as toughening agents but would not provide the reduction in film modulus and noise imparted by lower density polymers.

The olefinic copolymer preferably comprises a copolymer of ethylene and at least one ester containing comonomer, or a blend thereof, modified (grafted or copolymerized) with 0.1 to 2% by weight of an unsaturated carboxylic anhydride (serving as a compatiblizing agent having amine reactive sites). The density of the modified olefinic copolymer may be as high as 0.95 g/cc.

The olefinic copolymer can be functionalized by copolymerization or grafting with an unsaturated carboxylic anhydride. While it is believed that other unsaturated carboxylic anhydrides may be used to provide the functional groups, maleic anhydride is considered particularly effective for that purpose. The level of maleic anhydride needed to functionalize the olefinic copolymer is quite low, usually less than 2% by weight. The density of the olefinic copolymer is essentially unaffected by anhydride modification at these low levels.

As indicated, the modifier may be formed from ethylene and at least one ester-containing comonomer, or a blend thereof, grafted or copolymerized with between 0.1 to 2% by weight of the unsaturated carboxylic anhydride, the anhydride content preferably being well under 0.5% by weight. The ester-containing comonomer is preferably an alkylacrylate, most preferably an ethylacrylate. One such copolymer is available from Atofina Chemicals, Inc., of France, under the designation Lotader 4720. Lotader 4720 is an ethylene-ethyl acrylate-maleic anhydride terpolymer with a density of 0.944 g/cc, an ethyl acrylate content of about 30% by weight and a maleic anhydride content of about 0.3% by weight.

Due to the immiscible nature of these blends, mixing of the nylon with the anhydride-modified olefinic copolymer is best conducted in a separate step using a twin screw compounder extruder with either corotating or counterrotating screws. This allows an intimate dispersion of the olefinic phase into the nylon phase. The compounded blend is extruded and cut into pellets which can then be used for extrusion into film.

Skin layers 14 and 15 are typically formed of an ethylene-based polymer or copolymer. A suitable resin is metallocene-catalyzed polyethylene with an alpha olefin comonomer such as the ethylene octene copolymer marketed under the designation Exact 8201 by Exxon Chemical. Also suitable as skin layers are copolymers of ethylene with vinyl esters such as ethylene vinyl acetate copolymer (EVA) available, for example, from the DuPont Company under the designation Elvax.

Tie layers 12 and 13 must be capable of bonding to both the core barrier layer and the adjacent layers. Polyethylene, ethylene vinyl acetate copolymers (EVA), or ethylene methyl acrylate copolymers (EMA), modified with functional anhydride groups are believed particularly suitable. EVA-based anhydride-modified resins such as Bynel 3860 or Bynel 3861, or polyethylene-based anhydride-modified resins such as Bynel 41E557, all available from DuPont Company, have been found suitable. The ability of these anhydride-modified resins to act as adhesion promoters is believed to be due to an interfacial reaction between the anhydride groups in the tie layer and the amine groups of nylon in the barrier layer.

The total thickness of the multilayer film, assuming five layers are present, should fall within the general range of about 50.8µm to 127µm (2 to 5 mil), preferably about 76.2µm to 101.6µm (3 to 4 mil). As to the barrier layer 11, its thickness should fall generally within the range of 2.54µm to 12.7µm (0.1 to 0.5 mil) with the lower limit being established by the capability of the extrusion process and the upper limit by the physical properties contributed by the barrier layer in achieving a multilayer film having low modulus and low noise characteristics. Preferably, the barrier layer thickness should fall within the range of about 5.08µm to 7.62µm (0.2 to 0.3 mil), when factors such as odor barrier properties, softness, quietness, and ease of extrusion are all considered together. By contrast, the skin layers 14 and 15 are each considerably thicker than the barrier layer sandwiched between them. For example, each skin layer may have a thickness within the general range of about 12.7µm to 63.5µm (0.5 to 2.5 mil), preferably 25.4µm to 50.8µm (1 to 2 mil), which may be nearly one order of magnitude greater than the thickness of the odor barrier layer 11.

Figure 2 illustrates a typical ostomy pouch 16 having its walls 16a and 16b formed from the multilayer film of Figure 1. The films are arranged with their heat sealable skin layers facing each other and sealed together along the outer periphery of the pouch as indicated at 17. One wall of the pouch has a stoma-receiving opening is formed therein and an adhesive attachment ring 19 is located about that opening for adhesive attachment to the peristomal skin surfaces of a patient. The pouch as shown is of the type generally referred to as a one-piece appliance but, if desired, a mechanical coupling ring may be substituted for adhesive ring 19, with the pouch therefore becoming one component of a two-piece ostomy appliance, all as well known in the art.

In order that the invention may be more readily understood, reference is made to the following example which is intended to be illustrative of the invention, but is not intended to be limiting in scope.

<u style="single">Example 1</u>

Monolayer films were prepared by extrusion using a Brabender extruder and Grivory G21 (from EMS-Chemie AG) as the amorphous nylon. The modifier was Lotader 4720 (from Atofina Chemicals, Inc.). Secant modulus at 2% elongation of the monolayer films was measured in the machine direction according to ASTM D882-97 at a strain rate of 0.1 in./in.min. The results shown in Table 1 illustrate the effect of the addition of Lotader 4720 to Grivory G21 monolayer films. The modulus is progressively reduced as the level of Lotader 4720 is increased. <tables id="tabl0001" num="0001"><table frame="all"><title><b><u style="single">Table 1</u></b></title><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="24mm" /><colspec colnum="2" colname="col2" colwidth="25mm" /><colspec colnum="3" colname="col3" colwidth="38mm" /><thead><row rowsep="0"><entry namest="col1" nameend="col2" align="center" valign="top">Monolayer Film Composition %</entry><entry align="center" valign="top">Secant Modulus Pa (psi)</entry></row><row><entry align="center" valign="top">Grivory G21</entry><entry align="center" valign="top">Lotader 4720</entry><entry align="center" valign="top" /></row></thead><tbody><row rowsep="0"><entry align="center">100</entry><entry align="center">0</entry><entry align="center">8.6x10⁸ (125,000)</entry></row><row rowsep="0"><entry align="center">75</entry><entry align="center">25</entry><entry align="center">4.5x10⁸ (65,800)</entry></row><row rowsep="0"><entry align="center">70</entry><entry align="center">30</entry><entry align="center">3.1x10⁸ (44,300)</entry></row><row><entry align="center">65</entry><entry align="center">35</entry><entry align="center">1.7x10⁸ (25,100)</entry></row></tbody></tgroup></table></tables>