RELATED APPLICATION 
     This application is a continuation-in-part of my application Ser. No. 09/083,800, filed May 22, 1998, now abandoned. 
    
    
     BACKGROUND AND SUMMARY 
     Films for ostomy applications should have good odor barrier properties and produce minimal noise when flexed or wrinked 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. Pat. No. 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 acrylontrile or methacrylontrile 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. Pat. Nos. 5,496,295, 5,643,375, and 5,407,713. 
     One aspect of this invention lies in the discovery that if a chlorine-free multilayer film is composed of polyester resin coextruded with at least one skin layer, preferably two such skin layers, of a homopolymer of ethylene or copolymer with alpha-olefin or ester-containing comonomer, the resulting multilayer film is of relatively low modulus and exhibits low noise upon flexing. The polyester resin barrier layer, although having limited oxygen permeability, is highly effective as an odor barrier, thereby resulting in a multilayer film particularly suitable for the fabrication of ostomy pouches. The polyester resin of choice is polyethylene terephthalate, and the skin layers are composed of a copolymer of ethylene and an ester-containing monomer such as methyl acrylate, ethyl acrylate, butyl acrylate or vinyl acetate. While the skin layers and barrier layer may be coextruded in direct contact with each other, it has been found that the interlaminar strength of the film may be significantly increased by interposing adhesive tie layers between the skin layers and barrier layer. Each such tie layer may be an ethylene copolymer with reactive functional groups, such as an anhydride modified copolymer of ethylene and an acrylic or methacrylic ester. 
     In addition to being heat-sealable and having exceptional odor-barrier properties, the multilayer films of this invention are relatively soft (have low modulus) and are superior in quietness to known chlorine-free films in which the odor-barrier layers are 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. 
    
    
     DRAWINGS 
     FIG. 1 is a schematic cross-sectional view of an embodiment of the multilayer barrier film of this invention. 
     FIG. 2 is a schematic cross-sectional view of a second embodiment of the multilayer barrier film of this invention. 
     FIG. 3 is an elevational view of an ostomy pouch formed from the multilayer film of FIGS. 1 or  2 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The multilayer barrier film of the present invention may be produced using standard coextrusion techniques involving either casting or blowing. Preferably, the multilayer film includes three primary layers—a chlorine-free barrier layer sandwiched between two heat-sealable skin layers—but the advantages of the invention may be partially achieved in a structure having only two primary layers, that is, a barrier layer and a single skin layer. Also, as described hereinafter, while the skin layer(s) may be coextruded in direct contact with the barrier layer, optimum interlayer adhesion is achieved by interposing a suitable tie layer as an adhesion promoter between each barrier layer and skin layer, resulting in a preferred embodiment in which there are a total of five layers. 
     FIG. 1 schematically illustrates a multilayer barrier film  10  having a barrier layer  11  disposed between skin layers  12  and  13 . The chlorine-free barrier layer  11  is composed of polyester resin. While various polyester resins are believed suitable, particularly effective results are achieved with polyethylene terephthalate resin. A toughened grade of polyethylene terephthalate such as Selar PTX184 commercially available from duPont Co. is suitable. Even though such a polyester resin is only a moderate barrier to oxygen and is inferior in oxgen barrier properties to conventional chlorinated barrier resins based on PVDC, it has been found to be an excellent barrier to simulated fecal odorants and is therefore especially useful for use in fabricating ostomy pouches. Because of its effectiveness as an odor barrier, a polyester layer having a thickness of only 0.2 mil has been found sufficient to provide excellent odor barrier properties. In general, the thickness of the barrier layer should fall within the range of 0.1 to 1.0 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 0.1 to 0.4 mil, with 0.2 mil being considered optimal when factors such as odor barrier properties, softness, quietness, and ease of extrusion are all considered together. 
     Skin layers  12  and  13  are formed of an ethylene-based polymer or copolymer with an alpha-olefin such as hexene or octene or with an ester-containing comonomer such as methyl acrylate, ethyl acrylate, butyl acrylate, or vinyl acetate. A particularly effective skin layer composition suitable for coextrusion with barrier layer  11  is a copolymer of ethylene and methyl acrylate (EMA) having a methyl acrylate content in the range of about 10 to 30% by weight. A methyl acrylate content in the range of about 18 to 20% of the skin layer composition is believed optimal. 
     While the term “skin” is used to describe outer layers  12  and  13 , such layers are in general considerably thicker than the barrier layer sandwiched between them. For example, each skin layer may have a thickness within the general range of 0.5 to 3 mil, preferably 1 to 2 mil, which may be nearly one order of magnitude greater than the thickness of the odor barrier layer  11 . The skin layers provide strength, softness, and heat sealability for the multilayer film. EMA as the composition for the skin layer is preferred because of its softness and quietness, its compatability with polyester resins, its good heat sealability (including sealing by RF methods), and its wide processing window and heat stability which allows extrusion processing at the elevated temperatures required for polyester extrusion (515-535 F.). EMA having a methyl acrylate content in the range of 18 to 20%, such as Emac SP2255 (18% methyl acrylate), Emac SP2242 (20% methyl acrylate), or Emac SP1257 (20% methyl acrylate), all available from Chevron Chemical Co. have been found particularly effective. 
     Although adequate interlayer adhesion is obtained with the skin layers  12 ,  13  in direct contact with the polyester barrier layer  11  (as depicted in FIG.  1 ), it is preferable to use an intermediate adhesive tie layer between the barrier layer and each skin layer for optimal interlayer adhesion. FIG. 2 illustrates a five-layer film in which the barrier layer  11 ′ and skin layers  12 ′ and  13 ′ have the same compositions and thicknesses described above and in which tie layers  14 ,  15  are coextruded between the barrier and skin layers. The tie layers can be any of a number of ethylene copolymers suitable for use as adhesion promoters in coextrusion. Several resins suitable for use as tie layers are available commercially under the trademark “Bynel” (dupont Co.) and “Primacor” (Dow Chemical Co.). For a multilayer film with EMA skins, a suitable choice is anhydride-modified ethylene acrylate copolymer such as Bynel 2169, Bynel 2174 or Bynel 21E533 available from duPont Co. 
     FIG. 3 illustrates a typical ostomy pouch  16  having its walls  16   a  and  16   b  formed from the multilayer films of FIGS. 1 or  2 . 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  18  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 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 examples which are intended to be illustrative of the invention, but are not intended to be limiting in scope. 
     EXAMPLE 1 
     A three-layer barrier film was produced in accordance with the present invention and included a core barrier layer and two outer skin layers joined directly to the core layer. The film was made by coextrusion casting at 535° F. and had a total thickness of 2.5 mil with a barrier layer thickness of 0.2 mil. The core barrier layer was a toughened grade of polyethylene terephthalate (Selar PTX184, duPont Co.) and each skin layer was a copolymer of ethylene and methyl acrylate having an 18% methyl acrylate content (EMAC SP2255, Chevron Chemical Co.). 
     For comparison purposes, a commercially-available multilayer film with a chlorinated barrier was selected as a control. The control film was composed of low density polyethylene coextruded with a barrier layer of polyvinylidene chloride. 
     The tensile moduli (psi) of the films were measured on an Instron tester (ASTM D882) with the secant modulus at 2% elongation being determined in both machine direction (MD) and transverse direction (TD). The results, tabulated in Table 1 below, reveals the film made in accordance with this invention to be considerably softer than the control film. 
     The lower modulus of the film having a polyester barrier layer was consistent with the results of quietness tests also tabulated below. Samples measuring approximately 4 inches by 4 inches of each film were formed into a cylinder and mounted on a test fixture wherein one end of the cylinder was held fixed and the other rotated around the cylinder&#39;s axis at an angle of 15°, 70 cycles/minute. Noise emissions produced by the film flexing were analyzed with a sound level meter. In the table, dBA is a weighted average that takes into account the human perception of noise over the entire frequency range, whereas dB values in the 8 and 16 kHz octave bands are indicative of the noise in the high frequency ranges and represent the crispness of the noise. The dBA and dB values in the 8 and 16 kHz octave bands therefore reveal that the film sample embodying the invention having a polyester core layer was considerably quieter than the control sample in which the core layer was PVDC. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Tensile Modulus 
                 Noise 
                   
               
             
          
           
               
                   
                 psi 
                   
                 dB, 
                 dB, 
               
             
          
           
               
                 Film 
                 MD 
                 TD 
                 dBA 
                 8 kHz 
                 16 kHz 
               
               
                   
               
               
                 EMA/Polyester/EMA 
                 24400 
                 24800 
                 64 
                 49 
                 42 
               
               
                 Prior art film 
                 30000 
                 31500 
                 74 
                 55 
                 49 
               
               
                 with chlorinated 
               
               
                 barrier layer 
               
               
                   
               
             
          
         
       
     
     The samples were tested for odor transmission using British Standard 7127, Part 101, “Method for Determining Odor Transmission of Colostomy and Ileostomy Bag Materials,” British Standard Institution, London, England. No odors were transmitted by the films. It is noteworthy that the odor barrier effectiveness of the film embodying this invention was achieved with a polyester barrier layer having a thickness of only 0.2 mil (in a total film thickness of 2.5 mil). 
     EXAMPLE 2 
     A three-layer barrier film in accordance with this invention was produced by coextrusion using conventional coextrusion casting techniques at 535° F., resulting in a multilayer film having a total thickness of 3 mil and a core barrier layer thickness of 0.2 mil. The composition of the barrier layer was toughened polyethylene terephthalate (Selar PTX184, duPont Co.) and skin layers of ethylene methyl acrylate copolymer with 20% methyl acrylate (EMAC SP1257, Chevron Chemical Co.). 
     Using the same procedure described in Example 1, the tensile moduli (psi) of the films were measured with the secant modulus at 2% elongation being determined in both machine direction and transverse direction. Noise emissions produced by the films were analyzed with a sound level meter in the same manner as described in Example 1. The comparative data appears in Table 2 below: 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Tensile Modulus 
                 Noise 
                   
               
             
          
           
               
                   
                 psi 
                   
                 dB, 
                 dB, 
               
             
          
           
               
                 Film 
                 MD 
                 TD 
                 dBA 
                 8 kHz 
                 16 kHz 
               
               
                   
               
               
                 EMA/Polyester/EMA 
                 12960 
                 14000 
                 61 
                 43 
                 28 
               
               
                   
               
             
          
         
       
     
     Tensile modulus and noise data reveal that a film embodying the invention having an EMA skin layer with a 20% methylacrylate content is even softer and quieter than the film of the previous example in which the methyl acrylate content of the EMA skin layer was 18%. As in the previous example, odor barrier effectiveness was achieved with a polyester barrier layer having a thickness of only 0.2 mil (no odor transmitted using the test method referenced above). 
     EXAMPLE 3 
     A five-layer barrier film was produced in accordance with this invention by coextrusion casting, resulting in a film with a total thickness of 3.5 mil and a barrier layer thickness of 0.3 mil. Unlike the films of the previous examples which utilize EMA resin as the skin layer, in this example the skin layer is based on polyethylene. Specifically, the film structure is A/B/C/B/A, wherein A is a polyethylene-based resin (2M042), Exxon Chemical Co.) modified by the addition of 5% of a slip/antiblock concentrate (EXT4226TSE, A. Schulman Co.) and 3% of a low density polyethylene (LD200.48, Exxon Chemical Co.); B is a tie layer consisting of anhydride-modified EMA (Bynel 21E533); and C is toughened polyethylene terephthalate (Selar PTX174, duPont Co.). The Bynel tie layer is particularly advantageous in this film structure to maximize adhesion to the polyethylene skin. Again, the tensile modulus at 2% elongation and the film noise were measured as described in the previous examples. The data is shown in Table 3 below: 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 Tensile Modulus 
                 Noise 
                   
               
             
          
           
               
                   
                 psi 
                   
                 dB, 
                 dB, 
               
             
          
           
               
                 Film 
                 MD 
                 TD 
                 dBA 
                 8 kHz 
                 16 kHz 
               
               
                   
               
               
                 PE/tie/Polyester/ 
                 25400 
                 22800 
                 65 
                 40 
                 30  
               
               
                 tie/PE 
               
               
                   
               
             
          
         
       
     
     Modulus and noise data indicate that the film of this example is noticeably softer and quieter than the commercial film reported in Example 1. 
     EXAMPLE 4 
     The barrier properties of the film of Example 3 were tested using three model compounds for fecal odor: dimethyldisulfide, indole and skatole. For comparison, the same test was conducted on a commercial ostomy film with chlorinated barrier. Analysis of effluent gases was conducted by gas chromatography using a flame ionization detector. The table below shows breakthrough times and concentration of each component in the effluent stream after 60 hrs. 
     
       
         
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
             
             
               
                   
                   
               
               
                   
                 Breakthrough Times, min 
                 Concentration at 60 hrs 
               
             
          
           
               
                   
                 Dimethyl 
                   
                   
                 Dimethyl 
                   
                   
               
               
                   
                 disulfide 
                 Indole 
                 Skatole 
                 disulfide 
                 Indole 
                 Skatole 
               
               
                 Film 
                 min 
                 min 
                 min 
                 ppm 
                 ppb 
                 ppb 
               
               
                   
               
               
                 Film of 
                 2280 
                 1670 
                 2180 
                  29 
                 140 
                 38 
               
               
                 Example 3 
               
               
                 Control 
                  720 
                 1140 
                 1610 
                 137 
                 292 
                 91 
               
               
                 Film 
               
               
                   
               
             
          
         
       
     
     Better barrier properties are expected for films that show longer breakthrough times and lower effluent concentration. The film of Example 3 is superior to the chlorinated control in both respects, indicating superior performance as a barrier to fecal odorants. 
     While in the foregoing, embodiments of the invention have been disclosed in detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.
A multilayer heat-sealable chlorine-free film of relatively low modulus, high interlaminar strength, and low noise upon flexing is provided. The film comprises an odor barrier layer of polyester resin and at least one heat-sealable skin layer, preferably two such skin layers on opposite sides of said odor barrier layer, composed of a homopolymer of ethylene or a copolymer of ethylene and an alpha-olefin or an ester-containing monomer. In a preferred embodiment, the odor barrier layer is formed of polyethylene terephthalate and adhesive tie layers are interposed between the odor barrier layer and the skin layers, resulting in a multilayer film of five layers. Pouches formed of such multilayer films are also disclosed.