Abstract:
A multilayer heat-sealable chlorine-free odor barrier film having relatively low modulus, high interlaminar strength, and low noise upon flexing is provided. The film comprises an odor barrier layer of an amorphous polyamide resin blended with an anhydride-modified olefinic polymer or copolymer. The film also includes at least one heat-sealable skin layer, preferably two such skin layers on opposite sides of said odor barrier layer, composed of an ethylene polymer or copolymer, and an adhesive tie layer between each skin layer and the odor barrier layer. Pouches formed of such multilayer films are also disclosed.

Description:
BACKGROUND AND SUMMARY  
         [0001]    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.  
           [0002]    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.  
           [0003]    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 acrylonitrile or methacrylonitrile of high nitrile content, commonly known as nitrile resins.  
           [0004]    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, 5,407,713, and 5,895,694.  
           [0005]    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 polymer or copolymer having a density of 0.89 g/cc or lower. The anhydride-modified olef polymer or copolymer should be present in the range of about 10% to 30%, preferably 15% to 25%, per total weight of the barrier layer.  
           [0006]    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.  
           [0007]    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.  
           [0008]    Other features, advantages and objects of the invention will become apparent from the specification and drawings. 
       
    
    
     DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic cross-sectional view of an embodiment of the multilayer barrier film of this invention.  
         [0010]    [0010]FIG. 2 is an elevational view of an ostomy pouch formed from the multilayer barrier film of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0011]    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.  
         [0012]    [0012]FIG. 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 polymer or 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 5s 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. Req. 26,667 (1987), the disclosure of which is incorporated by reference herein.  
         [0013]    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 polymer or 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 polymer should be less than 0.89 g/cc, preferably less than 0.87 g/cc. Anhydride-modified olefinic polymers with densities higher than 0.89 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 polymer or copolymers are functionalized by reactive processing with an unsaturated carboxylic anhydride. Although the mechanism of anhydride modification is not fully understood, it is believed that a grafting reaction occurs between the polymer and the unsaturated 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 polymer is quite low, less than 2% by weight. The density of the olefinic polymer is essentially unaffected by anhydride modification at these low levels. One example of an anhydride-modified olefinic copolymer is Fusabond MN493D available from DuPont ccrpany. Fusab.cd MN493D is an ethylene oatene c-Folymer that is modified with 0.5% maleic anhydride and has a density of 0.869 g/cc. While it is known to function as a toughening agent for crystalline nylon, rusabond MN493D performs an unexpected function here in decreasing modulus and noise of amorphous nylon without destroying or significantly reducing the odor barrier properties of layer  11 . Similar performance can be achieved with other anhydride-modified olefinic polymers having comparable low density, such as ethylene-propylene copolymers and terpolymers (EPM and EPDM). EPM and EPDM have a density in the 0.85 to 0.86 g/cc range and are suitable for modification with maleic anhydride. Due to the immiscible nature of these blends, mixing of the nylon with the anhydride-modified olefinic polymer 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.  
         [0014]    Skin layers  14  and  15  are formed of an ethylene-based polymer or copolymer with an alpha-olefin such as hexene or octene. A suitable resin is metellocene-catalyzed polyethylene with an octene comonomer such as the ethylene octene copolymer marketed under the designation Exact  8201  by Exxon Chemical.  
         [0015]    Tie layers  12  and  13  must be capable of bonding to both the skin layers and the core barrier layer. Polyethylene, ethylene vinyl acetate copolymers (EVA), or ethylene methyl acrylate copolymers (EKA), modified with functional anhydride groups are believed particularly suitable. EVA-based anhydride-modified resins such as Bynel 3860 or Bynel 3861, or polyethylene-based ahydride-modified resins such as Bynel 4lE557, 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.  
         [0016]    The total thickness of the multilayer film, assuming five layers are present, should fall within the general range of about 2 to 5 mil, preferably about 3 to 4 mil. As to the barrier layer  11 , its thickness should fall generally 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 about 0.2 to 0.4 mil, with 0.3 mil being considered optimal 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 0.5 to 2.5 mil, preferably 1 to 2 mil, which may be nearly one order of magnitude greater than the thickness of the odor barrier layer  11 .  
         [0017]    [0017]FIG. 2 illustrates a typical ostomy pouch  16  having its walls  16   a  and  16   b  formed from the multilayer film of FIG. 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  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 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.  
         [0018]    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  
       [0019]    This example illustrates the properties of blends of amorphous nylon (Selar PA3426, DuPont Company) with anhydride-modified polyolefin (Fusabond MN493D, DuPont Company). The two resins were compounded and pelletized using a twin screw compounder extruder. The compounded resins were then coextruded using a Killion extruder into a A/B/A three-layer film structure, wherein A was polyethylene and B was the nylon blend. Because of the absence of tie layers, it was possible to strip the polyethylene skin layers A from the nylon blend layer B and to test the resulting monolayer B films against a monolayer film consisting of 100% amorphous nylon (Selar PA3426). Secant modulus at 2% elongation of the monolayer films was measured in the machine and transverse directions according to ASTM D882 at a strain rate of 0.1 in./in.min. Results are shown below in Table 1:  
                                                                                         TABLE 1                                       Monolayer Film Composition   Secant Modulus                Selar PA3426   Fusabond MN493D   psi                %   %   MD   TD                            100   0   323,500   312,600           85   15   235,600   215,000           75   25   190,000   120,000                      
 
         [0020]    The data in Table 1 shows the reduction in modulus resulting from the addition of Fusabond MN493D to Selar PA3426. The lower modulus values indicate that the compounded resins are considerably softer than the control resin with 100% amorphous nylon. The reduction in modulus allows the production of nylon-based multilayer films which are soft and quiet, as indicated in further examples below.  
       EXAMPLE 2  
       [0021]    A five-layer film was produced in accordance with this invention by coextrusion casting, resulting in a film with a total thickness of 3.3 mil and a barrier layer thickness of 0.32 mil. The film structure was A/B/C/B/A, where A was a polyethylene-based resin (Exact 8201, 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 are tie layers consisting of anhydride-modified ethylene vinyl acetate copolymer (Bynel 3601, DuPont Co.), and C is a blend of amorphous nylon (Selar PA3426) with an anhydride-modified rubbery polyolefin (Fusabond MN493D) at 85% to 15% weight ratio.  
         [0022]    The film was tested for quietness by forming a 4 inch by 4 inch sample into a cylinder and mounting it on a test fixture wherein one end of the cylinder was held fixed and the other was rotated around the cylinder axis at an angle of 15 degrees at 70 cycles per minute. Noise emissions produced by the film&#39;s flexing were analyzed with a sound level meter. For comparison, the same test was conducted on a commercial ostomy film with a chlorinated barrier. Results are shown below;  
                           TABLE 2                       Sample   dBA   dB, 8 kHz   dB, 16 kHz                   Film of Example 2   64   49   39       Control Film   74   55   49                  
 
         [0023]    In this table, dBA is a weighted average that takes into account the human perception of noise over the entire frequency range, whereas B values in the 8 and 16 kHz octave bands are indicative of the noise in the higher frequency range and represent the crispness of the noise. The dBA and dB values therefore reveal that the film sample embodying the invention is considerably quieter than the control sample in which the core layer is based on PVDC.  
       EXAMPLE 3  
       [0024]    A five-layer film was produced in accordance with this invention by coextrusion casting, resulting in a film with a total thickness of 3.2 mil and a barrier layer thickness of 0.28 mil. The film construction was A/B/C/B/A, having the same composition as the film of Example 2 except that the tie layers B were polyethylene-based (Bynel 41E557,DuPont Co.). The film was tested for quietness as described in Example 2. Results are shown in the table below which includes a control sample of a commercial ostomy film having a chlorinated barrier layer of PVDC.  
                                   TABLE 3                                   Sample   dBA   dB, 8 kHz   dB, 16 kHz                           Film of Example 3   65   51   45           Control Film   74   55   49                      
 
         [0025]    As in Example 2, the dBA and dB values at 8 and 16 kHz reveal that the film sample of Example 3 is considerably quieter than the control sample in which the core layer is PVDC.  
       EXAMPLE 4  
       [0026]    The films of Examples 2 and 3 were tested for odor transmission using British Standard 7127, Part 101, Appendix G: Method for Determining Odour Transmission of Colostomy and Ileostomy Bag Materials, British Standard Institution, London. Both films passed the test, indicating that the modification of the nylon barrier layer does not have a detrimental effect on odor barrier properties of the films.  
         [0027]    In addition, a quantitative test of the barrier properties of the film of Example 2 was conducted using three model compounds for fecal odor: dimethyldisulfide, indole, and skatole. For comparison, the same test was conducted on a commercial ostomy film with a chlorinated (PVDC) barrier layer. Analysis of effluent gases was conducted by gas chromatography using a flame ionization detector. Table 4 shows breakthrough times and concentration of each component in the effluent stream after 60 hours.  
                                                                                       TABLE 4                                       Breakthrough   Concentration at           Times, min   60 hours                Dimethyl           Dimethyl                   disulfide   Indole   Skatole   disulfide   Indole   Skatole       Film   min   min   min   ppm   ppb   ppb                    Film of   2680   1880   2180   25   102   51       Example 2       Control   722   1140   1610   137   292   91       Film                  
 
         [0028]    Better barrier properties are expected for films that show longer breakthrough times and lower effluent concentration. The film of Example 2 is superior to the chlorinated control film in both respects, indicating superior performance as a barrier to fecal odorants.  
         [0029]    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.