Multilayer flexible film

Abstract: In a multilayer flexible film suitable for medical solution packaging, film-derived extractables are controlled by the use of a small amount of a high molecular weight stabilizer in the outer layer of the film. Solution pH can be controlled by the addition of a carbonate of an alkali metal to at least one intermediate adhesive layer and/or the core layer of the film.

Description: This invention relates to autoclavable flexible films suitable for the packaging of medical solutions. Currently, it is common medical practice to supply liquids such as medical solutions for parenteral administration in the form of disposable, flexible pouches. These pouches should be characterized by collapsibility, transparency, and adequate mechanical strength. They must also be able to resist the relatively high temperatures required for heat sterilization of their contents, for example in an autoclave. Typically, medical solutions and the like are autoclaved at about 253°F (123°C) for periods of 15 to 30 minutes. Presently, such flexible pouches are typically made from a highly plasticized polyvinyl chloride. While meeting the requirements mentioned above, polyvinyl chloride may have some undesirable properties for use as a medical solution pouch because of the possibility of migration of plasticizer from the polyvinyl chloride into the medical solution or the other contents of the pouch so that the solution may become contaminated by potentially toxic material. A question has also arisen concerning whether PVC is adequately chemically neutral to medical solutions. It has also been found that polyvinyl chloride becomes brittle at relatively low temperatures. Embrittlement and stress-cracking, particularly of the outer surface of medical pouches, has been found to occur in other non-PVC pouches. It is desirable to provide a pouch for the packaging of medical solutions which substantially reduces or eliminates stress-cracking and embrittlement of the pouch material. One such pouch is made from a flexible film comprising a sealant layer of an ethylene propylene copolymer or modified ethylene propylene copolymer, a core layer of a very low density polythylene, and an outer layer of a flexible copolyester. The core layer is adhered to the sealant and outer layers respectively with a suitable adhesive resin such as a modified ethylene vinyl acetate copolymer or a modified ethylene methacrylate copolymer. An alternative structure includes a blend layer of about 50% very low density polyethylene and about 50% of a modified ethylene propylene copolymer between the sealant layer and core layer. In packaging medical solutions, the amount of extractables in the medical solution from the packaging material must be strictly controlled. Similarly, a medical solution is often pH sensitive, and the pH of the solution must therefore also be kept within strict limits. U.S. Patent No. 4,188,443 issued to Mueller et al discloses a multilayer film of at least three layers, at least one of the inner layers comprising a copolymer or homopolymer of ethylene and at least one of the outer layers comprising a polyester or copolyester. The film is for shrink packaging. Example 4 discloses a film comprising a sealant layer of ethylene-propylene copolymer, a core layer of polyester or copolyester, an outer layer of polyester or copolyester and intermediate layers of EVA copolymer. There is no disclosure of a high molecular weight stabiliser in the outer layer of the shrinkable film. U.S. Patent No. 4,528,220 issued to Hwo discloses a plastic bag for medical solutions comprising an outer and inner layer of blended materials, the blend of the outer layer having ethylene propylene copolymer as one component and the blend of the inner layer having ethylene propylene copolymer as one component. The present invention provides a flexible film suitable for the packaging of medical solutions, in which extractables from the film are strictly controlled, and/or the pH of the medical solution in a pouch formed from the flexible film is relatively unaffected by the film. The terms "flexible" and the like and "elastomeric" and the like are used herein to define specific polymeric materials as well as characteristics of a resulting pouch or bag whereby improved flexibility and/or collapsibility of the pouch or bag is obtained by the use of these specific polymeric materials. Flexible materials may be characterized by a modulus of preferably less than 50,000 PSI (ASTM D-882-81; 345000kPa) and more preferably less than 40,000 PSI (ASTM D-882-81; 276000kPa). The term "film" and the like refers to a thermoplastic material suitable for packaging and having one or more layers of polymeric materials which may be bonded by any suitable means well known in the art. The term "polymer", "polymeric", and the like, unless specifically defined or otherwise limited, generally includes homopolymers, copolymers and terpolymers and blends and modifications thereof. The term "very low density polyethylene" is used herein to define a copolymer of polyethylene with densities below 0.910 g/cm³, preferably between 0.900 and 0.906 g/cm³. and including densities as low as 0.860 g/cm³, as measured by ASTM D-1505. The term "ethylene vinyl acetate copolymer" (EVA) is used herein to refer to a copolymer formed from ethylene and vinyl acetate monomers wherein the ethylene derived units in the copolymer are present in major amounts and the vinyl acetate derived units in the copolymer are present in minor amounts. The term "ethylene propylene copolymer" is used herein to refer to a copolymer formed from polypropylene monomer and minor amounts, usually less than 6%, of ethylene. The term "copolyester" and the like is applied to polyesters synthesized from more than one diol and a diacid. Copolyesters as used herein may also be characterized as copolymers of polyether and polyethylene terephthalate. More preferably copolyesters as used herein may be characterized as polymeric materials derived from 1,4 cyclohexane di-methanol, 1,4 cyclohexane dicarboxylic acid, and polytetramethylene glycol ether, or equivalents of any of the above, as reactants. The term "modified" and the like is used herein to refer to a polymeric material in which some or all of the substituents are replaced by other materials, providing a change in properties such as improved flexibility or elastomeric properties. The present invention provides a multilayer flexible film comprising a sealant layer, a core layer of a polymeric material which imparts flexibility to the film, an outer layer of a flexible polyester or copolyester including a high molecular weight stabilizer, and intermediate adhesive layers. The invention also provides a multilayer flexible film comprising a sealant layer, a core layer of a polymeric material which imparts flexibility to the film, an outer layer of a flexible polyester or copolyester, and intermediate layers comprising ethylene ester copolymers or modified ethylene ester copolymers, in which at least one intermediate layer and/or core layer contains a carbonate of an alkali metal. Thermoplastic film useful for packaging medical solutions must be not only flexible, but also able to withstand autoclaving temperatures during an autoclaving step typically employed after the film has been converted into a pouch, and a medical solution has been introduced into the pouch. One example of such a film is a multilayer film having a sealant layer, a core layer of a polymer which contributes flexibility to the film, and an outer layer of a flexible polyester or copolyester. Intermediate adhesive layers provide interlaminar bonding between the core layer and the sealant and outer layers respectively, holding the film together during and after autoclaving. The sealant layer can be an ethylene propylene copolymer or modified ethylene propylene copolymer. Representative resins include M355E, a polyallomer ethylene propylene block copolymer available from Eastman, and Z4650, a modified ethylene propylene copolymer available from Cosden Oil and Chemical Company. The core layer can be a very low density polyethylene such as DXFD 1362 available from Dow Chemical Company. The outside layer is a flexible polyester or copolyester such as PCCE 9967 from Eastman Chemical Products, Inc. The intermediate adhesive layers may be identical or differ from each other depending on the particular structure and application. CXA-E181 a modified ethylene vinyl acetate copolymer from Dupont, and Plexar 3382, modified ethylene methacrylate copolymer available from Norchem are examples of such adhesive materials. An alternative intermediate adhesive layer for bonding the sealant layer to the core layer may comprise a blend of about 50% Z4650 with about 50% of the same very low density polyethylene that comprises the core layer. Limiting the amount of extractables that can migrate from the outer copolyester layer into a medical solution is of primary importance. Blending a high molecular weight stabilizer, such as Irganox 1010 available from Ciba-Geigy Corporation into the polyester or copolyester prior to extrusion of the film, limits the amount of extractables that enter the medical solution. Preferred ranges for the stabilizer are between about .3 and 1%, and preferably about .7% by weight of the copolyester. Irganox is described by the Condensed Chemical Dictionary, 10th Edition, at page 569 as a series of complex, high molecular weight stabilizers that inhibit oxidation and thermodegradation of many organic materials. Although Irganox 1010 is currently added to commercial copolyesters in the amount of about .2% by weight of the resin, it has been found that this amount of additive is insufficient to control the extraction of degraded copolyester material into medical solutions. Amounts of the high molecular weight stabilizer above about 1% by weight of the copolyester are not preferred because the additive itself can become an extractable material. Many medical solutions are also pH sensitive and such solutions should not vary greatly in acidity or basicity. It is believed that acetic acid may be produced in certain intermediate adhesive polymeric materials, and thereafter migrate into the packaged solution. In accordance with the invention, preferably between about .05% and .15% of a carbonate of an alkali metal, preferably sodium, is blended into at least one of the intermediate adhesive resins prior to extrusion. More preferably, about .1% of a carbonate of an alkali metal, preferably sodium, is blended into the modified EVA, or modified ethylene methacrylate copolymer. Alternatively, preferably between about .005% and .015% of a carbonate of an alkali metal, preferably sodium, is blended into the very low density polyethylene or other polymeric material comprised in the core layer of the flexible film. More preferably, about .01% sodium carbonate is blended into the very low density polyethylene. It is believed that the sodium carbonate neutralizes acetic acid or other acid components of the intermediate adhesive resins, and possibly the core layer resin. The invention is further illustrated in the following examples showing actual embodiments of the invention. In the following Examples "M355E","Z4650" "DXFD 1362", "PCCE 9967", "CXA-E181", "PLEXAR 3382" and "IRGANOX 1010" are Trade Marks. EXAMPLE 1 About 0.6% of Irganox 1010 was blended with the flexible copolyester PCCE 9967. About .1% sodium carbonate was blended into a modified ethylene vinyl acetate copolymer, CXA E181. A five layer film was coextruded, the film having a sealant layer of M355E ethylene propylene block copolymer, a core layer of very low density polyethylene DXFD 1362, and the outer layers of PCCE 9967, with the intermediate adhesive layers of CXA E181. EXAMPLE 2 About 0.6% of Irganox 1010 was blended into PCCE 9967 copolyester resin. About .1% sodium carbonate was blended into a CXA E181 resin. A blend of 50% by weight DXFD 1362 and 50% by weight modified ethylene propylene copolymer Z4650 was prepared, to which .1% sodium carbonate was added. A multilayer film was coextruded having a sealant layer of Z4650, a core layer of the DXFD 1362, an outer layer of the copolyester, an adhesive layer between the core layer and sealant layer comprising the blend of 50% very low density polyethylene and 50% ethylene propylene copolymer, and an intermediate adhesive layer between the core layer and copolyester layer comprising CXA E181. In Examples 3 through 6, a multilayer coextruded film substantially like that of Example 1 was prepared with varying levels of sodium carbonate in the core layer, ie. the layer containing the very low density polyethylene. This film differed from Example 1 in that CXA 190, a modified ethylene vinyl acetate copolymer was used in place of the CXA E181 of Example 1. CXA 190 has 1000 ppm Na₂CO₃ in the resin itself. Also, Examples 1 through 6 included 0.1% sodium carbonate in an additional sacrificial layer coextruded with and adhering to the multilayer film at the sealant layer of M355E ethylene propylene block copolymer. Finally, the copolyester layer contained 0.5% Irganox 1010 instead of the 0.6% level of Example 1. The film of Examples 3 through 6 had a total thickness of 9.5 mils (0.24 mm). This includes a core layer of 4.45 mils (0.11 mm), intermediate adhesive layers of 0.4 mils (0.01 mm) each, a sealant layer of 0.75 mils (0.02 mm), an outer layer of 1.5 mils (0.04 mm), and a sacrificial layer of 2.0 mils (0.051 mm) thickness. As seen in Table 1 below, increasing the sodium carbonate content of the core layer, with the remainder of the multilayer structure remaining constant, resulted in very significant improvement in the reduction of pH shift in the contained solution. The multilayer film described above was formed into a pouch having dimensions of 3.9 inches by 5.3 inches (9.9 by 13.5 cm), and filled with 150 milliliters of water, then overwrapped with an 8 mil (0.2 mm) thick overwrap of polypropylene, and autoclaved at a temperature of 250°F (121°C) for 20 minutes. The initial pH of the water was 5.96. EXAMPLE INITIAL pH Na₂ CO₃ (ppm) FINAL pH DROP IN pH 3 5.96 0 4.89 1.17 4 5.96 50 5.01 .95 5 5.96 100 5.45 .51 6 5.96 200 5.68 .28 pH determinations were made on a pH meter according to USP 21 (page 1124). A multilayer film was coextruded substantially like that of Example 1 with sealant layer thickness of 1.0 mils (0.025 mm), intermediate adhesive layers each having a thickness of 0.5 mils (0.013 mm), a core layer with a thickness of 4.75 mils (0.12 mm), and an outer layer of a copolyester with a thickness of 1.75 mils (0.04 mm). This multilayer material also included a 2.0 mil(0.05 mm) thick sacrificial layer of low density polyethylene as used in Examples 3 through 6. This structure was irradiated with 2 x 10⁴Gy (two megarads) dosage of radiation and formed into a pouch with dimensions of 10 centimeters by 15 centimeters. The pouch was filled with 50 milliliters of distilled water, having an initial pH of 8.0. The pouch was overwrapped with a nylon polyethylene overwrap filled with water, and autoclaved at 250°F (121°C) for 20 minutes at 28 psi (193 kPa) over pressure. Example 7 listed in Table 2 below indicates the drop in pH as an average of three samples tested. No Irganox 1010 was blended in the outer copolyester layer, and no sodium carbonate was added to any of the other layers of Example 7. Example 8 was identical to Example 7, but with the presence of 0.5% Irganox 1010 by weight in the outer layer, and 0.1% sodium carbonate in the intermediate adhesive layers and in the sacrificial layer. Examples 9 and 10 in Table 2 below were substantially similar to Examples 7 and 8 respectively, but with an initial pH of 6.5 in the contained water. The structures of Claims 9 and 10 were irradiated to 5 x 10⁴Gy (5 megarads) instead of 2 x 10⁴Gy (2 megarads). All pH data represents an average of 3 samples for each example. Examples 7 and 9 are Reference Examples EXAMPLE INITIAL pH Na₂ CO₃ (ppm) FINAL pH DROP IN pH 7 8.0 0 4.2 3.8 8 8.0 1000 5.7 2.3 9 6.5 0 4.6 1.9 10 6.5 1000 5.7 0.8 Films in accordance with the present invention are preferably cross-linked. This is preferably done by irradiation, i.e. bombarding the film with particulate and non-particulate radiations such as high energy electrons from the accelerator to cross-link the materials of the film. Cross-linking may also be accomplished chemically by the use of, for example, peroxides. The detailed description and specific examples which indicate the presently preferred embodiments of the invention are given by way of illustration only. Various changes will be apparent to those of ordinary skill in the art upon review of the above detailed description and Examples. For example, where two different intermediate adhesive layers are used, or where identical intermediate adhesive layers are extruded through separate extruders, the carbonate of an alkali metal can be blended with only one of the adhesive resins. The invention also contemplates the use of the carbonate of an alkali metal in either one or both of the intermediate adhesive layers, the core layer, or a combination of these.

Claims: A multilayer flexible film comprising a sealant layer, a core layer of a polymeric material which imparts flexibility to the film, an outer layer of a flexible polyester or copolyester including a high molecular weight stabilizer, and intermediate adhesive layers. A film according to claim 1 in which the polymeric material is very low density polyethylene. A film according to claim 1 or 2 wherein the high molecular weight stabilizer comprises between about .3% and 1% weight of the outer layer. A film according to claim 3 wherein the outer layer includes about .7% of the high molecular weight stabilizer. A multilayer flexible film comprising a sealant layer, a core layer of a polymeric material which imparts flexibility to the film, an outer layer of a flexible polyester or copolyester, and intermediate layers comprising ethylene ester copolymers or modified ethylene ester copolymers, the core layer and/or at least one intermediate layer comprising a carbonate of an alkali metal. A film according to claim 5 in which the polymeric material is very low density polyethylene. A film according to claim 5 or 6 wherein at least one intermediate layer contains about .05% to .15% by weight of the alkali metal carbonate. A film according to claim 7 wherein at least one intermediate layer contains about .1% by weight of the alkali metal carbonate. A film according to claim 5 or 6 wherein the core layer contains about .005% to .015% by weight of alkali metal carbonate. A film according to claim 9 wherein the core layer contains about .01% of the alkali metal carbonate. A film according to any one of claims 5 to 10 wherein the alkali metal is sodium. A film according to any one of the preceding claims which comprises a first and a second intermediate adhesive layer, wherein the first adhesive layer bonds the core layer to the sealant layer and the second adhesive layer bonds the core layer to the outer layer. A multilayer flexible film which combines the features of any one of claims 1 to 4 and the features of any one of claims 5 to 12. The use of a film as claimed in any one of the preceding claims for packaging medical solutions. A method of making a multilayer flexible film according to any one of claims 1 to 4 which comprises (a) blending a flexible polyester or copolyester with a high molecular weight stabilizer; and (b) coextruding a multilayer film comprising a sealant layer, a core layer of a polymeric material which imparts flexibility to the film, an outer layer containing the blend of (a) and intermediate adhesive layers. A method of making a multilayer flexible film according to any one of claims 5 to 13 which comprises: (a) blending a polymeric material which imparts flexibility to the film with a carbonate of an alkali metal; and (b) coextruding a core layer of the blend of (a), a sealant layer, an outer layer of a flexible polyester or copolyester, and intermediate layers comprising ethylene ester copolymers or modified ethylene ester copolymers. A method of making a multilayer film according to any one of claims 5 to 13 which comprises: (a) blending an ethylene ester copolymer or modified ethylene ester copolymer with a carbonate of an alkali metal; and (b) coextruding a sealant layer, a core layer of a polymeric material which imparts flexibility to the film, an outer layer of a flexible polyester or copolyester and intermediate layers comprising ethylene ester copolymers or modified ethylene ester copolymers, at least one of the intermediate layers comprising the blend of (a).

Inventors: MUELLER WALTER BERNDT, SCHIRMER HENRY GEORGE, MUELLER, WALTER BERNDT, SCHIRMER, HENRY GEORGE
Applicants: GRACE W R & CO, W.R. GRACE & CO.-CONN.
Application year: 1987
Main classification: B32B27
IPC codes: A61J1, B32B27, B65D81, B65D65