LAMINATES FOR FORM-FILL-SEAL PACKAGING

Abstract: The instant invention is directed to a laminate (18) comprising a core layer (24) comprising an oxygen barrier polymer, a heat sealable layer (28) comprising a homogeneous ethylene alpha-olefin copolymer, an outer abuse-resistant polymeric layer (20); and an intermediate layer (22, 26) disposed between the core layer and each of the heat sealable layer and the outer layer, and comprising a polymeric adhesive. In another aspect of the present invention, a package comprises a food product, a pouch containing the food product, the pouch having a longitudinal seal, and the pouch constructed from a laminate comprising a core layer comprising an oxygen barrier polymer, a heat sealable layer comprising a homogeneous ethylene alpha-olefin copolymer, an outer abuse-resistant polymeric layer, and an intermediate layer disposed between the core layer and each of the heat sealable layer, and the outer layer, and comprising a polymeric adhesive.

Description: LAMINATES FOR FORM-FILL-SEAL PACKAGING BACKGROUND OF THE INVENTION This invention relates generally to thermoplastic laminates for packaging food and other products. It is common practice to package articles such as food products in thermoplastic films or laminates to protect the product to be packaged from abuse and exterior contamination, and to provide a convenient and durable package for transportation and ultimate sale to the end user. In the field of packaging food and non-food liquid and/or flowable food and non-food products, a convenient method of packaging such products in thermoplastic film has been developed and is generally known as a form/fill/seal process. In such a process a tube is formed from thermoplastic film and an end seal is made by transversely sealing across the tube with heated seal bars to form a conveniently wide heat seal and, consequently, producing a bag or pouch ready to receive a product. After the heat seal is made, the bag or pouch is filled and then another transverse heat seal is made across the width of the tube in a relatively wide band. After cooling, this seal is transversely severed to separate the filled bag or pouch from the next bag or pouch to be filled. Thus, one wide band seal serves as a first seal for one bag and a second seal for another. A machine for making pouches in a vertical form/ fill/ seal machine is described in United States Patent No. 4,506,494, incorporated herein by reference in its entirety, which issued on March 26, 1985 to Mamoru Shimoyama et al. In the Shimoyama et al. patent a vertically held tube with a bottom end that has been closed by a transverse heat seal is filled with a liquid, semiliquid, or paste charge or contents and squeeze rollers spaced apart and above the bottom end seal squeeze the filled tube and pinch the walls of the flatted tube together. When a length of tubing of the desired height of the bag has been fed through the squeeze rollers a heat seal is made transversely across the flattened tubing by heat seal bars which clamp and seal the film of the tube therebetween. After the seal bars have been withdrawn the film moves downwardly to be contacted by cooled clamping and severing bars which clamp the film therebetween and are provided with a cutting knife to sever the sealed film at about the midpoint of the seal so that approximately half of the seal will be on the upper part of a tube and the other half on the lower. When the sealing and severing operation is complete, the squeeze rollers are separated to allow a new charge of product to enter the flattened tube after which the aforementioned described process is repeated thus continuously producing vertically form /fill /sealed pouches which have a bottom end and top end heat seal closure, As an alternative to transverse seals, metal clips can be used to close the tubular film at each end of the tube. Horizontal and vertical form-fill-seal equipment is commonly used in many packaging applications. Manufacturers of form-fill-seal equipment include Hayssen, Omori, Triangle, Rovema, Key, Ilapak, and Kartridge Pak. The Onpack VFFS system is supplied by W.R. Grace & Co. -Conn. SUMMARY OF THE INVENTION The instant invention is directed to a laminate comprising a core layer comprising an oxygen barrier polymer; a heat sealable layer comprising a homogeneous ethylene alpha-olefin copolymer; an outer abuse-resistant polymeric layer; and an intermediate layer disposed between the core layer and each of the heat sealable layer and the outer layer, and comprising a polymeric adhesive. In another aspect of the present invention, a package comprises a food product; a pouch containing the food product, the pouch having a longitudinal seal, and the pouch constructed from a laminate comprising a core layer comprising an oxygen barrier polymer, a heat sealable layer comprising a homogeneous ethylene alpha-olefin copolymer, an outer abuse-resistant polymeric layer, and an intermediate layer disposed between the core layer and each of the heat sealable layer, and the outer layer, and comprising a polymeric adhesive. DEFINITIONS "Laminate" is used herein to mean a multilayer film, laminate, web, or sheet made by extrusion, coextrusion, extrusion coating, conventional lamination, extrusion lamination, cast or blown, or other suitable processes. "Oxygen barrier" is used herein to refer to polymeric materials having oxygen transmission rates of less than about 150cc/ square meter in 24 hours at 73 degrees F (STP), and preferably less than about 10cc/ square meter, 24 hours, 73 degrees F (STP). Such materials include e.g. ethylene vinyl alcohol copolymer, vinylidene chloride copolymer with comonomer such as vinyl chloride or methyl acrylate, polyamides or copolyamides, and polyesters or copolyesters. "Polyamide" is used herein to refer to high molecular weight polymers having amide linkages along the molecular chain, and refers more specifically to synthetic polyamide such as various nylons. "Ethylene vinyl alcohol copolymer" is used herein to refer to a vinyl alcohol copolymer having an ethylene comonomer, and prepared by e.g. hydrolysis of vinyl acetate copolymers, or by chemical reactions with polyvinyl alcohol. "Polyolefin" is used herein broadly to include polyethylene; ethylene copolymers having a comonomer such as vinyl acetate, alkyl acrylate, acrylic acid, and alpha-olefin; polypropylene; propylene copolymers; polybutene; butene copolymers; etc. As used herein, the phrase "alpha-olefin" refers to olefinic compounds, whether unsubstituted or substituted, in which the first two carbon atoms in the chain have a double bond therebetween. As used herein, the phrase "ethylene alpha-olefin copolymer" refers to such heterogeneous materials as linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE); and homogeneous polymers such as metallocene catalyzed polymers such as EXACT (TM) materials supplied by Exxon, and TAFMER (TM) materials sup¬ plied by Mitsui Petrochemical Corporation. These materials generally include copolymers of ethylene with one or more comonomers selected from C 4 to C , Q alpha-olefins such as butene- 1 (i.e., 1-butene), hexene- 1 , octene- 1 , etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. LLDPE, as used herein, has a density usually in the range of from about 0.91 grams per cubic centimeter to about 0.94 grams per cubic centimeter. Other ethylene alpha-olefin copolymers, such as the long chain branched homogeneous ethylene alpha-olefin copolymers available from the Dow Chemical Company, known as AFFINITY (TM) resins, are also included as another type of alpha-olefin copolymer useful in the present invention. In general, the ethylene alpha-olefin copolymer comprises copolymer resulting from the copolymerization of from about 80 to 99 weight percent ethylene and from 1 to 20 weight percent alpha-olefin. BRIEF DESCRIPTION OF THE DRAWINGS Further details are given below with reference to the drawings, wherein: Figs. 1 through 4 are schematic cross-sections of embodiments of a laminate of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring specifically to the drawings, in Fig. 1 a schematic cross- section of a preferred embodiment of a laminate 18 of the invention is shown. The laminate structure is directed to a multi-layer composite having the generalized structure of (outside) A/B/C/B/E (inside) where A is an outer abuse-resistant layer, B is an intermediate adhesive layer, C is an oxygen barrier layer, and E is a heat sealable layer. Preferably, outer layer 20 serves as an abuse-resistant layer. Preferably, outer layer 20 comprises a polymer such as ethyene alpha-olefin copolymer, ethylene vinyl acetate copolymer, polyamide, copolyamide, propylene polymer or copolymer, and blends thereof. Preferably, layer 24 serves as an oxygen barrier layer. Preferably, layer 24 comprises a polymer such as ethylene vinyl alcohol copolymer, vinylidene chloride copolymer, polyamide, polyester, and blends thereof. Preferably, layer 28 serves as a heat sealable layer. Preferably, layer 28 comprises a homogeneous ethylene copolymer such as metallocene catalyzed ethylene alpha-olefin copolymer, metallocene catalyzed ethylene alpha-olefin copolymer with long-chain branching, metallocene catalyzed ethylene styrene copolymer, or blends thereof. The homogeneous ethylene copolymer of layer 28 can be blended with a heterogeneous ethylene copolymer, e.g. heterogeneous ethylene alpha-olefin copolymer such as linear low density polyethylene and very low density polyethylene. The heat sealable layer can in effect comprise two layers: the sealable layer per se as just described, and a bulk sealant layer which is preferably disposed adjacent to the sealable layer, and preferably provides a relatively low-cost material compatible with the homogeneous ethylene copolymer, and which contributes to the overall seal performance of the laminate. These materials are preferably heterogeneous ethylene copolymer, e.g. heterogeneous ethylene alpha-olefin copolymer such as linear low density polyethylene or very low density polyethylene. By practicing this alternative embodiment, the benefits of the heat sealable homogeneous ethylene copolymer are substantially retained, while reducing the cost of the overall laminate by using a relatively thin heat sealable layer combined with a relatively thicker lower cost adjacent bulk layer. Preferably, layers 22 and 26 serve as adhesive layers, to enhance the adhesion between layer 24 and outer layer 20 and heat sealable layer 28 respectively. These adhesive layers can be identical or different from each other, and can comprise a wide range of acid or acid anhydride /grafted polyolefins including those based on ethylene vinyl acetate copolymer, polypropylene, low density polyethylene, and ethylene alpha-olefin based adhesives such as linear low density polyethylene and very low density polyethylene. Commercial examples of such materials are those marketed under the name Plexar available from Norchem, the CXA series from DuPont, Admer adhesives from Mitsui, and the like. In Figure 2, the laminate structure 30 is directed to a multi-layer composite having the generalized structure of (outside) A/B/C/D/C/B/E (inside) where A is an abuse-resistant layer, B is an intermediate adhesive layer, C is a polyamide layer, D is an oxygen barrier layer, and E is a heat sealable layer. Preferably, outer layer 32 comprises the same polymers or blends disclosed for layer 20 of laminate 18. Oxygen barrier layer 38 preferably comprises the same polymers or blends disclosed for layer 24. On either side of the barrier layer 38 are polyamide layers 36 and 40. These are preferably the same, and preferably comprise nylon 6, nylon 12, nylon 66, nylon 6, 12, nylon 6,66, nylon 1 1 , or blends thereof. Heat sealable layer 44 preferably comprises the same polymers or blends disclosed for layer 28. Polymeric adhesive layers 34 and 42 preferably comprise the same polymers or blends disclosed for layers 22 and 26. Figure 3 shows an alternative embodiment 1 18 of the laminate in which layers 120, 122, 124, 126, and 128 of laminate 129 correspond in composition to layers 20, 22, 24, 26, and 28 respectively. A second laminate or film 121 is shown adhered to the five-layer laminate 129 by means of a conventional lamination adhesive 119, such as polyurethane adhesive. Film 121 is preferably a heat-resistant film, and preferably comprises ethylene alpha-olefin copolymer, blends of ethylene alpha- olefin copolymer and ethylene unsaturated ester copolymer, oriented polypropylene, biaxially oriented nylon, polyethylene terephthalate, or blends thereof. Film 121 is shown as a monolayer film, but can be a multilayer film. Adherence to lami¬ nate 129 can be by any suitable means, such as corona treatment, heat sealing, extrusion lamination, etc. in lieu of conventional lamination. Fig.4 shows still another embodiment 130 in which layers 132, 134, 136, 140, 142, and 144 correspond in composition and structure to layers 32, 34, 36, 38, 40, 42, and 44 of film 30. Laminate 146 corresponds in composition to laminate 121 of laminate 1 18. The laminate of the present invention offers good hot tack strength, and good seals at high speed, relatively low seal initiation temperature, and substantially no off-flavors or off-odors, when used to package items such as shredded cheese in FFS equipment. Laminates in accordance with the present invention can be made e.g. by coextruding by means well known in the art. Although as used in a VFFS application, the laminate is neither oriented nor irradiated, the laminate can be oriented or irradiated as needed. In order to optionally orient the laminate, it could be longitudinally oriented, calendared, and/or tenterframed. The laminate of the present invention is particularly suited for packaging of shredded cheese. The invention may be further understood by reference to the following examples. EXAMPLE 1 A laminate was prepared in accordance with the present invention by extruding the various resins listed below to produce a seven layer laminate. An outer abuse-resistant layer comprised a low density polyethylene (PE 1042 CS 15 from Rexene). A second layer comprised 65% (all percentages herein by weight) ethylene octene copolymer (Attane 4201 from Dow), 25% anhydride-grafted polyolefin (Tymor 1N04 adhesive concentrate from Morton International), and 10% low density polyethylene (PE 1042 CS 15 from Rexene). A third layer comprised a nylon 6, i.e. a polycaprolactam (Ultramid KR-4407 F from BASF). A fourth layer comprised ethylene vinyl alcohol copolymer (Soarnol ET from Morton International). Fifth and sixth layers comprised the same composition as the third and second layers respectively. The seventh layer, forming the heat sealable layer of the laminate, comprised 77% ethylene octene copolymer (Dowlex 2244 A from Dow), 15% ethylene/hexene/butene copolymer ( a homogeneous polymer, Exact 3016 from Exxon), and 8% of an antiblock polyethylene masterbatch including 86% linear low density polyethylene, 13% diatomaceous silica, and 1% amide of erucic acid. The relative percent of the laminate formed by each layer, measured by relative thickness, starting with the first layer: 25/7/7/5/8/8/40 These extrudates were joined in the arrangement described where they entered a coextrusion die. The resulting composite exited the die lips and was quenched, then wound into mill logs. The resulting laminate had an overall thickness of about 3 mils. EXAMPLE 2 The laminate of Example 1 was bonded at an outer sealant layer to a heat-resistant film by means of conventional lamination methods. The heat-resistant film was a biaxially oriented polyethylene terephthalate film (EG polyester film from STC Films) having a thickness of .48 mils. Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be utilized without departing from the principles and scope of the invention, as those skilled in the art will readily understand. Accordingly, such modifications and variations may be practiced within the scope of the following claims. For example, layer 20, the outer abuse layer, can also function as a heat sealable layer. This would be useful for example in applications where a fin seal ' is to be made, such as in certain VFFS operations. Layer 20 can therefore comprise any of the materials of layer 28 discussed above. Layer 20 can in effect comprise two layers: the sealable layer per se as described above, and a bulk sealant layer which is preferably disposed adjacent to the sealable layer, and preferably provides a relatively low-cost material compatible with the homogeneous ethylene copolymer, and which contributes to the overall seal performance of the laminate. These materials are preferably heterogeneous ethylene copolymer, e.g. heterogeneous ethylene alpha-olefin copolymer such as linear low density polyethylene or very low density polyethylene. By practicing this alternative embodiment, the benefits of the heat sealable homogeneous ethylene copolymer are substantially retained, while reducing the cost of the overall laminate by using a relatively thin heat sealable layer combined with a relatively thicker lower cost adjacent bulk layer.

Claims: WHAT IS CLAIMED IS: 1. A laminate comprising: a) a core layer comprising an oxygen barrier polymer; b) a heat sealable layer comprising a homogeneous ethylene copolymer; c) an outer abuse-resistant polymeric layer; and d) an intermediate layer disposed between the core layer and each of the heat sealable layer and the outer layer, and comprising a polymeric adhesive. 2. The laminate of claim 1 further comprising a polyamide layer disposed on each surface respectively of the core layer, between the core layer and each respective intermediate layer. 3. The laminate of claim 1 further comprising a heat resistant polymeric film which is bonded to the outer abuse-resistant polymeric layer of the laminate. 4. The laminate of claim 3 further comprising a polyamide layer disposed on each surface respectively of the core layer, between the core layer and each respective intermediate layer. 5. The laminate of claim 1, wherein the oxygen barrier polymer comprises a member selected from the group consisting of ethylene vinyl alcohol copolymer, vinylidene chloride copolymer, polyamide, polyester, and blends thereof. 6. The laminate of claim 1, wherein the homogeneous ethylene copolymer comprises a member selected from the group consisting of metallocene catalyzed ethylene alpha-olefin copolymer, metallocene catalyzed ethylene alpha-olefin copolymer with long-chain branching, metallocene catalyzed ethylene styrene copolymer, and blends thereof. 7. The laminate of claim 1, wherein the heat sealable layer comprises a blend of a homogeneous ethylene copolymer and a heterogeneous ethylene copolymer. 8. The laminate of claim 1, wherein the heterogeneous ethylene copolymer comprises ethylene alpha-olefin copolymer. 9. The laminate of claim 1, wherein the outer polymeric abuse-resistant layer comprises a member selected from ethylene alpha-olefin copolymer, ethylene vinyl acetate copolymer, polyamide, copolyamide, propylene polymer or copolymer, and blends thereof. 10. The laminate of claim 1 wherein the polymeric adhesive comprises an acid or acid anhydride grafted polyolefin. 11. The laminate of claim 2, wherein the polyamide comprises a member selected from the group consisting of nylon 6, nylon 12, nylon 66, nylon 6, 12, nylon 6,66, nylon 1 1, and blends thereof. 12. The laminate of claim 3, wherein the heat resistant film comprises a member selected from the group consisting of ethylene alpha-olefin copolymer, blends of ethylene alpha- olefin copolymer and ethylene unsaturated ester copolymer, oriented polypropylene, biaxially oriented nylon, polyethylene terephthalate, and blends thereof. 13. A package comprising: a) a food product; b) a pouch containing the food product, the pouch having a longitudinal seal, and the pouch constructed from a laminate comprising i) a core layer comprising an oxygen barrier polymer; ii) a heat sealable layer comprising a homogeneous ethylene alpha-olefin copolymer; iii) an outer abuse-resistant polymeric layer; and iv) an intermediate layer disposed between the core layer and each of the heat sealable layer and the outer layer, and comprising a polymeric adhesive. 14. The package of claim 13, wherein the longitudinal seal comprises a lap seal. 15. The package of claim 13, wherein the longitudinal seal comprises a fin seal. 16. The package of claim 13, wherein the ends of the pouch are closed by transverse seals. 17. The package of claim 13, wherein the ends of the pouch are closed by metal clips. 18. The package of claim 13, wherein the pouch has a generally tubular shape. 19. The package of claim 13, wherein the laminate further comprises a polyamide layer disposed on each surface respectively of the core layer, between the core layer and each respective intermediate layer. 20. The package of claim 13, wherein the laminate further comprises a heat resistant polymeric film which is bonded to the outer abuse-resistant polymeric layer of the laminate. 21. The package of claim 20, wherein the laminate further comprises a polyamide layer disposed on each surface respectively of the core layer, between the core layer and each respective intermediate layer. 22. The package of claim 13, wherein the homogeneous ethylene copolymer is a member selected from the group consisting of metallocene catalyzed ethylene alpha-olefin copolymer, metallocene catalyzed ethylene alpha-olefin copolymer with long-chain branching, and metallocene catalyzed ethylene styrene copolymer. 23. The laminate of claim 1 wherein the outer polymeric abuse-resistant layer comprises a homogeneous ethylene copolymer. 24. The laminate of claim 1 wherein the outer polymeric abuse-resistant layer comprises a first, outermost layer comprising a homogeneous ethylene copolymer, and a second, bulk sealant layer comprising a heterogeneous ethylene copolymer. ' 25. The laminate of claim 1, wherein the heat sealable layer comprises a first, outermost layer comprising a homogeneous ethylene copolymer, and a second, bulk sealant layer comprising a heterogeneous ethylene copolymer.

Inventors: BAUER FRANK T, DAVIS MARK, KENNEDY THOMAS D, WATSON RICHARD K, BAUER, FRANK, T., DAVIS, MARK, KENNEDY, THOMAS, D., WATSON, RICHARD, K.
Applicants: GRACE W R & CO, W.R. GRACE & CO.-CONN.
Application year: 1995
Main classification: B32B27
IPC codes: B32B27, B65D65