Search

US-12617914-B2 - Composite polymeric film

US12617914B2US 12617914 B2US12617914 B2US 12617914B2US-12617914-B2

Abstract

A composite film comprising a of amide substrate layer having a first and second surface, and a primer coating layer disposed on the first surface of the substrate layer, wherein the primer coating layer is derived from a composition comprising an acid copolymer resin, an organic crosslinker and an acid catalyst. A heat-sealable coating is applied on the primer.

Inventors

  • Shengsheng Liu
  • ERIK JEVON NELSON

Assignees

  • MYLAR SPECIALTY FILMS U.S. LIMITED PARTNERSHIP

Dates

Publication Date
20260505
Application Date
20210324
Priority Date
20200331

Claims (20)

  1. 1 . A composite film comprising a polyamide substrate layer having a first and second surface; a primer coating layer disposed on the first surface of the substrate layer, wherein the primer coating layer is derived from a composition comprising an acid copolymer resin, an organic crosslinker and an acid catalyst; and a heat-sealable polymeric coating layer disposed on the primer coating layer, wherein the heat-sealable polymeric coating layer has a thickness of between from 2 to 6 microns.
  2. 2 . A composite film according to claim 1 , wherein the polyamide substrate is uniaxially or biaxially oriented.
  3. 3 . A composite film according to claim 1 , wherein the polyamide is a thermoplastic crystallisable linear aliphatic polyamide.
  4. 4 . A composite film according to claim 1 , wherein the thickness of said polyamide substrate is from about 5 to about 150 μm.
  5. 5 . A composite film according to claim 1 , wherein the acid copolymer resin is selected from ethylene/acrylic acid (EAA) copolymers; ethylene acrylate copolymers functionalized with COOH groups; ethylene/methacrylic acid (EMAA) copolymers; methyl acrylate/acrylic acid (MAAA) copolymers; and ethylene/vinyl acetate (EVA) copolymers functionalized with COOH groups; and mixtures thereof.
  6. 6 . A composite film according to claim 1 , wherein the primer coating layer comprises from 60% to 99.9% by weight of the acid copolymer resin based on the total weight of the primer coating layer.
  7. 7 . A composite film according to claim 1 , wherein the organic crosslinker is selected from melamine crosslinking agents, polyisocyanate crosslinking agents, polycarbodiimide crosslinking agents, crosslinkers comprising multiple oxazoline groups, crosslinkers comprising multiple aziridine groups, and mixtures thereof.
  8. 8 . A composite film according to claim 1 , wherein the organic crosslinker is one or more melamine crosslinking agent(s).
  9. 9 . A composite film according to claim 1 , wherein the primer coating layer is derived from a composition comprising from 0.05% to 25% by weight of the organic crosslinker based on the total weight of the primer coating layer.
  10. 10 . A composite film according to claim 1 , wherein the acid catalyst is selected from an organic sulfonic acid, sulphuric acid and ammonium nitrate.
  11. 11 . A composite film according to claim 1 , wherein the acid catalyst is an organic sulfonic acid, wherein the organic sulfonic acid is selected from p-toluenesulfonic acid and dodecylbenzenesulfonic acid.
  12. 12 . A composite film according to claim 1 , wherein the primer coating layer is derived from a composition comprising from 0.01% to 2% by weight of the acid catalyst based on the total weight of the primer coating layer.
  13. 13 . A composite film according to claim 1 , wherein the primer coating layer further comprises a slip-aid, an anti-blocking agent and/or a tackifying resin.
  14. 14 . A composite film according to claim 1 , wherein the primer coating layer is derived from a composition further comprising a coating vehicle.
  15. 15 . A composite film according to claim 1 , wherein the primer coating layer has a dry thickness of 0.1 to 1.0 μm.
  16. 16 . A composite film according to claim 1 , wherein the heat-sealable polymeric coating layer is formed from a polymer selected from the group consisting of polyvinylidene chloride (PVDC), ethylene vinyl acetate (EVA), polyolefins, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, and mixtures thereof.
  17. 17 . A composite film according to claim 16 , wherein the heat-sealable polymeric coating layer is formed from EVA polymer having a vinyl acetate content in the range of 9% to 40%.
  18. 18 . A composite film according to claim 1 , wherein the heat-sealable polymeric coating layer has a thickness of from 2 to 4 μm.
  19. 19 . A composite film according to claim 1 , wherein the composite film has a total thickness of no more than 60 μm.
  20. 20 . A sealed container comprising a receptacle containing a food product, and a lid formed from a composite film as defined in claim 1 .

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a national stage filing under 35 U.S.C. § 371 of International Application No. PCT/IB2021/052423, filed Mar. 24, 2021, which claims the benefit of United Kingdom Application No. GB 2004676.9, filed Mar. 31, 2020. International Application No. PCT/IB2021/052423, filed Mar. 24, 2021, is hereby incorporated herein by reference in its entirety. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a composite film (10), in which the composite film comprises a polyamide film (2), a primer coating layer (3) and a heat-sealable polymeric coating layer (4). FIG. 2A shows the evaluation of the peelability of the composite film of Comparative Example 3 to a polypropylene (PP) substrate. FIG. 2B shows the evaluation of the peelability of the composite film of Comparative Example 3 to a crystalline polyethylene terephthalate (CPET) substrate. FIG. 3 shows the evaluation of the peelability of the composite film of Example 13 to itself, to a CPET substrate and to a PP substrate (left to right). The present invention relates to composite polymeric films which comprise a polyamide substrate layer, and processes for the production thereof. The film is particularly suitable for use as a sealable film, particularly a sealable and peelable film for packaging applications, particularly for the packaging of food, such as ready-prepared ovenable meals. In particular, the film of the present invention is suitable for use as a lid for a container which contains a foodstuff such as a ready-prepared ovenable meal. Plastic containers are commonplace in packaging applications, such as food packaging, and in particular for packaging convenience foods, for example ready-prepared ovenable meals which are warmed either in a microwave oven or in a conventional oven. Also known are “dual-ovenable” containers which may be warmed in either a microwave or a conventional oven. The container may be formed of polyester, such as polyethylene terephthalate (PET), polypropylene (PP) or polyethylene (PE) or may be PVDC-coated. A container in widespread use for ovenable meals is an APET/CPET container, which consists of a composite material having an amorphous PET layer on top of a crystalline PET layer. Other suitable types of container include a foil tray (particularly an aluminium foil tray), a metallised tray and a tray formed from PET-coated cartonboard or paperboard. Of particular utility are trays formed from metallised (particularly flash-metallised) PET cartonboard. Such containers require lids which not only securely seal the container, in order to prevent leakage and drying out of the packaged contents, and to provide a protective barrier against insects, bacteria and air-borne contaminants during storage, but which are also able to be readily peeled from the container on opening. Other important requirements of the lids are that they should not stick to the packaged contents and that they should be able to withstand the heat generated in the oven. Container lids are typically made from composite films comprising a flexible polymeric substrate and a heat-sealable polymeric layer, and are often referred to as “lidding” films. The manufacture of sealed containers using lidding films involves the formation of a seal between the lidding film and the container. This seal is formed by placing the lid on top of the container and applying heat and pressure in order to soften or melt the sealable coating layer so that it adheres to the surface of the container and forms an effective seal between the lid and the container. Polyamide film has been used as a flexible substrate for lidding films because of its excellent thermal stability, puncture resistance, chemical resistance and abrasion resistance. However, polyamide films are not readily heat-sealable and cannot be heat sealed below their melting point. Thus, it is necessary to use composite films. It is challenging to provide composite films consisting of a polyamide substrate and a heat-sealable polymeric layer because it has proven difficult to identify heat-sealable polymeric layers which can adhere directly to polyamide substrates and form good coating layers, particularly ones which exhibit the adhesive strength and cohesive strength required to provide good heat seal properties. For instance, the heat-sealable polymeric layer tends to delaminate and the continuous peel force tends to sharply decrease during the peel. Another problem with known composite films is that the films tend to exhibit poor peelability characteristics, in that the films typically do not exhibit a clean peel, i.e. residue of the heat-sealable layer is visible on the surface of the container after peeling the lidding film therefrom. In order to improve the sealability characteristics, composite films may be provided with one or more additional polymer film interlayer(s) between the polyamide substrate and the heat-sealable polymeric layer. Typically, the polyamide sub