FIBROUS CONTAINERS FOR OVENABLE PRODUCTS

Abstract

A laminate and a method for preparing a laminate are provided. The method comprises the steps of providing a container or sheet which comprises a fibrous material, disposing a primer composition onto at least one surface of the container or sheet to form a primer layer on the container or sheet, and also disposing a polymeric liner film onto a surface of the primer layer to form a lined container or sheet. The primer composition comprises at least one sulfopolyester.

Claims

1. A method for preparing a laminate, the method comprising the steps of: a) providing a container or sheet (A) which comprises a fibrous material; b) disposing a primer composition onto at least one surface of the container or sheet to form a primer layer (B) on the container or sheet, wherein the primer composition comprises at least one sulfopolyester; c) disposing a polymeric liner film (C) onto a surface of the primer layer (B), to form a lined container or sheet, wherein the polymeric liner film comprises a polymeric substrate film (C.sub.2) and a heat-sealable layer (C.sub.1), wherein the heat-sealable layer is formed from a PET-based copolyester; d) where a lined sheet is obtained from step c), optionally forming (preferably thermoforming) a lined container from the lined sheet, wherein the laminate consists of the container or sheet (A), the primer layer (B), the heat-sealable layer (C.sub.1) and the polymeric substrate film (C.sub.2).

2. A laminate consisting of a container or sheet (A), a primer layer (B) disposed on at least one surface of the container or sheet, and a polymeric liner film (C) disposed on the primer layer, wherein the container or sheet (A) comprises a fibrous material, wherein primer layer (B) is derived from a primer composition comprising at least one sulfopolyester, and wherein the polymeric liner film comprises a polymeric substrate film (C.sub.2) and a heat-sealable layer (C.sub.1), wherein the heat-sealable layer is formed from a PET-based copolyester.

3. A method for preparing a sealed package, wherein the package comprises a product encapsulated within a lined container which is sealed with a polymeric lidding film, the method comprising the steps of: a) providing a container or sheet (A) which comprises a fibrous material; b) disposing a primer composition onto at least one surface of the container or sheet (A) to form a primer layer (B) on the container or sheet, wherein the primer composition comprises at least one sulfopolyester; c) disposing a polymeric liner film (C) onto a surface of the primer layer (B) to form a lined sheet or lined container; d) where a lined sheet is obtained from step c), forming (preferably thermoforming) a lined container from the lined sheet; e) placing a product within the lined container obtained from step c) or d); f) bonding a polymeric lidding film to the lined container with product therein obtained from step e) in order to obtain a sealed package.

4. A sealed package comprising a product encapsulated within a lined container which is sealed with a polymeric lidding film, wherein the lined container comprises a container (A), a primer layer (B) disposed on at least one surface of the container, and a polymeric liner film (C) disposed on the primer layer, wherein the container (A) comprises a fibrous material and wherein primer layer (B) is derived from a primer composition comprising at least one sulfopolyester.

5. A method as claimed in claim 1 or claim 3, wherein step d) comprises thermoforming a lined container from the lined sheet.

6. A method as claimed in claim 5, wherein steps c) and d) occur simultaneously, such that the heat and pressure applied during the thermoforming step softens the polymeric liner film to a sufficient extent that it forms a bond to the surface of the primer layer (B).

7. A method as claimed in claim 3, or a sealed package as claimed in claim 4, wherein the product comprises a foodstuff.

8. A method or sealed package as claimed in claim 7, wherein the foodstuff is ovenable.

9. A method or sealed package as claimed in claim 8, wherein the ovenable foodstuff is a ready-meal.

10. A method or sealed package according to claim 3 or 4, or according to any of claims 5 to 10 when dependent from claim 3 or 4, wherein the polymeric liner film (C) comprises, or consists of, a polymeric substrate film (C.sub.2).

11. A method or laminate according to claim 1 or 2, or a method or sealed package as claimed in claim 10 wherein the polymeric substrate film comprises polyethylene terephthalate (PET), polyethylene 2,6.sup.naphthalate (PEN), copolyesters comprising (or consisting) of monomeric units derived from terephthalic acid, at least one aliphatic dicarboxylic acid and at least one diol, polylactic acid (PLA), polyethylene furanoate (PEF) and/or polyhydroxybutyrate (PHB), or wherein the polymeric substrate film comprises polyethylene terephthalate or polyethylene naphthalate.

12. A method or laminate according to claim 1 or 2, or a method or sealed package as claimed in claim 10 wherein the polymeric substrate film comprises, and preferably is, a copolyester film wherein the copolyester is derived from: (i) one or more diol(s); (ii) an aromatic dicarboxylic acid; and (iii) one or more aliphatic dicarboxylic acid(s) of the general formula C.sub.nH.sub.2n(COOH).sub.2 wherein n is 2 to 10, preferably 4 to 10, wherein the aliphatic dicarboxylic acid is present in the copolyester in an amount of from about 1 to about 20 mol %, preferably from about 1 to 10 mol %, preferably from about 3 to about 10 mol %, based on the total amount of dicarboxylic acid components in the copolyester, preferably wherein the aromatic dicarboxylic acid is selected from terephthalic acid, isophthalic acid, phthalic acid, 2,5-, 2,6- or 2,7-naphthalenedicarboxylic acid, and is preferably terephthalic acid; preferably wherein the diol is selected from aliphatic and cycloaliphatic glycols, preferably from aliphatic glycols and is preferably ethylene glycol; and preferably wherein the aliphatic dicarboxylic acid is saturated and preferably selected from succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid, preferably from succinic acid, adipic acid, azelaic acid and sebacic acid, and preferably is azelaic acid.

13. A method, laminate or sealed package as claimed in any of claims 1 to 2 or 10 to 12 wherein the polymeric substrate film is a thermoformable film.

14. A method, laminate or sealed package as claimed in any one of claims 1 to 2 or 10 to 13, wherein the polymeric substrate film is uniaxially or biaxially oriented, preferably biaxially oriented.

15. A method, laminate or sealed package as claimed in any one of claims 10 to 14 when dependent from claim 3 or 4, wherein the polymeric liner film further comprises a heat-sealable layer (C.sub.1).

16. A method, laminate or sealed package as claimed in claim 1, 2 or 15, wherein the heat-sealable layer (C.sub.1) is disposed on the polymeric substrate film (C.sub.2) such that the heat-sealable layer (C.sub.1) is in direct contact with both the polymeric substrate film (C.sub.2) and primer layer (B) in the laminate or sealed package.

17. A method, laminate or sealed package as claimed in claim 1, 2 or 15 to 16, wherein the heat-sealable layer is a coating layer.

18. A method, laminate or sealed package as claimed in any of claims 15 to 17 when dependent from claim 3 or 4, wherein the heat-sealable layer is a PET-based copolyester heat-sealable layer.

19. A method or laminate as claimed in claim 1 or 2, or a method or sealed package as claimed in claim 18, wherein the heat-sealable layer is an amorphous PET-based copolyester heat-sealable layer.

20. A method, laminate or sealed package as claimed in any one of claims 1, 2 or 15 to 19 wherein the polymer of the heat-sealable layer is one or more copolyester(s) derived from an aliphatic glycol (preferably ethylene glycol), a first dicarboxylic acid (preferably terephthalic acid) and a second dicarboxylic acid (preferably isophthalic acid or azelaic acid).

21. A method, laminate or sealed package as claimed in any of claims 1, 2 or 15 to 19, wherein the heat-sealable layer softens at a temperature such that a heal-seal bond can be formed at a temperature which is from about 5 C. to about 100 C. below the melting temperature of the polymeric substrate film and the primer layer.

22. A method, laminate or sealed package as claimed in any one of claims 1 to 21, wherein the polymeric liner film is a thermoformable and/or thermoformed polymeric liner film.

23. A method, laminate or sealed package as claimed in any one of claims 1 to 22, wherein the container or sheet comprises paperboard and/or cartonboard.

24. A method, laminate or sealed package as claimed in claim 23, wherein the container or sheet comprises a paperboard tray.

25. A method, laminate or sealed package as claimed in any preceding claim, wherein the primer composition comprises an aqueous coating vehicle.

26. A method, laminate or sealed package as claimed in any preceding claim, wherein the sulfopolyester is derived from 5-sodium sulfo-isophthalic acid and/or or dimethyl 5-sodium sulfo-isophthalate.

27. A method, laminate or sealed package as claimed in claim 26 wherein the primer composition comprises the sulfopolyester in an amount of about 25% to about 35% by weight based on the total weight of the sulfopolyester and the coating vehicle.

28. Use of a primer composition comprising at least one sulfopolyester in a method as claimed in claim 3, or in any one of claims 5 to 27 when dependent from claim 3, for preparing a sealed package.

29. A sealed package having a product therein and obtained and/or obtainable by a method as claimed in claim 3 or any one of claims 5 to 28 when dependent from claim 3.

30. A laminate obtained and/or obtainable by a method as claimed in any of claim 1 or any one of claims 10 to 27 when dependent from claim 1.

Description

THE INVENTION IS ILLUSTRATED BY THE FOLLOWING NON-LIMITING FIGURE WHERE

[0196] FIG. 1 is bar chart plotting the lamination bond strength of various comparative laminates and laminates of the invention as described below.

PROPERTY MEASUREMENT

[0197] The following analyses were used to characterize the laminates described herein: [0198] (i) Intrinsic viscosity (in units of dL/g) of the polyester and polyester film is measured by solution viscometry in accordance with ASTM D5225-98(2003) on a Viscotek Y-501 C Relative Viscometer (see, for instance, Hitchcock, Hammons & Yau in American Laboratory (August 1994) The dual-capillary method for modern-day viscometry) by using a 0.5% by weight solution of polyester in o-chlorophenol at 25 C. and using the Billmeyer single-point method to calculate intrinsic viscosity:

=0.25.sub.red+0.75(ln .sub.rel)/c [0199] wherein: [0200] =the intrinsic viscosity (in dL/g), [0201] .sub.rel=the relative viscosity, [0202] c=the concentration (in g/dL), & [0203] .sub.red=reduced viscosity (in dL/g), which is equivalent to (.sub.rel1)/c [0204] (also expressed as nsp/c where nsp is the specific viscosity). [0205] (ii) Lamination bond strength is measured by the following procedure. The polymeric liner film is sealed (where present, by means of the heat-sealable layer) to a container or, where present, to a primer layer which is disposed on said container. Sealing is effected by using a Sentinel heat-seal machine at a temperature of 140 C., and pressure of 30 psi for 1 sec. Strips (25 mm) of the sealed liner film and tray are cut out and undergo a 180 peel test. The load required to pull the seal apart measured using an Instron Model 4301 operating at a crosshead speed of 250 mm/min. The procedure is repeated and a mean value of results calculated. [0206] (iii) Molecular weight is measured by GPC performed on a Malvern/Viscotek TDA 301 using an Agilent PL HFIPgel guard column plus 230 cm PL HFIPgel columns. A solution of HFIP with 25 mM NaTFAc was used as eluent, with a nominal flow rate of 0.8 mL min.sup.1. All experimental runs were conducted at 40 C., employing a refractive index detector. Molecular weights are referenced to polymethylmethacrylate calibrants. Data capture and subsequent data analysis were carried out using Omnisec software. Samples were prepared at a concentration of 2 mg mL.sup.1, with 20 mg of sample dissolved in 10 mL eluent. These solutions were stirred for 24 h at room temperature and then warmed at 40 C. for 30 mins to fully dissolve the polymer. Each sample was filtered through a 0.45 m polytetrafluoroethylene membrane prior to injection. It will be appreciated that once the M.sub.w and M.sub.n values are known, the PDI may be determined. [0207] (iv) Glass transition temperature is measured by Differential Scanning Calorimetry (DSC). A 10 mg polymer specimen taken from the film is dried for 12 hours under vacuum at 80 C. The dried specimen is heated at 290 C. for 2 minutes and then quenched onto a cold block. The quenched specimen is heated from 0 C. to 290 C. at a rate of 20 C./minute using a Perkin-Elmer DSC7B. The glass transition temperature quoted is onset.

EXAMPLES

[0208] The invention is further illustrated by the following examples. It will be appreciated that the examples are illustrative only and are not intended to limit the scope of the invention as described herein. Unless otherwise specified all parts, percentages, and ratios are on a weight basis. The prefix C before an example indicates that it is comparative example.

[0209] In the examples, coated polymeric liner films were prepared as follows. An uncoated thermoformable transparent biaxially oriented PET-based copolyester film with a thickness of 25 m was used as the polymeric substrate film (C.sub.2), which is commercially available from DuPont Teijin Films under the trade designation Mylar P25. A heat-sealable layer (C.sub.1) was coated on one surface of the film. The heat-sealable layer comprised an amorphous copolyester derived from ethylene glycol, terephthalic acid and azelaic acid.

[0210] A primer composition (B) was then prepared. The primer composition comprised an aqueous dispersion of a sulfopolyester derived from 5-sodium sulfo-isophthalic acid, in an aqueous solution containing 2% n-propanol and 30 wt % solids and a Cymel crosslinking agent. A thin continuous coating of the primer composition was applied directly to the surface of a fibrous sheet (A). Thus, a primer coating layer was formed. The mean thickness of the primer coating was in the range of 20 nm to 5 m. The primer compositions and sheets used in each case are detailed in the specific examples.

[0211] In the following examples, the polymeric liner film was bonded, via the heat-sealable coating layer (C.sub.1) to the fibrous or APET sheet, via the primer layer (B) where present. The lamination bond strength between the sheet and the heat-sealable layer of the polymeric liner film was assessed. The results are provided in FIG. 1.

Reference Example 1

[0212] Reference Example 1 was prepared from a conventional APET sheet. The APET sheet was directly bound to the heat-sealable coating layer of the polymeric liner film described above. Thus, the laminate had an AC.sub.1C.sub.2-layer structure, wherein layer A is the APET sheet, layer C.sub.1 is the heat-sealable coating layer and layer C.sub.2 is the polymeric substrate film.

Example 1

[0213] In this example, Invercote G was used as the fibrous sheet. Invercote G is a paperboard which is commercially available from Iggesund Paperboard. The primer composition and polymeric liner film was as described above. Thus, the laminate had an ABC.sub.1C.sub.2-layer structure, wherein layer A is the fibrous sheet, layer B is the primer layer, layer C.sub.1 is the heat-sealable coating layer and layer C.sub.2 is the polymeric substrate film.

Comparative Example 1

[0214] Invercote G was used as the fibrous sheet and the polymeric liner film was as described above. However, no primer layer was used. Thus, the laminate had an AC.sub.1C.sub.2-layer structure.

Example 2

[0215] In this example, Everest was used as the fibrous sheet. Everest is a cartonboard which is commercially available from Graphic Packaging International. The primer composition and polymeric liner film was as described above. Thus, the laminate had an ABC.sub.1C.sub.2-layer structure.

Comparative Example 2

[0216] Everest was used as the fibrous sheet and the polymeric liner film was as described above. However, no primer layer was formed. Thus, the laminate had an AC.sub.1C.sub.2-layer structure.

Results

[0217] FIG. 1 shows the effect that primer layer (B) had on the lamination bond strength. The laminates of the inventive Examples 1 and 2 exhibit an advantageously strong lamination bond strength relative to the comparative laminates of Comparative Examples 1 and 2 respectively. In particular, the laminate of Example 1 exhibited optimal binding between the polymeric liner film and the sheet, and the lamination bond strength exhibited was similar to the lamination bond strength exhibited by the commercially available APET sheet of Reference Example 1.

[0218] The laminates of the present invention were formed into containers which, after a suitable lidding film was applied, provided leak-free hermetically sealed packages. Additionally, once the package has been used, the polymeric liner film was found advantageously to be readily removed from the fibrous container.