Vinylidene chloride polymer composition comprising at least one sorbate ester

Abstract

The invention pertains to an improved PVDC composition including certain dienophiles qualified for food contact, which possess an optimized balance of effectiveness in preventing discoloration upon exposure to radiation, with no negative impact on the barrier properties, in particular sorbate esters of formula (I), wherein R.sub.1 is a C.sub.1-C.sub.12 hydrocarbon group, preferably a C.sub.1-C.sub.6 alkyl group, to layers made therefrom, to multi-layer assemblies comprising the same, and to the use of said assemblies for packaging, in particular for packaging foodstuffs. ##STR00001##

Claims

1. A composition (C) for the manufacture of flexible films for packaging articles, comprising: a a vinylidene chloride (VDC) polymer, wherein the amount of recurring units derived from vinylidene chloride in the VDC polymer varies from 50 to 99.5 wt %, with respect to the total weight of the VDC polymer; and from 0.05 to 3% by weight (wt %), with respect to the weight of VDC polymer, of at least one sorbate ester of formula (I): ##STR00004## wherein R.sub.1 is a C.sub.1-C.sub.6 hydrocarbon group.

2. The composition (C) of claim 1, wherein the VDC polymer is a copolymer comprising recurring units derived from at least one ethylenically unsaturated monomer copolymerisable with vinylidene chloride selected from the group consisting of vinyl chloride, maleic anhydride, itaconic acid, styrene, styrene derivatives, and the acrylic or methacrylic monomers corresponding to the below general formula:
CH.sub.2=CR.sub.1R.sub.2 wherein R.sub.1 is chosen from hydrogen and —CH.sub.3 and R.sub.2 is chosen from —CN and —COR.sub.3, wherein R.sub.3 is chosen from —OH, —OR.sub.4, and —NR.sub.5R.sub.6 radicals, wherein R.sub.4 is a C.sub.1-C.sub.18 linear or branched alkyl group optionally bearing one or more —OH groups, a C.sub.2-C.sub.10 epoxy alkyl group and a C.sub.2-C.sub.10 alkoxy alkyl group, and wherein R.sub.5 and R.sub.6, same or different, are chosen from hydrogen and C.sub.1-C.sub.10 alkyl groups, optionally bearing one or more —OH groups.

3. The composition (C) of claim 2, wherein the at least one ethylenically unsaturated monomer copolymerisable with vinylidene chloride is selected from the group consisting of maleic anhydride, itaconic acid, acrylic or methacrylic monomers selected from the group consisting of methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, acrylamide, N-methylolacrylamide, and N,N-di(alkyl)acrylamide.

4. The composition (C) of claim 3, wherein the at least one ethylenically unsaturated monomer copolymerisable with vinylidene chloride is methyl acrylate (MA).

5. The composition (C) of claim 4, wherein the VDC polymer has a weight ratio VDC/MA of 90/10 to 94/6.

6. The composition (C) according to claim 1, wherein said sorbate ester of formula (I) is ethyl sorbate.

7. The composition (C) according to claim 1, wherein the amount of said sorbate ester of formula (I) in composition (C) is of at least 0.25% wt, with respect to the weight of VDC polymer; and at most 3% wt, with respect to the weight of VDC polymer.

8. The composition (C) according to claim 7, wherein the amount of said sorbate ester (I) in composition (C) is of at least 0.5% wt, with respect to the weight of VDC polymer; and at most 3% wt, with respect to the weight of VDC polymer.

9. The composition (C) of claim 1, wherein the amount of recurring units derived from vinylidene chloride in the VDC polymer varies from 60 to 98 wt %, with respect to the total weight of the VDC polymer.

10. The composition (C) of claim 9, wherein the amount of recurring units derived from vinylidene chloride in the VDC polymer varies from 85 to 95 wt %, with respect to the total weight of the VDC polymer.

11. A method for manufacturing the composition (C) according to claim 1, wherein the VDC polymer and the sorbate ester of formula (I) are compounded together.

12. A layer (B) made from the composition (C), according to claim 1.

13. A method for manufacturing the layer (B) of claim 12 by extrusion-blowing process, the method comprising: supplying the composition (C) to an extruder and bringing the composition (C) into the molten state by simultaneous action of heat and shear forces; and extruding the the composition (C) which is molten through an annular die to form a tube, and inflating the tube with a gas as it leaves the die surface, so as to obtain the layer (B).

14. A multi-layer assembly (A) comprising at least one layer (B), according to claim 12, said at least one layer (B) being assembled to at least one additional layer (O).

15. The multi-layer assembly (A) of claim 14, wherein materials used for providing at least one layer (O) assembled to a layer (B) are selected from the group consisting of polyolefins, polyethylene, polypropylene, polybutylene; polystyrenes; cellulose esters, cellulose acetate, cellulose propionate, cellulose nitrate; polyvinyl acetate; polymethyl methacrylate, polybutyl methacrylate; polyvinyl alcohol; polyvinyl acetal; polyallyl alcohol; polyallyl acetate; polyesters, polyethylene terephthalate; polyamides, and nylon.

16. The multi-layer assembly (A) of claim 15, wherein at least one layer (O) is made from a thermoplast composition comprising a polyethylene (PE) and/or wherein the at least one layer (O) is made from a thermoplast composition comprising an ethylene-vinyl acetate copolymer (EVA).

17. The multi-layer assembly (A) of claim 14, wherein the layer (B) of the composition (C) is sandwiched between an outer layer (O) and inner layer (O), optionally through the use of one or more than one additional adhesive or tie-layer (T).

18. A method of making the multi-layer assembly (A) of claim 14, wherein the layer (B) is incorporated into an assembly created by coextrusion lamination, adhesive lamination, cast sheet extrusion, tubular water quenched extrusion, air blown extrusions or other film-making process.

19. A package made from the multi-layer assembly (A) according to claim 14, said package being selected from the group consisting of conventional pouches, boil-in-bag pouches, turkey bags, shrinkable pouches, grease resistant pouches, rust and/or mold inhibiting films, pouches and bags, red meat protective film, pouches and bags, moisture control films, vacuum forming raw material, window films, improved weathering films, improved abuse resistant films at a wide range of temperatures, drum and other container liners, bread wraps, wrapping for cheese, containers which are required to be resistant to gas and liquid transmission for medicine, pharmaceuticals, cosmetics, perfumes, pipe line wrapping, floor tiles, bottle cap liners, and crown cap liners.

Description

EXAMPLES

(1) The following reagents were used in the Examples:

(2) Masterbatch (M/B) of PVDC composition: VDC/MA copolymer, which has a weight ratio VDC/MA of 92/8, commercially available as PV910 TAX5A-24-01, and comprises traces of additives (from Solvay).

(3) Dienophiles (All available from Aldrich):

(4) Methyl trans-cinnamate (CAS No. 1754-62-7; purity 99%);

(5) Ethyl trans-cinnamate (CAS No. 103-36-6; purity 99%);

(6) Diethyl maleate (CAS No. 141-05-9; purity 97%);

(7) Diethyl fumarate (CAS No. 623-91-6; purity 98%);

(8) Diallyl maleate (CAS No. 999-21-3; purity 93%);

(9) Ethyl sorbate (CAS No. 2396-84-1; purity ≥97%).

(10) Manufacture of Mono-Layer Films of PVDC Incorporating Different Dienophiles:

(11) Mono-layer films of PVDC composition were produced by extruding 98 wt % of said M/B of PVDC composition incorporating 2 wt % of a different dienophile using one extruder (D=19 mm, L/D ratio of screw=20) with a sheet die of 200×0.6 mm. On exiting the die, the films were cooled to quench and drawn, to a greater or lesser extent, in the machine direction by a 3-roll chill calender. Several films with thicknesses varying from 10 to 60 μm were produced by controlling the drawing rate of the film.

(12) The films were treated at 40° C. in an oven for 2 days and then stored at 23° C. under 50% of relative humidity.

(13) PVDC compositions used in the Examples are summarized in Table 1 below.

(14) TABLE-US-00001 TABLE 1 Comp. Comp. Comp. Comp. Comp. (in wt %) Ex. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 M/B 98  98  98  98  98  98  Ethyl sorbate 2 — — — — — Methyl — 2 — — — — trans-cinnamate Ethyl — — 2 — — — trans-cinnamate Diethyl maleate — — — 2 — — Diethyl fumarate — — — — 2 — Diallyl maleate — — — — — 2

(15) Manufacture of Multi-Layer Assemblies Including a Barrier Layer Made from a Composition of PVDC Incorporating Different Dienophiles

(16) Three-layer film samples of A/B/A (A: EVA copolymer, ESCORENE® UL909 available from Exxon Mobil; B: M/B of PVDC composition available from Solvay) were produced by coextrusion using two extruders, with a feed block with several temperature zones and a sheet die of 200×0.6 mm.

(17) On exiting of the die, the multi-layer films were similarly cooled to quench and drawn, to a greater or lesser extent, in the machine direction by a 3-roll chill calender, so as to have various thicknesses.

(18) Irradiation of Mono-Layer and Multi-Layer Films:

(19) Mono-layer and multi-layer films were irradiated using an electron accelerator with 20 kW power and 10 MeV by IONISOS SA. Said films were handled by computer with automatic continuous treatment by pallet layer conveyor. The radiation doses were adjusted to 30 kGy and/or 120 kGy by controlling the speed of the conveyor belt.

(20) Yellowness Index (YI) Determination

(21) The YI measurement of polymer films was performed according to the standard ASTM E-313 (D65 and 10°) using BYK Gardner Spectrophotometer.

(22) For the mono-layer films, ethyl sorbate (Ex. 1) as a dienophile exhibited very outstanding YI (0.58) at 30 kGy of radiation dose, whereas diethyl maleate (Comp. Ex. 3) showed 0.97, and diethyl fumarate (Comp. Ex. 4) and diallyl maleate (Comp. Ex. 5) followed thereafter (1.37 for both).

(23) For the coextruded multi-layer films (20 μm of PVDC and 50 μm of thickness in total), as also shown in Table 2 below, the experimental results demonstrated that ethyl sorbate (Ex. 1) of the present invention substantially contributed to the reduction of ΔYI (difference of YI before irradiation and after irradiation with 30 kGy and 120 kGy of radiation doses) of PVDC films in comparison with methyl trans-cinnamate (Comp. Ex. 1) and ethyl trans-cinnamate (Comp. Ex. 2).

(24) TABLE-US-00002 TABLE 2 ΔYI 0 kGy 30 kGy 120 kGy Irradiation dose Irradiation dose Irradiation dose Ex. 1 0 0.14 1.96 Comp. Ex. 1 0 0.17 1.47 Comp. Ex. 2 0 0.26 1.46

(25) Oxygen Transmission Rate (OTr) Determination:

(26) OTr measurement was performed according to ASTM D-3985, using OX-TRAN® 2/21, available from MOCON, Inc., at 23° C. and under 0% of relative humidity. Each multi-layer film was sealed between one chamber containing oxygen and the other chamber void of oxygen so that a coulometric sensor measured the oxygen transmitted through the films.

(27) After irradiation, mono-layer films broke during OTr determination because of their brittleness. Therefore, OTr measurement was implemented only for the coextruded multi-layer films before radiation and after irradiation with 30 kGy and 120 kGy of radiation doses. The results were summarized in Table 3 below:

(28) TABLE-US-00003 TABLE 3 Coextruded multi-layer film (in cm.sup.3 .Math. 10 μm/m.sup.2.d.b.) OTr (0 kGy) OTr (30 kGy) OTr (120 kGy) Ex. 1 12.3 8.5 6.9 Comp. Ex. 1 12.3 9.6 6.8 Comp. Ex. 2 12.5 9.3 7.9

(29) As demonstrated in Table 3, all the coextruded multi-layer films exhibited good performance in view of OTr after irradiation with 30 kGy and 120 kGy of radiation doses, suitable for food packaging. However, ethyl sorbate (Ex. 1) exhibited better barrier properties against oxygen.

(30) All the experimental supporting data proved that the films prepared by using PVDC compositions of the present invention, with incorporation of at least one sorbate ester, notably ethyl sorbate as a dienophile, could provide an optimized balance of effectiveness in preventing discoloration of the films upon exposure to radiation, while still ensuring barrier properties to be maintained.