Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-01-19
2002-09-17
Woodward, Ana (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S066000, C525S069000, C525S179000
Reexamination Certificate
active
06451911
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is related to a concurrently filed application entitled, “Composition Based On An Ethylene-Vinyl Alcohol Copolymer And Its Use” the inventors being, Denis Bertin, and Yves Germain, based on priority French application 99/00490 filed Jan. 19, 1999, said application being incorporated by reference herein.
The present invention relates to a composition based on an ethylene-vinyl alcohol copolymer (EVOH) and to its use.
EVOH copolymers provide a barrier to many gases and in particular to oxygen. Thus, many articles of food packaging comprise a layer consisting of an EVOH film.
SUMMARY OF THE INVENTION
The present invention relates more particularly to compositions comprising (the total being 100%):
50 to 98% by weight of an EVOH copolymer
1 to 50% by weight of a polyethylene (A)
1 to 15% by weight of a polymer (B) resulting from the reaction (i) of a copolymer (B1) of ethylene and of an unsaturated monomer X grafted or copolymerized with (ii) a polyamide (B2).
BACKGROUND OF THE INVENTION
In general, EVOH copolymers have various excellent properties such as oxygen impermeability, mechanical strength, etc., and find application, as they are, in many uses as films, sheets, materials for containers, textile fibres, etc. However, this copolymer gives rise to a variation in the thickness of the product in the moulding process for manufacturing a film or a sheet, with a consequent reduction in the marketability of the product, and, because of the shortcoming in stretchability and flexibility, gives rise to non-uniform drawing during deep drawing and other processes involving a stretching force, or pinholes during the use of the product, thus imposing serious limitations on its application as a raw material for packaging. The oxygen barrier of EVOH copolymers is greatly reduced when the relative humidity (RH) increases.
In order to overcome these drawbacks, it has been attempted to laminate a material made of an impermeable resin, such as a polyolefin film, on a sheet of EVOH copolymer or to improve the stretchability and flexibility of the moulding by incorporating a polyolefin into the EVOH copolymer.
Patent Application EP 820,381 describes blends of an EVOH copolymer and 5 to 60% by weight of a polar polymer chosen from ethylene-acrylic ester copolymers, ethylene-vinyl acetate copolymers and ethylene-acrylic ester-carboxylic acid anhydride or acrylic acid copolymers. These blends become very difficult to convert as soon as the amount of polar polymer exceeds 10% by weight. The dispersion of the polar copolymer is very poor, which in turn gives poor mechanical properties. If the amount of polar copolymer exceeds 40% by weight the blend is no longer an oxygen barrier.
Application EP 440,535 describes blends of 50 to 99.5% of an EVOH copolymer, 0.4 to 50% of a polyethylene having a relative density of between 0.900 and 0.940 and of the product of the reaction of a polyolefin grafted by an unsaturated carboxylic acid with a polyamide oligomer. The compositions of the present invention are an oxygen barrier and can be easily converted. Further advantages will be described in the following text.
DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described in detail.
The EVOH copolymer is also called a saponified ethylene-vinyl acetate copolymer. The saponified ethylene-vinyl acetate copolymer to be employed according to the present invention is a copolymer having an ethylene content of 20 to 60 mol %, preferably 25 to 55 mol %, the degree of saponification of its vinyl acetate component not being less than 95 mol %.
With an ethylene content of less than 20 mol %, the property of oxygen impermeability under high humidity conditions is not as high as would be desired, whereas an ethylene content exceeding 60 mol % leads to reductions in the oxygen impermeability property, in the printability and in other physical properties. When the degree of saponification or of hydrolysis is less than 95 mol %, the oxygen impermeability property and the wet strength are sacrificed. Among these saponified copolymers, those which have melt flow indices in the range of 0.5 to 100 g/10 minutes are particularly useful.
It should be understood that this saponified copolymer may contain small amounts of other comonomer ingredients, including &agr;-olefins, such as propylene, isobutene, &agr;-octene, &agr;-dodecene, &agr;-octadecene, etc., unsaturated carboxylic acids or their salts, partial alkyl esters, complete alkyl esters, nitriles, amides and anhydrides of the said acids, and unsaturated sulphonic acids or their salts.
The oxygen permeability of the EVOH copolymer films, measured according to ASTM D 3985, is expressed in cm
3
of oxygen per m
2
for 24 hours for a pressure difference of 1 bar and a thickness of 25 &mgr;m. To simplify matters, the oxygen permeability is called O
2
GTR in the rest of the text.
O
2
GTR varies inversely proportionally to the thickness of the film.
An EVOH comprising 38 mol % of ethylene units has an O
2
GTR of 0.72 at 0% RH and 3.1 at 75% RH.
An EVOH comprising 29 mol % of ethylene units has an O
2
GTR of 0.1 at 0% RH and 1.41 at 75% RH. These grades are produced on an industrial scale and are commercially available.
One or the other of these grades is used in different thicknesses depending on the required barrier (type of product to be preserved, preservation time, etc.). The Applicant has discovered that the compositions of the invention, based on an EVOH copolymer containing 29 mol % ethylene, have, in film form, the same barrier properties as a film essentially consisting of an EVOH copolymer containing 38 mol % ethylene but can be very easily converted. This is because the EVOH copolymer, although it is a thermoplastic, is very rigid. Its flexural modulus is about 2000 MPa. The compositions of the invention have a flexural modulus of 1500 MPa as soon as the proportion of polyethylene (A) is at least 15% by weight.
The Applicant has also discovered that films consisting of the compositions of the invention are much less sensitive to moisture, that is to say that O
2
GTR at 75% RH is only 1.3 to 9 times the O
2
GTR at 0% RH and preferably 1.3 to 3.5 times, whereas this factor is 14 in the case of films made of EVOH containing 29% ethylene.
The invention is particularly suitable for EVOH copolymers having an ethylene content ranging from 25 to 45 mol % and MFIs (Melt Flow Index according to ASTM D 1238) ranging from 1.5 to 4 (g/10 minutes at 190° C./2.16 kg) and from 5 to 30 (g/10 minutes at 230° C./2.16 kg).
With regard to the polyethylene (A), this is chosen from ethylene homopolymers or ethylene copolymers.
By way of comonomers, mentioned may be made of:
alpha-olefins, advantageously those having from 3 to 30 carbon atoms.
Examples of alpha-olefins having 3 to 30 carbon atoms as possible comonomers comprise propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene, 1-dococene, 1-tetracocene, 1-hexacocene, 1-octacocene and 1-triacontene. These alpha-olefins may be used by themselves or as a mixture of two or more of them;
the esters of unsaturated carboxylic acids such as, for example, alkyl (meth)acrylates, the alkyls possibly having up to 24 carbon atoms.
Examples of alkyl acrylates or methacrylates are, especially, methyl methacrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and 2-ethylhexyl acrylate;
vinyl esters of saturated carboxylic acids such as, for example, vinyl acetate or vinyl propionate;
unsaturated epoxides.
Examples of unsaturated epoxides are especially:
aliphatic glycidyl esters and ethers, such as allyl glycidyl ether, vinyl glycidyl ether, glycidyl maleate, glycidyl itaconate, glycidyl acrylate and glycidyl methacrylate, and
alicyclic glycidyl esters and ethers, such as 2-cyclohexen-1-yl glycidyl ether, diglycidyl cyclohexene-4,5-dicarboxylate, glycidyl cyclohexene-4-carboxylate, glycidyl 2-methyl-5-norbornene-2-carboxylate and di-glycidyl endo-ci
Bertin Denis
Germain Denis
Robert Patrice
Atofina
Millen White Zelano & Branigan P.C.
Woodward Ana
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