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
1995-03-07
2003-12-02
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S074000, C525S193000, C525S285000
Reexamination Certificate
active
06657006
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a coextrusion binder composition and to coextruded multilayer composites in which the said composition is employed as adhesive layer.
BACKGROUND OF THE INVENTION
Coextruded multilayer composites which have an outer layer of polystyrene, polycarbonate or polyester, especially polystyrene, are commonly employed for food containers such as cups and containers of the yogurt or compote pot type and the like, or for films such as thermoformed or heat-sealed lids. However, in these composites the above-mentioned outer layer is generally lined with a layer of ethylene-vinyl alcohol copolymer, polyamide, polyesteramide, polyolefin and the like, or of a mixture of these polymers, which have a poor affinity for it, with the result that provision must be made for an adhesive layer between the two. By way of examples of multilayer composites there may be mentioned those containing three layers (for example polyethylene/binder/polystyrene), or five layers (for example polyethylene/binder/ethylene-vinyl alcohol copolymer/binder/polystyrene) and the like.
The present invention also includes the composites formed by hot lamination or resin-coating, a technology according to which a multilayer including the binder is extruded over a sheet of poly(methyl methacrylate), polystyrene, poly(ethylene terephthalate) and the like, the binder providing especially the adhesion to the sheet.
Many adhesive formulations have been developed for this purpose and are described in the literature. Most of the time these formulations include an ethylene-vinyl acetate copolymer grafted with maleic anhydride and/or styrene, in combination with another component which is especially an ungrafted ethylene-vinyl acetate copolymer, polystyrene, impact polystyrene, a petroleum resin and the like. The compositions described in U.S. Pat. Nos. 4,861,676 and 4,861,677 may be mentioned, among others.
French Patent Application No. 2 677 658 also discloses an adhesive composition obtained by grafting an unsaturated carboxylic acid or a derivative thereof onto a mixture including 40 to 95% by weight of ethylene-(meth)acrylic ester copolymer which has a (meth)acrylic ester content of 25 to 45% by weight, 5 to 30% by weight of polystyrene and 0 to 30% by weight of a polymer which may be an ethylene-vinyl acetate copolymer.
While, among the many resins presented in the literature, some are satisfactory from the viewpoint of adhesive performance, the latter must still be improved. In addition, the multilayer composites very often do not cut out properly. Such cutting out, generally carried out after the thermoforming or after the filling of the containers and fitting the lid, is performed either by pressure of a metal “net” on a table, or by shearing. If the cutting out is not correct, the thermoformed article remains attached to the sheet from which it has been formed. This gives rise to uncontrolled production stoppages and the changing of the cutter blades.
SUMMARY OF THE INVENTION
We have therefore investigated compositions which have adhesive performances that are correct, or even superior to those of the known compositions, but which can offer the additional advantage of allowing a greater ease of cutting out than the latter.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
These compositions include:
at least one out of
(A1) the graft polymers resulting from the grafting of at least one grafting monomer such as maleic anhydride onto (a) impact or crystal styrene homopolymers and copolymers and/or (b) optionally hydrogenated styrene-diene elastomer block polymers, (b) not being the only polymer in the mixture of (A) and (B);
(A2) at least one copolymer (b) mixed with at least one polymer (B1);
(A3) graft polymers resulting from the cografting of at least one grafting monomer onto a mixture of at least one polymer (a) and of at least one of (c) ethylene-vinyl acetate copolymers, ethylene-&agr;-alkyl (meth)acrylate copolymers, ethylene homopolymers, and ethylene-&agr;-olefin copolymers;
(A4) graft polymers resulting from the cografting of at least one grafting monomer onto at least one polymer (a) to which at least one tackifying resin (d) has been added, these graft polymers being mixed with at least one polymer (B1); and optionally
at least one out of
(B1) graft polymers resulting from the grafting of at least one grafting monomer onto a polymer (c); and
(B2) (ethylene-&agr;-olefin or vinyl acetate or alkyl (meth)acrylate-monomer of the type of the above-mentioned grafting monomers) terpolymers; and
(C) the polymers (a), (b), and (c).
In accordance with the present invention, a coextrusion binder composition is proposed first of all, characterized in that it includes:
at least one polymer (A) chosen from:
(A1) graft polymers resulting from the grafting of at least one grafting monomer chosen from carboxylic acids containing ethylenic unsaturation, the corresponding acid anhydrides and the derivatives of these acids and acid anhydrides, onto
(a) impact or crystal styrene homopolymers and copolymers; and/or
(b) styrene-diene elastomer block polymers and these same copolymers in the hydrogenated state, provided that (b) is not the only polymer in the mixture of (A) and optionally (B);
(A2) at least one copolymer (b) as defined above mixed with at least one polymer (B1) as defined below;
(A3) graft polymers resulting from the cografting of at least one grafting monomer as defined above onto a mixture:
of at least one polymer (a) as defined above; and
of at least one out of (c) ethylene-vinyl acetate copolymers, ethylene-alkyl (meth)acrylate copolymers, ethylene homopolymers and ethylene-&agr;-olefin copolymers, provided that the ethylene-alkyl (meth)acrylate copolymers may not represent more than 40% by weight of the mixture subjected to the cografting in the case of a polystyrene content lower than 30% by weight if (A3) represents the major constituent of the binder composition;
(A4) graft polymers resulting from the cografting of at least one grafting monomer as defined above onto at least one polymer (a) as defined above, to which at least one tackifying resin (resin possessing adhesive bondability) (d) has been added, these graft polymers being furthermore mixed with at least one polymer (B1) as defined below; and optionally
at least one out of:
(B) the polymers chosen from:
(B1) graft polymers resulting from the grafting of at least one grafting monomer as defined above onto a polymer (c) chosen from ethylene-vinyl acetate copolymers, ethylene-&agr;-olefin copolymers, ethylene-alkyl (meth)acrylate copolymers, ethylene homopolymers; and
(B2) (ethylene-&agr;-olefin or vinyl acetate or alkyl (meth)acrylate-monomer of the type of the abovementioned grafting monomers) terpolymers; and
(C) the polymers (a), (b) and (c) as defined above.
In general, each of the graft polymers (A1), (B1), the cografted copolymers (A3) and all the polymers comprising a cografted resin (d), included within the formulations of the compositions of the invention, comprise from 0.005 to 5% by weight of units originating from the grafting monomer(s) relative to the polymer of to the mixture of polymers subjected to grafting. The grafting monomers are chosen especially from (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, itaconic anhydride, maleic anhydride or a substituted maleic anhydride, such as dimethylmaleic anhydride or else a salt, amide, imide and ester of a carboxylic acid containing ethylenic unsaturation, such as mono- and disodium maleate, acrylamide, maleimide and diethyl fumarate. Maleic anhydride and maleic acid are preferred.
The grafting may be performed by a known method consisting in melting the polymer(s) to be grafted, adding thereto the grafting monomer and from 50 to 20 000 ppm, relative to the polymer(s) of a radical polymerization initiator, mixing so as to obtain a uniform distribution of the grafting monomer and of the initiator in the polymer(s), kneading the resulting mixture in an extruder at a temperature above the melting point of the polymer(s), ex
Beuzelin Catherine
Bouilloux Alain
Jammet Jean-Claude
Trolez Yves
Atofina
Cain Edward J.
Pennie & Edmonds LLP
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