FR2717489A1 - Co-extrudable binder for easily cuttable multi-layer laminates - Google Patents

Abstract

Co-extrusion binder compsns. are claimed, as are also co-extruded multi-layer composites in which the binder forms a layer between (i) a polystyrene, polycarbonate or polyester layer and (ii) a polyolefin, ethylene/vinyl alcohol copolymer, polyamide or polyester layer, the binder comprising, (A) a polymer which is (A1) a polymer obtd. by grafting an ethylenically unsatd. acid or anhydride (or deriv.) onto (a) a high impact or crystalline styrene homo-or co-polymer or (b) an elastomeric styrene diene or sequence block copolymer which is opt. hydrogenated and which is not the only polymer (A) or (B); (A2) at least one polymer (b) admixed with at least one polymer (B1) defined below; (A3) co-grafted polymer obtd. by grafting a polymer already grated with one of the above grafting monomers on a mixt. of (i) polymer (a) above and (ii) at least one of (c) EVA copolymers, ethylene homopolymers or ethylene/ alpha -olefin copolymers with the provisos that the acrylate copolymer is not more 40 wt.% of the mixt. and that the polystyrene content is below 30 wt.% when (A3) is the predominant component of the binder; or (A4) a grafted polymer obtd. by co-grafting of one or more of the grafting monomers above a polymer (a) to which a tackifying resin has been added, this grafted polymer also contg. a polymer of type (B1) below; and opt. also (B) a polymer (B) which is (B1) a polymer obtd. by grafting \- one of th above grafting monomers (see(A1)) onto polymer (c) (see(A3)); or (B2) ethylene/ alpha -olefin/vinyl acetate terpolymer or alkyl(meth)acrylate monomer of the type of the above grafting monomers, and/or (C) polymers (a), (b) and (c).

Description

i

  COEXTRUSION BINDER COMPOSITION AND MULTILAYER COMPLEX

  COEXTRUDE IN WHICH SUCH COMPOSITION IS USED AS

ADHESIVE LAYER.

  The present invention relates to a coextrusion binder composition, as well as coextruded multilayer complexes in which said composition is used.

as an adhesive layer.

  Coextruded multilayer complexes having an outer layer of polystyrene, polycarbonate or polyester, especially polystyrene, are commonly used for food containers such as cups and containers such as jars of yogurt, compote, etc., or for

  films, such as thermoformed or heat sealed lids.

  However, in these complexes, the aforementioned outer layer is

  usually lined with a layer of ethylene copolymer -

  vinyl alcohol, polyamide, polyesteramide, polyolefin, etc., or a mixture of these polymers, which have a poor affinity for it, so that there must be an adhesive layer therebetween. By way of examples of multilayer complexes, mention may be made of those with three layers (for example, polyethylene / binder / polystyrene), with five layers (for example, polyethylene / binder / ethylene-vinyl alcohol copolymer / binder / polystyrene), etc. . In the present invention, the complex formed by hot lamination, or plaxing, is also included, wherein a multilayer comprising the binder is extruded on a plate of poly (methyl methacrylate), polystyrene, poly (ethylene terephthalate),

  etc., the binder ensuring in particular the adhesion on the plate.

  Many adhesive formulations have been put

  developed for this purpose and are described in the literature.

  These formulations include, most of the time, an ethylene-vinyl acetate copolymer grafted with maleic anhydride and / or styrene, in combination with a

  another component which is in particular an ethylene copolymer -

  ungrafted vinyl acetate, polystyrene, impact polystyrene, petroleum resin, etc. The compositions described in US Pat. Nos. 4,861,676 and 4,861,677 can be cited 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. thereof to a mixture comprising 40 to 95% by weight of ethylene-(meth) acrylic ester copolymer having 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 can be

  an ethylene-vinyl acetate copolymer.

  European Patent Application No. 0 027 375 also discloses a modified elastomer consisting of

  grafting product of an unsaturated carboxylic acid or its anhydride on a styrene-butadiene copolymer optionally in admixture with a crystalline polyolefin.

  Although some of the many resins presented in the literature are satisfactory in terms of adhesive performance, the latter still needs to be improved. In addition, very often, the multilayer complexes are badly cut out. Such cutting, usually performed after thermoforming, or after filling containers and lidding, is done either by pressing a "net" on a metal table, or by shearing. If the cut is not correct, the thermoformed object remains attached to the sheet from which it was formed. This causes uncontrolled production stoppages and the change of cutting knives. The Applicant Company has therefore sought compositions having adhesive performance correct, or even greater than those of known compositions, but may offer the additional advantage of allowing greater ease of cutting than the latter. For this purpose, according to the present invention, it is firstly proposed a coextrusion binder composition, characterized in that it consists essentially of: at least one polymer (A) chosen from: (Al) graft polymers resulting from the grafting of at least one grafting monomer chosen from ethylenically unsaturated carboxylic acids, the corresponding acid anhydrides and derivatives of these acidic acids and anhydrides, on (a) homopolymers and copolymers of styrene , shock or crystal; and / or (b) styrene-diene elastomeric block or block polymers and those same copolymers in the hydrogenated state;

  (A2) at least one copolymer (b) as defined above.

  top mixed with at least one polymer (B1) as defined below; (A3) graft polymers resulting from cografting from

  at least one grafting monomer as defined above.

on a mixture:

  at least one polymer (a) as defined above

  above; and at least one of (c) ethylene-vinyl acetate copolymers, ethylene-alkyl (meth) acrylate copolymers, ethylene homopolymers and ethylene-α-olefin copolymers, with

  provided that the ethylene-copolymers

  The alkyl (meth) acrylate may not account for more than 40% by weight of the blend subjected to cografting at a polystyrene content of less than 30% by weight, if (A3) is the major constituent of the binder composition; (A4) graft polymers resulting from cografting from

  at least one grafting monomer as defined above.

  on at least one polymer (a) as defined above added with at least one tackifying resin (resin having tackiness) (d), these graft polymers being otherwise mixed

  with at least one polymer (B1) as defined above

  after; and - optionally at least one of: (B) 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 copolymers -acetate

  vinyl, ethylene copolymers -

  alkyl (meth) acrylate, homopolymers of ethylene and ethylene-α-olefin copolymers; and (B2) ethylene-α-olefin or vinyl acetate or alkyl (meth) acrylate-monomer terpolymers of the type of the aforementioned graft monomers; and

  (C) polymers (a), (b) and (c) as defined above

above,

  provided that the polymer (Ai) (b) is not the sole polymer of the binder composition.

  The graft polymers (A1), (B1), the grafted copolymers (A3), all the polymers comprising a resin (d), which is included in the formulations of the compositions of the invention, generally comprise, in a general manner, 0.005 to 5% by weight of units derived from the grafting monomer or monomers, relative to the polymer or mixture of polymers subjected to grafting. The grafting monomers are chosen in particular from (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, itaconic anhydride, maleic anhydride or substituted maleic anhydride. , such as dimethyl maleic anhydride, or a salt, amide, imide and ester of an ethylenically unsaturated carboxylic acid, such as mono- and disodium maleate, acrylamide, maleimide and fumarate.

  Diethyl. Maleic anhydride and maleic acid are preferred.

  The grafting may be carried out by a known method consisting of melting the polymer (s) to be grafted, adding to it grafting monomer and from 50 to 20,000 ppm, relative to the polymer (s), of an initiator. radical polymerization mixture, to be mixed in order to obtain a uniform distribution of the grafting monomer and of the initiator in the polymer (s), to mix the resulting mixture in an extruder at a temperature above

  melting point of the polymer (s), extruding the resultant graft polymer into a shaped article, into pellets or other forms which are then used as such or in admixture with other polymers, for the coextrusion of multilayer structures as will be described below

  after. Apart from this extruder grafting, another possible method may also be the solution grafting of dissolving the polymer (s) to be grafted in a solvent, and adding the grafting monomer (s) and the initiator (s) to the graft. perform the graft polymerization at a temperature between 80 and 150 ° C. The free radical initiator may belong to different families well known to those skilled in the art. Among them, mention may be made of peroxides, peresters, hydroperoxides and diazo compounds. Examples of peroxide include dicumyl peroxide, ditertiobutyl peroxide, benzoyl peroxide, lauroyl peroxide, α, α'-bis (t-butylperoxy-m-isopropyl) benzene, and the like.

  2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-

  2,5-di (t-butylperoxy) -3-hexane. As perester, there may be mentioned tertiary butyl perbenzoate; as

  hydroperoxide, t-butyl hydroperoxide and cumene hydroperoxide, and as a diazo compound, azobisisobutyronitrile.

  Referring to the general definition of the compositions according to the invention, it can be seen that grafting can be carried out, for example on polystyrene, and then, if appropriate, "diluting" the resulting graft polymer with at least one another polymer, itself can be grafted. A

  Another solution is to carry out a cografting for example on a polystyrene and an ethylene-vinyl acetate copolymer, which has the advantage of simplifying the manufacture, the desired composition being obtained directly if the cografting is not followed by a dilution. .

  The polymers (a) used in the composition according to the invention comprise the homopolymers and copolymers of the

  styrene (crystal polymers), and polystyrenes with rubber components (impact polymers), especially those with high impact strength.

  Examples of the styrene copolymers include chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymers, styrene-propylene copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-vinyl chloride copolymers, styrene-vinyl acetate copolymers, copolymers

  styrene-alkyl acrylate (methyl, ethyl, butyl, octyl, phenyl acrylate), styrene-alkyl methacrylate copolymers (methyl, ethyl, butyl, phenyl methacrylate), styrene-α-chloroacrylate copolymers and styrene copolymers -

  acrylonitrile - alkyl acrylate. In these copolymers, the comonomer content is generally up to 20% by weight. Polystyrenes with rubbery components are especially those comprising from 1 to 20% by weight of units derived from the rubbery components which are, for example, butadiene and isoprene. The copolymers (b) are the aforementioned block or block copolymers obtained by copolymerization of styrene and

  a diene such as butadiene and isoprene. Mention may be made of styrene-butadiene, styrene-diblock copolymers

  isoprene and triblock, styrene-butadiene-styrene and styrene-isoprene-styrene. Their preparation makes it possible to obtain linear or branched products. These same copolymers can be hydrogenated. SEBS or SEPS are thus obtained, depending on whether SBS or SIS is used as a base for the hydrogenation. The styrene content of these copolymers is less than or equal to 50% by weight. Styrene / diene weight ratios are in particular between 10/90 and 50/50. Polymers (c), also included in the definition of component (A3), are especially: ethylene-vinyl acetate copolymers having a content of vinyl acetate generally less than% by weight, especially less than 50% by weight; homopolymers of ethylene and copolymers of ethylene and at least one alpha-olefin (all copolymers commonly referred to as PE, LDPE, LLDPE, VLDPE, HDPE, EPR). The alpha-olefin generally has 3 to 12 carbon atoms and is chosen in particular from propylene, butene-1, methyl-4-pentene-1, hexene-1, octene-1 and mixtures thereof. The content of units derived from ethylene is generally at least% by weight and the density of these homo- and copolymers is generally between 0.880 and 0.970; ethylene (meth) acrylate copolymers, in particular of C1-C12 alkyl, having a content of (meth) acrylate generally of between 5 and 60% by weight, preferably between 7 and 40% by weight; alkyl (meth) acrylates, mention may be made of

  Methyl, ethyl and butyl (meth) acrylates.

  On the other hand, an amount of at least one resin having tackiness (d) can be added to at least

  one of the polymers or polymer blends grafted or cografted to result in a grafting or grafting product included in the composition of the invention.

  As tackifying resins (d) which can be used in the composition of the coextrusion binder according to the invention

  in the cografted state, mention may be made of styrenic resins such as poly-methylstyrene resins, rosin resins, rosin ester resins, aliphatic petroleum resins, terpenic resins, terpene-terpene resins and the like.

  phenolic, coumarone, coumarone-indene, aromatic. These resins can not generally represent more than 40% by weight of the composition. Preferably, the content of the composition in these tackifying resins, which depends on the desired melt index, does not exceed 10% by weight.

  On the other hand, some may be hydrogenated, such as rosin resins, aliphatic petroleum resins and terpene resins. Compositions according to the invention which have proved to be particularly advantageous are the following (the total composition representing in each case 100% by weight): compositions consisting of: 5 to 70% by weight, in particular 5 to 45% by weight polystyrenes consisting of at least one impact polystyrene or crystal grafted optionally with non-grafted impact polystyrene, the latter possibly representing up to 40% by weight of the composition; and 30 to 95% by weight, in particular 55 to 95% by weight, of a grafted ethylene-vinyl acetate copolymer or an ethylene-(meth) acrylate copolymer

  grafted alkyl or an ethylene terpolymer -

  vinyl acetate or alkyl (meth) acrylate -

  maleic anhydride, the graftings being grafting with maleic anhydride, optionally mixed with impact polystyrene or crystal and / or an ethylene-vinyl acetate copolymer and / or an ethylene-alkyl (meth) acrylate copolymer; compositions consisting of the maleic anhydride co-grafting product on a mixture of: 5 to 70% by weight, in particular 5 to 45% by weight, of at least one impact polystyrene or crystal; and 30 to 95% by weight, in particular 55 to 95% by weight, of an ethylene-vinyl acetate copolymer and / or an ethylene-alkyl (meth) acrylate copolymer, the condition indicated for A3) being furthermore observed, optionally mixed with impact polystyrene or crystal and / or an ethylene-vinyl acetate copolymer and / or an ethylene-alkyl (meth) acrylate copolymer; compositions consisting of: 10 to 40% by weight of the maleic anhydride co-grafting product on a mixture of impact polystyrene and a minor amount of a tackifying alpha-methylstyrene resin; and 60 to 90% by weight of grafted ethylene-vinyl acetate copolymer or grafted methyl-methyl (meth) acrylate; and compositions consisting of: 10 to 30% by weight of a styrene-butadiene-styrene block copolymer; and 70 to 90% by weight of ethylene-acetate copolymer

  of vinyl grafted with maleic anhydride.

  The present invention also relates to a coextruded multilayer complex, comprising at least once the succession of the following three layers: a layer of polystyrene or polycarbonate or polyester; a layer of the coextrusion binder composition as defined above; and a layer consisting of at least one resin chosen from polyolefins and ethylene-alcohol copolymers

  vinyl, polyamides and polyesters.

  In particular, the following combinations can be mentioned: PS / Binder / EVOH, PS / Binder / PA, PS / Binder / PET, PS / Binder / PO, PS / Binder / EVOH / Binder / PS, PS / Binder / EVOH / binder / PO,

  PS / Binder / EVOH / Binder / PET, PS / Binder / EVOH / PA / Binder / PS o PS = polystyrene; EVOH: ethylene-vinyl alcohol copolymer; PA = polyamide; PET = poly (ethylene terephthalate); PO = polyolefin.

  Polystyrenes PS are as defined above.

  The PO polyolefins here comprise an ethylene-α-olefin copolymer, an ethylene-vinyl acetate copolymer, the ethylene (meth) acrylate copolymers having an alkyl (meth) acrylate content of less than 25% by weight, the low density polyethylenes, high density polyethylenes, polypropylenes and mixtures of these polymers. EVOH ethylene-vinyl alcohol copolymers include saponified ethylene-vinyl acetate copolymers having a degree of saponification of at least 50 mol%. It is preferred that these copolymers contain at least 30 mol% of vinyl alcohol units to obtain good adhesion properties and impermeability to gases. PA polyamides are linear polymers

  having amide acid bonds, obtained by condensation of diamines and dicarboxylic acids, condensation of

  acids or decyclisation of lactams. Representative examples of these polyamides are nylon 6, nylon 6-6, nylon 6-10, nylon 11 and nylon 12.

  The polyesters used in the coextruded complexes of the present invention are polymers obtained by condensation of saturated diacids and glycols. Polyethylene terephthalate obtained from ethylene glycol and terephthalic acid may be mentioned in particular: poly (ethylene terephthalate) copolymers having as copolymerization component a saturated diacid such as

  phthalic acid, isophthalic acid, sebacic acid, adipic acid, azelaic acid, glutamic acid, succinic acid, oxalic acid, etc .; copolymers of poly (ethylene terephthalate) having as copolymerization component a diol such as cyclohexane-1,4-

  dimethanol, diethylene glycol, propylene glycol, etc .; and mixtures of these polymers. The thickness of the complex of the present invention is from 100 Dm to 3 mm, preferably 500 Dm to 2 mm. In the case of the three-layer polystyrene / binder / sealant complex (such as low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer, etc.), the thickness of the complex is from 10035 to 1000 gm, preferably 100 to 600 gm. The thickness of the polystyrene layer of the complex according to the present invention is 30 to 96%, preferably 60 to 90%, of the total thickness of the laminate. The thickness of the composition layer

  binder is 1 to 35%, preferably 2 to 20%, of the total thickness of the complex, and the thickness of the sealant layer is 1 to 35%, preferably 25 to 20%, the total thickness of the complex.

  The peel strength of the complexes of the present invention, in the case where the thickness of the binder layer is 30 μm, is greater than 6 N / 15 mm, generally at least 9 N / 15 mm. Binder compositions according to the present invention and the multilayer complexes using these compositions possess excellent adhesive strength and coextrusion layer separation resistance properties, as well as excellent cutting properties, so that they are very effective. useful for food containers, etc. The following Examples illustrate the invention without however limiting its scope. In these examples, percentages are by weight unless otherwise indicated. The particular compositions of coextrusion binders used in these examples belong to the types II to IX explained in the following Table 1, the type I representing the reference composition. In this table, the constituents are designated using the following abbreviations: PS: Copo EVA polystyrene: ethylene vinyl acetate copolymer Copo EMA: ethylene-methyl acrylate copolymer Terpo EVA / AM ethylene terpolymer - vinyl acetate - maleic anhydride Terpo EDA / AM ethylene terpolymer - butyl acrylate - maleic anhydride

  g AM: grafted with maleic anhydride.

Table 1

  Component Type binder composition of (A) (B) (C) coextrusion I copo EVA g AM (reference) II PS shock g AM copo EVA g AM PS shock III PS shock g AM copo EVA g AM IV copo seq. SBS + copo EVA g AM V PS shock g AM copo EMA g AM VI PS shock g AM terpo EDA or

EVA / AM

  VII PS shock g AM + copo EVA g AM PS crystal g AM VIII (PS shock + copo EVA g AM poly resin α-methylstyrene) g AM IX (PS shock + copo EVA) g AM X (PS crystal + copo EVA) In addition, in these examples, the particular constituents hereinafter have been implemented (see also first column of Table 2). The contents of 20 constituent units of the various graft copolymers are here weight contents, measured by FTIR spectroscopy; the fluidity indices, expressed in g / 10 min. were measured according to ASTM D-1238 in condition (L) (230 ° C / 2.16 kg) in the case of shock PS, crystal PS, and in condition (E) (190 ° C / 2, 16 kg) in the case of shock PS AM, PS crystal AM, and other copolymers and terpolymers; IZOD impact resistance was measured according to ISO 180 / 1A; and the VICAT softening temperature according to ISO 306 B. The melting points were obtained according to

the ATD method.

  Specific constituents used The impact PS 1, 2, 3 and 4 and the PS crystal used in the Examples are polystyrenes marketed under the name "Lacqrène" series by ELF 5 ATOCHEM SA Their characteristics are recalled in Table 2 below:

Table 2

  PS Lacqrene Resistance index Softening temperature m softening (g / 10 min) IZOD VICAT (kJ / m) (OC) shock 1 8350 4.5 13 85 shock 2 7240 4.5 il 87 shock 3 5240 4.5 13 85 shock 4 3351 4.5 8 94 crystal 1160 2.5 98 Preparation of PS shock 1 q AM (Lacqrene 8350 q AM) In a twin screw extruder corotative type Werner 30 (12 sheaths, 30 mm diameter), Lacqrene 8350 impact polystyrene and maleic anhydride were introduced at a rate of 1.5% by weight relative to the impact polystyrene. Laterally, 8500 ppm of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (Trigonox 101) is injected into the extruder at the No. 4 sheath. The displayed temperatures of the sheaths are between 180 ° C. (sheath No. 1) and 210 ° C. (sheath No. 10). The temperature of the material is about C. The residues of free maleic anhydride are removed by degassing at the sheath ne 10. The overall flow rate of the extruder is 20 kg / hour and the speed of rotation of the

  screw of 280 rpm. The graft polystyrene grafted with 0.9% maleic anhydride and having a melt index of 3.2 is obtained.

  Preparation of PS shock 2 q AM (lacqcrene 7240 q AM) The procedure is as for the preparation of PS shock 1 g AM, except that the PS shock 2 is used. The polymer

  obtained is a high impact polystyrene grafted with 0.96% maleic anhydride and having a melt index of 3.3.

  Preparation of shock PS 3 a AM (Lacarene 5240 a AM) The procedure is as for the preparation of PS shock 1 g AM, except that PS shock 3 and 15,000 ppm of

  Trigonox 101. The polymer obtained is a high impact polystyrene grafted with 1.2% maleic anhydride and having a melt index of 3.1.

  Preparation of Crystal PS AM (Lacarene 1160 AM) The procedure is essentially the same as for the preparation of shock PS 1 g AM, except that Lacqrene crystal PS 1160 is used. The level of maleic anhydride introduced is 1.5 % by weight and 1.1% by weight of Trigonox 101 are laterally injected, these amounts being related to crystal PS. The speed of rotation of the screws is rpm, and the flow rate is 10 kg / hour. We get the

  crystal polystyrene grafted with 0.98% maleic anhydride, having a melt index of 3.3.

  Preparation of the EVA to AM Copo In the hopper of a Werner type co-rotating twin screw extruder (see above), an ethylene-vinyl acetate copolymer (vinyl acetate level: 28% by weight; 4), maleic anhydride 0.25% relative to the EVA copolymer and 2,5-dimethyl-2,5-di (t-butyl peroxy) hexane (Luperox 101) at a rate of 200 ppm with respect to the EVA copolymer. The displayed temperatures of the sheaths are between 1709C (sleeve 1) and 220C (sheath 8). The temperature of the material is about 200 ° C. Residues of free maleic anhydride are removed by degassing at the sheath No. 10. The overall flow rate of the extruder is 15 kg / hour. A copolymer is obtained

  EVA grafted with 2000 ppm maleic anhydride, having a melt index of 3 to 3.5, a melting point of 75 ° C and a VICAT softening point of 51 ° C.

  Preparation of the copo EMA g AM In the hopper of a Werner 30 co-rotating twin-screw extruder (see above), an ethylene-methyl acrylate copolymer (methyl acrylate content: 29%, melt index) is introduced. 3.1), maleic anhydride at 0.5% with respect to the EMA copolymer and Luperox 101 at 150 ppm relative to the EMA copolymer. The temperature of the material is about 200 C. The residues of free maleic anhydride are removed by degassing in line. The expected polymer is obtained, an EMA grafted with 2300 ppm of maleic anhydride and having a melt index of 2.5, a melting point of 66 ° C. and a point of

  VICAT softening below 40C.

  The EVA copolymer used in the Examples, marketed by the company ELF ATOCHEM S.A. under the

  denomination "EVATANE 2805", has a vinyl acetate content of 27- 29% by weight, a melt index of 5-

  8 g / 10 min., A melting point of 73 ° C. and a VICAT softening point of 43 ° C.

  The SBS block copolymer used in the Examples is the linear styrene-butadiene-styrene triblock copolymer marketed under the name

"CARIFLEX KX 139".

  The poly-α-methylstyrene resin used in the Examples is the resin marketed by DSM under

  the denomination "KRISTALLEX F 120".

  The EVA / AM terpolymer used in the Examples is an ethylene-vinyl acetate-maleic anhydride terpolymer having a melt index of 7 g / 10 min. and an

  vinyl acetate content by 26%.

  The EDA / AM terpolymer used in the Examples, marketed by the company ELF ATOCHEM S.A. under the name "LOTADER 3700", is an ethylene-butyl acrylate-maleic anhydride terpolymer having a

  fluidity of 6 g / 10 min. and a weight content of butyl acrylate of 30%.

  The following Examples 1 to 25 illustrate the preparation of reference binder compositions and according to the invention (Examples 2 to 25). These compositions were evaluated, for adhesion, after coextrusion at 220 ° C of a five-ply sheet, with a total thickness of 790 microns and having the characteristics reported in the following Table 315:

Table 3

  Number Composition of the layer Denomination Commercial thickness (mm) layer 1 PS shock Lacqrene 600

(ELF ATOCHEM

S.A.) Binder tested

2 30

  3 Copo EVOH Soarnol ET 30 (ethylene-vinyl alcohol copolymer with 62 mol% vinyl alcohol) Binder tested

4 30

Low density PE Lacqten 100

1020 FN 24

(ELF ATOCHEM

  SA) For the evaluation of adherence, the coat is carried out in a laboratory meeting the standards of a material evaluation laboratory, according to the NFT 76-112 part 2 standard, with the following modifications: coat of 90 'instead of 180' and width of

  15 mm test pieces instead of 25 mm.

  The test pieces are taken from the center of the coextruded sheets in the direction of the extrusion. The peel rate is 200 mm / minute. The determination of the peel strengths on the obtained recordings is made according to ISO 6133. The reproducibility of the

  Complete chain (coextrusion / peeling) was checked using the same binder several times at different times and days.

  Example 1 (Reference Example) The five-layer film described above was made with the EVA g AM copo as a binder. This example

  illustrates what can be achieved in terms of peel strength.

Example 2

  In the hopper of a co-kneader Buss PR 46/70 (L / D = 11), equipped with a retaining screw, is introduced a mixture prepared by dry mixing of granules having the weight composition reported in Table 5 The overall flow rate of the plant is 25 kg / h, the speed of rotation of the mixer is 200 rpm and the temperatures of the

  materials between 200 C and 205 C. The speed of rotation of the retaining screw is 33 rpm. It is evacuated at the level of the well 3 of the comalaxer. The "compound" obtained has a melt index of 2.6. It is then used in a five-layer complex prepared as indicated above.

  The peel forces are reported in Table 6.

  Examples 3 to 16 The procedure is as in Example 2 by varying the constituents in their nature and their proportion as

  Table 5 shows the results, indicated in this same table, in terms of peel strength, are always greater than those of Reference Example 1.

Example 17

  Copo EVA g AM and a "cograft" are mixed as in Example 2: (PS shock 1 + polyalpha-methyl resin).

  styrene) prepared as described in the following Example. The results, as to the peel strength, are indicated in the

Table 5.

Example 18

  In a Werner-type twin-screw extruder (12 sheaths), a mixture of granules consisting of 30% by weight of impact PS 4 and 70% by weight of Copo EVA, 0.5% by weight of maleic anhydride and 150 ppm Luperox 101 on a powdery polyethylene carrier. The mixture is extruded at a rate of 15 kg / hour (200 rpm) and a material temperature of about 210 ° C. Volatiles (ungrafted maleic anhydride and peroxide residues) are degassed in line at the barrel 10 of the extruder. The "co-grafted" obtained at the exit of the extruder has a melt index of 2, 2 and a grafting rate of 1600 ppm grafted AM. The binder thus obtained is introduced into a five-layer complex and then coextruded

  as shown in Example 2. The peel strengths obtained are reported in Table 5.

  Examples 19 to 25 The procedure is as in Example 18, but with the variants reported in Tables 4 and 5 below. The

  Table 5 gives the composition and the results concerning the peeling forces.

Table 4

  Example% Flow rate Melt extrusion rate index of maleic graft peroxide grafting (kg / h) co-grafted (AM input organic ppm) intro- (g / 10 min) selected (190- C / (ppm) 2.16kg)

19 0.5 150 15 1.8 2500

0.375 114 20 2.8 2000

21 0.5 150 15 3.8 3300

22 0.5 150 15 4 2700

23 0.5 150 15 3.6 4000

24 0.5 150 15 3 3300

0.375 114 20 3.3 1700

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Claims (7)

  1 - Coextrusion binder composition, characterized in that it consists essentially of: at least one polymer (A) chosen from: (Ai) the graft polymers resulting from the grafting of at least one grafting monomer selected among the ethylenically unsaturated carboxylic acids, the corresponding acid anhydrides and the derivatives of these acidic acids and anhydrides, on (a) homopolymers and copolymers of styrene, shock or crystal; and / or (b) block polymers or styrene-diene elastomer blocks and those same copolymers in the hydrogenated state;   (A2) at least one copolymer (b) as defined above.   top mixed with at least one polymer (B1) as defined below; (A3) graft polymers resulting from cografting from   at least one grafting monomer as defined above. on a mixture:   at least one polymer (a) as defined above   above; and at least one of (c) ethylene-vinyl acetate copolymers, ethylene-alkyl (meth) acrylate copolymers, ethylene homopolymers and ethylene-α-olefin copolymers, with   provided that the ethylene-copolymers   The alkyl (meth) acrylate may not account for more than 40% by weight of the blend subjected to cografting at a polystyrene content of less than 30% by weight, if (A3) is the major constituent of the binder composition; (A4) graft polymers resulting from cografting from   at least one grafting monomer as defined above.   on at least one polymer (a) as defined above added with at least one tackifying resin (d), these graft polymers being furthermore mixed with at least one polymer (B1) as defined below; and - optionally at least one of: (B) 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 copolymers -acetate   vinyl, ethylene copolymers -   alkyl (meth) acrylate, homopolymers of   ethylene and ethylene copolymers -   a-olefin; and (B2) ethylene-α-olefin or vinyl acetate or alkyl (meth) acrylate-monomer terpolymers of the type of the aforementioned graft monomers; and   (C) polymers (a), (b) and (c) as defined above above,   provided that the polymer (A1) (b) is not the sole polymer of the binder composition.   2 - coextrusion binder composition according to claim 1, characterized in that the graft or graft polymers included in its formulation each comprise from 0.005 to 5% by weight of units derived from the grafting monomer or monomers. 3 - Composition of coextrusion binder according to one   Claims 1 and 2, characterized in that the grafting monomers are chosen from the acid   (meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, itaconic anhydride, maleic anhydride or substituted maleic anhydride, such as dimethyl maleic anhydride, or a salt, amide, imide and ester of an ethylenically unsaturated carboxylic acid, such as mono- and disodium maleate, acrylamide, maleimide and diethyl fumarate, and   especially maleic anhydride and maleic acid. 4 - coextrusion binder composition according to one of claims 1 to 3, characterized in that the   Polymers (a) are selected from homopolymers of styrene, styrene copolymers and rubbery styrene polymers having from 1 to 20% by weight of units derived from rubbery components. 5 - Composition of coextrusion binder according to one   Claims 1 to 4, characterized in that the block copolymers are chosen from copolymers   styrene-butadiene, styrene-isoprene, styrene-butadiene-styrene, styrene-isoprene-styrene, the styrene / diene weight ratios being between 10/90 and 50/50. 6 - Coextrusion binder composition according to one of claims 1 to 5, characterized in that the   Ethylene-vinyl acetate copolymers (c) have a vinyl acetate content of less than 60% by weight. 7 - Composition of coextrusion binder according to one   Claims 1 to 6, characterized in that an amount of at least one resin having tackiness (d)   is added to at least one of the polymers or polymer blends grafted or cografted to yield a grafting or grafting product entering the composition.   8 - coextrusion binder composition according to one of claims 1 to 7, characterized in that the   Tackifying resins (d) are chosen from amethylstyrene resins, optionally hydrolyzed rosin resins, rosin ester resins, optionally hydrogenated aliphatic petroleum resins,   terpenic resins where appropriate hydrogenated, terpenesphenolic, coumarone, coumarone-indene resins, aromatic resins. Composition according to one of claims 1 to   8, characterized in that its content of tackifying resin (s) does not exceed 40% by weight, in particular not   does not exceed 10% by weight of the total composition. 10 - Composition according to one of claims 1   at 9, characterized in that it consists of: - 5 to 70% by weight of polystyrene constituted by at least one impact polystyrene or crystal grafted optionally with ungrafted impact polystyrene, the latter possibly representing up to 40% by weight of the composition; and 30 to 95% by weight of a grafted ethylene-vinyl acetate copolymer or an ethylene-grafted alkyl (meth) acrylate copolymer or an ethylene-vinyl acetate or alkyl (meth) acrylate terpolymer maleic anhydride, the graftings being grafting with maleic anhydride, optionally mixed with impact polystyrene or crystal and / or an ethylene-vinyl acetate copolymer and / or   ethylene-alkyl (meth) acrylate copolymer. 11 - Composition according to one of claims 1   at 9, characterized in that it consists of the maleic anhydride co-grafting product on a mixture of: 5 to 70% by weight of at least one impact polystyrene or crystal; and - from 30% to 95% by weight of an ethylene-vinyl acetate copolymer and / or an ethylene-alkyl (meth) acrylate copolymer, the condition set forth in claim 1 in the definition of (A3) being respected, possibly mixed with shock polystyrene or crystal   and / or an ethylene-vinyl acetate copolymer and / or an ethylene-alkyl (meth) acrylate copolymer.   12 - Composition according to one of claims 1   at 9, characterized by the fact that it consists of: - 10 to 40% by weight of the cografting product of maleic anhydride on a mixture of polystyrene shock and a minor amount of a tackifying alpha resin methylstyrene; and 60 to 90% by weight of grafted ethylene-vinyl acetate copolymer or grafted methyl-methyl (meth) acrylate copolymer.   13 - Composition according to one of claims 1   at 9, characterized by the fact that it consists of:   10 to 30% by weight of a styrene-block copolymer   butadiene-styrene; and 70 to 90% by weight of impact polystyrene grafted with maleic anhydride.   14 - multilayer coextruded complex, characterized in that it comprises at least once the succession of the following three layers: a layer of polystyrene or polycarbonate or polyester; a layer of the coextrusion binder composition   as defined in one of claims 1 to 13; and   a layer consisting of at least one resin chosen from polyolefins and ethylene-alcohol copolymers   vinyl, polyamides and polyesters.   15 - Coextruded multilayer complex according to claim 14, characterized in that it consists of one of the following combinations: PS / Binder / EVOH, PS / Binder / PA, PS / Binder / PET, PS / Binder / PO, PS / Binder / EVOH / Binder / PS, PS / Binder / EVOH / Binder / PO, 25 PS / Binder / EVOH / Binder / PET, PS / Binder / EVOH / PA / Binder / PS o PS = polystyrene; EVOH: ethylene alcohol copolymer   vinyl; PA = polyamide; PET = poly (ethylene terephthalate); PO = polyolefin.