WO2007135342A1

WO2007135342A1 - Multiple layer coextrusion method using an intermediate ductile layer

Info

Publication number: WO2007135342A1
Application number: PCT/FR2007/051316
Authority: WO
Inventors: Pierre Gerard; Christophe Le Crom
Original assignee: Arkema France
Priority date: 2006-05-23
Filing date: 2007-05-23
Publication date: 2007-11-29
Also published as: FR2901557B1; FR2901557A1

Abstract

The invention relates to a method for protecting a thermoplastic polymer, whereby the following layers are superimposed by coextrusion, hot-pressing or multi-injection, in the following order: a protective layer (I) comprising a PMMA; an intermediate ductile layer (II) comprising a sequenced copolymer of formula BAn consisting of a polymer sequence B comprising at least 60 wt. % of at least one (meth)acrylic monomer having a T<SUB>g</SUB> lower than -5°C, and n polymer sequences A which are connected to the polymer sequence B by covalent bonds, n representing an integer between 1 and 10, and comprise at least 60 wt. % of at least one (meth)acrylic monomer having a T<SUB>g</SUB> higher than 0°C, such that sequence B and/or sequences A comprise between 0.2 and 20 wt. % of at least one compound selected from acrylic acid, methacrylic, styrene, alphamethyl styrene, maleic anhydride, acrylonitrile, glycidyl acrylate, and glycidyl methacrylate; and a layer of at least one thermoplastic polymer (III).

Description

MULTILAYER COEXTRUSION PROCESS USING LAYER

INTERMEDIATE DUCTILE

The present invention relates to a method for protecting a thermoplastic polymer with an acrylic polymer. The invention also relates to a multilayer structure comprising the thermoplastic polymer and the acrylic polymer and to the uses of this multilayer structure. Certain thermoplastic polymers such as high impact polystyrene (HIPS), ABS (acrylonitrile-butadiene-styrene) resins, PVC are widely used in the manufacture of articles and molded articles that are frequently encountered in everyday life caravans or mobile homes, profiles of windows, doors or shutters, ...). Although these polymers have a certain mechanical strength and are relatively inexpensive, they have poor resistance to aging (in the broadest sense, that is to say, resistance to light, scratch, solvents and chemicals ...). This is why it is now common to cover these plastics with a protective layer.

Due to their mechanical properties and excellent resistance to aging, scratching and chemicals, acrylic polymers are ideally suited to protect thermoplastic polymers. In addition, once protected, thermoplastic polymers also have a better gloss (gloss) characteristic of acrylic polymers. The protective layer must adhere perfectly to the polymer to be protected in order to guarantee a good level of protection over time. The plastic protected by the The protective layer must also maintain its resistance to impact.

European applications EP 1541339 A1 and EP 1543953

A2 both describe a multilayer acrylic film that can protect thermoplastic polymers and give them a new appearance. According to one of the forms of the invention, the film comprises an acrylic surface layer (A), a layer (B3) made from a block copolymer and a possible acrylic layer (C). The film is applied in two stages. In the ^st step, the film, which may be previously stored in roll form, is preformed to the required geometry, and in a 2 ^nd step, the thermoplastic melt is injected into a mold and the film is applied on the molten thermoplastic.

The use of an acrylic film has disadvantages. First of all, because of its rigidity, such a film is not handled (that is, stored in roll form, then unrolled) easily. Then, the dimensions of the film sold to a transformer are not necessarily adapted to those of the mold, which can cause significant rejects. Finally, there may be the problem of adhesion of the film to the polymer to be protected. Indeed, the film is rigid when applied to the molten thermoplastic. In contact with the latter, it softens which facilitates the contact and adhesion but the softening may not be homogeneous and regular, especially in the presence of a mold with complicated geometry, resulting in inhomogeneous adhesion of the film. In the two aforementioned European applications, the thickness of the film (that is to say the set of layers (A) / (B3) / optionally (C)) is limited to 300 microns, preferably even to 100 microns. , to guarantee a good easy handling of the film and a good adhesion to the plastic by the "Film Insert Molding" technique used.

The Applicant has found that it is possible to protect a thermoplastic polymer with a protective layer which adheres perfectly and which does not affect the impact resistance of the thermoplastic polymer. The process used is simpler and more economical than the process that uses an acrylic film. It also provides thicker protective structures.

The prior art

European application EP 1174465 A1 discloses a multilayer structure comprising a substrate coated with a surface layer composed of an acrylic copolymer, which is preferably a copolymer based on methyl methacrylate (MMA) and butyl methacrylate.

European application EP 1548058 A1 describes a multilayer structure comprising a substrate covered with a surface layer composed of a core-shell type acrylic copolymer.

International Application WO 00/08098 discloses a multilayer structure comprising a substrate covered with a surface layer composed of an acrylic copolymer based on MMA and an alkyl acrylate and optionally a kernel-type impact modifier. bark.

International application WO 2004/087786 discloses a monolayer film comprising an acrylic block copolymer. The film is used to cover structural plastics (ABS, PC, PP, PVC, ...). US Pat. No. 4,350,742 discloses a multilayer structure comprising a polystyrene layer and a layer of an acrylic polymer. Membership between layer is reinforced when the polystyrene contains as comonomer a carboxylic acid CC, β-unsaturated.

US Pat. No. 6,455,171 discloses a multilayer structure comprising an acrylic surface layer, an intermediate ductile layer based on a copolymer of an olefin and an acrylate or block copolymer composed of a conjugated diene and a a vinylaromatic monomer.

US Pat. No. 6,239,226 B1 describes a block copolymer that can be used to form a layer on the surface of various types of plastics such as ABS, ASA, PVC, impact PS or impact-strengthened PMMA. There is no mention of the protective surface layer (I).

Brief description of the invention

The invention relates to a method for protecting a thermoplastic polymer consisting of superimposing in the order of coextrusion, hot pressing or multiinjection: • a protective layer (I) comprising a PMMA,

An intermediate ductile layer (II) comprising a block copolymer of formula BA _n composed of: a polymer block B comprising by weight at least 60% of at least one (meth) acrylic monomer having a T _{g of} less than -50 ^%; C, and n polymer sequences A, linked to the polymer block B by covalent bonds, n denoting an integer of between 1 and 10, comprising by weight at least 60% of at least one (meth) acrylic monomer having a T _g greater than ⁰ ° C., and as the B block and / or the a blocks comprise from 0.2 to 20 weight% of at least one compound selected from acrylic acid, methacrylic acid, styrene, alpha methyl styrene, maleic anhydride, acrylonitrile, glycidyl acrylate, glycidyl methacrylate. A layer of at least one thermoplastic polymer (III). According to a variant, an intermediate layer (I ') comprising at least one pigment and / or a dye is placed between the layers (I) and (II).

The invention also relates to a multilayer structure comprising in the order the layers (I), optionally (I '), (II) and (III) previously described, these layers being arranged one on the other in the order (I) to (III) indicated.

The invention also relates to the use of the multilayer structure for the manufacture of objects and articles of everyday life such as: housings or casings for lawnmowers, chainsaws, jet skis, household appliances ; car roof boxes, body parts; - number plates; exterior wall panels of caravans and mobile homes; exterior panels of refrigerators; shower enclosure panels; - building doors; window moldings; cladding panels.

The invention will be better understood on reading the following detailed description and nonlimiting examples of implementation thereof, and on examining the appended figures. figures

FIG. 1 represents a multilayer structure 1 comprising three layers referenced 2, 3 and 4 arranged one on the other. Layer 2 corresponds to the protective layer (I), layer 3 to the intermediate ductile layer (II) and layer 4 to the thermoplastic polymer (III).

FIG. 2 represents a multilayer structure 5 comprising four layers referenced 2, 2 ', 3 and 4 arranged one on the other. The layer 2 corresponds to the protective layer (I), the layer 2 'to the intermediate layer (I'), the layer 3 to the intermediate ductile layer (II) and the layer 4 to the thermoplastic polymer (III). FIG. 3 represents a diagram of the device for measuring the resilience 6. The bar 7 is placed on supports 8 and 8 '. The striker 9 applies a force F to the bar 7. A device not shown continuously records the force and displacement.

Detailed description of the invention definitions

Tg is the glass transition temperature of a polymer. By extension, be denoted T _g of a monomer Tg of one homopolymer obtained by radical polymerization of said monomer. The term (meth) acrylate designates for simplicity an acrylate or a methacrylate.

The term "(meth) acrylic monomer" denotes a monomer which may be: an acrylic monomer such as alkyl acrylates, preferably C ₁ -C 10 alkyl acrylates, cycloalkyl or aryl acrylates such as methyl acrylate, ethyl, propyl, n-butyl, isobutyl, tert-butyl, 2- ethylhexyl, hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate, alkyl ether acrylates such as 2-methoxyethyl acrylate, alkoxy- or aryloxypolyalkyleneglycol acrylates such as methoxypolyethylene glycol acrylates or ethoxypolyethylene glycol acrylates aminoalkyl acrylates such as 2- (dimethylamino) ethyl acrylate, silyl acrylates, glycidyl acrylate, methacrylic monomer such as alkyl methacrylates, preferably C ₂ -C ₁₀ alkyl, , cycloalkyl or aryl such as ethyl, propyl, n-butyl, isobutyl, tert-butyl, 2-ethylhexyl, hydroxyalkyl methacrylates such as 2-hydroxyethyl methacrylate, ether alkyl methacrylates such as 2-methoxyethyl methacrylate, alkoxy- or aryloxypolyalkylene glycol methacrylates such as methacrylates of methoxypolyethylene glycol or ethoxy-polyethylene glycol, methacrylates aminoalkyl lates such as 2- (dimethylamino) ethyl methacrylate, silyl methacrylates, glycidyl methacrylate.

PMMA means a homo- or copolymer of MMA, comprising by weight at least 50% MMA. The copolymer is obtained from MMA and at least one comonomer copolymerizable with MMA. Preferably, the copolymer comprises, by weight, from 70 to 99.5%, advantageously from 80 to 99.5%, preferably from 80 to 99% by MMA, respectively from 0.5 to 30%, advantageously from 0.5 to 20%, preferably 1 to 20% comonomer.

Preferably, the comonomer copolymerizable with MMA is a (meth) acrylic monomer or a monomer vinylaromatic such as for example styrene, substituted styrenes, alpha-methylstyrene, monochlorostyrene, tertbutyl styrene. Preferably, it is an alkyl (meth) acrylate, in particular methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate or butyl methacrylate.

PMMA is prepared by radical polymerization according to the techniques known to those skilled in the art. The polymerization may take place in solution, in bulk, in emulsion or in suspension. PMMA can also be prepared by anionic polymerization.

With respect to the protective layer (I), this comprises a PMMA. The protective layer (I) serves to protect the thermoplastic polymer against scratches, chemicals and against aging. It also improves the brightness of the whole. Preferably, the PMMA has a time to crack according to the conditions of the EN 13559 standard which is greater than 2 minutes, advantageously greater than 5 minutes, or even better than 10 minutes. The test of this standard which is used to determine crack resistance is to deposit isopropanol on a flat, rectangular test specimen held over a rounded shaper of constant radius so as to apply a bending stress on the outer surface (see paragraph 5.6 of standard NF EN 13559 of May 2004, entitled "Specifications of coextruded ABS / Acrylic sheets for bathtubs and shower trays for domestic use").

Preferably, the PMMA-index melt (measured at 230 ^° C., under a load of 3.8 kg) is between 0.5 and 10 g / 10 min, advantageously between 1 and 5 g / 10 min. The PMMA or the acrylic copolymer can be impact strengthened with at least one impact modifier. The impact modifier can be, for example, an acrylic elastomer. The acrylic elastomer may be a block copolymer having at least one elastomeric block. For example, it may be a styrene-butadiene-methyl methacrylate copolymer or methyl methacrylate-butyl acrylate-methyl methacrylate copolymer. The impact modifier may also be in the form of fine multilayer particles, called core-shell, having at least one elastomeric (or soft) layer, that is to say a layer formed of a polymer having a Tg less than -5 ^° C. and at least one rigid (or hard) layer, that is to say formed of a polymer having a T _g greater than 25 ^° C.

Preferably, the polymer of T _g lower than -5 ^° C. is obtained from a monomer mixture comprising from 50 to 100 parts of at least one C 1 -C 10 alkyl (meth) acrylate, from 0 to 50 parts of a monounsaturated copolymerizable comonomer, from 0 to 5 parts of a copolymerizable crosslinking monomer and from 0 to 5 parts of a copolymerizable grafting monomer.

Preferably, the T _g polymer greater than 25 ^° C. is obtained from a monomer mixture comprising from 70 to 100 parts of at least one C 1 -C 4 alkyl (meth) acrylate, from 0 to 30 carbon atoms. parts of a monounsaturated copolymerizable monomer, from 0 to 5 parts of a copolymerizable crosslinking monomer and from 0 to 5 parts of a copolymerizable grafting monomer.

C1-C10 alkyl (meth) acrylate is preferably butyl acrylate, 2-ethylhexyl, octyl. The C1-C4 alkyl (meth) acrylate is preferably methyl methacrylate. The monounsaturated copolymerizable monomer may be a C 1 -C 6 alkyl (meth) acrylate ClO, styrene, alpha-methyl styrene, butyl styrene, acrylonitrile. It is preferably styrene or ethyl acrylate. The grafting monomer may be allyl (meth) acrylate, diallyl maleate, crotyl (meth) acrylate. The crosslinking monomer may be diethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, divinyl benzene, trimethylolpropane triacrylate (TMPTA). The multilayer particles can be of different morphologies. For example, it is possible to use particles of the type:

"Soft-hard" having an elastomeric core (inner layer) and a rigid bark (outer layer) as described for example in the European application EP 1061100 A1;

"Hard-soft-hard" having a rigid core, an elastomeric intermediate layer and a rigid bark, as described for example in US applications 3793402 and US 2004/0030046 A1;

"Soft-hard-soft-hard" having in the order an elastomeric core, a rigid intermediate layer, another elastomeric intermediate layer and a rigid bark as described for example in the French application FR-A-2446296 describes examples of such particles;

The size of the particles is generally less than 1 μm and advantageously between 50 and 300 nm. The multilayer particles are prepared by means of the aqueous emulsion polymerization in several stages. During the ^st step, forming nuclei around which will constitute the layers. The final particle size is determined by the number of germs that are formed during the l ^st step. During each of the following steps, by polymerizing the appropriate mixture, a new layer is successively formed around the seeds or particles of the preceding step. At each stage, the polymerization is conducted in the presence of a radical initiator, a surfactant and optionally a transfer agent. For example, sodium, potassium or ammonium persulfate is used. The particles once formed are recovered by coagulation or spraying. An anti-clumping agent may be added to prevent the particles from clumping together.

The proportion of impact modifier in PMMA varies from

0 to 60 parts, advantageously from 1 to 60 parts, preferably from 5 to 40 parts, more preferably from 10 to 30 parts, per 100 parts of PMMA. Preferably, the PMMA having a cracking time

("Time to craze") according to the conditions of the standard

EN 13559 greater than 2 minutes, and advantageously greater than 5 minutes, contains more than 20% shock modifiers, and even more preferably 20 to 40% impact modifiers, inclusive limits.

As examples of usable PMMA, mention may be made of those marketed by ARKEMA under the references ALTUGLAS ^® DRT, ALTUGLAS ^® MI 7T, ALTUGLAS ^® HFI 10, ALTUGLAS ^® MI 4T, ALTUGLAS ^® MI 2T, ALTUGLAS ^® V044 or by ROEHM GmbH under the references PLEXIGLAS ^® 6N, PLEXIGLAS ^® 8N, PLEXIGLAS ^® ZK5BR.

With regard to the intermediate ductile layer (II), this comprises a block copolymer of formula BA _n composed of: a polymer block B comprising by weight at least 60% of at least one (meth) acrylic monomer having a T _g less than -5 ⁰ C, and n polymer sequences A, linked to the polymer block B by covalent bonds, n denoting an integer of between 1 and 10, comprising by weight at least 60% of at least one (meth) acrylic monomer having a T _g greater than 0 ⁰ C, and such that the sequence B and / or the sequences A comprise, by weight, from 0.2 to 20%, preferably from 0.2 to 10%, of acrylic and / or methacrylic acid. It is also conceivable that the B block and / or the A blocks comprise, by weight, from 0.2 to 20%, and preferably from 0.2 to 10%, of styrene and / or alpha methyl styrene and / or maleic anhydride and / or acrylonitrile, and / or glycidyl acrylate and / or glycidyl methacrylate. With regard to the sequence B, this is obtained from a mixture M _B comprising by weight (the total making 100%):

From 60% to 100% of at least one (meth) acrylic monomer having a T _g lower than -5 ^° C., from 0 to 40% of at least one comonomer copolymerizable with the (meth) acrylic monomer,

And if the sequence B contains from 0.2 to 20%, and preferably from 0 to 10%, of acrylic and / or methacrylic acid and / or styrene, and / or of alpha methyl and / or styrene, and / or maleic anhydride, and / or acrylonitrile, and / or glycidyl acrylate and / or glycidyl methacrylate.

Preferably, the T _g of the (meth) acrylic monomer is less than -15 ^° C., more preferably still less than -25 ^° C. Preferably, the monomer

(Meth) acrylic of the polymer block B is butyl, 2-ethylhexyl or octyl (meth) acrylate. Preferably, the copolymerizable comonomer is a (meth) acrylic monomer different from the meth) acrylic monomer of T _g lower than -5 ^° C. or a vinylaromatic monomer. The weight-average molecular weight of the B block is between 40,000 and 200,000 g / mol, advantageously between 50,000 and 150,000 g / mol (expressed in PMMA equivalents).

With regard to the A sequences, these are obtained from a M _A mixture comprising (the total making 100%): from 60% to 100% of at least one (meth) acrylic monomer having a T _g greater than 0 ⁰ C,

From 0 to 40% of at least one monomer copolymerizable with the (meth) acrylic monomer,

And if the A sequences contain from 0 to 20%, and preferably from 0 to 10%, of acrylic and / or methacrylic acid, and / or of styrene, and / or of alpha methyl styrene, and / or maleic anhydride, and / or acrylonitrile, and / or glycidyl acrylate and / or glycidyl methacrylate. Preferably, the T _g of the (meth) acrylic monomer of the polymer blocks A is greater than 25 ^° C., still more preferably greater than 50 ^° C. Preferably, the (meth) acrylic monomer of the polymer A blocks is methyl methacrylate. . The sequences A can be identical or different.

Preferably, the copolymerizable comonomer is a (meth) acrylic monomer different from the (meth) acrylic monomer of T _g greater than 0 ^° C. or a vinylaromatic monomer. The weight-average molecular weight of each of the A blocks is between 10,000 and 150,000 g / mol, advantageously between 30,000 and 100,000 g / mol (expressed in PMMA equivalents). Sequence B has a T _{3 of} less than -5 ^° C., preferably less than -15 ^° C., more preferably less than -25 ^° C. Sequences A have a T _g greater than 0 ^° C., preferably greater than 25 ⁰ C, still more preferably greater than 50 ^° C. Those skilled in the art can choose the monomers constituting the sequences A and B to adjust their Tg. It can use in particular the law of Fox (see in this regard: Bulletin of the American Physical Society 1, 3, page 123 (1956)).

Preferably, the sequence B and the sequences A will be chosen so that they are incompatible, that is to say as they have a Flory-Huggins% _AB interaction parameter at room temperature. . This results in a phase separation with formation of a diphasic structure at the microscopic scale (phenomenon called microseparation of phase). The block copolymer is nanostructured, that is to say that phases are formed whose size is less than 100 nm, preferably between 10 and 50 nm.

The intermediate ductile layer (II) may also comprise a core-shell shock additive whose proportion varies from 0 to 60 parts, preferably from 0 to 30 parts, per 100 parts of block copolymer. The intermediate ductile layer (II) has the function of reinforcing the impact resistance of the thermoplastic polymer / protective layer assembly and of ensuring adhesion between the layers which are in contact with it. The presence of acid, anhydride, epoxy, styrenic or nitrile functions in the B sequence and / or in the A sequences makes it possible to reinforce this adhesion. In addition, the surface PMMA being a fragile material, the impact resistance of the protective layer (I) / polymer assembly thermoplastic (III) is less than that of the thermoplastic polymer alone, or even substantially equivalent to that of the protective layer. During an impact, a crack initiated in the protective layer propagates unabated to the thermoplastic polymer and can damage it. In the presence of the intermediate ductile layer, the impact resistance of the assembly is maintained or improved compared to the thermoplastic polymer because, in this case, the crack is stopped by the intermediate ductile layer.

the block copolymer BA _n

According to the definition given by IUPAC (see IUPAC Compendium of Chemical Terminology, 2 ^nd edition (1997), 1996, 68, 2303), a block copolymer consists of macromolecules having several contiguous polymer sequences, chemically different that is ie derived from different monomers or derived from the same monomers but in different distributions. We can also refer to Kirk-Othmer Encyclopedia of Chemical Technology ^3rd ed., Vol.6, p.798 for details on block copolymers.

The block copolymer may be linear, star or comb (brush copolymer). The linear copolymer is of the ABA type (n = 2) (that is to say compound in the order of two A sequences connected to two sides of a central sequence B). In the case of a star-block or comb copolymer, n is greater than 2.

The block polymers can be prepared by so-called living polymerization. It may be a group transfer polymerization using a silylketene-Lewis acid coupling system as described in Japanese Application JP 62-292806. It could be also a controlled radical polymerization technique such as NMP (Nitroxide-Mediated Polymerization), ATRP (Atom Transfer Radical Polymerization) or RAFT (Reversible Addition-Fragmentation Chain Transfer). Information on these techniques can be found in the following publications: DA Shipp et al., "Water-borne block copolymer synthesis and a simple and effective one-pot synthesis of acrylate-methacrylate block copolymers by atom transfer radical polymerization," Am. Chem. . Soc, Polym. Prep., 1999, Vol. 40, p.448; YK Chong et al, "A more versatile route to block copolymers and other polymers of complex architecture by living radical polymerization: the RAFT process". Macromolecules, March, 1999, Vol.32, N ⁰ 6, pp. 2071-2074; G. Moineau et al., "Synthesis and characterization of poly (methyl methacrylate) -block-poly (n-butyl acrylate) -block-poly (methyl methacrylate) copolymers by two-step controlled radical polymerization (ATRP) catalyzed by NiBr ₂ (PPH ₃ ) ₂ , Macromolecules 1999, Vol.32, No. 25, pp. 8277-8282. Advantageously, the NMP type polymerization is used to prepare the block copolymer in the presence of an alkoxyamine of formula ZT _n in which Z denotes a multivalent group and T denotes a nitroxide. Z denotes a multivalent group, that is to say a group capable of releasing after activation n radical sites. The activation in question occurs by breaking covalent ZT bonds.

By way of example, Z may be chosen from the following groups (I) to (VIII):

I I

Rs-CH-CO- (B) _5T OC-CH-R ₄ (I) OO in which R3 and R4, which are identical or different, represent a linear or branched alkyl radical having a number of carbon atoms ranging from 1 to 10, phenyl or thienyl radicals optionally substituted by a halogen atom such as F, Cl, Br or a linear or branched alkyl radical having a number of carbon atoms ranging from 1 to 4, or alternatively by nitro, alkoxy, aryloxy, carbonyl or carboxy radicals; a benzyl radical, a cycloalkyl radical having a number of carbon atoms ranging from 3 to 12, a radical containing one or more unsaturations; B represents a linear or branched alkylene radical having a number of carbon atoms ranging from 1 to 20; m is an integer from 1 to 10;

R ₅ _S -DC: HHHCCCHHH ₉₉₂ --- --- OoO CCLC --- (œ (DD "i) _P --- CAC --- --- OOO CCCHHH ₉₉₂ CHIC-R ₆ (H) OO in which R5 and Re, which are identical or different, represent aryl, pyridyl, furyl or thienyl radicals optionally substituted by a halogen atom such as F, Cl, Br, or by an alkyl radical, linear or branched, having a number of carbon atoms ranging from 1 to 4, or alternatively by nitro, alkoxy, aryloxy, carbonyl or carboxy radicals; D represents a linear or branched alkylene radical having a number of carbon atoms ranging from 1 to 6, a phenylene radical, a cycloalkylene radical, p being an integer ranging from 1 to 10;

wherein R?, Rs and Rg, which are the same or different, have the same meanings as R3 and R4 of the formula (I), q, r and s are integers ranging from 1 to 10;

wherein Rio has the same meaning as R5 and Re of formula (II), t is an integer from 1 to 4, u is an integer of 2 to 6 (the aromatic moiety is substituted);

wherein Rn has the same meaning as the radical Rio of the formula (IV) and v is an integer of 2 to 6;

[W] _W = PO-CH ₂ -CH-R _{13 (} VI ₎

0-CH ₂ -CH-R ₁₄ wherein R12, Ri3 and R14, identical or different, represent a phenyl radical optionally substituted by a halogen atom such as Cl, Br, or an alkyl radical, linear or branched having a number of carbon atoms ranging from 1 to 10; W is oxygen, sulfur, selenium, w is zero or 1; O

R ₁₅ -CH-CO-CH ₂ -CH-R ₁₆ ( _V π) wherein R 15 has the same meaning as R 3 of formula (I), R 16 has the same meaning as R 5 or R 5 of formula (II);

in which R ₁ and R _6, which are identical or different, represent a hydrogen atom, a linear or branched alkyl radical having a number of carbon atoms ranging from 1 to 10, an aryl radical, optionally substituted with a halogen atom or a hetero atom.

T denotes a nitroxide which is a stable free radical having a group = N-O ^*, that is to say a group on which is present a single electron. The term "stable free radical" denotes a radical that is so persistent and non-reactive with respect to air and moisture in the ambient air that it can be handled and stored for a much longer period than the majority free radicals (see Accounts of Chemical Research 1976, 9, 13-19). The stable free radical is thus distinguished from free radicals whose lifetime is ephemeral (from a few milliseconds to a few seconds) such as free radicals from conventional polymerization initiators such as peroxides, hydroperoxides or azo initiators. Free radicals initiating polymerization tend to accelerate polymerization whereas stable free radicals generally tend to slow it down. It can be said that a free radical is stable within the meaning of the present invention if it is not a polymerization initiator and if, under the usual conditions of the invention, the average life of the radical is at least one minute.

T is represented by the structure:

R ₂ O

R ₁ -CR ₂ I

_N _O- (IX)

R ₂₂ Ç R ₂₄

R ₂₃ in which R ₁₉ , R ₂₀ , R ₂₁ , R 22, R 24 and R 24 denote linear or branched C ₁ -C ₂₀ and preferably C ₁ -C ₁₀ alkyl groups, such as methyl, ethyl, propyl, butyl or isopropyl, isobutyl, tert-butyl, neopentyl, substituted or unsubstituted, substituted or unsubstituted C 6 -C 30 aryls such as benzyl, aryl (phenyl) cyclic saturated C 1 -C 30 and wherein the groups R 19 and R 22 may be part of a ring structure R 19 CNC-R22 optionally substituted which can be chosen from:

in which x denotes an integer between 1 and 12.

By way of examples, the following nitroxides may be used:

TEMPO OXO-TEMPO

In a particularly preferred manner, the nitroxides of formula (X) are used in the context of the invention:

R _a and R ₃ denote identical or different alkyl groups having from 1 to 40 carbon atoms, optionally linked to each other so as to form a ring and optionally substituted by hydroxyl, alkoxy or amino groups, R _L denoting a monovalent group of molar mass greater than 16 g / mol, preferably greater than 30 g / mol. The group R _L may for example have a molar mass of between 40 and 450 g / mol. It is preferably a phosphorus group of general formula (XI):

wherein X and Y, which may be the same or different, may be selected from alkyl, cycloalkyl, alkoxyl, aryloxyl, aryl, aralkyloxy, perfluoroalkyl, aralkyl and may include from 1 to 20 carbon atoms; X and / or Y may also be a halogen atom such as a chlorine, bromine or fluorine atom. Advantageously, RT is a phosphonate group of formula:

in which R _c and R _d are two identical or different alkyl groups, optionally linked so as to form a ring, comprising from 1 to 40 carbon atoms, optionally substituted or not.

The R _L group may also comprise at least one aromatic ring such as the phenyl radical or the naphthyl radical, substituted for example by one or more alkyl radicals comprising from 1 to 10 carbon atoms.

The nitroxides of formula (X) are preferred because they make it possible to obtain good control of the radical polymerization of (meth) acrylic monomers as taught in WO 03/062293. They make it possible to obtain higher molecular weights than nitroxides such as TEMPO. Alkoxyamines of formula (XIII) having a nitroxide of formula (X) are therefore preferred:

in which :

Z is a multivalent group;

R _a and Rb denote identical or different alkyl groups having from 1 to 40 carbon atoms, optionally linked to each other so as to form a ring and optionally substituted with hydroxyl, alkoxy or amino groups;

R _L denotes a monovalent group of molar mass greater than 16 g / mol, preferably greater than 30 g / mol. The group R _L may for example have a molar mass of between 40 and 450 g / mol. It is preferably a phosphorus group of general formula (XI):

wherein X and Y, which may be the same or different, may be selected from alkyl, cycloalkyl, alkoxyl, aryloxyl, aryl, aralkyloxy, perfluoroalkyl, aralkyl and may include from 1 to 20 carbon atoms; X and / or Y may also be a halogen atom such as a chlorine, bromine or fluorine atom.

Advantageously, R _L is a phosphonate group of formula:

wherein R _c and Rd are two identical or different alkyl groups, optionally joined to form a ring, comprising from 1 to 40 carbon atoms, optionally substituted or not.

By way of example of a nitroxide of formula (X) which may be borne by the alkoxyamine (XIII), mention may be made of: N-tert-butyl-1-phenyl-2-methylpropyl nitroxide; N- (2-hydroxymethylpropyl) -1-phenyl-2-methylpropyl nitroxide; N-tert-butyl-1-dibenzylphosphono-2,2-dimethylpropyl nitroxide; N-tert-butyl-1-di (2,2,2-trifluoroethyl) phosphono-2,2-dimethylpropyl nitroxide; the N-tert-butyl [(1-diethylphosphono) -2-methylpropyl] nitroxide; N- (1-methylethyl) -1-cyclohexyl-1- (diethylphosphono) nitroxide; N- (1-phenylbenzyl) - [(1-diethylphosphono) -1-methylethyl] nitroxide; N-phenyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide; N-phenyl-1-diethylphosphono-1-methylethyl nitroxide; N- (1-phenyl-2-methylpropyl) -1-diethylphosphonomethylethylnitroxide; as well as the nitroxide of formula:

The nitroxide of formula (XIV) is particularly preferred:

This is N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide, commonly referred to as SG1 for simplicity. This nitroxide makes it possible to effectively control the polymerization of the (meth) acrylic monomers.

The alkoxyamines can be prepared by recipes described for example in US590549 or in FR99.04405. One method that can be used consists in coupling a carbon radical with a nitroxide. Coupling can be carried out from a halogenated derivative in the presence of an organometallic system such as CuX / ligand (X = Cl or Br) according to an AtRR (Atom Transfer Radical Addition) type reaction as described by D. Greszta and al. in Macromolecules 1996, 29, 1661-1610. + n CuX / ligand

Z (-X) _n + n T -; * ~ Z (-T) _n solvent

- n CuX ₂ / ligand

Alkoxyamines that can be used in the context of the invention are represented below:

DIAMS

DIAMINS

Alkoxyamine DIAMINS is the preferred alkoxyamine. It is not within the scope of the present invention to incorporate several alkoxyamines corresponding to the formula (I), in particular several alkoxyamines of formula (XIII).

A process for obtaining the block copolymer BA _n comprises the following steps: 1. the sequence B is prepared by heating the mixture M _B in the presence of at least one alkoxyamine ZT _n , the heating being carried out at a temperature sufficient to activate 1 alkoxyamine and polymerize the mixture M _B to a conversion of at least 60%, 2. the A sequences are prepared by heating the sequence B obtained in step 1 in the presence of the mixture M ^, the heating being carried out at a temperature sufficient to activate the sequence B and polymerize the MA mixture. The initiation of the polymerization leading to the sequence B is carried out by alkoxyamine ZT _n . The initiation of the polymerization leading to the A sequences is achieved by the reactivation of the B sequence.

In order to ensure better control of the polymerization, it is possible to add in stage 1 and / or 2 a nitroxide, identical or different from that which is carried on the alkoxyamine. The molar proportion of the added nitroxide relative to the alkoxyamine ZT _n is between 0 and 20%, preferably between 0 and 10%. The conversion to monomer (s) of the mixture M _B in step 1 is between 60 and 100%. Preferably, in order to maintain control of the polymerization, the conversion is between 60 and 95%, advantageously between 70 and 95%. At each stage, all or part of the non-converted monomer (s) may be removed under vacuum, possibly by heating. We can also finish converting all or part of the monomer (s) not converted at each step by introducing during this step at least one radical initiator. The radical initiator may be introduced at each stage before or after the preparation of the corresponding sequence (s). In the case where the radical initiator is introduced after the preparation of the sequence B, it will be chosen so that it has a temperature T1 _/ 2, ih (that is to say the temperature to have a time with a half-life of 1 h) which is 20 ^° C. below the reactivation temperature of the B-block. The radical initiator can be an organic or inorganic initiator, for example a persulfate. The azobisisobutyronitrile or Luperox ^® 546 are two examples of suitable radical initiators. It is possible that the control of the polymerization is not perfect and that the mixture of monomer (s) leading to the A blocks also leads in part to a polymer A of the same composition as the A sequences. A composition comprising from 50 to 100 parts of BA _n block copolymer and from 0 to 50 parts of polymer A having the same composition as the A blocks. This composition can also be used for the intermediate ductile layer.

Each of the steps of the process can be carried out according to a mass process, in solution in a solvent or in an aqueous dispersed medium (emulsion, suspension).

In the case where it is desired to prepare the block copolymer in an aqueous dispersed medium, the two stages can be carried out in an aqueous dispersed medium or only in step 2. In this case, the B-block will have been previously prepared at the stage 1 according to a mass method or in solution in a solvent. An example of a process for preparing the BA _n block copolymer in aqueous dispersed medium in which the B block has been previously prepared by a mass process or in solution in a solvent using an alkoxyamine ZT _n comprises the following steps: a) introducing water, at least one dispersing agent, the sequence B and the mixture M _A , b) polymerizing the mixture M _A by heating to a temperature sufficient to activate the sequence B, c) recovering the block copolymer BA _n . Steps a) and b) are made with stirring.

The dispersing agent is a compound that stabilizes the emulsion or suspension. It may be for example a surfactant or a protective colloid. The block copolymer is recovered in the form of particles whose size depends on the operating conditions and the process used (emulsion, suspension). The copolymer is subsequently advantageously put into the form of granules, for example using an extruder. It is possible to introduce a radical initiator before and / or at the end of step b). If the radical initiator is introduced between step a) and step b), that is to say before reactivation of the sequence B, it is preferably chosen so that its temperature Ti _{/ 2} , ih (That is to say, the temperature to have a half-life time of 1 h) is 20 ^° C. lower than the temperature of reactivation of the sequence B.

It is also possible to introduce a transfer agent before and / or at the end of step b). For example, the transfer agent may be the octyl mercaptan. additives

The protective layer (I), the intermediate layer (I ') and the intermediate ductile layer (II) can each comprise one or more additives chosen from:

• thermal stabilizers;

• lubricants;

• flame retardants;

• Sun Creme; • antioxidants;

• antistatic;

• matting agents which may be mineral fillers such as for example talc, calcium carbonate, titanium dioxide, zinc oxide or magnesium or organic fillers such as for example crosslinked beads based on styrene and or MMA (examples of such beads are given in EP 1174465).

• pigments and / or dyes. The proportion of anti-UV varies from 0 to 10 parts, advantageously from 0.2 to 10 parts, preferably from 0.5 to 5 parts, of anti-UV per 100 parts of polymer. A list of useful UV-stabilizers can be found in the document "Plastics Additives and Modifiers Handbook, chap. 16, Environmental Protective Agents ", J. Edenbaum, Ed., Van Nostrand, pp. 208-271, incorporated by reference into the present application. Preferably, the anti-UV is a compound of the family of HALS, triazines, benzotriazoles or benzophenones. Combinations of several anti-UV agents can be used to obtain better UV resistance. Examples of anti-UV used include TINUVIN ^® 770, Tinuvin ^® 328, Tinuvin ^® P or TINUVIN ^® 234. When seeking an effect called color depth, the protective layer (I) is transparent and without any pigment and the intermediate ductile layer (II) comprises at least one pigment and / or dye, the proportion of which varies from 0 to 20 parts, advantageously from 0.2 to 10 parts, preferably from 0.5 to 5 parts, per 100 parts of polymer. A list of useful pigments can be found in the document "Plastics Additives and Modifiers Handbook, Section VIII, Colorants", J. Edenbaum, Ed., Van Nostrand, pp. 884-954, incorporated by reference into the present application. Examples of usable pigments, titanium dioxide may be mentioned (white), clay (beige), metal particles (metallic effect) or the particles of mica treated in the Iriodin trade mark ^® marketed by MERCK.

According to a variant for obtaining this effect, an intermediate layer (I ') comprising at least one pigment and / or a dye is placed between the layers (I) and (II). The pigment and / or dye is dispersed in a thermoplastic polymer, which is preferably a PMMA, that is, a homo- or copolymer of MMA comprising at least 50% by weight of MMA. The proportion of pigment and / or dye varies from 1 to 50 parts of pigment per 100 parts of the thermoplastic polymer. With regard to the thermoplastic polymer, this may be chosen from the list of the following polymers:

• saturated polyester (PET, PETg, PBT, ...);

• ABS;

• SAN (styrene-acrylonitrile copolymer); • ASA (acrylic-styrene-acrylonitrile copolymer)

• polystyrene (crystal or shock);

• polypropylene (PP); • polyethylene (PE);

• polycarbonate (PC);

• PPO;

• polysulphone; • PVC;

• chlorinated PVC (CPVC);

• expanded PVC.

It can also be mixtures of two or more polymers from the previous list. For example, it may be a PPO / PS or PC / ABS blend.

Process

The invention relates to a method for protecting a thermoplastic polymer consisting of superposing in order by coextrusion, hot compression or multiinjection:

A protective layer (I) comprising a PMMA,

An intermediate ductile layer (II) comprising a block copolymer of formula BA _n composed of: a polymer block B comprising by weight at least 60% of at least one (meth) acrylic monomer having a T _g less than -5 ⁰ C, and n polymer sequences A, linked to the polymer block B by covalent bonds, n denoting an integer of between 1 and 10, comprising by weight at least 60% of at least one monomer

(meth) acrylic acid having a T _g greater than 0 ^° C., and such that the sequence B and / or the sequences A comprise, by weight, from 0.2 to 10% of at least one compound chosen from acrylic acid and methacrylic acid , styrene, alpha methyl styrene, maleic anhydride, acrylonitrile, glycidyl acrylate, glycidyl methacrylate. A layer of at least one thermoplastic polymer

(III) • Hot compression of diapers is a technique that can be used. One can also use a technique of coinjection or multiinjection. The multiinjection technique consists of injecting into the same mold the melts constituting each of the layers. According to the technical ^era of multiinjection, the molten materials are injected simultaneously into the mold. According to 2 Technical ^Similarly, a movable insert is located in the mold. By this insert, a melt is injected into the mold, and then the movable insert is moved to inject another melt.

The preferred technique is coextrusion which relies on the use of as many extruders as there are layers to extrude (for more details, see the book Principles of Polymer Processing Z. Tadmor, Wiley edition, 1979). This technique is more flexible than the previous ones and makes it possible to obtain multilayer structures even for complicated geometries, for example profiles. It also allows to have excellent mechanical homogeneity. The technique of coextrusion is a technique known thermoplastic processing (see, e.g., Precis plastics, Patterns properties 1989 implementation and standardization ^4th edition, Nathan, p. 126). US 5318737 discloses an example of coextrusion with a thermoplastic polymer.

Preferably, the total thickness of the layers (I) and (III) is greater than 310 μm, preferably 350 μm. Of preferably, the total thickness of the layers (I), (II) and (III) is greater than 310 μm, preferably 350 μm.

Multilayer structure The multilayer structure comprises in order:

A protective layer (I) comprising PMMA as defined above, optionally an intermediate layer (I ') comprising at least one pigment and / or a dye, an intermediate ductile layer (II) comprising a block copolymer of formula BA _n as defined above, • a layer of at least one thermoplastic polymer

(III), the layers being arranged one on the other in the order

(I) to (III) indicated.

Preferably, if the pigmented layer is not present, the total thickness of the layers (I) and (II) is greater than 310 μm, preferably greater than 350 μm. Preferably, the total thickness of the layers (I), (I ') and

(II) is greater than 310 μm, preferably 350 μm. With FIM technology, it is not possible to obtain a thick protection of the thermoplastic polymer as described in applications EP 1541339 A1 and EP 1543953 A2 for which the total thickness of the layers of the film is between 40 and 300. .mu.m.

Preferably, the layers (I) to (III) are coextruded, heat-compressed or multi-injected.

Preferably, the protective layer (I) has a thickness of between 10 and 1000 μm, preferably between 50 and 200 μm. Preferably, the intermediate ductile layer (II) has a thickness of between 100 and 1000 μm, preferably between 100 and 400 μm. Preferably, the optional intermediate layer (I ') has a thickness of between 10 and 80 μm, preferably between 10 and 50 μm.

applications

The multilayer structure, in particular that obtained by one of the processes described above, can be used for the manufacture of objects and articles of everyday life. It can be for example:

• housings or casings of lawnmowers, chainsaws, jet skis, household appliances, ...;

• car roof boxes; • body parts;

• number plates;

• exterior wall panels of caravans and mobile homes;

• exterior panels of refrigerators; • shower enclosure panels;

• building doors;

• window moldings;

• cladding panels.

PVC is advantageously used as a thermoplastic polymer in the manufacture of parts which are intended for exterior applications such as building doors, gutters, window moldings or cladding. However, the degradation of PVC under the effect of UV rays causes a change of color (especially in dark shades such as blue or black) and / or a decrease in its resistance to impact. In addition, PVC panels contain generally as a UV stabilizer of titanium dioxide which also plays the role of white pigment. The proportion of titanium dioxide is generally of the order of 3%, which makes it difficult to obtain dark shades. Panels can only be dyed in light or pastel shades. The invention solves the problem of coloring and / or UV protection of PVC outer facade panels while preserving the impact resistance of PVC.

ABS is advantageously used as a thermoplastic polymer in the manufacture of housings or casings, in particular household electrical appliances, license plates, refrigerator outer panels or bodywork parts. ABS has a gloss in the range of 40-50 at an angle of 60 °. Thanks to the invention, it is possible to obtain a gloss between 70 and 95, preferably between 85 and 90 at an angle of 60 ° while maintaining the impact resistance of ABS and protecting the ABS.

Preferably, if the pigmented layer (II) is not present, the total thickness of the layers (I) and (III) is greater than 310 μm, preferably greater than 350 μm.

Preferably, in the case of PVC, the multilayer structure is a cladding panel. Preferably, in the case of ABS, the multilayer structure is a bodywork part.

Examples:

The following examples illustrate the invention according to the best form envisaged by the inventors. They are given for illustrative purposes only and do not limit the scope of the invention. Multilayer structures were obtained by coextrusion and then evaluated using a rapid bending test. Notched Izod shock was also measured on some samples.

Coextrusion conditions:

The multilayer structures were made on a trilayer co-extrusion line AMUT brand. A lamella layer distribution block was used for coextrusion and a 650 mm wide coat rack. Calibration of the structure was carried out on a vertical grille consisting of three independently thermoregulated rolls. The ABS is extruded at a temperature between 245 and 255 ⁰ C using a 70 mm diameter machine, length equal to 32D provided with a degassing well. The extruder used for the triblock copolymer layer has a diameter of 30 mm and a length of 24D. The temperature is regulated at about 250 ^° C. The surface PMMA (or protective layer) (I) is itself extruded with an extruder of diameter 30 mm and length 25D at a temperature of about 25O ⁰ C also. This protective layer is

Notch Izod impact measurement conditions: ISO 180 test pieces: 80x10 mm V-notch: 8 mm pendulum: 1 J speed: 3, 46 m / s

Quick bending test:

Resilience (Re), expressed in kJ / m ² , is measured on ABS specimens protected or not by a layer acrylic protector. Resilience is measured using a fast bending test. The specimen is flexed in the middle of the span at a constant speed. During the test, the load applied to the specimen is measured. The bending test is carried out at constant speed on the MTS-831 servo-hydraulic equipment. The force is measured by means of a piezoelectric cell embedded in the nose of the striker 569.4 N. The displacement of the specimen during the stress is measured by an LVDT sensor on the hydraulic cylinder of 50 mm range.

During the test, the force (expressed in N) and the displacement (in mm) of the firing pin are recorded. From the experimental curves, we calculate the area under the curve which represents the force as a function of the displacement until rupture of the specimen or the limit of displacement before sliding (evaluated at 20 mm). This area, expressed in Joule, is representative of the energy supplied to the system during loading. The flexural strength, denoted Re, is the breaking energy relative to the central cross section of the bar expressed in kJ / m ² .

Preparation of test pieces:

Bars corresponding to the dimensions below are manufactured using a Charlyrobot CRA digital milling machine from multilayer structures. 6 bars per plate are cut.

The dimensions of the test specimen, in millimeters, are: - length: 1 = 70 +/- 0,2

- width: b = 10.0 +/- 0.2

- thickness: h = measured for each specimen. The distance L, distance between the supports, is set to L = 40 mm. The applied loading speed is 0.1 m / s. For each sample, the face in contact with the striker is ABS. The thin layer is stressed in tension.

Example 1 (comparative):

In a 20 liter reactor stirred at 200 rpm, 14000 g of butyl acrylate are polymerized at 117 ^° C. in the presence of 140 g of DIAMINS to a conversion rate of 70%, measured by dry extract.

12200 g of the above mixture are then poured into a 20-liter vat with stirring at 100 rpm, and the unconverted butyl acrylate is then evaporated under vacuum (4h30, 80 ^° C., 20 mm Hg) until a polyacrylate is obtained. viscous butyl having a solid content of about 96%. Butyl polyacrylate is redissolved by adding 10500 g of MMA. The solution obtained has a solid content of 45%. It comprises 45% of living butyl polyacrylate (ie reactivatable) for 55% of MMA.

7150 g of deionized water are charged to a 20-liter reactor which has been degassed beforehand and purged with nitrogen in the presence of 375 g of a 5.4% by weight solution of PAMS and 0.37 g of NaOH.

This solution is brought to 70 ^° C. with stirring at 200 rpm. When the temperature reaches 70 ^° C., 4389 g of the solution of butyl polyacrylate living in the MMA obtained in the preceding step are cast. The reaction mixture is brought to 100 ^° C. for a period of 2 hours at the end of which a mixture of 3.7 g of octyl mercaptan diluted in 11.2 g of MMA is introduced. The reaction mixture is left stirring at 100 ⁰ C for 1 hour. At the end of this period, is introduced a mixture of 15 g of Luperox ^® 531 and 100 g of MMA at one time, and then the reactor temperature is raised to 12O ⁰ C for 2 hours. At the end of this period, the reactor is cooled to 95 ^° C. and a solution of 4.5 g of potassium persulfate in 150 ml of water is introduced in one go. The reaction mixture is maintained at 95 ^° C. for 1 hour.

The suspension is then cooled, filtered using a wringer, plumped with 7000 g of water and then dewatered again. This is done 3 times. The triblock copolymer 2 is in the form of beads whose average size is 209 microns.

Example 2: Triblock 2 PMMA-PABUco acrylic acid-PMMA

In a 20 liter reactor stirred at 200 rpm, 13600 g of butyl acrylate and 700 g of acrylic acid are polymerized at 117 ^° C. in the presence of 140 g of DIAMINS up to a conversion of 70%. measured by dry extract.

12200 g of the above mixture are then poured into a 20 liter vat with stirring at 100 revolutions / min, then the unconverted monomers are evaporated under vacuum (4h30, 80 ^° C., 20 mm Hg) until a polybutyl acrylate is obtained. viscous acrylic acid having a solid content of about 96%. The butyl polyacrylate-acrylic acid is redissolved by adding 10500 g of MMA. The solution obtained has a solid content of 45%. It comprises 45% living butyl acrylic acid polyacrylate (ie reactivatable) for 55% MMA.

7150 g of deionized water are charged to a 20-liter reactor which has been degassed beforehand and is purged with nitrogen in the presence of 375 g of a solution containing 5.4% by weight of PAMS and 0.37 g of NaOH.

This solution is brought to 70 ^° C. with stirring at 200 rpm. When the temperature reaches 70 ^° C., 4389 g of the solution of butyl polyacrylate living in the MMA obtained in the preceding step are cast.

The reaction mixture is brought to 100 ^° C. for a period of 2 hours at the end of which a mixture of 3.7 g of octyl mercaptan diluted in 11.2 g of MMA is introduced. The reaction mixture is stirred at 100 ^° C. for 1 hour. At the end of this period, is introduced a mixture of 15 g of Luperox ^® 531 and 100 g of MMA at one time, and then the reactor temperature is raised to 12O ⁰ C for 2 hours. At the end of this period, the reactor is cooled to 95 ^° C. and a solution of 4.5 g of potassium persulfate in 150 ml of water is introduced in one go. The reaction mixture is maintained at 95 ^° C. for 1 hour. The suspension is then cooled, filtered using a wringer, plumped with 7000 g of water and then dewatered again. This is done 3 times. The triblock copolymer 2 is in the form of beads whose average size is 255 microns.

Example 3: Triblock 3 PMMAco styrene-PABU-PMMA co styrene

12200 g of the above mixture are then poured into a 20-liter vat stirred at 100 rpm, and then evaporated under vacuum (4h30, 80 ^° C., 20 mm Hg) unconverted butyl acrylate until obtaining a viscous butyl polyacrylate having a solid content of about 96%. Butyl polyacrylate was redissolved by adding 9975 g of MMA and 525 g of styrene. The solution obtained has a solid content of 45%. It comprises 45% of living butyl polyacrylate (that is to say reactivatable) for 55% of MMA and styrene mixture. 7150 g of deionized water are charged to a 20-liter reactor which has been degassed beforehand and purged with nitrogen in the presence of 375 g of a 5.4% by weight solution of PAMS and 0.37 g of NaOH.

This solution is brought to 70 ^° C. with stirring at 200 rpm. When the temperature reaches 70 ^° C., 4389 g of the butyl polyacrylate solution living in the MMA styrene mixture obtained in the preceding step are cast. The reaction mixture is brought to 100 ^° C. for a period of 2 hours at the end of which a mixture of 3.7 g of octyl mercaptan diluted in 11.2 g of MMA is introduced. The reaction mixture is stirred at 100 ^° C. for 1 hour. At the end of this period, is introduced a mixture of 15 g of Luperox ^® 531 and 100 g of MMA at one time, and then the reactor temperature is raised to 12O ⁰ C for 2 hours. At the end of this period, the reactor is cooled to 95 ^° C. and a solution of 4.5 g of potassium persulfate in 150 ml of water is introduced in one go. The reaction mixture is maintained at 95 ^° C. for 1 hour. The suspension is then cooled, filtered using a wringer, plumped with 7000 g of water and then dewatered again. This is done 3 times. The triblock copolymer 2 is in the form of beads whose average size is 225 μm. Results:

After impact rupture of the test pieces, attempts are made to separate the layers at the level of the fracture facies.

In the case of the comparative example, this is often possible.

In the cases of Examples 2 and 3 it becomes very difficult to separate the layers indicating a good adhesion between them.

Table 1

ABS: MAGNUM 3904 marketed by DOW, having an indexing melt of 1.5 g / 10 min (230 ^° C., 3.8 kg) -thickness 3 mm) ALTUGLAS V044: marketed by ARKEMA obtained from MMA and about about 4 to 9% ethyl acrylate.

Claims

1. Process for protecting a thermoplastic polymer consisting of superimposing in order by coextrusion, by hot compression or by multiinjection:

•a protective layer (I) comprising a PMMA, •an intermediate ductile layer (II) comprising a block copolymer of formula BA _n composed of: a polymer block B comprising by weight at least 60% of at least one monomer (meth ) acrylic having a T _g less than -5 ⁰ C, and n polymer sequences A, connected to the polymer sequence B by covalent bonds, n designating an integer between 1 and 10, comprising by weight at least 60% of at least one monomer

(meth) acrylic having a T _g greater than O ⁰ C, and such that the sequence B and/or the sequences A comprise by weight from 0.2 to 20% of at least one compound chosen from acrylic acid, l methacrylic acid, styrene, alpha methyl styrene, maleic anhydride, acrylonitrile, glycidyl acrylate, and glycidyl methacrylate.

•a layer of at least one thermoplastic polymer

(III) •

2. Method according to claim 1 characterized in that the sequence B and/or the sequences A comprise by weight from 0.2 to 10% of at least one compound chosen from acrylic acid, methacrylic acid, styrene , alpha methyl styrene, maleic anhydride, acrylonitrile, glycidyl acrylate and glycidyl methacrylate.

3. Method according to claim 1 or 2 characterized in that the polymer sequence B is obtained from a mixture M _B comprising by weight: - from 60% to 100% of at least one (meth) acrylic monomer having a T _g less than -5 ⁰ C, from 0 to 40% of at least one comonomer copolymerizable with the (meth)acrylic monomer and, if sequence B contains it, from 0.2 to 20%, and preferably from 0 .2 to 10%, of at least one compound chosen from acrylic acid, methacrylic acid, styrene, alpha methyl styrene, maleic anhydride, acrylonitrile, glycidyl acrylate and methacrylate glycidyl.

4. Method according to any one of the preceding claims characterized in that the T _g of the polymer sequence B is less than -5 ⁰ C.

5. Method according to any one of the preceding claims characterized in that the polymer sequences A are obtained from a mixture M _A comprising by weight: from 60% to 100% of at least one (meth) acrylic monomer having a T _g greater than O ⁰ C, from 0 to 40% of at least one monomer copolymerizable with the (meth)acrylic monomer and, if the A sequences contain from 0.2 to 20%, and preferably from 0, 2 to 10%, of at least one compound chosen from acrylic acid, methacrylic acid, styrene, alpha methyl styrene, maleic anhydride, acrylonitrile, glycidyl acrylate and glycidyl methacrylate.

6. Method according to any one of the preceding claims, characterized in that the polymer sequences A have a T _g greater than O ⁰ C.

7. Method according to any one of the preceding claims characterized in that the sequence B and the sequences A have a Flory-Huggins interaction parameter χAB>0 at room temperature.

8. Method according to any one of the preceding claims, characterized in that the block copolymer is nanostructured.

9. Method according to any one of the preceding claims, characterized in that the block copolymer is obtained by a process comprising the following steps: 1. sequence B is prepared by heating a mixture M _B as defined in claim 3 in the presence of at least one alkoxyamine ZT _n , the heating being carried out at a temperature sufficient to activate the alkoxyamine and polymerize the mixture M _B until a conversion of at least 60%,

2. the sequences A are prepared by heating the sequence B obtained in step 1 in the presence of a mixture Nk as defined in claim 5, the heating being carried out at a temperature sufficient to activate the sequence B and polymerize the mixture _MY .

10. Method according to any one of the preceding claims, characterized in that the PMMA is a homo- or copolymer of MMA, comprising by weight at least 50% of MMA.

11. Method according to any one of the preceding claims characterized in that the PMMA has a cracking time according to standard EN 13559 greater than 2 minutes.

12. Method according to any one of the preceding claims, characterized in that the PMMA is reinforced on impact using at least one impact modifier.

13. Method according to claim 12, characterized in that the proportion of impact modifier in the PMMA varies from 0 to 60 parts, advantageously from 1 to 60 parts, preferably from 5 to 40 parts, even more preferably from 10 to 30 parts , for 100 parts of PMMA.

14. Method according to any one of the preceding claims characterized in that an intermediate layer (I ') comprising at least one pigment and/or a dye is placed between the layers (I) and (II).

15. Method according to any one of the preceding claims, characterized in that the thermoplastic polymer is a saturated polyester, ABS, SAN, ASA, a crystal or impact polystyrene, a polypropylene, a polyethylene, a polycarbonate , a PPO, a polysulphone, a PVC, a chlorinated PVC or an expanded PVC.

16. Multilayer structure capable of being obtained by a method according to one of claims 1 to 15.

17. Multi-layer structure comprising in order:

•a protective layer (I) comprising a PMMA as defined in any one of claims 1 or 13,

•optionally an intermediate layer (I') comprising at least one pigment and/or dye,

•an intermediate ductile layer (II) comprising a block copolymer of formula BA _n as defined in one of claims 1 to 9,

•a layer of at least one thermoplastic polymer

(III), the layers being arranged one on top of the other in the order (I), (I'), (II) and (III) indicated.

18. Multilayer structure according to claim 16 or 17 characterized in that the layers (I), (I'), (II) and (III) are coextruded, hot compressed or multiinjected.

19. Multilayer structure according to one of claims 16 to 18 characterized in that the total thickness of the layers (I), (I') and (II) is greater than 310 μm, preferably greater than 350 μm.

20. Multilayer structure according to one of claims 16 to 19 characterized in that the thermoplastic polymer is PVC or ABS.

21. Use of the multilayer structure according to any one of claims 16 to 20 for the manufacture of everyday objects and articles such as: housings or casings of mowers, chainsaws, jet-skis, household appliances; car roof boxes, body parts; - number plates; exterior wall panels for caravans and mobile homes; exterior panels of refrigerators; shower cabin panels; - building doors; window moldings; cladding panels.