FR2852963A1 - Acrylic film for use e.g. for in-mould decoration, comprises a methacrylic/acrylic block copolymer made by radical polymerisation in presence of an alkoxyamine derived from a sterically-hindered nitroxide - Google Patents

Abstract

Acrylic film obtained by extrusion of a block copolymer with blocks (A) derived from methacrylic monomers and blocks (B) derived from acrylic monomers, in which the copolymer is obtained by radical polymerisation in presence of an alkoxyamine derived from a sterically-hindered nitroxide. Acrylic film obtained by extrusion of a composition containing 95-100 wt% block copolymer(s) of formula (I) and 0-5 wt% polymer(s) (A). (A) n-(B) (I) [Image] n : 2 or more; A, A : mainly methacrylic blocks; B : mainly acrylic blocks, formed by radical polymerisation controlled by alkoxyamines of formula (IIa-IId); Z : an n-valent organic or mineral radical; X : a group of formula R1-CH 2-N(O.)-; R1 : a radical with a mol. wt. of more than 16 g/mol An independent claim is also included for objects based on polystyrene, polycarbonate, polypropylene, PVC or ABS, surface-treated with this film.

Description

NEW PROCESS FOR THE SYNTHESIS / MANUFACTURE OF ACRYLIC FILMS

  The present invention relates to the field of acrylic materials, particularly to acrylic materials for coating certain thermoplastic materials and more particularly to the field of acrylic monolayer films.

  Acrylic resins are thermoplastic polymers that are increasingly used because of their exceptional optical properties. They include, in particular, their gloss appearance, their very high degree of transparency with at least 90% light transmission, their hardness, their thermoforming ability, their resistance to aging, especially to atmospheric agents (more particularly to UV), and their ease of formatting.

  For both technical and aesthetic reasons, it is important to find clear, ductile acrylic films to protect plastic parts with limited aging resistance. Indeed, if such films, by their nature acrylic resistance to UV (durability) and allow to bring to the room on which they are deposited the same property, they 20 risk by the fragile nature of methacrylic materials to weaken the whole of the coated part. Having acrylic materials sufficiently ductile to be deposited on ABS parts (acrylonitrile butadiene styrene copolymer), PVC (polyvinyl chloride), PC (polycarbonate), PP (polypropylene), PS (polystyrene) .... is therefore an issue of first importance.

  Among the shaping techniques suitable for this purpose, mention may in particular be made of the decorative molding technique, also known by the English name of "in-mold decoration".

  According to this technique, an acrylic film, preferably stored in the form of a roll, is, in a first step (possibly preceded by a continuous heat-bonding with another thermoplastic film or substrate in a step called collapsing), preformed to the geometry to fit the inner surface of the mold to form the desired object.

  In a second step, the thermoplastic resin in the molten state is injected into the mold and brought into contact with the film, which has the effect of adhering to the surface of the object thus formed.

  A particularly preferred embodiment of this technique comprises the simultaneous implementation of the 2 steps previously described, by means of an appropriate apparatus. This embodiment is referred to as Film Insert Molding (FIM).

  Acrylic films used in this technique can be used as such, in other words by maintaining their transparency. They can be 1o also colored, while maintaining their glossy appearance. Finally, they can receive by a particular printing process a drawing, a pattern, an image or characters, text or logo to convey to the consumer some information. As an example of printing, one can quote that of a drawing imitating the appearance of wood.

  The drawings or patterns printed on the transparent acrylic film can therefore be applied to the surface of the thermoplastic resin object, in particular by FIM. The film thus printed improves the aging of the object thus coated. In addition, carrying the pattern or pattern printed on that of its two surfaces which is in contact with the substrate, it also protects the pattern of contact 20 with the atmospheric agents, and adds to the drawing a visual effect of relief particularly sought after.

  Among the ways that currently exist to produce such products, let us note the following two: the first is to mix with an acrylic resin, enough impact modifier heart bark type (Röhm WO 99 25 29766 and US 6 420 033 Bl, Sumitomo EP 1000 978 Ai, Mitsubishi Ray EP 0 763 560 Ai) to make it ductile.

  US 6147162 discloses a monolayer acrylic film made from a composition comprising 50 to 95% of a specific acrylic resin, and 5 to 50% of a multi-layer acrylic polymer containing an elastomeric layer. The said polymer (also known to those skilled in the art under the name of impact modifier) is dispersed in the acrylic resin. This film is adapted to the technique of FIM, and provides a good surface hardness to the object thus coated.

  EP 1000978 A1 also describes an acrylic film made from a composition comprising 50 to 95% of a specific acrylic resin, and 5 to 50% of a shock modifier, suitable for coating by using the FIM technique. and having improved surface hardness. This document also mentions a laminated film (that is to say a multilayer film), and more specifically a bilayer film, the inner layer of which consists of the composition previously described, and the outer layer of an acrylic resin. without modifying shock. This bilayer film, presented as having excellent surface hardness, can also be rolled up in the form of a roll.

  US Patent 6444298 Bi describes a laminated (or multilayer) acrylic film comprising a layer containing an acrylic resin and acrylic elastomer particles (corresponding to a shock modifier), called a flexible layer, and a layer containing an acrylic resin without modifying shock, called surface layer. A three layer system is also disclosed wherein 2 surface layers are separately adhered to both surfaces of the flexible layer. Such a multilayer film makes it possible to improve the coloring treatment, avoiding bleaching and weakening of the coloration of the resin, linked to the presence of impact modifiers. This patent recommends to ensure that the ratio of the thickness of the flexible layer 20 to the total thickness of the film is between 50 and 100%, preferably between 60 and 100%.

  In the context of a highly automated industrial process for printing on acrylic film, the latter during its passage in rotary presses is subjected to very high tensile stresses, which it must, to withstand, exhibit an elongation at break. (measured at room temperature) high, for example greater than 50%, preferably 60%.

  The passage of the film in the rollers present in the printing devices, and its capacity to roll in the form of a roll for continuously feeding such devices, also require a very high flexibility, corresponding to an elastic modulus of traction ( or Young's modulus) of between 300 and 1800 MPa, preferably between 500 and 1200 MPa.

  This method consists of mixing with an acrylic resin, enough bark-like shock modifier finds its limits in the fact that the size of the core bark particles being greater than or equal to 50 nm, the transparency of the material is ensured only by the adequacy of the refractive indices of the particles and the acrylic resin. This adequacy is valid only in a given temperature range and outside this temperature, the material whitens.

  The second method, also tries to solve the problem of transparency: it consists in using block copolymers of type (A) nB where A is a block compatible with PMMA and B is a block of acrylate of low Tg. Such products are known to be organized on a nanometric scale in the areas of acrylate and methacrylate domain. The fineness of these areas ensures good transparency of materials at visible wavelengths whatever the temperature.

  Thus, Kaneka (Patent Application 2000-397401 (JP2000397401)) claims materials containing at most 95% block copolymers for use as a film. Although it demonstrates the interest of block copolymers, this invention is of limited industrial interest because it requires the mixing of block copolymers and PMMA homopolymer in addition to the manufacture of these materials. In addition, this invention uses copper complex catalysis to synthesize these block copolymers which is unacceptable for applications where the level of transparency of the resins should be the best possible since the copper complexes are highly colored molecules. On the other hand, for the block copolymers described in this invention to be useful in the manufacture of acrylic film, they must be blended with core-bark additives at a content of between 5 and 95%. Such a mixture, in addition to constituting an additional step in the manufacture of the film, limits the scope of the invention since it suffers from the same defects as those mentioned in the first film manufacturing method (maintenance of the optical properties in the presence heart-bark particles).

  The Applicant, in seeking to solve the problems mentioned above, namely the obtaining of a film having good mechanical resistance properties and resistance to external aggressions and good transparency, has found that certain block copolymers judiciously selected from known families of block copolymers make it possible to achieve the objective described above without resorting to additional core-shell additives. The particularity of the invention is to prepare films containing at least 95% of block copolymers. The copolymers of the invention are obtained by controlled radical polymerization in the presence of nitoxides as described by WO 97/27233. In particular, the present invention reveals the chemical compositions of block copolymers (A) nB necessary for producing acrylic films with a module between 300 MPa and 1800 MPa, high transparency.

  By chemical composition, the Applicant intends to specify, the nature of the monomers involved in the formation of each block, the ratio of these monomers, the number-average molecular weight and the weight of the copolymer in the final material.

  The object of the present invention is therefore to obtain an acrylic film which, while maintaining its qualities of transparency, simultaneously has a very high elongation at break (in particular enabling it to withstand the passage through the printing devices), combined with an elastic module offering the very good flexibility required for the storage of the roll film.

  The first subject of the invention is an acrylic film obtained by extrusion from a composition comprising from 95 to 100% by weight of at least one block copolymer corresponding to the formula (A) nB and from 0 to 5 % by weight of at least one homopolymer A, n being an integer greater than or equal to 2, A predominantly methacrylic block and B a predominantly acrylic block.

  Block B of the copolymers of the invention is advantageously constituted from a core of general formula (1) and a monomer or a mixture of monomers leading to a block B whose glass transition temperature (Tg ) is less than 00C. The core (1) is a radical having n (integer greater than or equal to 2) functions connectable to a polymer chain. The radicals of the general formulas are preferably chosen from the general formula: ## STR1 ## wherein: ## STR2 ## The molecular weight Mw of the block may be as follows: ## EQU1 ## B is between 40,000 g / mol and 200,000 g / mol and the polymolecularity index is between 2.5 and 1.1, preferably between 2 and 1.1. By way of example, alkyl acrylates with an alkyl chain containing at least two carbon atoms and preferably at least four carbon atoms, such as butyl acrylate, octyl acrylate, nonyl acrylate, and the like, will be chosen as monomers. hexyl ethyl. Other acrylates such as polyethylene glycol alcrylate or acrylonitrile may be used.

  Block A of the copolymers consists of a monomer or a mixture of monomers such that the resulting block A by polymerization has a glass transition temperature greater than 50 C. Block A must have a good affinity with the materials that we want to cover with the film. In particular, alkyl methacrylates having from 1 to 12 carbon atoms, linear or branched, will be chosen. Examples of these are methyl, ethyl, propyl, butyl, octyl, nonyl or 2-ethylhexyl methacrylates. It will also be possible to use functional methacrylics such as methacrylic acid, glycidyl methacrylate, methacrylonitrile or any methacrylate having an alcohol, amide or amine function.

  Optionally, anhydrides such as maleic anhydride or vinyl aromatic monomers such as styrenic or substituted styrene, in particular alpha methyl styrene, may be used as comonomer of this block.

  In addition, a proportion of the monomers serving for the block B may be kept in the mixture at most equal to 20% of the mixture of the monomers serving in block A. The weight average molecular weight of the compound (A) nB is between 80000 g / mol and 300000 g / mol with a polydispersity of between 1.5 and 2.5.

  Since monomers from block B can enter the composition of block A, to fully describe the copolymer, it is necessary to specify its overall content of monomers specific to block B and the ratio between block B and block A. These two ratio are not necessarily equal.

  The polymer (A) n-B contains between 60% and 10% of monomers of the block B but preferably between 50 and 25%. The proportion of block B in the block copolymer is between 10 and 50%, preferably between 20 and 50%.

  Method of obtaining: The choice of initiators of general formula It is essential to the success of the manufacture of the material: these initiators make it possible to control the number of arms of the block copolymer as well as its good sequencing. This last characteristic depends on the choice of the nitroxide control agent produced by decomposition of the initiating alkoxyamines. The general formulas of the initiators chosen for the invention are therefore as follows: ## STR1 ## ## STR2 ## methacryl Acryl Styryl a Styryl b x x C) x 0 X z x

R -Z

  ## EQU1 ## where R 1 is a heavy radical with a molecular weight greater than 16 g / mol. The choice of n> 1 makes it possible in particular to ensure a very high level of block copolymers in the final material by limiting the presence of the unreacted B block after the formation of A. The choice of X is particularly important so as to ensure during the formation of B a good control of the polymerization which makes it possible to maintain a high reactivity of B during the reintroduction of A. preferably, the following two nitroxides Xl and X2 will be mentioned: XN -If N

NOT

  The manufacturing process therefore consists in first polymerizing the block B in the presence of an initiator of formula II and optionally an additional amount of compound X at a temperature of between 600 ° C. and 1500 ° C., under 10 ° C. a pressure ranging from 1 to 10 bar. The polymerization may be carried out in the presence or absence of a solvent or in a dispersed medium. The polymerization is stopped before 90% conversion. It is chosen to evaporate or not the residual monomer of the block B according to the facility related to the synthesis process. The quantity of monomer for block A is then added. The polymerization of block A is carried out under conditions similar to that of block B. The polymerization of block A is continued at the targeted conversion. The recovery of the product is simply by drying the polymer according to a means known to those skilled in the art. During this step, the various additives necessary for the UV and thermal protection required for the acrylic film application are added and by extrusion with a flat die a film is produced at the desired thickness.

  The material obtained contains at least 95% of block copolymers.

  Optionally, a quantity of homopolymer A may be added so that the level of copolymer present in the material is between 95 and 100%. This addition may be necessary during the formation of block A since the conversion of the last traces of monomers may lead the skilled person to add a new initiator capable of converting these residual monomers. Within these limits the properties of the material are in accordance with a use in acrylic film.

  The film of the invention also contains all the additives necessary for its implementation and its coloration such as organic or inorganic pigments.

  The film of the invention is in the form of a thin layer 5 of thickness between 50 and 200 microns and preferably between 70 and 90 microns.

  The film of the invention can be obtained by well-known extrusion techniques such as calendering, blowing and casting.

  The film of the invention can be used as a surface treatment for the protection of materials such as ABS, PVC, PS, PP or PC. Among the protection techniques that may be mentioned as indicative and not limiting are the decoration in the mold (in mold decorating, insert molding film), the decoration by lamination, the screen coating and as a substitute for paint.

EXAMPLES

  The characterizations of the materials are made according to standard methods of analysis. In addition we measure the content of block copolymer by liquid absorption chromatography.

  The films are made with a RHEOCORD laboratory extruder with thermoplastic screw, through a flat die. The films then go through a heat-regulated calender with 3 rollers and are then cooled in a water bath.

  Before extrusion, the samples are parboiled under vacuum at 800 ° C. for at least 3 hours.

  Extruder temperatures zones 1,2,3: 1,750C Temperatures zone 4: 1,900C Screw speed: 33 rpm.

  Distance die / calender roll axis: at contact 30 Die gap: 0. 1 mm Thickness of the films: 100 to 1 50pm The screw is purged 1 hopper before sampling or disassembled and cleaned.

  The films thus obtained were evaluated mechanically and optically according to the respective standards: ASTM Standard D882: Determination of tensile properties on films Standard ASTM D1003: Determination of total light transmission and haze (Haze) An atomic force microscope analysis ( Digital Instrument Dimension 3100) validated the fact that the size of the elastomeric domains (dark on the snapshot) is well below 50 nm.

  Example of block copolymer synthesis and size of elastomer domains: Quantity introduced into the reactor Initiator: 65 g, X1 o initiator 111 Excessary nitroxide: Xl: 10 mol% relative to the initiator Synthesis block B: quantity of d butyl acrylate: 6000 g Synthesis temperature of the block B: 115 C Conversion achieved: 55.3 in 225 min Mn: 33000 Mw: 44000 Ip: 1.3 Synthesis of the block A: Qty of MMA introduced into the reactor: 4000 g Qty of acid introduced into the reactor: 444 g Qty of solvent: MEC: 2000 g Temperature of polymerization of block A: 90 C.

  Conversion reached: 51% Mn: 77160 g / mol; Mw: 134000 g / mol; lp: 1.75 Block copolymer ratio:> 99% Butyl acrylate content (determined by NMR): 42% MMA content: 53% Methacrylic acid content: 5% Domain size: The AFM photo given in Annex 1 highlights elastomer domain sizes well below 50 nm.

  Synthesis of Examples 1,2 and 3 The following table reports the synthesis conditions of the following examples (in these examples, the butyl acrvylate remaining at the end of block B is preserved for the synthesis of block A) References Copo: nature composition aim Type of alkoxyamine 1 block: nature (+ composition) Mn theory Excess of SG1 function Tc obtained (%) Time of poly (min) Mn (eq PS) Mw (eq PS) Ip 2 block: nature (+ composition) Tc Target Tc obtained (%) Time of poly (min) DTDDS (ppm) Final composition Block A Block B Mn (eq PS) Mw (eq PS) lp PABu / PMMA PABu / PMMA PABu / PMMA 50/50 Abu 100 60 000

I

  67 180 40 000 72 000 1.8 MMA / BuA 75/25 100 83 130 100 54% PMMA 46% PABu 62% 2 block 38% 1 block 71000 139000 40/60 Il1 Abu 100 45,000 60/45 II1 Abu 100 45 000 55.3 180 42 000 76 000 1.8 MMA / BuA 100 100 63 145 100 59% PMMA 41% PBuA 61% 2 block 39% 1 block 71130 138600 1.9 55.3 180 43 000 61 150 1.4 MMA / BuA 100 55 57 140 60 67% PMMA 33% PBuA 70% 2 block - 30% 1 Block 72220 143000 1.95 Example 1 according to the invention Composition: PMMA 54%; Pabu 46%; Mw = 139k; Ip = 1.9.10 Haze (%) <2 Modulus (MPa) = 368 Plastic Threshold Stress (MPa) = 8.5 Deformation at Break (%) = 125 Example 2: according to the invention Composition: PMMA 59%; Pabu 41%; Mw = 138k; Ip = 1.9 Haze (%) <2 Module (MPa) = 451 Plastic threshold stress (MPa) = 15.6 Breaking strain (%) = 79 Example 3: according to the invention Composition: PMMA 67%; Pabu 33%; Mw = 143k; Ip = 1.95 Haze (%) <2 Modulus (MPa) = 921 Plastic Threshold Stress (MPa) = 28.4 Deformation at Break (%) = 56 Example 4: (Comparative A block copolymer of Mn = 83000 g / mol Mw = 108 000 g / mol containing 48% of n-butyl polyacrylate and 52% of methyl methacrylate is prepared according to patent JP 2000-397401. The product obtained is placed in an oven under a nitrogen atmosphere at 200 ° C. for 1 hour. blackens and can not be extruded without degradation to form a film.

  EXAMPLE 5 (Comparative) Copo: Typical Nature of Alkoxyamine 1 Block: Nature (+ Composition) Mn and Time of Poly (Min) Mn (eq PS) Mw (eq PS) 1 Block 2: Nature (+ Composition) Tc Obtained (%) Time of poly (min) DTDDS (ppm) Final composition Mn (eq PS) Mw (eq PS) Ip PABu / PM

MA Ili1

  Abu 100 60 000 240 54 910 80 000 MAM / AMA 99/1 55 100 100 45% MCS

AT

  55% PABu 0.44 101600 Module: 7MPa This product is sticky and can not be extruded to form a film. This example illustrates the importance of choosing the amount of acrylate contained in the block copolymer and that all the copolymers claimed in WO 97/27233 are not usable as a monolayer film.

Claims (19)

  An acrylic film obtained by extrusion from a composition comprising from 95 to 100% by weight of at least one block copolymer of formula (A) nB and from 0 to 5% by weight of at least a polymer A ', characterized in that n is an integer greater than or equal to 2, A and A' may be identical or not are predominantly methacrylic blocks and B a predominantly acrylic block consisting of controlled radical polymerization from alkoxyamines of general formulas: embedded image in which: Z is an organic or inorganic radical having n valences; and X a compound of the general formula: I   RIiN ,, X = o RI is a heavy radical with a molecular weight greater than 16 g / mol.   2. Film according to claim 1 characterized in that X is the radical: j -, o r0 3. Film according to the preceding claims characterized in that the alkoxyamines II are the products described by the following formulas: oJ O <P% -C o NQN O N O R He n -   With R: o0 p with p integer between 2 and 10.   4. Film according to the preceding claims characterized in that the block B is obtained by the polymerization of at least one monomer (b) selected from alkyl acrylates with an alkyl chain having at least two carbon and preferably at least four carbon atoms such as butyl acrylate, octyl, nonyl, 2-ethyl hexyl, polyethylene glycol alcrylate or acrylonitrile.   5. Film according to one of the preceding claims characterized in that the block B has a Tg less than Oc.   6. Film according to one of the preceding claims, characterized in that the block A is obtained by the polymerization of at least one methacrylic monomer (a) chosen from alkyl methacrylates, such as methyl, butyl, dicarboxylic acid and the like. octyl, nonyl, 2-ethyl hexyl), or functional methacrylics such as methacrylic acid, glycidyl methacrylate, methacrylonitrile or any methacrylate containing an alcohol, amide or amine function, anhydrides such as anhydride maleic or aromatic vinyl monomers such as substituted styrenic or styrene, in particular alpha methyl styrene, and optionally at least one acrylic monomer (b) representing at most 20% by weight of the total monomers a and b to be polymerized. .   7. Film according to any one of the preceding claims, characterized in that the monomer b represents at most 60% of the composition.   8. Film according to any one of the preceding claims, characterized in that the monomer b represents from 10 to 50% by weight of the composition and preferably from 20 to 50%.   9. Film according to any one of the preceding claims characterized in that the block B represents at most 50% of the copolymer.   10. Film according to any one of the preceding claims characterized in that it has elastomeric domains B of size less than 50nm.   11. Film according to any one of the preceding claims, characterized in that it has a thickness of between 50 and 200 microns and preferably between 70 and 90 microns.   A film according to any one of the preceding claims having an elastic modulus of between 300 and 1800 MPa, a Haze less than 2 and an elongation at break greater than 60%.   13. Film according to any one of the preceding claims, characterized in that it further comprises a mineral or organic pigment.   14. Use of a film according to any of claims 1 to 13 as a surface treatment for the protection of ABS, PC, PVC, PS, or PP materials. 15. Use of a film according to any one of claims 1 to 13 for decoration in the mold.   16. Use of a film according to any one of claims 1 to 13 in lamination decoration.   17. Use of a film according to any one of claims 1 to 13 for the coating of screens.   18. Use of a film according to any one of claims 1 to 13 as a paint substitute.   Surface-treated PS, PC, PP, PVC or ABS parts according to any one of claims 14 to 18.