COMPOSITE MATERIAL

Abstract: A composite material comprises a first layer and a second layer, said layers being bonded together, wherein said first layer comprises 40 - 95 % by weight of an acrylic polymer formed from a monomer comprising 60 - 100 % methyl methacrylate and 0 - 40 % of a vinylic comonomer and 5 - 60 % of a copolymer wherein at least 10 % of the monomer residues are (optionally substituted) styrene and said second layer comprises a thermoplastic polymer. The material is particularly useful for forming sanitary articles, e.g. shower trays by thermoforming. A preferred second layer material is HIPS.

Description: Composite material The present invention relates to thermoplastic composite materials especially materials having a layer of acrylic resin. Composite materials having a layered structure including a layer of an acrylic polymer are known and useful in many applications. For example, articles such as bathtubs and other sanitaryware are often made from an acrylic upper or shell layer which is bonded to a reinforcing substrate layer. The reinforcement has conventionally been of fibre-reinforced thermoplastic or thermosetting resin applied by spraying onto the bottom surface of an acrylic shell. There has recently been a desire to eliminate such reinforcing processes, which may be costly and messy to apply, in favour of using laminates of acrylic polymer with another thermoplastic material. Examples of such laminates and processes for making them are given in EP-A-0781201 and EP-A-0225500 which describe a composite plate for drawing into a bathtub shape which has an acrylic layer arranged upon a layer of an acrylonithle-butadiene-styrene (ABS) thermoplastic material, the composite being formed by coextrusion. EP-A-0647177 describes the application of a thermosetting polyester material to the rear face of an acrylic bathtub by injection moulding techniques. EP-A-0495026 describes a continuous lamination process for forming a laminate of an acrylic polymeric layer to an ABS substrate. EP-A-0454520 describes a further method for providing a laminate of acrylic and ABS for thermoforming applications by calendering sheets of polymethyl methacrylate with molten ABS. From the above references, acrylic bathtubs are known to be reinforced by a layer of ABS material. Acrylic materials are compatible with and adhere well to ABS so that such laminates may be formed by a variety of methods. However, ABS is a relatively expensive material compared to the readily available polystyrene thermoplastic polymers. High impact polystyrene (HIPS) is a suitable substrate material for many applications in which acrylic sheet is used and it is often considerably cheaper than ABS. One problem with the use of HIPS as a substrate for acrylics is the difficulty of adhering acrylic polymers to HIPS. This problem is described in EP-A-0458520 which describes a multi-layered structure and suggests the use of an ABS layer to bond an acrylic layer to a HIPS substrate. It is an object of the present invention to provide a composite material which overcomes at least some of the problems with the prior art. According to the invention, a composite material comprises a first layer and a second layer, said layers being bonded together, wherein said first layer comprises 40 - 95% by weight of an acrylic polymer formed from a monomer comprising 60 - 100% methyl methacrylate and 0 - 40% of a vinylic comonomer and 5 - 60% of a styrenic polymer wherein at least 10 % of the monomer residues are (optionally substituted) styrene and said second layer comprises a thermoplastic polymer. The composite is useful for forming articles such as shower trays, washbasins, bathtubs, panelling and similar articles e.g. by thermoforming. Composites having the first layer formed from the composition described above exhibit improved inter-layer bonding, especially when the second layer is a HIPS material. Therefore in a preferred composite material the second layer comprises HIPS. According to a second aspect of the invention we provide a process for the manufacture of a composite layered material comprising the steps of: (i) forming a first layer comprising 40 - 95% by weight of an acrylic polymer formed from a monomer comprising 60 - 100% methyl methacrylate and 0 - 40% of a vinylic comonomer and 5 - 60% of a copolymer wherein at least 10 % of the monomer residues are (optionally substituted) styrene; (ϋ) forming a second layer of a thermoplastic material; (iii) bonding together said first and second layers to form a layered composite material. The first and second layers may be bonded together by any suitable method, e.g. extrusion-coating, by coextrusion of the two layers or by laminating, e.g. by passing heated layers together through a nip roller. The first acrylic layer may be formed by a casting process wherein a syrup comprising acrylic polymer or copolymer dissolved in a monomer or mixture of monomers with initiator and optionally other additives is poured into a space between two constraining surfaces separated by a gasket or similar spacing device and then heated to cause the syrup to polymerise, usually to form a high molecular weight polymer sheet. Cast acrylic processes may be either batch or continuous. If the first acrylic layer is formed by casting then the cast acrylic sheet may be laminated to the thermoplastic substrate. Alternatively the first acrylic layer may be formed by casting directly onto a preformed thermoplastic second layer substrate. A particularly convenient method of forming the composite is by coextrusion. According to a third aspect of the invention we therefore provide a process for the manufacture of a composite layered material comprising the steps of: (i) forming a first molten polymer stream comprising 40 - 95% by weight of an acrylic polymer formed from a monomer comprising 60 - 100% methyl methacrylate and 0 - 40% of a vinylic comonomer and 5 - 60% of a copolymer wherein at least 10 % of the monomer residues are (optionally substituted) styrene; (ϋ) forming a second molten polymer stream of a thermoplastic substrate material; (Hi) coextruding said first and second polymer streams by means of a coextrusion apparatus to form a layered composite material. Particularly when the composite material is formed by coextrusion, one or both layers may contain a proportion of material of which the other layer is formed, e.g. by incorporating edge-trims or other off-cuts or reworked material from the coextruded material into the feed. It is highly desirable to provide an acrylic material for coextrusion onto a substrate which has similar rheological properties at the extrusion temperature to those of the substrate material. Therefore one preferred form of the first layer acrylic material has a rheology, e.g. melt flow index (MFI) which is similar to HIPS grades for extrusion. The composite may vary between 0J - 50 mm in thickness, preferably 1 - 20 mm. The acrylic layer preferably comprises 1 - 40%, preferably 5 - 20% of the total thickness of the composite. The composite material may comprise more than two layers. For example the composite may comprise a thermoplastic second layer having an acrylic material bonded to each side of it. The acrylic first layer material comprises 40 - 95% by weight of an acrylic polymer formed from a monomer comprising 60 - 100% methyl methacrylate and 0 - 40% of a vinylic comonomer. Preferred comonomers include C 1-10 aikyl acrylate or C,.,,, alkyl (C^-alk)acrylate, optionally having a functional group, e.g. hydroxy ethyl methacrylate, isobornyl methacrylate; styrene and other vinyl aromatics, polyfunctional monomers such as ethylene giycol dimethacrylate. The acrylic may comprise a copolymer of methyl methacrylate and an alkyl acrylate or alkacrylate. Preferred comonomers include methyl acrylate, ethyl acrylate and butyl acrylate. The acrylic material may also contain other additives commonly used in acrylic formulations such as chain transfer agents, (e.g. various mercaptans), stabilisers, lubricating agents, fire retardents, colourants, initiator residues, residues of chain-transfer compounds, cross-linking agents, fillers, release agents, impact modifiers, UV absorbing compounds etc. The acrylic first layer material contains 5 - 60%, preferably 15 - 40%, especially at least 25% by weight of a styrene-containing polymer wherein at least 10 % of the monomer residues are (optionally substituted) styrene. Suitable styrene-containing polymers include methyl methacrylate- butadiene - styrene copolymer (MBS), styrene - maleic anhydride copolymer, styrene - butadiene rubbers such as the Cariflex ™ polymers supplied by Shell, styrene - olefin copolymers such as styrene ethylene-butylene styrene (optionally containing succinic anhydride) , styrene - ethylene - propylene, e.g. the polymers sold under the Kraton trademark and thermoplastic polymers such as styrene-acrylonitrile (SAN) copolymers, including optionally terpoiymers with acrylate comonomers (ASA copolymers), and blends of such polymers with other materials, e.g. SAN blends with EPDM rubber sold as ROYALTUF. Preferred styrene copolymers include MBS, styrene - maleic anhydride copolymer, styrene - butadiene rubbers, styrene - olefin copolymers and core-shell particles containing a suitable proportion on styrene residues. Particularly preferred are MBS polymers. The acrylic first layer may additionally contain up to 60% by weight (based on total weight of the layer material) of a particulate impact modifier such as a core-shell type impact modifier. Core-shell impact modifiers are known in the art and normally comprise a hard core, e.g. of (optionally cross-linked) polymethyl methacrylate, a rubbery shell of relatively low Tg polymer, e.g. a styrene/alkyl acrylate copolymer and optionally further shells of an acrylate and/or a methacrylate polymer or copolymer. Such particles are usually made by emulsion polymerisation techniques and may contain additional components, such as functional comonomers to promote grafting between the core and shell(s). The foregoing describes one common general type of core-shell impact modifying particle but other types are also known and used, e.g. having a relatively soft core and harder shell or containing different comonomers in various proportions. A suitable core-shell particle is described in WO96/37531. The acrylic polymer and styrene polymer forming the first layer material may be combined by blending, e.g. melt blending. This may be achieved by mixing together particles of each polymer in the feed of a moulding apparatus, e.g. extruder and then processing into a compounded pellet for subsequent moulding of the first layer of the composite material or the materials may be dry-blended, e.g. by tumbling and then melted and shaped directly into the first layer of the composite. Other methods of blending together the polymers are also envisaged, e.g. dissolving one polymer in a solution of the other or in a monomer or pre-polymer mixture which is a precursor to the other polymer. For example the styrene-containing polymer may be dissolved or otherwise dispersed in methyl methacrylate or in a solution of polymethylmethacrylate in methyl methacrylate, optionally containing other comonomers or copolymers from which the first layer material may be formed by initiating the mixture e.g. by adding an azo or peroxide initiator, casting the solution in a mould or on a continuous belt and then maintaining the mixture at a suitable temperature to polymerise the acrylic monomer to form a cured material. The substrate material is selected according to the application and may include a range of commonly used commercial thermoplastics e.g. polyolefins, e.g. polypropylene, ABS, PVC, other acylic polymers, MBS etc, however the process of the present invention is particularly suitable for producing a composite material of the acrylic first layer in contact with a high impact polystyrene (HIPS) substrate by coextrusion methods because the incorporation of the styrenic polymer into the acrylic of the first layer greatly improves the adhesion between the layers, whereas previously acrylic materials did not adhere well to HIPS substrate polymers. The styrene polymer is therefore useful as an adhesion promoter for the acrylic material. Therefore in a fourth aspect of the invention we provide a method of forming a composite material comprising coextruding together an acrylic material with a high impact polystyrene material characterised in that the acrylic material consists of a) 50 - 100% by weight of a polymer blend comprising: (i) 40 - 95% by weight of an acrylic polymer formed from a monomer comprising 60 - 100% methyl methacrylate and 0 - 40% of a vinylic comonomer and (ii) 5 - 60% of a styrene copolymer wherein at least 10 % of the monomer residues are (optionally substituted) styrene; b) 0 - 50% of one or more additives selected from stabilisers, lubricating agents, fire retardents, colourants, initiator residues, residues of chain-transfer compounds, cross-linking agents, fillers, release agents, impact modifiers, UV absorbing compounds, in the absence of biocidal compounds. The composite articles of the invention and which may be formed by the methods of the invention may be beneficially used to manufacture sanitary articles, such as shower trays, bathtubs etc, building components such as walls, doors, floors etc, parts for vehicles, household appliances and other articles in a wide variety of end-uses. The invention will be further described in the following examples. Example 1 An acrylic polymer comprising 86% methyl methacrylate + 14% ethyl acrylate copolymer (Polymer 1), having a molecular weight of about 90,000 Daltons and melt flow index (MFI) of 27 g/10 mins was compounded together with 35% w/w of MBS (Kane-Ace B56) and extruded into pellets. The resulting material had an MFI of 2 g/10 minutes, measured at 230 °C with a 3.8 kg weight according to the standard test described in ASTM D 1238. The acrylic compound was then coextruded with HIPS (BP4230 available from BP) which has a MFI of 23.7 g/10 mins at 230 °C. The total thickness of the composite was 1.02 mm; the acrylic layer being 0J3 mm thick. The adhesion between the layers was moderate - good. The adhesion was also estimated using a single asperity scratch apparatus in which the samples were scratched in the direction of extrusion using a 35° (apical angle) tungsten carbide stylus and a traverse rate of 100 mm/min. Scratches were generated at single loads. A scratch was generated with a normal force of 5N and checked for visual evidence of delamination. Further scratches were generated at 1N increments of normal force until delamination was observed. Delamination was said to have occurred when the delamination was continuous, or very nearly continuous around the scratch. All experiments were carried out at 23°C and 50% relative humidity. Samples were kept in the laboratory environment for 24 hours prior to testing. The results are shown in the table. Example 2 Polymer 1 was compounded with 5% styrene - maleic anhydride copolymer (Stapron S obtained from DSM). The resulting acrylic compound was coextruded onto HIPS and the resulting adhesion was moderate. Example 3 Polymer 1 was compounded with 5% styrene - maleic anhydride copolymer and an additional 35% w/w of MBS. The resulting acrylic compound was coextruded onto HIPS and the resulting adhesion was moderate. Example 4 Polymer 1 was compounded with 8% styrene-butadiene rubber (SBR) (Cariflex™ by Shell) and 20% of a core-shell impact modifier. The resulting mixture had an MFI of 9 g/10 minutes. The resulting acrylic compound was coextruded onto HIPS and the resulting adhesion was moderate - good. Example 5 An acrylic copolymer comprising 90% methyl methacrylate + 10% butyl acrylate residues (Polymer 2), having a molecular weight of about 90,000 Daltons was compounded with 35% Kraton™ G1650E manufactured by Shell, which is a linear styrene-ethylene-butylene-styrene polymer . The resulting acrylic compound was coextruded onto HIPS and the resulting adhesion was moderate - good. Example 6 Polymer 2 was compounded with 35% Kraton G1701 E , which is a linear styrene-ethylene-propylene polymer . The resulting acrylic compound was coextruded onto HIPS and the resulting adhesion was moderate - good. Example 7 Polymer 2 was compounded with 35% Kraton FG1901X , which is a linear styrene-ethylene-butylene-styrene polymer containing 1.7% bound succinic anhydride. The resulting acrylic compound was coextruded onto HIPS and the resulting adhesion was moderate - good. Example 8 A number of coextruded samples were made by extruding an acrylic capstock formed from Polymer 2 blended with a specified amount of a styrene-containing polymer onto a HIPS substrate and subjected to the scratch test as generally described in Example 1. The coextruded layer was between 100 and 200 mm thick. Table 1 shows the materials used and whether the layers delaminated at each loading tested. The materials shown in the table are: BP2220: medium impact HIPS, MFI of 40gms/10mins BP4230: high impact HIPS, MFI of 24gms/10mins BP5300: super high impact HIPS, MFI of 12gms/10mins ASA: acrylate-styrene-acrylonitrile (BASF Luran S) SAN: styrene-acrylonitrile (BASF Luran N) MBS: methylmethacrylate-butadiene-styrene acrylic copolymer (Kane-Ace) B56 Kraton G 1701 : linear styrene-ethylene-propylene (Shell) SBR: styrene-butadiene-rubber (Shell Cariflex) Core -shell: methylmethacrylate-butylacrylate / styrene-butylacrylate core shell particle. Royaltuf: 50% SAN/50%EPDM(ethylene/propylene diene rubber). A control sample of polymer 2 without any styrenic polymer added, coextruded onto BP 4230 HIPS, showed no delamination at 5 N but delaminated when tested at forces of 8, 9, 10 and 12.5 N. The results show that incorporation of the styrene-containing copolymer into the acrylic capstock material leads to no delamination of the capstock from the substrate HIPS layer at most loadings tested. The preferred systems do not delaminate even at the highest loading. Table 1 Acrylic = Polymer 1

Claims: Claims 1. A composite material comprising a first layer and a second layer, said layers being bonded together, wherein said first layer comprises 40 - 95% by weight of an acrylic polymer formed from a monomer comprising 60 - 100% methyl methacrylate and 0 - 40% of a vinylic comonomer and 5 - 60% of a styrenic polymer wherein at least 10 % of the monomer residues are (optionally substituted) styrene and said second layer comprises a thermoplastic polymer. 2. A composite material as claimed in claim 1 , wherein the second layer comprises high impact polystyrene (HIPS). 3. A composite material as claimed in either claim 1 or claim 2, wherein the acrylic layer comprises 1 - 40% of the total thickness of the composite. 4. A composite material as claimed in any of the preceding claims, wherein the acrylic polymer comprises a copolymer of methyl methacrylate and an alkyl acrylate or alkacrylate. 5. A composite material as claimed in any of the preceding claims, wherein the styrene-containing polymer is selected from the group consisting of methyl methacrylate- butadiene - styrene copolymer, styrene - maleic anhydride copolymer, styrene - butadiene rubbers, styrene - olefin copolymers, styrene-acrylonitrile copolymers and blends with rubbery polymers. 6. A composite material as claimed in any of the preceding claims, wherein the acrylic first layer additionally contains up to 60% by weight (based on total weight of the layer material) of a particulate impact modifier such as a core-shell type impact modifier. 7. A process for the manufacture of a composite layered material comprising the steps of: (i) forming a first layer comprising 40 - 95% by weight of an acrylic polymer formed from a monomer comprising 60 - 100% methyl methacrylate and 0 - 40% of a vinylic comonomer and 5 - 60% of a styrenic polymer wherein at least 10 % of the monomer residues are (optionally substituted) styrene; (ii) forming a second layer of a thermoplastic material; (iii) bonding together said first and second layers to form a layered composite material. 8. A process as claimed in claim 7, wherein the first and second layers are bonded together by extrusion-coating, by coextrusion of the two layers or by laminating. 9. A process as claimed in claim 7, wherein the first acrylic layer is formed by a casting process wherein a syrup comprising acrylic polymer or copolymer and the styrene-containing copolymer dispersed or dissolved in a monomer or mixture of monomers with initiator and optionally other additives is poured into a space between two constraining surfaces separated by a gasket or similar spacing device and then heated to cause the syrup to polymerise to form a high molecular weight polymer sheet. 10. A process as claimed in claim 9, wherein the cast acrylic sheet is subsequently laminated to the thermoplastic substrate. 11. A process as claimed in claim 9, wherein the first acrylic layer is formed by casting the acrylic syrup directly onto a preformed thermoplastic second layer substrate. 12. A process as claimed in claim 7, wherein the styrene-containing material is added to the acrylic polymer to form the first layer material by blending and then the first layer is subsequently formed by extrusion. 13. A process as claimed in any preceding claim wherein said second layer comprises high impact polystyrene (HIPS). 14. A method of forming a composite material comprising coextruding together an acrylic material with a high impact polystyrene material characterised in that the acrylic material consists of a) 50 - 100% by weight of a polymer blend comprising: (i) 40 - 95% by weight of an acrylic polymer formed from a monomer comprising 60 - 100% methyl methacrylate and 0 - 40% of a vinylic comonomer and (ii) 5 - 60% of a styrene copolymer wherein at least 10 % of the monomer residues are (optionally substituted) styrene; b) 0 - 50% of one or more additional compounds selected from stabilisers, lubricating agents, fire retardents, colourants, initiator residues, residues of chain-transfer compounds, cross-linking agents, fillers, release agents, impact modifiers, UV absorbing compounds. 15. Use of a styrenic polymer selected from the group consisting of methyl methacrylate- butadiene - styrene copolymer, styrene - maleic anhydride copolymer, styrene - butadiene rubbers, styrene - olefin copolymers, styrene-acrylonitriie copolymers and blends with rubbery polymers as an additive to an acrylic polymer formed from a monomer mixture comprising 60 - 100% methyl methacrylate and 0 - 40% of a vinylic comonomer to promote adhesion between the acrylic material and high impact polystyrene, said styrenic polymer being present at a level in the range 10 - 50 % by weight of the total weight of styrenic polymer and acrylic polymer.

Inventors: LARDER ALAN PAUL, WILFORD-BROWN JACQUIN HILARY, LARDER, ALAN, PAUL, WILFORD-BROWN, JACQUIN, HILARY
Applicants: INEOS ACRYLICS UK LTD, LARDER ALAN PAUL, WILFORD BROWN JACQUIN HILARY, INEOS ACRYLICS UK LIMITED, LARDER, ALAN, PAUL, WILFORD-BROWN, JACQUIN, HILARY
Application year: 1999
Main classification: B32B27
IPC codes: B29C47, B29C51, B29K105, B29L9, B32B7, B32B27, B32B37, C08J5, C08L25, C08L33, C08L51, C08L53