POLYMERIC BLENDS BASED ON VINYL-AROMATIC POLYMERS ENDOWED WITH HIGH TENACITY AND CHEMICAL RESISTANCE

Abstract: Polymeric blends based on vinyl-aromatic polymers endowed with high tenacity and chemical resistance comprising: - from 10 to 90 % by weight of a vinyl-chloride polymer; - from 90 to 10 % by weight of a vinyl-aromatic copolymer containing from 2 to 25 % by weight of an ethylenically unsaturated nitrile and a quantity not exceeding 15 % by weight of a rubber.

Description: The present invention relates to polymeric blends based on vinyl-aromatic polymers showing high tenacity and chemical resistance. More particularly, the present invention relates to blends based on vinyl-aromatic polymers having high tenacity and chemical resistance suitable to be transformed into shaped bodies endowed with self-extinguishing and good physical properties. As known, vinyl-aromatic polymers are thermoplastic resins suitable to be transformed in warmth into shaped bodies by injection or extrusion molding. Said vinyl-aromatic poly­ mers have a fair tenacity, but they are not suitable to be used in applications where a high tenacity associated with a good chemical resistance are required. A way to improve these lacking properties is to provide blendswith other polymers, having the necessary properties to give a material showing the desired combination of pro­ perties. However, this approach has been successful only in a limited number of cases; in fact, the blending re­ sults in combining the worst characteristics of each com­ ponent, the result being a material of such poor proper­ ties as not to be of any practical or commercial value. The reasons for this failure are due to the fact that not all polymers are compatible with each other and therefore do not perfectly adhere. As a result, interfaces are formed among the components of the blend, which represent weakness and breaking points. EP-A-21537 discloses thermoplastic moulding compositions with enhanced fire-resistant characteristics, composed of vinyl­ chloride polymers as a graft copolymer (of a vinyl-aromatic and a nitrile monomer) on a synthetic rubber-like polymer and a zinc-titanium(IV)oxide compound as fire retardant. Mechanical and chemical properties of the prepared composit­ ions are not given particular attention in said document. The applicant has now found that tenacity and chemical resistance of vinyl-aromatic polymers can be improved, without modifying substantially the other mechanical pro­ perties, by intimately mixing from 10 to 90% by weight of a vinylchloride polymer; with from 90 to 10% by weight of a vinyl-aromatic copolymer containing copolymerized from 2 to 25% by weight of an ethylenically unsaturated nitrile and containing a quanti­ ty of rubber not exceeding 15% by weight. Preferably, the blends contain from 25% to 75% ty weight of a vinylchloride polymer and from 25% to 75% by weight of a viny-aromatic copolymer containing copolymerized an ethylenically unsatured nitrile and a quantity not exceeding 15% by weight of rubber. The term "viny-aromatic copolymer" as used in the present invention and claims is to be understood to include any solid thermoplastic polymer and respective copolymer essentially consisting of, i.e. containing chemically bound, at least 50% by weight of one or more vinyl-aromatic compounds of general formula: wherein X represents hydrogen or an alkyl radical having from 1 to 4 carbon atoms; n is zero or an integer from 1 to 5 and Y represents halogen, e.g. fluorine, chlorine, bromine and iodine or an alkyl radical having from 1 to 4 carbon atoms, i.e. the methyl, ethyl, propyl or butyl groups, the two last mentioned groups being straight chain or branched. Examples of vinyl-aromatic compounds having the above re­ ported general formula are: styrene, methyl-styrene, mono-, di-, tri-, tetra- and penta-chlorostyrene and the respective alpha-methyl-styrenes, styrenes alkylated in the nucleus and the respective alpha-methyl-styrenes such as ortho- and para-methyl-styrene, ortho- and para-ethyl-­ styrenes; ortho- and para-methyl-alpha-methyl-styrenes, etc. These monomers may be used either alone or in admixture with each other copolymerizable co-monomers such as, for instance, maleic anhydride. Rubbers are used for making the vinyl-aromatic polymers impact or shock resistant and, according to the present invention, they are present in a quantity not exceeding 15% by weight. Quantities comprised between 2% and 12% by weight are preferred. The rubbers which are used to this purpose are: poly-buta­ diene, poly-isoprene, copolymers of butadiene and/or iso­ prene with styrene or with other monomers, or the saturated rubbers such as ethylene-propylene rubber, ethylene-pro­ pylene-diene terpolymers and silicon rubbers containing unsaturated groups, etc. As ethylenically unsaturated nitrile copolymerized with vinyl-aromatic monomers it is to be understood firstly and preferably acrylonitrile. Other ethylenically unsaturated monomers, such as methacrylonitrile, can be advantageously used. The modified vinyl-aromatic copolymers can be obtained ac­ cording to any known polymerization process, such as sus­ pension, bulk-suspension or continuous bulk polymerization, provided that the above mentioned compounds are used as starting monomers. Said modified vinyl-aromatic copolymers differ from the known acrylonitrile-butadiene-styrene resins, known as ABS resins, as far as the morphology, structure and size of the rubber particles dispersed in the rigid polymeric matrix are concerned. As consequence of such morphological difference, the blends of the present invention display a resilience or impact resistance higher than that of the ABS resins, especially when the content in rubber is lower than 15% and preferably lower than 10% by weight. Vinylchloride polymers to be used in the blends of the pre­ sent invention may be either the vinylchloride homopolymer or copolymers thereof containing less amounts of other co­ polymerizable ethylenically unsaturated compounds. Although vinylchloride homopolymers are preferred in the embodiment of the present invention, vinylchloride copoly­ mers containing up to 20% by weight of other copolymer­ izable unsaturated compounds can be also used. Suitable copolymerizable unsaturated compounds may be, for instance, vinylidene chloride, vinylidene bromide, vinylidene fluoro­ chloride and so like; unsaturated hydrocarbons such as ethylene, propylene, isobutene; allyl compounds such as allylacetate, allylchloride, allyl-ethyl-ether; vinyl esters such as vinylacetate, vinylpropionate; acrylic or meth­ acrylic acid and their esters containing from 1 to 8 car­ bon atoms in the alkyl group, acrylonitrile etc. Instead of a single unsaturated monomer of the above de­ scribed type, mixtures of said comonomers can be used, provided that these comonomers are not used in amounts ex­ ceeding 20% and do not substantially modify the proper­ ties of polyvinylchloride. The blends of the present invention may be prepared by mixing them at low or high temperature in any known type of mixer. For instance quick mixers (Henschel type), single-­ screw or double-screw extruders, Banbury mixers, mixing rollers, etc. may be used. If the blend is prepared at high temperature, temperatures comprised between 140 and 200°C can be used up to obtain a homogeneous and uniform composition. The compositions may comprise little amounts, generally comprised between 1 and 5% by weight of a stabilizer or other additives intimately mixed. Suitable stabilizers are lead basic carbonate, lead dibasic stearate, lead tribasic phosphate, lead dibasic phosphate, cadmium stearate, cad­ mium laurate, cadmium ricinolate, glyceryl-monostearate, dibutyltin-mercaptide and organo-tin-compounds containing sulfur such as for instance, dibutyl-tin-S,S′-bis(3,5,5-­ trimethylhexylmercaptoacetate). Other additives such as plasticizers, lubricants, anti-­ flame agents, flowing agents, anti-static agents, dye­ stuffs, pigments, foaming agents to provide lighter bodies and semi-finished products may be added during the mixing step of the components, in quantities ranging from 0.1 to 10% by weight. The blends of the present invention can be easily processed and show a set of properties which on the whole are better than those of the single components. For this reason, the polymeric blends of the present invention find a useful application for obtaining materials endowed with high tenacity combined with high chemical and flame-resistance up to be self-extinguishing. Therefore, said blends are used in the field of domestic electric apparatus and app­ liances, electronics and generally in the field of tech­ nical materials in form of films, sheets, tapes, bands, rods, boxes, cups, containers, etc. The blends may be used to provide foamed articles by the techniques known in the art. The invention as claimed will be further described with reference to the following illustrative but not limiting examples. In the examples, all the parts are expressed by weight, unless indicated otherwise. EXAMPLES 1-4 By means of a quick Henschel mixer there was prepared a blend having the following composition: The thus obtained blend is mixed in cold in a tumbler with: The thus obtained blend is extruded by means of a single-­ screw extruder, having a diameter of 60 mm, a length/dia­ meter ratio of 25, a compression ratio of 3: 1 and temper­ atures at the hopper and head of 160, 170, 180, 175°C. To determine the properties, the granules are injection molded at a temperature of 190°C on a NEGRI & BOSSI V-17-­ 110FA injection molding press in order to get test pieces having sizes according to standard specifications. The properties measured on the thus obtained test pieces are reported in the following table. To measure the characteristics of the blends of the pre­ sent invention, the following methods were used: A. Mechanical properties Tensile strength and elasticity modulus were measured ac­ cording to ASTM-D 638; IZOD resilience with indent at 23°C, was measured according to ASTM D 256, on test pieces hav­ ing a 3.2 mm thickness. B. Thermal properties Softening temperature VicatB (5 kg in oil) was determined according to ISO 306. C. Rheologic properties Melt-index was determined according to ASTM D 1238, at 220°C and 10 kg. D. Resistance to cracking under load was measured on test pieces of 2.1 mm thickness, shape and sizes of which are according to ASTM D 2552 (Environmental Stress Cracking). Test pieces have been obtained by press molding, at 180°C, pressure 160 kg/cm², for 6 minutes. Cooling rate was about 10°C/min. Said test pieces underwent a tensile stress with constant load of 10 MPa (creep) deepes in an olive oil/ oleic acid 50: 50 by weight mixture. Resistance to crack is measured and expressed as the time necessary to break the test piece. E. Self-extinction is determined according to UL-94 EXAMPLE 5 Example 1 is repeated by blending 30 parts by weight of polyvinylchloride K 58 and 70 parts by weight of a vinyl-­ aromatic copolymer having the following composition: 72% styrene, 20% acrylonitrile, 8% polybutadiene rubber. The properties of the thus obtained blend are as follows:

Claims: 1. Vinyl-aromatic polymeric blends having high tenacity and chemical resistance, characterized in that they comprise: from 10 to 90% by weight of a vinylchloride poly­ mer and from 90 to 10% by weight of a vinyl-aromatic copo­ lymer, containing from 2 to 25% by weight of an ethylenically unsaturated nitrile and a quantity of rubber not exceeding 15% by weight. 2. Blends according to claim 1, characterized in that they comprise from 25 to 75% by weight of a vinyl-­ chloride polymer and from 75 to 25% by weight of a vinyl-aromatic copolymer containing from 2 to 25% by weight of an ethylenically unsaturated nitrile and a quantity of rubber not exceeding 15% by weight. 3. Blends according to claim 1 or 2, characterized in that the vinyl-aromatic copolymer contains at least 50% by weight of one or more vinyl-aromatic monomers of the general formula: wherein X represents hydrogen or an alkyl radical having from 1 to 4 carbon atoms; Y represents a halo­ gen or an alkyl radical having from 1 to 4 carbon atoms, and n is zero or an integer comprised between 1 and 5. 4. Blends according to anyone of the preceding claims, characterized in that the vinyl-aromatic copolymer contains from 2 to 12% by weight of rubber. 5. Blends according to anyone of the preceding claims, characterized in that the copolymerized ethylenically unsaturated nitrile is acrylonitrile. 6. Blends according to anyone of the preceding claims, characterized in that the vinylchloride polymers are selected from vinylchloride homopolymer and copolymers thereof containing up to 20% by weight of other co­ polymerizable unsaturated compounds. 7. Blends according to anyone of the preceding claims, characterized in that they contain further from 1 to 5% by weight of a stabilizer and/or other additives.

Inventors: BIGLIONE, GIANFRANCO, DR., MATTIUSSI, ANDREA, VITTADINI, GIORGIO, DR.
Applicants: MONTEDIPE S.R.L.
Application year: 1986
Main classification: C08L27
IPC codes: C08L1, C08L25, C08L51, C08L33, C08L27, C08L101, C08L21, C08L23, C08L7, C08L55, C08L77