LIGHT STABLE THERMOPLASTIC RESIN COMPOSITIONS

Abstract: A thermoplastic composition having improved resist­ ance to discoloration upon exposure to light, comprising: a thermoplastic resin base polymer; and at least one dye capable of bleaching upon exposure to light in an amount effective for compensating for a change in color of said thermoplastic resin base polymer upon expo­ sure to said light.

Description: Field of the Invention The invention relates to a polymer mixture which maintains its color upon exposure to light. Background of the Invention Many polymers have the unpleasant property of losing their color upon exposure to light. Such polymers include polyphenylene ethers, aromatic polyesters such as polybutylene terephthalate, polyethylene terephthalate and styrene-containing (co)polymers, for example, polystyrene, rubber-modified "high-impact" polystyrene, styrene-acrylonitrile (SAN) copolymers, acrylonitrile-butadienestyrene (ABS) polymers, especially such styrene-containing (co)polymers which have been made self-extinguishing by the addition of aromatic bromine compounds, as well as polymer mixtures comprising one or more of the said polymers. The present invention relates to a thermoplastic composition having improved resistance to discolorization upon exposure to light consisting essentially of : a polyphenylene ether or a polyphenylene ether admixed with conventional additives or a polyphenlyene ether-styrene polymer blend with a weight ratio of the polyphenylene ether to the styrene polymer varying between 1:5 and 5:1 or a polyphenylene ether-styrene polymer blend with a weight ratio of the polyphenylene ether to the styrene polymer varying between 1:5 and 5:1 admixed with conventional additives; and at least one dye. Such mixtures and their mode of preparation are to be found in numerous patent publications, for example, the United States Patent Specifications 3,306,874; 3,306,875; 3,257,357; and 3,257,358. The use of styrene polymers in such mixtures is described more in particular in the United States Specifications 3,383,435 and 3,663,661. These mixtures can be colored by incorporating dyes therein. Generally, when articles formed from these mixtures are exposed to light, discoloring occurs. This discoloring is probably associated with a yellowing of the polyphenylene ether polymer used. The present invention provides a solution to this problem. Description of the Invention The polymer mixture according to the invention is characterized in that it comprises at least one dye capable of bleaching upon exposure to light in an amount effective for compensating for a change in color of the polyethylene ether upon exposure to said light. Good results are obtained when the polymer mixture comprises a yellow quinophthalone dye with the following structural backbone: which may carry substituents, with the exception of such yellow quinophtalone dyes having a hydroxyl substituent in position 3′ of the structural backbone possibly admixed with a purple anthrapyridone dye. Quinophtalone dyes are known per se; a list of suitable quinophtalone dyes can be found in Helvetia Chimica Acta, vol. 52, fasc. 5 (1969) p. 1259-1273 enumerating some quinophtalone dyes of which the yellow ones without hydroxyl substituent in position 3′ are suitable for the purpose of this invention. The quinophtalone dyes with a hydroxyl group in position 3′ are not suitable for the purpose of this invention since they are too stable upon exposure to light. The use of quinophtalone dyes with a 3′-hydroxylsubstituent in polymers is known from French patent specification 2,252,372. The yellow quinophtalone dye is preferably used in a quantity from 0.001 to 0.5% by weight: the purple anthrapyridone dye is used in a quantity from 0.001 to 0.2% by weight. Good results have been obtained with Solvent Yellow 33 (Color Index No. 47,000 Amaplast Yellow Y of the American Color & Chemical Co., a quinophtalone dye wihout any substituents on the quinophtalone backbone), Solvent Yellow 138 (Paliotol Yellow 1090 of BASF a quinophtalone dye substituted with halogen atoms and one or more aromatic groups and without an hydroxyl group in position 3′).) and with Solvent Red 52 (Color Index No. 68,210 Macrolex Red 5B of Messrs. Bayer AG). The invention is based on the recognition of the fact that the yellowing of the polyphenylene ether polymer can be compensated in color by a complete or partial decomposition of the selected dyes upon exposure to light. The best results are obtained by using a yellow quinophtalone dye together with a purple anthrapyridone dye. As a result of this combination a color compensation occurs over a wavelength of approximately 400-600 nanometers, in which range a visible discoloring of the polyphenylene ether polymer occurs upon exposure to light. The preferably used polyphenylene ether polymers have the following formula: wherein Q is a monovalent substituent, for example, a hydrogen atom, a hydrocarbon radical, a hydrohalogenic radical having at least two carbon atoms between the halogen atom and the phenyl nucleus, an alkoxy radical or a halogen alkoxy radical having at least two carbon atoms between the halogen atoms and the phenyl nucleus, Q′ and Q″ may be the same as Q or in Addition represent a halogen atom, wherein Q, Q′ and Q″ may not comprise a tertiary alpha carbon atom and wherein n is an integer of 50 or more. In addition to a polyphenylene ether polymer the polymer mixture according to the invention preferably also comprises a styrene polymer. The styrene polymer may be mixed physically with the polyphenylene ether polymer. The polymer mixture may also comprise a graft-copolymer product, for example, as may be formed upon co-extrusion of the polyphenylene ether polymer and the styrene polymer at elevated temperature (230-320°C). The styrene polymer is preferably a polymer in which at least 25% by weight of the units of the polymer may consist of a vinylaromatic compound of the formula: wherein R is a hydrogen atom, a lower alkyl group (having, for example, 1-6 carbon atoms) or a halogen atom; Z is a vinyl group, a chlorine atom or a lower alkyl group and p=0 or an integer from 1-5. The expression "styrene polymer" as defined above and as used in the Claims of the present Patent Application therefore comprises, by way of example, homopolymers, for example, polystyrene, polychlorostyrene and polybromostyrene, rubber-modified polystyrenes, for example, the commercially available high-impact polystyrene polymers and also the styrene-comprising copolymers, for example, styrene-acrylonitrile copolymers (SAN), styrene butadiene copolymers, styrene acrylonitrile butadiene terpolymers (ABS), poly- a methyl styrene and copolymers of ethylvinylbenzene and divinylbenzene. Styrene homopolymers and rubber-modified high-impact polystyrene are preferred. A dye which may be added to the polymer mixture according to the invention is a yellow quinophtalone dye possibly admixed with a purple anthrapyridone dye. A mixture of these dyes is preferably used. These dyes have the property of bleaching upon exposure to light, i.e. after exposure they reflect more in the blue and green spectral range. Therefore they compensate for the yellowing of the polymeric constituents in the polymer mixture, which results in a decrease of the reflection in the blue and green ranges of the visible light spectrum. In addition, the polymer mixture may comprise other dyes to obtain the desired color. The term "dyes" also includes pigments. The polymer mixture according to the invention can be prepared according to usual techniques. The further processing to articles is also carried out according to conventional methods. It has been found that the said yellow quinophtalone dyes and purple anthropyridone dyes can readily be mixed in the polymer mixture and are not attacked and maintain their color at extrusion temperatures up to 300°C. The polymer mixture according to the invention can easily be prepared by dry-mixing powdered or granular starting products, succeeded by mixing in the viscous state, for example, on a warm roller or in an extruder. After cooling, the resulting product is reduced to grains or pellets. In addition to the above-mentioned constituents the polymer mixture according to the invention may include any conventional additives for such mixtures. Examples of such additives are flame-retarding agents, antidrip agents, softeners, antioxidation agents, stabilizers, reinforcing agents, fillers, dyes, auxiliary substances to improve the processibility, means to increase the impact strength etc., each in amounts conventional for the stated purpose. The invention will be described in greater detail with reference to the following specific examples. Example I Two polymer mixtures were prepared with the same green color; mixture A without the dyes according to the invention, and Example I with a mixture of two dyes according to the invention. The mixtures were prepared by dry mixing of the following constituents: The pigments in themselves are well stable upon heating and exposure to light. The total quantity of pigments is approximately equal in both mixtures. The mutual ratio of the pigments differs to obtain an equal green color for both mixtures. The mixtures were passed through an extruder (approximately 290°C). The extrudates were processed to pellets. The pellets were processed to test plates having a dimension of 50 x 50 x 3 mm. The test plates were placed in a Suntest apparatus (Original Hanau Quarzlampen GmbH) and exposed to light for 300 hours with filtered Xenon radiation (daylight D65). The discoloring as compared with non-exposed test plates was calculated according to CIELAB (DIN 6174) from reflection spectra obtained by means of a Zeiss RFC3 spectrophotometer. The test plates prepared from mixture A showed a strong discoloring (delta E ab* = 8.3); the test plates prepared from mixture I according to the invention showed a much smaller discoloring (delta E ab* = 2.1 ). Example II Two polymer mixtures were prepared with the same beige color; mixture B without the dyes according to the invention and Example II with a mixture of two dyes according to the invention. Test plates of the mixtures B and II were manufactured according to the same method as described for Example I. The plates were exposed to light for 200 hours only. The test plates of the polymer mixture II in accordance with the invention showed a small discoloring (delta E ab* = 1.8), those of mixture B showed a stronger discoloring (delta E ab* = 4.6). Example III Two mixtures were prepared from the same components as indicated in Example II. Moreover, 5 parts by weight of triphenyl phosphate were added to each of the mixtures (a flame retarding agent). Test plates were manufactured from the resulting mixtures and exposed to light for 200 hours. The test plate without the dyes in accordance with the invention discolored (delta E ab* = 4.4) more than the test plate with the dyes according to the invention (delta E ab* = 1.9).

Claims: A thermoplastic composition having improved resistance to discolorization upon exposure to light consisting essentially of : a polyphenylene ether or a polyphenylene ether admixed with conventional additives or a polyphenlyene ether-styrene polymer blend with a weight ratio of the polyphenylene ether to the styrene polymer varying between 1:5 and 5:1 or a polyphenylene ether-styrene polymer blend with a weight ratio of the polyphenylene ether to the styrene polymer varying between 1:5 and 5:1 admixed with conventional additives; and at least one dye capable of bleaching upon exposure to light in an amount effective for compensating for a change in colour of the polyphenylene ether upon exposure to said light. Composition according to claim 1, wherein said dye is selected from the group consisting of yellow quinonaphtalone dyes possibly admixed with a dye selected from the group consisting of purple anthrapyridone dyes. A composition according to claim 2, wherein said yellow quinophthalone dye has the structural backbone which may carry substituents, with the exception of such yellow quinophthalone dyes having a hydroxy substituent in position 3′ of the structural backbone. A Composition as in Claim 2 wherein said yellow quinophthalone dye is present in an amount of 0.001 to 0.5% by weight of the composition. A composition as in Claim 2 wherein said purple anthropyridone dye is present in an amount of 0.001 to 0.2% by weight of the composition. An article formed from the thermoplastic composition of Claim 1.

Inventors: LOHMEIJER, JOHANNES, H.G.M.
Applicants: GENERAL ELECTRIC COMPANY
Application year: 1983
Main classification: C08L71
IPC codes: C08K5