Polymer mixture comprising polybutylene terephthalate, aromatic polycarbonate and polydialkysiloxane

Abstract: The invention relates to polymer mixtures which comprise a polybutylene terephthalate, an aromatic poly­ carbonate, and a dialkyl silicone fluid. Due to the pre­ sence of the dialkyl silicone fluid compound a good lacquer bonding is obtained.

Description: The invention relates to a polymer mixture which comprises a polybutylene terephthalate, an aromatic polycarbonate and a dialkyl silicone fluid homopolymer. Such mixtures are known per se . For this purpose reference may be made, for example, to GB-A-1569296. Polymer mixtures which comprise a polybutylene terephthalate, a polycarbonate, and an agent to improve the impact strength are disclosed in US-A-4,257,937 and US-A-4,280,949. The known mixtures generally have favourable properties: they have good mechanical properties and can withstand the influence of organic solvents. As a result of this, these mixtures are suitable to manufacture therefrom parts for motor-cars, for example, bumpers. It is sometimes desirable to provide the articles formed from the polymer mixtures with a decorative lacquer layer. In the known polymer mixtures bonding problems may occur between the polymer surface and the lacquer layer. The invention provides polymer mixtures which comprise A. a polybutylene terephthalate and B. an aromatic polycarbonate to which a polymeric auxiliary substance has been added which ensures a better bonding with the lacquer layer. The polymer mixture according to the invention is characterised in that it comprises 0.1-5 parts by weight of a dialkyl silicone fluid (C) per 100 parts by weight of A + B. Patent Abstracts of Japan, vol. 9 no. 228 (C-303) (1951) of september 13, 1985 describes an electrically conductive resin composition obtained by blending a polycarbonate resin, a polybutylene terephthalate resin, silicone oil and aluminium fibres having a diameter of 1-50 micrometer and an aspect ratio of 50 or above. The polymer mixture according to the invention preferably comprises a dimethyl silicone fluid as the dialkyl silicone fluid. The weight ratio of the polybutylene terephthalate to the aromatic polycarbonate in the polymer mixture according to the invention is preferably chosen to be so that it is more than 0.7. The polymer mixture according to the invention may comprise 0.1-100 parts by weight of conventional additives per 100 parts by weight of A + B. The polymer mixture according to the invention preferably comprises 0.1-50 parts by weight of an agent to improve the impact strength per 100 parts by weight of A + B. As an agent to improve the impact strength is preferably used a core-shell polymer built up from a rubber-like core on which one or more shells have been grafted. The polymer mixture according to the invention comprises at any rate the following constituents: A. one or more polybutylene terephthalates B. one or more aromatic polycarbonates, and C. one or more dialkyl silicone fluids. The polymer mixture may comprise one or more of the following constituents: D. conventional additives. E. one or more agents to improve the impact strength. A. Polybutylene terephthalate Polybutylene terephthalate is a polymer known per se . It is derived from butane-1,4-diol and terep-tfralic acid. It is possible to use copolyesters in the polymer mixtures in which a part of the diol compound and/or a part of the terephthalic acid has been replaced by another diol and/or carboxylic acid. For the polymer mixtures according to the invention it is to be preferred to use a polybutylene terephthalate which is built up for more than 70 mol% from units derived from butane-1,4-diol and terephthalic acid. It is possible to use polybutylene terephthalate in which a branching agent, for example, a glycol having three or more hydroxyl groups or a trifunctional or a polyfunctional carboxylic acid has been incorporated. B. Aromatic polycarbonate Aromatic polycarbonates are materials known per se . They are generally prepared by reacting a dihydric phenol compound with a carbonate precursor, for example, phosgene, a halogen formiate or a carbonate ester. Aromatic polycarbonates are polymers which comprise units of the formula wherein A is a bivalent aromatic radical derived from the dihydric phenol used in the preparation of the polymer. Dihydric phenols which may be used in the preparation of the aromatic polycarbonates are mononuclear or polynuclear aromatic compounds which comprise two hydroxy radicals which are each directly bonded to a carbon atom of an aromatic nucleus. The branched polycarbonates as described, for example, in US-A-4,001,184 are also suitable. Suitable aromatic polycarbonates are also the so-called polyester carbonates which are obtained by performing the polymerization reaction in the presence of an ester precursor, for example, terephthalic acid or an ester-forming derivative thereof. These polyester carbonates have ester compounds and carbonate compounds in the polymeric chain. Polyester carbonates are described, for example, in US-A-3,169,121. C. Dialkyl silicone fluids Dialkyl silicone fluids are compounds known per se . For this purpose reference may be made, for example, to Kirk-Othmer, Vol. 20, 1982, pp . 936-940. Dimethyl silicone fluids are preferably used as a dialkyl silicone fluid. It is essential that dialkyl silicone fluids are used; in fact it has been found that an alkylaryl silicone fluid, for example, phenyl silicone and copolymers of dialkyl silicones and diaryl silicones do not provide the desired improvement of the bonding. The dialkyl silicone fluid may comprise two different alkyl groups or even a mixture of various alkyl groups. The relative quantity of the various alkyl groups may be chosen arbitrarily. It is of importance for each silicon atom in the chain to be bonded with on an average approximately two alkyl groups but not with aryl groups. D. Conventional additives In addition to the constituents mentioned hereinbefore the polymer mixture according to the invention may comprise one or more additives, with the exception of alluminium fibres. Examples of suitable additives are stabilisers, transesterification inhibitors, dyes, pigments, fillers and reinforcing fibres, for example, glass fibres, release agents. E. Agent to improve the impact strength The polymer mixture according to the invention may comprise one or more agents to improve the impact strength. So-called core-shell polymers built up from a rubber-like core on which one or more shells have been grafted are preferably used. The core usually consists substantially of an acrylate rubber or a butadiene rubber. One or more shells have been grafted on the core. Usually these shells are built up for the greater part from a vinylaromatic compound and/or a vinylcyanide and or an alkyl(meth)acrylate and or (meth)acrylic acid. The core and/or the shell(s) often comprise multifunctional compounds which may act as a cross-linking agent and/or as a grafting agent. These polymers are usually prepared in several stages. The polymer mixture according to the invention can be obtained according to any conventional method of preparing polymer mixtures. The individual constituents are preferably mixed collectively in the melt (compounded) in an extruder. The extrudate (in strand form) which emanates from the extruder is chopped to pellets. The pellets may, for example, be further processed in an injection moulding machine. Examples I to IV, comparative examples A, B and C Various polymer mixtures were prepared starting from the following constituents: PBT 1: a polybutylene terephthalate having an intrinsic viscosity of 1.19 dl/g, measured in a 60/40 mixture of phenol and tetrachloroethane at 25°C. PBT 2: polybutylene terephthalate having an intrinsic viscosity of 1.10 dl/g. PC: an aromatic polycarbonate derived from bisphenol A and phosgene having an intrinsic viscosity of 58.5 ml/g measured in methylene chloride at 25° C. IM: an agent to improve the impact strength of the core-shell type having a core consisting substantially of a butadiene rubber on which a shell of a copolymer substantially built up from methylmethacrylate and styrene has been grafted. ST: a mixture of various conventional stabilisers. PE: polyethylene. SC1: a dimethyl silicone fluid having a nominal viscosity of 125 x 10⁻⁴ m².s⁻¹ (12,500 centistokes) (cSt). SC2: a dimethyl silicone fluid having a nominal viscosity of 50 x 10⁻⁴ m².s⁻¹ (5000 cSt) at 25°C. SC3: a methyl phenyl silicone fluid having a nominal viscosity of 0.3 x 10⁻⁴ m².s⁻¹ (30 cSt) at 25°C. SC4: a dimethyl diphenyl silicone fluid having a nominal viscosity of 4 x 10⁻⁴ m².s⁻¹ (400 cSt) at 25°C. The various constituents were compounded in a Werner Pfleiderer extruder in the quantities as indicated in the table hereinafter(average of the adjusted temperatures: 235°C). The resulting extrudate was chopped to pellets. Disks were injection-moulded from the pellets to determine the lacquer bonding (diameter of the disks: 10 cm, thickness 3 mm). The surface of the disks was slightly roughened by moving the bottom of a beaker glass over it. The surface was then degreased with isopropyl alcohol. The treated surface was then painted by means of a spray gun. The lacquer used was lacquer No. 47020 of Messrs. Herberts. The lacquered disks were cured at 50°C for 48 hours. The bonding strength was then determined according to DIN 53151 with TESA¾ tape 4651. Evaluation "GtO" denotes a good bonding; evaluation "Gt5" denotes a poor bonding. In most of the cases the test was carried out four times. The results obtained are recorded in the table. The lacquer bonding was also determined after the so-called "Schwitzwasser test" (DIN 50017). In this test the lacquered disks were stored at 40°C and a relative humidity of 100% for 240 hours, after which the lacquer bonding was determined according to DIN 53151. Test pieces were also injection-moulded from the resulting pellets to determine the Vicat B value. The results obtained are also recorded in the following table. It may be seen from the table that the addition of a dimethyl silicone fluid (SC1 and SC2) leads to an improvement of the lacquer bonding. Only a slight reduction of the Vicat B value results from the addition of the dimethyl silicone fluid in the quantity required for the improvement of the lacquer bonding. A methyl phenyl silicone fluid or a copolymer of dimethyl silicone and diphenyl silicone (comparative examples B and C) does not provide any improvement of the lacquer bonding.

Claims: A polymer mixture which comprises (A) a polybutylene terephthalate and (B) an aromatic polycarbonate, characterised in that the polymer mixture comprises 0.1-5 parts by weight of a dialkyl silicone fluid homopolymer (C) per 100 parts by weight of A + B. A polymer mixture as claimed in Claim 1, characterised in that the polymer mixture comprises dimethyl silicone fluid homopolymer. A polymer mixture as claimed in Claim 1, characterised in that the weight ratio polybutylene terephthalate to the aromatic polycarbonate is more than 0.7. A polymer mixture as claimed in Claim 1, characterised in that the polymer mixture comprises 0.1-100 parts by weight of one or more further additives per 100 parts by weight of A + B. A polymer mixture as claimed in Claim 1, characterised in that the polymer mixture comprises 0.1-50 parts by weight of an agent to improve the impact strength per 100 parts by weight of A + B. A polymer mixture as claimed in Claim 5, characterised in that the agent to improve the impact strength is a core-shell polymer built up from a rubber-like core on which one or more shells have been grafted. Object made out of the polymer mixture according to claim 1. Painted object made out of the polymer mixture according to claim 1.

Inventors: DE BOER JAN, DE WIT GERRIT, HAMERSMA WILHELMUS JOZEFUS LUD, ROOVERS WILHELMUS, DE BOER, JAN, DE WIT, GERRIT, HAMERSMA, WILHELMUS JOZEFUS LUDOVICUS, ROOVERS, WILHELMUS
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1988
Main classification: C08L67
IPC codes: C08L67, C08L69