POLYMER MIXTURE WHICH COMPRISES AN AROMATIC POLYCARBONATE, A POLYBUTYLENE TEREPHTALATE AND AN AGENT TO IMPROVE THE IMPACT STRENGTH

Abstract: The invention relates to polymer mixtures which comprise an aromatic polycarbonate, a polybutylene terephthalate and an agent to improve the impact strength. By using an aromatic polycarbonate and polybutylene terephthalate having a comparatively low intrinsic viscosity, a polymer mixture is obtained which has both a good impact strength at low temperatures and good flow properties.

Description: The invention relates to a polymer mixture which comprises an aromatic polycarbonate, a polybutylene terephthalate and an agent to improve he impact strength. Polymer mixtures which comprise an aromatic polycarbonate, a polyalkylene terephthalate and an agent to improve the impact strength are known per se , for example, from US-A-3,864,428; EP-A-­ 020605, EP-A-79477 and EP-A-110222. The known polymer mixtures have a good re­ sistance to chemicals and good mechanical prop­ erties, in particular a good impact strength. The known polymer mixtures are used, for example, to manufacture therefrom car bumpers by injection moulding. An additional requirement for car bump­ ers is hat they should have a good impact strength also at low temperatures. Upon injection moulding polymer mixtures, the flow properties of the polymer mixture are of great importance. This applies in particular to the injec­ tion moulding of large components, for example, car bumpers. There exist various possibilities to improve the flow of polymers, for example, by adding special additives or by reducing the molec­ ular weight of the polymer. When the flow properties are improved by re­ ducing the molecular weight, a deterioration of me­ chanical properties usually occurs, for example, the impact strength. EP-A-0107048 deals with polymer mixtures comprising an aromatic polycarbonate resin, a poly(ethylene terephtalate) resin and an acrylate based core-polymerized acrylate shell polymer in an amount effective to improve the notched impact strength. The intrinsic viscosity of the aromatic polycarbonate lies between 30 and 100 ml/g and that of he poly(ethylene terephtalate) resin be­ tween 20 and 150 ml/g. Examples 2-10 investigate the influence of the intrinsic viscosity of the poly­ (ethylene terephtalate) on he impact properties : it is concluded there is "very little dependence on he intrinsic viscosity". Out of said examples the best flow properties (as shown by the "spiral flow") are obtained in example 5, wherein a poly­ (ethylene terephtalate) with a medium value for the intrinsic viscosity has been used. NL-A-7702101, corresponding with GB-A- 1,568,625, describes polymer mixtures comprising a poly(l,4-butylene terephtalate), an aromatic polycar­ bonate and glass fibres. Polymer mixtures of this known type have very poor notch impact strength and bad flow properties. EP-A-0158822 describes polymer mixtures comprising an aromatic polycarbonate, a thermo­ plastic polyester, an impact modifier and an ester plasticizer. As a polyester there can be used a poly(ethylene terephtalate) having an intrinsic vis­ cosity "more preferably" of 70-120 ml/g or a poly­ (butylene terephtalate) having an intrinsic viscosity of "more preferably 80-105 ml/g ". The examples deal with poly(ethylene terephtalate) only. In the examples the polycarbonate used is characterized by a melt flow rate of about 3.0-5.9 g/10 min., which corresponds with an intrinsic viscosity of about 57.5-65 ml/g. The melt viscosity has to be im­ proved by adding a plasticizer; this is not required for the polymer mixture of the invention! The invention provides polymer mixtures of the type mentioned hereinbefore which have improved flow properties in combination with a good impact strength. In the polymer mixture according to the invention the aromatic polycarbonate has an intrisic viscosity of less than 52 ml/g, measured in methylene chloride at 25°C and the polybutylene terephthalate has an intrisic viscosity of less than 105 ml/g measured in a 60/40 (wt./wt.) phenol/tetrachloroethane mixture at 30°C, the polymer mixture does not comprise glass fibres and has a weight ratio of the aromatic polycarbonate to the polybutylene terephthalate of more than 0.9. It has been found quite unexpectedly that when an aromatic polycarbonate and a polybutylene terephthalate having the viscosity as stated herein­ before is used, a polymer mixture is obtained which has a good impact strength, also at low temperatures. This is surprising because polycar­ bonate having a higher intrinsic viscosity has a better impact strength at low temperatures than a polycarbonate having a lower intrinsic viscosity. In particular a shift of the ductile/brittle transition tem­ perature to higher values occurs. The polymer mixture according to the invention comprises an agent to improve the impact strength. Such an agent is used in a quantity from 5 to 30, preferably 5 to 15% by weight calculated with respect to the total quantity of the aromatic polycar­ bonate, the polybutylene terephthalate and the agent to improve the impact strength. In addition to the above-mentioned constitu­ ents, the polymer mixture according to the inven­ tion may comprise further conventionally used ad­ ditives with the exception of glass fibres. When glass fibres are used, the impact strength, also at low temperatures, is considerably reduced. The additives are usually used in a quantity from 0 to 40% by weight calculated with respect to the total quantity of aromatic polycarbonate, polybutylene terephthalate and agent to improve the impact strength. The invention also relates to articles formed from the above-meant polymer mixtures according to the invention. The polymer mixture according to the invention comprises one or more constituents selected from each of the three mentioned groups: A. aromatic polycarbonates and B. polybutylene terephthalates and C. agents to improve the impact strength. The polymer mixture according to the invention may comprise in addition one or more constituents selected from: D. conventionally used additives. A Aromatic polycarbonates Aromatic polycarbonates are materials known per se. They are generally prepared by reacting a dihydric phenol compound with carbonate precur­ sor, 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 which is derived from the dihydric phenol which is used in the preparation of the polymer. As dihydric phenols may be used in the preparation of the aromatic polycarbonates mononuclear or polynuclear ar­ omatic compounds which comprise two hydroxy radicals which are each bonded directly to a car­ bon atom of an aromatic nucleus. Polycarbonates having an intrinsic viscosity of less than 52 ml/g methylene chloride at 25°C (according to ASTM D 2857-70 by means of a viscosimeter according to DIN 51562) are used in this polymer mixture according to the invention. The intrinsic viscosity is preferably between 46 and 50. Examples of suitable dihydric phenols are: 2,2-bis-(4-hydroxyphenyl)propane; hydroquinone; resorcinol; 2,2-bis-(4-hydroxyphenyl)pentane; 2,4′-(dihydroxydiphenyl)methane; bis-(2-hydrox­ yphenyl) methane; bis-(4-hydroxyphenyl)methane; bis-(hydroxy-5-nitro-phenyl)methane; 1,1-bis(4­ hydroxyphenyl)ethane; 3,3-bis(hydroxyphenyl)­ pentane; 2,2-dihydroxyphenyl; 2,6-dihydroxynaph­ thalene; bis-(4-hydroxydiphenyl)sulphone; bis-3,5- diethyl-4-hydroxyphenyl)sulphone; 2,2-bis-(3,5- dimethyl-4-hydroxyphenyl)propane; 2,4′-dihydrox­ ydiphenyl sulphone; 5′-chloro-2,4′-dihydrox­ ydiphenyl sulphone; bis (4-hydroxyphenyl)diphenyl sulphone; 4′4′-dihydroxydiphenyl ether; 4,4′­ dihydroxy-3,3/-dichlorodiphenyl ether; 4,4′- dihydroxy-2,5-dihydroxydiphenyl ether. Other, likewise suitable,dihydric phenols are disclosed in US-A-2,999,835; 3,038,365; 3,334,154 and 4,131,575. The aromatic polycarbonates may be prepared according to methods known per se : for example, by reacting a dihydric phenol with a carbonate precursor, for example, phosgene. For this purpose reference may be made to the United States Patent Specifications just mentioned and to US-A- 4,018,750 and 4,123,426.They may also be prepared by a transesterification as described in US-A- 3,153,008. The branched polycarbonates known per se as described, for example, in US-A-4,001,184 are also suitable. It is also possible in the polymer mixtures according to the invention to use as an aromatic polycarbonate a mixture of various polycarbonates, for example, as mentioned hereinbefore. B. Polybutylene terephthalates One or more polybutylene terephthalates hav­ ing an intrinsic viscosity of less than 105 ml/g, preferably from 70 to 90 ml/g, are present in the polymer mixture according to the invention. The intrinsic viscosity has been determined in a phenol­ tetrachloroethane 60 to 40) at 30°C according to ASTM D 2857-70 by means of a viscosimeter according to DIN 51562. Polybutylene terephthalates are compounds known per se. They are derived from butadien-1,4- diol and terephthalic acid. It is also possible to use copolyesters in which a part of the said glycol and/or of the terephthalic acid has been replaced by another glycol and/or carboxylic acid. In gen­ eral, not more than 30 mol.%, preferably not more than 10 mol% of the glycol and/or terephthalic acid are replaced by other comonomers in such copolyesters. It is preferred that the polymer mixture comprises as a polybutylene terephthalate a polymer or copolymer which is built up for more than 90 mol.% from units derived from terephthalic acid and butane-1,4-diol. It is also possible to use so-called block copolyesters as a polybutylene terephthalate. These block copolyesters are prepared, for exam­ ple, by converting a polybutylene terephthalate with reactive terminal groups with a reactive polyester or copolyester in the presence of a transesterifica­ tion catalyst. Furthermore it is possible to incorporate a branching agent in the polybutylene terephthalate, for example, a glycol having three or more hydroxyl groups or a three-fold or multifold carbox­ ylic acid. C. Agents to improve the impact strength The polymer mixture according to the invention comprises one or more agents to improve the impact strength. Any known agent to improve the impact strength of polymer mixtures which com­ prise an aromatic polycarbonate and a polyalkylene terephthalate may be used in the polymer mixture according to the invention. The agent to improve the impact strength is generally used in a quantity from 5 to 30, prefer­ ably from 5 to 15% by weight calculated with re­ spect to the overall quantity of aromatic polycar­ bonate, polyalkylene terephthalate and agent to improve the impact strength. As an agent to improve the impact strength, a core-shell polymer prepared in several steps and consisting of a rubber-like core on which one or more shells have been grafted is preferably used in the polymer mixture according to the invention. The rubber-like core may be built up from rubber­ like polyacrylates or from rubber-like polydienes, for example, polybutadiene. The rubber-like core may comprise comonomers, for example, styrenes, acrylonitrile. The rubber-like core is preferably built up for more than 50 mol.% from units derived from butadiene. One or more shells have been grafted on the rubber-like core. The shell preferably con­ sists for more than 50 mol.% of units derived from C 1 -6 alkyl methacrylates, for example, meythyl ethacrylate. The shell may also comprise comonomers, for example, acrylonitrile and sty­ rene. D. Conventionally used additives In addition to the constituents mentioned hereinbefore, the polymer mixture may comprise one or more of the additives conventionally used for polymer mixtures. In the polymer mixture ac­ cording to the invention, these additives are usually used in a quantity from 0 to 40% by weight cal­ culated with respect to the overall quantity of the constituents mentioned above sub A, B and C. The polymer mixture according to the invention may comprise as additives, for example, polyolefins, mould-release agents, agents to im­ prove the flame-retarding properties, stabilisers, pigments and dyes. The polymer mixture accord­ ing to the invention may not comprise any glass fibres. In fact, polymer mixtures comprising glass fibres have an unfavourable notch impact value. The weight ratio aromatic polycarbonate to polyalkylene terephthalate in the polymer mixture according to the invention preferably lies at a value exceeding 0.9, even more preferably between 2.5 and 0.9. In other words, in the polymer mixture according to the invention, preferably a larger quantity by weight of the aromatic polycarbonate is used than of the polyalkylene terephthalate. When a weight ration of less than 0.9 is used, a further improvement of the flow properties occurs, it is true, but the ductile/brittle transition temperature is shifted to higher, less favourable values. When a weight ratio as described above of more than 2.5 is used, a polymer mixture having a reduced resis­ tance to chemicals, for example, petrol, is obtained. The polymer mixture according to the invention can be obtained according to the conventional methods of preparing polymer mixtures, for exam­ ple, by melt extrusion. The invention will now be described with refer­ ence to the ensuing specific examples. Comparative examples A, B; and I examples 11 and 111 according to the invention Five polymer mixtures were prepared starting from aromatic polycarbonates derived from 2,2-bis- (4-hydroxyphenyl) propane and phosgene having different intrinsic viscosity values, namely of 49 ml/g and 47.5 ml/g for the polymer mixtures ac­ cording to the invention and of 53 ml/g for the comparative examples. As a polyalkylene tereph­ thalate, two different polybutylene terephthalates having different intrinsic viscosities were used, namely of 88 ml/g for the polymer mixture accord­ ing to the invention and of 115 ml/g for the compara­ tive examples. As an agent to improve the impact strength was used in all the polymer mixtures a core built up from butadiene and styrene units (more than 50 mol.% of butadiene) on which a shell of methyl methacrylate had been grafted. Moreover, all the polymer mixture comprised the same combination of additives. The said constituents were mixed in an ex­ truder in quantities as recorded hereinafter in the following table. The resulting extrudate was chopped up. Standardized test pieces were man­ ufacturated from the resulting parts by injection moulding to determine the impact strength accor­ ing to Izod with notch (ASTM D256 method A; test pieces with thickness 3.2 mm). When lowering the temperature a lower value for the impact strength occurs. The temperature at which the impact strength is less than 50% of the impact strength at room temperature was determined. This value is indicated as ductile/brittle transition temperature (D/B temperature). In addition, standardized rods were injection moulded to determine the tensile strength and the elongation at fracture (according to ASTM D368). The values found for the elonga­ tion at fracture (tensile rate 50 mm per minute, 20°C) are recorded in the table below. The flow properties were determined by mea­ suring the melt viscosity (MV) according to DIN 54811 at 260°C and a shear rate of 1500 s -1 . The corresponding values for the various ar­ omatic polycarbonates and polybutylene tereph­ thalates used in a pure form are recorded in the table below. It may be seen from a comparison of the examples A and B that the use of a polycarbonate having a comparatively low intrinsic viscosity of 49 ml/g instead of polycarbonate having an intrinsic viscosity of 53 ml/g results in a small improvement of the flow properties with the D/B temperature remaining the same. A considerable improvement in the flow properties is obtained only when using both a polycarbonate and polybutylene tereph­ thalate having low instrinsic viscosities (compare examples 11 and 111 with comparative example A). It is surprising that the D/B temperature remains suf­ ficiently low. This is surprising, considering that pure polycarbonate having an intrinsic viscosity of 49 ml/g and 47.5 ml/g has a much higher D/B temperature than polycarbonate having an intrinsic viscosity of 53 ml/g. It may also be considered surprising that the elongation at fracture of the polymer mixtures ac­ cording to the invention (examples 11 and 111), in­ spite of the use of a polybutylene terephthalate having a low intrinsic viscosity of 88 ml/g, is equal­ ly large as in polymer mixtures which comprise a polybutylene terephthalate having an intrinsic vis­ cosity of 115 ml/g. Compare also the values for the elongation at fracture for pure polybutylene tereph­ thalate. The preference for the choice of a given weight ratio polycarbonate to polybutylene terephthalate appears from a comparison of example 1 with ex­ ample 11 according to the invention. By using a weight ratio of approximately 1.25 (example 11) a more favourable value for the D/B temperature with an approximately equal melt viscosity is obtained than when a weight ratio of approximately 0.8 is used.

Claims: 1. A polymer mixture which comprises an aromatic polycarbonate, a polyalkylene terephthalate and a agent to improve the impact strength, wherein the aromatic polycarbonate has an intrinsic viscosity of less than 52 ml/g, measured in methylene chloride at 25°C and the polyalkylene terephthalate is polybutylene terephtalate polymer or copolymer which has an intrinsic viscosity of less than 105 ml/g, measured in a 60/40 (wt.wt.) phenol/tetrachloroethane mixture at 30°C and wherein the polymer mixture does not comprise glass fibres and has a weight ratio of the aromatic polycarbonate to the polybutylene terephthalate of more than 0.9. 2. A polymer mixture as claimed in Claim 1, characterized in that the polymer mixture com­ prises 5-30% by weight of the agent to improve the impact strength calculated with respect to the total quantity of the aromatic polycarbonate, the poly­ butylene terephthalate and the agent to improve the impact strength. 3. A polymer mixture as claimed in Claim 1, characterized in that the polymer mixture com­ prises 0-40% by weight of additives calculated with respect to the total quantity of aromatic polycar­ bonate, polybutylene terephthalate and the agent to improve the impact strength. 4. A polymer mixture as claimed in Claim 1, characterized in that the polymer mixture com­ prises as a polybutylene terephthalate a polymer or copolymer which is built up for more than 90 mol.% from units derived from terephthalic acid and butane-1,4-diol. 5. A polymer mixture as claimed in Claim 1, characterized in that the polymer mixture com­ prises as an agent to improve the impact strength a core-shell polymer which is prepared in several steps and consists of a rubber-like core on which one or more shells have been grafted. 6. A polymer mixture as claimed in Claim 5 characterized in that the agent to improve the im­ pact strength is built up from a rubber-like core having more than 50 mol.% of units derived from butadiene and at least one shell having more that 50 mol.% of units derived from a C 1-6 alkyl­ methacrylate. 7. Articles formed from the polymer mixture as claimed in one or more of the preceding Claims.

Inventors: PEARSON, RAYMOND ALBERT, VERHOEVEN, JEROEN JOHANNES
Applicants: GENERAL ELECTRIC COMPANY
Application year: 1987
Main classification: C08L69
IPC codes: C08L67, C08L69