AROMATIC POLYSULFONE RESIN COMPOSITIONS

Abstract: An aromatic polysulfone resin composition comprises from 30% to 95% by weight of an aromatic polysulfone and from 5% to 70% by weight of a potassium titanate fiber having a free potassium content of not more than 0.25% by weight. The polysulfone may contain ether and/or isopropylidene link­ ages. The composition has improved heat resistance, strength, rigidity and, in particular, does not undergo gelation during melting.

Description: This invention relates to aromatic polysulfone resin compositions having excellent mechanical properties, thermal properties and dimensional stability and, in particular, improved heat stability during melting. Because of their excellent heat resistance, strength, rigidity, flame retardancy and chemical resistance, aromatic polysulfone resins have been used as engineering plastics from which electrical and automobile parts have been fabricated. With the recent technical developments in these fields of application, there has been a demand for a resin material having further improved heat resistance, strength and rigidity, while retaining the properties characteristic of the aromatic polysulfone resins, such as flame retardancy, chemical resistance, hot water resistance, and molding processability. In this connection a resin composition comprising an aromatic polysulfone and a potassium titanate fiber has been proposed e.g. in JP 59-182853. As the proportion of a potassium titanate fiber is increased to ensure a high reinforcing effect, gelation occurs with a consequent loss in fluidity, making molding impossible while the composition is retained at high temperatures in melt processing, e.g., in injection molding. Accordingly, an object of this invention is to provide a resin composition comprising an aromatic polysulfone and potassium titanate fiber having excellent mechanical properties, thermal properties and dimensional stability, and in particular, improved heat stability in the molten state. As a result of extensive studies, it has now been found that the above objects can be achieved by a resin composition comprising from 30% to 95% by weight of an aromatic polysulfone and from 5% to 70% by weight of a potassium titanate fiber having a free potassium content of not more than 0,20% by weight. The preferred aromatic polysulfones which may be used in the composition of this invention can be identified as polyarylene compounds in which arylene units are regularly or irregularly bonded together via an ether linkage and/or an isopropylidene group, as well as via a sulfone group. Examples of such polyarylene compounds are shown below. Of these, those having structures (1), (2) and (6) are preferred owing to their well-balanced physical properties and processability. Further, those having a reduced viscosity of from 0.3 to 0.6 (in 100 cc dimethylformamide solution containing 1 g of a sample, at 25°C) are more preferred for achieving a balance between physical properties, such as heat resistance, strength, rigidity and toughness, and molding processability. The aromatic polysulfone is used in an amount of from 30% to 95% by weight based on the total amount of the aromatic polysulfone and the potassium titanate fiber, and the potassium titanate fiber is used in an amount of from 5% to 70% by weight on the same basis. If the amount of the aromatic polysulfone exceeds 95% by weight and the amount of the potassium titanate fiber is less than 5% by weight, sufficient improvement in heat resistance, rigidity and dimensional stability cannot be obtained. On the other hand, if the amount of the aromatic polysulfone is less than 30% by weight, and the amount of the potassium titanate fiber exceeds 70% by weight, dispersion in a melt mixer is insufficient and also the melt viscosity of the composition markedly increases to reduce fluidity, thus making it difficult to effect molding under normal conditions. The potassium titanate fiber which can be used in the present invention is one of the so-called whiskers, i.e., high-strength needle single crystal fibers, and has a basic chemical composition of K₂O·6TiO₂ or K₂O·6TiO₂·1/2H₂O. It has a typical melting point of from 1,300°C to 1,350°C, an average fiber length of from 5 µm to 150 µm, and preferably from 10 µm to 30 µm, and an average fiber diameter of from 0.05 µm to 2.0 µm, and preferably from 0.1 µm to 0.5 µm. In the present invention, the potassium titanate fiber must have a free potassium content of not greater than 0,20% by weight. If the free potassium content exceeds 0,20% by weight, the resulting aromatic polysulfone resin composition has a reduced heat stability during melting and undergoes extreme rise in viscosity through retention in a molten state. In particular, such a rise in viscosity becomes conspicuous at higher temperatures for longer retention times and with higher proportions of the potassium titanate fiber, leading to gelation to lose fluidity, thus making molding impossible. The most remarkable effect of limiting the free potassium content of the potassium titanate fiber can be exerted when the potassium titanate fiber content in the resin composition is 20% by weight or more. The free potassium content in the potassium titanate fiber being not greater than 0,20% by weight, an increase in melt viscosity can be minimized to a very slight degree. Prevention of increase of melt viscosity can further be ensured even under severe conditions by controlling the free potassium content to not greater than 0.05% by weight. The free potassium content of the potassium titanate fiber can be determined by boiling a given amount of the fiber in water for a long time and determining the thus extracted potassium by flame spectrophotometry, atomic-absorption spectrophotometry, ICP (high frequency-induced combined plasma) emission spectroanalysis, and the like. The process for producing potassium titanate fibers to be used in the present invention is not particularly restricted. For example, known proceses for synthesizing potassium titanate include calcination, melting, hydration and fluxing. The chemical composition (K₂O·nTiO₂) of potassium titanate and the fiber length vary depending on the mixing ratio of K₂O and TiO₂, reaction temperature, basicity of reaction system, and the like. The free potassium content of the resulting fiber can be adjusted so as to fall within the above-recited range by reducing a free K₂O content by selecting proper reaction conditions. Further, potassium titanate fiber having a free potassium content within the above-recited range can also be obtained by subjecting a potassium titanate fiber containing from 0.27% to 0.40% by weight of free potassium that is obtainable by a general industrial process to calcination at a high temperature, e.g., 500°C or higher, or by removing free K₂O from the above-described potassium titanate fiber by extracting with water or an acid. The mode of blending the aromatic polysulfone and the potassium titanate fiber to prepare the composition of this invention is not particularly limited. For example, the aromatic polysulfone and the potassium titanate fiber may be fed to a melt mixer separately, or these raw materials may be preliminarily mixed by means of a mortar, a Henschel mixer, a ball mill, a ribbon blender, etc. and then fed to a melt mixer. The composition according to the present invention may further contain one or more of additives, such as antioxidants, heat stabilizers, ultraviolet light absorbents, lubricants, parting agents, colorants e.g., dyes or pigments, flame retarding aids and antistatic agents, as far as they do not impair the effects of the present invention. In the present invention, the potassium titanate fiber, when blended with the aromatic polysulfone, is effective to improve various properties, such as resistance to heat distortion, strength, rigidity, and dimensional accuracy. Further, an unfavorable increase in viscosity due to gelation can effectively be prevented by controlling the free potassium content in such a potassium titanate fiber within 0.25% by weight. This is believed to be ascribable to prevention of free potassium from reacting with an active group of the aromatic polysulfone, e.g., a terminal hydroxyl group, in a molten state to cause increase in viscosity. The present invention will now be illustrated in greater detail with reference to the following Examples and Comparative Examples, but it should be understood that the present invention is not limited thereto. In these Examples, the free potassium content in potassium titanate fiber was determined by boiling a prescribed amount of the potassium titanate fiber in water for 20 hours and analyzing the water containing eluted potassium by the use of an apparatus for both flame spectrophotometry and atomic-absorption spectrophotometry (Model 650 manufactured by Shimazu Seisakusho Ltd.; double-beam spectrophotometer; wavelength of measurement: 7,665 Å). EXAMPLES 1 TO 3 A polyether sulfone having a repeating unit of the formula: ("3600P", a trade name produced by Imperial Chemical Industries Co., Ltd.; reduced viscosity 0.36) and a potassium titanate fiber containing 0.03% by weight of free potassium ("HT-200", a trade name produced by Titan Kogyo K.K.; fiber diameter: 0.3 µm to 1.0 µm; fiber length: 20 µm to 120 µm) were mixed at a ratio shown in Table 1, and the mixuture was melt-kneaded in a biaxial extruder ("PCM-30", a trade name manufactured by Ikegai Iron Works Co., Ltd.) at 340°C. The resulting strand was cooled with cold water and cut into pellets. The resulting pellets were molded using an injection molding machine, (Sumitomo Nestal 47/28 at a cylinder temperature of 360°C to 380°C and a mold temperature of 130°C to prepare a bending test piece, an Izod impact test piece and a test piece for determining heat distortion temperature. Flexural modulus of elasticity, Izod impact strength and heat distortion temperature were determined using these test pieces in accordance with ASTM D-790, D-256 and D-648, respectively. Heat stability of the resin composition in a molten state was evaluated by determining melt viscosity by means of a Koka-type flow tester (produced by Shimazu Seisakusho Ltd.) under conditions of a temperature of 400°C, a load of 50 kg/cm², a nozzle diameter of 1 mm, a land length of 10 mm and a retention time of 5 minutes or 30 minutes. The results obtained are shown in Table 1. These results demonstrate that the resin compositions according to the present invention have high flexural modulus of elasticity, impact strength, heat distortion properties and heat stability in the molten state. When the resin composition was retained in the injection molding machine at 380°C for 30 minutes, no appreciable change in injection moldability was noted in any sample. COMPARATIVE EXAMPLES 1 TO 3 The same procedures as described in Examples 1 to 3 were repeated except for using a potassium titanate fiber containing 0.28% by weight of free potassium. The results obtained are shown in Table 1. It can be seen from Table 1 that each of the resin compositions can be molded using an injection molding machine without suffering any inconvenience to provide molded articles having equal properties to those in Examples 1 to 3 as far as the retention time is short. However, the comparative data of melt viscosity indicate poor heat stability of the molten resin compositions. In the injection molding, when the resin composition was retained at 380°C for 30 minutes, gelation of the molten resin occurred to make molding impossible. EXAMPLES 4 TO 6 The same procedures as described in Examples 1 to 3 were repeated except for using a potassium titanate fiber having a free potassium content of 0.16% by weight (a TISMO heat-treated product produced by Otsuka Chemical Co., Ltd.; fiber diameter: 0.3 µm to 1.0 µm; fiber length: 20 µm to 120 µm). The test results obtained are shown in Table 1 below.

Claims: An aromatic polysulfone resin composition comprising an aromatic polysulfone and potassium titanate fiber, characterised in that the composition contains from 30% to 95% by weight of aromatic polysulfone and from 5% to 70% by weight of potassium titanate fiber having a free potassium content of not more than 0.20% by weight. A composition as claimed in Claim 1, wherein the potassium titanate fiber is present in an amount of not less than 20% by weight. A composition as claimed in Claim 1 or 2, wherein the potassium titanate fiber has a free potassium content of not more than 0.05% by weight. A composition as claimed in any preceding claim, wherein the potassium titanate fiber has an average fiber length of from 10 µm to 30 µm and an average fiber diameter of from 0.1 µm to 0.5 µm. A composition as claimed in any preceding claim, wherein the aromatic polysulfone is one in which ether and/or isopropylidene linkages are present. An article moulded from a composition as claimed in any preceding claim.

Inventors: HIEDA, KAZUO, SAITO, TERUO
Applicants: SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1985
Main classification: C08K7
IPC codes: C08K7