Polyarylene sulphide resin composition

Abstract: A polyarylene sulphide resin composition having excellent general properties and particularly excellent conductivity and antistatic properties comprises: (A) 100 parts by weight of a polyarylene sulphide resin, (B) 3 to 50 parts by weight of expandable graphite having an average particle diameter of 5 to 800 mm, and (C) 0.01 to 5 parts by weight of an alkoxysilane compound. The composition optionally further comprises: (D) 0 to 300 parts by weight of a filler other than the component (B) which is selected from among fibrous, powdery and platy fillers, and (E) 0.5 to 30 parts by weight of a specified polyolefinic copolymer.

Description: The present invention relates to a polyarylene sulphide resin composition having good general properties, in particular, excellent conductivity and antistatic properties. Recently, thermoplastic resins having excellent thermal resistance, mechanical properties and chemical resistance and, in addition, a high flame retardancy have come to be required as the materials of the parts of electric and electronic appliances, automobile appliances and chemical instruments. Polyarylene sulphide (PAS) resins typified by polyphenylene sulphide (PPS) also belong to the resins satisfying these requirements. Demand is increasing for these resins having further improved properties usually by the incorporation of a fibrous reinforcing material such as glass fibres or another inorganic filler. As the uses of these resins are enlarged, further improved properties or special properties are often required of them. These properties include conductivity and antistatic properties. The importance of these properties is increasing in order to prevent dust from adhering to the parts of electric or electronic appliances by static electricity and also to prevent problems caused by electromagnetic waves. Conductivity and antistatic properties are usually imparted to thermoplastic resins by a process wherein an organic antistatic agent is incorporated into the resins or applied to the surfaces of the molded articles, or a process wherein a metallic or carbon filler is dispersed in the resins. In practice, however, the process using an antistatic agent has the following defects: the antistatic agent is apt to deteriorate during melt kneading when it is incorporated into a PAS resin having a high melting point. When the antistatic agent is applied to the surfaces, problems of adhesion and an influence of humidity are also posed. In both cases, changes in the antistatic properties with time are considerable and the dispersion in the resistance value is large. On the other hand, metallic filler is expensive and has a high specific gravity which makes weight reduction impossible. Another problem of the metallic filler is that it has such a high hardness that it seriously abrades the barrel, screw, mold, etc., of an extruder or molding machine during the processing. On the contrary, the above-described problems are not so serious in the case of the incorporation of a carbon conductive substance such as conductive carbon black, carbon fibres or graphite, and various methods have been proposed for imparting conductivity to thermoplastic resins. In particular, it is believed that graphite is effective in improving both conductivity and abrasion properties. When PAS resin is used as the object, however, the effect of improving its conductivity and antistatic properties cannot always be obtained and, in particular, a bad influence is exerted on the general properties such as moldability, mechanical properties and thermal stability. The effect of such methods is still insufficient in view of the balance with the general properties, and a further improvement is demanded. After extensive investigations made for the purpose of substantially improving the conductivity and antistatic properties of particularly polyarylene sulphide resins to obtain a PAS resin material also having excellent general properties, the inventors have found that although incorporation of a specified graphite into PAS resin is particularly effective in obtaining a stable conductivity (resistance value), graphite has a marked tendency to impair the general properties, particularly mechanical properties such as toughness. After further investigations, the inventors have succeeded in producing a conductive PAS resin material having well-balanced properties by improving the conductivity and antistatic properties while maintaining excellent general properties, particularly mechanical properties, by adding other requirements. Thus the present invention provides a polyarylene sulphide resin composition having improved conductivity and antistatic properties which comprises: (A) 100 parts by weight of a polyarylene sulphide resin, (B) 3 to 50 parts by weight of expanded graphite having an average particle diameter of 5 to 800 µm, and (C) 0.01 to 5 parts by weight of an alkoxysilane compound. The base resin in the present invention is a PAS resin (A) which is a polymer comprising at least 70 molar % of repeating units represented by the structural formula: -Ar-S- (Ar being an arylene group). A typical PAS resin (A) is a polyphenylene sulphide comprising at least 70 molar % of repeating units represented by the structural formula: -Ph-S- (Ph being a phenylene group). Particularly suitable is a polyphenylene sulphide having a melt viscosity, determined under the conditions comprising a temperature of 310°C and a shear rate of 1200/sec, in the range of 1 to 2000 PaS (10 to 20000 P), particularly 10 to 500 PaS (100 to 5000 P). In general, known PAS resins are categorized into those having substantially linear molecular structure and being free from branched or crosslinked structure and those having branched or crosslinked structures according to the production process therefor. The present invention is effective for PAS resins of both types. The PAS resins for the present invention are preferably homopolymers or copolymers comprising at least 70 molar %, more desirably at least 80 molar %, of p-phenylene sulphide units as the repeating unit. When the repeating unit content is below 70 molar % the inherent crystallinity is reduced and the good mechanical properties which are characteristic of crystalline polymers tend to be difficult to obtain. The copolymer constituting units include, for example, m-phenylene sulphide, o-phenylene sulphide, p,p'-diphenylene ketone sulphide, p,p'-diphenylene sulphone sulphide, p,p'-biphenylene sulphide, p,p'-diphenylene ether sulphide and 2,6-naphthalene sulphide units. More preferably, the PAS resins of the present invention are substantially linear PPS homopolymers comprising p-phenylene sulphide as the repeating unit, and PPS copolymers mainly comprising p-phenylene sulphide as the repeating unit and at most 20 molar % of m-phenylene sulphide. A branched or crosslinked polyarylene sulphide resin produced by polymerizing a mixture containing a small amount of a monomer having three or more functional groups as a part of the monomers is also usable as the polyarylene sulphide resin of the present invention in addition to the above-described substantially linear polymers. Also suitable is a compounded resin produced by blending the above-described linear polymer with such a branched or crosslinked polyarylene sulphide resin. The PAS resin to be used as the component (A) in the present invention may be a polymer produced by crosslinking a linear polymer of a relatively low molecular weight by oxidation or by heat to increase the melt viscosity and thereby to improve its moldability. The expanded graphite (B) to be used in the present invention is one produced by treating natural, artificial, or other graphite with a strong acid such as sulphuric or nitric acid, a strong oxidising agent, a halogen compound or the like to form an intercalation substance between the crystal lattices of the graphite, washing the resultant product with water, dehydrating it, rapidly heating it (800 to 1200°C) to expand the resultant product several hundred times by volume, and pulverizing the expanded product to give an average particle diameter of 5 to 800 µm. It has been found that as compared with ordinary natural or artificial graphites, the expanded graphite exhibits an extremely remarkable conductivity-improving effect on the PAS and that a very small amount of the expanded graphite can impart to the PAS a low surface resistivity. It has been found, however, that the incorporation of the graphite exerts a significant adverse effect on the properties of the PAS resin, particularly mechanical properties such as toughness. The present invention is, therefore, characterized in that components which will be further described below are incorporated into the PAS resin in order to overcome this adverse effect. When the amount of the expanded graphite exceeds 50 parts by weight (for 100 parts by weight of PAS), the good mechanical properties cannot be maintained even by using the component (C) or the like and, on the contrary, when the amount it is below 3 parts by weight, the improvement in conductivity is insufficient. The alkoxysilane compounds (C) usable in the compositions of the present invention are epoxyalkoxysilanes, aminoalkoxysilanes, vinylalkoxysilanes and mercaptoalkoxysilanes, which can be used either singly or in combination of two or more of them, wherein the epoxyalkoxysilanes include, for example, γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and γ-glycldoxypropyltriethoxysilane, the aminoalkoxysilanes include, for example, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropylmethyldimechoxysilane, γ-aminopropylmethyldiethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-diallylaminopropyltrimethoxysilane and γ-diallylaminopropyltriethoxysilane, the vinylalkoxysilanes include, for example, vinyltriethoxysilane, vinyltrimethoxysilane and vinyltris(β-methoxyethoxy)silane, and the mercaptoalkoxysilanes include, for example, γ-mercaptopropyltrimethoxysilane and γ-mercaptopropyltriethoxysilane. The amount of the alkoxysilane compound used as the component (C) is 0.01 to 5 parts by weight, preferably 0.1 to 3 parts by weight, for 100 parts by weight of the polyarylene sulphide resin. Although the reaction mechanism of the component (C) has not yet been fully elucidated, the component (C) inhibits the deterioration of the mechanical properties of PAS caused by the incorporation of the expanded graphite, does not inhibit the conductivity effect of the expanded graphite at all but rather improves this effect, thus being effective in both reducing the dispersion of the surface resistivity and improving the toughness. A filler (D) other than the expanded graphite used as the component (B) is preferably incorporated in the composition in order to obtain molded articles having excellent mechanical strength, rigidity, thermal resistance and dimensional stability. The filler (D) is a fibrous, powdery or platy filler depending on the required end use of the composition. Suitable fibrous fillers include inorganic fibrous substances such as fibres of glass asbestos, carbon, silica, silica/alumina, zirconia, boron nitride, silicon nitride, boron and potassium titanate. Particularly typical fibrous filler is glass fibres. High-melting organic fibrous substances such as polyamides, fluororeslns and acrylic resins are also usable. The powdery fillers include silicates such as silica, quartz powder, glass beads, glass powder, calcium silicate, aluminium silicate, kaolin, talc, clay, diatomaceous earth and wollastonite; metal oxides such as iron oxide, titanium oxide and alumina; metal carbonates such as calcium carbonate and magnesium carbonate; metal sulphates such as calcium sulphate and barium sulphate; and, in addition, silicon carbide, silicon nitride, boron nitride and metal powders. The platy fillers include mica and glass flakes. These inorganic fillers can be used either singly or in combination of two or more of them. A combination of a fibrous filler, particularly glass fibre, with a powdery or platy filler is preferred for obtaining both mechanical strength and dimensional accuracy. The amount of the filler (D) is at most 300 parts by weight, desirably at most 200 parts by weight, for 100 parts by weight of the PAS resin. If it is present in excess of these amounts the moldability of the resin composition tends to be impaired. It is preferred to incorporate a specified olefinic copolymer (E) into the antistatic polyarylene sulphide resin composition of the present invention for further improving the toughness of the composition. The olefinic copolymers (E) to be used herein are the following copolymers or graft copolymers mainly comprising an α-olefin: (a) copolymers of ethylene with an α-olefin having 3 or more carbon atoms (such as propylene, butene-1, hexane-1, 4-4-methylbutene-1 or 4-methylpentene-1; particularly propylene or butene-1), (b) copolymers of an α-olefin (such as ethylene, propylene or butene-1) with an α,β-unsaturated carboxylic acid or ester thereof (such as acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, fumaric acid or an alkyl ester, glycidyl ester or anhydride thereof), (c-1) graft copolymers comprising the copolymer (a) grafted with an α,β-unsaturated carboxylic acid or a derivative thereof (such as acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, fumaric acid or an alkyl ester, glycidyl ester, anhydride or imide thereof), and (c-2) graft copolymers having a structure formed by chemically bonding the copolymer (b) to a polymer or copolymer comprising at least one of vinyl compounds such as styrene or acrylonitrile, α,β-unsaturated carboxylic acids and derivatives thereof. These olefinic copolymers or graft copolymers (a) to (c) may be used either singly or in the form of a mixture of two or more of them, or they may be used in the form of a polymer having a multiphase structure produced by stepwise (co)polymerization or graft polymerization. Particularly preferred substances include graft copolymers produced by grafting an ethylene/propylene or ethylene/butene-1 copolymer with maleic anhydride or maleimide; ethylene/alkyl acrylate copolymers optionally grafted with maleic anhydride; copolymers of an α-olefin, particularly ethylene, with glycidyl acrylate or glycidyl methacrylate, and graft copolymers obtained by grafting onto this copolymer at least one polymerizable or copolymerizable monomer such as styrene acrylonitrile, alkyl acrylate or alkyl methacrylate. The PAS resin composition of the present invention may further contain a small amount of thermoplastic resins other than those described above, such as vinyl resins, e.g., polyvinyl chloride resin, polyvinylidene chloride resin and polystyrene, polycarbonate resins, polyamide resins, polyimide resins, other polyolefinic resins, polyester resins, polyether resins, polysulphone resins, epoxy resins, natural rubbers and synthetic rubbers without departing from the object of the invention. Further, additives such as flame retardants, stabilizers e.g. antioxidants and ultraviolet screening agents, lubricants, release agents, nucleating agents, foaming agents, crosslinking agents and colorants can also be included if required. The composition of the present invention can be prepared by various well-known methods such as a method wherein the necessary components are fed at once to a mixer such as a Henschel mixer and homogeneously mixed, and the resultant mixture is melt-kneaded and pelletized on an extruder. If necessary, a specified component may be premixed with other components to form a master batch, which is then mixed with the other components to finally homogeneously disperse them, thereby obtaining an intended composition. EXAMPLES The following non-limiting Examples further illustrate the present invention. The substances (A), (B), (C), (D) and (E) used in the following Examples and Comparative Examples were as follows: (A) polyphenylene sulphide resin (PPS): Fortron KPS; a product of Kureha Chemical Industry Co., Ltd., (B) Graphites: B-1: expanded graphite, B'-I: natural scaly graphite, B'-2: natural earthy graphite, B'-3: artificial graphite, B'-4: conductive carbon black, and B'-5: carbon fibre. (C) Alkoxysilane compounds: C-1: aminopropyltriethoxysilane, C-2: glycidoxypropyltrimethoxysilane, C-3: mercaptopropyltrimethoxysilane. (D) Glass fibres (average diameter: 13 mm) and calcium carbonate, (E) Olefinic copolymers: E-1: ethylene/glycidyl methacrylate (weight ratio: 85/15) copolymer, E-2: graft copolymer prepared by grafting E-1 with styrene/acrylonitrile copolymer (weight ratio of E-1 to copolymer: 70:30) E-3: graft copolymer prepared by grafting E-1 with polymethyl methacrylate (weight ratio: 70:30), E-4: graft copolymer prepared by grafting ethylene/ethyl acrylate (weight ratio: 75/25) copolymer with maleic anhydride (weight ratio: 97:3). The methods for the determination of the properties in the Examples and Comparative Examples were as described below. Surface resistivity and variation thereof The surface resistivity was determined according to ASTM D-257. The average of the five samples, and the range from the minimum to the maximum as the variation were given. Tensile test The tensile strength and tensile elongation were determined according to ASTM D-638. Izod impact strength The Izod impact values on the notched side and unnotched side were determined according to ASTM D-256. Example 1 and Comparative Examples 1 to 8 The components (A), (B) and (C) listed in Table 1 were mixed together on a Henschel mixer for 5 min and the resultant mixture was melt-kneaded on a double-screw extruder at a cylinder temperature of 310°C to form pellets. Then the ASTM test pieces were prepared on an injection molding machine at a cylinder temperature of 320°C and a mold temperature of 150°C to determine the above-described properties of the test pieces. For comparison, the properties were determined as described above except that the composition lacking in any of the indispensable components of the present invention was used and the expanded graphite was replaced by other graphite or other carbonaceous substance. The results are given in Table 1. Examples 1 to 5 and Comparative Examples 9 to 11 The same test as that of Example 1 was conducted except that the average particle diameter and amount of the expanded graphite were altered. The results are given in Table 2. Examples 1 and 6 to 10 and Comparative Examples 2 and 12 The same test as that of Example 1 was conducted except that the amount and variety of the alkoxysilane were altered. The results are given in Table 3. Example 11 and Comparative Examples 13 to 19 The same test as that described above was conducted except that glass fibre, calcium carbonate and an olefinic copolymer were further incorporated in addition to the components listed in Table 1. The results are given in Table 4. Examples 11 to 17 The same test as that of Example 11 was conducted except that the amount and variety of the olefinic copolymer (E) were altered. The results are given in Table 5.

Claims: A polyarylene sulphide resin composition having improved conductivity and antistatic properties which comprises: (A) 100 parts by weight of a polyarylene sulphide resin, (B) 3 to 50 parts by weight of expanded graphite having an average particle diameter of 5 to 800 µm, and (C) 0.01 to 5 parts by weight of an alkoxysilane compound. A polyarylene sulphide resin composition according to Claim 1, wherein the polyarylene sulphide resin (A) is a homopolymer or copolymer comprising at least 70 molar % p-phenylene sulphide units as the repeating unit. A polyarylene sulphide resin composition according to Claim 1, wherein the polyarylene sulphide resin (A) is selected from substantially linear polyphenylene sulphide homopolymers comprising p-phenylene sulphide as the repeating unit, and polyphenylene sulphide copolymers mainly comprising p-phenylene sulphide as the repeating unit and at most 20 molar % of m-phenylene sulphide. A polyarylene sulphide resin composition according to any preceding claim, wherein the alkoxysilane compound (C) is at least one silane compound selected from the group consisting of epoxyalkoxysilanes, aminoalkoxysilanes, vinylalkoxysilanes and mercaptoalkoxysilanes. A polyarylene sulphide resin composition according to any preceding claim, wherein the amount of the alkoxysilane compound (C) is 0.1 to 3 parts by weight. A polyarylene sulphide resin composition according to any preceding claim, which further comprises: (D) up to 300 parts by weight of a filler other than the component (B) and which is selected from among fibrous, powdery and platy fillers. A polyarylene sulphide resin composition according to any preceding claim, which further comprises: (E) 0.5 to 30 parts by weight of a component comprising one or more olefinic copolymers selected from among (a) copolymers of ethylene with an α-olefin having 3 or more carbon atoms, (b) olefinic copolymers of an α-olefin with an α,β-unsaturated acid or ester thereof and (c) a graft copolymer obtained by grafting onto copolymer (a) or (b) at least one of styrene, acrylonitrile, α,β-unsaturated carboxylic acids and esters thereof which chemically bond to the respective copolymer (a) or (b). A polyarylene sulphide resin composition according to Claim 7, in which the olefinic copolymer (E) is selected from graft copolymers produced by grafting an ethylene/propylene or ethylene/butene-1 copolymer with maleic anhydride or maleimide; ethylene/alkyl acrylate copolymers optionally grafted with maleic anhydride; copolymers of an α-olefin, particularly ethylene, with glycidyl acrylate or glycidyl methacrylate, and graft copolymers obtained by grafting onto this copolymer at least one polymerizable or copolymerizable monomer such as styrene, acrylonitrile, alkyl acrylate or alkyl methacrylate. A polyarylene sulphide resin composition according to any preceding claim, which further comprises one or more other thermoplastic resins selected from polyvinyl chloride resin, polyvinylidene chloride resin and polystyrene, polycarbonate resins, polyamide resins, polyimide resins, other polyolefinic resins, polyester resins, polyether resins, polysulphone resins, epoxy resins, natural rubbers and synthetic rubbers.

Inventors: UOTA KATSUMI, UOTA, KATSUMI
Applicants: POLYPLASTICS CO, POLYPLASTICS CO. LTD.
Application year: 1993
Main classification: C08L81
IPC codes: C08K5, C08K7, C08K3, C08L81, C08L51, C08L23, C08L101