Method of producing a polyphenylene sulfide composition

Abstract: A polyphenylene sulfide composition for use in injection molding is prepared by kneading a mixture comprising 100 parts by weight of a substantially linear polyphenylene sulfide which has been treated with an aqueous solution of an acid or of a salt of a strong acid and a weak base and of which not less than 70 mol% is composed of the repeating unit and 0.05 to 5 parts by weight of at least one aminoalkoxysilane compound, at a temperature higher than the melting point of said polyphenylene sulfide.

Description: The present invention relates to a method of producing a polyphenylene sulfide composition having improved melt flow properties and particularly low generation of flash when injection molded, as well as excellent strength at a welded part thereof (hereinafter referred to as "weld strength") and impact strength. Injection molded products made of a polyphenylene sulfide composition (hereinafter referred to as "PPS") containing a reinforcing fiber or filler have excellent heat resistance and chemical resistance, and moreover have advantages which molded products made of other engineering plastics do not have, such as excellent electric insulation and dimensional stability. Accordingly, PPS is used in many industrial fields. However, since the molecular weight of conventional PPS which is not treated after its polymerization reaction is low, namely its melt viscosity is too low to be fabricated as it is, in order to apply PPS to practical use, curing by a treatment such as a thermal treatment in the presence of oxygen gas cannot so far be avoided. Usually, as such curing is performed with cross-linking, the molded products of such a polymer have relatively poor toughness. Even when a reinforcing material or filler is added to the polymer, its molded products have poor impact strength and weld strength. Accordingly, an improvement in such properties is desired. As an example of such an improvement, PPS which is manufactured by the process described in US-A-4,645,826 has excellent toughness. This PPS has not less than 70 mol% of the total repeating units composed of the unit and has a substantially linear structure (hereinafter referred to as "the linear PPS"). Molded products of a composition made of the linear PPS have a much better impact strength and weld strength than molded products of a conventional PPS composition. This is the reason why the linear PPS is suitable for molded products which have many thin parts or products which have a piece of metal in them. However, even when this linear PPS having excellent toughness is fabricated, for example injection-molded into precision molds, it is prone to generate a large amount of flash on the molds. The present inventors have already proposed in JP-A-62-84,110/1987 (=EP-A-286 257, postpublished) a method to obtain a composition which has good anti-flash property by blending a specific silane compound with the linear PPS, increasing the melt viscosity and, further, raising the dependency of the viscosity upon its shear rate. There are several disclosures of compositions obtained by blending a conventional PPS with a silane compound, for example: (1) JP-A-59-31,503 (1984) discloses an electronic part encapsulated with a composition comprising PPS and mercaptosilane, which has excellent water resistance and electric properties under a high temperature and high humidity; (2) US-A-4,451,601 (=EP-A-74 632) discloses a composition containing a polyarylene sulfide and at least one organosilane, which has an improved anti-hydrolytic property; and (3) JP-A-55-29,526 (1980) discloses a composition comprising 100 parts by weight of PPS, 0 to 30 parts by weight of fillers and 0.01 to 10 parts by weight of aminoalkoxysilane or its hydrolytic condensate, which has excellent water resistance, humidity resistance and electric properties. Furthermore, JP-A-61-285,255 discloses a PPS composition containing a fibrous filler and/or another silicate filler and a silane compound having at least two unsaturated double bonds in its molecule and/or a non-hydrochloride silane compound having at least one unsaturated double bond and at least one amino group in its molecule, which has excellent strength and electrical properties. In these known arts, the silane compound has been used to improve various properties of the composition, namely (1) adhesion between PPS and an inorganic filler; and (2) strength, humidity resistance and electric properties. Among these improvements, JP-A-55-29,526 (1980) discloses the increase of the melt flow, namely the reduction of the melt viscosity, by adding aminoalkoxysilane to PPS; and US-A-4,451,601 discloses a similar effect to reduce the melt viscosity by adding γ-ureidopropyl-triethoxysilane to PPS. Such an effect of silane compounds to reduce the melt viscosity is contrary to the object of the present invention. The present invention provides a method of producing a polyphenylene sulfide composition, which method comprises (1) treating a linear polyphenylene sulfide, of which not less than 70 mol% is composed of the repeating unit with an aqueous solution of an acid or of a salt of a strong acid and a weak base; (2) blending 0.05 to 5 parts by weight of at least one aminoalkoxysilane compound with 100 parts by weight of the treated polyphenylene sulfide to form a mixture; and (3) melt-kneading the mixture at a temperature which is higher than the melting point of said polyphenylene sulfide. A PPS composition obtained by the above method has excellent impact and weld strength and improved anti-flash properties accompanied with a high melt viscosity. The above method is inexpensive. The present inventors have found the following: (1) a composition obtained by treating the linear PPS with an aqueous solution of an acid or a salt of a strong acid and a weak base, blending an aminoalkoxysilane compound with the treated PPS and melt-kneading the blend at a temperature higher than the melting point of the linear PPS, can improve its melt properties, such as increasing the melt viscosity and the dependency of the melt viscosity on the shear rate, no matter what the polymerization degree is, that is what melt viscosity the PPS has. The linear PPS without treatment by the aqueous solution does not have such a remarkable improvement of the melt property after blending an aminoalkoxysilane compound and melt kneading the blend; (2) the composition obtained by treating the linear PPS with the above aqueous solution, blending with an aminoalkoxysilane compound and melt-kneading, can have a remarkably improved impact strength compared with the linear PPS without the above treatments or the linear PPS only treated with the aqueous solution. This composition can also have a largely improved anti-flash property during its molding. However, there is a sign that a trace of ejector pin remains on the molded product and also that release of the product from the mold is not smooth; and (3) the composition obtained by treating the linear PPS with said aqueous solution, blending with an aminoalkoxysilane compound and a releasing agent and melt-kneading has less of an improvement in its melt property but still has an excellent anti-flash property. Furthermore, release of its molded products from the mold proceed smoothly. On the other hand, a composition, for comparison, obtained by treating the linear PPS with said aqueous solution, blending a releasing agent (without an aminoalkoxysilane compound) and melt-kneading has an improved property of release from the mold but generates much flash, making its melt viscosity lower. The linear PPS can be produced by a known method, for example, the method described in US-A-4,645,826, that is: (1) reacting a dihaloaromatic compound with sodium sulfide at a temperature of from 180 to 235°C in the presence of from 0.5 to 2.4 moles of water per mole of the sodium sulfide in an organic amide solvent to produce a polyphenylene sulfide having a melt viscosity of from 0.5 to 30 Pas (5 to 300 poise) with the conversion ratio of the dihaloaromatic compound being from 50 to 98 mol%; and (2) adding water to the reaction system to make the mole ratio of water to sodium sulfide to from 2.5:1 to 7.0:1, and raising the temperature of the system to from 245 to 290°C and continuing the polymerization. By this method, the linear PPS comprising not less than 70 mol% of paraphenylene sulfide units, which is a main constituent of PPS, as a repeating unit and of which the melt viscosity is from 1 to 3,000 Pas (10 to 30,000 poise) is easily manufactured. The term "melt viscosity" of a polymer used in the present application is the viscosity measured using a capillary viscometer equipped with a capillary of 10 mm length and 1 mm diameter at 310°C and a shear rate of 1,200/second, unless otherwise specified. The term "the linear PPS" used in the present application is a PPS which is obtained when no, or not more than 1 mol%, of polyfunctional monomer is used in the polymerization reaction and the obtained polymer is not treated with a known heat curing or, if the curing is performed, the melt viscosity of the polymer after curing is less than 3 times that of before curing. The linear PPS used in the present invention is a polymer which has not less than 70 mol%, preferably not less than 80 mol%, of the paraphenylene sulfide unit as a repeating unit. If the repeating unit content is less than 70 mol%, the PPS is prone to have a reduced crystallization degree, which is a characteristic of a crystalline polymer, and poor strength. The linear PPS used in the present invention may also contain less than 30 mol% of other repeating units. Examples of other repeating units include the following: a metaphenylene sulfide unit, a diphenylketone sulfide unit, a diphenylsulfone sulfide unit, a biphenyl sulfide unit, a diphenylether sulfide unit, a 2,6-naphthalene sulfide unit, and a trifunctional unit, The content of the trifunctional unit among these units is preferably not more than 1 mol% in order not to reduce the crystallization degree. As the linear PPS used in the present invention, homopolymers having paraphenylene sulfide repeating units and block copolymers having from 70 to 95 mol% of paraphenylene sulfide repeating units and from 5 to 30 mol% of metaphenylene sulfide repeating units are particularly preferable. Examples of dihaloaromatic compounds which can be used to produce the linear PPS are p-dichlorobenzene, m-dichlorobenzene, p-dibromobenzene, 2,6-dichloronaphthalene, 2,6-dibromonaphthalene, 4,4'-dichlorobiphenyl, 4,4'-dibromobiphenyl, 4,4'-dichlorodiphenyl ether, 4,4'-dichlorodiphenyl sulfone and 4,4'-dichlorodiphenylketone. Examples of organic amide solvents which can be used in the polymerization reaction to obtain the linear PPS are N-methylpyrrolidone (NMP), N-ethylpyrrolidone, N,N'-dimethylformamide, N,N'-dimethylacetoamide, N-methylcaprolactam, tetramethylurea, hexamethylphosphoric triamide and mixtures thereof. The PPS block copolymer preferably used in the present invention can be manufactured by the method described in EP-A-166,451. For example, the block copolymers can be manufactured by a method comprising a first step in which an organic amide solvent containing paradihalobenzene and sodium sulfide is heated to from 160 to 300°C to produce a reaction liquid containing a paraphenylene sulfide having an average polymerization degree of from 20 to 5,000, and having a repeating unit (A), and a second step in which the dihaloaromatic compound, which essentially consists of metadihalobenzene, is added to the reaction liquid of the first step, the mixture is heated to from 160 to 300°C in the presence of sodium sulfide and an organic amide solvent and a block copolymer comprising blocks of the above-mentioned repeating unit (A) and a repeating unit (B), is obtained, in relative amounts such that the mol% of the repeating unit (A) is from 70 to 95 mol%. The linear PPS used in the present invention may be manufactured by another method than that described in US-A-4,645,826 or EP-A-166,451, namely any method which can manufacture a substantially linear PPS by a polycondensation reaction of an dihaloaromatic compound and an alkaline metal sulfide. The linear PPS is treated with an aqueous solution of an acid or a salt of a strong acid and a weak base after completion of the polymerisation reaction. This treatment with an aqueous solution can be economically performed by being incorporated into a sequence of steps using the polymerization equipment as a post-treatment of the polymer after polymerization. As a method to perform the treatment, the method described in EP-A-216,116 can be applied. Namely, a treatment with an aqueous solution of hydrochloric acid or sulfuric acid having a pH of less than 2 or with an aqueous solution containing from 0.1 to 30% by weight of a salt of a strong acid and a weak base (for example ammonium chloride or ammonium sulfate). Suitable aqueous solutions include solutions obtained by using water or mixed solvents containing water, as a main component, and an alcohol, a ketone or an ether. The linear PPS which is treated with an aqueous solution of an acid or a salt of a strong acid and a weak base has a melt viscosity slightly lower than that of the polymer without the treatment. A melt viscosity of from 1 to 2,000 Pas (10 to 20,000 poise) is preferable, and from 3 to 1,000 Pas (30 to 10,000 poise) is more preferable. One of the objects of the present invention is to obtain a composition which has an improved anti-flash property during molding without spoiling the excellent toughness and weld strength of the linear PPS. To make the composition sufficiently applicable in practical use, it is preferable to include an inorganic filler or reinforcing fibers. When it comes to injection molding, if the melt viscosity of a composition is over 2,000 Pas (20,000 poise), the injection pressure has to be high, and a large molding machine with high mold clamping pressure is therefore required. Accordingly, such a high melt viscosity is not preferable. For a composition which cannot exhibit its characteristic properties in practical use unless a relatively large amount of filler is blended (for example in a plastic magnet), it is common sense in the field to use a polymer having a low melt viscosity. However, in the present invention, a polymer having a melt viscosity of not more than 1 Pas (10 poise) cannot satisfy the necessary tensile strength or impact strength in many cases of practical use. Accordingly such polymer is not preferable. The objects of the present invention cannot be achieved unless an aminoalkoxysilane compound is added to the treated linear PPS and, if necessary, a releasing agent is added to the PPS and the mixture is melt-kneaded at a temperature higher than the melting point of the treated linear PPS and is blended in a uniform composition. In other words, the composition obtained by melt-heading the linear PPS exhibits an increased melt viscosity and increased dependency of the melt viscosity on its shear rate, as compared with a raw material, the linear PPS. The composition can be used to obtain a molded product having an improved anti-flash property as well as excellent impact and weld strength. Flash generated on the molded products during injection-molding is formed when a molten polymer composition flows into line gaps designed as parts of the mold, on the internal wall of a cavity, when the molten composition is filled in the cavity and solidified. Although the flash generation depends upon many factors such as a melt viscosity, injection pressure, holding pressure, mold temperature and mold clamping pressure, as well as the balance between a cavity and a gate, and the position of a venting hole (these factors all relate together), in view of the flow properties of a molten polymer, flash generation is suppressed by lowering its melt viscosity at a place such as the gate at which the molten polymer receives high shear stress and flows at a high speed and by increasing the melt viscosity in a place such as inside the cavity in which the molten polymer receives a relatively low shear stress and flows at a slightly lower speed, namely by increasing the dependency of the melt viscosity on the shear rate. The most direct and simple means to increase the dependency of the melt viscosity on the shear rate is to increase the melt viscosity of the polymer. However, when the melt viscosity is increased by adding an inorganic filler, suppression of the flash generation can hardly be expected unless the melt viscosity of the matrix polymer itself is increased. As the aminoalkoxysilane compound, amino,(C₁ to C₄)-alkyl,(C₁ to C₄)-alkoxysilanes are preferably used, and γ-aminopropyl,tri-(C₁ to C₄)-alkoxysilanes, which have an excellent effect and are easily available, are more preferably used. Examples of aminoalkoxysilane compounds include γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropylmethyldiethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane and γ-ureidopropyltriethoxysilane. The amount of the aminoalkoxysilane compound added is from 0.05 to 5 parts by weight, preferably from 0.1 to 3 parts by weight, per 100 parts by weight of the treated linear PPS. Addition of less than 0.05 parts by weight of the compound in some cases does not sufficiently produce the effect intended by the present invention, and the addition of over 5 parts by weight of the compound is prone to generate gases easily during the molding process and to increase the number of products containing voids. Examples of the releasing agent which is used according to necessity in the present invention are fatty acid esters of polyhydric alcohols, metal salts of stearic acid or polyethylene wax or fatty acid bisamide compounds. The fatty acid esters of polyhydric alcohols which effectively improve releasing properties even in small amounts and produce small amounts of gases during the molding process are particularly preferable. The amount of the releasing agent to be added according to necessity in the present invention is from 0.01 to 3 parts by weight, preferably from 0.05 to 1.5 parts by weight, more preferably from 0.1 to 1.0 parts by weight, based on 100 parts by weight of the linear PPS polymer treated with the aqueous solution. The addition of over 3 parts by weight of the releasing agent is undesirable because it reduces the effect of increasing viscosity of the composition by the addition of an aminoalkoxysilane compound and, moreover, increases the generation of gases during the molding process. The addition of less than 0.01 parts by weight of the releasing agent is meaningless because no effect can be expected. The resin composition produced by the method of the present invention containing the treated linear PPS and an aminoalkoxysilane compound or containing the above components and the releasing agent is produced by melt-kneading the mixture for a sufficient time to uniformly mix all the components under a condition of the PPS being melted. The condition which the PPS is melted generally means a state at a temperature which is from 5 to 100°C higher than the melting point of the PPS. In the present invention, a temperature of from 10 to 70°C higher than the melting point of the PPS is preferable. The aminoalkoxysilane compound is preferably reacted with the PPS for at least 30 seconds, more preferable from 30 seconds to 15 minutes, much more preferably from 1 to 10 minutes, with kneading in a molten state. The apparatus used for heating and kneading the composition is not particularly limited provided that the apparatus has a heating and kneading unit which can generally be used for treating polymers. A single or twin screw extruder having a vent part is preferably used. The composition obtained by the method of the present invention essentially contains the treated linear PPS and the aminoalkoxysilane compound and may contain other substances such as a releasing agent, a filler, such as an inorganic non-fibrous filler, a reinforcing material, such as a fibrous reinforcing material, a stabilizer or a pigment, according to necessity. The filler is selectively used particularly for the purpose of improving the dimensional stability, heat conductivity or electrical characteristics of the composition. Examples of fillers that can be used include granular and powdered mica, silica, talc, alumina, kaoline, titanium oxide, calcium sulfate, calcium carbonate, carbon black, graphite and ferrite and other magnetic powders. The reinforcing material is used particularly for the purpose of improving the mechanical strength in addition to the same purpose as the filler. Examples of reinforcing materials that can be used include glass fibers, carbon fibers, calcium silicate fibers, potassium titanate fibers, alumina fibers and aromatic polyamide fibers. The amount of the reinforcing material and/or the filler to be added to the composition can be selected from within a range which is effective to improve the thermal properties and friction properties, for example, from 0.1 to 400 parts by weight, preferably from 1 to 200 parts by weight, based on 100 parts by weight of the PPS. The composition can contain a small amount of another thermoplastic polymer, according to necessity. Examples of thermoplastic polymers that can be blended with the composition include polyether ether ketone, polyether ketone, polyacrylate, polycarbonate, polyether sulfone, modified polyphenylene oxide, polysulfone, polyamide, polyethylene terephthalate, polybutylene terephthalate, polytetrafluoroethylene and other polyarylene sulfides such as polymers having the following repeating unit: The composition can be used in the fields of injection molding, extrusion molding and others, as a PPS composition having excellent mechanical and processing characteristics. The PPS composition maintains the excellent toughness, represented by the excellent impact resistance, which is a characteristic of the linear PPS or improves the toughness and remarkably improves the melt properties such as increasing the melt viscosity and its dependency on the shear rate, as well as providing injection molded products wherein the generation of flash is reduced and the weld strength is improved. The PPS composition also exhibits an excellent releasing property and is suitable to obtain precision molded products in a high yield, particularly thin molded products and injection molded products which are designed to have metal parts forced into them and which have complicated shapes. The present invention is now further described in the following Examples. SYNTHETIC EXPERIMENTAL EXAMPLE 1 (Synthesis of Polyparaphenylene Sulfide) : 920 kg of N-methylpyrrolidone (hereinafter referred to as NMP) and 424 kg of Na₂S·5H₂O (containing 46.07% by weight of Na₂S) were charged in an autoclave and 168 kg of water was then distilled out by gradually raising the temperature of the mixture to 203°C. 5 kg of water and 50 kg of NMP were added to the residue, 362 kg of paradichlorobenzene was then charged in the autoclave and the polymerization reaction was performed at 220°C for 5 hours. 69 kg of water was then added to the reaction liquid, which was further subjected to polymerization reaction at 255°C for 5 hours. After cooling the reaction mixture, a granular polymer was separated with a screen having 0.1 mm openings. The granular polymer was then washed with acetone and water to obtain a wet granular polymer. About 1/3 of the wet polymer was dried as it was to obtain a polymer (1-A). The melting point of the polymer (1-A) was 280°C and the melt viscosity was 114 Pas (1,140 poise). On the other hand, half the remaining polymer was immersed in an aqueous solution of 2% by weight NH₄Cl to be treated at 40°C for 30 minutes under agitation. The treated polymer was washed with water and dried to obtain a polymer (1-B). Half of the remaining wet polymer was immersed in an aqueous solution of hydrochloric acid having a pH of 1, and treated at 40°C for 30 minutes. The treated polymer was neutralized with ammonia water, washed with water and dried to obtain a polymer (1-C). SYNTHETIC EXPERIMENTAL EXAMPLE 2 (Synthesis of PPS) : 930 kg of NMP and 423 kg of Na₂S·5H₂O (containing 46.07% by weight of Na₂S) were charged in an autoclave and 170 kg of water was then distilled out by gradually raising the temperature of the mixture to 203°C. 4 kg of water and 43 kg of NMP were added to the mixture, 365 kg of paradichlorobenzene was charged in the autoclave and the polymerization reaction was performed at 220°C for 5 hours. 135 kg of water was added to the reaction mixture, which was further polymerized at 255°C for 4.5 hours. After cooling the reaction mixture, a granular polymer was separated with a screen having 0.1 mm openings. The granular polymer was then washed with acetone and water to obtain a wet granular polymer. About half of the wet granular polymer was dried as it was to obtain a polymer (2-A). The melting point of polymer (2-A) was 283°C and its melt viscosity was 60 Pas (600 poise). The remaining granular polymer was treated with an aqueous solution of 2% by weight NH₄Cl in the same way as in Synthetic Experimental Example 1, washed with water and dried to obtain a polymer (2-B). SYNTHETIC EXPERIMENTAL EXAMPLE 3 (Synthesis of Paraphenylene Sulfide-Metaphenylene Sulfide Block Copolymer) : (a) 80 kg of NMP and 37.0 kg of Na₂S·5H₂O (containing 45.9% by weight of Na₂S) were charged in an autoclave and 14.9 kg of water and 12.8 kg of NMP were distilled out by gradually raising the temperature of the mixture to 200°C. 31.0 kg of metadichlorobenzene, 40 kg of NMP and 1.0 kg of water were then added to the mixture, followed by polymerization at 220°C for 2 hours and then at 230°C for 5 hours. (b) 75 kg of NMP and 30.5 kg of Na₂S·5H₂O (containing 45.9% by weight of Na₂S) were charged in another autoclave, and 12.8 kg of water and 13.7 kg of NMP were distilled out by gradually raising the temperature of the mixture to 200°C. 26.5 kg of paradichlorobenzene, 25 kg of NMP, 1.0 kg of water and 23.5 kg of the polymetaphenylene sulfide slurry obtained in (a) were added to the mixture, followed by polymerization at 220°C for 10 hours. 13.0 kg of water was added to the reaction liquid, which was further subjected to polymerization at 260°C for 5 hours. After cooling the reaction liquid, a granular polymer was separated with a screen having 0.1 mm openings. The granular polymer was then washed with acetone and water to obtain a wet polymer. About half of the wet polymer was dried as it was to obtain a polymer (3-A) (melting point, 275°C; melt viscosity, 130 Pas (1,300 poise)). The remaining polymer mixture was treated with an aqueous solution of 2% by weight of NH₄Cl, washed with water, dried and obtained polymer (3-B) (melting point, 275°C; melt viscosity, 130 Pas (1,300 poise)). The results of analysis of the block copolymers with infrared absorption spectra indicate that the ratio of paraphenylene sulfide to metaphenylene sulfide of each of the copolymers was 85:15. SYNTHETIC EXPERIMENTAL EXAMPLE 4 : A PPS polymer (4) treated with an aqueous solution of 2% by weight of NH₄Cl (melting point, 284°C; melt viscosity, 37 Pas (370 poise)) was obtained by the same method as employed in Synthetic Experimental Example 2 except that 370 kg of paradichlorobenzene was charged in an autoclave. EXAMPLES 1 to 2 AND COMPARATIVE EXAMPLES 1 to 4 : A PPS polymer (4) obtained in Synthetic Experimental Example 4 was preliminarily mixed with γ-aminopropyltriethoxysilane A-1100 (hereinafter referred to as AS-1; manufactured by NIPPON UNIKA Co. Ltd.), glass fibers (diameter; 13 µm: manufactured by NIPPON Electric Glass Co., Ltd.) and neopentylglycol distearate as a releasing agent in the ratios shown in Table 1. Each of the mixtures was kneaded for 3 minutes at a cylinder temperature of 320°C and then extruded with a co-rotating twin-screw kneading extruder into pellets. The procedure for preliminary mixing was as follows: The PPS and an aminoalkoxysilane compound were first mixed with a Henschel mixer, a releasing agent was then added to the mixture and again mixed by the Henschel mixer and glass fibers were finally added to the mixture and mixed by a tumbler mixer. Melt viscosities of these pellets were measured with a Capillograph, having a nozzle of L/D = 10 mm/1mm, (manufactured by TOYO SEIKI Co., Ltd.) at 310°C. The results of the measurements are in Table 1. To indicate the index for the dependency of melt viscosity on the shear rate, the ratios of the melt viscosities at a shear rate of 200/second and at a rate of 1,200/second were calculated and the results are also given in Table 1. A higher ratio means a greater dependency of the melt viscosity on the shear rate. A test piece of each pellet to measure the physical properties are prepared by an injection molding machine (temperature of the mold = 145°C). The various physical properties of the test pieces (without heat treatment) were measured and the results are given in Table 2. It can be seen from Table 1 that the melt viscosity and its dependency on the shear rate of PPS (4) treated with an aqueous solution of 2% by weight of NH₄Cl are significantly increased owing to the reaction of PPS with the aminoalkoxysilane. It can also be seen from Table 2 that the mechanical strength of the PPS composition reacted with an aminoalkoxysilane is relatively better than that of the unreacted PPS and that the composition containing both an aminoalkoxysilane and a releasing agent is well-balanced with respect to the reduction ratio of flash generation and the releasing property. The degree of flash generation was determined by measuring the length of flash generated on each test piece. The length of a flash was measured by an enlarged photograph, and its evaluation was determined according to the following three criteria: (X): The length of a flash is not less than 0.5 mm and there is a problem in practical use. (▵): The length of a flash is about 0.3 mm and there is no significant problem in practical use, although a small flash exists. ( ○): The length of a flash is not more than 0.2 mm and there is no problem in practical use. The releasing property was determined by injection molding test pieces, under constant molding conditions, using a box-shaped mold with an inner size of 40 mm x 60 mm and a thickness of 4 mm (the temperature of the mold; cavity side, 147°C; core side, 176°C) and measuring the time (injection time + cooling time) taken until no mark of the ejector pin used remained on a molded product at the releasing. The times were used as an index of the releasing property and are given in Table 2. EXAMPLES 3 TO 10 AND COMPARATIVE EXAMPLES 5 TO 16 As PPS, each granular PPS obtained in the Synthetic Experimental Examples 1 to 3 or a commercially available PPS, which is thermally cured, is used and as an aminoalkoxysilane, AS-1, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (Code no. A-1120; manufactured by NIPPON UNIKA Co., Ltd.) or γ-ureidopropyltriethoxysilane (Code no. A-1160; manufactured by NIPPON UNIKA Co., Ltd.) is preliminarily blended with 100 parts by weight of above PPS, in amounts shown in Table 3, by a Henschel mixer at room temperature for 5 minutes. At the same time, 0.2 parts by weight of neopentylglycol distearate is also blended with the PPS. Each blend was extruded with a co-rotating twin-screw kneading extruder (Plastic Engineering Institute BT-30) into pellets at a cylinder temperature of 320°C. The melt viscosity of each sample was measured according to the method described in page 18 and the results are in Table 3. The ratio of the melt viscosities at shear rates of 200/second and 1,200/second was used as an index expressing the dependency of the melt viscosity on the shear rate. As can be seen from Table 3, only the mixture of an aminoalkoxysilane and the PPS treated with hydrochloric acid or NH₄Cl leads to an increased viscosity and dependency on the shear rate. EXAMPLE 11 and COMPARATIVE EXAMPLE 17 : Polymer (1-B) obtained in Synthetic Experimental Example 1 was blended with γ-aminopropyltriethoxysilane as an aminoalkoxysilane, glass fibers having a diameter of 13 µm (produced by NIPPON Electric Glass Co., Ltd.) and pentaerythritol tetrastearate as a releasing agent in the ratios shown in Table 4. Each blend obtained was melt-kneaded and pelletized by melt extrusion in the same manner as in the above Examples. The procedure for blending was as follows: The PPS and the aminoalkoxysilane were first blended by a Henschel mixer, then the releasing agent was blended with the obtained blend by the same Henschel mixer, and finally the glass fibers were blended by a tumbler mixer. The melt viscosities of the pellets were measured according to the method described in page 18. Pellets of each composition were fabricated in to test pieces for measuring the physical properties by an injection molding machine (mold temperature, 145°C and cylinder temperature, 310°C). These test pieces (as molded) were used for evaluating the physical properties and the degree of flash generation and for measuring the weld strength and releasing property. The results of tests are in Tables 4 and 5. As can be seen from these tables, the melt viscosity and the dependency thereof on the shear rate of the composition containing an aminoalkoxysilane compound are higher than those of the composition containing no aminoalkoxysilane compound. As can also be seen from these tables, the composition containing both the aminoalkoxysilane compound and the releasing agent exhibits increased tensile strength and elongation, a reduced amount of flash and well-balanced relationship between the weld strength and the releasing property, as compared with those of the composition containing neither the aminoalkoxysilane compound nor the releasing agent.

Claims: A method of producing a polyphenylene sulfide composition, which method comprises (1) treating a linear polyphenylene sulfide, of which not less than 70 mol% is composed of the repeating unit with an aqueous solution of an acid or of a salt of a strong acid and a weak base; (2) blending 0.05 to 5 parts by weight of at least one aminoalkoxysilane compound with 100 parts by weight of the treated polyphenylene sulfide to form a mixture; and (3) melt-kneading the mixture at a temperature which is higher than the melting point of said polyphenylene sulfide. A method according to claim 1, wherein the mixture further comprises from 0.01 to 3 parts by weight of a releasing agent. A method according to claim 2, wherein said releasing agent is a fatty acid ester of a polyhydric alcohol. A method according to any one of the preceding claims, wherein said polyphenylene sulfide is a block copolymer comprising from 70 to 95 mol% of the repeating unit and from 5 to 30 mol% of the repeating unit A method according to any one of the preceding claims, wherein said aminoalkoxysilane is an aminoalkylalkoxysilane having an alkyl group of from 1 to 4 carbon atoms and an alkoxy group of from 1 to 4 carbon atoms. A method according to any one of the preceding claims, wherein the mixture further comprises a reinforcing material and/or a filler. A method according to claim 6, wherein the reinforcing material and/or filler is present in an amount of from 0.1 to 400 parts by weight per 100 parts by weight of said polyphenylene sulfide. A method according to any one of the preceding claims, wherein the said acid or salt treatment is performed between polymerization and drying of said polyphenylene sulfide. A method according to any one of the preceding claims, wherein said salt of a strong acid and a weak base is ammonium chloride or ammonium sulfate. A method according to any one of the preceding claims, further comprising injection molding the polyphenylene sulfide composition thus formed.

Inventors: FUKUDA MAKOTO, ICHIKAWA YUKIO, KATTO TAKAYUKI, NITOH TOSHIKATSU, FUKUDA, MAKOTO, ICHIKAWA, YUKIO, KATTO, TAKAYUKI, NITOH, TOSHIKATSU
Applicants: KUREHA CHEMICAL IND CO LTD, KUREHA KAGAKU KOGYO KABUSHIKI KAISHA
Application year: 1988
Main classification: C08K5
IPC codes: C08K5, C08L81, C08G75