PROCESS FOR REMOVING IMPURITIES FROM POLYPHENYLENE SULFIDE RESIN

Abstract: Process comprises the following steps: (1) mixing and heating at 100-270 deg.C for 10 mins. - 10 hrs. powdery PPS and a solvent selected from (I) - (IV). The ratio of PPS to solvent is 1-15 (by wt.); (2) effecting intimate contact between the solvent and PPS in a partially dissolved state; (3) cooling and filtering the mixt.; (4) washing with a solvent in which PPS is insoluble (selected from aromatic or aliphatic hydrocarbons, ketones, alcohols or water). Solvents used are (I) One or a mixt. of more than one selected from dimethyl sulphoxide, sulpholane, glycerin, ethyleneglycol, diethylene glycol. (II) A mixt. of a solvent selected from dimethyl sulphoxide, sulpholane, ethylene glycol, and diethylene glycol, with alpha-halogenated naphthalene or biphenyl. (III) A mixt. of N-methyl-2-pyrrolidone with one or more solvents selected from among a mixt. of (II), benzyl alcohol, sulpholane, glycerin. (IV) A mixt. of water and a solvent from (I) or N-methyl-2-pyrrolidone. Powdery PPS can be obtd. by either a dry or a wet method. The process produces high pure PPS.

Description: The present invention relates to a method for removing impurities composed mainly of sodium chloride and other alkali metal compounds from polyphenylene sulfide (hereinafter referred to as "PPS") to obtain PPS having a high purity. PPS has excellent characteristics such as a high heat resistance, high dimension stability, and low melt viscosity. However, ordinary PPS contains sodium chloride and other alkali metal compounds resulting from the preparation process as impurities, and therefore, the product does not have a reliable moisture resistance and the use thereof is considerably restricted even though the use of PPS as an encapsulant for integrated circuits (IC) or large scale integration integrated circuits (LSI) is desired. Various methods for removing impurities such as alkali metal compounds from PPS have been proposed. For example, JP-A- 57-108,135 discloses a method in which PPS is treated with a mixed solvent comprising ethylene glycol and N-methyl-2-pyrrolidone; JP-A- 57-108,136 discloses a method in which a chemical such as sodium carbonate is added to an aqueous slurry of PPS and the mixture is treated at a high temperature under a high pressure; and JP-A- 59-219,331 discloses a method in which PPS is heat-treated in an aromatic solvent such as diphenyl ether, diphenyl, 1-chloronaphthalene, p-chlorophenol or benzonitrile. In the method where PPS is treated with a mixed solvent of ethylene glycol and N-methyl-2-pyrrolidone, a large quantity of the solvent must be used and the same operation must be repeated at least two times, preferably 3 to 5 times, for removing impurities to a required level. The effect of removing impurities is not sufficient in the method where sodium carbonate is added to an aqueous slurry of PPS and the mixture is treated. Moreover, the method in which PPS is heat-treated in an aromatic solvent such as diphenyl ether or diphenyl has a problem in that, since the melting point of the solvent is relatively high, the treatment must be carried out at a high temperature and separation of the solvent is relatively difficult. It is an object of the present invention to provide a method for removing impurities such as alkali metal compounds from PPS with a high efficiency. In accordance with the present invention, there is provided a method for removing impurities from a polyphenylene sulfide resin, which comprises heating and mixing a powdery polyphenylene sulfide resin with a first solvent to bring the powder and the solvent sufficiently in contact with each other in the partially dissolved state, cooling and filtering the mixture, and washing the filter cake with a second solvent, that is incapable of dissolving the polyphenylene sulfide resin therein, characterized in that first solvent is dimethylsulfoxide or a mixed solvent of dimethylsulfoxide with water. The PPS referred to in the present invention is a PPS having a particle size in the range of from 5 to 200 µm and an average particle size of 30 to 50 µm, which is prepared according to a method as disclosed in JP-B- 45-3,368 or JP-B- 52-12,240, and this PPS ordinarily contains 1,000 to 4,000 ppm of impurities such as alkali metal compounds. The PPS prepared through the ordinary preparation steps is in the powdery form, but in order to increase the contact area, preferably the PPS is finely divided by the dry method or the wet method. The first solvent used is dimethylsulfoxide or a mixed solvent of dimethylsulfoxide with water. The mixing ratio of dimethylsulfoxide to water in the mixed (first) solvent is preferably from 70/30 to 95/5 by weight. It is sufficient if the amount of the first solvent is about 1 to about 15 times by weight the amount of PPS. Namely, the solvent is used in an amount such that the concentration of PPS in the slurry is lower than about 50%, preferably 5 to 30% by weight. The temperature for heating the mixture of PPS and the first solvent depends on the kind of PPS and the kind and quantity of the solvent used, but the heating temperature is ordinarily 100 to 250°C, and preferably, 150 to 250°C. If the PPS/solvent mixture is thus heated, PPS is brought to the partially dissolved state, that is, the swollen state. In the present invention, the PPS is not completely dissolved or molten but is partially dissolved or swollen. Accordingly, the PPS should be in the powdery form, and in view of the efficiency of extraction of impurities, preferably the PPS is as finely divided as possible. The PPS is maintained in the partially dissolved state for 10 minutes to 10 hours, preferably 10 minutes to 4 hours. The first solvent used in the present invention. partially dissolves PPS therein at a high temperature and further dissolves sodium chloride and other alkali metal compounds. Accordingly, while the PPS is kept in the partially dissolved state, impurities present in the interior of the PPS, such as sodium chloride, are easily extracted. After the PPS has been maintained in the partially dissolved state for a predetermined time, the mixture is cooled and filtered at an appropriate temperature, for example, 60 to 80°C, and the filter cake is washed with a second solvent, that is incapable of dissolving PPS therein. The solvent adhering to the filter cake may be recovered by heating and evaporation prior to this washing, and the filter cake having the solvent adhering thereto may be directly washed. By this washing, the solvent containing the extracted impurities therein is removed. As the second solvent, that is incapable of dissolving PPS therein, there can be used aromatic and aliphatic hydrocarbons such as benzene, toluene, xylene, n-hexane, 2-methylpentane, n-heptane and cyclohexane; esters such as methyl acetate, ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; ethers such as diethyl ether, dipropyl ether and di-isopropyl ether; nitrogen compounds such as nitroethane and 1-nitropropane; alcohols such as methanol, ethanol, n-propyl alcohol and isopropyl alcohol; water, and mixtures thereof. Washing can be carried out repeatedly according to need. After washing, the cake is dried, preferably under a reduced pressure. Ordinarily, impurities can be sufficiently removed to a desired degree by bringing the PPS in the partially dissolved state into contact with the solvent only once. However, if this contact is repeated two times or three times according to need, the impurity content can be further reduced. The present invention will now be described in detail with reference to the following examples. Note, all of "%" in the examples are by weight. Examples 1 through 4 An autoclave having a capacity of 1 ℓ equipped with a stirrer was charged with 20 g of PPS (100 - 200 mesh fraction = 55%, 200 - 300 mesh fraction = 45%, melting point = 285°C, melt viscosity- = 370 poise at 300°C, Na₂O concentration = 1,150 ppm measured by flame photometry after pre-treatment by the sulfuric acid ashing method) obtained by reacting p-dichlorobenzene with sodium sulfide according to the known method and 200 g of dimethylsulfoxide (DMSO) (the PPS concentration in the slurry was about 9%). Elevation of the temperature was initiated simultaneously with stirring, and the temperature was elevated to 160°C, 180°C, 200°C or 220°C within 1 hour. The slurry was maintained at this temperature for 4 hours with stirring, and the slurry was cooled with stirring. When the temperature was lowered to 60 to 80°C, the slurry was taken out from the autoclave and filtered under a reduced pressure. The wet cake left after filtration (the volatile component content was about 50%) was washed at 60°C with 100 ml of acetone. This acetone washing was conducted two times, and the cake was washed two times with 100 ml of deionized water at 90°C. The obtained PPS was allowed to stand in an oven maintained at 150°C for about 1 hour and was then dried at 160°C by a rotary drier. The properties of the obtained dry PPS are shown in Table 1. Examples 5 and 6 The procedures of Example 2 were repeated in the same manner except the heating time was changed to 30 minutes or 10 minutes. The results are shown Table 1. Examples 7 through 9 The procedures of Example 3 were repeated in the same manner except that the heating time was changed to 2 hours, 3 hours or 6 hours. The results are shown in Table 1. Example 10 The procedures of Example 2 were repeated in the same manner except that 200 g of hydrous DMSO (comprising 90% of DMSO and 10% of deionized water) was used instead of 200 g of DMSO used in Example 2. The results are shown in table 1. Example 11 The procedures of Example 2 were repeater in the same manner except that 200 g of hydrous DMSO (comprising 95% of DMSO and 5% of deionized water) was used instead of 200 g of DMSO used in Example 2 and the treatment was carried out at 143°C under atmospheric pressure for 2 hours. The results are shown in Table 1. Examples 12 and 13 The procedures of Example 3 were repeated in the same manner except that the PPS concentration in the slurry was changed to 20% or 30%. The results are shown in Table 1. Example 14 The procedures of Example 3 were repeated in the same manner except that instead of washing with acetone and water after the high-temperature treatment, washing with 100 ml of water at 100°C was conducted 4 times. The results are shown in Table 1. Example 15 The procedures of Example 14 were repeated in the same manner except that instead of washing with water at 100°C, conducted 4 times, washing with 100 ml of water at 100°C was conducted 3 times and washing with 100 ml of acetone at 60°C was conducted once. The results are shown in Table 1. Example 16 The filter cake having a volatile component content of about 50% obtained after the high-temperature treatment in Example 3 was placed under a reduced pressure to recover DMSO and reduce the volatile component content to 3.0%. The cake was washed with 100 ml of water at 100°C three times and with 100 ml of acetone at 60°C once and was then dried. The results are shown in Table 1. Example 17 The procedures of Example 16 were repeated in the same manner except that instead of washing with 100 ml of water at 100°C, conducted 3 times, and washing with 100 ml of acetone at 60°C, conducted once, washing with 100 ml of water at 100°C was conducted 4 times. The results are shown in Table 1. Example 18 Polyethylene glycol as a hydrophilic property-imparting agent was added to the filter cake having a volatile component content of about 50% obtained after the high-temperature treatment in Example 3, in an amount of 10% by weight based on the PPS solids. DMSO was recovered under a reduced pressure to reduce the volatile component content to 5.1%. The cake was washed with 100 ml of water at 100°C four times and was then dried. The results are shown in Table 1. Example 19 The procedures of Example 18 were repeated in the same manner except that instead of washing with water at 100°C, conducted 4 times, washing with 100 ml of water at 100°C was conducted three times and washing with 100 ml of acetone at 60°C was conducted once. The results are shown in Table 1. Example 20 The procedures of Example 3 were repeated in the same manner except that PPS (100 mesh fraction = 67%, 100 - 200 mesh fraction = 33%, melting point = 285°C, melt viscosity = 1,320 poise, Na₂O content = 1,800 ppm) obtained by reacting p-dichlorobenzene with sodium sulfide in the presence of disodium phthalate as a co-catalyst (0.5 mole per mole of p-dichlorobenzene) according to the known method was used instead of the PPS used in Example 3. The results are shown in Table 1. According to the method of the present invention, impurities can be removed from PPS at an efficiency as high 80 to 98%. A product of PPS obtained according to the method of the present invention has a very reliable moisture resistance, and therefore, is very valuable as a sealing agent for general electronic parts, IC's and LSI's.

Claims: 1. A method for removing impurities from a polyphenylene sulfide resin, which comprises heating and mixing a powdery polyphenylene sulfide resin with a first solvent to bring the powder and the solvent sufficiently in contact with each other in the partially dissolved state, cooling and filtering the mixture, and washing the filter cake with a second solvent, that is incapable of dissolving the polyphenylene sulfide resin therein, characterized in that the first solvent is dimethylsulfoxide or a mixed solvent of dimethylsulfoxide with water. 2. A method for removing impurities according to claim 1, wherein the ratio by weight of the polyphenylene sulfide resin to the first solvent is from about 1/1 to about 1/15. 3. A method for removing impurities according to claim 1 or 2, wherein the polyphenylene sulfide resin and the first solvent are heated at 100 to 250°C and the mixture is maintained at said temperature for 10 minutes to 10 hours. 4. A method for removing impurities according to claim 1, 2, or 3, wherein the second solvent, that is incapable of dissolving the polyphenylene sulfide resin therein is selected from aromatic and aliphatic hydrocarbons, ketones, alcohols and water.

Inventors: MARUKAWA, KIICHI, NAGAKI, KAZUYOSHI, NAKAMURA, YOSHIAKI
Applicants: TOHPREN CO., LTD.
Application year: 1987
Main classification: C08J3
IPC codes: C08J3, C08G75