Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From sulfur-containing reactant
Reexamination Certificate
1995-07-21
2002-04-09
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From sulfur-containing reactant
C528S373000
Reexamination Certificate
active
06369191
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for controlling a particle size of polyarylene sulfide and polyarylene sulfide thus produced, particularly, high molecular weight polyarylene sulfide having a particle size suitable for powder coating.
PRIOR ART
A basic process for the preparation of polyarylene sulfide (hereinafter referred to as PAS) is known where a dihaloaromatic compound is reacted with an alkali metal sulfide in an organic amide solvent (Japanese Patent Publication No. Sho-45-3368/1970). The PAS prepared in this process is in a form of powder.
It is desired to control a particle size of a product PAS. If this is possible, a product with a desired particle size may be prepared directly without operations such as crushing, granulation or classification. Further, making-up after preparation, such as filtration, is simplified and handling, for instance, in packing in paper bags is easier. Thus, control of a particle size is very meaningful.
It is known to add water in a reaction system after the completion of reaction in order to make a particle size larger for easier handling (Japanese Patent Publication No. Hei-1-25493/1989). This process requires a step of adding water, which makes operations complicated. Moreover, pressure is higher and, therefore, previous low pressure reactors may not be applied.
It is known to slowly cool a reactor after the completion of polymerization to precipitate a particulate polymer with larger bulk density (Japanese Patent Publication No. Sho-59-49232/1984). The present inventors have tried this method in various stirring conditions, but failed to obtain a satisfactory effect in any conditions.
Paints based on PAS are used in the fields of rust prevention and anticorrosion for metals and electric insulation as PAS has good properties in heat resistance, water resistance, chemical resistance, anti-abrasion and electric insulation. Paints based on PAS are usually applied in a way where a powdery or slurry paint is coated on a substrate and heat-melted to form a coating, or a powdery paint is heat-melted and sprayed on a substrate to form a coating. Methods for such powder coating include electrostatic spray coating, fluid dip coating and flame coating. It is said that the best PAS for powder coating usually has an average particle size of 70 to 80 &mgr;m, and a particle size distribution range of from about 40 to about 150 &mgr;m. In order to form a smooth and even coating, coarse particles, particularly those of 200 &mgr;m or more, should not be present in a powder. Further, in order to form a thick coating, low molecular weight PAS was used, which is rapidly cross-linked upon melting. However, high molecular weight PAS is needed to improve mechanical properties of a coating.
Various processes are known to prepare high molecular weight PAS. In a process described in Japanese Patent Publication No. Sho-52-12240/1977, a sulfur source, p-dihalobenzene, an organic amide, a base and an alkali metal carboxylate are contacted together to form a composition, which is then maintained under polymerization conditions to form a polymer. Japanese Patent Application Laid-Open (or Kokai) No. Sho-61-7332/1986 discloses a process for the preparation of PAS by reacting alkali metal sulfide with a dihaloaromatic compound in an organic solvent, wherein the reaction is conducted at 180 to 235° C. in the presence of 0.5 to 2.4 moles of water per mole of alkali metal sulfide to form PAS of a melt viscosity of 5 to 300 poises at a conversion of a dihaloaromatic compound of 50 to 98 mole % in a first step. In a second step, water is added and the reaction is conducted at 245 to 290° C. in the presence of 2.5 to 7.0 moles of water. The PAS prepared in these processes is substantially linear and in a form of coarse particles of a particle diameter of 500 &mgr;m or more. Accordingly, to be used in powder coating, the PAS particles should be made smaller by crushing and classification within the aforesaid particle size distribution range suitable for powder coating. This adds to facility investment and operation costs. In reality, it is commercially impossible to crush the powder into fine particles of 150 &mgr;m or less and a yield is awfully bad. Thus, this is not economical. In addition, the PAS has a high flowability upon melting so as to cause sagging in coating formation, and is accordingly unsuitable to form a thick coating.
SUMMARY OF THE INVENTION
A purpose of the invention is to provide a process to control a particle size of polyarylene sulfide, which process allows precise control of the particle size and is convenient and economical.
Another purpose of the invention is to provide high molecular weight polyarylene sulfide which has a particle size suitable for powder coating and gives a smooth, thick and mechanically excellent coating.
The present invention is a process for the preparation of polyarylene sulfide by reacting an alkali metal sulfide with a dihaloaromatic compound in an organic amide solvent at an elevated temperature, characterized in that a gaseous phase part of a reactor is cooled or heated after starting decreasing a temperature of a reaction system to thereby control a particle size of a product polyarylene sulfide.
The process of the present invention may provide high molecular weight polyarylene sulfide suitable for powder coating, wherein a water content in the reaction system is 0.8 to 1.7 moles per mole of the alkali metal sulfide; the gaseous phase part of the reactor is cooled also in a polymerization stage at an elevated temperature to thereby condense a part of a gaseous phase in the reactor and the condensed liquid is refluxed to a liquid phase in the reactor; and the gaseous phase part of the reactor is cooled after starting decreasing the temperature of the reaction system.
The polyarylene sulfide thus obtained is high molecular weight polyarylene sulfide suitable for powder coating which has a weight average molecular weight of at least 30,000, characterized in that the polyarylene sulfide as prepared has an average particle size of 50 to 80 &lgr;m; particles of 40 to 150 &mgr;m account for at least 90% by weight of the whole particles in a particle size distribution; and the amount of particles of 180 &mgr;m or more is 0.5% by weight or less.
DETAILED DESCRIPTION OF THE INVENTION
In the present process for controlling a particle size of polyarylene sulfide, an essential requirement is to cool or heat a gaseous phase part of a reactor after starting decreasing a temperature of a reaction system. The cooling or heating of a gaseous phase part makes a particle size smaller or larger, respectively.
The cooling or heating of a gaseous phase part of a reactor may be effected by any means known per se, which may be external or internal. There may be used an internal coil mounted in an upper part of a reactor, through which a cooling or heating medium flows; an external coil or a jacket mounted on an upper outer wall of a reactor, through which a cooling or heating medium flows; or a unit for spraying or blowing a cool or hot gas (e.g., air or nitrogen) or liquid. The last-mentioned means is preferred only for the cooling. However, these are not restrictive, but any other means may be used as far as such lowers or raises the temperature of the gaseous phase part of a reactor. For instance, if an ambient temperature is relatively low (e.g., room temperature), proper cooling may be effected by removing a heat insulating material usually provided on an upper part of a reactor.
The cooling or heating is conducted after starting decreasing the temperature of a reaction system, preferably, for at least 20 minutes. The cooling or heating may be initiated before starting decreasing the temperature of a reaction system, preferably, at a point of time not earlier than one hour before starting decreasing the temperature of the reaction system. It may preferably be initiated at a point of time in a range of from 40 minutes before to 10 minutes after the moment of starting decreasing the temperature of the reaction s
Ichikawa Kazuhiro
Imai Yoichi
Komiyama Osamu
Cowen, Liebowitz & Latman, P.C.
Dainippon Ink and Chemicals Incorporated
Dawson Robert
Dippert William H.
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