Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
2002-07-17
2004-06-01
Boykin, Terressa (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C528S388000, C528S499000, C528S503000
Reexamination Certificate
active
06743890
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for purifying polyarylene sulfide (this will be hereinafter abbreviated as PAS) resin. More precisely, the invention relates to a process for purifying PAS resin by efficiently removing impurities such as alkali metal halides existing in the resin, and to thermally stable PAS resin of few impurities.
BACKGROUND OF THE INVENTION
Polyarylene sulfides, especially polyphenylene sulfides are known as stiff engineering plastics of good mechanical strength, good heat resistance and good electric properties, and are widely used for various materials, for example, for parts of electronic and electric appliances.
One general method of producing such PAS heretofore known in the art comprises reacting a dihalogenoaromatic compound such as p-dichlorobenzene with a sodium salt such as sodium sulfide in an aprotic organic solvent such as N-methyl-2-pyrrolidone (this will be hereinafter abbreviated as NMP). In this method, however, the side products, sodium halides are insoluble in the solvent such as NMP and are therefore caught by PAS, and it is not easy to remove them by washing PAS.
On the other hand, in a different method of using a lithium salt in place of the sodium salt for the polymerization, the side products, lithium halides are soluble in many aprotic organic solvents (solvents for polymerization) such as NMP, and it is relatively easy to reduce the lithium content of PAS produced, and the method of using a lithium salt has come into the limelight for PAS production. However, even the method of using a lithium salt for polymerization to give PAS is still problematic in that the side products, lithium halides remain in PAS as impurities therein. In particular, for reducing the remaining monomer in the polymer product PAS so as to increase the molecular weight of PAS and to increase the degree of conversion in polymerization, it is often desired to increase the ratio of Li/S in reacting the lithium salt and the sulfur compound in the method, for example, to at least 2. This has produced another problem in that the excess lithium remains more in the polymer product PAS to further increase the impurities therein.
For removing the impurities such as lithium halides that remain in PAS, one general method is to wash PAS with a solvent such as NMP. However, the process efficiency is not good since the washing frequency inevitably increases with the increase in the impurities existing in the product PAS. In addition, the amount of the washing solvent to be used must be increased, and the production costs thereby increase.
On the other hand, another method of adding ammonium chloride or the like to PAS to remove the impurities such as lithium halides has been proposed. However, this is still problematic in that the thermal stability of PAS obtained therein is not good, and the molecular weight of PAS decreases at high temperatures.
Accordingly, it is desired to develop an efficient method of purifying PAS that enables easy removal of impurities to give thermally stable PAS.
The present invention has been made in consideration of the problems noted above, and its object is to provide a method of purifying PAS which makes it possible to reduce impurities, especially alkali metal halides such as lithium halides in PAS to give thermally stable PAS.
Another object of the invention is to provide thermally stable PAS that contains few alkali metal halides.
DISCLOSURE OF THE INVENTION
I, the present inventor have assiduously studied and, as a result, have found that, when PAS is washed with a mixture of specific compounds (detergent), then the above-mentioned objects can be attained. On the basis of this finding, I have completed the present invention. Specifically, the invention is summarized as follows:
[1] A polyarylene sulfide, which is characterized in that, when it is added to a solvent N-methyl-2-pyrrolidone of the same quantity (by mass) and kept at 265° C. for 8 hours, the reduction in its intrinsic viscosity [&eegr;] at 206° C. is at most 0.05 dl/g.
[2] The polyarylene sulfide of above [1], of which the residual alkali metal content is at most 100 ppm.
[3] A method of purifying a polyarylene sulfide by washing it with a mixture of 100 parts by mass of an aprotic organic solvent and from 0.005 to 10 parts by mass of an alkyl halide.
[4] A method of purifying a polyarylene sulfide by washing it with a mixture of 100 parts by mass of an aprotic organic solvent, from 4 to 60 parts by mass of water, and from 0.05 to 10 parts by mass of an alkyl halide.
[5] The method of purifying a polyarylene sulfide of above [3] or [4], wherein the alkyl halide is a primary alkyl halide.
[6] The method of purifying a polyarylene sulfide of any of above [3] to [5], wherein the alkyl halide is methyl chloride.
[7] A method of purifying a polyarylene sulfide by washing it with a mixture prepared by adding from 0.1 to 10 parts by mass, relative to 100 parts by mass of the polyarylene sulfide, of a halogenoaromatic compound having an electron-withdrawing group to an aprotic organic solvent.
[8] A method of purifying a polyarylene sulfide by washing it with a mixture of 100 parts by mass of an aprotic organic solvent and from 0.005 to 10 parts by mass of a salt prepared through reaction of a strong acid with a weak base, followed by further washing it with a mixture prepared by adding from 0.1 to 10 parts by mass, relative to 100 parts by mass of the polyarylene sulfide, of a halogenoaromatic compound having an electron-withdrawing group to an aprotic organic solvent.
[9] A method of purifying a polyarylene sulfide by washing it with a mixture of 100 parts by mass of an aprotic organic solvent, from 4 to 60 parts by mass of water, and from 0.005 to 10 parts by mass of a salt prepared through reaction of a strong acid with a weak base, followed by further washing it with a mixture prepared by adding from 0.1 to 10 parts by mass, relative to 100 parts by mass of the polyarylene sulfide, of a halogenoaromatic compound having an electron-withdrawing group to an aprotic organic solvent.
[10] The method of purifying a polyarylene sulfide of any of above [7] to [9], wherein the halogenoaromatic compound having an electron-withdrawing group is at least one of 4,4′-dichlorobenzophenone and 4,4′-dichlorodiphenyl sulfone.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention is described concretely hereinunder.
1. Polyarylene Sulfide (PAS)
The polyarylene sulfide (PAS) resin of the invention is characterized in that, when it is added to a solvent N-methyl-2-pyrrolidone of the same quantity (by mass) and kept at 265° C. for 8 hours, the reduction in its intrinsic viscosity [&eegr;] at 206° C. is at most 0.05 dl/g, preferably at most 0.03 dl/g, more preferably at most 0.02 dl/g. The resin of the type is thermally stable and bears various severe applications.
For evaluating the thermal stability of resin in the invention, one favorable method comprises keeping a mixture of PAS and NMP at a high temperature (265° C.) for 8 hours and monitoring the change of the intrinsic viscosity [&eegr;] of PAS. In this method, the ratio of PAS to NMP is not specifically defined, but for higher reproducibility in the method, in general, the two are mixed in a ratio of 1/1 (by mass), for example, 2.5 g each. In consideration of the solubility of the resin of the type, it is advantageous that the intrinsic viscosity [&eegr;] of the resin is measured and expressed at 206° C.
In addition to its thermal stability as above, PAS of the invention has a residual alkali metal content of at most 100 ppm, preferably at most 50 ppm, more preferably at most 30 ppm. The resin containing few residual alkali metals has a good property of electric insulation, and its value in use, for example, for materials for parts of electric and electronic appliances is extremely high.
The method
Boykin Terressa
Idemitsu Petrochemical Co. Ltd.
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