Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-07-19
2003-10-21
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S056000, C525S060000, C525S061000, C525S386000, C526S202000, C526S344200, C526S344000
Reexamination Certificate
active
06635709
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dispersion stabilizer for suspension polymerization of a vinyl compound. More specifically, the invention relates to a dispersion stabilizer for suspension polymerization of a vinyl compound which, by the use of a small amount, exhibits quite an excellent suspension polymerization stability upon providing an effect that polymer scales are less adhered to an inner wall of a polymerization vessel and can produce, through suspension polymerization of a vinyl compound, vinyl polymer granules having a high plasticizer absorption, a sharp particle size distribution, a porosity and a high bulk density.
2. Discussion of the Background
The production of a vinyl polymer such as a vinyl chloride resin has been widely conducted industrially by suspension polymerization in which a vinyl compound such as vinyl chloride is dispersed in an aqueous medium in the presence of a dispersion stabilizer and polymerization is conducted using an oil-soluble initiator. In general, the factors governing the quality of a vinyl polymer include a conversion, a water/monomer ratio, a polymerization temperature, a type and an amount of an initiator, a type of a polymerization vessel, a stirring rate and a type of a dispersion stabilizer. Among these factors, a type of a dispersion stabilizer has a great effect.
The performances required of a dispersion stabilizer for suspension polymerization of a vinyl compound are as follows. (1) It functions, by the use of a small amount thereof, to exhibit quite an excellent suspension polymerization stability and to make the particle size distribution of vinyl polymer granules obtained as sharp as possible, (2) it functions to make polymer granules as uniform and porous as possible to increase a rate of plasticizer absorption for increasing a processability, to facilitate the removal of a monomer such as vinyl chloride remaining in polymer granules and to prevent the formation of fish eyes in a molded product, (3) it functions to form polymer granules having a high bulk density, and (4) scales are not adhered to a polymerization vessel.
As a dispersion stabilizer for suspension polymerization of a vinyl compound, cellulose derivatives such as methylcellulose and carboxymethylcellulose and partially saponified polyvinyl alcohol have been so far used either singly or in appropriate combination. The ordinary dispersion stabilizer, however, do not necessarily meet the foregoing performances satisfactorily.
Further, Japanese Patent Laid-Open Nos. 127,490/1979, 95,104/1989, 140,303/1991, 80,709/1994 and 259,609/1996 propose a dispersion stabilizer for suspension polymerization of a vinyl compound made of a modified polyvinyl alcohol containing an ethylene unit. A dispersion stabilizer made of an ethylene-modified polyvinyl alcohol as proposed in Japanese Patent Laid-Open No. 127,490/1979 is problematic in that the use of a modified polyvinyl alcohol having a high content of an ethylene unit decreases a workability owing to a poor water solubility of a dispersion stabilizer or requires the use of a water-organic solvent medium for improving the solubility of the dispersion stabilizer and the use of the organic solvent invites a factor that waste water after suspension polymerization exerts an adverse effect on the environment. A dispersion stabilizer made of an ethylene-modified polyvinyl alcohol having an ionic group in a side chain as proposed in Japanese Patent Laid-Open Nos. 95,104/1989 and 140,303/1991 is problematic in that a water solubility is improved, but bubbling is liable to occur in the suspension polymerization of vinyl chloride which leads to adhesion of scales to a polymerization vessel. A dispersion stabilizer made of an ethylene-modified polyvinyl alcohol as proposed in Japanese Patent Laid-Open No. 80,709/1994 gives a relatively well-balanced vinyl chloride resin, but a plasticizer absorption or a sharpness of a particle size distribution of the vinyl chloride resin does not necessarily reach a satisfactory level. Further, a dispersion stabilizer using a combination of an ethylene-modified polyvinyl alcohol and a polyvinyl alcohol polymer as proposed in Japanese Patent Laid-Open No. 259,609/1996 improves, because of an excellent anti-foaming effect in a polymerization vessel, a problem that scales are adhered to a reaction vessel by bubbling in the suspension polymerization of vinyl chloride. However, a plasticizer absorption or a sharpness of a particle size distribution of the resulting vinyl chloride resin does not necessarily reach a satisfactory level.
Under these circumstances, the invention aims to provide a dispersion stabilizer for suspension polymerization of a vinyl compound which, by the use of a small amount, exhibits quite an excellent suspension polymerization stability and can produce, through suspension polymerization of a vinyl compound, vinyl polymer granules having a high plasticizer absorption, a sharp particle size distribution, a porosity and a high bulk density. Further, it aims to provide a dispersion stabilizer for suspension polymerization of a vinyl compound which can produce vinyl polymer granules having characteristics that a vinyl compound remaining in vinyl polymer granules is easy to remove, scattering of a powder less occurs in handling and a biting property into a molding machine is good.
SUMMARY OF THE INVENTION
The present inventors have assiduously conducted investigations, and have consequently found that the foregoing aims are attained by a dispersion stabilizer for suspension polymerization of a vinyl compound comprising a vinyl alcohol polymer (A) having a content of an ethylene unit of 0.5 to 10 mol %, a degree of saponification of 60 mol % or more and a degree of polymerization of 600 or more and a vinyl alcohol polymer (B) selected from a vinyl alcohol polymer (B1) having a content of an ethylene unit of 0.5 to 10 mol %, a degree of saponification of 20 to 80 mol % and a degree of polymerization of 100 to 600, a vinyl alcohol polymer (B2) having a degree of saponification of 20 to 60 mol % and a degree of polymerization of 100 to 600 and a vinyl alcohol polymer (B3) having a content of an ethylene unit of 0.5 to 10 mol %, a degree of saponification of 90 mol % or more and a degree of polymerization of 1,000 or more. This finding has led to the completion of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is described in detail below.
The content of the ethylene unit of the vinyl alcohol polymer (A) used in the invention is 0.5 to 10 mol %, preferably 1 to 10 mol %, more preferably 1.5 to 8 mol %. When the content of the ethylene unit is less than 0.5 mol %, adhesion of scales to a reaction vessel is increased in the suspension polymerization of the vinyl compound. When it exceeds 10 mol %, a water solubility of the vinyl alcohol polymer is decreased to worsen a handleability.
The degree of saponification of the vinyl alcohol polymer (A) is 60 mol % or more, preferably 65 to 95 mol %, more preferably 70 to 90 mol %. When the degree of saponification is less than 60 mol %, the water solubility of the vinyl alcohol polymer is decreased to worsen the handleability.
The degree of polymerization of the vinyl alcohol polymer (A) is 600 or more, preferably 600 to 8,000, more preferably 650 to 3,500. When the degree of polymerization of the vinyl alcohol polymer is less than 600, the polymerization stability is decreased in the suspension polymerization of the vinyl compound.
The content of the ethylene unit of the vinyl alcohol polymer (B1) used in the invention is 0.5 to 10 mol %, preferably 1 to 10 mol %, more preferably 1.5 to 8 mol %. When the content of the ethylene unit is less than 0.5 mol %, adhesion of scales to a reaction vessel is increased in the suspension polymerization of the vinyl compound. When it exceeds 10 mol %, the water solubility of the vinyl alcohol polymer is decreased to worsen the handleability.
The degree of saponification of the vinyl alcohol polymer (B1) is 20 to 80 mol %,
Inomata Naokiyo
Kato Masaki
Tanimoto Seiji
Kuraray Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Reddick Judy M.
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