Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-12-08
2001-05-22
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S515000, C524S523000, C525S330300
Reexamination Certificate
active
06235821
ABSTRACT:
TECHNICAL FIELD
The present invention relates to purging thermoplastic resin compositions for use in the purging of molding machines for thermoplastic resins. More particularly, this invention relates to a thermoplastic resin composition for purging which comprises a thermoplastic resin and a methyl methacrylate/styrene copolymer and a thermoplastic resin composition for purging which comprises a thermoplastic resin, a methyl methacrylate/styrene copolymer, and a metal salt of an alkylbenzenesulfonic acid.
BACKGROUND ART
In the molding of plastics, change of a resin being used has conventionally necessitated various means for eliminating the influences of the preceding resin. Especially in the molding of colored resins, when the resin to be molded is changed from one of a dark color, e.g., blue or black, to one of a light color, e.g., white, a complicated cleaning operation has been necessary which comprises, for example, disassembling and cleaning the molding machine or purging the molding machine with a general or reclaimed resin or the like and is accompanied by a prolonged suspension of production. As a means for eliminating these problems, various thermoplastic resin compositions for purging molding machines have been developed.
For example, Unexamined Published Japanese Patent Application No. 62-195045 proposes a composition obtained by incorporating a sodium alkylbenzenesulfonate and a water-repellent compound (a metal salt of a higher fatty acid, wax, liquid paraffin, synthetic wax, etc.) into a thermoplastic resin in respective amounts of from 2 to 30% by weight and from 0.5 to 10% by weight based on the composition; Unexamined Published Japanese Patent Application No. 05-060768 proposes a composition obtained by incorporating the calcium salt of a boric ester of a higher fatty acid monoglyceride and an inorganic filler into a thermoplastic resin; and Unexamined Published Japanese Patent Application No. 03-283805 proposes a purging composition obtained by incorporating a neutral salt of an alkylbenzenesulfonic acid and basic magnesium stearate into a thermoplastic resin in respective amounts of from 2 to 40% by weight and from 1 to 10% by weight based on the composition.
However, the conventional purging compositions described above are still insufficient in cleaning ability, and there is a desire for a thermoplastic resin composition for purging which has a high cleaning ability.
As apparent from the above description, an object of the present invention is to provide a thermoplastic resin composition for purging a molding machine, which has an excellent cleaning ability.
DISCLOSURE OF THE INVENTION
The present inventor made extensive studies in order to develop a purging resin composition having an excellent cleaning ability. As a result, it has been found that a composition comprising a thermoplastic resin and a methyl methacrylate/styrene copolymer contained therein and a composition comprising the above composition and further a metal salt of an alkylbenzenesulfonic acid contained therein are purging thermoplastic resin compositions having an excellent cleaning ability. The present invention has been completed based on this finding.
The present invention has the following constitutions.
(1) A thermoplastic resin composition for purging, which comprises a thermoplastic resin and a methyl methacrylate/styrene copolymer contained in the thermoplastic resin.
(2) The thermoplastic resin composition for purging as described in the above (1), wherein the methyl methacrylate/styrene copolymer is contained in an amount of from 1 to 30% by weight based on the composition.
(3) The thermoplastic resin composition for purging as described in the above (1), wherein the thermoplastic resin further contains the methyl methacrylate/styrene copolymer and a metal salt of an alkylbenzenesulfonic acid.
(4) The thermoplastic resin composition for purging as described in the above (3), wherein the methyl methacrylate/styrene copolymer and the metal salt of an alkylbenzenesulfonic acid are contained in amounts of from 0.5 to 10% by weight and from 1 to 30% by weight, respectively, based on the composition.
(5) The thermoplastic resin composition for purging as described in any one of the above (1) to (4), wherein the methyl methacrylate/styrene copolymer has a number-average molecular weight of from 10,000 to 150,000.
(6) The thermoplastic resin composition for purging as described in the above (3) or (4), wherein the alkyl group in the metal salt of an alkylbenzenesulfonic acid has from 6 to 20 carbon atoms and the metal salt is a salt of sodium, calcium, magnesium or potassium.
(7) The thermoplastic resin composition for purging as described in any one of the above (1) to (4), wherein the thermoplastic resin comprises at least one compound selected from polypropylene, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, poly(ethylene terephthalate), poly(butylene terephthalate), polystyrene, acrylonitrile/butadiene/styrene copolymers, acrylonitrile/styrene copolymers, and poly(methyl methacrylate).
BEST MODES FOR CARRYING OUT THE INVENTION
The thermoplastic resin for use in the present invention means a resin which is capable of repeatedly undergoing a cycle in which the resin, upon heating, softens and fluidizes with increasing temperature and, upon cooling, comes into a relatively rigid state having a strength. The thermoplastic resin is not particularly limited as long as it has the above property. However, from the standpoint of obtaining a purging thermoplastic resin composition which has a satisfactory cleaning ability, in particular, which is less apt to remain in the molding machine or extruder and is capable of shortening the time period required for purging, it is preferred to use one or more thermoplastic resins selected from polypropylene, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, poly(ethylene terephthalate), poly(butylene terephthalate), polystyrene, acrylonitrile/butadiene/styrene copolymers, acrylonitrile/styrene copolymers, and poly(methyl methacrylate). These thermoplastic resins may be used alone or as a mixture of two or more thereof. These resins are not limited to fresh ones, and may be reclaimed ones for recycling which have been obtained by recovering used resins and pulverizing the same.
The methyl methacrylate/styrene copolymer for use in the present invention is not particularly limited as long as it is a polymer obtained by copolymerizing methyl methacrylate and styrene. However, from the standpoint of attaining an excellent cleaning ability, the copolymer has a number-average molecular weight of preferably from 10,000 to 150,000, more preferably from 30,000 to 100,000, especially preferably from 50,000 to 80,000.
From the standpoints of cleaning ability and the replaceability of the composition itself with a succeeding resin, methacrylic acid and styrene are copolymerized in such a ratio that the proportion of methyl methacrylate is preferably from 5 to 50% by weight, more preferably from 10 to 40% by weight, especially preferably from 15 to 30% by weight.
The methyl methacrylate/styrene copolymer for use in the present invention can be obtained by a known process, e.g., the suspension polymerization method or emulsion polymerization method. The suspension polymerization method, for example, comprises introducing pure water, styrene monomer, methyl methacrylate monomer, poly(vinyl alcohol) as a dispersant, and lauroyl peroxide as a polymerization initiator into a vessel equipped with a stirrer and heating the resultant mixture to 70 to 80° C. with stirring to copolymerize the monomers. The copolymer slurry obtained is dehydrated with a centrifugal separator and dried in an air stream, whereby the target copolymer can be obtained as a powder. Commercially available products can also be used. Examples thereof include New Frontier MS-750P (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).
The metal salt of an alkylbenzenesulfonic acid for use in the present invention may be an indus
Chisso Corporation
Leydig Voit & Mayer Ltd
Yoon Tae H.
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