Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-07-01
2001-03-06
Yoon, Tae (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S803000
Reexamination Certificate
active
06197865
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing an aqueous emulsion. More precisely, the present invention relates to a process for producing an aqueous emulsion, said process allowing to produce an aqueous ethylene-vinyl acetate copolymer emulsion having an extremely high solid concentration, and said process enabling suppression of increase in viscosity of the reaction system during copolymerization reaction and formation of a stable emulsion.
2. Prior Art
Aqueous ethylene-vinyl acetate copolymer emulsions have found wide applications in the field of adhesive. From the viewpoint of drying efficacy, it is required that aqueous emulsions for adhesive have a high solid concentration. When aqueous ethylene-vinyl acetate copolymer emulsions with high solid content were produced according to conventional processes, however, there was a problem that the viscosity in the reaction system increased during copolymerization reaction, resulting in difficulty in stable completion of the desired copolymerization reaction due to insufficient stirring or insufficient removal of heat of reaction.
The present inventors have extensively studied for a process for producing an aqueous ethylene-vinyl acetate copolymer emulsion having no such problems, and found that an aqueous emulsion having a high solid cotent can be stably produced by adding vinyl acetate and a polyvinyl alcohol as an emulsifying dispersant to the copolymerization system in divided portions so that the increase in viscosity is suppressed. The present invention has been completed
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a process for producing an aqueous emulsion having a solid content of 70% by weight or more, a viscosity of 5,000 mpa.s or less and containing an ethylene-vinyl acetate copolymer having 10-40% by weight of ethylene unit and 90-60% of by weight of vinyl acetate unit, wherein said process satisfies the following conditions:
(1) 50-90% of vinyl acetate is placed in the copolymerization reaction system before the reaction and the remaining 50-10% of vinyl acetate is supplied to the reaction system after the initiation of the copolymerization reaction;
(2) An emulsifying dispersant is used in 2-6 parts by weight per 100 parts by weight of vinyl acetate. Said emulsifying dispersant comprises a polyvinyl alcohol having a degree of hydrolysis of 80% by mole or more and an average degree of polymerization of 200-1,000% and a polyoxyethylene nonionic surfactant having a HLB of 10-20;
(3) The amount of the polyvinyl alcohol to be used as above is 0.4-3 parts by weight per 100 parts by weight of vinyl acetate. 10-50% of said polyvinyl alcohol is placed in the copolymerization reaction system before the reaction and the remaining 50-90% is supplied to the reaction system after the initiation of the copolymerization reaction; and
(4) The amount of said polyoxyethylene nonionic surfactant to be used is 1-5 parts by weight per 100 parts by weight of vinyl acetate. The total amount of said polyoxyethylene nonionic surfactant is placed in the copolymerization reaction system before the reaction.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention is required to satisfy the whole of the above-described conditions. According to the condition described under (1), it is required that 50-90% of the total amount of vinyl acetate subjected to copolymerization reaction is placed in the copolymerization reaction system before the reaction and the remaining 50-10% of the total amount of vinyl acetate subjected to copolymerization reaction is supplied to the reaction system after the initiation of the copolymerization reaction. In the present invention, the portion placed in the copolymerization reaction system before the reaction may be referred to as “initial charge” and the portion supplied to the reaction system after the initiation of the copolymerization reaction may be referred to as “subsequent addition”. Further, in the present invention, the expression ‘after the initiation of the copolymerization reaction’ means ‘after a polymerization catalyst is added to the reaction system and the temperature in the reaction system begins to rise’. If the amount of initial charge of vinyl acetate is too little or too much, the viscosity of emulsion increases. In the present invention, the manner of subsequent addition includes continuous addition and intermittent addition. The addition time is usually 2-4 hours.
According to the condition described under (2), it is required that an emulsifying dispersant is used in 2-6 parts by weight per 100 parts by weight of the total amount of vinyl acetate subjected to copolymerization reaction. Said emulsifying dispersant comprises a polyvinyl alcohol having a degree of hydrolysis of 80% by mole or more and an average degree of polymerization of 200-1,000, preferably 250-800, and a polyoxyethylene nonionic surfactant having a HLB of 10-20. If the amount of the emulsifying dispersant is too little, the emulsion contains much amount of sediment. On the contrary, if the amount of the emulsifying dispersant is too much, the viscosity of the emulsion increases. If the degree of hydrolysis of the polyvinyl alcohol is too low, the emulsion contains much amount of sediment. If the average degree of polymerization of the polyvinyl alcohol is too low, the emulsion contains much amount of sediment. On the contrary, if the average degree of polymerization is too high, the viscosity of the emulsion increases. If the HLB of the polyoxyethylene nonionic surfactant is too low, the emulsion contains much amount of sediment. On the contrary, if the HLB of the polyoxyetliylene nonionic surfactant is too high, the viscosity of the emulsion increases. The term HLB used herein refers to numerical expression of a relative balance of hydrophilicity and lipophilicity for surfactant and described under “hydrophilic-lipophilic balance” in Rikagaku-Jiten (Dictionary of Physico-chemistry), 5th Ed.
Examples of the polyvinyl alcohol include normal partially hydrolyzed polyvinyl alcohol, completely hydrolyzed polyvinyl alcohol and modified type polyvinyl alcohols such as sulfonic acid-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silanol group-modified polyvinyl alcohol, acetacetylated polyvinyl alcohol and the like.
Examples of the polyoxyethylene nonionic surfactant include polyethylene oxide-polypropylene oxide block copolymer, polyethylene oxide-alkyl phenyl ether, polyethylene oxide-alkyl ether and the like.
According to the condition described under (3), it is required that the total amount of the polyvinyl alcohol used as above is 0.4-3 parts by weight per 100 parts by weight of vinyl acetate. 10-50%, preferably 20-40% of said total amount of the polyvinyl alcohol is placed in the copolymerization reaction system before the reaction and that the remaining 50-90%, preferably 60-80% of said total amount of the polyvinyl alcohol is supplied to the reaction system after the initiation of the copolymerization reaction. If the total amount of the polyvinyl alcohol is too little, the emulsion contains much amount of sediment. On the contrary, if said amount is too much, the viscosity of the emulsion increases. If the amount of initial charge of the polyvinyl alcohol is too little, the emulsion contains much amount of sediment. On the contrary, if said amount of initial charge is too much, then the viscosity of the emulsion increases.
According to the condition described under (4), it is required that the amount of said polyoxyethylene nonionic surfactant used is 1-5 parts by weight per 100 parts by weight of vinyl acetate, and the total amount of said polyoxyethylene nonionic surfactant is placed in the copolymerization reaction system before the reaction. If the total amount of the polyoxyethylene nonionic surfactant is too little, the emulsion contains much amount of sediment. On the contrary, if said amount is too much, the viscosity of the emulsion increases.
A preferred embodiment of the present inven
Koizumi Tatsuya
Mitsutake Tatsuo
Birch & Stewart Kolasch & Birch, LLP
Sumitomo Chemical Company Limited
Yoon Tae
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