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
2002-08-06
2004-08-17
Harlan, Robert D. (Department: 1713)
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...
C524S524000, C524S458000, C524S460000
Reexamination Certificate
active
06777483
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for preparing a synthetic rubber latex having a large particle size. More particularly, the present invention relates to a method for preparing a diene rubber latex having a large particle size by pretreating a seed diene rubber latex with anionic and nonionic emulsifiers prior to agglomeration and then adding the pretreated seed diene rubber latex to an agglomerating agent comprised of a copolymer latex that contains unsaturated carboxylic acid monomers.
BACKGROUND OF THE INVENTION
In general, a diene rubber latex having a large particle size is used in preparation of a regular ABS (acrylonitrile-butadiene-styrene) resin, a high-impact ABS (acrylonitrile-butadiene-styrene) resin, a non-glossy ABS resin, a foam rubber and so on. Several methods are known for the preparation of a synthetic rubber latex having a large particle size and these are as follows: (1) regulation of the particle size by controlling the pH value in the polymerization of latex through addition of a base or an acid, (2) addition of an inorganic electrolyte or an emulsifier during polymerization, (3) agglomeration of the latex by freezing, and (4) mechanical or chemical agglomeration of the synthetic rubber latex particles after polymerization.
These methods have been known and applied up to now. However, these methods are disadvantageous because methods (1) and (2) require a long polymerization time and methods (3) and (4) produce undesirably large amounts coagulum.
In order to overcome the shortcomings above and prepare a synthetic rubber latex with a uniform particle size, Japanese Patent Laid-open No.63-117006 discloses a method of preparing a stable synthetic rubber latex by lowering pH of the latex to 6 or below, adding a polymeric coagulant having both polar and nonpolar groups in the molecule to the small-particle diameter polymer latex formed by emulsion polymerization by using an emulsifier based on an emulsifier which decreases in surface activity in an acidic condition, and adding an acid. However, in the polymerization of graft-ABS by using the synthetic rubber latex, it is difficult to collect the polymer.
U.S. Pat. No. 3,049,500 discloses a process of increasing the particle of a diene latex wherein a polyvinyl methyl ether containing an alkali salt electrolyte is added to the diene latex.
U.S. Pat. No. 6,365,669 discloses a method of preparing a polybutadiene latex by adding a surfactant to the latex when the conversion rate of the butadiene monomer greater than 80% and then adding an agglomerating agent to the polymerization mixture wherein the temperature of the polymerization mixture is raised about 5 to about 20° C. higher than the polymerization temperature during the agglomerating step.
U.S. Pat. Nos. 5,468,788 and 5,633,304 disclose a process for agglomerating small rubber particles in an aqueous latex to form large rubber particles, the process involving the addition of a water soluble organic acid and a water organic anhydride to the latex prior to agglomeration of the rubber particles to facilitate agglomeration of the rubber particles into large rubber particles which are essentially free of coagulum. However, in the process involving the addition of a water soluble organic acid and a water organic anhydride, a little coagulum still occurs, which has been a target to the research and development of agglomeration of rubber particles. Further, in case small particle size latex (“PASS latex”) is prepared in a large amount, the latex is not uniform because a bimodal type latex is formed. Such latex cannot be utilized for applications requiring uniform distribution of the latex.
Copending Ser. No. 09/699,311, herein incorporated by reference, discloses a process of preparing a synthetic rubber latex having a large particle size by adding a pretreated seed diene rubber latex to an agglomerating agent comprised of a copolymer latex containing unsaturated carboxylic acid monomers.
The present inventors have developed a method of preparing a diene rubber latex which has a large particle size, and, compared to the process of Ser. No. 09/699,311, has better stability and less coagulum during polymerization, and more uniform particle size.
SUMMARY OF THE INVENTION
The present invention provides a method of preparing a diene rubber latex having large size particles, good stability and reduced coagulum during polymerization wherein the method comprises:
(a) pretreating a seed diene rubber latex with an anionic emulsifier and a non-ionic emulsifier,
(b) adjusting the pH of an unsaturated carboxylic acid-containing copolymer latex to about 5 to 11 and adjusting the solids content of the copolymer latex to about 1 to 10% by weight solids content to produce an agglomerating latex solution, and
(c) adding the pretreated seed diene rubber latex of step (a) to the agglomerating latex solution of step (b).
Step (c) must be carried out by adding the pretreated seed diene rubber latex to the agglomerating latex. If the agglomerating latex is added to the rubber latex, an undesirable level of coagulum is produced.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a method of preparing a diene rubber latex having large size particles, good stability and reduced coagulum during polymerization. The method of preparing a diene rubber latex having large size particles according to the present invention comprises: (a) pretreating a seed diene rubber latex with an anionic emulsifier and a non-ionic emulsifier, (b) preparing a copolymer latex by polymerization of unsaturated carboxylic acid monomer and then treating the copolymer latex with a pH adjusting agent to produce an agglomerating latex solution having a solids content of about 1 to 10% by weight and a pH of about 5 to 11, (c) adding the pretreated seed synthetic rubber latex of step (a) to the agglomerating latex solution of step (b). Step (c) must be carried out by adding the pretreated seed diene rubber latex to the agglomerating latex solution. If the agglomerating latex solution is added to the rubber latex, an undesirable level of coagulum is produced. Optionally, an anti-foaming agent may be added in step (a) to remove undesirable foam formed by residual volatile components and emulsifier that may be present in the rubber latex.
Step (a): Pretreatment of Seed Diene Rubber Latex
Known seed diene rubber latices can be used in the method according to the present invention. Such latices can be prepared by any conventional emulsion polymerization process. Known seed diene rubber latices that can be used in the method of the present invention include but are not limited to the seed diene latices disclosed in U.S. Pat. Nos. 3,049,500, 6,365,669, and 5,468,788 and 5,633,304 all of which are herein incorporated by reference. Preferred diene rubber latices are polybutadiene, butadiene-styrene copolymer, butadiene-&agr;-methyl styrene copolymer, butadiene-acrylate copolymer, and butadiene-methacrylate copolymer.
It is preferable that the seed diene rubber latex has a solids content of from about 30 to about 50% by weight. It is preferable that the seed diene rubber latex has particle sizes from about 700 to about 1,500 Å. When the range of the particle size is between about 700 to about 1,500 Å, it is easier to control the average particle size of the latex to between about 2,000 to about 5,000 Å after agglomeration. If necessary, it is desirable to adjust the pH value of the seed diene rubber latex to greater than about 7.0 prior to the agglomeration step. If the pH of the agglomerating latex is higher than that of the seed diene rubber latex, the agglomerating effect is rapidly decreased. Therefore, it is desirable to adjust the pH value of the seed diene rubber latex to equal or higher value than that of the agglomerating agent in order to maximize the agglomerating effect. In addition, since a grafted ABS copolymer is polymerized at pH 10-12, it is preferable to adjust the pH value of the seed diene rubber latex to greater than 7.0. If the pH value is lo
Chang Ki-bo
Jun Dong-Won
Lee Byeong-Do
Lim Kwang-Yeol
Cheil Industries Inc.
Harlan Robert D.
Tungol Maria Parrish
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