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
2001-12-27
2004-06-08
Cheung, William (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...
C524S832000, C525S070000, C525S080000
Reexamination Certificate
active
06747083
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a rubber latex containing water in particles, a process for preparing the same and an impact modifier.
BACKGROUND ART
In order to improve impact resistance of a thermoplastic resin, it is known to mix a copolymer containing a diene-based rubber or an acrylate-based rubber. For example, there is a process disclosed in Japanese Examined Patent Publication No. 39-19035. Rubber components are resourcefully studied for achieving higher impact resistance. Suggestions are, for example, a method of increasing a particle size of a rubber component (Japanese Examined Patent Publication No. 42-22541/1967) and a method of lowering Tg of a rubber component (Japanese Unexamined Patent Publication Nos. 2-1763/1990 and 8-100095/1996).
In these methods, however, there are problems that it is difficult to meet the demands for significant improvement of impact resistance, and that cost for raw materials increases drastically.
For improving impact resistance of thermoplastic resins such as a vinyl chloride resin, what plays important roles are stress concentration of a molded article and formation and expansion of voids in a rubber by mixing the above copolymers (impact modifier). For obtaining the stress concentration, it is essential to introduce a rubber component having elastic modulus significantly lower than that of a thermoplastic resin. Formation and expansion of voids in a rubber are expected to contribute intensely to growth of shearing yield particularly having large energy absorption in an impact test, and to lead to improvement in impact resistance of a thermoplastic resin which contains a rubber.
Therefore, how to promote formation and expansion of voids in a rubber component is extremely important at impact to a molded article, i.e. under stress. It is considered that formation and expansion of voids in the rubber component is significantly influenced by cross-linking state of the rubber. Also, when a rubber component is previously made hollow, there is possibility that voids are easily propagated under stress.
Then, various investigations were made with respect to a novel process for preparing a rubber latex used for an impact modifier which remarkably improves impact resistance of a thermoplastic resin. As a result, it has been found that a rubber latex having water in particles, obtained by seed polymerization with a small amount of seedpolymers which is highly hydrophilic and swellable to rubber monomers, is the most suitable.
DISCLOSURE OF INVENTION
Namely, the present invention relates to a rubber latex containing water in particles, which is obtained by seed polymerization with seed polymers which are hydrophilic and swellable into a rubber monomer.
In the above rubber latex, 0.1 to 25 parts by weight of the seed polymer is preferably used based on 100 parts by weight of a latex rubber.
In the above rubber latex, it is preferable that an extraction ratio of a water-soluble substance to water is 10 to 100% after adding water to dry seed polymers in twentyfold amount and stirring for an hour, and that a swelling volume ratio, measured from the ratio of a latex particle size to an original particle size, is 3 to 20 times, said latex particle size being the value after adding a rubber latex to the seed polymer latex in an amount of 50 times the seed polymer and stirring for an hour.
More preferably, the extraction ratio is 50 to 100% and the swelling volume ratio is 5 to 15 times.
The present invention also relates to a process for preparing a rubber latex containing water in particles, which is obtained by seed polymerization with seed polymers which are hydrophilic and swellable into a rubber monomer.
In the process for preparing a rubber latex, it is preferable that the seed polymerization is performed by adding monomers continuously, an extraction ratio of a water-soluble substance to water is 10 to 100% after adding water to dry seed polymers in twentyfold amount and stirring for an hour, and that a swelling volume ratio, measured from the ratio of a latex particle size to an original particle size, is 3 to 20 times, the latex particle size being the value after adding a rubber latex to the seed polymer latex in an amount of 50 times the seed polymer and stirring for an hour.
More preferably, the extraction ratio is 50 to 100% and the swelling volume ratio is 5 to 15 times.
In the above process for preparing a rubber latex, the seed polymer is preferably synthesized by emulsion polymerization with a water-soluble initiator.
The present invention also relates to an impact modifier for a thermoplastic resin, which is obtained by graft copolymerization with the above rubber latex.
BEST MODE FOR CARRYING OUT THE INVENTION
There are various methods for preparing hollow rubber particle in the fields of coating materials and weight saving for plastics. For example, the following methods are well known (“Gosei Latex no Oyo (application of synthetic latex)”, Takaaki Sugimura et al., p 285):
(a) a method wherein a W/O/W emulsion is prepared, and a monomer in the O layer is polymerized (O: lipophilic, W: hydrophilic);
(b) a method wherein core-shell particles having swellable core is swelled at temperature of at least glass transition temperature of shell layer to make hollow;
(c) a method by using two-step polymerization of polymers having different solubility parameter;
(d) a method wherein a polymerizable monomer containing a cross linkable monomer and a hydrophilic monomer, and an oil substance are finely dispersed in water to make an O/W emulsion, and the monomer is polymerized to remove the oily substance; and
(e) a method by using migration of a carboxylic acid copolymerized into a particle under acidic or alkaline condition in the particle.
The process for preparing a rubber latex containing water in particles of the present invention differs from these methods. It is the process for preparing a latex having voids filled with water through the polymerization progress by seed polymerization with a small amount of seed polymers which are highly hydrophilic and swellable to rubber monomer to be prepared. It is possible to confirm the state that water is contained in rubber particles and voids are present in a latex state by embedding a rubber latex in an epoxy resin and the like, and then according to TEM observation by dying it with ruthenium tetraoxide and the like. Further, the void ratio can be calculated by exactly measuring the particle size of a rubber latex by Microtrac UPA (Ultrafine Particle Analyzer) and the like, and then measuring light scattering strength of the same rubber latex.
High impact resistance can be obtained by preparing a rubber-containing graft copolymer by graft polymerizing a monomer or the like, which generates a polymer compatible with thermoplastic resins, onto the rubber latex containing water in particles obtained in the present invention, and then mixing it with a thermoplastic resin and molding the same.
The seed polymer used in the present invention can be prepared by usual emulsion polymerization, but the method of synthesis is not particularly limited. The seed polymer is not limited to a rubber component such as butyl acrylate rubber or butadiene rubber, but there is no problem when a hard polymer such as a butyl acrylate-styrene copolymer or a styrene-acrylonitrile copolymer is used. However, they are required to be highly swellable to the monomer generated in the following step and have strong hydrophilic property for incorporating water into the particles.
As a method for improving swelling property of the seed polymer to a rubber monomer, it is important to make the polarity suitable for the rubber monomer at first. Then it is effective to lower the molecular weight of the seed polymer to a notable degree by using a chain transfer agent, selecting high polymerization temperature and adding a large amount of initiator.
Effective methods for imparting hydrophilic property to the seed polymer include (a) a method for using a hydrophilic monomer for the seed polymer, (b) a method for introdu
Hashimoto Tomomichi
Kakutani Mitsuo
Mizuta Toshio
Mori Toshiyuki
Takaki Akira
Armstrong Kratz Quintos Hanson & Brooks, LLP
Cheung William
Kaneka Corporation
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