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
2001-06-06
2003-08-12
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S209000, C525S221000, C525S222000, C525S232000, C525S238000, C525S239000, C525S241000, C525S243000, C525S244000, C525S317000, C525S326100, C525S329100, C525S330300, C525S330700, C525S331500, C525S333300
Reexamination Certificate
active
06605672
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an impact modifier for a vinyl chloride resin.
BACKGROUND ART
Conventionally, there have been various suggestions for improving the impact resistance of thermoplastic resins. For example, in the case of vinyl chloride resins it is known that a copolymer of diene-based rubber or acrylate-based rubber may be mixed thereto (Japanese Examined Patent Publication No. 39-19035/1964). Further, there are the suggestions of 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) to improve impact resistance. However, with these methods, there are the problems that it is difficult to significantly improve impact resistance, and cost for raw material drastically increases.
Stress concentration of a molded article and formation and expansion of voids in a rubber play an important role in improving impact resistance of thermoplastic resins such as vinyl chloride resins. For obtaining stress concentration, it is essential to introduce a rubber component having elastic modulus significantly lower than that of a thermoplastic resin. Actually, optimization of the size and a shape of the rubber component has been investigated by introducing various rubbers. Formation and expansion of voids in the 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, the method of promoting formation and expansion of voids in a rubber component at impact (under stress) of a molded article is extremely important, and formation and expansion of voids in the rubber component are considered to be significantly influenced by the 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, the relationship between void (hollow) state of a rubber component in a latex, hollow state of a thermoplastic resin molded article mixed with an impact modifier containing a rubber component, and impact strength of the molded article has been investigated by changing the amount of a cross-linking agent controlling the cross-linking condition of the rubber component. As a result, it has been found that an impact modifier comprising 30 to 90% by weight of a hollow rubber of which Tg is at most 0° C. and an amount of a cross linking agent is 0 to 5% by weight, and which is not hollow after molding and has a void ratio of 3 to 90% by volume in a latex, and 10 to 70% by weight of a monomer or monomers comprising 60 to 100% by weight of at least one vinyl monomer selected from the group consisting of a (meth)acrylate compound, an aromatic vinyl compound and a vinyl cyanide compound, and 0 to 40% by weight of a monomer copolymerizable therewith, has an extremely large effect on improving impact resistance of a thermoplastic resin. Namely, though it is basic to provide stress concentration by introducing a rubber component (Tg is at most 0° C.) having elastic modulus significantly lower than that of a thermoplastic resin such as a vinyl chloride resin which becomes a continuous phase of a molded article, it is also important to change the rubber particle to a void at impact (under stress) by decreasing the amount of a cross linking agent for this soft rubber component.
However, it has also been found that there is a tendency that a rubber particle collapses at molding and is finely dispersed and the rubber particle does not easily act as a stress concentration point when any cross linking agents become 0% by weight. Further it has been recognized from TEM observation and specific gravity measurement that a hollow rubber having a low content of a cross linking agent has voids filled with water in a latex, but in the processes of coagulation, thermal treatment, drying, blending and molding after graft polymerization, water in the rubber particle is removed, and after drying and molding, voids in the rubber collapse and disappear to become non-hollow.
On the other hand, it has been found that voids in the rubber particle are easily formed and expanded at impact (under stress) in an impact modifier containing a hollow rubber having voids in the rubber in a latex to significantly improve in impact strength. A larger amount of the cross linking agent used in a rubber is more suitable to keep the rubber particle in a hollow state. But judging from easiness of total expansion of voids, the largest improving effect is obtained by using an impact modifier containing a rubber which is hollow in a latex and is not hollow at drying and after molding by controlling an amount of a cross linking agent in a rubber to a small amount thereof.
DISCLOSURE OF INVENTION
Namely, the present invention relates to an impact modifier for a vinyl chloride resin, which is prepared by polymerizing 10 to 70% by weight of a monomer containing 60 to 100% by weight of at least one vinyl monomer selected from the group consisting of a (meth)acrylate compound, an aromatic vinyl compound, a vinyl cyanide compound and vinyl chloride, and 0 to 40% by weight of the other monomer copolymerizable therewith, in the presence of 30 to 90% by weight of a hollow rubber particle of which glass transition temperature Tg is at most 0° C., a void ratio is 3 to 90% by volume in a latex state and which contains a cross linking agent in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the total rubber component monomer.
In the impact modifier, the amount of the cross linking agent is preferably 0.1 to 1.5 parts by weight.
In the impact modifier, the amount of the cross linking agent is more preferably 0.2 to 0.7 parts by weight.
In the impact modifier, an average particle diameter of the hollow rubber in a latex state is preferably 50 to 300 nm.
Further, the present invention relates to a vinyl chloride resin composition comprising a vinyl chloride resin containing at least 50% by weight of vinyl chloride, and the above-mentioned impact modifier.
BEST MODE FOR CARRYING OUT THE INVENTION
There are various methods for preparing hollow rubber particles. For example, the following methods are well known (“Gosei Latex no Oyo (application of synthetic latex)”, Takaaki Sugimura et al., p 285). The rubber particle of the present invention having voids in a latex may be prepared by any of these methods.
(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 cores are swelled at a temperature of at least the glass transition temperature of the shell layer to make hollow
(c) a method using a two-step polymerization of polymers having different solubility parameter values
(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
(e) a method using migration of a carboxylic acid copolymerized into a particle under acidic or alkaline condition in the particle.
There is no particular limitation for the hollow rubber component used in the present invention, as long as it is a rubber elastomer of which the glass transition temperature is at most 0° C. But the lower the glass transition temperature is, the better. The glass transition temperature is required to be at most 0° C., and preferably −20 to −130° C. When the glass transition temperature is more than 0° C., an improving effect for impact resistance remarkably decreases.
Examples of the rubber satisfying these conditions are a diene rubber, an acrylic rubber, a silicon rubber and an olefin rubber, but the rubber is not limited thereto. Examples of the diene rubber are a butadiene rubber,
Hashimoto Tomomichi
Mizuta Toshio
Mori Toshiyuki
Takaki Akira
Kaneka Corporation
Nutter Nathan M.
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