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
1999-11-16
2001-12-25
Seidleck, James J. (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...
C525S070000, C525S083000, C525S243000, C525S316000
Reexamination Certificate
active
06333381
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a rubber-containing styrenic resin of which the rubber component dispersed therein is controllable in its morphology and particle size, and to a process for producing the same.
BACKGROUND OF THE INVENTION
As a means for improving the impact resistance of a styrenic resin, there has been proposed a styrenic resin containing a rubber component (styrene-butadiene rubber, polybutadiene rubber) such as high impact resistant polystyrene HIPS. Various techniques have been adopted to improve the impact resistance, in which a rubber dispersed in a HIPS is increased in particle size or the rubber content is raised. According to such methods, while the impact resistance of a shaped article is improved to some extent, the surface gloss thereof or other characteristics are deteriorated. On the other hand, a rubber component of smaller particle size or a lower rubber content improves the surface gloss of a shaped article but deteriorates the impact resistance. Therefore, the external appearance and impact resistance cannot both be held at high levels.
Control of the morphology of the rubber component dispersed in particles in the resin (morphology of particles) is suggested to improve the impact resistance or characteristics related to external appearance such as surface gloss. For example, a rubber particle formed such as to have a small particle size and a microdomain structure of the core/shell type (core/shell structure) is useful for improving the surface gloss of a styrenic resin. However, the formation of a styrenic resin having a core/shell morphology requires a rubber component to be efficiently dispersed in a styrenic resin matrix, consequently limiting the range of rubber components available therefor [e.g., rubber components highly compatible with styrenic resins (styrene-butadiene rubber, etc.)]. Therefore, a styrenic resin having a core/shell structure cannot be produced with a conventional diene rubber. Moreover, when a diene rubber is used, the morphology of the resultant resin is a salami structure with a large particle size, and hence no improvement in the surface gloss of a shaped article thereof.
Moreover, for improvements in both surface gloss and impact resistance, there has been proposed an idea of using a HIPS containing small rubber particles having a core/shell structure in combination with a HIPS containing larger rubber particles having a salami structure. However, this method requires specific and peculiar polymerization conditions and a blending step, and hence the operation much complicated.
On the other hand, there has been known a living radical polymerization process which is a combination method of a living polymerization method whereby a primary structure of a polymer (e.g., molecular weight, molecular-weight distribution) is easily controllable and a radical polymerization method which is less sensitive to impurities or solvents. Though the living radical polymerization process is a radical polymerization, this process enables control of the molecular weight and provides a polymer having a narrow molecular-weight distribution.
Japanese Patent Publication No. 6537/1993 (JP-B-5-6537) corresponding to USP or WO discloses a compound as an initiator for the living radical polymerization of an unsaturated monomer. Japanese Patent Application Laid-Open No. 199916/1994 (JP-A-6-199916) corresponding to USP or WO discloses a polymerization method for a thermoplastic resin having a narrow polydispersity, comprising a step of heating a free radical initiator, a stable free radical agent and a polymerizable monomer compound.
Further, Japanese Patent Application Laid-Open No. 239434/1996 (JP-A-8-239434) corresponding to USP or WO discloses a process for producing a composition containing a vinyl aromatic polymer and a rubber, comprising a step of polymerizing a vinyl aromatic monomer in the presence of a rubber. The literature teaches the presence of a stabilized free radical in the polymerization step. However, considering the amount of the rubber used, the degree of improvement in impact resistance in this process, in other words, rubber efficiency, is low.
SUMMARY OF THE INVENTION
Thus, an object of the present invention is to provide a rubber-containing or rubber-modified styrenic resin of which the dispersed rubber is easily controllable in its particle morphology and size according to the intended use, and a process for producing the same.
Another object of the present invention is to provide a rubber-containing or rubber-modified styrenic resin having surface gloss and impact resistance both at high levels, and a process for producing the same.
Still another object of the present invention is to provide a rubber-containing or rubber-modified styrenic resin which is excellent in rubber efficiency, and a process for producing the same.
Another object of the present invention is to provide a rubber-containing or rubber-modified styrenic resin having a microdomain structure of the core/shell type even if the rubber component contained therein is a diene rubber such as polybutadiene, and a process for producing the same.
The inventors of the present invention did intensive and extensive studies to achieve the above objects and found that the morphology or particle size of a rubber component dispersed in a polymer and the molecular weight of a styrenic resin forming a matrix can be controlled by, in the presence of a rubber component, radical-polymerizing a styrenic monomer in a specific manner. The present invention was accomplished based on the above findings.
Thus, the rubber-containing styrenic resin of the present invention comprises a matrix of a styrenic resin and a rubber component in particle form dispersed in the matrix, wherein the graft ratio of a styrenic monomer relative to the rubber component is not less than 1, and the mean particle size of the dispersed rubber component is 0.1 to 3 &mgr;m, satisfying the following equation (1):
Mn=aT+b
(1)
wherein Mn is the number average molecular weight of the matrix resin; T is the conversion of the styrenic monomer; a is a constant greater than 0; and b is a constant of not less than 0.
The present invention further includes a styrenic resin comprising a styrenic resin matrix and a rubber component dispersed therein in particles, in which the graft ratio of a styrenic monomer relative to the rubber component is not less than 2.5 and the mean particle size of the dispersed rubber component is about 0.3 to 3 &mgr;m.
The above-mentioned rubber component may be a butadiene-series rubber (e.g., a diene rubber). The particle-size distribution of the dispersed rubber component may show, for example, a plurality of peaks (i.e., the particle-size distribution having a plurality of peaks, particularly two peaks) or a single-peak, and the morphology (microdomain structure) of the dispersed rubber component may for example be of the salami type (salami structure), core/shell type (core/shell structure), or a mixed or complex type thereof.
The present invention further includes a process for producing a rubber-containing styrenic resin in which, under such conditions that the relationship between the conversion T of a styrenic monomer and the number average molecular weight Mn of the resulting polymer can be approximated by a linear equation, at least a styrenic monomer is polymerized in the presence of a rubber component at a graft ratio of not less than 1.
In this specification, acrylic monomers and methacrylic monomers are collectively referred to as “(meth)acrylic monomer.
DETAILED DESCRIPTION OF THE INVENTION
The rubber-containing styrenic resin of the present invention comprises a matrix of a styrenic resin and a rubber component dispersed in the matrix, and the graft ratio of the styrenic monomer relative to the rubber component is not less than 1.
The styrenic resin forming the matrix may comprises a homopolymer or copolymer of a styrenic monomer, a copolymer of a styrenic monomer and a copolymerizable vinyl monomer, or the lik
Asada Takeshi
Sekiguchi Junichi
Teranishi Tadashi
Umemoto Koichi
Yanagita Soko
Asinovsky Olga
Birch & Stewart Kolasch & Birch, LLP
Daicel Chemical Industries Ltd.
Seidleck James J.
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