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
1999-12-10
2003-12-09
Mullis, Jeffrey (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...
C525S080000, C525S083000, C525S084000
Reexamination Certificate
active
06660806
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a rubber-modified styrenic resin composition which provides a molded article which is excellent in plane impact strength and gloss, and a molded article thereof. In particular, the present invention relates to a rubber-modified styrenic resin composition which provides a molded article plane impact strength of which is greatly increased, and gloss of which is excellent by the addition of a specific polymer to a specific rubber-modified styrenic resin, and a molded article thereof.
DESCRIPTION OF CONVENTIONAL ART
In the fields of office automation equipments and household appliances, good balance of various properties such as processability in a molding process, accuracy of finished sizes of processed products, mechanical properties (e.g. tensile strength, flexural strength, etc.), heat resistance, and so on is required. In particular, when a resin is used as an exterior material, further improvement of gloss and plane impact resistance is required. In these years, such requirement reaches to a very high level. When the resin is used as a wrapping material, high level plane impact strength and appearance are required. When the resin is used as a cushioning material, one of the essential properties which the resin should have is good shock absorbability. However, the rubber-modified styrenic resin does not necessarily satisfy all the above requirements.
As a method for improving the impact resistance of the rubber-modified styrenic resin, there is known the addition of specific amounts of an organic polysiloxane and an ethylene-unsaturated carboxylate copolymer to the rubber-modified styrenic resin. However, the dispersed rubber particles have an average particle size of 0.1 to 2.5 &mgr;m, and the plane impact strength of the composition is insufficient.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above problems and provide a rubber-modified styrenic resin composition excellent in the properties which are required for the exterior materials, wrapping materials and molded foam articles, for example, excellent in plane impact strength and gloss, as well as molding properties and other physical properties.
According to a first aspect of the present invention, there is provided a rubber-modified styrenic resin composition comprising (A) 100 wt. parts of a rubber-modified styrenic resin which contains 10 to 35 wt. % of soft component particles having an average particle size of 0.1 to 0.5 &mgr;m, where said soft component particles have a single occlusion structure comprising a core part which consists of a single continuous phase of a styrenic resin and a shell part which comprises a rubber polymer and occludes said core part, and (B) 0.1 to 10 wt. parts of a polymer having a solubility parameter (SP) of 8.45 to 8.70 and comprising no aromatic vinyl compound unit therein.
According to a second aspect of the present invention, there is provided an injection molded article, an extrusion molded article or a molded foam article comprising the above rubber-modified styrenic resin composition.
DETAILED DESCRIPTION OF THE INVENTION
The rubber-modified styrenic resin (A) used in the present invention may be a rubber-modified styrenic resin which is obtained by polymerizing at least one styrenic monomer, or at least one styrenic monomer and a compound copolymerizable therewith in the presence of a rubber polymer
Examples of the styrenic monomer which is used as a raw material of the rubber-modified styrenic resin (A) used in the present invention are styrene, &agr;-alkyl-substituted styrenes such as &agr;-methylstyrene, nucleus substituted alkylstyrenes such as p-methylstyrene, and so on. Examples of the compound copolymerizable with the styrenic monomer are vinyl monomers such as acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate, etc., maleic anhydride, maleimide, nucleus substituted maleimide, and so on.
As the rubber polymer, polybutadiene, styrene-butadiene copolymers, ethylene-propylene-non-conjugated diene terpolymers, and so on are used. Among them, polybutadiene and the styrene-butadiene copolymers are preferred. As the polybutadiene, high-cis polybutadiene having a high cis-structure content and low-cis polybutadiene having a low cis-structure content are both used.
A content of the soft component particles in the rubber-modified styrenic resin (A) is from 10 to 35 wt. %. When this particle content is less than 10 wt. %, the plane impact strength is not sufficiently improved, while it exceeds 35 wt. %, properties other than the plane impact strength, for example, stiffness, heat resistance, etc. are deteriorated unpreferably.
A content of the soft component particles in the rubber-modified styrenic resin (A) is measured as follows:
About 0.5 g of a sample of the rubber-modified styrenic resin is weighed (weight: W
1
), and the sample is dissolved in a mixed solvent of methyl ethyl ketone and methanol (a volume ratio of 10/1) (50 ml) at room temperature (about 23° C.). Then, undissolved components are isolated by centrifugation, dried, and then weighed (weight: W
2
). A content of the soft component particles in the rubber-modified styrenic resin is calculated by the equation:
(W
2
/W
1
)×100(%).
An average particle size of the soft component particles are from 0.1 to 0.5 &mgr;m, preferably from 0.1 to 0.3 &mgr;m. When the average particle size is less than 0.1 &mgr;m, the plane impact strength of the molded article is not sufficiently improved, while when it exceeds 0.5 &mgr;m, the appearance of the molded article such as gloss is deteriorated unpreferably.
Herein, the average particle size is defined as follows:
A very thin section of the rubber-modified styrenic resin is prepared, and its transmission electron microscopic photograph is taken. Particle sizes of the soft component particles in the photograph are measured and the average particle size is calculated by the following equation:
Average particle size=&Sgr;
n
i
D
i
2
/&Sgr;n
i
D
i
wherein D
i
is a particle size, and n
i
is the number of the particles having the particle size D
i
.
In the present invention, the soft component particles in the rubber-modified styrenic resin (A) should have a single occlusion structure comprising a core part which consists of a single continuous, phase of a styrenic resin and a shell part which comprises a rubber polymer and occludes said core part, which structure may be referred to as a core-shell structure or a capsule structure. The gloss is deteriorated when the particles have other structure, for example, a salami-like structure in which plural minute particles of the styrenic resin are dispersed in a continuous phase of the rubbery polymer. The structure of the soft component particles is observed with a transmission electron microscope as in the above measurement of the average particle size.
The synthesis of the rubber-modified styrenic resin (A) in which the structure of the soft component particles is the single occlusion structure is described in, for example, Die Angewandte Macromolekulare Chemie, 58/59, 175-198 (1977), and such resin can be synthesized by polymerizing a styrenic monomer in the presence of a styrene-butadiene block copolymer having a styrene content of 15 to 65 wt. %.
According to the present invention, the composition contains 0.1 to 10 wt. parts of a polymer (B) having a solubility parameter (SP) of 8.45 to 8.70 and comprising no aromatic vinyl compound unit therein per 100 wt. parts of the rubber-modified styrenic resin (A). When the content of the polymer (B) is less than 0.1 wt. part, the plane impact strength is not sufficiently improved, while when it exceeds 10 wt. parts, other physical properties such as heat resistance are deteriorated unpreferably.
The content of the polymer (B) in the composition of the present invention can be obtained by preparing a very thin section of the composition, taking a transmission electron microscopic photograph of the slice piece, calculating an a percentage of areas of the polymer (B) in the who
Ishii Takahiro
Kihara Hayato
Yoshimi Shuji
Birch & Stewart Kolasch & Birch, LLP
Mullis Jeffrey
Sumitomo Chemical Company Limited
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