Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-06-14
2001-04-24
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S056000, C521S057000, C521S060000, C521S053000, C521S139000, C521S140000, C521S054000
Reexamination Certificate
active
06221926
ABSTRACT:
TECHNICAL FIELD
The present invention relates to foamable modified polystyrene resin particles, a process for preparation thereof and a foamed article which is produced by using the foamable modified polystyrene resin particles and has excellent break resistance.
BACKGROUND ART
It is well known that a foamed article produced by expanding foamable polystyrene resin particles obtained by impregnating polystyrene resin particles with a blowing agent is broken easily. To improve such a defect, there has been proposed a process for mechanically blending a styrene-butadiene block copolymer with a polystyrene resin (cf. JP-B-47-17465 and JP-A-54-158467) and a process employing particles of a resin which is excellent in impact strength and so-called high impact polystyrene resin (HIPS), wherein the particles are prepared by polymerizing a styrene monomer in the presence of conjugated diene polymer particles (JP-B-47-18428 and JP-A-7-90105).
However it is necessary for those foamable polystyrene resin particles to be subjected to pelletizing through extrusion molding, which results in increase in cost. Further in commercially available high impact polystyrene resin, a molecular weight of its polystyrene cannot increase beyond a certain level.
JP-A-6-49263 discloses foamable polystyrene resin particles prepared by impregnating polystyrene resin particles with a mixture obtained by adding a polymerization initiator to a monomer mixture of a styrene monomer and conjugated diene monomer, polymerizing the monomer mixture to give polystyrene resin particles containing the obtained copolymer rubber particles gathering densely around the surface portion of the resin particle, and then impregnating the polystyrene resin particles with a blowing agent. Also it is disclosed that the center portion of the foamable resin particle is rich with polystyrene and, since the blowing agent is kept in the center portion, the resin particles having high expansion ratio can be obtained. Further, it is described that the resin before impregnated with the blowing agent has impact resistance.
The process mentioned above does not require a pelletizing step and is excellent from the viewpoint of cost. However the obtained foamed article, particularly the foamed article produced by molding pre-expanded particles within a mold is low in percentage of fused particles (fusion rate) and is insufficient in break resistance (in impact strength by a falling weight method).
An object of the present invention is to provide foamable modified polystyrene resin particles which can be prepared without being subjected to pelletizing and give a foamed article having excellent break resistance and high fusion rate; a process for preparation thereof; and a foamed article produced by expansion-molding the foamable modified polystyrene resin particles.
DISCLOSURE OF THE INVENTION
The present invention relates to foamable modified polystyrene resin particles, wherein the foamable modified polystyrene resin particle (E) comprises a particle of a modified polystyrene resin (C) containing a blowing agent (D); said resin (C) comprises conjugated diene polymer rubber particles (B) dispersed uniformly throughout a polystyrene resin (A) and when said foamable modified polystyrene resin particle (E) is expanded, there is substantially no deformation of the rubber particles (B) before and after the expansion
Further the present invention relates to foamable modified polystyrene resin particles, wherein the foamable modified polystyrene resin particle comprises modified polystyrene resin particle containing a blowing agent; said modified polystyrene resin particle being prepared by polymerizing a conjugated diene monomer or a monomer mixture of the conjugated diene monomer and other monomer in polystyrene resin particle to form rubber particles of the conjugated diene polymer dispersed uniformly in the polystyrene resin particle and subjecting the obtained polystyrene resin particle containing the rubber particles to impregnation polymerization of a styrene monomer.
Still further the present invention relates to foamable modified polystyrene resin particles, wherein the foamable modified polystyrene resin particle (E) comprises a particle of modified polystyrene resin (C) containing a blowing agent (D);
said resin (C) comprises conjugated diene polymer rubber particles (B) dispersed uniformly throughout a polystyrene resin (A),
an Izod impact strength of said modified polystyrene resin (C) is from 1 to 5 kg·cm/cm,
a fusion rate between expanded particles of a foamed article (F) obtained by expansion-molding said foamable modified polystyrene resin particles (E) is not less than 50%, and
a 50% failure height according to falling weight method of the foamed article (F) is from 1.35 to 1.84, when a 50% failure height according to falling weight method of a foamed article (H) obtained by expansion-molding a foamable polystyrene resin particle (G) which comprises the polystyrene resin (A) containing a blowing agent (D) is 1.
Such foamable modified polystyrene resin particles of the present invention can be obtained by:
polymerizing a conjugated diene monomer or a monomer mixture of the conjugated diene monomer and other monomer in polystyrene resin particle to form rubber particles of the conjugated diene polymer uniformly dispersed in the polystyrene resin particle,
subjecting the obtained polystyrene resin particles containing the rubber particles to impregnation polymerization of a styrene monomer to give a modified polystyrene resin particle, and
impregnating the modified polystyrene resin particle with a blowing agent.
As the polystyrene resin particle, there can be used one which contains 0.001 to 1.0% (% by weight, hereinafter the same) of a nucleating agent and has a concentration of the nucleating agent in the surface neighborhood of the polystyrene resin particle which is lower than that of the nucleating agent in the inside portion of the polystyrene resin particle. The nucleating agent-containing polystyrene resin particles can be obtained by a process, wherein the polystyrene resin particles are prepared by suspending polystyrene resin seed particles in an aqueous dispersion medium, adding a styrene monomer in the aqueous dispersion medium continuously or intermittently and polymerizing with impregnating the seed particles with the styrene monomer, characterized in that the whole or a part of 0.001 to 1 part (part by weight, hereinafter the same) of the nucleating agent to be contained in 100 parts of the finally obtained polystyrene resin particles is present in the seed particles at a stage prior to addition of the styrene monomer.
Also the present invention relates to a foamed article of a modified polystyrene resin which has a cell membrane of the modified polystyrene resin comprising a polystyrene resin and conjugated diene polymer rubber particles dispersed uniformly in the polystyrene resin, wherein a fusion rate is not less than 50% and the rubber particles maintain substantially their spherical form in the cell membrane.
The foamed article can be obtained by expansion-molding the above-mentioned foamable modified polystyrene resin particles.
In this specification, the foamed article includes both pre-expanded particles obtained by expanding foamable resin particles mentioned hereinafter and a molded article obtained by molding the pre-expanded particles within a mold (hereinafter referred to as “in-mold molding”). The foamed article represents both unless otherwise noted.
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Nakamura Kyoichi
Oohara Hidekazu
Yamaguchi Hidehiro
Foelak Morton
Kaneka Corporation
Leydig , Voit & Mayer, Ltd.
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