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
1999-02-19
2001-02-20
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S084000, C525S243000, C525S316000
Reexamination Certificate
active
06191226
ABSTRACT:
TECHNICAL FIELD
The present invention relates to novel polybutadiene rubber, a high-impact aromatic vinyl resin composition comprising such polybutadiene rubber, and a preparation process of the resin composition.
BACKGROUND ART
High-impact polystyrene (HIPS) resins are generally produced by subjecting a styrene monomer to bulk polymerization, solution polymerization or bulk-suspension polymerization in the presence of any of various kinds of unvulcanized rubber and have a structure that rubber particles are dispersed in a matrix of a polystyrene resin, whereby the impact resistance of the polystyrene resin, which is rigid and brittle, is markedly improved. Since the high-impact polystyrene resins are cheap and excellent in processability and various physical properties, they have been used in wide application fields.
Polybutadiene rubber and styrene-butadiene copolymer rubber are generally used as the unvulcanized rubber for the high-impact polystyrene resins. In the case where high impact resistance at a low temperature is particularly required, various kinds of polybutadiene rubber are in use. More specifically, for example, the so-called low-cis-polybutadiene rubber obtained by anionic polymerization making use of a catalyst composed of an organolithium alone or comprising the organolithium as a main component, or the so-called high-cis-polybutadiene rubber obtained by using an anionic coordination catalyst comprising a compound of a transition metal such as cobalt, nickel or titanium as a main component is in use.
In recent years, the high-impact polystyrene resins have shown a tendency to be used in wider application fields because of their good various physical properties and processability. As the high-impact polystyrene resins are used in wider application fields, the performance characteristics required of the resins become higher than before. With respect to the physical properties, there is a demand for improvements in balance between impact resistance and stiffness (modulus in flexure), low-temperature impact resistance, and appearance such as gloss. The high-impact polystyrene resins obtained by polymerizing a styrene monomer in the presence of unvulcanized rubber are also required not to deteriorate their physical properties or scarcely deteriorate the physical properties even when the resins are used after they are further diluted with a polystyrene resin or the like or compounded with various kinds of additives such as a flame retardant.
As a method for more improving the low-temperature impact resistance, it has heretofore been proposed in Japanese Patent Publication No. 14689/1992 to prepare polybutadiene rubber having an extremely low 1,2-vinyl bond content and a narrow molecular weight distribution using a special catalyst comprising a rare earth metal compound as a main component and use the polybutadiene rubber thus obtained as an impact modifier. According to this method, a high-impact polystyrene resin excellent in resistance to heat deterioration and weather resistance can be obtained. However, its improving effect on low-temperature impact resistance is not yet sufficient, and its improving effects on stiffness and impact resistance are also not satisfactory.
Japanese Patent Publication No. 5789/1995 has proposed a method of producing a high-impact polystyrene resin improved in impact resistance and gloss, in which a blend of polybutadiene rubber having a high intrinsic viscosity and polybutadiene rubber having a somewhat lower intrinsic viscosity is used as an impact modifier. According to this method, the improving effects on impact resistance and gloss can be brought about. However, since the molecular weight of a low molecular weight component in the blend is high, and the molecular weight distribution thereof is narrow, the impact resistance of the resulting polystyrene resin is not sufficient, and the impact resistance is more markedly deteriorated when the resin is used after diluted with a polystyrene resin or the like or compounded with various kinds of additives.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a high-impact aromatic vinyl resin composition which is well balanced between impact resistance and stiffness (modulus in flexure), has good low-temperature impact resistance and is prevented from being deteriorated in physical properties by dilution with an aromatic vinyl resin or compounding of various kinds of additives, and novel polybutadiene rubber which permits the provision of such a resin composition.
The present inventors have carried out an extensive investigation with a view toward solving the above-described problems involved in the prior art. As a result, it has been found that when polybutadiene rubber, wherein:
(1) a molecular weight distribution curve of the rubber as determined by gel permeation chromatography (GPC) has 2 peaks attributable to a high molecular weight component and a low molecular weight component,
(2) a molecular weight corresponding to a top of the peak (hereinafter referred to as “peak top molecular weight”) of the high molecular weight component and a peak top molecular weight of the low molecular weight component fall within ranges of from 100,000 to 1,500,000 and from 10,000 to 50,000, respectively,
(3) a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), Mw/Mn, falls within a range of from 4.5 to 14.5, and
(4) the content of a cis-1,4 structure is at least 80 wt. %,
is used as a rubber component in a high-impact polystyrene resin, a high-impact aromatic vinyl resin composition, which is well balanced between impact resistance and stiffness (modulus in flexure), has good low-temperature impact resistance (low-temperature impact strength) and is prevented from being deteriorated in physical properties by dilution with an aromatic vinyl resin or compounding of various kinds of additives, can be obtained. The present invention has been led to completion on the basis of this finding.
According to the present invention, there is thus provided polybutadiene rubber wherein a molecular weight distribution curve of the rubber as determined by gel permeation chromatography (GPC) has 2 peaks attributable to a high molecular weight component and a low molecular weight component, a peak top molecular weight of the high molecular weight component and a peak top molecular weight of the low molecular weight component fall within ranges of from 100,000 to 1,500,000 and from 10,000 to 50,000, respectively, a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), Mw/Mn, falls within a range of from 4.5 to 14.5, and the content of a cis-1,4 structure is at least 80 wt. %.
According to the present invention, there is also provided a process for preparing a high-impact aromatic vinyl resin composition, which comprises radical-polymerizing 99 to 60 wt. % of (B) an aromatic vinyl monomer or a mixture of the aromatic vinyl monomer and a monomer copolymerizable therewith in the presence of 1 to 40 wt. % of (A) the above-described polybutadiene rubber.
According to the present invention, there is further provided a high-impact aromatic vinyl resin composition having a structure that polybutadiene rubber is dispersed in a matrix of an aromatic vinyl resin, wherein:
(a) the polybutadiene rubber is the above-described polybutadiene rubber,
(b) the aromatic vinyl resin is at least one selected from the group consisting of polymers of aromatic vinyl monomers and copolymers of an aromatic vinyl monomer and a monomer copolymerizable therewith,
(c) proportions of the polybutadiene rubber and the aromatic vinyl resin are 1 to 40 wt. % and 99 to 60 wt. %, respectively, and
(d) the polybutadiene rubber is dispersed in the form of rubber particles having an average particle diameter ranging from 0.01 to 10 &mgr;m in the aromatic vinyl resin.
BEST MODE FOR CARRYING OUT THE INVENTION
Polybutadiene Rubber:
In the present invention, polybutadiene rubber having specific physical properties, structure and composition is used
Matsuda Hiroaki
Noguchi Kohkichi
Armstrong, Westerman Hattori, McLeland & Naughton
Nippon Zeon Co. Ltd.
Teskin Fred
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