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
1998-05-15
2001-10-23
Wilson, Donald R. (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...
C525S095000, C525S232000, C525S241000, C524S451000
Reexamination Certificate
active
06306972
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polypropylene-based resin composition and an injection molded article thereof. More particularly, it relates to a polypropylene-based resin composition having an excellent flowability because of its specific rubber component and specific composition ratio, as well as excellent rigidity and impact resistance in physical properties, which is particularly useful as a molded article, and an injection molded article thereof.
2. Prior Art
Crystalline propylene-ethylene block copolymers have recently been used as automobile materials and domestic electric appliance materials in view of lightening and cost saving. However, conventional crystalline propylene-ethylene block copolymer materials had a low impact strength and contained a large amount of an inorganic filler to impart thermal properties such as heat distortion temperature. Therefore, a specific gravity was relatively high.
For example, in JP-A-53-22552 and JP-A-53-40045, it is disclosed to incorporate an ethylene-propylene copolymer rubber into a crystalline propylene-ethylene block copolymer to improve the impact strength. However, the rigidity, thermal properties such as heat distortion temperature, etc. and flowability are inferior because the ethylene-propylene copolymer rubber is incorporated. Furthermore, for example, in JP-A-51-136735, JP-A-53-64256, JP-A-53-64257, JP-A-57-55952, JP-A-57-207630, JP-A-58-17139, JP-A-58-111846, JP-A-59-98157, or JP-B-55-3374, it is disclosed to incorporate inorganic fillers such as calcium carbonate, barium sulfate, mica, crystalline calcium silicate, talc, etc. to improve the thermal properties. However, the flowability was liable to becomes inferior by adding the inorganic filler.
In such way, it has been required to develop a material having a good flowability while maintaining good balance between the impact strength and rigidity, and many proposals have been done. However, properties of the proposed materials have been insufficient.
SUMMARY OF THE INVENTION
Under these situations, an object of the present invention is to provide a polypropylene-based resin composition having a good flowability and good balance between impact strength and rigidity in comparison with the conventional polypropylene-based resin composition obtained by incorporating an ethylene-propylene copolymer rubber, and an injection molded article thereof.
The present inventors have intensively studied. As a result, the present inventors have found that the above object of the present invention can be accomplished by using a polypropylene resin as a main component and adding a specific rubber component to this resin at a specific composition ratio. Thus, the present invention has been completed.
According to the present invention, there is provided a polypropylene-based resin composition comprising:
(1) 95 to 50% by weight of a polypropylene-based resin (A) composed of the following (i) and (ii);
(i) a crystalline propylene-ethylene block copolymer (referred to simply as “propylene-ethylene block copolymer”, hereinafter) comprising a propylene homopolymer portion as a first segment and a propylene-ethylene random copolymer as a second segment, said propylene-ethylene block copolymer having a melt flow rate at 230° C. measured according to JIS-K-6758 of not less than 25 g/10 min., and
(ii) a crystalline propylene homopolymer (referred to simply as “propylene homopolymer”, hereinafter) having a melt flow rate at 230° C. measured according to JIS-K-6758 of not less than 70 g/10 min.;
(2) 5 to 20% by weight of at least one rubber (B) selected from the following rubbers (a) and (b);
(a) an ethylene-&agr;-olefin copolymer rubber, and
(b) an alkenyl aromatic compound-containing rubber; and
(3) 0 to 30% by weight of talc having an average particle diameter of not more than 3 &mgr;m, the total amount of (1) to (3) being 100% by weight, wherein said polypropylene-based resin composition satisfies the following expression:
0.05≦{(
A
)′/[(
A
)′+(
a′
)+(
b′
)]}≦0.20
in which (A)′ represents an amount by weight of the second segment of the crystalline propylene-ethylene block copolymer (i) in the polypropylene-based resin composition, (a′) represents an amount by weight of the ethylene-&agr;-olefin copolymer rubber in the polypropylene-based resin composition, and (b′) represents an amount of the alkenyl aromatic compound-containing rubber in the polypropylene-based resin composition, and
wherein the melt flow rate at 230° C. measured according to JIS-K-6758 of said polypropylene-based resin composition is not less than 35 g/10 min. and the flexural modulus at 23° C. is not less than 8000 kg/cm
2
.
Furthermore, the present invention provides a molded article obtained by injection molding the polypropylene-based resin composition described above.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
In the present invention, the polypropylene-based resin (A) is a mixture of the above (i) and (ii). The proportion of (i) to (ii) is not specifically limited, but the proportion is preferably 10 to 40% by weight of the (i) to 90 to 60% by weight of the (ii) (provided that the total of (i) and (ii) is 100% by weight).
In the polypropylene-based resin (A) used in the present invention, the Q value as a ratio of weight average molecular weight (Mw)
umber average molecular weight (Mn), which represents a molecular distribution of a propylene homopolymer portion of polypropylene-based resin (A) according to gel permeation chromatography (GPC) method, is preferably from 3.0 to 5.0, more preferably from 3.5 to 4.5. When the Q value is less than 3.0, the flowability of the polypropylene-based resin composition sometimes becomes inferior. On the other hand, when the Q value exceeds 5.0, preferable results are not sometimes obtained in balance between the rigidity and impact resistance. The term “propylene homopolymer portion of polypropylene-based resin (A)” used herein refers to the first segment portion of the propylene-ethylene block copolymer (i), and the propylene homopolymer (ii).
In addition, particularly preferable properties of the propylene homopolymer (ii) in the polypropylene-based resin (A) are as follows.
That is, as described above, the Q value is preferably from 3.0 to 5.0, more preferably from 3.5 to 4.5, and the isotactic pentad fraction calculated by
13
C-NMR is preferably not less than 0.97, more preferably not less than 0.98. When the isotactic pentad fraction is less than. 0.97, it is sometimes difficult to satisfy the desired rigidity, heat resistance, etc. The melt flow rate at 230° measured according to JIS K6758 (referred to as “MFR at 230° C.” herein-after) is not less than 70 g/10 min., preferably not less than 80 g/10 min. When the MFR at 230° C. is less than 70 g/10 min., the flowability becomes poor.
In the propylene-ethylene block copolymer (i) composed of the propylene homopolymer portion as the first segment and the propylene-ethylene random copolymer portion as the second segment, particularly desired properties, composition, etc., are as follows.
The MFR at 230° C. of the propylene-ethylene block copolymer (i) is not less than 25 g/10 min., preferably not less than 30 g/10 min. In the propylene-ethylene block copolymer (i), the properties described below of the propylene homopolymer portion as the first segment are the same as those in case of the above propylene homopolymer (ii). That is, the Q value is preferably from 3.0 to 5.0, more preferably from 3.5 to 4.5, and the isotactic pentad fraction calculated by
13
C-NMR is preferably not less than 0.97, more preferably not less than 0.98.
The propylene-ethylene block copolymer (i) can be obtained by a known method, for example, by a method of polymerizing propylene in the presence of a stereoregular olefin in polymerization catalyst to produce the first segment in the first step and subsequently random copolymerizing ethylene and propylene to produc
Kondo Shin-ichi
Ohkawa Kenichi
Shimojo Moriyasu
Birch & Stewart Kolasch & Birch, LLP
Sumitomo Chemical Company Limited
Wilson Donald R.
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