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
2000-02-03
2001-06-26
Nutter, Nathan M. (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...
C525S207000, C525S210000, C525S211000, C525S221000, C525S222000, C525S232000, C525S236000, C525S240000, C525S241000
Reexamination Certificate
active
06251997
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polypropylene resin composition and to injection molded articles made of this resin composition.
DESCRIPTION OF RELATED ARTS
Polypropylene has widely been used in various fields including parts in automobile, parts for machines, parts for electric appliances, household commodities, kitchen utensils, packaging films and so on, wherein improvements in the performances thereof have been proposed by incorporation of additives therein which provide facilitation of requisite properties. For example, addition of an inorganic filler, such as talc, has been practised for improving stiffness and heat resistance. By incorporating a large amount of inorganic filler, such as talc and others, satisfactory stiffness and heat resistance can be attaied. However, a plastic resin containing talc exhibits disadvantages, such as higher specific gravity, tendency to easy occurrence of surface damages and scratches on articles molded therefrom and tendency to whitening of the damaged portion.
Therefore, polypropylene resin compositions have been in a progressive development, which exhibit stiffness and heat resistance comparable to those with addition of a large amount of talc and in which the specific weight is rendered lower and the scratch-proof property is improved.
In Japanese Patent Kokai Hei-6-93034 A (corresponding European Patent Application No. EP 573862 A2), a polypropylene product is described in which the processibility in molten state is improved. This polypropylene product exhibits, however, insufficient improvements in the mechanical properties, such as inferior flexural modulus and lower thermal deformation temperature.
In Japanese Patent Kokai Hei-4-202507 A, a process for producing a polypropylene resin in multiple polymerization staged in the presence of a catalyst having a specific solid titanium catalyst component is described, in which it is said that the resulting polypropylene resin is superior in the stiffness, heat resistance and so on. However, this process requires a prepolymerization of, such as, 3-methyl-1-butene, and is complicated. The polypropylene resin obtained by this process exhibits insufficient improvement in the stiffness.
In Japanese Patent Kokai Sho-59-172507 A, a process for producing a polypropylene resin superior in the stiffness, processibility and heat resistance is described, in which propylene is polymerized in two polymerization stages using a Ziegler catalyst. In this polypropylene resin, however, the improvements in the flexural modulus and in the stiffness are insufficient.
Japanese Patent Kokai Hei-4-370103 discloses a process for producing a polypropylene resin superior in the processibility and stiffness in a multi-stage polymerization using a specific catalyst. This polypropylene resin provides, however, insufficient improvement in the flexural modulus.
When alteration in the composition and in the molding conditions is incorporated in such polypropylene resin compositions as above for improving the flexural modulus and heat resistance, the flowability of resin upon injection molding may often be deteriorated with the result of frequent occurrence of rejects and, even if the resulting flexural modulus and heat resistance are satisfactory, the elongation at break is steeply decreased, whereby occurrence of cracks in the molded articles upon molding and fracture at the engagement junction upon assemblage of the molded products may sometimes become observed. Therefore, there have been demands for polypropylene resin compositions in the market, which cause no cracking even under severe molding conditions, have lower density and are superior in the stiffness and in the heat resistance.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a polypropylene resin composition, which is light-weighing and has very high values of stiffness and heat resistance, superior scratch-proof or anti-damaging property and better flowability upon molding or shaping with superior processibility without occurence of cracking upon molding, as well as injection molded articles made of such polypropylene resin composition.
The present invention provides for the following polypropylene resin composition and injection-molded articles:
(1) A polypropylene resin composition comprising 5-25% by weight of a higher molecular weight polypropylene (A) having an intrinsic viscosity [&eegr;], determined in decalin at 135° C., in the range from 6 to 11 dl/g and 95-75% by weight of a lower molecular weight polypropylene (B) having an intrinsic viscosity [&eegr;], determined in decalin at 135° C., in the range from 0.6 to 1.6 dl/g,
wherein the said resin composition has the following characteristic features <<1>> and <<2>>, namely,
<<1>> an isotactic pentad fraction (mmmm-fraction), determined by
13
C-NMR, of at least 96.5% and
<<2>> a molecular weight distribution expressed by Mw/Mn (weight-average molecular weight
umber-average molecular weight), determined by gel permeation chromatography (GPC), of at least 8.
(2) A polypropylene resin composition as defined in the above (1), wherein the resin composition has the following characteristic features <<3>> to <<6>>, namely,
<<3>> a flexural modulus (ASTM D 790) of at least 2,700 MPa,
<<4>> an elongation at break (ASTM D 638) of at least 7%,
<<5>> a heat distortion temperature (ASTM D 648, under a load of 0.45 MPa) of at least 145° C., and
<<6>> a flowability of at least 85 cm, determined using a flow length testing mold having a spiral flow path of a depth of 3 mm, a width of 10 mm and a length of 2,000 mm by performing an injection molding at a resin temperature of 210° C. and at a mold temperature of 40° C. to observe the flow length (the length of spiral flow).
(3) A polypropylene resin composition as defined in the above (1) or (2), wherein the resin composition is obtained by a continuous multistage polymerization.
(4) A polypropylene resin composition as defined in any one of the above (1) to (3), wherein it contains an inorganic filler (C).
(5) A polypropylene resin composition as defined in the above (4), wherein it has the following characteristic feature <<7>>, namely,
<<7>> a specific gravity, determined by the water-displacement method (ASTM D 1505), of not higher than 0.930.
(6) A polypropylene resin composition as defined in the above (4) or (5), wherein it has the following characteristic features <<8>> and <<9>>, namely,
<<8>> a pencil hardness {JIS K-5400, under a load of 9.8 N (1 kgf)} of F or harder and
<<9>> a color-difference value &Dgr;E* after scratch test of 8.0 or lower.
(7) A polypropylene resin composition as defined in any one of the above (1) to (6), wherein it contains a nucleating agent (D).
(8) A polypropylene resin composition as defined in any one of the above (1) to (7), wherein it is devoid of any cross-linked structure.
(9) Injection-molded articles obtainable by injection-molding a polypropylene resin composition as defined in any one of the above (1) to (8).
In the context of this specification, the above-mentioned isotactic pentad fraction (mmmm-fraction) corresponds to the proportion of the isotactic chains as pentad unit in the polypropylene molecular chains, which is determined using
13
C-NMR and which is the proportion of the number of propylene monomeric units present in each center of the sequences of 5 monomeric propylene units bound each successively by meso-coupling. This can be determined in the practice as the proportion of the mmmm-peaks relative to the entire absorption peaks within the methyl carbon region in the
13
C-NMR spectrum.
In the context of this specification, the values of Mw/Mn and Mz/Mw are determined by gel permeation chromatography (GPC).
The flexural modulus is determined under the condition according to ASTM D 790.
The elongation at break is determined under the co
Harima Shigeru
Hashimoto Mikio
Imai Tadashi
Grand Polymer Co Ltd
Nutter Nathan M.
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