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
2001-09-28
2003-07-08
Wu, David W. (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...
C525S333700, C525S088000, C525S515000, C525S387000, C525S374000, C525S383000, C524S451000, C524S423000, C524S436000, C524S425000, C524S445000
Reexamination Certificate
active
06590038
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of Korea patent Application No. 2000-64690, filed on Nov. 1, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polypropylene resin composition and more particularly, to the polypropylene resin composition comprising a high crystalline polypropylene, an ethylene-&agr;-olefin elastomer, an inorganic filler, an organic peroxide and a crosslinking assistant. This polypropylene resin composition exhibits excellent scratch resistance, rigidity, heat resistance, and impact strength and thus, it can be suitable for automobile interior materials such as glove box, console, center crash pad and the like.
Conventional polypropylene resin composition has been widely used in automobile interior materials such as various pillar as well as exterior materials such as a bumper due to its excellent formability, impact resistance chemical resistance, low viscosity and low cost.
However, it is required to satisfy both scratch resistance and impact resistance to use in automobile interior material such as glove box, console, center crash pad and the like. Though conventional polypropylene resin composition has good physical properties such as impact resistance and rigidity, there is no such a product satisfying both said properties, scratch resistance and impact resistance.
Hitherto, it is common practice to use the polypropylene resin graded to several tens in accordance with the intended use. In this case, it needs extra painting process to satisfy both impact resistance and scratch resistance, resulting in cost increase.
Therefore, development of the polypropylene resin having superior impact resistance and scratch resistance is highly demanded in the automobile industry.
SUMMARY OF THE INVENTION
There are some disadvantages in that the cost is high and it requires additional painting process to increase scratch resistance because of the use of polypropylene resin graded to several tens in the conventional automobile industry.
Therefore, an object of the present invention is to provide a polypropylene resin composition having excellent impact strength and scratch resistance, which is suitable for automobile interior materials, by incorporating typical polypropylene resin with a propylene homopolymer and/or ethylene-propylene block copolymer, ethylene-&agr;-olefin elastomer, organic peroxide, crosslinking assistant and inorganic filler.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a polypropylene resin composition comprising:
(A) 30-70 wt. % of polypropylene resin comprising propylene homopolymer, ethylene-propylene block copolymer, or a mixture thereof;
(B) 10-30 wt. % of ethylene-&agr;-olefin elastomer;
(C) 10-40 wt. % of an inorganic filler;
(D) 0.01-0.2 wt. % of an organic peroxide based to 100 wt. % of said polypropylene resin (A); and
(E) 0.06-1.2 wt. % of a crosslinking assistant based to 100 wt. % of said polypropylene resin (A).
The present invention is described with detailed description of each component as set forth hereunder.
(A) Component
High crystalline polypropylene is used to enhance rigidity, heat resistance, chemical resistance and formability of the polypropylene composition of the present invention. This high crystalline polypropylene is used having pentad fraction (% mmmm) measured by
13
C-NMR higher than 96%, preferably higher than 97%. If the pentad fraction is below 96%, the rigidity and heat resistance are degraded. And further, said high crystalline polypropylene of this invention may be propylene homopolymer, ethylene-propylene block copolymer, or a mixture thereof.
Also, for said high crystalline propylene homopolymer, the one with melt index of from 2 to 15 g/10 min and intrinsic viscosity [&eegr;] measured in 135° C. of decalin in the range of from 1.0 to 3.0 dL/g, preferably in the range of from 1.5 to 2.5 dL/g, is used. If the intrinsic viscosity [&eegr;] is below 1.0 dL/g, the impact strength worsens; otherwise if it exceeds 3.0 dL/g, the formability worsens.
For said ethylene-propylene rubber of ethylene-propylene block copolymer, the one with intrinsic viscosity [&eegr;] of higher than 3.0 dL/g, preferably higher than 4.0 dL/g, is used. If the intrinsic viscosity [&eegr;] is below 3.0 dL/g, the impact strength is rapidly. Said high crystalline polypropylene may be used alone or as a mixture of propylene homopolymer and ethylene-propylene block copolymer. And ethylene-propylene rubber of sad ethylene-propylene block copolymer contains more than 70% of the propylene homopolymer content, preferably more than 80%, to obtain desired impact resistance and flexibility. Said high crystalline polypropylene is used in 30-70 wt. % based to the entire polypropylene resin composition, preferably in 45-65 wt. %. If the content exceeds 70 wt. %, the impact strength is degraded; otherwise if it is below 30 wt. %, the formability is degraded.
(B) Component
Even though the polypropylene resin of (A) component provides excellent impact resistance due to high crystalline property, there are some disadvantages in that cracks or bending in the product can occur due to large changes in volume during cooling process after molding process, rapid molding shrinkage can also occur during injection process, and impact strength is deficient at low temperature.
Therefore, the ethylene-&agr;-olefin elastomer of the present invention is used in order to solve such problems. A preferred ethylene-&agr;-olefin elastomer of the present invention is a mixture of ethylene-propylene rubber (hereinafter referred to as “EPR”) and ethylene-octene elastomer (hereinafter referred to as “EOM”).
EPR having a melt index of 0.3-10 g/10 min is preferred to use, and more preferably 0.5-5 g/10 min. If said melt index is less than 0.3 g/10 min, appearance and mechanical properties of the molded product are degraded because the dispersion becomes poor during the molding process. On the other hand, in case of exceeding 10 g/10 min, impact resistance is decreased due to excess use of the elastomer. Physical properties of the EPR can be changed with comprised amount of propylene which is preferable in the range of from 20 to 70 wt. %, more preferably in the range of from 40 to 60 wt. %. If the amount exceeds 70 wt. % rigidity worsens; otherwise if it is less than 20 wt. %, impact strength becomes poor.
The use of EPR in the present invention increases the impact strength of the entire polypropylene resin composition, but it can also affect to degrade the rigidity. Thus, it is required to use another ethylene-olefin elastomer (EOM) to complement this problem. For this purpose, EOM having a Mooney viscosity ML
1+4
(121° C.) of 1-50 dL/g, and the density of 0.86-0.91 g/cm
3
, preferably 0.87-0.90 g/cm
3
, is used. And further, it is preferred to use EOM containing 15-45 wt. % of C
8
(octane), more preferably 25-35 wt. %.
These two elastomers are used to complement each other, and a preferred compounding ratio (EPR:EOM) is in the of from 20:80 to 80:20 wt. %, preferably from 60:40 to 40:60 wt. %. The content of this mixture incorporated is 10-30 wt. % to the entire polypropylene resin composition, preferably 15-25 wt. %. If the content exceeds 30 wt. %, the rigidity and formability are inferior; otherwise if it is below 10 wt. %, the impact strength is degraded.
(C) Component
An inorganic filler is used to improve tensile strength and impact strength and lower cost to the polypropylene resin composition of the present invention. It is preferred to use the filler having an average particle size of from 0.5 to 7 &mgr;m and when the particle size is smaller than 0.5 &mgr;m, the dispersion of the resin becomes degraded; otherwise if it is larger than 7 &mgr;m, cracks are formed due to large particle size and the impact strength is inferior and thus, it does not provide the desired physical properties. The inorganic filler is used in 10-40 wt. % to the entire polypropylene resin composition. If the content is below 10 wt. %, the rigidity
Chung Hun-Uck
Song Young-Bong
Whang Tae-Won
Yu Young-Hwan
Christie Parker & Hale LLP
Hyundai Motor Company
Lee Rip A.
Wu David W.
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