Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-09-03
2003-06-10
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
active
06576699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a vibration-damping resin composition which exhibits excellent damping properties at ambient temperature and low temperatures while having high mechanical strength, and a molded article made of such vibration-damping resin composition.
2. Description of the Related Art
In recent years, vehicle parts have been in practice changed from metallic parts to plastic parts to meet the social demand for weight reduction leading to fuel saving. Of various plastic materials, polypropylene resins have been used in large quantities in interior and exterior vehicle trim parts because of their well-balanced physical properties and relative inexpensiveness.
In particular, reinforced polypropylene resins comprising polypropylene resins loaded with inorganic fillers, such as talc, glass fiber, calcium carbonate and mixtures thereof, have high strength and heat resistance and are used in bumpers, body side moldings, dashboards, timing belt covers, blower cases, cooler housings, ducts, and the like.
In addition to weight reduction, reduction of noise of vehicles has also been demanded to improve comfort. Countermeasures against noise include vibration damping, sound insulation, vibration insulations, and sound absorption. For the noise of air conditioning equipment, different countermeasures are taken depending on whether the noise is chiefly transmitted through solid or air. Where noise is to be abated by material displacement, it is necessary to use materials having improved damping properties.
Conventional polypropylene resin compositions with improved damping properties include the one disclosed in Japanese Patent Publication No. Sho. 62-43443. The composition disclosed is still insufficient in satisfying both damping properties and mechanical strength when used in a temperature range from low temperatures to ambient temperature, e.g., from −40° C. to +40° C.
By the way, among the aforementioned exterior vehicle trim parts made of resins, there is a rocker-panel molding, which is attached to the lower side body either directly or via a rocker panel, is generally used for improvement of automobile appearance, protection of a car body from scratches or improvement of aerodynamic characteristics.
The conventional vehicle rocker-panel molding comprises a bottom section and a side section almost perpendicular to the bottom section, showing a nearly L-shaped crosswise profile. The rocker-panel molding should have rigidity to some extent because drivers or passengers may touch them on getting in or out. For the sake of convenience in molding, i.e., in order to obtain a uniform flow of a resin molding material through a mold, conventional rocker-panel moldings have a uniform thickness in the bottom section and the side section. That is, in conventional rocker-panel moldings the side section has a prescribed thickness, e.g., 3 mm, so as to secure necessary rigidity, and the bottom section has the same thickness as the side section.
When a spinning tire sends gravel or sand flying and striking against a rocker-panel molding especially the bottom section thereof, the impact generates vibration energy. Conventional rocker-panel moldings having the above-mentioned structure often have insufficient performance in reducing the vibration energy. The vibration energy produces noise (impact sound), which is transmitted from the rocker-panel molding through a rocker panel to the body, resulting in noise in the space of the car through pneumatic transmission.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a damping resin composition which exhibits excellent damping properties and high mechanical strength in a low to ambient temperature range.
Another object of the present invention is to provide a rocker-panel molding which can suppress transmission of noise generated by collision of foreign matter against it into the space of the car without impairing its own function.
The present invention provides a damping resin composition comprising 100 parts by weight of a polymer blend of (A) 40 to 70% by weight of a polypropylene resin and (B) 30 to 60% by weight of a thermoplastic elastomer and 5 to 60 parts by weight of an inorganic filler, the thermoplastic elastomer (B) comprising (B1) at least one member selected from the group consisting of an elastomer having a glass transition temperature (hereinafter abbreviated as Tg) of 0° C. to 20° C. (hereinafter referred to as elastomer B11) and an elastomer having a Tg of −20° C. to 0° C. (hereinafter referred to as elastomer B12) and (B2) an ethylene-&agr;-olefin copolymer.
What is to be noted in the present invention is as follows: A damping resin composition contains: a polymer blend comprising (A) a polypropylene resin and (B) a specific thermoplastic elastomer; and an inorganic filler at a specific mixing ratio and that the thermoplastic elastomer (B) comprises (B1) an elastomer having a specific Tg and (B2) an ethylene-&agr;-olefin copolymer.
The polypropylene resin (A) which can be used in the present invention is preferably a crystalline polypropylene resin, including a general polypropylene resin and a modified polypropylene resin.
The general polypropylene resin includes a propylene homopolymer, a propylene-ethylene random copolymer (ethylene content: 20% by weight or less), a propylene-ethylene block copolymer (ethylene content: 20% by weight or less), and a mixture thereof. The modified polypropylene resin is a resin obtained by modifying a polypropylene resin with an unsaturated carboxylic acid or a derivative thereof in the presence of an organic peroxide.
It is preferable to use, as the crystalline polypropylene resin, a mixture of the general polypropylene resin and the modified polypropylene resin. In this case, the modified polypropylene resin is preferably used in a proportion of 1 to 20% by weight based on the total polymer blend. It is preferred for the crystalline polypropylene resin to have a melt flow index of 5 to 100. If the melt flow index is less than 5, the resin composition tends to have poor molding properties to provide molded articles with poor appearance. If it exceeds 100, the molded articles tend to have reduced impact strength.
The resin matrix (polymer blend) of the composition according to the present invention comprises 40 to 70% by weight of the polypropylene resin (A) and 30 to 60% by weight of the thermoplastic elastomer (B) hereinafter described in detail. If the proportion of the polypropylene resin is less than 40% by weight, mechanical strength is lessened. If it exceeds 70% by weight, the damping properties are reduced. If the proportion of the thermoplastic elastomer is less than 30% by weight, the damping properties are reduced. If it exceeds 60% by weight, mechanical strength is reduced.
The inorganic filler is added in an amount of 5 to 60 parts by weight per 100 parts by weight of the polymer blend. If its proportion is less than 5 parts by weight, the resin composition has insufficient mechanical strength. If it is more than 60 parts by weight, the damping properties and impact resistance are reduced.
The inorganic filler which can be used in the present invention includes talc, mica, clay, silica, alumina, calcium carbonate, magnesium carbonate, zinc oxide, titanium oxide, calcium oxide, magnesium oxide, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, calcium sulfate, barium sulfate, basic magnesium sulfate, calcium silicate, glass, potassium titanate, and aluminum borate. These inorganic fillers can be in the form of fiber, whisker, flake or powder.
The thermoplastic elastomer (B) comprises an elastomer (B1) having a specific Tg and an ethylene-&agr;-olefin copolymer (B2)
The ethylene-&agr;-olefin copolymer (B2) includes ethylene-propylene rubber (EPM), ethylene-butadiene rubber (EBM), and ethylene-octene rubber (EOM).
The elastomer (B1) having a specific Tg is an elastomer B11 having a Tg of 0° C. to 20° C., an elastomer B12 having a Tg of −20° C. to 0° C. or a mixture of the
Furusawa Yasuhide
Koizumi Junji
Komori Takahiro
Mizutani Haruyasu
Nakagawa Hiroyuki
Mulcahy Peter D.
Posz & Bethards, PLC
Toyoda Gosei Co,., Ltd.
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