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
2000-08-23
2002-05-07
Michl, Paul R. (Department: 1714)
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
active
06384137
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and claims priority under 35 USC §119 on Japanese Patent Application No.: JP236,624/1999, filed on Aug. 24, 1999.
FIELD OF THE INVENTION
The present invention relates to the formation of various molded resin products having varied wall thicknesses. The present invention also relates to a resin composition for making such products in a way that prevents visible imperfections often associated with changes in wall thickness of molded products.
BACKGROUND OF THE INVENTION
Injection molding is a known molding technique for forming a molded product from a resin material. In injection molding, a molten resin is injected from a gate of a mold into a cavity thereof, so as to fill the cavity with the resin. After the resin has cooled, the mold is opened to permit removal of the molded resin product.
FIG.
6
(
a
) illustrates a molded resin product produced by conventional injection molding techniques using conventional molding materials. The molded resin product
9
has a portion
910
with reduced thickness (e.g. a groove). Flashing stripes
914
and
915
(i.e., areas of luster unevenness) have formed in the surface of the product
9
in the areas were the wall thickness changes. In the molded resin product
9
, illustrated in FIG.
6
(
a
), the groove
910
extends generally orthogonal to the direction of resin flow, illustrated by arrow
95
. The flashing stripes
914
and
915
are generated on both sides of the groove
910
.
FIG.
6
(
b
) illustrates another molded resin product
90
produced by conventional injection molding techniques also using conventional molding materials. The molded resin product
90
has a stepwise reduction in wall thickness and a flashing stripe
914
is generated in the surface adjacent the reduction in wall thickness thereof.
The flashing stripes
914
and
915
produced in the molded resin product
9
and the flashing stripe
914
produced in the molded resin product
90
may be produced by residual stresses and negative pressures. The flashing stripes
914
in FIGS.
6
(
a
) and FIG.
6
(
b
) are formed in the area where the wall thickness of the product is reduced. Flow of resin through the mold is choked in this area, which produces residual stresses causing grain gap.
The flashing stripe
915
in FIG.
6
(
a
) is formed in the area where there is an increase in the thickness of the wall of the product
9
. In this area, there is poor flow of resin based on the negative pressure associated with the enlarged wall thickness.
Consequently, there is a need for a resin composition that forms a molded product free of visual imperfections where such products have varying wall thicknesses and where appearance is important.
OBJECTS OF THE INVENTION
It is, therefore, an object of the present invention to produce a molded resin product that is free of visual imperfections.
It is also an object of the present invention to provide a molded resin product having improved visual properties.
It is another object of the present invention to provide a resin composition for use in forming molded products having varying wall thicknesses.
It is another object of the present invention to provide a molded resin product without flashing stripes in areas of changes of wall thickness.
It is another object of the present invention to provide a resin composition containing a delustering agent.
Additional objects and advantages of the invention are set forth, in part, in the description which follows, and, in part, will be apparent to one of ordinary skill in the art from the description and/or practice of the invention.
SUMMARY OF THE INVENTION
In response to the foregoing challenges, applicants have developed an innovative resin composition for forming molded resin products that are substantially free of visual imperfections. The resin composition in accordance with the present invention includes a delustering agent and a blend of components. The resin composition includes 0.01-0.1 part by weight of the delustering agent, and 100 parts by weight of a blend of components. The blend of components includes 30-50% by weight of a polypropylene block copolymer containing 4-20% by weight of ethylene, 0-10% by weight of polyethylene, 5-15% by weight of a propylenelbutene copolymer, and 40-60% by weight of an ethylene/&agr;-olefm copolymer rubber.
In accordance with the present invention, the ethylene/&agr;-olefin copolymer rubber may have a glass transition point of −45° C. or lower. The polyethylene may have a density of not more than 0.95 g/cm
3
. It is also contemplated that the polyethylene content in the resin composition is 0% by weight. The butene content by percentage in the propylene/butene copolymer may vary from 10% to 30% by weight.
The present invention is also directed to a molded resin product. The molded resin product includes at least one thick wall portion, and at least one thinner wall portion. Also, the molded product can have at least one changing thickness portion that extends between thick and thinner wall portions, mentioned above. The molded resin product molded in accordance with the present invention is formed from a resin composition comprising 0.01-0.1 part by weight of a delustering agent and 100 parts by weight of a blend of components. The blend of components may be as noted above and include 30-50% by weight of a polypropylene block copolymer containing 4-20% by weight of ethylene, 0-10% by weight of polyethylene, 5-15% by weight of a propylene/butene copolymer, and 40-60% by weight of an ethylene/&agr;-olefin copolymer rubber.
The molded resin product may be formed by injection molding. However, other methods of forming molded resin products are also to be considered well within the scope of the present invention.
In accordance with the present invention, the thickness of the portion changing in thickness may gradually decrease from the thick wall portion to the thinner wall portion. Similarly, the thickness of the portion that is changing in thickness may gradually increase from the thinner wall portion to the thicker wall portion.
It is also contemplated that the portion changing in thickness may exhibit stepwise thickness changes as well as or in lieu of gradual changes. The portion changing in thickness may have at least one stepwise decrease in thickness between the thick wall portion and the thinner wall portion. Alternatively, the changing in thickness portion may have at least one stepwise increase in thickness between the thinner wall portion and the thicker wall portion.
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Masuya Chisato
Mizutani Haruyasu
Tanaka Yasuaki
Yamamoto Tadashi
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