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
2001-12-26
2003-11-04
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...
C525S240000, C524S425000, C524S447000, C524S449000, C524S451000, C524S452000, C524S492000
Reexamination Certificate
active
06642312
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polyolefin-based composite resin composition having high strength and low linear expansion, and more particularly, to a polyolefin-based composite resin composition having excellent dimensional stability due to low molding shrinkage, low linear thermal expansion coefficient and low heat sag as well as excellent mechanical strength, impact resistance, heat resistance, injection molding plasticity and smoothness of a product.
BACKGROUND OF THE INVENTION
Thermoplastic resins such as polyethylene and polypropylene have relatively low specific gravity, are inexpensive as compared to other resins, and have superior mechanical strength and processability. These resins have been widely applied in industry such as conventional plastic products, automobiles, electronic and aeronautical industry. However, it is difficult to apply the polyolefin-based resins to a field requiring highly specific functions due to the large limitations in properties of the resins themselves. The polypropylene resins in particular are much restricted in their industrial applications because their glass transition temperature is 0° C. and thus the impact strength is very low both at room temperature and a low temperature.
As a way to solve these problems of the polyolefin-based resins, composite polyolefin-based resins with an added function have been prepared wherein different kinds of resins are blended or mineral filler is added to a given resin, thus enabling the composite to be used as parts for automobiles and electronic goods, which has been otherwise seldom possible when conventional polyolefin-based resins are employed.
Polyolefin-based resins are widely used in the above-mentioned case, and the above polyolefin-based resins, for instance, comprise polypropylene, a polyolefin-based resin, as a substrate; an ethylene-&agr;-olefin copolymer or an elastomer as an impact fortifier; and an inorganic filler as a rigidity fortifier. Further, the kinds and the contents of the above additives have been modified in order to produce compositions having improved physical properties as well as thermal properties, and some of them are already placed into practical fields.
In general, a composite resin is a material with a newly added function, which cannot be acquired by the polymer itself, wherein a polymer is used as a substrate and a filler or a fortifier is melt-mixed by using a kneader or an extruder. However, the composite resin has a few disadvantages. First, the kind, property, size and content of a resin, a filler and a fortifier should be adjusted based on the uses and the characteristics of a field to be applied. Second, the processor and the processing conditions of a resin should be properly determined so that the processability and the reproducibility of a resin can be continuously maintained. The specific property of a resin can be improved by the addition of a filler because the physical property of the composite resin is greatly influenced by the change in processing conditions of a resin. Moreover, the kinds and the contents of additives such as stabilizers for heat resistance and for weather resistance, which are added for the purpose of preventing deterioration of a resin due to a modification or aging especially under high temperature and high pressure condition within the extruder during the process of a resin, are also important factors used in determining the properties of a composite resin.
There exists an interface between materials with different properties such as the above-mentioned polymer substrate, a filler and additives. The raw materials, the processor and the processing conditions of a resin should be carefully selected because the property of a composite resin can be greatly influenced by the level of interfacial adhesiveness at a given interface.
The conventional resins that have been used in the manufacture of interior and exterior parts of an automobile include acrylonitrile-butadiene-styrene copolymer, polycarbonate/acrylonitrile-butadiene-styrene copolymer alloy, polycarbonate/polybutylene terephthalate alloy, polyamide, polyurethane, etc. The resins except the polyamide can be used as a polyolefin-based composite resin with respect to light-weight, cost-effectiveness and recycle-ability. However, polyamide can generate problems when used as a polyolefin-based composite resin because of the drawbacks in mechanical and thermal properties and is thus not suitable for a polyolefin-based composite resin.
If the above-mentioned resins are to be used as polyolefin-based composite resins, the resins should have superiorities in mechanical strength, impact resistance, heat resistance, dimensional stability, and scratch resistance. The resins to be substituted by polyolefin-based resins should also have a superior plasticity to comply with the current trend to manufacture light-weight parts and automobiles and the processing time should be also reduced for the improvement of the productivity as well as cost-effectiveness. Moreover, the external appearance and the coating property should be excellent depends on whether it is a coating type or a non-coating type. Intensive studies have been conducted to produce polyolefin-based composite resins that can satisfy all the above-mentioned requirements. In particular, the studies to develop polyolefin-based composite resin compositions are directed to their use as relatively large parts of an automobile such as bumper fascia, door garnish, side sill molding, and instrument panel, and more specifically to those compositions having low shrinkage and low linear thermal expansion coefficient. The essential properties of raw materials to be considered when using them as parts of an automobile are rigidity, tensile strength, elongation, density, heat deflection temperature, linear thermal expansion coefficient, etc. Of these, rigidity is the most critical property for a raw material and it is expressed in terms of flexural modulus and surface hardness. Bumper fascia and instrument panel have relatively large surface area for their relatively low thickness and thus they can be easily bent or sagged when they do not have sufficient rigidity. In fact, the thickness of final products of those parts tend to become thinner due to the effort to reduce the cost of raw materials and the recent trends toward the manufacture of light-weighted automobiles and thus it is required to develop raw materials having higher flexural modulus. In addition, the raw materials are also preferred to have low linear thermal expansion coefficient as well as low heat sag and dimensional stability for the assembly into a given automobile.
The linear thermal expansion coefficient of plastic is generally 4-8 times greater than that of steel and thus the final product becomes sagged or distorted after assembly according to the change in temperature/weather. Therefore, composite products, manufactured by properly adding inorganic filler into a basic resin such as polypropylene or rubber, have been developed in order to solve the above problems. These products containing inorganic filler exhibit a reduced linear thermal expansion coefficient along with an increased flexural modulus. However, the impact strength of the products is low at a low temperature and therefore it is necessary to adjust the kinds and the amount of a selected inorganic filler to be added to harmonize with the overall properties of the final product. Moreover, it is also required to develop a product with low shrinkage to meet the requirements of a product such as easiness in designing a mold to form a product, dimensional stability in coating, and little post-modification of a product.
The conventional composite polyolefin-based resins used in forming parts of an automobile comprise crystalline polypropylene as an active ingredient. The crystalline polypropylene may have ethylene-propylene copolymer (propylene content is 92-95 weight % and ethylene content is 5-8 weight %) characterized by having 7-12 weight % of ethylene-propylene rubber and 20-45
Lee Sung-Jun
Park Bong-Hyun
Hyundai Motor Company
Nutter Nathan M.
Pennie & Edmonds LLP
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