Polyolefin-based composite resin composition having low...

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

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C524S451000, C524S449000, C524S425000, C524S447000, C524S452000, C524S494000, C524S536000, C525S240000

Reexamination Certificate

active

06569935

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application is based on application No 99-66381 filed in the Korean Industrial Property Office on Dec. 30, 1999, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a polyolefin based composite resin composition having a low coefficient of linear thermal expansion, more particularly to a polyolefin-based composite resin composition having a low coefficient of linear thermal expansion which not only exhibits excellent mechanical rigidity, impact resistance, heat resistance, and product flatness, but also has excellent dimensional stability due to its low shrinkage, low coefficient of linear thermal expansion, and low heat sag.
(b) Description of the Related Art
Thermoplastic resins, particularly polyethylene and polypropylene polyolefin-based resins are low in density and inexpensive when compared to other resins, as well as have excellent mechanical properties, processability, etc. These resins are therefore widely used in industries such as in the general purpose plastics, automotive, electronics, and aerospace industries, among others. However, it is difficult to apply polyolefin-based resin to fields requiring special functions due to the property limits of these resins, and this particularly restricts industrial applications since a polypropylene resin with a glass transition temperature of 0° C. has a disadvantage of having low impact strength at low and room temperatures.
Polyolefin-based composite resins, which provide new functions by the blending of heterogeneous resins or the adding of mineral filler, etc. to the resins in order to overcome the above disadvantage, have been developed and are being applied to the various fields in which it was difficult to utilize only a conventional polyolefin-based resin by itself. Examples of the above applications, wherein polyolefin-based resin compositions are widely being used include automobile parts, electronic components, etc. The required properties in these fields are achieved by adding a polypropylene main material, a sort of polyolefin-based resin, ethylene-alpha-olefin copolymer impact reinforcing agents, elastomer, etc., together with a rigidity reinforcing agent inorganic filler. Many compositions have been proposed and are being partially put into practical use by changing the types of the above polypropylene resins and the types and contents of the impact reinforcing agents and rigidity reinforcing agents in order to improve various physical and thermal characteristics.
Generally, a composite resin is a material in which new functions that can not be embodied by the polymer itself are provided by fusing and kneading the primary material of the polymer, fillers, or reinforcing agents with a kneader or an extruder. The types, external aspects, sizes, and contents of the resins, fillers, and reinforcing agents should be selected according to the uses and desired characteristics of the above composite resin in the field of application. As the resin properties are particularly and greatly influenced by the variation of resin processing conditions, the resin processing equipment and processing conditions should be properly selected so that processability, reproducibility, etc. of resin itself can be maintained and the specific properties can be improved by fillers.
Furthermore, the important factors that determine the composite resin characteristics also include the types, contents, etc. of the additives, such as heat resisting stabilizers, weather resisting stabilizers, etc. These are added in order to prevent property deterioration during resin deformation and under the high temperature and pressure environment inside an extruder during the resin processing, or are added to achieve characteristics that are specially required after molding. Interfaces exist among the raw material constituents that have different properties, such as the above polymer, filler, additive, etc. The raw materials, processing equipment, and processing conditions should be carefully selected, taking into account the fact that the composite resin properties are greatly influenced by the interfacial adhesive force at these interfaces.
The resins that are mainly used in the manufacture of a conventional automobile interior and exterior components and electronic components include acrylonitrile-butadiene-styrene copolymer, polycarbonate/acrylonitrile-butadiene-styrene copolymer alloy, polycarbonate/polybutylene terephthalate alloy, polyamide, polyurethane, etc. With the exception of polyamide from among the above resins, the other resins can possibly be replaced with polyolefin-based composite resin when considering aspects of light-weight automobile production, cost reduction, recycling, etc. However, polyamide can not be replaced with polyolefin-based composite resin since there are problems with mechanical properties and thermal characteristics when polyamide is replaced with polyolefin-based composite resin.
In order to replace the above described resins with polyolefin-based composite resins, the polyolefin-based composite resins should have excellent mechanical rigidity, impact resistance, dimensional stability, scratch resistance, etc. It should also have outstanding moldability since component thicknesses, etc. are tending to become thinner due the trend of light-weight automobiles and other components. Furthermore, these polyolefin-based composite resins should require a short molding time in consideration of the aspects of manufacturing expenses and productivity improvements. Finally, coating properties and appearance after the molding of components should be excellent for both coated and non-coated components. Many studies are now in progress on polyolefin-based composite resin compositions in which the above required properties are all satisfied.
Materials having a low contraction rate and a low coefficient of linear thermal expansion are given a great deal of weight in the development of polyolefin-based composite resin compositions which are used in molding large sized components such as automobile components, particularly bumper fascia, door garnish, instrument panels, etc. The properties considered in the raw materials for automobile components include rigidity, tensile strength, elongation, density, heat deflection temperature, coefficient of linear thermal expansion, etc. However, the most important property is the raw material rigidity, which is indicated with flexural modulus and surface hardness. Molded products can be easily bent or sagged when their raw materials do not have sufficient rigidity, since bumper fascia, instrument panels, etc. have a wide surface area compared to their relatively thin thickness. The thickness of molded products has recently tended to becoming thinner in consideration of the aspects of light-weight automobile production and raw material reduction concerns. Due to this trend, the development of raw materials having a higher flexural modulus is required. Furthermore, raw materials having a low coefficient of linear thermal expansion or a low degree of heat sag are required due to needs of the assembling ability and dimensional stability of molded product itself. Additionally, improvements in the flexural modulus are also required.
Generally, plastics have a linear coefficient of expansion that is 4 to 8 times higher when compared to steel, and thus molded products sag or are bent according to weather or temperature variations after assembling the bodyworks. Composite products containing inorganic fillers, which are appropriately added to a basic resin of polypropylene, rubber, etc., have been developed in order to reduce these phenomena. However, it is necessary to harmonize the physical properties of the products by controlling the types and amount of inorganic fillers, since although a product's coefficient of linear thermal expansion is reduced and its flexural modulus is improved, there is still a problem in that the impact strength of such products is

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