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
2000-09-20
2002-02-05
Yoon, Tae H. (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...
C525S330200, C525S331700, C525S385000
Reexamination Certificate
active
06344525
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermoplastic resin composition and more particularly, to a thermoplastic resin composition that exhibits excellent scratch resistance, heat resistance, weather resistance, scratch resistance, vacuum formability and impact strength at low temperature thus suitable for the fabrication of interior sheathing of an automobile.
BACKGROUND OF THE INVENTION
For many years, polyvinyl chloride (PVC) resins had been widely used in the fabrication of interior sheathing of an automobile; however, PVC resins are now known to have a few serious drawbacks such as the difficulty in recycling, generation of environmental hormones upon incineration and also a so-called fogging phenomenon induced by a platicizer introduced to said PVC with a view to providing a soft surface texture, wherein said plasticizer volatizes out of the interior parts of an automobile and eventually dews on the interior window of an automobile, and therefore there has been an urgent request to find a substitute material which can remedy said drawbacks present in PVC.
One of the strong candidate materials to substitute said PVC is thermoplastic polyolefin (TPO) material mainly comprising polypropylene and ethylene propylene rubber, and numerous companies have been exerting their efforts to develop a substitute material using TPO.
For example, Korean Patent No. 199283 disclosed a thermoplastic cross-linking elastomer mainly blended with polypropylene and cross-linked ethylene-propylene-diene rubber (EPDM) wherein said elastomer was used as a material for the outer layer of door panel of an automobile, and the Montell Company is attempting a thermoplastic polyolefin mainly composing of polypropylene and non-cross-linked ethylene propylene rubber as a PVC substitute for the same purpose.
U.S. Pat. No. 4,785,045 disclosed a thermoplastic cross-linking elastomer that used peroxide as a cross-linking agent for the skin material of door panel of an automobile.
The thermoplastic polyolefin materials are in general characterized by having a low density and a rather inexpensive cost of materials as well as excellent film formability thus providing an easier sheet production by extrusion forming or calendering forming. However, said thermoplastic polyolefins have a low melt strength to cause the deterioration of vacuum formability thus being inappropriate as such a material as an instrument panel of an automobile having deep drawing. Moreover, the low temperature range in vacuum forming of thermoplastic polyolefins makes it hard to finalize the optimal forming conditions and the inferior maintaining capacity of embossing attributes to the inapplicability to the fabrication of interior sheathing of an automobile.
In an effort to remedy said drawbacks of thermoplastic polyolefin materials, Du Pont Company attempted to improve the vacuum formability by enhancing both the melt strength and embossing maintaining capacity by adding an ionomer as a modifier to a polyolefin blend as disclosed in U.S. Pat. Nos. 5,206,294, 4,968,752 and 4,871,810. The new modified thermoplastic polyolefin materials by Du Pont Company are shown to have improved impact resistance at low temperature, scratch resistance, melt strength and vacuum formability; as a result, the new thermoplastic polyolefin materials are now expanding their applications to molded products such as an instrument panel of an automobile, which requires a high deep drawing.
Being adherent to metals, the ionomer resins are only applicable to extrusion sheet forming and are not applicable to calendering sheet forming. Further, the melt strength and the formability of said ionomer resins, although shown to be improved as compared with the conventional thermoplastic polyolefins, are still inferior to those of PVC.
SUMMARY OF THE INVENTION
The present invention has been completed by providing thermoplastic polyolefins, which is composed of polypropylene and ethylene-propylene-diene rubber, alloyed with low density polyethylene or polyethylene copolymer.
The object of the present invention is to provide a thermoplastic resin composition having excellent impact resistance at low temperature, heat resistance, weather resistance, scratch resistance, and vacuum formability, thus suitable for the fabrication of interior sheathing of an automobile.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
A thermoplastic resin composition in accordance with the present invention comprises (A) 5-45 parts by weight of polypropylene resin, (B) 10-50 parts by weight of ethylene-propylene-diene rubber, (C) 5-25 parts by weight of an ethylene copolymer, (D) 15-45 parts by weight of an ionomer, (E) 2-10 parts by weight of phenol cross-linking agent and 3-15 parts by weight of a cross-linking accelerator per 100 parts by weight of the (B), and (F) 3-15 parts by weight of epoxy polymer based on 100 parts by weight of the (D), wherein (A+B) is 30-40 parts by weight and (C+D) is 20-70 parts by weight.
The present invention is described in detail hereunder.
The outer layer for the interior of an automobile in accordance with the present invention is prepared by alloying a thermoplastic polyolefin material, which is composed of polypropylene and ethylene-propylene-diene rubber, with a low density polyethylene or polyethylene copolymer.
(A) Polypropylene Resin
The examples of polypropylene resins used in the present invention are homo polypropylene, block or random copolymer of ethylene propylene, and they are used in the range of 5-45 parts by weight. The melt index thereof is in the range of 0.1-2 dg/min.
The amount of said polypropylene used in this invention can vary depending on the mechanical properties and surface hardness of the interior parts required. In order to maximize the melt strength of the final product, the amount of said polypropylene should be restricted to a minimum level while the amount of the ethylene copolymer be increased. If the amount of polypropylene is used more than the above range, the mechanical properties such as tensile strength and surface hardness are increased; however, the impact strength becomes decreased and both the vacuum formability and the calendering sheet formability become deteriorated.
(B) Ethylene-propylene-diene Rubber.
If the ethylene-propylene-diene rubber is cross-linked with the polypropylene resin mentioned above, heat resistance, weather resistance, sheet formability and embossing maintaining capacities are improved.
When peroxide is used as a cross-linking agent, the polypropylene becomes decomposed so that the mechanical properties of the alloy are deterioarted and subsequently the copolymer of either polyethylene or ethylene will participate in cross-inking thus the overall cross-linking cannot be under control.
On the contrary, when phenols or quinones are used as cross-linking agent, it will affect neither the decomposition nor the cross-linking reaction and will only have an influence on the ethylene-propylene-diene rubber; therefore, the methylol based phenol resin is preferred to be mainly used for the cross-linking of the ethylene-propylene-diene rubber in the present invention.
Examples of cross-linking accelerators are tin(II) chloride, zinc oxide, magnesium oxide, stearic acid or their mixture, and they can be used to control the rate of the cross-linking reaction and the degree of cross-linking.
In cross-linking, it is very crucial that blends are to be dynamically cross-linked under high shear stress upon mixing so that the size of the cross-linked rubber should be minutely distributed not to deteriorate the formability of said blends.
The cross-linked ethylene-propylene-diene rubber in the present invention is located as a domain that is minutely distributed within the matrix formed by the thermoplastic material composed of polypropylene, ethylene copolymer or its mixture, thus retaining its thermoplastic properties.
The ethylene-propylene-diene rubber in the present invention is excellent in ozone resistance and weather resistance, well miscible with the p
Hwang Min Jae
Jeong Kie Youn
Lee Tae Seung
Lim Byung Yun
Hyundai Motor Company
Yoon Tae H.
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