Polypropylene resin composition

Details Polypropylene resin composition Polypropylene resin composition

2002-12-30

2004-08-17

Cheung, William (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...

C524S425000, C524S426000, C524S427000, C524S562000, C524S570000, C524S847000, C524S445000, C524S451000, C524S495000, C524S496000, C524S491000, C524S477000, C524S490000, C525S191000, C525S216000, C525S232000, C525S240000, C525S241000

Reexamination Certificate

active

06777476

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a polypropylene resin composition for automobile interior materials, and more particularly, to a polypropylene resin composition comprising crystalline polypropylene, rubber, inorganic filler, atactic polypropylene, and process oil, wherein the composition has good flexibility, heat-resistance, cold-resistance, extrusion coating property and calender processing property as well as no offensive odor. The present invention also relates to a mat made thereof, particularly an automobile mats wherein the polypropylene resin composition forms the back coating material.
BACKGROUND OF THE INVENTION
At present, polyvinyl chloride (PVC) compositions are widely used as automobile interior materials—including surface materials such as an instrument panel, a door trim and a sun visor and automobile interior mat back coat—because it has a wide mechanical property range and can be processed in various forms at a reasonable cost. However, PVC-based formulations require addition of large amount of plasticizer, which in the confines of an automobile give off offensive odor, and also requires a heat stabilizer, which presents environmental concerns relating to heavy metals contained in the heat stabilizer.
Generally, the automobile interior automobile mat consists of three layers. In prior art mats the top layer is mostly made of the nylon fiber; the intermediate layer comprises polyethylene terephthalate and polyvinyl acetate copolymer; and the bottom layer, that is the back coat, is made of aforementioned polyvinyl chloride or styrene-butadiene-styrene (SBS) copolymer. This three-layered mat is formed by extrusion or calendering molding and then cut by the press and tailored to generate a finished product.
The odor of a mat can substantially detract from the quality and ambiance of automobiles. Polyvinyl chloride, commonly used for the bottom layer of the automobile mat, requires the flexibility of rubber to be used as the back coat. This flexibility is typically achieved by compounding the PVC with large quantities of plasticizers. However, an offensive odor caused by the plasticizer cannot be avoided because the plasticizers are odiferous and a large amount of plasticizer is used to obtain the flexibility.
Also, polyvinyl chloride has poor heat-resistance and cold-resistance when used in an automobile, for example as a floor mat. Automobiles experience extremes in heat in the summer and also can reach the coldest temperatures the automobile experienced during the winter, and the floor mat is stressed in both of these environments. Also, automobile mats are washed frequently. PVC-based automobile mats will be weakened and fail, i.e., crack or lose adhesion, in the cold of winter season or in the heat of tropical regions. Heat stabilizers can be used to improve its heat-resistance of the PVC composition, but these heat stabilizers contain a large amount of undesirable heavy metals. Therefore, polyvinyl chloride-based compositions are not environmentally friendly.
Also in the prior art a styrene-butadiene-styrene copolymer formulation has been used to form the back-coat of an automobile mat. Compared with polyvinyl chloride, styrene-butadiene-styrene copolymer has better flexibility, heat-resistance and cold-resistance. But, styrene-butadiene-styrene copolymer formulations also give out an offensive odor and less than ideal moldability.
Another alternative material tried by industry is the use of olefinic thermoplastic. Although the olefinic thermoplastic resins have good injection, extrusion and blow moldability, a large amount of rubber must be admixed with the olefinic thermoplastic resins to obtain the flexibility required for the back coat of automobile mats. The use of a large amount of rubber causes the viscosity problems during extrusion coating and calendering molding, and also gives negative effect on the heat-resistance of the finished product. Also, the use of a large amount of expensive rubber increases the production cost.
Polypropylene is an inexpensive polyolefin. However, polypropylene does not readily make a composition with the required hardness. A polypropylene-based composition having a rubber to polypropylene ratio of 90 wt %:10 wt % does not exhibit the required low hardness level. And, the high rubber content as mentioned above causes cohesion to the roll during extrusion coating and reduces heat-resistance. Although inorganic fillers can be used to address the moldability and heat-resistance problems, these increase the hardness of the blend so that the flexibility required for the back coat cannot be obtained. Additionally, the composition with the required rubber is not economical compared with polyvinyl chloride-based compositions.
As used herein, the term “automobile” is meant to encompass motorized vehicles, including for example trucks, buses, and the like. As used herein, the term “mat” is meant to encompass a material placed on or over a floor. As used herein, the term “back coat” means a layer, which may or may not be continuous, below the top of a mat.
The units for composition and properties are as is usually known in the art, unless otherwise defined here. As used herein, polymeric compositions are characterized by the parts by weight of reactants that are put into the polymeric composition, wherein the number of parts is typically around 100, and is usually 100. Therefore, the term “parts” is generally synonymous with the term “percent by weight”. It is recognized that one or more of the ingredients may lose its identity or may be lost during the processing and/or during subsequent aging of the polymeric product, for example by partially reacting with other components or by losing semivolatile materials. The properties of the composition are generally measured on the composition after mixing and curing.
SUMMARY OF THE INVENTION
As mentioned above, there has been a long-standing recognized need in the industry for the development of materials for automobile interiors, especially with respect to this invention for a material useful for automobile mat back coats. It is desirable to have the back coat of automobile mats made of a material that:
1) has a low hardness as to offer the flexibility to the back coat, for example less than 50A (Shore A hardness), preferably less than 40A, for example between about 30A and 40A, to offer good adhesion to the floor and to prevent deformation;
2) has good extrusion coating and calendering properties, known collectively herein as moldability;
3) has good heat-resistance and good low-temperature impact resistance over the temperature range which may be experienced by a significant number of automobiles;
4) has low emissions of volatile and semivolatile compounds, especially odiferous compounds, as compared to prior art alternative materials; and
5) that is cost effective with the materials in the prior art alternatives.
It is advantageous that the rubber content of the material be lower than about 70 wt %, preferably lower than about 50%, for example between about 35% and about 50%. It is advantageous that the hardness is lower than 50 A, preferably lower than 45A, more preferably lower than about 40A, for example between about 30A and about 40A. It is advantageous that the material have a good fogging value, that is, emits little material that forms a fog-like film on for example a glass.
Accordingly, one embodiment of the invention is a polypropylene composition, and an automobile mat comprising a layer thereof, the composition comprising atactic polypropylene, rubber, fillers, for example one or more inorganic fillers, and process oil. This composition has the mentioned properties required for automobile mat back coats and can be processed by various molding methods.
Accordingly another embodiment of the invention is a resin composition, and an automobile mat comprising a layer thereof, said resin composition comprising: crystalline polypropylene in an amount sufficient to obtain enhanced moldability; atactic polypropylene in an amount sufficient to reduce hardness

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