Wear resistant resin composition

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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C524S432000, C524S449000, C524S515000, C524S493000, C524S494000, C260S001000, C264S211230, C428S500000, C428S515000

Reexamination Certificate

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06664321

ABSTRACT:

DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a novel wear resistant resin composition. More specifically, it relates to a wear resistant resin composition which is excellent in wear resistance and heat resistance, has rubber-like physical properties with good balance between compressive stress and compressive stress relaxation, and can be re-molded.
Out of thermoplastic resins, polyolefin resins are excellent particularly in chemical resistance, insulating properties, heat stability and the like and therefore widely used as raw materials for molding various products.
Out of such polyolefin resins, thermoplastic polyolefin resins having rubber-like properties are used for various purposes that require flexibility, such as interior and exterior parts for an auto-movil, materials for covering rod-like and linear products which are extrusion molded at a high speed, and further mud guards and desk mats.
For the above applications, an inorganic filler is blended into a polyolefin to improve the mechanical strength of the obtained molded product or provide flame retardancy to the molded product.
However, the above polyolefin has such a problem that its wear resistance is lowered by blending the inorganic filler. Particularly when the flexural modulus of the obtained molded product is 2,000 MPa or less, there is seen a strong tendency that a contact portion of the molded product wears away through repetitions of its sliding contact with the same molded product or another member.
To improve the wear resistance of a molded product of a polyolefin containing an inorganic filler, JP-A 2-53846 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and U.S. Pat. No. 5,418,272 have proposed a resin composition which comprises a polyolefin-based resin, a thermoplastic elastomer having an organic acid group bonded by acid modification and an inorganic filler (inorganic flame retardant).
The above polyolefin-based resin is a copolymer or rubber essentially composed of ethylene.
The above acid modification technology is aimed to improve the adhesion of the composition to the inorganic filler by bonding the organic acid group to the polyolefin or to improve wear resistance by partly crosslinking the inorganic filler with a metal.
However, a composition obtained by adding an ethylene-based resin to the above polyolefin to achieve flexibility is still unsatisfactory in terms of heat resistance.
When a resin having a high melting point such as polypropylene is used as a matrix resin, a large amount of a soft resin such as the above ethylene-based resin or rubber material must be added to achieve flexibility. The obtained composition has low heat resistance and further low mechanical properties such as tensile strength like the above composition.
It is an object of the present invention to provide a wear resistant resin composition which is a polyolefin composition containing an inorganic filler and excellent in wear resistance, rubber-like physical properties and heat resistance, and can be re-molded.
Other objects and advantages of the present invention will be apparent from the following description.
According to the present invention, the above objects and advantages of the present invention are attained by a wear resistant resin composition comprising: (A) 100 parts by weight of a modified microblend obtained by bonding an organic acid group to a microblend (may be referred to as “specific microblend” hereinafter) consisting of 1 to 70 wt % of polypropylene and 99 to 30 wt % of a propylene-ethylene random copolymer (may be referred to as “P-E random copolymer” hereinafter) consisting of 15 to 50 mol % of an ethylene polymer unit and 85 to 50 mol % of a propylene polymer unit, or a mixture of the microblend and the modified microblend, the concentration of the organic acid group in the modified microblend or the mixture being 0.01 to 1 mmol based on 1 g of the microblend, and the microblend containing 10 to 90 wt % of a component eluting at a temperature of −40 to +30° C. (may be referred to as “low-temperature eluting component” hereinafter) based on the total of all the eluting components fractionated by temperature rise elution fractionation using o-dibromobenzene as a solvent; and
(B) 1 to 1,000 parts by weight of at least one filler selected from the group consisting of a fibrous filler and a lamellar filler,
and having a flexural modulus of 2,000 MPa or less.
According to the present invention, there is also provided a wear resistant resin composition having more improved heat resistance by further blending polypropylene as a resin composition.
In the present invention, the flexural modulus is a value measured in accordance with JIS K7203.
The temperature rising elution fractionation used in the present invention is a means of analyzing the composition or the distribution of stereoregularity or non-crystallinity of a crystalline polymer such as a polyolefin and carried out by the following operation. A high-temperature solution of the specific microblend is first introduced into a column filled with a filler such as diatomaceous earth or glass beads, and components having higher melting points are crystallized one after another on the surface of the filler by gradually reducing the temperature of the column. Thereafter, components having lower melting points are eluted and dispensed one after another by gradually increasing the temperature of the column. In the present invention, the rate of reducing the temperature of the column in the above measurement is 2° C./hr. The rate of increasing the temperature of the column is 4° C./hr.
As for the concrete operation, please refer to the Journal of Applied Polymer Science; Applied Polymer Symposium, 45, 1-24 (1990). In the fractionation of a copolymer composition by the above method, a resin composition having no crystallinity or extremely low crystallinity is fractionated at a relatively low temperature lower than normal temperature and components having higher crystallinity are fractionated along with a rise in elution temperature. The amount of each fractionated component can be calculated from an elution curve drawn by plotting elution temperature as the axis of abscissa and integrated weight percentage as the axis of ordinate.
In the present invention, it is important that the specific microblend should satisfy the following conditions at the same time.
(1) The amount of a component eluting at a temperature of −40 to +30° C. is 10 to 90 wt %, preferably 30 to 80 wt % based on the total of all the eluting components fractionated by temperature rising elution fractionation using an o-dibromobenzene solvent.
(2) The specific microblend consists of 1 to 70 wt %, preferably 1 to 40 wt % of polypropylene and 99 to 30 wt %, preferably 99 to 60 wt % of a propylene-ethylene random copolymer which consists of 15 to 50 mol %, preferably 15 to 40 mol % of an ethylene polymer unit and 85 to 50 mol %, preferably 85 to 60 mol % of a propylene polymer unit.
That is, the above specific microblend is characterized in that a sufficiently large amount of a low-temperature eluting component is contained although the content of the propylene polymer unit in the P-E random copolymer is large. Due to this feature, the obtained wear resistant resin composition exhibits excellent wear resistance and rubber-like physical properties and exhibits superior in heat resistance to a conventional wear resistant resin composition comprising a polyolefin essentially composed of an ethylene polymer unit. Due to use of the above specific microblend, the wear resistant resin composition of the present invention is also excellent in physical properties such as tensile strength.
When the low-temperature eluting component of the above specific microblend is contained in an amount of less than 10 wt %, flexibility lowers as a large amount of a crystal component is contained in the resin, thereby making it difficult to obtain a resin composition having a flexural modulus of 2,000 MPa or less which t

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