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
1998-12-21
2001-01-23
Cain, Edward J. (Department: 1714)
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...
C524S528000, C524S529000, C524S536000, C524S505000, C524S425000, C525S240000
Reexamination Certificate
active
06177502
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an injection molding composition using a propylene block copolymer used in an injection-molded article having high matte feel, a method of producing an injection-molded article thereof, and a matted injection-molded article.
2. Description of the Related Art
A principal method of producing principal interior automotive parts includes, for example, powder slush molding method, vacuum molding method and injection molding method. With the view of enhancing the quality, a powder flush molding method capable of producing parts having high matte feel has hitherto been used in the production of interior materials for high-grade automobile. However, with the view of reducing the cost, it has been increased to use injection-molded articles as parts such as glove rid, meter food and center console in the vicinity of the instrument panel.
However, an injection-molded article of the prior art has gloss better by far than that of a powder slush-molded article, thereby to cause a problem of a difference in gloss between it and the instrument panel made by the powder slush molding method. It has been known that a factor for deciding the gloss of the molded article is surface reflection caused by fine irregularity in the order of &mgr;m on the surface of the molded article and the molded article is matted when this fine irregularity increases. Therefore, a technique capable of forming or providing fine irregularity on the surface of the molded article in the order of &mgr;m is required. In the case of a polypropylene resin which occupies half or more of the amount of the resin used in automotive parts at present, use of which being increased, plate-shaped fine talc particles are used for matting. However, the molded article is not sufficiently roughened only by blending fine talc particles and, therefore, sufficient matte effect is not obtained at present.
Furthermore, a method of matting a molded article by transferring fine roughness on the surface of a mold used in the case of injection molding onto the surface of the molded article is used (Japanese Laid-Open Patent Publication No. 3-87213). However, the molded article is not sufficiently roughened and the same matting as that of the powder slush molding method has never been attained.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an injection molding composition which has the same gloss as that of the molded article obtained by the powder slush molding method, that is, high matte feel, and which can satisfy mechanical characteristics such as processability on injection molding, rigidity and impact resistance, and heat resistance, a method of producing an injection-molded article thereof, and a matted injection-molded article.
The present inventors have intensively studied to solve the above problems. As a result, they have found that, when an injection molding composition including a propylene-ethylene copolymer composition having a melt flow rate, a molecular weight distribution, a content of a crystalline polymer and a content of a non-crystalline polymer, each of them being within a specific range, and inorganic particles in a specific proportion is molded by using a mold having fine surface roughness, an injection-molded article having both high matte feel and good mechanical characteristics and good heat resistance can be obtained by an effective operation such as (1) island like dispersed phase in the copolymer, (2) contained inorganic particles and (3) roughening of the surface caused by transfer of the surface configuration of a mold. Thus, the present invention has been completed.
The injection molding composition according to the present invention preferably includes: 100 parts by weight of a propylene-ethylene copolymer containing a crystalline portion and a non-crystalline portion; and 17 to 33 parts by weight of inorganic particles capable of imparting at least one of rigidity and heat resistance to the propylene-ethylene copolymer. The propylene-ethylene copolymer has a melt flow rate of 15 to 50 g/10 min and a molecular weight distribution (Mw/Mn) of not less than 5. The molecular weight distribution (Mw/Mn) is defined as a ratio of a weight average molecular weight (Mw) to a number average molecular weight (Mn). The crystalline portion contains a crystalline propylene polymer and a crystalline ethylene polymer, the non-crystalline portion contains a non-crystalline propylene-ethylene copolymer. The crystalline ethylene polymer and the non-crystalline propylene-ethylene copolymer have a total amount ranging from 10 to 20% by weight.
The propylene-ethylene copolymer preferably includes a component soluble in n-decane and a component insoluble in n-decane in the fractional thermal dissolution using n-decane. The component insoluble in n-decane is the crystalline portion composed of the crystalline propylene polymer and the crystalline ethylene polymer. On the other hand component soluble in n-decane is the non-crystalline propylene-ethylene copolymer. A molecular weight distribution (Mw/Mn) of the crystalline portion may be within a range from 5 to 7. The content of the crystalline ethylene polymer contained in the crystalline portion may be in the proportion of 2 to 5% by weight based on the propylene-ethylene copolymer, and the content of the non-crystalline propylene-ethylene copolymer in the propylene-ethylene copolymer may be in the proportion of 8 to 15% by weight.
The inorganic particles used in the injection molding composition may contain spherical calcium carbonate particles having an average particle diameter of 1.5 to 15 &mgr;m. The inorganic particles may also contain talc. In that case, a blending ratio of calcium carbonate to talc may be within a range from 3:1 to 1:3. The inorganic particles may also be spherical calcium carbonate particles having an average particle diameter of 1.5 to 15 mm.
To further matte the injection molding composition, at least one elastomer capable of forming an island like dispersed phase, selected from an ethylene-propylene copolymer, an ethylene-propylene group terpolymer, an ethylene-butene copolymer and an olefinic thermoplastic elastomer, can be contained together with the non-crystalline propylene-ethylene copolymer in the amount of 2.5 to 30 parts by weight based on 100 parts by weight in which the non-crystalline propylene-ethylene copolymer is removed from the propylene-ethylene copolymer. The elastomer may be an olefinic thermoplastic elastomer wherein the rubber component is an ethylene-propylene terpolymer and the amount of the rubber component in the elastomer can be from 40 to 60% by weight.
The method of producing the injection-molded article according to the present invention preferably includes the steps of: dispersing inorganic particles capable of imparting at least one of rigidity and heat resistance to a propylene-ethylene copolymer having a melt flow rate of 15 to 50 g/10 min. and a molecular weight distribution Mw/Mn) of not less than 5 in the propylene-ethylene copolymer with melting and therby forming a dispersion; injecting the dispersion into a mold having fine surface roughness wherein a pitch of a cross sectional shape is from 16 to 20 &mgr;m and a depth is from 2.0 to 3.0 &mgr;m; and solidifying the dispersion under a fixed pressure, thereby to impart surface roughness smaller than that of the fine surface roughness.
The matted injection-molded article according to the present invention includes: the propylene-ethylene copolymer having the melt flow rate of 15 to 50 g/10 min. and the molecular weight distribution (Mw/Mn) of not less than 5 as a matrix; and inorganic particles having the particle diameter of 3 to 15 &mgr;m in the matrix in the amount of 10 to 20 parts by weight based on 100 parts by weight of the matrix. The matted injection-molded article is imparted an island like dispersed phase formed by the crystalline ethylene polymer and the non-crystalline propylene-ethylene copolymer contained in the propylene-ethylene copolymer.
Adachi Daisaburo
Hara Masao
Matsuda Yushi
Nakata Tetsuya
Ohsugi Masakatsu
Cain Edward J.
Mazda Motor Corporation
Nixon & Peabody LLP
Studebaker Donald R.
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