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
2002-05-30
2004-04-06
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S217000, C525S221000, C525S222000, C525S232000, C525S238000, C525S240000, C525S241000
Reexamination Certificate
active
06716923
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to an olefin resin composition for powder molding, and more particularly to a resin composition for powder molding that is improved in terms of powder flowability and moldability.
BACKGROUND ART
Skin materials for automotive interior parts such as instrument panels, console boxes, door trims and glove boxes have so far been substantially molded of vinyl chloride-based resin materials. In consideration of recent environmental problems, however, there is growing demand for parts molded of easy-to-recycle olefin resin materials classified as non-halogen type resins.
Numerous olefin resin compositions have thus been put forward as powder-molding materials (for instance, Japanese Patent Application Laid-open (A) Nos. 7-178742, 6-226763, 8-217927, 6-170871, 5-1183 and 5-5050). However, these compositions are so poor in powder flowabillty that particles are susceptible to agglomeration, often resulting in products having thickness variations, deficiencies, and pinholes.
To solve such poor-flowability problems with these powder-molding olefin resin composition, the deposition of inorganic dusting agents such as finely divided talc, calcium carbonate, calcium silicate and aerosol onto the surfaces of resin particles has generally been relied upon. However, the presence of the inorganic dusting agent on the surfaces of resin particles gives rise to an increase in the resin surface's melting viscosity, which in turn results in the need of carrying out molding at considerably high temperatures for considerably long periods of time. This eventually makes moldability worse.
JP-A 6-106553 comes up with a process wherein finely divided resin powders having an average particle diameter of up to 30 &mgr;m such as those based on polypropylene resins, polyethylene resins and vinyl resins are used as dusting agents for thermoplastic elastomers comprising ethylene &agr;-olefin copolymer rubber and olefin resins. However, since these components have a glass transition temperature that is lower than room temperature, the temperature of the resin composition rises locally upon repeated powder molding cycles and so the particles are likely to agglomerate. As a consequence, the flowability of powders drops, often resulting in sheet moldings having thickness variations, and pinholes. After long-term storage, the flowability of such resin compositions becomes extremely worse, ending up with a drop of powder moldability.
DISCLOSURE OF THE INVENTION
Situations being like this, an object of the present invention is to provide an olefin resin composition that ensures improved powder flowability and long-term storability, and has moldability so improved that even upon powder sintering and molding, there is no need of elevating molding temperature and extending molding time or there is no moldability-disturbing factor.
The inventors have now found that the aforesaid object is achieved by the incorporation into an olefin resin of a non-halogen type thermoplastic resin having a specific glass transition temperature and a specific particle diameter and shape. On the basis of such findings, the present invention has now been accomplished.
More specifically, the present invention provides an olefin resin composition for powder molding, comprising (A) 100 parts by weight of an olefin resin having a glass transition temperature of up to 25° C. and (B) 0.5 to 30 parts by weight of a non-halogen type thermoplastic resin having a glass transition temperature in the range of 60 to 200° C. an average primary particle diameter in the range of 0.1 to 10 &mgr;m and a sphericity in the range of 0.8 to 1.0.
The olefin resin composition for powder molding according to the present invention is excellent in powder flowability and long-term storability, and is improved in terms of powder moldability as well.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is now explained at great length.
The olefin resin (A) used herein includes a homopolymer or copolymer of olefin monomers having 2 to 10 carbon atoms such as ethylene, propylene and 1-butene, and a copolymer of at least 50% by weight of one or two or more such monomers and other monomers copolymerizable therewith. The olefin resin (A) should have a glass transition temperature (Tg) of up to 25° C., and preferably up to 20° C. When the Tg of component (A) is too high, high temperature is needed to mold powders. In addition, the resulting molded product has limited use, because it is hard, and cannot be released out of the mold unless its configuration is simple. It is noted that Tg may be determined by means of a differential calorimeter.
Typical examples of such an olefin resin (A) are ethylene resin and propylene resins.
The ethylene resins include high density polyethylene, medium density polyethylene, low density polyethylene and linear low density polyethylene as well as ethylene copolymers containing at least 50% by weight of ethylene such as ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-1-butene copolymers, ethylene-1-hexene copolymers, ethylene-1-heptene copolymers, ethylene-1-octene copolymers (EOR), ethylene-4-methyl-1-pentene copolymers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid alkyl ester copolymers, ethylene-methacrylic acid copolymers and ethylene-methacrylic acid alkyl ester copolymers. The preferred ethylene resins are linear low density polyethylene, ethylene-1-butene copolymers, ethylene-1-hexene copolymers, ethylene-1-heptene copolymers and ethylene-1-octene copolymers (EOR).
Exemplary propylene resins are propylene homo-polymers and copolymers of at least 50% by weight of propylene and other &agr;-olefins. The &agr;-olefins used herein, for instance, are ethylene, 1-butene, 4-methyl-1-pentene and 1-octene. It is noted that the copolymers of propylene and &agr;-olefins include random copolymers, alternating copolymers and block copolymers, and may be produced by any desired production processes.
According to the present invention, the olefin resin (A) also includes an aromatic thermoplastic elastomer exemplified by styrene-butadiene-styrene block copolymers (SBS) and styrene-isoprene-styrene block copolymers (SIS) as well as their hydrogenated products (SEBS, SEPS).
According to the present invention, the aforesaid olefin resins (A) may be used alone or in combination of two or more.
Referring to the properties of the olefin resins (A) used herein, they should have a melt flow rate of at least 5 g/10 min., and preferably at least 20 g/10 min. (MFR: as measured according to JIS K 7210 and at 230° C. under 2.16 Kg load for resins having a melting point of 160° C. or higher and at 190° C. under 2.16 Kg load for resins having a melting point of less than 160° C.). With resins having an excessively low MFR, viscosity sintering becomes difficult and the resulting molded product is likely to have defects such as pinholes.
The non-halogen type thermoplastic resin (B) used herein is a polymer in which any halogen type compound is not used as a monomer, and has a glass transition temperature (Tg) in the range of 60 to 200° C., and preferably in the range of 80 to 130° C. At an excessively low Tg, the flowability of powders tends to become worse in the process wherein molding temperature rises. At an excessively high Tg, to the contrary, the melting properties of powders may possibly degrade upon molding.
The non-halogen type thermoplastic resin (B) has an average primary particle diameter in the range of 0.1 to 10 &mgr;m, and preferably 0.5 to 5 &mgr;m. When the average primary particle diameter is excessively small, the powder flowability of the present composition tends to dwindle with time in the case where the amount of the thermoplastic resin (B) added is relatively small. Where the thermoplastic resin (B) added is large, the resulting molded product is likely to have defects such as color variations. On the other hand, when the average primary particle diameter is excessively large, the thermoplastic resin (B) h
Ogiwara Manabu
Yada Seiki
Dinsmore & Shohl LLP
Nutter Nathan M.
Zeon Kasei Co. , Ltd.
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