Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Process of treating scrap or waste product containing solid...
Reexamination Certificate
2000-02-22
2002-02-05
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Process of treating scrap or waste product containing solid...
C521S044500, C525S192000, C525S199000
Reexamination Certificate
active
06344493
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a melt tension enhancer for polyolefin resins that contains (A) polytetrafluoroethylene and (B) a polymer based on an alkyl (meth)acrylate of 5-30 carbon atoms, and to a process for its production.
BACKGROUND ART
Polyolefin resins have been widely used in the past for a variety of molded products because of their low cost and excellent physical properties. However, because of low tension upon melting (hereunder referred to as “melt tension”) in the case of polypropylene, for example, there are some disadvantages in terms of processability, including inferior vacuum moldability, blow moldability, foam moldability, extrusion moldability and calender moldability.
Polyethylene and the like are often blended with polypropylene toward the aim of improving these processability, but since the improvement in processability is insufficient, large amounts of polyethylene are required and this leads to the disadvantage of lower rigidity of the resulting blend. It has been attempted to raise the melt tension by increasing the molecular weight of the polyolefin, but higher molecular weight is a problem because it reduces the melt flow property which is one parameter of the processability, thus making it impossible to achieve a suitable balance between the melt tension and the melt flow property.
As a polyolefin resin with improved processability there has been disclosed polypropylene having a free-ended long-chain branched structure, in Japanese Unexamined Patent Publication No. 62-121704, Japanese Unexamined Patent Publication No. 2-298536 and elsewhere. The unique viscoelasticity of this polypropylene allows it to maintain the strength of resin films during foam molding, thus making it possible to produce foams with highly independent cells that have not been possible with conventional straight-chain polypropylene. However, because this type of polypropylene requires a special treatment method or synthesis method involving electron beam irradiation or peroxide addition in order to produce the free-ended long-chain branched structure, it has the disadvantage of greatly increased production costs for the resin.
On the other hand, metallocenes that work with methylaluminoxane as a co-catalyst have high uniformity in terms of activity compared to conventional catalysts, exhibit excellent copolymerization properties, and give polyethylene with a narrow molecular weight distribution and composition distribution at a high activity. Polyolefins obtained by metallocene catalysts have excellent heat seal properties and hot tackiness, but their narrow molecular weight distribution results in a low melt tension and they are hence known to have problems in terms of molding processability; an improvement in melt tension, therefore, is still desired.
Polytetrafluoroethylene has high crystallinity and low intermolecular force and therefore has the property of becoming fibrous under slight stress, while its combination with thermoplastic resins provides improved molding processability and mechanical properties, so that it has come to be used as an additive for thermoplastic resins.
For example, Japanese Unexamined Patent Publication No. 5-214184 and Japanese Unexamined Patent Publication No. 6-306212 disclose resin compositions comprising polyolefins added to polytetrafluoroethylene. Also, Japanese Unexamined Patent Publication No. 7-324147 discloses a process for production of a polyolefin resin composition obtained by mixing polytetrafluoroethylene and a dispersing medium powder under high shear, wherein a polyolefin is combined therewith after first rendering the polytetrafluoroethylene fibrous. In addition, Japanese Unexamined Patent Publication No. 9-25420 discloses a process that uses polytetrafluoroethylene encapsulated with styrene/acrylonitrile copolymer to improve the melting rate of various resins such as polyvinyl chloride resin.
However, polytetrafluoroethylene has the disadvantage of poor dispersability in common thermoplastic resins including no halogen atoms, and as taught in Japanese Unexamined Patent Publication No. 5-214184 and Japanese Unexamined Patent Publication No. 6-306212, it fails to uniformly disperse by simple blending and thus notably lowers the surface appearance of molded products.
Even with the process of Japanese Unexamined Patent Publication No. 7-324147, it is difficult to render all of the polytetrafluoroethylene fibrous by shear force, and the fibrous polytetrafluoroethylene therefore also aggregates in the matrix resin making it impossible to obtain a homogeneous composition.
Moreover, while the process of Japanese Unexamined Patent Publication No. 9-25420 attempts to improve affinity with the matrix resin by encapsulation, there is no effect of improved dispersability in polyolefin resins.
In other words, all of these processes leave the problem of dispersability of polytetrafluoroethylene in polyolefin resins, with the disadvantages of requiring large amounts of polytetrafluoroethylene to exhibit the useful properties mentioned above, and giving molded products with impaired surface appearance.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a melt tension enhancer that increases the dispersability of polytetrafluoroethylene in polyolefin resins and improves the molding processability of polyolefins without impairing the surface appearance of molded products.
As a result of diligent research aimed at overcoming the problems discussed above, the present inventors have completed the present invention upon finding that the melt tension of a polyolefin resin can be improved without impairing the surface appearance of molded products, by adding to the polyolefin resin a resin composition containing polytetrafluoroethylene and a polymer based on an alkyl (meth)acrylate of 5-30 carbon atoms.
The present invention therefore provides a melt tension enhancer for polyolefin resins comprising (A) polytetrafluoroethylene and (B) a polymer based on an alkyl (meth)acrylate of 5-30 carbon atoms, and to a process for its production.
BEST MODE FOR CARRYING OUT THE INVENTION
As examples of polyolefin resins to be used for the invention there may be mentioned resins wherein the main component is a homopolymer of an olefin monomer or a copolymer of olefin monomers obtained by radical polymerization, ion polymerization or the like, a copolymer of a dominant amount of an olefin monomer and a minor amount of a vinyl-based monomer, or a copolymer of an olefin monomer and a diene-based monomer, and any of these may be used alone or in combinations of two or more. The polymerization catalysts used for these resins may be known ones such as Ziegler catalysts, chromium catalysts or metallocene catalysts.
As the olefin monomer referred to here there may be mentioned ethylene, propylene, 1-butene, 1-hexene, 1-decene, 1-octene, 4-methyl-1-pentene and the like, among which ethylene and propylene are particularly preferred. As specific examples of homopolymers or copolymers of these olefinic monomers there may be mentioned low-density polyethylene, very low-density polyethylene, very very low-density polyethylene, linear low-density polyethylene, high-density polyethylene, ultrahigh molecular weight polyethylene, polypropylene, ethylene-propylene copolymer, polymethylpentene, polybutene and the like. These olefinic polymers may be used alone or in combinations of two or more. Particularly preferred among these are polyolefin resins whose main components are mixtures of one or more selected from the group consisting of polyethylene, polypropylene and ethylene-propylene copolymer.
The (A) polytetrafluoroethylene in the melt tension enhancer of the invention may be obtained by polymerization of a monomer component composed mainly of tetrafluoroethylene by a known process. The (A) polytetrafluoroethylene may contain, as copolymerized components, fluorine-containing olefins such as hexafluoropropylene, chlorotrifluoroethylene, fluoroalkylethylenes, perfluoroalkylvinyl ethers, etc. and fluorine-containing alkyl (meth)acrylates
Koshirai Atsunori
Yanagase Akira
Mitsubishi Rayon Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Szekely Peter
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