Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1997-12-12
1999-05-11
Cooney, Jr., John M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
521 82, 521 98, 521134, 521140, 521150, 525 55, 525 64, 525244, 525260, 525264, 525313, C08F255/06
Patent
active
059028580
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a modified polypropylene resin obtained by melt-kneading a polypropylene resin, an isoprene monomer and a radical polymerization initiator, a process for the preparation thereof, a foam made of the modified polypropylene resin and a process for the preparation thereof.
BACKGROUND ART
Polypropylene resins have various uses such as films, fibers and other molded articles of various shapes, since they are inexpensive and molded articles thereof are superior in rigidity, heat resistance, chemical resistance and electrical insulating property.
However, since conventional polypropylene resins are crystalline resins, the melt viscosity, particularly the elongational viscosity, is very low. Thus, they have the problem that in a process wherein a molten resin is remarkably deformed, e.g., blow molding, extrusion, and foaming, ranges of processing conditions capable of producing suitable molded articles are narrow.
As one of manners for solving such a problem in processability of polypropylene resins, physical blending of the polypropylene resins with polyethylene has been widely used. However, according to this manner, a large amount of polyethylene is required for sufficiently improving the processability, so the molded articles obtained from the thus improved resins result in low rigidity.
Another manner is to use a polypropylene resin having a high molecular weight. However, such a resin has the problem that in case of conducting extrusion, a load on an extruder becomes large because of high viscosity. Also, since the resin is difficult to largely deform in the molten state, blow molding thereof is difficult to provide molded articles in a high draw ratio and foaming thereof is difficult to provide foamed articles having a high expansion ratio.
Also, polypropylene resins are radical-degradable polymers. Therefore, in general, it is difficult to increase the molecular weight by crosslinking the polymer molecules, even if radical polymerization initiators capable of serving as an intermolecular crosslinking agent are used.
In order to solve these problems, it is proposed in Japanese Patent Publication Kokai No. 62-121704 to irradiate radiation to a semi-crystalline polypropylene resin having a linear molecular structure in a gas atmosphere having a controlled specific oxygen concentration, thereby raising the melt viscosity and melt tensile strength of the polypropylene resin. The Japanese publication discloses that the polypropylene resin modified in this manner has a structure such that the polymer molecule has long chain branches, and is suitable for molding methods such as blow molding, extrusion coating molding and the like.
It is also disclosed therein that the reason why the polypropylene resin modified in this manner is suitable for these molding methods is that the resin has the characteristics that the elongational viscosity measured in the molten state of this resin rapidly increases as the strain increases, that is to say, when this resin is subjected to tensile deformation in the molten state, the elongational viscosity increases with increasing the elongational strain and, after reaching a specific elongational strain, the elongational viscosity rapidly increases.
However, in case of modifying polypropylene in this manner, it is unavoidable that because of utilizing radiation, the apparatus to be used becomes large scale and complicated in structure. Also, in order to prevent degradation and gelation of polypropylene resins in the radiation exposure step so as to stably produce products, it is required to strictly control the radiation dose and the oxygen concentration of the surrounding gas. Further, because of necessity to strictly control the production conditions like this, it is not easy to give variety to the physical properties of the objective modified polypropylene resins.
Foamed articles made of polypropylene resins have good chemical resistance, impact resistance and heat resistance and, therefore, they have been suitably utilized as hea
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Miyama Osamu
Okura Tetsuo
Tomita Haruo
Cooney Jr. John M.
Kaneka Corporation
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