Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1996-12-05
1998-05-05
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 56, 521142, 521143, C08J 922
Patent
active
057475490
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to foamed particles of a polypropylene homopolymer and a molded article of foamed particles obtained by molding the foamed particles of the polypropylene homopolymer.
BACKGROUND ART
It is known to obtain a molded article of foamed particles by filling foamed particles composed of a polypropylene-based polymer into a mold which can be closed but cannot be hermetically sealed, and heating the foamed particles, whereby the foamed particles are secondarily foamed and mutually fusion-bonded. For example, Japanese Patent Publication No. 43491/1984, and Japanese Patent Application Laid-Open Nos. 242638/1989, 50945/1990, 253741/1992 and 9327/1993 disclose techniques for producing a molded article of foamed particles by such a process.
The molded articles of foamed particles, which are obtained by using the foamed particles composed of a polypropylene-based polymer and molding them, have had such properties that cushioning characteristics and impact resilience are excellent, their weights are light and residual strain is also small. However, their stiffness such as compressive strength has not been always satisfactory.
More specifically, in the molded articles of the foamed particles of the polypropylene-based polymer, an ethylene-propylene random copolymer, ethylene-propylene block copolymer, 1-butene-propylene random copolymer, 1-butene-propylene block copolymer, ethylene-1-butene-propylene random copolymer or the like is mainly used as a base resin from the standpoint of foamability and the like. However, these polymers themselves have low stiffness by nature. Therefore, various attempts have been made for the purpose of improving the stiffness of the resulting molded article, for example, by making the content of a comonomer in the copolymer lower or mixing linear polyethylene with an .alpha.-olefin-propylene copolymer. The improvement in the stiffness of the molded articles has been limited.
On the other hand, polypropylene itself is a polymer high in stiffness. It is thus expectable to obtain a molded article of foamed particles, which has high stiffness, when molding is conducted by using foamed particles composed of a polypropylene homopolymer. However, the attempt to obtain a molded article from the foamed particles composed of the polypropylene homopolymer causes problems that the range of molding temperatures necessary for successfully conducting expansion is very limited, extreme difficulty is encountered on the control of expanding temperature, and the resulting molded article is accompanied by disadvantages that a failure in fusion bonding is caused, and the appearance of the surface of the molded article becomes poor. Any production technique suitable for industrial production has not been yet established. Of course, such problems arise even in the production of foamed particles. Namely, when foamed particles are produced by using a polypropylene homopolymer as a base resin, the range of foaming temperatures necessary for successfully conducting foaming has been limited, resulting in difficulty in realizing industrial production.
As described above, any foamed particles obtained by using a polypropylene homopolymer as a base resin and any molded articles produced by using such foamed particles have not been yet marketed. The attempt to use the polypropylene-based copolymer containing various kinds of comonomers as a base resin to enhance the stiffness of the resulting molded article while retaining good moldability as described above is only being made.
It is an object of the present invention to provide foamed particles comprising a polypropylene homopolymer as a base resin. Another object of the present invention is to provide foamed particles of a polypropylene homopolymer, which have good moldability.
A further object of the present invention is to provide a molded article produced by using such foamed particles of the polypropylene homopolymer. A still further object of the present invention is to provide a molded article of foamed particles comp
REFERENCES:
patent: 4587270 (1986-05-01), Kuwabara et al.
Oikawa Masaharu
Tokoro Hisao
Tsurugai Kazuo
Foelak Morton
JSP Corporation
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