Polypropylene based resin composition, expanded moldings comprising the same and method for production thereof

Abstract

A polypropylene based resin composition for injection expansion molding, which comprises (A) 50 to 95 parts by weight of a linear polypropylene based resin having a melt flow rate of 10 g / 10 min to 100 g / 10 min and a melt tension of 2 cN or less, (B) 5 to 50 parts by weight of a modified polypropylene based resin having a melt flow rate of 0.1 g / 10 min or more and less than 10 g / 10 min and a melt tension of 5 cN or more and exhibiting the strain hardening property (provided that the sun of the linear polypropylene based resin (A) and the linear polypropylene based resin (B) is 100 parts by weight); expanded moldings comprising the resin composition; and a method for producing said expanded moldings. Said expanded moldings are produced along with good injection expansion molding properties and comprises a skin layer having a surface being almost free of silver streaking or the like and an inner core layer being expanded in a high expansion ratio and having uniform and fine pores, and further is excellent in appearance, lightweight property and rigidity.

Description

[0001] Technical division [0002] The present invention relates to a polypropylene-based resin composition suitable for injection foam molding, a foam-molded article containing the composition, and a method for producing the same. Background technique [0003] In the injection molding of polypropylene-based resins, so-called injection foam molding in which foaming is performed to reduce weight, reduce costs, and prevent warping and sinking of molded articles has been performed for a long time. However, since polypropylene resin is crystalline and has low melt tension (melt tension), bubbles are destroyed during foaming, and therefore, silver streaks (silver streaks) (or silver streaks) (or Swirl marks (スワールマク)) poor appearance, and even internal pores, etc., so it is difficult to increase the expansion ratio. In addition, since the cells are large and uneven, the rigidity of the molded body obtained is not sufficient. [0004] As a method of improving foamability, a method ...

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Problems solved by technology

However, any of the expanded molded articles obtained by these methods is a molded article with a low expansion ratio of less than 2 times, and a molded article with a high expansion ratio is not listed.

In addition, when the pre-pressurization of the mold is high pressure, when foaming, when the gas escapes from the mold, the gas is likely to remain in the mold, and there is a tendency to have a bad influence on the foaming. Attention, and prone to lack of stability

In addition, polystyrene, polycarbonate, etc. are listed, but polypropylene is not specifically listed.

[0008] In addition, even when these surface improvement methods are combined with the above-mentioned polypropylene-based resin with improved foamability, it is difficult to obtain fluidity at the thin wall, high expansion ratio of 2 times or more, and surface Excellent polypropylene resin foam molding

[0009] In addition, as a method of improving the surface properties, there have been methods such as coating the surface of a molded body and attaching a skin material to the surface, but these methods have problems of environmental pollution and recycling. In addition, from the viewpoint of cost reduction, especially From the perspective of automobile manufacturers, it is required to omit these processes

[0010] As described above, until now, it has been difficult to obtain a polypropylene resin injection foam molded product with good injection foam moldability, high expansion ratio, high light weight, beautiful surface appearance and excellent rigidity.

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