Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-08-02
2003-06-10
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S230000, C524S233000, C524S210000, C524S579000, C524S570000, C521S059000, C521S060000
Reexamination Certificate
active
06576693
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to polypropylene resin pre-expanded particles used for thermal insulation materials, cushioning packaging materials, returnable containers and automobile bumper cores, and in-mold expanded articles of a polypropylene resin using the above particles.
Inmolded expanded articles obtained from polypropylene are excellent in chemical resistance, heat resistance and distortion restoration rate after compression as compared to inmolded expanded articles of polystyrene, and are also excellent in heat resistance and compression strength as compared to inmolded expanded articles of polyethylene. Therefore, polypropylene resin inmolded expanded articles are widely used as cushioning packaging materials, returnable containers, automobile bumper cores and the like.
However, despite the above excellent properties in general, a polypropylene resin has a defect that it is harder and more fragile than polyethylene resins.
For these reasons, when products containing synthetic resin housing, for example, electrical appliances such as computers and televisions are wrapped by polypropylene resin expanded articles and transported, there are problems that surface of such products may be damaged due to vibration and that the expanded articles may be chipped to generate polypropylene powder. Recently, in accordance with diversification of electrical appliances particularly, more products contain emboss on the surface thereof, and color variation is also extended to dark colors such as black and gray. The above problems are remarkably seen in these products. The synthetic housing in this case means housing which has, as a basic material, an ABS resin, an ABS/PC blended resin, a poly(vinyl chloride) resin, a polyethylene resin, a polypropylene resin or the like.
In addition, there is a problem that polypropylene powder can be also generated in course of preparing polypropylene resin pre-expanded particles by friction between particles and the inner wall of a passage pipe in product line or because of mechanical impact within a transport blower. Particularly, in case of inmold expansion molding by using polypropylene resin pre-expanded particles, the above polypropylene powder adheres to the mold and the vapor slit of the mold as well as to the inside of the pipe of a molding machine, polluting the machine and preventing vapor flow to decrease moldability.
Conventionally, as a means to solve the problem with the surface scratching by expanded articles, electric appliances are once covered with a polyethylene bag and the like and then packed by the expanded articles. However, this process of packing by the expanded articles after covering electric appliances with a polyethylene bag and the like requires many steps and cost is increased because polyethylene bags must be prepared.
As a means to solve the problem with polypropylene powder generation and mold pollution due to the powder, there are a process for separating the polypropylene powder mechanically, and a process for cleaning the mold of a molding machine regularly. However, cost for the machine increases in case of the process of mechanical separation of the polypropylene powder, while productivity is remarkably decreased in case of the process of regular mold cleaning.
Also, there is a process for reducing friction between pre-expanded particles and inner wall of a passage pipe, and friction between inmolded expanded articles and a product caused by vibration in transport, by adding a lubricant to a polypropylene resin. Generally, in order to improve slip properties of a polypropylene resin, a process for adding a fatty acid amide compound is known. The fatty acid amide compound is added in an amount of 0.2 to 0.5 part by weight, at most about 1 part by weight.
The process for adding a fatty acid amide compound to the basic resin of polypropylene resin pre-expanded particles is disclosed in Japanese Patent No. 1686282, Japanese Unexamined Patent Publication No. 59876/1996 and Japanese Unexamined Patent Publication No. 209503/1999.
In Japanese Patent No. 1686282, 0.01 to 2 parts by weight of ethylene bisfatty acid amide or methylene bisfatty acid amide is added thereto aiming at making minute but uniform cell structure of a pre-expanded particle. However, the above problems cannot be solved by employing these pre-expanded particles and inmolded expanded articles using the same.
In Japanese Unexamined Patent Publication No. 59876/1996, 0.05 to 2.0 parts by weight of a fatty acid amide compound and 0.05 to 3.0 parts by weight of a metallic salt aiming at improving secondary processability of inmolded expanded articles. The above problems cannot be solved even by employing these pre-expanded particles and inmolded expanded articles using the same.
In Japanese Unexamined Patent Publication No. 209503/1999, 0.01 to 4.0 parts by weight of a mixture containing both of a polyhydric alcohol fatty acid ester and fatty acid amide are added (the fatty acid amide compound is added in an amount of 0.08 to 3.2 parts by weight according to the claims). The process aims at providing polyolefin resin expanded particles having uniform and large foam diameter which are excellent in expansion strength at expansion of polyolefin resin particles to be expanded and adhesion of particles at inmold molding, as well as surface appearance, cushioning properties and toughness of inmolded foamed articles. Examples described in this publication are limited to the cases of using a polyethylene resin, which does not cause problems mentioned above.
SUMMARY OF THE INVENTION
An object of the present invention is to prevent powder generation, thereby stopping pollution of a mold and the like at inmold expansion molding in preparation of polypropylene resin pre-expanded particles. Another object of the present invention is to provide inmolded expanded articles by which products are not damaged and polypropylene powder is not generated. According to the present invention, the above problems can be solved by using pre-expanded particles containing specific fatty acid amide and inmolded expanded articles comprising the pre-expanded particles.
That is, the present invention relates to polypropylene resin pre-expanded particles comprising a resin composition containing 2.5 to 15 parts by weight of a fatty acid amide compound based on 100 parts by weight of a polypropylene resin.
It is preferable that the fatty acid amide compound is at least one selected from the group consisting of erucic amide, oleic amide and stearic amide.
It is preferable that copolymerization ratio of butene in the polypropylene resin is at most 10% by weight.
The present invention also relates to an inmolded expanded article of a polypropylene resin comprising the above polypropylene resin pre-expanded particles, and to an inmolded expanded article of a polypropylene resin, wherein a density of the inmolded foamed article of a polypropylene resin is 10 to 45 g/l.
It is described in Japanese Unexamined Patent Publication No. 59876/1996 that a foam diameter of expanded cell becomes smaller by using fatty acid amide, and chip and crack are easily generated when the foam diameter becomes small. According to the present invention, however, a foam diameter does not become so small even if a large amount of a fatty acid amide compound is used.
Furthermore, a general expanded article has a problem that it takes time to bleed out an additive mixed to a basic resin on the article surface due to the cell structure, and thus, when the additive is to be active on the surface, the effect is not easily shown. In case of a conventional inmolded expanded article, a fatty acid amide compound is added only in a small amount, and thus bleeding amount to the surface of the inmolded expanded article becomes small. Therefore, lubricating effect caused by the fatty acid amide compound cannot be achieved sufficiently. However, according to the present invention, bleeding amount of a fatty acid amide compound can be increased and its lubricating effect can be achieved by adding the f
Ogita Tetsuya
Yamaguchi Takema
Lee Rip
Wu David W.
LandOfFree
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