Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – By gas forming or expanding
Reexamination Certificate
1998-10-14
2001-09-25
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
By gas forming or expanding
C264S054000
Reexamination Certificate
active
06294116
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for producing a crosslinked foamed article. During the process when the article is produced, the resin extrudate can progress through the mold smoothly.
2. Description of the Prior Art
Crosslinked foamed articles have the advantage of light weight and have been frequently used as insulating material, shoe material, cushion material, and in sporting goods. The raw materials for producing crosslinked foamed articles include thermoplastics (e.g., PE, PP, and EVA) and thermoset resins (such as rubbers). Nowadays, the production of crosslinked foamed articles can be classified into the following two methods:
(1) The polymer composition is mixed, extruded or molded to a sheet, and finally molded under pressure batchwise into a crosslinked foamed article:
(2) The polymer composition is mixed, extruded or molded to a foamed sheet, and finally subjected to batchwise crosslinking into a crosslinked foamed article.
However, the above two methods are employed in batches, thus increasing energy and production cost. Therefore, a continuous process of simultaneous crosslinking and foaming has been developed.
For example, Kimura et al. in U.S. Pat. No. 4,552,708 uses a long-land die to maintain the pressure in order to obtain a foamed article of good properties. However, in order to make the plastic materials progress smoothly through the mold, lubricant should be continuously applied to decrease friction.
Yamamoto et al. in U.S. Pat. No. 5,310,513 uses a two-zone long die. In the front zone, the plastic material is heated to cause crosslinking. In the rear zone, the crosslinked product is cooled. Finally, the crosslinked product is heated to freely expand and foam to obtain a final crosslinked foamed article. Thus, the final cross-linked foamed article having nonuniform and large bubbles is generated due to free foaming.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the afore-mentioned problems and to provide an improved method and apparatus for producing a crosslinked foamed article. During the process when the article is produced, the resin extrudate can progress through the mold smoothly.
Another object of the present invention is to provide an improved method and apparatus for producing a crosslinked foamed article having uniform and smaller bubbles.
To achieve the above object, the method for producing a crosslinked foamed article comprises the steps of:
(a) uniformly mixing at least one crosslinkable resin, at least one crosslinking agent, at least one foaming agent, and some additives into a resin composition;
(b) extruding the resin composition through a die into an extrudate of a predetermined shape; and
(c) heating the extrudate to a temperature sufficient to cause crosslinking and foaming of the crosslinkable resin while being driven by a driving device to move in the extruding direction, thereby obtaining a crosslinked foamed article.
The apparatus for producing a crosslinked foamed article of the present invention comprises:
an extruder for heating a crosslinkable resin composition into a molten resin composition, the resin composition containing at least one crosslinkable resin, at least one crosslinking agent, and at least one foaming agent;
a die, connected to the extruder, from which the molten resin composition can be extruded into a extrudate of a predetermined shape;
a heating mold for receiving and heating the extrudate to a temperature sufficient to cause crosslinking and foaming of the crosslinkable resin; and
a driving means for driving the extrudate in the heating mold to move in the extruding direction.
One aspect of the present invention is that the resin extrudate can progress smoothly through the heater or mold; thus, no lubricants are required.
The second aspect of the present invention is that the resin extrudate is foamed under pressure, rather than foamed freely; therefore, bubbles generated in the final crosslinked foamed article will be uniform and smaller.
Further applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 3812225 (1974-05-01), Hosoda et al.
patent: 4552708 (1985-11-01), Kimura et al.
patent: 4882108 (1989-11-01), Nakajima et al.
patent: 4960549 (1990-10-01), Brooks et al.
patent: 5043115 (1991-08-01), Aoshima et al.
patent: 5227852 (1993-07-01), Spydevold
patent: 5310513 (1994-05-01), Yamamoto et al.
patent: 5700407 (1997-12-01), Branger
Huang Chi-Chou
Liou Shihn-Juh
Shih Hsi-Hsin
Tsai Chin-Chin
Wang Yu-Chi
Industrial Technology Research Institute
Kuhns Allan R.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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