Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Producing or treating porous product
Reexamination Certificate
2001-02-08
2003-02-11
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Producing or treating porous product
C264S054000, C264S321000
Reexamination Certificate
active
06517764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field OF The Invention
The present invention relates to a method of making polyethylene resinous open cell cellular bodies, in particular a polyethylene resin open cell cellular body that is excellent in both recyclability and heat resistance and further has a maximum degree of cell interconnection.
2. Description of the Prior Art
There has hitherto been proposed in the art, as disclosed in patent literatures JP SHO 59-23545 A and JP SHO 56-146732 A, a method of making a polyethylene resin open cell cellular body by partially decomposing a foaming (expanding) and a crosslinking agent in a foamable and crosslinkable composition of polyethylene resin material in a closed mold, then decomposing the remaining parts of the foaming and crosslinking agents under an atmospheric pressure to obtain a body with closed cells from the composition, and finally compressing the thus obtained body to cause the closed cells to be destructed.
In this conventional method, while the composition is in the closed mold in which the foaming and crosslinking agents are heated under pressure to be partially decomposed, crosslinking reaction does occur but foaming or cell formation does not take place. The foaming takes place after pressure removal. In the method, therefore, in which crosslinking completely precedes cell formation, i.e., chemical links have already been established in the process step of forming closed cells, the cell membrane becomes strong, tough and tenacious. As a result, the subsequent compressing step is difficult to interconnect isolated cells to be unable to yield a cellular body that has a degree of cell interconnection of 100% or even approaching 100%.
We have proposed several techniques designed to solve these problems met by the prior method mentioned above. These include a method as disclosed in JP SHO 62-19294 B and JP HEI 1-44499 B in which a foamable and crosslinkable composition having its base composed of ethylene acetate copolymer or low density polyethylene is heated and preformed into a preselected shape and then under atmospheric pressure is heated to cause a foaming and a crosslinking agent in the composition to be decomposed simultaneously to form a cellular body having cells therein and the cellular body is then mechanically deformed to cause the cells to be interconnected therein. In another method that we have proposed, a polyethylene resin open cell cellular material as disclosed in JP HEI 2-22345 A is further irradiated with a beam of electrons, thereby imparting heat resistance thereto. In a further method as we have disclosed in JP HEI 11-315161, a foamable and crosslinkable composition having its base composed of polyethylene derived from polymerization of ethylene catalyzed by a metallocene is heated and preformed and then under atmospheric pressure is heated to cause to a foaming and a crosslinking agent in the composition to be decomposed simultaneously to form a cellular body having cells therein, the cellular body being then mechanically deformed to cause the cells to be interconnected therein.
These methods permit making an open cell cellular body as desired that has a degree of cell interconnection as high as or nearly 100%. Despite its satisfactory degree of cell interconnection, however, a body made by any of the methods mentioned has been found still unsatisfactory. First, its crosslinked structure does not allow remelting a body on recovery after use and thus makes it unsuitable for recycling. Second, use of an ethylene acetate copolymer leaves an open cell cellular body still relatively poor in heat resistance by having a change in dimensions according to JIS K 6767 as much as −10 to −20% at 70° C.
Proposals have also been made to make non-crosslinkable, polyethylene resin open cell cellular bodies. For example, JP SHO 60-55290 B discloses an exclusion method in which a low-density and a high-density polyethylene are mixed together on specifying their melt indices and mixing ratio, and the mixture is mixed with a volatile organic liquid for exclusion on specifying a particular extrusion temperature. JP HEI 3-8379 B discloses a method in which an olefin resin is mixed with an ionic copolymer and a foaming agent to form a resinous composition, and then the composition is excluded and foamed. In a method disclosed in JP P 10-279724, a polyolefin resin is mixed with a resinous composition of an ethylene-methacrylic acid copolymer (ionomer resin), a nucleation agent and an anti-shrink agent, which upon softening or melting by heating is supplied and mixed with a volatile foaming agent, to form a composition, and then the composition is excluded into a low pressure region.
Open cell cellular bodies made by these latter methods are indeed good in recyclability, but are poor in the degree of cell interconnection and therefore are unsuitable for use as carriers in an organism filtration tank included in an organic filterable water-purifier tank system and as a filter, which are important applications of such bodies.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to solve the above mentioned problems met by the prior art and to provide a method of making a polyethylene resin open cell cellular body that is excellent in both recyclability and heat resistance or resistance to heat distortion and further has a maximum degree of cell interconnection.
In order to achieve the object mentioned above there is provided in accordance with the present invention in a first aspect thereof a method of making a polyethylene resin open cell cellular body, characterized in that it comprises the steps of: preparing a polyethylene resin material that is derived from polymerization of ethylene catalyzed by a metallocene compound; adding 4,4′-oxy bis (benzene sulfonyl hydrazide) to the polyethylene resin material to form a foamable composition and shaping the foamable composition of polyethylene resin material; heating the shaped foamable composition of polyethylene resin material to be foamed under an atmospheric pressure to form a cellular body thereof with cells therein; and mechanically deforming the said cellular body of polyethylene resin material to cause the cells to be interconnected therein, thereby producing the open cell cellular body of polyethylene resin material.
The present invention also provides in a second aspect thereof a method of making a polyethylene resin open cell cellular body, characterized in that it comprises the steps of: preparing a polyethylene resin material that is an ethylene-vinyl acetate copolymer; adding 4,4′-oxy bis (benzene sulfonyl hydrazide) to the polyethylene resin material to form a foamable composition and shaping the foamable composition of polyethylene resin material; heating the shaped foamable composition of polyethylene resin material to be foamed under an atmospheric pressure to form a cellular body thereof with cells therein; and mechanically deforming the said cellular body of polyethylene resin material to cause the cells to be interconnected therein, thereby producing the open cell cellular body of polyethylene resin material. In a preferred form of embodiment of the present invention in this aspect, the ethylene-vinyl acetate copolymer contains not less than 5% of vinyl acetate. It has been found that if the ethylene-vinyl acetate copolymer contains less than 5% of vinyl acetate, the foam breakability of the cellular body is significantly lowered, presumably by reason of stiffness properties of the resin.
In a specific form of embodiment of the present invention in either the first or second aspect thereof mentioned above, it is preferable that the fomable composition be freely foamed in three-dimensional directions under the atmospheric pressure. Otherwise, it has been found that there develops in the mold a pressure that acts to compress the composition, thus to hinder its foaming and to cause it to shrink.
The present invention also provides in a third aspect thereof a method of making a polyethylene resin open cell cellular body,
Fujimura Kazuyoshi
Miyano Yoshio
Shibata Tomoyoshi
Frishauf Holtz Goodman & Chick P.C.
Kuhns Allan R.
Sanwa Kako Co., Ltd.
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