Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-01-08
2003-04-01
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S139000
Reexamination Certificate
active
06541533
ABSTRACT:
TECHNICAL FIELD
This invention relates to extruded polyolefin resin foam used in cushion material, packaging material, sound absorbing material, water absorbing material, anti-vibration material, and various kinds of industrial filters, etc.
BACKGROUND ART
The open cell foams made of synthetic resins known to the prior art include urethane foams, foam rubber, and ethylene-vinyl acetate copolymer foams, etc. These foams, because they are flexible and exhibit good processability, have been used in such applications as cleaning sponges, shock absorbing materials, cushion materials, sound absorbing materials, and various industrial filters. Nevertheless, applications for these open cell extruded foams have been limited due to their inferiority in terms of chemical resistance (acid resistance, alkali resistance, etc.) and weatherability. Furthermore, urethane foams and foam rubber are very difficult to recycle back to raw materials, while ethylene-vinyl acetate copolymer foams are problematic because of their large amount of foul odor during manufacture.
Polyolefin resins, on the other hand, exhibit very outstanding chemical resistance and weatherability, as well as outstanding recyclability. Accordingly, the problems noted above can be overcome if the open cell extruded foam is made of a polyolefin resin.
That being so, attempts have been made before to develop open cell polyolefin resin foams. Art is known, for example, for subjecting a closed cell polyolefin resin foam to pinhole processing to form open cell foam. However, open cell polyolefin resin foams obtained by simply subjecting closed cell foams made from polyethylene resin or polypropylene resin base material to pinhole processing exhibit high permanent compression set, and do not have sufficient shock-absorbing properties to stand up under prolonged use.
Other methods have also been reported, such as that described in Japanese Patent Publication No. S60-55290/1985 which uses a mixture of low-density polyethylene and high-density polyethylene, and that described in Japanese Patent Application Laid-Open No 2000-7817 which uses a mixture of low-fluidity and high-fluidity low-density polyethylenes as the base resin for obtaining an open cell extruded foam. With those methods, however, foam of sufficient thickness, width, and expansion ratio are not obtained, nor do such foams exhibit adequate practical usability. Also known are open cell foams made of polyolefin resins and ionomer resins. In Japanese Patent Application Laid-Open No. H10-279724/1998, for example, a foam is disclosed wherein for 0 to 50 parts by weight of a polyolefin resin are used 100 to 50 parts by weight of a costly ionomer resin. However, when foam extrusion of an open cell foam of such mixture as noted above is performed, the extrusion pressure is high, wherefore heat generation at the die is severe, making it very difficult to obtain good open cell extruded foams exhibiting a high expansion ratio and high thickness. In addition, the molten resin setting temperature (hereinafter called the foaming temperature) must be regulated within a narrow range during extrusion foaming in order to obtain the open cell extruded foam, making stable manufacture difficult. Also, in Japanese Patent Application Laid-Open No. 59-196384/1994, a foam wherein for 100 parts by weight of a polyolefin resin, 60 to 150 parts by weight of an ionomer resin are used, but this is small rod-shaped foam having a cross-sectional area of 0.1 cm
2
or so which is used as core material in sealers used in window frames and the like, for example.
In Japanese Patent Application No. 2000-23179, an open cell extruded foam is described wherein a mixture of two or three or more polyolefin resins having different melting points is used as the base resin. More specifically, in this patent application, an open cell extruded foam is described, the main component whereof is a mixed polymer configured by a component consisting of a polyolefin resin, and a component consisting either of one or two or more polymers selected from a group made up of ethylene-&agr;, or &bgr; unsaturated carboxylic acid copolymers (but excluding ionomers), olefin elastomers, styrene elastomers, and ethylene-vinyl acetate copolymers, or of such mixed polymer to which a heat reversible crosslinked polymer has been added.
With the resin mixture described above, the range of suitable foaming temperatures wherewith the open cell foam can be stably obtained is narrow, and, if the foaming temperature is higher than the suitable foaming temperatures, the foam contracts, making it difficult to obtain foam having the desired expansion ratio and thickness, whereas, if the foaming temperature is lower than the suitable foaming temperatures, the closed cell foaming ratio rises and the desired open cell foam is not obtained. If an attempt is made to obtain an open cell foam of high foaming expansion ratio, moreover, the cell wall thickness of the foam becomes thin, it becomes very difficult to retain the shape of the open cell foamed cell walls during extrusion foaming, and good foam is difficult to obtain.
Thus, in the prior art, it has been very difficult to stably manufacture foam exhibiting uniform physical product properties, and to stably manufacture polyolefin resin open cell extruded foam exhibiting high expansion ratio and high open cell foaming ratio, especially thick product exhibiting uniform physical properties.
With the foregoing in view, it is an object of the present invention to provide extruded open cell foam of uniform physical product properties, with a high expansion ratio, and uniform cell diameter, particularly such extruded open cell foam that is thick.
DISCLOSURE OF THE INVENTION
The present invention is an extruded polyolefin resin open cell foam having an open cell foaming ratio of 50% or higher. The base resin of the foam of the present invention has as its main component a mixed polymer consisting of 4.5 to 75 parts by weight of a component A consisting of an ethylene ionomer resin, 0.5 to 30 parts by weight of a component B consisting of a polyolefin resin having a melting point exceeding 120° C., and 20 to 95 parts by weight of a component C consisting of one or two or more polymers selected from a group of ethylene-propylene rubbers, styrene elastomers, and polyethylene resins having melting points of 120° C. or lower (where component A+component B+component C=100 parts by weight).
The component B consisting of the polyolefin resin having a melting point exceeding 120° C. should be one or two or more mixed resins selected from among polypropylene resin, linear low-density polyethylenes, and polyethylene resins having a density of 940 kg/m
3
or greater.
The polyethylene resin having a melting point of 120° C. or lower in component C should be one or two or more mixed resins selected from among low-density polyethylenes, ethylene-&agr;, or &bgr; unsaturated carboxylic acid copolymers (but excluding ionomers), and ethylene-vinyl acetate copolymers.
An anti-shrinking agent can be added to the base resin, whereupon the amount added should be 0.1 to 15 parts by weight for 100 parts by weight of the basic resin.
The extruded open cell foam of the present invention should have a density of 15 to 200 kg/m
3
and thickness of 0.5 to 200 mm, which can be configured either as sheet-form foam or plank-form foam. The shape is not limited to a flat shape, however, and rod-shaped foam can also be configured. The form of the rod shapes may be either one with a hollow cross-section or solid cross-section, with a density of 15 to 100 kg/m
3
and an area of cross-section (perpendicular to direction of extrusion) of 0.7 cm
2
or greater being preferred.
The polyolefin resin foam of the present invention is preferably such that the stress relaxation ratio is at least 30% after sustaining 50% compression for one minute, the 25% compression strength in the thickness direction is 1 to 50 kPa, and the 50% compression set is 7% or less. It is also preferable for the cell shape to satisfy the following formulas (a)
Kitahama Takashi
Kogure Naochika
Naito Masato
Takahashi Seiji
Foelak Morton
JSP Corporation
Sherman & Shalloway
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