Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-02-10
2003-09-02
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S079000, C156S244110, C264S045100, C264S051000
Reexamination Certificate
active
06613172
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing a foamable composite sheet mainly made of a polyolefin resin and to a composite foam obtained from this foamable composite sheet.
BACKGROUND ART
Since polyolefin resin foams made of polyethylene, polypropylene or the like are excellent in lightweight, thermal insulating properties, flexibility, and the like, the foams are widely used for various thermal insulators, cushioning materials, floating materials, etc. However, the polyolefin resin foams can not be used for, for example, roof thermal insulators and floor thermal insulators of buildings, since the polyolefin resin foams have a lower compressive strength than that of polystyrene resin foams.
In order to solve this problem, for example, Japanese Laid-open Patent Publication No. 150431/1997 proposes a foamable composite wherein a sheet-like facing material is laminated on at least one side of a foamable polyolefin resin sheet containing a thermally decomposable foaming agent, and the facing material has a strength sufficient to inhibit the foamable sheet from expanding in in-plane directions during foaming by heating.
In practice, the polyolefin resin is blended with a silane-modified polyolefin being incompatible with the resin, a thermally decomposable chemical foaming agent is added to the blend, the mixture is kneaded, the obtained foamable resin composition is shaped into a sheet, sheet-like facing materials made of polyethylene terephthalate non-woven fabric are simultaneously laminated on both sides of the obtained foamable sheet, the silane-modified polyolefin in the obtained foamable composite sheet is water crosslinked, and the sheet is foamed by heating to give the composite foam.
The obtained foamable resin sheet hardly expands in two-dimensional directions in the plane and expands only in a direction of thickness, since the sheet-like facing material having the strength capable of inhibiting expanding in the in-plane directions on foaming is laminated on at least one side of the foamable resin sheet. Accordingly, cells of the foam are arranged in the form of spindles of which major axis is oriented in the direction of the thickness, just like upright rugby balls oriented in the direction of the sheet thickness (see FIG.
1
). When the foam is compressed with compressive force in the direction of the sheet thickness, the force acts to the foam in a direction of a major axis of the spindle. Consequently, the obtained foam exhibits a high strength in the direction of the sheet thickness.
However, the above-mentioned prior art has the following problems.
The silane-modified polyolefin is expensive.
Since it takes a long period of time (usually one hour or longer) to carry out the crosslinking reaction, the foam cannot continuously be produced.
Some sheet-like facing materials are unsuitable for hot water immersion in the crosslinking.
Since the foamable composite sheet gets wet in the crosslinking reaction, drying process is required.
Since the foamable composite sheet is crosslinked, spindle-shaped cells having a high axis ratio (length of major axis/length of minor axis) cannot be produced.
Since blowing pressure is high, a sheet-like facing material having a low strength cannot be used.
Since the obtained foam is crosslinked, it cannot be recycled.
A foam made of polypropylene alone, which has high heat-resisting properties and mechanical physical properties, cannot be produced. Since the foam generally comprises a blend of polypropylene with polyethylene, the above-mentioned performances deteriorate.
Objects of the present invention are to solve the above-mentioned problems and to provide a composite foam having excellent properties and a process for producing a foamable composite sheet to obtain the foam.
DISCLOSURE OF THE INVENTION
A process for producing a foamable composite polyolefin resin sheet according to the present invention is characterized by reacting a polyolefin resin with a modifying monomer to modify the resin, adding a thermally decomposable chemical foaming agent to the obtained modified resin, kneading the obtained mixture, shaping the obtained foamable resin composition into a sheet, and laminating a sheet-like facing material on at least one side of the obtained foamable sheet, the facing material having a strength sufficient to inhibit the foamable sheet from expanding in in-plane directions during foaming by heating the foamable sheet.
Throughout the present specification, the “in-plane directions” mean any directions on the surface of the foamable sheet and include a lengthwise direction and a width direction. The “sheet” does not mean a form in the strict sense of the word on the basis of thickness but includes from relatively thin matter usually called film to relatively thick matter usually called plate material.
A composite foam can be obtained by thermally foaming the foamable composite polyolefin resin sheet obtained by the process of the present invention.
Polyolefin which is a main constituent of the polyolefin resin in the process of the present invention can be a homopolymer of an olefin monomer or a copolymer of the olefin monomer which is a main component with the other monomer(s), and the polyolefin is not particularly limited. Examples of the polyolefin are polyethylene such as low-density polyethylene, high-density polyethylene or linear low-density polyethylene; polypropylene such as homo type polypropylene, random type polypropylene or block type polypropylene; polybutene; copolymers mainly composed of ethylene such as an ethylene-propylene copolymer, an ethylene-propylene-diene terpolymer, an ethylene-butene copolymer, an ethylene-vinyl acetate copolymer and an ethylene-(meth)acrylate copolymer. They can also be used in combination.
The polyolefin which is the main constituent of the polyolefin resin in the process of the present invention is preferably one of the above-mentioned polyethylene and polypropylene or a combination thereof.
The polyolefin resin means a resin composition of which proportion of the above-mentioned polyolefin is 70 to 100% by weight. The other resin constituting the polyolefin resin than the polyolefin is not limited. Examples of the other resin are polystyrene, a styrene elastmer, etc. If the proportion of the polyolefin in the polyolefin resin is lower than 70% by weight, the resin cannot exhibit lightweight, chemical resistance, flexibility, elasticity, and the like which are characteristics of the polyolefin, and it is sometimes difficult to insure melting viscosity required for foaming. Accordingly, such a proportion is not preferable.
The modifying monomer to be used in the process of the present invention is a compound having two or more functional groups which can undergo radical reaction in its molecule. Examples of the above-mentioned functional group are an oxime group, a maleimide group, a vinyl group, an allyl group, a (meth)acryl group, etc. The modifying monomer is preferably a dioxime compound, a bismaleimide compound, divinylbenzene, an allylic polyfunctional monomer and a (meth)acrylic polyfunctional monomer. The modifying monomer can also be a cyclic compound having two or more ketone groups in its molecule such as a quinone compound.
Among the modifying monomers to be used in the process of the present invention, a compound having two oxime groups in its molecule, i.e. a dioxime compound, can be a compound having two oxime groups (formula I) or two structures wherein a hydrogen atom of the oxime group is replaced with other atomic group (mainly a hydrocarbon group) (formula II) in its molecule as represented by the following general formulae. Examples of the compound are p-quinonedioxime (formula III) and p, p-dibenzoylquinonedioxime (formula IV). The dioxime compounds can also be used in combination.
Among the modifying monomers to be used in the process of the present invention, examples of the bismaleimide compound having two maleimide structures (formula V) represented by the following general formula in its molecule are N,N′-p-phenylenebi
Fukuoka Takamasa
Kurio Hiroyuki
Okabe Masashi
Tsujimoto Michitaka
Rader & Fishman & Grauer, PLLC
Sekisui Kagaku Kogyo Kabushiki Kaisha
Yao Sam Chuan
LandOfFree
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