Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Patent
1998-09-03
2000-08-08
Copenheaver, Blaine
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
428213, 428218, 4283166, B32B 532
Patent
active
060999551
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a urethane foam for shoe soles where the sizes of the skin and core cells are markedly different.
BACKGROUND ART
Usually, a polyurethane foam is prepared by mixing and stirring a polyisocyanate and a polyol mixture comprising a polyol, a catalyst, a blowing agent, a foam stabilizer (a surfactant), and other optional auxiliaries, and thereby allowing the components to react.
Shoe soles made of polyurethane foam exhibit excellent properties such as lightness, impact resistance, chemical resistance, abrasion resistance, and bending resistance. With respect to midsoles, in particular, there has recently been a rapid trend toward density reduction for the purposes of reduction in cost and weight. Density reduction in a water-blown polyurethane foam for shoe soles is normally achieved by increasing the relative amount of water in the polyol mixture to increase the generation of CO.sub.2 gas for foaming.
However, increasing the relative amount of water as a blowing agent markedly deteriorates the foam's mechanical properties due to increased urea linkage. Deterioration of split tear strength, a particularly important mechanical property of midsoles, is a problem. Although many attempts have been made to improve the split tear strength through investigation of polyols, prepolymers, or catalysts, no useful means to improve the split tear strength has been found.
On the other hand, an integral skin foam method is used to mold automobile interiors without affecting the foam's mechanical properties. It is characterized in that the skin layer and inner foam are simultaneously molded. This can be achieved by suppressing the expansion of the skin portion which comes into contact with the mold's inner wall during the reaction.
However, because the skin layer is a high-density elastomer, reducing the molded density of the foam as a whole is limited. Also, a chlorofluorocarbon-type blowing agent is required for the integral skin method, which causes various problems in a process where water is used as a blowing agent.
Further, EP-A-0559216 discloses a process for producing a polyurethane integral skin foam by using no halogenated hydrocarbon as a blowing agent.
However, this document does not disclose a method for producing a polyurethane foam having a certain cell diameter distribution.
DISCLOSURE OF THE INVENTION
The object of the present invention is to solve the above problems. Accordingly, the present invention provides a polyurethane foam possessing excellent moldability which maintains a high split tear strength even when the relative amount of water is increased to reduce the molded density of the polyurethane foam.
In order to solve the above problem, the present inventors have made intensive studies and found that a polyurethane foam having a certain cell diameter distribution can solve the above problem, and thus have completed the present invention.
Accordingly, the present invention is directed to a urethane foam for shoe soles prepared by reacting a compound having at least two isocyanate-reactive hydrogen atoms and a molecular weight of 400 to 10000 with a polyisocyanate in the presence of a foam stabilizer, water and a catalyst, characterized in that the ratio r.sub.1 /r.sub.2 of a mean skin cell diameter r.sub.1 to a mean core cell diameter r.sub.2 is 0.02 to 0.80, wherein the mean skin cell diameter r.sub.1 is defined as the mean diameter of the cells which form the skin portion of a urethane foam extending from the surface to a depth of 5% of the foam thickness and the mean core cell diameter r.sub.2 is defined as the mean diameter of the cells which form the core portion of a urethane foam extending from a depth of 40% to a depth of 60% of the foam thickness;
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective of a polyurethane foam test piece for the determination of split tear value.
BEST MODE FOR CARRYING OUT THE INVENTION
The urethane foam for shoe soles of the present invention is obtained by reacting a compound having at least two i
REFERENCES:
patent: 5126181 (1992-06-01), Figuly et al.
WPI Derwent Publications Ltd., London, GB; Class A25, AN 86-343852 (no date).
Harada Shoichiro
Itoi Akito
Okubo Makoto
Sakai Mitsuru
Takemura Kazunari
Copenheaver Blaine
Kao Corporation
Ruddock Ula C.
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