In the past, catalysts for producing shoe soles were organic tin compounds and tertiary amine compounds. When the amount of catalyst is large, the resinization speed is fast, the flowability is poor, and the surface of the sole is often defective; the amount of the catalyst is reduced, and the obtained surface of the sole is intact, but the molding time is longer and the production efficiency of the sole is reduced.
Since the surface quality and productivity of the shoe sole are opposed, it is desirable that the catalyst for the polyurethane reaction has a low initial activity and the catalytic activity increases while the foaming reaction proceeds, that is, a so-called "delayed catalyst." As a delayed catalyst, for example, when used in hard foam heat insulation materials, a part of the tertiary amine is protected with a formic acid catalyst or a tertiary amine and a specific dicarboxylic acid constitute the catalyst system. However, these catalysts have almost no retarding effect at the initial stage of the reaction and do not improve the surface properties of polyurethane soles.
In addition, the polyol raw material component used for manufacturing the shoe sole is higher in viscosity than the rigid foam produced, and is completely used as a foaming agent. Therefore, the reaction starting temperature of the raw material is usually adjusted to 35 to 45° C. (hard foam is usually room temperature). .
Where both tertiary amines and saturated carboxylic acids are present, they are in the form of their salts. In the initial stage of the reaction, the salt is not dissociated and the catalytic activity is weak. As the reaction progresses, the accumulated heat releases the salt and the tertiary amine, and exerts catalytic activity. Formic acid or adipic acid exists as a salt with a tertiary amine at room temperature or lower, and the solution is separated at a temperature of 30° C. or more, so that no initial retardation effect is observed. The salt of oxalic acid or malonic acid does not undergo partial separation, so there is a delay in the initial stage of the reaction, so that the fluidity of the raw material mixture is sufficient, and a product with a good surface is obtained. Since the sole polyurethane reaction can reach a temperature of 80° C. or more, the tertiary amine salt can be fully dissociated to exert its catalytic activity, and therefore good mold release properties can be maintained.
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