1. Field of the Invention
The present invention relates to a method for producing polyisocyanurate foams having excellent heat resistance and flame resistance, more particularly to a method for producing polyisocyanurate foams having high heat resistance and flame resistance, which do not cause burst, crack and deformation when exposed to flame.
2. Description of the Prior Art
The method for producing foams having isocyanurate ring structure has been well known and the foundation of the production method has been disclosed in Japanese Pat. No. 503,912, which relates to a composition composed of an organic polyisocyanate, a blowing agent and a catalyst for polymerizing isocyanate group and the polymerization is promoted in the condition of excess of isocyanate group. This polyisocyanurate foam has substantially the same heat insulating performance as the polyurethane foam and is superior in the heat resistance and the flame resistance to the polyurehtane foam and has high usable value as high temperature insulating materials and low temperature insulating materials.
However, the heretofore produced polyisocyanurate foams are very brittle and are poor in physical properties and when exposed to flame, the foam causes burst, crack and deformation.
In order to improve these defects, a variety of processes for producing modified polyisocyanurate foams have been proposed. For example, as the modifying means, use of a polyether, use of a polyester, introduction of polyoxazolidone bond, use of a mixture of a polyol having a molecular weight of moe than 200 and a diolpolyether having a molecular weight of less than 200, use of xylene resin initial condensate, introduction of polycarbodiimido bond, introduction of urethane bond and carbodiimido bond and the like have been known. These modified polyisocyanurate foams can be actually more or less improved in the brittleness and the bursting property, while the fire-proof and the flame resistance decrease and the smoke generation increases.