During the preparation of polyurethane foam, the role of catalyst is mainly to adjust the speed of foaming reaction and gel reaction, so as to keep a good balance between them.
1. Amine catalyst
Triethylenediamine is an important tertiary amine catalyst in the production of soft foam. The efficiency of promoting the reaction of isocyanate with water, namely foaming reaction, is 60%. The 40% effect is used to promote the reaction between hydroxyl and isocyanate, that is, gel reaction. The width of triethylenediamine and organotin is narrow, but they can promote the late maturity of foam and are indispensable catalysts for all soft foam.
Bis (2-dimethylaminoethyl) ether (a-1) has been recommended as a general tertiary amine catalyst for soft foam. The foaming reaction efficiency is promoted to be 80%, the gel reaction efficiency is promoted to be 20%, the adjustable range of organotin catalyst is widened, and the product qualification rate is improved. At present, it is mainly used in combination with triethylenediamine.
Influence of improper dosage of amine catalyst on foam
1. Excessive amine will cause
(1) The reaction time is short, the initial viscosity increases too fast, and the smoke is large when foaming
(2) Foam burst
2. Too little amine
(1) The initial foaming speed is too slow.
(2) Affects foaming height.
2. Tin catalyst
Stannous octoate is an organotin catalyst commonly used to prepare general block polyether soft foam. It is easily hydrolyzed and oxidized in polyether mixture containing water and tertiary amine.
The dosage of tin oxide can be adjusted in a wide range. The lower the density of foam, the narrower the adjustable range. The influence of tin content is as follows:
Too few: foam bursts
Excessive dosage: viscosity increases rapidly, foam forms closed pores and shrinks, forming bottom skin and edge skin.
The influence of formula change on the demand of stannous octanoate is summarized as follows:
Formula change factor stannous octanoate demand
Reduce water consumption
Increase physical foaming agent
Reduced isocyanate index increases
In actual production, the balance state of foaming reaction and gel reaction is generally adjusted by changing the amount of stannous octanoate, rather than by changing the amount of amine catalyst.
