During the preparation of polyurethane foam, the role of catalyst is mainly to adjust the speed of foaming reaction and gel reaction to keep them in good balance.
1、 Amine catalysts
Triethylenediamine is the most important tertiary amine catalyst in soft foam production, with 60% efficacy in promoting the reaction between isocyanates and water, i.e. foaming reaction. The 40% effect is used to promote the reaction of hydroxyl and isocyanate, that is, gel reaction. The width of triethylenediamine to organotin is narrow, but it can promote the late maturing of foam, and is an indispensable catalyst for all soft foams.
Bis (2-dimethylaminoethyl) ether (A-1) has been recommended as a versatile tertiary amine catalyst for soft foam. It has 80% efficacy to promote foaming reaction, 20% efficacy to promote gel reaction, widening the adjustable range of organotin catalyst, and improving the qualification rate of products. Currently, it is mostly used in combination with triethylenediamine.
Influence of improper dosage of amine catalyst on foam
1. Excessive amine will cause
(1) Short reaction time, rapid increase in initial viscosity, and excessive smoking during foaming
(2) Cracking of foam
2. The amount of amine used is too low
(1) The initial foaming speed is too slow.
(2) Affects foaming height.
2、 Tin based catalysts
Stannous octanoate is the most commonly used organic tin catalyst for general-purpose block polyether soft foams. It is highly susceptible to hydrolysis and oxidation in polyether mixtures containing water and tertiary amines.
The adjustable range of tin octoate dosage is wide. The lower the foam density is, the narrower the adjustable range is. The influence of tin dosage is as follows:
Too little: foam cracks
Too much dosage: the viscosity increases quickly, and the foam forms closed pores and shrinks, forming bottom skin and edge skin.
The impact of formula changes on the demand for stannous octanoate can be summarized as follows:
Formula change factor tin octanoate requirement
Reduce water volume
Increase physical foaming agent
Reduce isocyanate index and increase
In actual production, the balance state of foaming reaction and gel reaction is generally adjusted by changing the amount of stannous octoate rather than the amount of amine catalyst.
According to data reports, when producing polyether type blocky soft foam, the relationship between the amount of stannous octoate and the density of foam is as follows:
Where d is the density of foam (kg/m3)
The limiting conditions of this formula are as follows:
(1) Formula dosage based on 100 parts of polyether
(2) When d ≥ 20kg/m3, the TDI index is 1.06
When d<20kg/m3, the TDI index is 1.10
The index should be between 1.03 and 1.15. If the index is increased, its usage will decrease by about one thousandth of the index increase
(3) If the amount of MC is increased, the increase in stannous octanoate is about two thousandths of MC.
Reference dosage of stannous octanoate at various densities:
Density (kg/m3) Amount of stannous octanoate (by weight)
12 0.34
16 0.27
20 0.23
26 0.21
30 0.2
35 0.19
46 0.17