In the process of polyurethane foam preparation, the role of catalysts is mainly to regulate the speed of foaming and gelation reactions to make them in a good balance.
I. Amine catalysts
Triethylenediamine is the most important tertiary amine catalyst in soft foam production, it has 60% efficacy for promoting the reaction between isocyanate and water, i.e. foaming reaction. 40% efficacy for promoting the reaction between hydroxyl and isocyanate, i.e. gel reaction. triethylenediamine has narrow width for organotin, but it has the function of promoting the late maturation of foam and is an indispensable catalyst for all soft foams.
Bis(2-dimethylaminoethyl) ether (A-1) has been recommended as the tertiary amine catalyst for general-purpose soft foam, it has 80% efficacy to promote the foam reaction and 20% efficacy to promote the gel reaction, which widens the adjustable range of organotin catalyst and improves the qualified rate of products, and is mostly used in combination with triethylenediamine.
The effect of improper dosage of amine catalyst on foam
1. Excessive amine will cause
(1) Short reaction time, too fast increase of starting viscosity, big smoke when foaming
(2) Foam cracking
2、The amount of amine used is too little
(1) The starting foaming speed is too slow.
(2) Affect the foaming height.
Two, tin catalyst
Stannous octanoate is the most commonly used organotin catalyst for general-purpose block polyether soft foam, which is very easy to hydrolyze and oxidize in the polyether mixture containing water and tertiary amine.
Stannous octanoate dosage is adjustable in a wide range, the lower the foam density, the narrower the adjustable range, the tin dosage affects as follows.
Too little amount: foam cracking
Too much: the viscosity increases quickly, the foam forms closed pores and shrinks, forming bottom and side skins.
The effect of recipe changes on the amount of stannous octanoate required is summarized as follows.
Formula change factor Stannous octanoate requirement
Decrease water volume Decrease
Increase physical foaming agent Increase
Decrease isocyanate index Increase
In practice, the equilibrium state of the foaming and gelation reactions is usually adjusted by changing the amount of stannous octanoate without changing the amount of amine catalyst.
According to the data, in the production of polyether block soft foam, the amount of stannous octanoate and foam density have the following relationship.
Where d is the density of foam (kg/m3)
The formula is qualified as follows.
(1) the amount of formulation 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 is 1.03~1.15, if the index is increased, the dosage is reduced to about one thousandth of the index increase
(3) If the amount of MC is increased, the amount of stannous octanoate is increased by about two thousandths of MC.
Reference amount of stannous octanoate under each density.
Density (kg/m3) Stannous octanoate dosage (wt%)
12 0.34
16 0.27
20 0.23
26 0.21
30 0.2
35 0.19
46 0.17
