In the preparation process of polyurethane foam, the main role of the catalyst is to adjust the speed of the foaming reaction and gelation reaction to keep them in a good balance.
1. Amine catalyst
Triethylenediamine is the most important tertiary amine catalyst in soft foam production. It has 60% efficiency in promoting the reaction between isocyanate and water, that is, the foaming reaction. 40% efficacy is used to promote the reaction between hydroxyl groups and isocyanates, that is, the gel reaction. Triethylenediamine has a narrow width for organotin, but it has the effect 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 a universal tertiary amine catalyst for soft foam. It has 80% efficacy to promote foaming reaction and 20% efficacy to promote gelation reaction and widening It increases the adjustable range of organotin catalysts and improves the qualification rate of products. Currently, it is mostly used in combination with triethylenediamine.
Effect of Improper Amine Catalyst Dosage on Foam
1. Excessive amine will cause
(1) The reaction time is short, the initial viscosity increases too quickly, and there is a lot of smoke during foaming
(2) Foam cracking
2. The amount of amine used is too small
(1) The initial foaming speed is too slow.
(2) Affects foaming height.
2. Tin Catalysts
Stannous octoate is the most commonly used organotin catalyst for general-purpose bulk polyether soft foam. It is extremely easy to hydrolyze and oxidize in polyether mixtures containing water and tertiary amines.
The dosage of stannous octoate has a wider adjustable range. The lower the foam density, the narrower the adjustable range. The influence of tin dosage is as follows:
Too little: foam cracks
Too much dosage: the viscosity increases quickly, the foam forms closed cells and shrinks, forming a bottom skin and an edge skin.
The impact of changes in the formula on the requirement of stannous octoate is summarized as follows:
Formula changing factors: Requirements of stannous octoate
Reduce the amount of water Reduce
Add physical foaming agent to increase
Reduce isocyanate index Increase
In actual production, the amount of amine catalyst is generally not changed, but the balance state of the foaming reaction and gelation reaction is adjusted by changing the amount of stannous octoate.
According to data reports, when producing polyether block soft foam, the dosage of stannous octoate has the following relationship with the foam density:
where d is the foam density (kg/m3)
The formula has the following qualifications:
(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 appropriate index is 1.03~1.15. If the index is increased, the dosage will be reduced, which is about one thousandth of the increase in the index
(3) If the dosage of MC is increased, the increase in stannous octoate will be about two thousandths of MC.
Reference dosage of stannous octoate at each density:
Density (kg/m3) Dosage of stannous octoate (parts by weight)
12 0.34
16 0.27
20 0.23
26 0.21
30 0.2
35 0.19
46 0.17
