Analysis of common problems and solutions for polyurethane soft foam – UV absorber manufacturer

1. High obturator rate
(1) Polyether polyols: have a high proportion of ethylene oxide and high activity, which often occurs when replacing polyether polyols with different activities;
(2) Process formula: A large amount of stannous octoate is used, the isocyanate activity is high, the cross-linking degree is large, and the cross-linking speed is fast. Excessive amines and physical foaming agents cause low internal pressure of the foam. When the foam elasticity is high, cells cannot be opened. TDI index If it is too large, it will also lead to a high obturator rate.
2. Shrinkage (gel speed is greater than foaming speed)
(1) The closed cell ratio is high and shrinks when cooling;
(2) Process conditions: low temperature and low material temperature;
(3) Process formula: excessive silicone oil, excessive physical foaming agent, and TDI index is too low.
3. Internal fissure
(1) Process conditions: low temperature, high reaction center temperature;
(2) Process formula: low TDI index, more tin, high early foaming strength;
(3) Silicone oil has high activity and low dosage.
4. Capping (unbalanced speed of air-generating gel)
(1) Process conditions: low temperature, low material temperature;
(2) Process formula: Insufficient amount of catalyst, small amount of amine, and poor quality of silicone oil.
5. Cracked bottom corners (too much amine is used and the foaming speed is too fast)
Large pores on the surface: The physical foaming dose is too large, and the quality of silicone oil and catalyst is poor.
6. Foam has poor low-temperature performance
Polyether polyols have poor intrinsic quality. With the same hydroxyl value, low functionality, high unsaturation, and the same amount of tin, the TDI index is low.
7. Poor ventilation
(1)Climate conditions: low temperature
(2) Raw materials: high polyether polyol and high activity of silicone oil;
(3) Process formula: more tin, or less water and amine content when the amount of tin is the same, the TDI index is high.
8. Poor rebound
(1) Raw materials: polyether polyol has high activity, small relative molecular weight, and silicone oil has high activity;
(2) Process formula: A large amount of silicone oil, a large amount of tin, a large amount of water at the same amount of tin, and a high TDI index.
9. Poor tensile strength
(1) Raw materials: too many low molecular weight polyether polyols and low functionality with the same hydroxyl value;
(2) Process formula: The gel reaction is not good with less tin. When the same amount of tin is used, the TDI index is high and the cross-linking degree is low with less water.
10. Smoke comes out when foaming
Excess amine causes water to react with TDI to release a large amount of heat, and low-boiling point substances evaporate and smoke. If there is no focus, the smoke is mostly composed of TDI, low-boiling point substances, and monomer cycloalkanes in polyether polyols.
11. Foam with white tendons
The reaction speed of foaming and gelling is fast, but the transfer speed is slow in continuous foaming, and a dense layer is formed due to local extrusion, resulting in white veins. The transfer speed should be increased in time, or the material temperature should be lowered, and the amount of catalyst should be reduced.
12. Crispy foam
There is too much water in the formula, which produces a lot of biurets that are not dissolved in silicone oil. The tin catalyst is poor, the cross-linking reaction is insufficient, the content of small relative molecular weight polyether polyols is high, the reaction temperature is too high, and the ether bonds are broken, which reduces the foam strength. .
13. Foam density is lower than the set value
The foaming index is too large due to inaccurate measurement, high temperature and low air pressure.
14. Foam has bottom skin, edge skin, and bottom step cavitation
There is less tin polyamine, the foaming speed is slow, the gel speed is fast, and the temperature is too low during continuous foaming.
15. Large elongation
(1) Raw materials: polyether polyols have high activity and low functionality;
(2) Process formula: low TDI index, insufficient cross-linking, too much tin, and too much silicone oil;