Common problems and solutions for polyurethane soft foam
1. High closed cell rate
(1) Polyether polyols: high ethylene oxide ratio, high activity, often occurs when replacing polyether polyols with different activities;
(2) Process formula: large amount of stannous octoate, high isocyanate activity, high degree of cross-linking, fast cross-linking speed, excessive amines and physical foaming agents; resulting in low internal pressure of the foam, inability to open cells when the foam elasticity is large, and high closed cell rate when the TDI index is too large.
2. Shrinkage (gel speed is greater than foaming speed)
(1) High closed-cell rate and shrinkage during cooling;
(2) Process conditions: low air temperature and low material temperature;
(3) Process formula: excessive silicone oil, excessive physical foaming agent, and too low TDI index.
3. Internal crack
(1) Process conditions: low air temperature and high reaction center temperature;
(2) Process formula: low TDI index, high tin content, and high early foaming strength;
(3) Silicone oil has high activity and requires little usage.
4. Capping (unbalanced aerogel speed)
(1) Process conditions: low air temperature and low material temperature;
(2) Process formula: insufficient catalyst dosage, small amount of amine, and poor quality of silicone oil.
5. Cracks at the bottom corners (too much amine, too fast foaming speed)
Large pores on the surface: The amount of physical foaming is too large, and the quality of silicone oil and catalyst is poor.
6. Foam has poor low temperature performance
The inherent quality of polyether polyols is poor. When the hydroxyl value is the same, the functionality is low, the unsaturation is large, and the TDI index is low when the tin dosage is the same.
7. Poor ventilation
(1) Climate conditions: low temperature
(2) Raw materials: high polyether polyol and high silicone oil activity;
(3) Process formula: more tin, or less water and amine content when the tin dosage is the same, and 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: large amount of silicone oil, large amount of tin, large amount of water at the same tin dosage, and high TDI index.
9. Poor tensile strength
(1) Raw materials: too much low molecular weight polyether polyol, low functionality with the same hydroxyl value;
(2) Process formula: less tin leads to poor gel reaction. When the tin dosage is the same, the TDI index is high and the crosslinking degree is low due to less water.
10. Smoke comes out when foaming
Excess amine promotes the reaction between water and TDI to release a large amount of heat, and the low-boiling point substances evaporate and smoke. If it is not burning, the smoke is mostly composed of TDI, low-boiling point substances and monomer cycloalkanes in polyether polyols.
11. Foam with white streaks
The foaming and gelling reaction speed is fast, and the transmission speed is slow in continuous foaming. Local extrusion forms a dense layer and produces white tendons. The transmission speed should be increased in time, or the material temperature should be lowered, and the catalyst should be reduced.
12. Crisp foam
There is too much water in the formula, and most of the biuret generated is not dissolved in the silicone oil. The tin catalyst is poor, the cross-linking reaction is not sufficient, the reaction temperature of the small molecular weight polyether polyol is too high, and the ether bond breaks, 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. The foam has bottom skin, side skin and bottom cavitation
There is less polyamine, the foaming speed is slow, the gelling 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 crosslinking, high tin content, and high silicone oil content.
