15 problems frequently encountered in polyurethane soft foam production and their causes

1
High obturator rate
Polyether polyols: have a high proportion of ethylene oxide and high activity, which often occurs when replacing polyether polyols with different activities.

Technical formula: high dosage of stannous octoate, high isocyanate activity, large degree of cross-linking, fast cross-linking speed, excessive amines and physical foaming agents cause low internal pressure of the foam, and the foam cannot open holes when the elasticity is high, 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]
It has a high closed cell ratio and shrinks when cooled.

Processing conditions: low temperature and low material temperature.

Process formula: excessive silicone oil, excessive physical foaming agent, and TDI index is too low.

3
Internal fissure
Process conditions: low temperature and high reaction center temperature.

Process formula: low TDI index, more tin, high early foaming strength.

Silicon oil has high activity and low dosage.

4
Capping [Unbalanced foaming gel speed]
Process conditions: low temperature and low material temperature.

Process formula: The amount of catalyst is insufficient, the amount of amine is small, and the quality of silicone oil is poor.

5
Cracked bottom corner [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
The intrinsic quality of polyether polyol is poor. With the same hydroxyl value, low functionality, high degree of unsaturation, and the same amount of tin, the TDI index is low.

7
Poor ventilation
Climatic conditions: low temperatures.

Raw materials: high polyether polyol and high activity of silicone oil.

Process formula: When there is more tin or the same amount of tin, the content of water and amine is small, and the TDI index is high.

8
Poor rebound
Raw materials: Polyether polyol has high activity, small relative molecular weight, and silicone oil has high activity.

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
Raw materials: There are too many low molecular weight polyether polyols and low functionality with the same hydroxyl value.

Technical 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 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 flue gas is mostly composed of TDI, low boiling point substances and monomer cycloalkanes in polyether polyols.

11
Foam with white ribs
The reaction speed of foaming and gelling is fast, and the transfer speed is slow during continuous foaming. A dense layer is formed due to local extrusion, resulting in the phenomenon of white veins. The transfer speed should be increased in time, or the material temperature should be lowered, and the catalyst dosage should be reduced.

12
Foamy and crispy
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 polyether polyol content of small relative molecular weight is high, the reaction temperature is too high, and the ether bonds are broken, which reduces the foam strength. .

13
The 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 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
Raw materials: Polyether polyol has high activity and low functionality.

Process formula: low TDI index, insufficient cross-linking, too much tin, and too much silicone oil.