PU soft foam common problems and solutions

1、High closed pore rate

(1) polyether polyol: high proportion of ethylene oxide, high activity, more occurring in the replacement of polyether polyol with different activities.

(2) process formula: more amount of stannous octanoate, high activity of isocyanate, large cross-linking, fast cross-linking, too much amine and physical blowing agent.

Cause low internal pressure of foam, foam elasticity can not open the hole, TDI index is too large will also lead to high closed-hole rate.

2、Shrinkage (gel speed is greater than the speed of foaming)

(1) High closed pore rate, shrinkage when cooling.

(2) process conditions: low temperature, low material temperature.

(3) process formula: excessive silicone oil, excessive physical foaming agent, TDI index is too low.

3、Inside crack

(1) Process conditions: low temperature, high temperature of reaction center.

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

(3) high activity of silicone oil, less dosage.

4, top crack (hair gas gel speed imbalance)

(1) process conditions: low temperature, low material temperature.

(2) process formula: catalyst dosage is not enough, amine dosage is less, silicone oil quality is not good.

5, bottom corner crack (too much amine, foaming speed is too fast)

Surface macropore: excessive amount of physical foaming agent, poor quality of silicone oil and catalyst.

6、Poor low temperature performance of foam

Poor intrinsic quality of polyether polyol, low functionality and unsaturation in the same hydroxyl value, low TDI index when the same amount of tin is used.

7、Poor ventilation

(1) climatic conditions: low temperature

(2) raw materials: high polyether polyol, high silicone oil activity;

(3) process formula: more tin, or the same amount of tin when the water and amine content is less, the TDI index is high.

8、Different inverse elasticity

(1) raw materials: high activity of polyether polyol, small relative molecular mass, high activity of silicone oil;

(2) process formula: large amount of silicone oil, more tin, more water in the same amount of tin, high TDI index.

9、Poor tensile strength

(1) raw materials: too many low-molecular polyether polyol, the same hydroxyl value of low functionality;

(2) process formula: less tin gel reaction is not good, in the same amount of tin, TDI index is high, less water cross-linking degree is low.

10、Smoke when foaming

Excess amine prompted by the reaction between water and TDI released a lot of heat, low boiling point material evaporation and smoke. If it is not scorched, the smoke is mostly from TDI, low boiling point substances and polyether polyethylene.

low boiling point substances and polyether polyol monomer naphthenic composition.

11、Foam with white rib

Foam and gel reaction speed, in the continuous foam transfer speed is slow, the local extrusion and generation of dense layer, the phenomenon of white tendons. Should

Timely increase the transfer speed, or reduce the material temperature, reduce the amount of catalyst.

12、Crispy foam

There is more water in the recipe, the generation of diurea has not been dissolved in silicone oil, poor tin catalyst, cross-linking reaction is not sufficient, small relative molecular mass of polyether polyol, the content of polyether polyol is high.

The content of polyether polyol is too much, the reaction temperature is too high, the ether bond breakage reduces the foam strength.

13、Foam density is lower than the set value

Foam index is too big because of inaccurate measurement, high temperature and low air pressure.

14、The foam has bottom skin, side skin, bottom step cavitation

Tin polyamine less, slow foaming speed, fast gel speed, in continuous foaming with temperature too low.

 

15、Large elongation rate

(1) raw materials: polyether polyol activity is high, functional degree is small;

(2) process formula: TDI index low crosslinking is not enough, more tin, more silicone oil;