Polyurethane Soft Foam: 15 Common Problems and Solutions

Polyurethane foam often encounters various accidents and problems during actual foaming production, each of which is caused by multiple factors. In the analysis of accidents caused by complex factors, it is generally difficult to list all influencing factors and the main factors that actually play a role. Below are 15 frequently encountered problems and their causes, let's take a look together!

1. High closed-cell content

  a. Polyether polyols: high proportion of ethylene oxide, high activity, often occurs when switching to polyether polyols with different activities.

  b. Process formulation: excessive tin octoate usage, high isocyanate activity, high crosslinking degree, rapid crosslinking speed, excessive amines and physical blowing agents causing low internal pressure of foam, inability to open cells when foam elasticity is high, and high TDI index can also result in high closed-cell content.

2. Shrinkage (gelation speed greater than foaming speed)

  a. High closed-cell content, shrinkage during cooling.

  b. Process conditions: low air temperature, low material temperature.

  c. Process formulation: excessive silicone oil, excessive physical blowing agent, low TDI index.

3. Internal cracking

  a. Process conditions: low air temperature, high reaction center temperature.

  b. Process formulation: low TDI index, excessive tin content, high early foaming strength.

  c. High activity of silicone oil, small usage.

4. Top cracking (unbalanced gasification gelation speed)

  a. Process conditions: low air temperature, low material temperature.

  b. Process formulation: insufficient catalyst usage, small amine usage, poor quality silicone oil.

5. Bottom corner cracking (excessive amine usage, too fast foaming speed)

  Large pore surface: excessive physical blowing agent, poor quality silicone oil and catalyst.

6. Poor low-temperature performance of foam

  Poor intrinsic quality of polyether polyols, same hydroxyl value, low functionality, high unsaturation, low TDI index with the same tin usage.

7. Poor air permeability

  a. Weather conditions: low air temperature.

  b. Raw materials: high polyether polyols, high activity silicone oil.

  c. Process formulation: excessive tin or same tin usage, low water and amine content, high TDI index.

8. Poor resilience

  a. Raw materials: high activity polyether polyols, low relative molecular weight, high activity silicone oil.

  b. Process formulation: large amount of silicone oil, excessive tin content, more water at the same tin usage, high TDI index.

9. Poor tensile strength

  a. Raw materials: excessive low molecular weight polyether polyols, low hydroxyl value functionality.

  b. Process formulation: insufficient tin causes poor gelation reaction, high TDI index at the same tin usage, low crosslinking degree with less water.

10. Smoking during foaming

  a. Excessive amine causes a large amount of heat to be released from the reaction of water and TDI, evaporating low boiling point substances and causing smoking.

  b. If not charring, the smoke is mostly composed of TDI, low boiling point substances, and monomeric cycloalkanes in polyether polyols.

11. Foam with white streaks

  Fast foaming and gelation reaction speed, slow transmission speed in continuous foaming, local compression to form a dense layer, resulting in white streaks phenomenon. The transmission speed should be increased promptly, or the material temperature should be reduced, and catalyst usage should be decreased.

12. Brittle foam

  The formula has excessive water, resulting in many unreacted urea formations that are not dissolved in silicone oil, poor tin catalyst usage, insufficient crosslinking reaction, high content of low relative molecular weight polyether polyols, excessively high reaction temperature, and ether bond breakage which reduces foam strength.

13. Foam density lower than set value

  Foaming index is too large due to inaccurate metering, high air temperature, low air pressure.

14. Foam with skin, edge skin, bottom voids

Excessive tin and insufficient amine, slow foaming speed, fast  

15、High elongation at break

a. Raw materials: high activity polyether polyols, low functionality.

b. Process formulation: insufficient crosslinking due to low TDI index, excessive tin, and high silicone oil content.