Soft foamCommon problems and solutions in production
Accidents and problems encountered in actual foam production are diverse, and each production accident 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 really play a role.
The following is a summary of some frequently encountered accidents and their causes:
1. Focus center (the temperature of the reaction center exceeds the antioxidant temperature of the raw material)
(1) There are problems with the quality of polyether polyols: During the production, storage and transportation process, the moisture in the product exceeds the standard, the content of peroxides and low-boiling impurities is too high, the concentration of metal ions is too high, and the type and type of antioxidants used are too high. Improper concentration;
(2) Formula: In the low-density formula, the TDI index is too high, the ratio of water to physical foaming agent in the foaming agent is inappropriate, the physical foaming dose is too small, and the water is excessive;
(3) Climate impact: summer temperatures are high, heat dissipation is slow, material temperature is high, air humidity is high, and the reaction center temperature exceeds the antioxidant temperature;
(4) Improper storage: When the TDI index increases, the heat energy accumulated during post-curing increases, which may cause the internal temperature to rise and cause stress.
2. Large compression deformation
(1) Polyether polyol: functionality less than 2.5, ethylene oxide ratio greater than 8%, many small molecule components, unsaturation greater than 0.05mol picture;
(2) Process conditions: The reaction center temperature is too low or too high, the post-curing is not good, the reaction is not complete or there is partial burn;
(3) Process formula: TDI index is too low, silicone oil stannous octoate is excessive, foam ventilation is low, and closed cell rate is high.
3. The foam is too soft (hardness decreases at the same density)
(1) Polyether polyol: low functionality, low hydroxyl value, high relative molecular mass;
(2) Process formula: The amount of stannous octoate is small, and the gel reaction speed is slow. When the amount of tin is the same, the amount of water is small, the physical foaming agent is more, the silicone oil activity is high, the dosage is large, and the TDI index is low.
4. Large cells
(1) Poor mixing; uneven mixing, short milky whitening period;
(2) Process formula: The dosage of silicone oil is lower than the lower limit, the dosage of stannous octoate is small, the activity is poor, and the gel speed is slow.
5. Higher than the set density
(1) Polyether polyol: low activity, large relative molecular mass;
(2) Process formula: The dosage of silicone oil is lower than the lower limit, the TDI index is low, and the foaming index is low;
(3) Climatic conditions: low temperature and high air pressure.
6. Collapse of foam holes (gas generation speed is greater than gel speed)
(1) Polyether polyol: acid value seriously exceeds the standard, many impurities, low activity, and large relative molecular weight;
(2) Process formula: The amount of amine is high and the amount of tin is small, the TDI index is low. At the same amount of tin, the TDI index is too high, the gas generation speed is greater than the gel speed, the skeleton strength is small and foam collapses or local holes appear.
2.
1. High closed cell ratio
(1) Polyether polyol: high proportion of ethylene oxide, high activity, 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, and the foam cannot open holes when the foam elasticity is large. , when the TDI index is too large, it will also lead to high obturator rate.
2. Shrinkage (gel speed is greater than foaming speed)
(1) High closed cell ratio: shrinks when cooling;
(2) Process conditions: low temperature, 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: small dosage.
4. Capping (air gel speedunbalanced)
(1) Process conditions: low temperature and low material temperature;
(2) 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 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. Poor low-temperature foam 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 resilience
(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 and a large amount of tin. When the same amount of tin is used, there is a large amount of water and a high TDI index.
Three
1. Poor tensile strength: n52Q-6H
(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.
2. Smoke when foaming: Excessive amine causes water and TDI to react 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.
3. Foam with white tendons: Foaming and gelation react quickly, and the transfer speed in continuous foaming is slow. Local extrusion generates a dense layer, resulting in white tendons. The transfer speed should be increased in time, or the material temperature should be lowered, and the catalyst dosage should be reduced.
4. Crispy foam: There is too much water in the formula, and a lot of biuret is formed that is not dissolved in the silicone oil. The tin catalyst is poor, the cross-linking reaction is insufficient, the content of small relative molecular weight polyether polyols is too high, and the reaction temperature is too high. , the ether bond breakage reduces the foam strength.
5. 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.
6. The 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.
7. Large elongation
(1) Raw materials: polyether polyol has high activity and low functionality;
(2) Process formula: low TDI index, insufficient cross-linking, too much tin, and too much silicone oil;
(3)High temperature
