Soft foam common problems and solutions

The amount of accidents and problems encountered in actual foaming production is diverse, and each accident production is caused by a variety of factors. In the analysis of accidents caused by complex factors, it is generally difficult to list all the influencing factors and the main factors that really play a role. The following is a summary of some of the commonly encountered accidents and their causes.

 

1, scorch (reaction center temperature exceeds the raw material antioxidant temperature)

(1) polyether polyol quality problems: production, storage and transportation process so that the product in the water exceeds the standard, peroxide, low boiling point impurity content is too high, metal ion concentration is too high, with the type and concentration of antioxidants improper;

(2) formula: low density formula, TDI index is too high, improper ratio of water and physical blowing agent in the blowing agent, the amount of physical blowing agent is too small, excessive water;

(3) Climate: high temperature in summer, slow heat dissipation, high material temperature, high air humidity, the reaction center temperature exceeds the antioxidant temperature;

(4) improper storage: when the TDI index rises, the heat energy of the pile increases during post-ripening causing the internal temperature to rise and scorch.

2、Large compression deformation

(1) polyether polyol: the functional degree is less than 2.5, the proportion of ethylene oxide is more than 8%, many small molecule components, unsaturation degree is more than 0.05 mol/kg;

(2) Process conditions: the temperature of the reaction center is too low or too high, the post-ripening is not good, and the reaction is not complete or there is partial scorching;

(3) Process formula: TDI index is too low, stannous silicone oil octanoate is too much, foam aeration is low, and closed pore rate is high.

3、The foam is too soft (hardness decreases under the same density)

(1) Polyether polyol: low functional degree, low hydroxyl value, large relative molecular mass;

(2) process formula: low amount of tin octanoate, slow gel reaction speed, less water in the case of the same amount of tin, more physical foaming agent, high dosage of silicone oil activity, low TDI index.

4、Bubble hole coarse

(1) bad mixing; uneven mixing, short emulsion period;

(2) process formula: silicone oil dosage is lower than the lower limit, low dosage of stannous octanoate and poor activity, slow gel speed.

5、Higher than the set density

(1) polyether polyol: low activity, large relative molecular mass;

(2) process formula: silicone oil dosage is lower than the lower limit, low TDI index, low foaming index;

(3) climatic conditions: low temperature and high air pressure.

6、Collapse bubble hole (gas velocity is greater than gel velocity)

(1) polyether polyol: acid value seriously exceeds the standard, many impurities, low activity, large relative molecular weight;

(2) process formula: amine dosage more tin dosage less, low TDI index, in the same tin dosage TDI index is too high, the gas velocity is greater than the gel speed, the skeleton strength is small and collapse bubbles or local holes.

 

1、High closed pore rate

(1) polyether polyol: high proportion of ethylene oxide, high activity, mostly occurring in the replacement of polyether polyol with different activity;

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

The internal pressure of the foam is low, and the foam elasticity cannot be opened when the TDI index is too large, which 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 Internal cracking

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

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

6、Poor low temperature performance of foam

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

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, 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

1、Poor tensile strength

(1) raw materials: too much 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.

2、Smoke when foaming

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

low boiling point substances and polyether polyol monomer naphthenic composition.

3、Foam with white rib

The reaction speed of foaming and gelation is fast, and the transfer speed is slow in continuous foaming, which generates a dense layer by local extrusion and produces the phenomenon of white rib. Should

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

4、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, and the breaking of ether bond reduces the strength of foam.

5、Foam density is lower than the set value

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

6、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.

7、Large elongation rate

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

(2) process formula: TDI index low cross-linking deficiency, more tin, more silicone oil;

(3)High temperature