Collapse of polyurethane foam parts, the cause of the collapse of polyurethane foam

Common influencing factors of collapsed bubbles.

The wide molecular weight distribution of monomeric polyether and the large difference in the activity of each component of the combined polyether are one of the main factors causing the slight collapse of PU hard foam. That is, the monomer contains some openable factors and some non-foaming factors, which causes the foaming-gel balance to be chaotic during the molding process, and then the product collapses slightly.

The unreacted propylene oxide contained in the monomer polyether is one of the most important factors causing the malignant collapse of the product. This is due to the fact that the structure of the silicone oil changes under the condition of alkaline (amine catalyst) of PO, and a substance with a defoaming structure is formed; At the same time, PO has a certain oxidation effect in the case of alkaline, which is easy to darken the color of the composition. Some polyether polyols (such as 403, amine catalytic 4110) and other polyether polyols that are not fortified must contain a large amount of PO, which should be paid special attention to.

Other factors: oil pollution has a certain defoaming effect on the foam system, which is easy to cause the occurrence of bubble collapse; The use of some release agents can also cause local collapse of the product.

There are two points: 1. There is a problem with the production process (the angle and the other is the exhaust).

2. Is the viscosity of the raw material a bit large? You can also adjust the catalyst!

Make a friend! Hehe!

The product collapse angle defect of the interior parts is the same as that of the 1L friend, the PU material and the mold exhaust. I have a friend who changed the materials of several houses to get normal.

The foaming material is divided into high-pressure (about 15MPa) and low-pressure (about a few MPa), and ask when selecting PU materials.

Consider the amount of PU to fill and see if there is any improvement!

The polyurethane foaming process is a process in which bubbles are formed as the polymerization reaction progresses and the molecular weight continues to grow, while bubbles are constantly generated in the liquid phase. The reactions that occur in this process can be divided into 3 types:

Chain growth reaction, gas reaction and cross-chain reaction.

Polyurethane foam uses water to produce urea from isocyanate to release CO2 as foaming gas**, and can also use a large amount of heat from the reaction of polyol or other active hydrides with isocyanate to vaporize the outer blowing agent (low boiling point inert solvent) as foaming gas**, so that it can carry out foaming reaction while the chain grows. The more gas produced in the foam, the smaller the density of the foam product, so the different densities of the foam product can be controlled by adjusting the amount of isocyanate and water or the amount of external blowing agent.

If too much foaming catalyst is used, the foaming is too fast; Or the gel catalyst is too little, the gel is too slow, resulting in the foam growing, the strength of the foam wall is not enough to support the weight of the foam, resulting in the collapse of the foam. On the contrary, if the gel is too fast or foaming too slow, the foam has not yet developed well, and the reaction is too fast, resulting in the foam wall strength is too high, and the foaming agent has induced the foam, resulting in the foam density becoming larger.

The adjustment process of polyurethane foam formula is the process of balance adjustment of gel and foaming reaction. Of course, there are many raw material factors, such as the functionality, hydroxyl value, structure of polyol raw materials, whether the type of chain extender and silicone oil is appropriate, and the ratio of black materials, etc., will affect whether the foam collapses?

Throw bricks and lead jade, and look at the master downstairs to explain in detail!