Usage of silicone oil
Foam stabilizers are a class of surfactants that can make polyurea well dispersed in the foaming system and play the role of “physical cross-linking point”, and can obviously improve the early viscosity of the foam mixture to avoid cracking. On the one hand, it has emulsifying effect, which can enhance the mutual solubility between the components of foam materials, on the other hand, the addition of silicone surfactant can reduce the surface tension of liquid, which can reduce the free energy required for gas dispersion and make the air dispersed in the raw material easier to nucleate during the mixing process, which can help the generation of small bubbles, adjust the size of foam pores, control the structure of pores and improve the stability of foaming; prevent the deflation and rupture of pores and improve the stability of foaming. The foam pore deflates and breaks, makes the foam wall elastic, and controls the foam pore size and uniformity. It stabilizes the foam in the early stage of foaming, prevents the foam in the middle of foaming, and makes the foam pores connected in the late stage of foaming. General foaming agent, POP dosage the more silicone oil dosage.
The amount of more: so that the late foam wall elasticity increases, should not break, the bubble hole fine. Cause closed pore.
The amount of less: foam rupture, collapse bubble after starting, pore size is larger, easy.
In the process of soft foam production depends on surfactant a lot, if there is no surfactant, the reaction mixture will boil or even collapse bubble, and it is impossible to form foam, the amount of silicone oil surfactant should be adjusted according to the type of silicone oil, activity, formulation situation and foam density, etc.
Generally speaking, when the foam density is above 30KG/M3, the amount of silicone oil per 100 parts of polyether is 0.7-1.0 parts, and for every 0.5 increase in foaming index, the corresponding increase in silicone oil is 0.1-0.3 parts.
Of course, the amount of silicone oil is also related to other components in the formula, especially with the amount of stannous octanoate and isoacid index has a great relationship, in the production of very low density foam, the amount of silicone oil is also increased accordingly. Usually, the formulation of the appropriate amount of silicone oil, can be made of uniform pore, clear structure, skin thickness of moderate foam, too much silicone oil, bubble film elasticity is too good, too firm, so that under normal circumstances can be broken bubble wall can not break, the foam body tends to close the pore, the skin more into the light, the foam body to increase the rate of closed pore, resilience, tin catalyst applicable range becomes smaller, the heavy bubble body closed pore Seriously, even cause foam shrinkage.
The amount of silicone oil is too little, the foam stability is not enough, serious and bubble, bubble pore coarse and uneven, and even collapse bubble.
In the use of silicone oil which should be used in addition to the appropriate amount, more attention should be paid to the selection of the appropriate activity of the silicone oil varieties, for different product series, the correct choice of silicone oil varieties, is the basis of success, never the same variety of silicone oil to meet the production needs of a variety of foam.
Increase the amount of silicone oil used, its bubble pore will be more delicate, the later foam wall elasticity increases, should not be broken, bubble pore fine. It will cause closed pores and increase certain toughness.
Recently, I have been busy with how to increase the hardness of the product, and by chance, I added less silicone oil almost without adding, the product is very rigid, of course, the liquidity is much worse, the main thing is that the bubble pore is particularly thick. Although there is no collapse of the bubble, but always feel that is playing with fire. Then test the extreme value of its collapse bubble, to reach the amount of product collapse bubble slowly add the amount of silicone oil, the amount of water correspondingly increase some. The product hardness also went up.
There is an experiment, the amount of silicone oil to reduce the product skin hardness rose, the bubble hole is relatively fine and uniform. However, the core foam is particularly soft and somewhat similar to cotton, almost no toughness and resilience. Increase the amount of silicone oil toughness is up, but the epidermis and core hardness are not ideal.
We added polyether with high hydroxyl value and low molecular weight from 20 parts to 60 parts, but the hardness of the product did not go up either.
The same is true for adding crosslinker, from 5 to 20 parts.
How much difference in hydroxyl value can reflect whether the hardness has increased or not?
Theoretically, the hardness of the product will increase if the polyether with low hydroxyl value is replaced by low molecular weight polyether with high hydroxyl value, however, it is not obvious in my pilot test.
I still need to match with small materials to improve the hardness of the product.
The product has 25 starting hair, 95 drawing, 24 free bubble density.
The product skin hardness is qualified, but its core hardness is very soft, almost no hardness. The bubble hole is also fine. I want the core hardness to increase, except for increasing the density and index. How should I change the formula?
The product made is required to be leveling, as long as the product is flat. Molded filled products.
Low silicone oil: its skin hardness increases, the overall hardness also rises (there is a certain range, which needs to be tested by yourself). Increase the amount of silicone oil, its overall toughness, resilience are significantly improved.
The diisocyanates commonly used in the preparation of waterborne polyurethane emulsions are aromatic diisocyanates: TDI, MDI, etc.; there are aliphatic and alicyclic diisocyanates: IPDI, HDI, H12MDI, etc.. Waterborne polyurethane emulsions made from them have higher hydrolysis resistance than those made from aromatic diisocyanates, and thus the storage stability of waterborne polyurethane products is good.
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