Most of the silicone oils are nucleating, emulsifying and stabilizing.
Silicone oil
The foam stabilizer is a kind of surfactant, which can make the polyurea disperse well in the foaming system, plays the role of "physical crosslinking point", and can obviously improve the early viscosity of the foam mixture and avoid cracking. On the one hand, it has an emulsification effect, which enhances the mutual solubility between the components of the foam material. On the other hand, the addition of the silicone surfactant reduces the surface tension r of the liquid, and the increased free energy required for gas dispersion is reduced, so that the dispersion is dispersed. The air in the raw material is more likely to nucleate during the stirring and mixing process, which contributes to the generation of fine bubbles, adjusts the size of the foam pores, controls the cell structure, improves the foaming stability, prevents the cells from foaming and cracking, and makes the foam wall have Elasticity controls foam aperture and uniformity. It stabilizes the foam at the initial stage of foaming, prevents the foam from foaming in the middle of the firing, and connects the cells at the late stage of foaming. Generally, the more foaming agent and POP are used, the greater the amount of silicone oil used.
The amount of use is increased: the elasticity of the foam wall is increased in the late stage, and it is not suitable for cracking and the cells are fine. Causes closed cells.
Less dosage: foam rupture, collapse after foaming, larger diameter and easy.
In the production process of soft foam, the dependence on surfactant is very large. If there is no surfactant, the reaction mixture will boil or even collapse, and it is impossible to form foam. The amount of silicone oil surfactant should be based on the type of silicone oil. The activity, formulation and foam density were adjusted.
The amount of silicone oil is highly correlated with the foam density. Generally speaking, when the foam density is above 30KG/M3, the amount of silicone oil per hundred parts of polyether is 0.7-1.0 parts, and the foaming index increases by 0.5, and the corresponding silicone oil increases. The amount is from 0.1 to 0.3 parts.
Of course, the amount of silicone oil is also related to other components in the formulation, especially the amount of stannous octoate and the isotonic acid index. In the production of very low density foam, the amount of silicone oil is also increased accordingly.
Generally, the amount of silicone oil in the formulation is appropriate, and a foam having uniform cells, a clear structure, and a moderate skin thickness can be obtained.
If the amount of silicone oil is too much, the bubble film is too elastic and too strong, so that the wall of the bubble that can be broken under normal conditions cannot be broken, the foam tends to be closed, the skin is more advanced, and the closed porosity of the foam is improved, and the rebound is improved. When it falls, the applicable range of the tin catalyst becomes smaller, and the weight causes the closed cells of the bubble body to be severely closed, and even causes the foam to shrink.
The amount of silicone oil is too small, the foam stability is insufficient, serious bubbles occur, the cells are coarse and uneven, and even collapse.
In addition to the appropriate amount of silicone oil, it should be noted that the selection of suitable active silicone oil varieties, the correct choice of silicone oil varieties for different product series, is the basis for success, and can never use the same variety of silicone oil. Meet the production needs of various foams.
When the amount of silicone oil is increased, the cells will be more delicate, and the elasticity of the foam wall will increase at the later stage, which is not suitable for cracking and the cells are fine. Causes closed cells and increases certain tenacity.
Recently, I have been busy how to increase the hardness of the product. Occasionally, there is almost no addition of silicone oil. The product is very rigid. Of course, the fluidity is much worse. The most important thing is that the cells are particularly coarse. Although there is no collapse, I always feel that it is playing with fire. Then, the extreme value of the collapse is tested, and how much product is slowly foamed and the amount of silicone oil is added, and the amount of water is increased accordingly. The hardness of the product has also gone up.
In another experiment, the amount of silicone oil decreased the hardness of the product skin, and the cells were relatively fine and uniform. However, the core foam is particularly soft and somewhat similar to cotton, with little toughness and resilience. Increasing the toughness of silicone oil is up, but the hardness of the skin and core are not ideal.
There is a high molecular weight low molecular weight polyether added, from 20 parts to 60 parts, but the hardness of the product is not added.
The same is true for the addition of the crosslinking agent, from 5 parts to 20 parts. How much difference in the hydroxyl value can reflect the increase in hardness?