【Technology】Foam stabilizer (silicone oil) handout
1. what is silicone oil
Silicone oil is a kind of silicone surfactant, which was firstly called foaming spirit in China and Silicone surfactant in Taiwan and Hong Kong, and later it is usually called foam leveler and foam stabilizer in China. This type of surfactant can be divided into Si- O- C type and Si- C type. The Si- C bond does not hydrolyze, while the Si- O- C bond is easy to hydrolyze under strong acid or alkali conditions, so the foam stabilizer made by this connection method is not suitable for the preparation of the combination, because after it is stored for a period of time with the tertiary amine catalyst and water, the product will lose its foam stabilizing effect due to the hydrolysis of the Si- O- C bond. The product will lose its stabilizing effect due to the hydrolysis of Si-O-C bond. Therefore, it is used for hard foam, semi-hard foam and high resilience foam leveling agent is generally Si-C type. Its structure is generally as follows
In a word, we say: silicone oil is a kind of silicone oil additive that can make the foam stable during the foaming process, make the foam body rise smoothly without collapsing the foam during the foam rise, and make the foam pore structure uniform and fine without breaking the foam. Ten years ago, the domestic production of silicone oil is relatively low, and did not enter the high-end market, the market is mainly controlled by European and American countries. After years of national efforts, the current market of hard foam silicone oil is mainly made by domestic companies, and there are a series of products from low-end to high-end, from insulation to refrigerator supply. Like us Dongjun Chemical produces more than 2000 tons of silicone oil every year, of which more than 500 tons are exported, and the export volume is still rising, and many products are exported to Europe and the United States market.
2. The role of silicone oil
The role of silicone oil is simply to make the foaming system to be able to foam, to stabilize the foam, to make the foam pore fine and uniform, high closed pore rate. Not to add silicone oil will collapse the bubble, is not to send the foam.
There is a set of pictures you can watch the difference between adding and not adding silicone oil in the foaming process (the right picture added silicone oil). So how silicone oil is to play a role in controlling the role of the foam, mainly in the following areas.
2.1 Emulsification role
Silicone oil is an emulsifier, one end of lipophilic, one end of hydrophilic, can make the white material in the components (especially polyether, polyester, foaming agent) in the mixing process can form a homogeneous, stable solution, so that the combination of materials do not stratify. As shown in the figure below.
In addition in the black and white material mixing process can also play a certain role in making the black and white material mixed evenly. We all know that the more uniformly the black and white materials are mixed, the more fully the reaction is, the more uniform the foam pores are, the better the fluidity is, and the smaller the density distribution gradient is.
2.2 Nucleation
In the reaction just happened, silicone oil has reduced the surface tension of the system, so that the system in the stirring of the mixed air to form a certain number of bubble nuclei, in the process of foam development, nucleation of air bubble nuclei play a role similar to the “crystal species”, so that the foam can be formed smoothly, slowly become larger, if the foam does not form a bubble nucleus, then it is not a uniform foam. If the bubble does not form a nucleus, then it will not form a uniform bubble body. Just like we blow soap bubbles, without adding some washing powder or detergent, who can not blow a string of bubbles, only add a little washing powder can blow out the colorful bubbles.
2.3 The role of stable foam
Foam just formed when very small very small, with the foam reaction, the foam is also growing, there is constantly gas into the bubble. In this process before the foam curing, the foam body is also still very fragile, and will break if not careful, silicone oil is a surfactant, with the presence of silicone oil, it can be directed to arrange on the surface of the foam, to protect the foam, to avoid the merging of bubble and bubble, so that the foam is stable, not to be the foam rupture, merging, endless expansion, so as to ensure the formation of an independent foam;
On the other hand, silicone oil can dissolve the urea formed by the reaction of black material (MDI) and water, so that the tension of the bubble wall is uniform and there is no stress point, which ensures that the foam does not break until the foam body is cured and a uniform foam with high closed-hole rate structure is formed.
2.4 Improving the fluidity and density distribution of the foam body
We say that silicone oil is a surfactant, which can reduce the surface tension of the system, as shown below
Reducing the surface tension is good for improving the wettability of the foam body to the substrate mold, thus improving the fluidity and density distribution and reducing the dark bubbles. The following is a comparison of two groups of liquid flow with and without surfactant.
3. Classification of silicone fluids
The classification of silicone oil is still based on its characteristics to classify, generally divided into three categories: first, nucleation ability of silicone oil; second, emulsification ability of silicone oil; third, good flowability of silicone oil. There are many classifications in other applications, such as classification according to the foaming agent: F-11 system, 141B system, cyclopentane system, all-water system; classification according to the use: home appliances, plates, spraying, etc.. This classification is a lot, but the essence is also based on the silicone oil’s own structure and its characteristics, we usually say that different blowing agents choose different silicone oil, different uses choose different silicone oil, in the final analysis or based on the above three requirements and different.
Silicone oil basic performance classification
For example: 1, we all say that the cyclopentane system is different from the 141B system of silicone oil, why? A very important reason is the poor compatibility of cyclopentane and conventional polyether system. Then, to make the combination of material system stability you either choose a special polyether, or choose a strong emulsification capacity of silicone oil.
2. Some people say that our combination material is not as high as others, that is because the fluidity of your combination material, the starting speed is not good enough, and the silicone oil you choose is a very poor fluidity of silicone oil, how can the rate be high?
4. choice of silicone oil
So how do we choose the right silicone oil in the actual application? Based on the same triangle diagram above, depending on what you need, what you require, and what kind of results you want.
For example, 1, if you require a particularly fine bubble pore, the closed pore rate to be particularly high, then you choose to favor the nucleation ability of the role of strong silicone oil, such as our company’s H-3625, H-350, H-3625A;
2、If you use a particularly large amount of foaming agent, but also add a considerable amount of polyester, then you should choose a strong emulsification capacity of the silicone oil, such as our H-3609, H-3618, H-3606, H-693, etc.;
3、If you require a silicone oil with high square rate or large mold foam, then you should choose a silicone oil with good fluidity, such as our H-3612, H-3625B.
4、If you want a better overall performance: to do refrigerator material, with cyclopentane as a foaming agent, not only require foam holes also require emulsification ability, liquidity can not be too bad, then you choose my company’s H-3610, H-3633, H-360, etc..
Different silicone oil has different characteristics and different focus of different silicone oil. You have to choose the suitable silicone oil for your system according to your raw material situation and different uses. After the direction of the main function of the silicone oil is determined, then according to the actual application needs, select the appropriate performance of the product, each major direction of the silicone oil has a series of fine-tuned products for users to choose to meet different needs. I think the choice of silicone oil is the same as looking for a date, there is no best, only the most suitable. You can’t ask for a silicone oil that has the best emulsification, the best flow, and the finest bubble pores. To be honest, it is still hard to find such a silicone oil. You have to be clear about your needs to find the right product.
5. silicone oil test (at least two bubbles per sample), I will say the most practical method.
Silicone oil test the most important test of two aspects of performance.
5.1 basic foaming applications
The most practical way to check silicone oil is foaming, other methods are not very representative: choose a single polyether (only 4110), silicone oil plus 0.5 to 1%, foaming density in about 20kg, the speed of foaming control in the starting speed of about 15-20S, the catalyst should not choose too complex, only A-33 can be used. Compare the foam pore structure and the length of the flow, so that you can see the difference in the effect of different silicone oil. Each species should do two samples to repeat the comparison, the experimental results can be repeated to be meaningful.
5.2 Stability performance
Test the storage stability of silicone oil and the combination of materials: with a good combination of materials, sealed up with a clean bottle, into the 60 ~ 70 ℃ oven for 48 hours, 96 hours, 120 hours were foaming, and not high-temperature storage of the combination of materials issued by the foam for comparison, such as bubble hole changes are not significant, then your combination of materials placed at room temperature for 3 ~ 5 months certainly will not be a problem. If the foam is obviously bigger, or even collapse bubble, it means that you must have problems with the combination of materials.
Of course, if you have used more than five batches of the same brand of silicone oil from the same manufacturer, then you can also test the physical indicators provided by the silicone oil manufacturer, the silicone oil manufacturer is not as good as the middle, unless you ask for a substantial price reduction, which is difficult to say.
However, I hereby declare that we will definitely not have such a situation, and if you ask for a price reduction, we can reduce the price if there is room for a price reduction after our calculation, and if not, there is no way. If you can really buy the same quality and cheap silicone oil, it only means that we have to work harder to provide you with better quality and cheaper products.
6. Silicone oil dosage
In general, we recommend the dosage of silicone oil to be 1.5~3.0% of total polyether+polyester. According to different seasons, different applications should be adjusted appropriately.
