Introduction to Silicone Insulating Paints-Part 2

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As what is introduced in last article, silicone insulating pant is one important type of application that have been applied widely. If we categorize it via the usages in insulating materials, it could have some subcategories which are applied in different industries.

Coil Varnish Paint

The first is coil varnish paint. It is mainly used for immersion for H-grade or above electrical engine or devices, wires in transformers, glass-fiber cables, glass cloth and some other insulating parts to fill the narrows and micro slots among them. It is after the thermal solidification of varnish, there will form continuously plain paint layer on the surface of the immersed product and to make the wire to be stick to a whole tight one. This could improve the resistance of heats, isolation, humidity, mechanical strength and heat conductivity of insulating structures. These take a big percentage inorganic silicone insulating paints. Coil varnish paint requires low viscosity, strong penetration, high solid percentage, strong adhesion, thick and dry layer, proper elasticity and mechanical strength. Coil Varnish paint is mainly methyl phenyl silicone resin and it has two forms of products.

One of the main applications of organic silicone insulating paint is the H-grade electrical engine and transformer’s coil varnish paint, half of it is silicone resin solvent (solvent type), the chemical name of coil varnish paint is polymethylphenylsiloxane.

It is to overcome the shortages like bad adhesion, weak solvent resistance and high cost, it could be modified by organic resins. There are usually two ways for the modifications: the first is to direct mix the organic silicone resin with the common organic resins according to certain ratio; another one is to use initial polycondensate polysiloxane to have polyceondensation with some other organic resins to make some chemical reactions to make new type of silicone resins.

In most cases, it is due to the insolubility between silicone resins and organic resins, therefore, to mix them in a physical way may not get satisfied result. So, for more times, it is to use two groups of components to make some chemical reactions to make the modification. It is via the chemical modification to grant the co-polymerization products to have both of silicone resins’ and organic resins’ properties and to improve silicone resin’s drying conditions to short drying time and improve paint layer’s surface hardness, adhesion, solvent resistance and the compatibility between pigments and organic resins. This allows it to be more useful then pure organic silicone resins. The silicone paint modified by organic resins could be compared to pure organic silicone paint, its thermal stability, weather resistance, waterproof and the insolubility with some other organic materials are all been improved and the relevant cost is also reduced.

The second subcategory is non-solvent varnish paint. It is in order to reduce the pollutions and to improve the operating conditions. Many countries have developed non-solvent H-grade insulating organic silicone varnish paint in 60s of 20^th century. They are pure silicone resin liquids and mainly are additional or peroxide type silicone resins. It is according to relevant researches, the silicone resins that contain vinyl will have a fast solidification speed than those ones do not contain it. This is because vinyl is more to be affected by peroxide catalysts. Therefore, they could have solidification in some lower temperature, and there will be no violating reactive side matters to be produced. Thus, the silicone resins that contain vinyl is very good at being used for varnish paint; what is more, the silicone resins that contain vinyl usually have lower viscosity, therefore in many cases, they could be used without solvents. At present, all non-solvent varnish paints contain some vinyl functional groups, there will produce stable paint layer with the existence of peroxide.

It is due to some solvents will be violated during the solidification process of solvent organic silicone, and some micro molecular matters will be produces and some small gas narrows will occur, therefore multiple-time varnishing is necessary. However, even though it is produced via this process, the whole property of the produced paint film will be affected, and its electrical isolation will also be influenced. Therefore, condensation type solvent organic silicone varnish paint could be only applied to some low-grade electrical engines.

Mica Insulating Paint for Sticking and Adhesion

Organic silicone adhesion insulating paint is mainly used to stick all kinds of heat-resistance insulating materials like mica slices, mica powders, glass wires, glass cloth and some other compressed products. This kind of paint requires fast solidification speed, strong adhesion, high mechanical strength, hard to peel and the resistance of oil and humidity.

Mica is a very good natural electrical isolation medium, it could maintain its electrical insulating property in very high temperature. Heat-resistance electrical isolation natural mica slices have many applications in industries. To use mica products which are stick by silicone resin, could produce hard or soft mica boards, tapes, slices or tubes without restrictions on sizes. Hard mica products are like mica boards for shaping, mica boards for flowing and soft mica boards; soft mica products are glass mica tapes, fire-resistance tapes, belt or slice products. Therefore, it is a must to provide mica adhesive of proper components and R/Si ratio to meet the requirements. It is in order to maintain the mica’s property like heat resistance and electrical isolation, it needs silicone resin that has heat resistance to be used as the insulating paint. The common one is the methyl phenyl silicone resin with low R/Si ratio to make special electrical heating mica boards. It is due to their excellent heat resistance, the corresponding produced mica boards are widely used for drying machines, heating pots, bread baking machines and some other heating devices.

Summary

Silicone insulating paints do have many subcategories. Also, we have introduced two main subcategories of silicone insulating paints in this article. Also, there are still some other subcategories to be introduced in the next coming articles, and they will be introduced in detail like today’s articles as well.