Types and characteristics of silicone release agent (2)


3. Emulsion release agent:


Pure silicone oil release agent is not easy to use and the release effect is not satisfactory. The use of solution release agent, there is the risk of fire and poisoning, so the development of emulsion release agent, and has become the mainstream products of the current release agent. The emulsion release agent can be obtained by mechanical emulsification, which is dispersed by the action of silicone oil and water under emulsifier. It can also be obtained by emulsion polymerization, starting from oligomeric siloxane, emulsifying polymerization in water system under the action of emulsifier and catalyst.


The emulsifiers used can be non-ionic, anionic and cationic, but in mechanical emulsification, non-ionic emulsifiers are mainly used. The emulsifier mainly consists of homogenizer, colloid mill or high speed agitator. The content of silicone oil in the emulsion product is generally 30%~60% (mass fraction). The emulsion is diluted to water with a concentration of 0.2%~1.0% (mass fraction). The stability of diluted emulsion is worse and should be used up as soon as possible. The emulsion type release agent is very advantageous in terms of cost, fire prevention and hygiene, so it has strong market competitiveness.


However, it also has three shortcomings: the volatility of water is too poor to be used as demoulding agent for low temperature die; the wettability of base material, especially for polymer material, is poor; and the use of emulsifier reduces the precision of products. If constant hard water is used to dilute, the scale will be produced on the surface of the mold. If not cleaned regularly, it will further affect the precision of the product, so the use of soft water diluted emulsion is good.


In emulsion products, some organic solvents are added to reduce the amount of emulsifier, so as to speed up the evaporation of water and reduce the deposition of solid deposits on the mold surface.


4. Silica paste release agent:


Usually, white translucent paste-like products are obtained by mixing fine powders such as white carbon black (including gas phase and precipitation products) into silicone oil. Its thermal oxidation stability and demoulding durability are superior to those of oil, liquid and emulsion products. It can be tested for more than 1 hour at 300 C. It is suitable for high temperature and high pressure moulding demoulding or anti-sticking. It can be used not only as moulding demoulding agent for long tubes (rubber, plastics, etc.), but also as an anti-sticking agent for nozzles of synthetic fibers such as nylon in melt spinning to prevent fiber adhesion and breakage of melt fibers, so as to realize long-term continuous and stable operation.


5, spray release agent:


Spray demoulding agent is actually a branch of the solution product. It is composed of silicone oil and additives and other organic solvents, such as three fluorochloromethane, two fluorodichloromethane, fluorochloromethane, low alkane such as propane, butane and isobutane, etc., mixed with low temperature chlorinated hydrocarbon such as trichloroethylene and three chloroethane. In a pressurized aerosol bottle, the nozzle is aligned with the die when used, and the lifting valve cover sprays the atomized release agent, which gives the release property and is suitable for rubber and plastic.


6. Curable release agent:


The effective components of the above five release agents are non-crosslinkable silicone oil, while the effective components of curable release agents are crosslinkable polysiloxane (including silicone resin and silicone rubber) under heating or catalytic action.


Silicone resin release agents usually dissolve low R/Si ratio silicone oligomers containing condensable reaction groups, silicone oil curing agents and thickeners in aromatic hydrocarbons or mixed solvents to prepare solutions with concentration of 20%-50%. When used, organic solvents were added to dilute the film, and brushing or spraying method was used to coat it on the surface of mould cavity or baking pan. After curing at 150-200 C, a smooth semi-permanent film was obtained. It is widely used in the defilm coating of food baking and non-stick pot. Compared with silicone oil mould release agent, resin mould release agent has the following advantages: 1) coating can be used dozens to hundreds of times at a time, which reduces material and labor costs; 2) improving production efficiency and equipment production capacity; 3) reducing waste and defective product rate; 4) improving product surface finish; 5) cleaning mould cavity and less harmful smoke; Extend the die cavity, etc.


Rubber type release agents such as service life are usually made from RTV silicone rubber and organic solvent, or HO (Me2SiO) nH emulsion is mixed with crosslinking agent, filler and catalyst to make O/W emulsion. After further dilution before use, it is sprayed or brushed on the surface of the mould or cavity, vulcanized into an anti-stick layer at room temperature or slightly heated, and its life is not as good as silicone resin.


Reference: Synthesis and Application of Silicone Products