Selection and application of silicone release agent (I)


1. How to select release agent:


There are many kinds of siloxane release agent, and their properties and uses are different. How to choose release agent to obtain the best effect?


Generally speaking, the material, structure and shape of the die, the type of products to be demoulded, the use of temperature, post-processability (printing, adhesion) and diluent are all prerequisites that must be considered. First, the temperature of the metal die is the main basis for the selection of demoulding agent. From the point of view of safety (ignition and poisoning), dissolution cannot be used in hot die. Liquid type, and the choice of emulsion type, silicone paste or silicone oil release agent, the use of emulsion release agent, due to the specific heat capacity of water, evaporation rate is slow, easy to remain on the surface of the mold with insufficient heat moisture, thereby affecting the uniform distribution of mold release, so the use should be heated quickly evaporated moisture. Cold mold can not use emulsion type, and more choice of solution and oil type release agent. Solution release agent is easy to wet and evenly distribute on the surface of the mould and products, so as to obtain smooth products. However, when the organic solvent evaporates naturally, it should be heated to further remove the residual solvents in the mould so as to avoid affecting the quality of the products.


In general, for a simple and high temperature mold, a cheap and safe emulsion release agent is used. Because it is difficult to demould complex dies, it is advisable to increase the dosage of demoulding agent, use high concentration of solution demoulding agent, each time have to be sprayed, the cost is higher, so it is better to use low concentration products, but the residual solvents should be cleaned up. The demoulding agent prepared with high viscosity silicone oil has a slightly worse wettability, but the demoulding effect is obviously better than that of silicone oil with lower viscosity than that of medium viscosity silicone oil. The use of oil and solvent release agents on the surface of the mold remains less than that of the emulsion products, and the solution and emulsion products made of high viscosity silicone oil have better demoulding durability. Silicone oil has no expansion and shrinkage effect on all kinds of rubber and plastics, so it is especially suitable for their release agent. However, silicone oil migrates more or less to the surface of the moulded products and affects their post-processing properties. For example, when moulding epoxy resin, polyurethane resin and polyurethane rubber, it is better to use cured release agent. Agent or mixed with curing release agent. For moulding that requires bonding, painting and imprinting, the release agent prepared with dimethyl silicone oil can not be used. If long chain alkyl (C8 ~ C16) silane is used as release agent, this disadvantage can be avoided.


No diluent, including organic solvents, propellants and water, shall remain on the die. Otherwise, the quality of products will be reduced. The improper selection of diluent can cause uneven distribution of silicone oil on the surface of die, resulting in stress cracking and accelerated aging of products.


II. Application in Plastic Forming and Processing


Siloxane release agent has been used in the preparation of plastics, rubber, polymers, metals, glass, casting and food by moulding, casting and packaging. The plastic forming process is the most important application object of silicone release agent.


Such as in polyurethane, polystyrene, polyvinyl chloride, melamine, acrylic resin, epoxy resin and polyester molding, transfer molding, injection molding, casting, lamination and other processes are used, in which the majority of polyurethane foam molding demoulding, commonly used is concentrated. A 0.5%-2.0% or 30min emulsion release agent can be sprayed on a clean mold and dried at a molding temperature for good demoulding. If durable release property is required, solidified release agent should be used. For the newly used mould, it is advisable to wipe it with a high concentration of release agent in the initial stage, and then reduce the concentration of release agent after a period of adaptation. For the release agent used in food packaging containers, the emulsion type release agent is mainly composed of medium viscosity two methyl silicone oil and food grade emulsifier. For materials that are difficult to demould, such as epoxy resin and polyurethane, it is better to use silicone oil containing silicone resin or fluoroalkyl silicone oil as demoulding agent.


Luhuan New Materials