EVA release agent is a type of isolation film applied between the molded composite material products and the mold to prevent them from sticking to the mold, making it easy for the products to detach from the mold while ensuring the surface quality of the products and the integrity of the mold. Release agents include wax, siloxane, metal stearate, polyvinyl alcohol, fluorinated oligomers, and polyolefins, as well as plant derivatives and fatty acids. Patents for polydimethylsiloxane and other complex polymerization mixtures are classified as mixtures. The traditional release agent is in the form of spray, solvent solution in the form of liquid, aqueous solution or paste. When in use, the mold surface is coated or polished by spray.
The commonly used release agents mainly include the following categories:
(1) There are two types of release agents according to their usage: external release agents and internal release agents. External release agent is directly applied to the mold; Internal release agent is a compound with a melting point slightly lower than that of ordinary molding temperature. It is added to the resin during the heating molding process. It is compatible with liquid resin but incompatible with cured resin. Under certain processing temperature conditions, it seeps out from the resin matrix and forms a layer of isolation film between the mold and the product.
(2) According to the different states of the release agent, there are film type (mainly polyester, polyethylene, polyvinyl chloride, glass paper, fluoroplastic film), solution type (mainly hydrocarbons, alcohols, carboxylic acids and carboxylic acid esters, metal salts of carboxylic acids, ketones, amides and halogenated hydrocarbons), paste and wax type (including silicone ester, HK-50 heat-resistant oil paste, cylinder oil, gasoline and asphalt solution and wax type) release agents. The wax based release agent is the most widely used type of release agent, which is cheap, easy to use, non-toxic, and has good release effect. The disadvantage is that it can cause oil stains on the surface of the product, affecting surface painting, and making it difficult to release when there is a missed coating. For large products with complex shapes, they are often used in combination with solution type release agents.
(3) According to the combination of release agents, there are single type and composite type release agents (including component composite and composite in terms of usage).
(4) According to the usage temperature of release agents, there are room temperature and high temperature release agents, such as normal temperature wax, high temperature wax, and stearic acid salts.
(5) According to their chemical composition, there are inorganic release agents (such as talc powder, kaolin, etc.) and organic release agents.
(6) There are disposable release agents and multiple release agents according to their reuse times.
Release agent is an interface coating used on two surfaces that are easily adhered to each other, which can make the surface of the object easy to detach, smooth, and clean. Release agents are used in various molding operations such as glass fiber reinforced plastics, cast plastics, polyurethane foam and elastomer, injection molding thermoplastics, vacuum foam sheets and extruded profiles. In molding, sometimes other plastic additives such as plasticizers may seep out onto the interface, and a surface remover is needed to remove it. There is no mold release agent that can have all encompassing effects and is suitable for all molding operations. The molding conditions such as molding materials and composition, cycle time, temperature, use of finished products, and secondary processing need to be considered. The performance of the release agent must be consistent with the molding conditions.
In theory, the release agent should have a high tensile strength so that it is not easily polished when in frequent contact with the molding resin. Especially when there are frosted mineral fillers or glass fiber reinforcements in the resin. Release agents should have chemical resistance so that they do not dissolve when in contact with the chemical composition of different resins, especially styrene and amines. Release agents should also have heat resistance and stress resistance, and be not easily decomposed or worn; The release agent should adhere to the mold without transferring to the processed parts, so as not to interfere with painting or other secondary processing operations.
After the carrier liquid (solvent or water) evaporates, a thin film coating is left on the surface of the mold.
Paste release agent or liquid wax is usually used for polyester, vinyl resin and epoxy reinforced mixture, gypsum and clay mold as master mold, etc., and is also widely used for the release of polyurethane foam and elastomer. Using paraffin release agent on the surface of porous molds can seal the pores and ensure reliable demolding. According to the mold structure, one use of wax release agent can achieve 6 demolding cycles. However, its application is both labor-intensive and time-consuming. Because the coating of paraffin is usually a thick film, the conjunctiva is quick and needs to be peeled off frequently. They may also flow onto the surface of the mold or the surface of the processed part, causing annoying adhesion or the appearance of bubbles on its surface coating.
Polyvinyl alcohol is a film-forming release agent widely used for demolding newly made polyester glass fiber molds. PVA has excellent properties in preventing styrene from evaporating from new and 'immature' molded parts. When the parts are demolded, PVA partially adheres to the mold and partially adheres to the parts. Therefore, after molding and before continuing to use, both surfaces must be cleaned with water.
Fluorinated oligomers, polydimethylsiloxane, and other polymer release agents can form a thin or monolayer film and can be repeatedly released. Semi durable release agents also belong to this category, which are easy to use, have less adhesion, but are more expensive than wax release agents Spray type siloxane release agent is widely used in thermoplastic processing, especially in injection molding, vacuum foaming and rotary molding. The lubricity of siloxane or siloxane polymer composites cannot be compared to any other type of release agent. Although this mold release agent has a spray type, many siloxanes are not conducive to spraying and other secondary processing operations. When spraying, siloxane is prone to spreading in the air, contaminating the processing surfaces of other parts within a certain distance in the same production equipment. Siloxanes also cause structural weaknesses in molded parts. When sprayed excessively, the excess part is easily moved by the melted thermoplastic, forming weak points on the bonding line. Siloxane spray is cheap and easy to get.
Biological and fluorinated oligomers, as well as blended polymers, can also be used as release agents without hindering secondary processing operations. Some of them have high temperature stability and are suitable for engineering plastics and rotational molding resins.
Although the mold release agent industry has always focused on environmental protection, since the 1990s, there has been a high global emphasis on reducing harmful vapors to the human body in work environments and phasing out the use of chlorofluorocarbons (CFCs) compounds that can damage the ozone layer in the atmosphere. By the end of 1989, release agent manufacturers and suppliers had generally banned the use of chlorofluorocarbons from sprays and solvent carriers. Instead, other solvents that are acceptable to the public according to the 1987 Montreal Convention guidelines will be used.
Currently, government regulations in the United States tend to further reduce commonly used solvents such as chlorinated hydrocarbons by the mid-1990s. Chlorine containing solvents are widely used as fast drying, non flammable solvent carriers for mold release agents and mold cleaning agents. Because many active demoulding ingredients are only soluble in a few agents, this may cause some problems in the formulation of demoulding agents. CFCS and other chlorine containing solvents belong to this category of solvents due to their solubility and rapid volatility in release agents. However, many formulations have introduced new water-based release agents into a wide range of thermosetting resin applications, such as unsaturated polyester, epoxy resin, phenolic plastics, and polyurethane.
