No matter what kind of process is used to form glass fiber reinforced plastic products, mold release agent must be used, whether it is external mold release agent or internal mold release agent. In short, mold release agent is an indispensable auxiliary material in the production process. The external release agent is to prevent the molded product from adhering to the mold, so as to apply a layer of separation film between the product and the mold, so that the product can be easily released from the mold, while ensuring the quality of the product surface and the mold intact. The external release agent is also called release agent. The internal mold release agent is a compound with a melting point slightly lower than the molding temperature. It is added to the resin and it is compatible with the liquid resin. Under certain temperature conditions, it oozes out from the resin matrix and forms a layer of isolation between the mold and the product. membrane.
Any kind of non-polar or weak polar substances with low adhesion to synthetic resins can be used as mold release agents. But the release agent must meet the following conditions:
(1) Easy to use and short film-forming time;
(2) Does not corrode the mold and does not affect resin curing;
(3) The film formation is uniform and smooth, and the adhesion to the resin is small;
(4) Safe operation and no harm to people;
(5) The price is cheap, the sources are wide, and the preparation is simple.
It is difficult for a release agent to meet the above conditions at the same time. In some cases, several release agents must be used at the same time to meet the requirements.
When selecting a release agent, the following two conditions are mainly considered:
(1) Mold material, resin type and curing conditions.
(2) The molding cycle of the product and the molding time of the release agent.
There are many types of mold release agents, common ones are film type, solution type and oil wax.
1. Film release agent
This category includes cellophane, polyester film, polyvinyl chloride film, polyethylene film, polytetrafluoroethylene film, etc. This type of release agent is easy to use, as long as the film is pasted on the working surface of the mold with general grease. This type of release agent is easy to release, but the film has low deformability, and has certain limitations in use. It is not easy to flatten on a complex surface. Polyvinyl chloride film and polyethylene film are not suitable for the release of polyester glass fiber reinforced plastics, because styrene in the resin easily swells these two release agents. For FRP products cured at high temperature, polytetrafluoroethylene film, polyimide film, etc. are used.
2. Solution type release agent
There are many such release agents and the most widely used. The following are commonly used:
(1) Polyvinyl alcohol solution
5-8 servings of polyvinyl alcohol
35-60 parts of ethanol
60-35 servings of water
Preparation method: add quantitative polyvinyl alcohol to room temperature quantitative water for several hours, and then gradually increase the temperature (preferably in a water bath) to 95-100 ℃, while continuously stirring, keep the temperature at this temperature for 45 minutes to After 1 hour, it can be completely dissolved. After filtration, a certain amount of ethanol was added dropwise. The ratio of water to ethanol is determined according to the requirements. The ethanol content is high and it is volatile to form a film.
In order to reduce the generation of bubbles during brushing, 0.01-0.05% anti-foaming agents such as octanol and tributyl phosphate can be added. Adding 4-5% glycerin can make the membrane elastic. When used in steel molds, 0.75% sodium benzoate can be added to prevent mold rust. In order to prevent missed coating, some pigment solutions can be added appropriately. Polyvinyl alcohol mold release agent is currently the most commonly used mold release agent in China. Its price is cheap, non-toxic, convenient source, good performance, and the use temperature is below 150℃. If it is used below 120℃, the demoulding effect is very good.
(2) Polystyrene release agent
5 parts of polystyrene resin (granular)
95 parts of toluene
Preparation method: Add polystyrene to toluene in proportion, leave it for a few days, stir evenly until completely dissolved, and then use. To accelerate the dissolution, it can be slightly heated below 50℃. This release agent is better for epoxy glass fiber reinforced plastic mold release, but it can not be used for the release of unsaturated polyester glass fiber reinforced plastic, because the styrene in the unsaturated polyester resin has a dissolving effect on polystyrene. The film-forming time of this release agent is short, and the film-forming is smooth and bright. However, the co-solvent toluene is highly toxic and should have good ventilation conditions when used. The use temperature is below 100℃.
(3) Perchloroethylene solution
5-10 copies of perchloroethylene powder
Toluene and acetone (1:1) 90-95 parts
Preparation method: Weigh the material according to the formula, mix it for one day, and then stir it evenly. When the material is completely dissolved, it can be used. It can also be varnished with vinyl chloride and diluted with banana water. This mold release agent has good permeability and is suitable for sealing pores of porous materials such as wood and gypsum. However, it is not suitable for direct contact with products. It is often used in combination with other mold release agents. Use temperature is below 120 ℃, storage should be sealed.
(4) Cellulose acetate solution
5 servings of cellulose diacetate
4 parts of ethanol
20 parts of ethyl acetate
5 servings of diacetone alcohol
24 copies of methyl ethyl ketone
48 parts of acetone
Preparation method: Add cellulose diacetate to the above mixed solvent, stir evenly, remove the residue, and then use. The cellulose acetate mold release agent is smooth, smooth, and easy to use with low toxicity. However, some solvents are inconvenient and expensive. This mold release agent is suitable for the demolding of polyester glass fiber reinforced plastics, and cannot be used for the demolding of epoxy glass reinforced plastics. Because it has a certain adhesion with epoxy glass reinforced plastics, it is not easy to remove after demolding, so it is best to Compound use. Apply the former to the mold, and then apply polyvinyl alcohol to its surface to contact the product, so that the demolding effect is better, and the use temperature can reach 150 ℃.
(5) Silicone release agent such as silicone oil, silicone grease and silicone rubber
After dissolving silicone oil, silicone grease or silicone rubber in a solvent, the solvent can be polychloroethane, xylene, toluene, etc., generally can be formulated to a concentration of 1-2% and applied by spraying or brushing. The greater the viscosity of silicone oil, the better the effect of mold sticking. This type of mold release agent has good mold release effect and high temperature resistance, so it is often used as a high temperature mold release agent, which can generally be used below 200℃. When using a solution release agent, it must be thoroughly dried to prevent unvolatile solvents from adversely affecting the solidification and quality of the product. For the release agent that is repeatedly applied, you must wait for the first application of the coating to dry before applying it a second time, otherwise not only will you not get the effect of repeated application, but sometimes it will damage the previous coating , Forming small protrusions and wrinkles.
3. Release agent for paraffin and ointment
Commonly used are paraffin wax, car wax, floor wax, heat-resistant ointment, paraffin gasoline liquid, petroleum jelly and so on. This type of release agent is easy to use, non-toxic, and has no corrosive effect on the mold. But it is easy to make the surface of the product stained, not smooth, and it is difficult to paint the surface of the product. It is generally suitable for curing at room temperature, so it is limited in use.
4. Compound release agent
The compound use of the two release agents is called a compound release agent. For large products or products with complex shapes, the use of two release agents in combination, the release effect is more ideal. This is because although the adhesion of various release agents is relatively low, it is inevitable that there is still some adhesion at the interface of the release agent and the mold and the product. When using a compound release agent, the product is separated between the two layers of release agent with the least adhesion when it is released, so that it is certain for large products and products with complex shapes, and when the mold strength is not high (such as gypsum mold) Effect. Compound release agents are commonly used: sealing holes with paint flakes, perchloroethylene varnish or nitro spray paint, cellulose acetate as the middle layer, and polyvinyl alcohol as the outer layer; or perchloroethylene or polystyrene as the middle Layer, polyvinyl alcohol as the outer layer and so on. What kind of release agent can be combined with each other can be determined experimentally. In short, it is advisable to achieve the best demolding effect without polluting the product.