First, external use of polyurethane release agent
In order to make the product easy to be taken out of the mold during molding, a coating agent, called external release agent, is coated on the surface of the mold.
External release agents can be divided into three types according to the use mode: durable, that is, once coated, they can be molded many times; Hydroxyl coating type, that is, coating once before molding; Multilayer compound. Generally, most of them are coated with hydroxyl groups. These external release agents can be divided into the following varieties according to the types of compounds used.
1. silicone release agent
Solvent (silicone oil, silicone paint); Emulsion type (silicone oil); Compound (silicone oil and silicon dioxide); Aerosol type (silicone oil); Dry type (bridged silica gel).
Silicone series release agents are widely used in plastics, rubber and other occasions because of their small surface tension, heat resistance, non-toxicity, good gloss and no affinity with resin. For example, in German patent DE29 198 1 1, Miehacl proposed a release agent with more stable performance than ordinary silicone, which can keep stable repeated demolding times and paintability of molded products. Its composition includes polydimethylsiloxane, siloxane resin, alkyl titanate or titanium chelate. This release agent is especially suitable for molding polyurethane parts and various foam moldings of elastomers.
For example, 26.3 parts of methyl polysiloxane resin prepared from methyl trimethoxysilane (60% solution, petroleum solvent), the molecular weight of the resin is 2500, and the methoxy group connected with silicon is about 10%. The resin was mixed with 1.7 parts of tetrapropyl titanate and left overnight, and the mixture was mixed with 72 parts of hydroxyl-terminated polysiloxane and diluted with hexane. The demoulding characteristics were tested and the results were as follows:
Number of demolding 1 2 3 4 5 6
The demoulding quality is 2222/36.
The above-mentioned demolding times indicate the number of reusable times, and the numbers in demolding quality indicate the quality grade. 1 grade is the best, as long as the mold tilts backward, it can be poured out; Level 2 is taken out with a little pressure; Level 3 peeled off with a little force; Level 4 is difficult to take out; Level 5 can't be taken out or at least partially. This example shows that when the demoulding is repeated for 5 times, the mass is 2-3, and the silicon-based demoulding agent generally shows good demoulding performance and little pollution to the mold.
2. Wax release agent:
Natural wax can be divided into vegetable wax (Kanoba wax) and mineral wax (FT wax). Synthetic wax (polyethylene wax).
In Japanese Patent 77/68266, it is proposed that paraffin mixed with other waxes is polyurethane foam release agent. For example, 40 parts of paraffin wax (melting point 68℃), 40 parts of microcrystalline wax (melting point 72-75℃) and 20 parts of microcrystalline wax (melting point 83-85℃) are melted at 65438 0℃, sprayed on an iron mold or an aluminum mold preheated to 80℃, cooled to 40℃ and foamed.
In the former Soviet Union, the following two formulas were put forward:
1) 0-30% refined ceresin, 60- 100% peat wax, 30-70% aqueous solution of 20% surfactant (surfactant is nonionic, such as OS-20), stearic acid as stabilizer, and water are added to make emulsion, which can be used as release agent for foamed polyurethane.
2) 2.7 parts of microcrystalline wax, 2 parts of silicone oil, 7.88 parts of thickened white oil, 0. 1 part of bactericide, 0.5 part of ethoxylated fatty alcohol 1.5 part of ethoxylated nonylphenol, 0.34 part of fatty alcohol polyethylene glycol ether and 84.78 part of water. The emulsion can be used for demoulding automobile polyurethane waterproof board.
Wax-based release agent has good adhesion and finishing processability, and its price is relatively low. As a release agent of polyurethane foam, it is easy to be widely used. However, this mold release agent pollutes the mold seriously, so it is necessary to clean the mold frequently.
3. Oil-based release agent
Animal fat (whale oil); Petroleum (vaseline). The vaseline in this release agent has low release price and simple formula, but it is easy to make the surface of the product greasy and pollute other items. A large number of fatty acid salts or soaps are used in the production. For example:
1) Riza Nur Ozell and others in Germany put forward a release agent mainly composed of aluminum salts of fatty acids, which is suitable for PU foam, especially for full-skin foam. As long as a very thin solution is coated on the mold, an extremely thin film is formed. Although the dosage is small, the effect is good, and the fine features on the mold can be copied to the molded product, and it can be coated and reused many times without purification. Its composition is mixed fatty acid aluminum salt, and the carbon number of fatty acid is 12 ~ 22. The preparation method is to dissolve the mixed fatty acid aluminum salt in dichloromethane to prepare a solution of 65438+/-0%. The solution is sprayed on the metal mold wall to form an extremely thin film, which can be reused 10 times after once coating, and the demoulding effect is first-class.
2) Water-based release agent for fatty acid soap. Robert wesala proposed a water-based release agent, which can be used for RIM reactive injection molding PU foam and high resilience open-cell PU foam. This release agent has the advantages of high film hardness, difficult peeling and penetration, reduced accumulation and improved water evaporation. In particular, water is used as a solvent, so that the pollution of organic solvents to the environment is avoided and the cost is low. The release agent contains fatty acid soap 1% ~ 30% (including unsaturated soap 40% ~ 90% and saturated soap 10%~60%), and the fatty acid is neutralized with alkali metal hydroxide to make the pH value 8.5 ~ 1 1. Sodium hydroxide is used in the RIM PU system, while the saturated fatty acid is C8-C 12 and the unsaturated acid is oleic acid and linoleic acid. This release agent combines the characteristics of saturated fatty acid soap and unsaturated fatty acid soap, improves the hardness of the film and has good release performance. Its preparation method is relatively simple. Firstly, human water is added into the container, and then human alkali metal hydroxide is added under stirring to completely dissolve it. Then slowly add unsaturated fatty acids and saturated fatty acids under stirring, and adjust the pH value to about 9.5 as needed after the feeding is completed. Filtering the obtained solution through a fine screen to remove solid particles, and obtaining a finished product.
4. Fluorine-based release agent
Perfluoroalkyl compounds can be divided into solvent type, water type and spray type; Perfluoroalkyl acrylate; Fluorine resin powder (low molecular weight polytetrafluoroethylene); Fluorocarbon coating (PTFE, FEP, PFA).
5. Inorganic release agent
This release agent is solid (talcum powder; Mica; Clay), it is more difficult to use, and most of them can be used only after being processed by a suitable formula. For example, clay release agent imported from Germany, 28.2 parts of 3- propyl trimethylsiloxane, 0. At 70℃, 5 parts of water and 25.5 parts of acidic activated clay were added into 1.276 parts of hexamethylcyclotrisiloxane, and the temperature was raised to 10℃ for 3 hours, resulting in a product with a HS content of 0.43%. It is an excellent release agent for polyurethane foam.
Mark and others put forward a release agent with talcum powder as raw material. Its advantages are that there is no residue on the surface of the molded product, the molded product is easy to paint and coat, and the foam core can be prevented from being separated from the whole skin when demoulding. Although talcum powder has satisfactory performance, it is difficult to apply directly. If talcum powder is directly taken out of the mold, the dust will rise, causing waste and affecting people's health, and it cannot be evenly dispersed on the surface of the mold.
Therefore, Mark and others dispersed talcum powder into water emulsion and organic solvent, so that talcum powder was evenly dispersed on the surface of the mold, which played a good demoulding role. The release agent consists of water, emulsifier, toluene (emulsion), talcum powder, organic solvent and metal compound (catalyst).
Water, toluene and emulsifier are mixed to form O/W emulsion, then talcum powder is added and stirred, and then mixed with organic solvent and catalyst, which can be used, and is suitable for polyurethane products.
6. Surfactant system
There are few reports about using surfactants as release agents. For example, in U.S. patents (U.S. patents. 365,438+0736) A 0.5% disodium salt solution layer of polyethylene glycol dodecyl monoether sulforaphane (10m l/ m) was sprayed on the flat glass and dried for 30 seconds. Then, a liquid reaction mixture of 1000 g condensate of propylene oxide and trimethylpropane, 1000g biuret of hexamethylene diisocyanate and 0.5g polyether made of dibutyltin dilaurate was added to the coated glass plate, and heated at 80.d egree. C. for 6 minutes to obtain a polyurethane film. After cooling to room temperature, the film can be easily separated from the glass.
Most surfactants are combined with other ingredients to make release agent. For example, wolfgang, Fisher and others in Germany put forward a water-based release agent containing surfactant. Because water reacts with isophthalate to produce R-NH2 and CO2, which changes the ratio of polyol to isocyanate and leads to partial collapse of foam, the application of water-based release agent is limited. Wolfgang, Fisher and others used nonionic surfactants to mask and fix water molecules, thus avoiding the side reaction between water and isophthalate. Suitable surfactants are ethylene oxide adducts of fatty alcohols and nonylphenol. The main function is that water molecules and ethylene oxide addition molecules of fatty alcohols combine through stable bridges to form an electrically neutral three-dimensional network combination, thus avoiding the occurrence of side reactions. It is especially suitable for sensitive cold curing soft foam. The specific formula is as follows: microcrystalline wax (containing emulsifier) 2.7%, polysiloxane 2%, thick vaseline fraction 7.8%, bactericide 0. 1%, fatty alcohol (meso-E O) adduct/kloc-0.5%, nonylphenol (E O) adduct 0.4%, and fat.
7. Fluorine-based release agent
Fluorine-based mold release agent has good demoulding property and little pollution to mold, but the cost of mold release agent is high and its use still has some limitations.
8. Other external release agents
For example, resin release agents mainly include polyethylene and polypropylene, and the polymerization degree of polyethylene should be 500- 1000. In addition, there are multi-layer composite release agents, the bottom layer is tetrafluoroethylene telomer, the second layer is polyethylene, and the third layer is polyvinyl alcohol. The bottom layer needs to be updated for a long time, and the second layer and the third layer need to be updated frequently, which is suitable for demoulding ultra-microporous PU parts. In addition, there are phosphates, shellac and so on.
Second, polyurethane internal release agent
Internal release agent is added to PU formula, which moves to the interface between foam and mold during each molding, so as to achieve the effect of demoulding. The requirements of internal release agent are: easy to disperse in resin system to become a stable dispersion; Does not change the original reactivity and physical characteristics; Does not affect nucleation, thereby not changing the porous structure or foaming stability; Does not affect the paintability of molded products.
In the United States, the automobile industry mostly uses internal release agents. Europe is also used for production. Except zinc stearate, amine stearate, etc. Most of the internal release agents are modified polysiloxane.
1. hydroxy acid modified polysiloxane internal release agent
Because hydroxymethylsiloxane will react with the catalyst, RIM ternary system is suggested, that is, the internal release agent will not be mixed with other components in advance. However, most commercial RIM machines are bi-directional systems, so AUTOD proposed the method of using hydroxyl dimethylsiloxane stripping agent to carry out the bi-directional system of RIM. The formula is as follows: the first route contains hydroxyl dimethyl siloxane with molecular weight of 7 1500 and chain extender with primary amine or secondary amine polyether as terminal group, with functionality of 2-6 and active hydrogen content of 75%. The second path contains aromatic polyisocyanate. RIMPU elastomer can be easily taken out of the mold by this method, and it is very effective to make automobile body parts with it.
2. Amino-modified polysiloxane internal release agent
Stuber et al. proposed an internal release agent containing amino polysiloxane. This hydrolyzable release agent containing primary or secondary amine end groups can be directly used in RIM. This release agent acts faster on PU substrate than hydroxyl polysiloxane. Suitable for forming large rim parts. The general formula of aminopolysiloxane is ECHR' chr' NH- olefin -( OSiR 1R2Z) m-O- olefin-NHCHR'CHR''E e, where R 1 and R2 are groups composed of methyl and phenyl, e is an electron-accepting group, and r'' and r' are hydrogen and phenyl. For example, the group of ECH R”CHR "is 2- cyanoethyl, and the average value of m is 40-50; For example, when the "CHR" group of ECHR is 2- methoxyformyl ethyl, the average value of m is about 30-40. According to different formulations, it can be demoulded continuously for 20-73 times.
3. Polyether modified polysiloxane internal release agent
Because it is not easy to react with other ingredients in the ingredients, such as polyol, it can be used in RIM bidirectional system and can be demoulded continuously for 20 times.