In order to make the product easy to take out from the mold during molding, a layer of coating agent is coated on the surface of the mold, which is called external release agent.
External release agent can be divided into three types according to the use mode: durable, that is, it can be molded many times once coated; Hydroxyl coating type, that is, coating once before molding; Multilayer compound. Generally, most of them are hydroxyl-coated, and these external release agents can be divided into the following varieties according to the types of compounds they use.
1) silicone-based release agent:
solvent-based (silicone oil, silicone paint); Emulsion type (silicone oil); Complex type (silicone oil and silica); Aerosol type (silicone oil); Drying type (bridging silicone).
silicone series release agents are widely used in various occasions such as plastics and rubber because of their small surface tension, heat resistance, non-toxicity, good gloss and no affinity with resin. For example, Miehacl in German patent DE2919811 puts forward a release agent with more stable performance than ordinary silicone, which can keep stable repeated demolding times and paintability of molded articles. Its composition includes polydimethylsiloxane, silicone siloxane resin, alkyl titanate or titanium chelate. This kind of mold release agent is especially suitable for molding PU parts and various foam moldings of elastomers.
For example, 26.3 parts of methyl polysiloxane resin (6% solution, petroleum solvent) made from methyl trimethoxysilane, the molecular weight of the resin is 25, and the methoxy group linked to silicon is about 1%. Mix the resin with 1.7 parts of tetrapropyl titanate, leave it overnight, mix the mixture with 72 parts of hydroxyl-terminated polysiloxane, dilute it with hexane to 1% solution. The demoulding characteristics were tested, and the results were as follows:
demoulding times 1 2 3 4 5 6
demoulding quality 2222/36
The above demoulding times indicate the number of reusable times, and the numbers in demoulding quality indicate the quality rating. Level 1 is the best, as long as the mold is overturned, it can be poured out; Level 2 is taken out with a little pressure; Level 3 is peeled off with a little pressure; Level 4 is difficult to take out; Level 5 can't be taken out or at least local parts can't be taken out. This example shows that when demoulding is repeated for 5 times, the quality is 2-3, and the silicon-based demoulding agent generally shows good demoulding performance and less pollution to the mold.
2) Wax-based release agent:
Natural wax can be divided into vegetable wax (Kanoba wax) and mineral wax (FT wax); Synthetic wax (polyethylene wax).
in Japanese patent No.77/68266, a polyurethane foam release agent was proposed by mixing paraffin with other waxes. For example, 4 parts of paraffin wax (m.p. 68 C), 4 parts of microcrystalline wax (m.p.72-75c) and 2 parts of microcrystalline wax (m.p.83-85c) are melted at 1C, sprayed on an iron mold or aluminum mold preheated to 8C, and cooled to 4C, and the foam can be easily ejected.
In the former Soviet Union, the following two formulations were put forward:
1) -3% refined ceresin, 6-1% peat wax, 3-7% aqueous surfactant (surfactant is nonionic, such as OS-2), stearic acid as stabilizer and water to make an emulsion, which can be used as a release agent for making foamed polyurethane.
2) 2.7 parts of microcrystalline wax, 2 parts of silicone oil, 7.88 parts of thickened white oil, .1 part of bactericide, 1.5 part of ethoxylated fatty alcohol, .4 part of ethoxylated nonylphenol, .34 part of fatty alcohol polyethylene glycol ether and 84.78 parts of water. The emulsion can be used for demoulding of automobile polyurethane flashing.
Wax-based release agent has good adhesion and finishing processability, and its price is relatively low, so it is easy to be widely used as a release agent for polyurethane foam. However, this mold release agent pollutes the mold seriously, so it is necessary to clean the mold frequently.
3) Oil-based release agent:
Animal oil (whale oil); Petroleum oils (vaseline). Vaseline in this kind of release agent has low release price and simple formula, but it is easy to make the surface of the product oily and pollute other articles. A large number of fatty acid salts or soaps are used in 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 whole 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 on the molded product, and it can be coated and reused many times without purification. Its composition is aluminum salt of mixed fatty acid with 12-22 carbon atoms. The preparation method is to dissolve the mixed fatty acid aluminum salt in dichloromethane to make a 1% solution. The solution is sprayed on the metal mold wall to form an extremely thin film, which can be reused for 1 times after once coating, and the demoulding effect is first-class.
2) aqueous release agent of fatty acid soap. Robert wesala proposed an aqueous release agent, which can be used for RIM reactive injection molding PU foam and high resilience open-cell PU foam. The advantages of this release agent are high hardness of coating film, difficult peeling and penetration, reduced accumulation and improved evaporation of water. Especially, water is used as the solvent, which avoids the pollution of organic solvents to the environment and has low cost. The release agent contains 1% ~ 3% fatty acid soap (4% ~ 9% unsaturated and 1%~6% saturated), and the fatty acid is neutralized with alkali metal hydroxide to make the pH value 8.5 ~ 11. Sodium hydroxide is used in RIM PU system, while saturated fatty acids used in sodium hydroxide for open-cell elastomer are C8-C12, and unsaturated acids are oleic acid and linoleic acid. This kind of release agent combines the characteristics of saturated fatty acid soap and unsaturated fatty acid soap, which improves the hardness of the film and has good release performance. Its preparation method is relatively simple, firstly, human water is added into a 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 sieve to remove solid particles, and obtaining the finished product.
4) Fluorine-based release agents:
Perfluoroalkyl compounds, which can be divided into solvent-based and water-based formulations and spray-type; Perfluoroalkyl acrylate; Fluororesin powder (low molecular weight polytetrafluoroethylene); Fluorine resin coating film (PTFE, FEP, PFA).
Fluorine-based mold release agent has good demoulding property and little pollution to the mold, but the cost of mold release agent is high, and there are still some limitations in its use.
5) Inorganic release agent:
This release agent is solid (talcum powder; Mica; Clay), it is difficult to use, and most of them can be used only after being processed with appropriate formula. For example, a clay release agent introduced by Germany, 28.2 parts of 3- oligomeric propyl trimethyl siloxane, . 5 parts of water and 25.5 parts of acidic activated clay were added to 1.276 parts of hexamethylcyclotrisiloxane at 7℃, and the temperature was raised to 1℃ for 3 hours to generate a product with .43% HS content. It is an excellent release agent for polyurethane foam.
Mark et al. proposed a release agent with talcum powder as raw material. Its advantages are that there is no residue left on the surface of the molded product, the molded product is easy to be painted and coated, and the separation of foam core and whole skin can be avoided when demoulding. Although talcum powder has satisfactory properties, it is difficult to apply it directly. If talcum powder is directly removed from the mold, the dust will rise, which will cause waste and affect 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-based release agent:
There are few reports about the use of surfactants as release agent, for example, it is reported in US patent (US 4331736) that a layer of .5% aqueous solution of disodium salt of polyethylene glycol dodecyl monoether sulfofumaric acid is sprayed on a flat glass plate (1m l/ m) heated at 8C and dried for 3s, Then, 1g of condensate of propylene oxide and trimethylpropane, 1 g of biuret of 1,6-hexamethylene diisocyanate and .5g of polyether made of dibutyltin dilaurate were added to the coated glass plate, and heated at 8C for 6 min to obtain a polyurethane film. After cooling to room temperature, the film was easily separated from the glass (with a force of 29.4-58.8 kPa) without coating.
most surfactants are combined with other components to make release agent. For example, wolfgang, Fisher and others in Germany put forward an aqueous release agent containing surfactant. Because water reacts with isophthalate to produce R-NH2 and CO2, which changes the ratio of polyol to isocyanate and causes the foam to partially collapse, the application of aqueous release agent is limited. Wolfgang, Fisher and others used nonionic surfactants to mask and fix water molecules, which avoided the side reaction between water and isophthalate. The suitable surfactant was fatty alcohol ethylene oxide adduct nonylphenol ethylene oxide adduct. The main function is that water molecules and fatty alcohol ethylene oxide adduct molecules are combined by stable bridge bonds 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 petrolatum fraction 7.8%, bactericide .1%, fatty alcohol (meso-E O) adduct 1.5%, nonylphenol (EO) adduct .4%, fatty alcohol polyethylene glycol ether mixture .32% and water 84.78%.
7) Other external release agents:
For example, resin release agents mainly include polyethylene and polypropylene, and the polymerization degree of polyethylene should be 5-1. In addition, there are multi-layer compound 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 when it is damaged for a long time, and the second and third layers need to be updated frequently, which is suitable for demoulding of molded ultra-microporous PU parts. In addition, there are phosphate ester, shellac and so on. The internal release agent is added to the PU formula and migrates to the interface between the foam and the mold during each molding, so as to achieve the release effect. 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 the nucleation, so as not to change the porous structure or foaming stability; Does not affect the paintability of the molded product.
in the United States, the automobile industry has mostly used internal release agents. Europe has also been used in production. Besides zinc stearate, amine stearate, etc., most of the internal release agents are modified polysiloxane.
1) hydroxy acid modified polysiloxane internal release agent:
Because Q2-7119 (hydroxy dimethyl siloxane) will react with the catalyst, RIM three-way system is initially suggested, that is, the internal release agent is not mixed with other ingredients in advance. However, the usual commercial RIM machines are mostly two-way systems, so Dominquez and others put forward a method of using hydroxydimethylsiloxane stripping agent for RIM two-way systems. Its formula is that the first route contains hydroxyl dimethyl siloxane with a molecular weight of 71,5 and a chain extender whose terminal group is primary amine or secondary amine polyether group, and the functionality of the amine-terminated polyether group is 2-6, and the active hydrogen content is 75%. The second path contains aromatic polyisocyanate. By using this method, RIMPU elastomer can be easily taken out of the mold, 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 terminal primary amine or secondary amine group can be directly used in RIM. This release agent acts faster with PU base material than hydroxyl polysiloxane. Suitable for molding large RIM parts. The general formula of amino polysiloxane is echr' chr' NH-olefin -( OSiR1R2Z) m-O- olefin--NHCHR'CHR''E e. In the formula, R1 and R2 are groups composed of methyl and phenyl, E is an electron accepting group, R'' and R' are groups composed of hydrogen and methyl, and the average value of m is 1-75. For example, the group of ECH R'' CHR' is 2-cyanoethyl, and the average value of m is 4-5; For example, when the ECHR''CHR' group is 2- methoxyformyl ethyl, the average value of m is about 3-4. According to different formulations, it can be demoulded continuously for 2-73 times.
3) polyether modified polysiloxane internal release agent:
Arthur proposed a silicone release agent that can be used in RIM two-way system, and the patent has been transferred, which has good release effect and can shorten the molding cycle.
because it is not easy to react with other components in the ingredients, such as polyols, it can be used in RIM two-way system and can be demoulded continuously for 2 times.