Enclosed water-based polyurethane coating crosslinking agent

Enclosed water-based polyurethane coating crosslinking agent,Two-component waterborne polyurethane is a polyol component and crosslinking agent component mix, mix without an exhausted, cannot continue to use again, cause waste of raw materials, components and crosslinking agent of NCO group activity is higher, room temperature can react with the water in the atmosphere so that it is bad.

If the NCO groups react with some sort of blocking agent, was prepared under normal temperature and stable material, when used by heating again to restore its original structure and isocyanate react with compounds containing hydroxyl, can get the original pu and can solve the above problems. Enclosed crosslinking agent has good stability in water, is widely used in water in the system, but the NCO group activity is very high, prone to adverse reactions, the deblocking temperature is high, the NCO group will happen dimer, melamine, affections generated formate or biuret, so it is very important to develop low deblocking temperature sealants.

Blocking agent and the reaction of isocyanate is typical of nucleophilic addition reaction. Mechanism of the reaction process can be used two explanations: one is to eliminate - bonus mechanism, namely, under a certain temperature, enclosed isocyanate is decomposed into sealants and free isocyanate, including free isocyanate continue to react with the hydroxyl component to generate two-component polyurethane. Another addition - elimination mechanism, namely the hydroxyl and closed the NCO group coordination reaction forming tetrahedral intermediate, then remove sealants.

Commonly used in closed waterborne polyurethane crosslinker sealants with isopropyl alcohol, phenol, caprolactam, methyl ethyl ketone oxime, imidazole, sodium bisulfite, diethyl malonate, etc. Generally choose sealants according to unlock the temperature and water soluble. In a closed reaction, when the NCO groups, even to the electronic substituents can promote closed reaction; But even with electron-withdrawing substituents can promote unsealed reaction.

Alcohols sealants have higher deblocking temperature and low reactivity, so can exist without a very stable in the water. Such as electrodeposition primer required storage stability is very strong, so 2 - ethyl hexanol as blocking agent.




Chinese name: Diethyl toluene diamine(DETDA)

Diethyltoluenediamine Uses:

The product is identical to Ethancure 100 and Lonza DETDA 80, DETDA is very effective polyurethane elastomer chain extender; also be used as polyurethane and epoxy resin curing agent, epoxy resin of an antioxidant, industrial oils and lubricants . In addition, also as intermediates in organic synthesis.Especially for the RIM (reaction injection molding), is important in the field of spray polyurea chain extender species. Also can be used for casting polyurethane elastomer (CPU) and a curing agent, epoxy curing agent, epoxy resin of antioxidants, lubricants and industrial oils other antioxidants.


Phenolic compounds and reaction mechanism of isocyanate with alcohol and isocyanate reaction mechanism, are all NCO group with active hydrogen reaction, respectively to generate carbamic acid ester and phenyl carbamate, phenolic compounds with benzene ring in the conjugate effect, lead to the reaction of phenolic hydroxyl activity than alcohol hydroxyl is weak, so the phenolic sealants compared with alcohols deblocking temperature is low, but closed reaction is slow, need to heat or add catalyst under the condition of the reaction speed.

Oxime class sealer is suitable for species of fat isocyanate closed, the deblocking temperature is lower than sealants as alcohols and phenols. Wang Li etc with TDI and TMP as raw material to synthesize polyurethane pre polymers, with methyl ethyl ketone oxime for sealants synthetic water-based polyurethane crosslinker, the results showed that the crosslinking agent closed low temperature storage stability and good solution.

Zhong Yan etc with isocyanate trimer and MPEG as reaction raw materials, with different sealants closed residual NCO groups, preparation of water dispersible polyurethane crosslinker, closed, the results show that when the MPEG molecular weight is less than 2000, with methyl ethyl ketone oxime as a blocking agent, preparation of enclosed waterborne polyurethane crosslinking agent with proper viscosity and good stability.

Due to the presence of hydrogen bonding, imidazole and amidine, pyrazole and triazole sealants deblocking temperature is relatively low. Zhou jing jing, etc with IPDI and TMP as raw material via addition reaction, DMPA as chain extender, again with triethylamine (TEA) and salt, 2 - methyl imidazole (2 - MI) for sealants seal end, get a room temperature can unlock water-based polyurethane crosslinker, results showed that the crosslinking agent can significantly reduce the reaction rate of isocyanate with water, increase the gel time.

Han-qing zhang with isocyanate trimer and DMPA as a raw material for chain extension reaction, again with 3, 5 - dimethyl pyrazole (DMP) for sealants, the remaining NCO group closed, with 2 methyl diethanolamine (activity) and finally into a salt, of water crosslinking agent can implement unsealed at lower temperatures.

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Diethyl toluene diamine(DETDA)  http://www.yaruichem.com