The influence of catalyst dosage on the crosslinking agent of synthetic coatings
The influence of catalyst dosage on the crosslinking agent of synthetic coatings
The experimental results show that the catalyst dosage has a great influence on the time of the catalyst and the dissociation effect. The dosage of catalyst has a great influence on the time of action. Excessive amount and too low can result in the synthesis failure. Too low a catalyst can lead to a reaction that can't be completed, and a gelatinous phenomenon occurs when the dosage is too high.
In the chemical reaction can change the chemical reaction rate of reactants (increase or decrease) without changing the chemical equilibrium, and itself quality and chemical properties in no change before and after chemical reaction substance called catalyst (also called catalyst solid catalyst).
There are various kinds of catalysts, which can be divided into liquid catalysts and solid catalysts. The phase states of the reaction system are divided into homogeneous catalysts and polyphase catalysts, which are both acid, alkali, soluble transition metal compounds and peroxide catalysts.
The increase in the dosage of amines is beneficial to removing free monomers, but it not only promotes monomer and tripolymerization. It also increased the reaction activity of the hydroxyl and carbamate to TDI, and caused further polyurea reaction and other side reactions.
Composite end point control of crosslinking agent is NCO instructions, found from the reaction of 3-2, catalyst in addition to promote the trimerization reaction reduce NCO, as also by other reactions to reduce the NCO, and not only for TDI monomer. Therefore, excessive catalyst introduction is counterproductive to reducing free TDI.
When the dosage of the catalyst is too low, a prolonged high temperature reaction can blunt the reaction of the catalyst. When the dosage of catalyst is low, even if the reaction is completed, there is no good dissociation effect, such as crosslinking agent F.
Chinese name: Diethyl toluene diamine(DETDA)
Physical and chemical properties: light yellow transparent liquid, slightly soluble in water, soluble in alcohols, ethers, ketones and other polar organic solvents, and polyether, polyester polyol compatibility.
Density 1.022
Viscosity (20 ℃) ??mPa·ss290±10
Pour Point ℃-9
Boiling point of310°C
Copyright: Zhang Jia Gang YaRui Chemical co.,Ltd
Catalyst effect the performance of the crosslinking agent, crosslinking agent synthesis of catalyst is A range, 7 groups of experiments in front of A and G group of catalyst outside the scope of use no complete reaction. In the range of use, different catalyst dosage will also affect the performance of the final product. Table 3-2 reflects the effect of catalyst on the storage period and viscosity of crosslinking agent.
The secondary reaction in the crosslinking agent increases with the increase of the dosage of the catalyst, so the viscosity of B and C is also larger. The catalyst can also catalyze the oxidation of TDI and the addition of trihydroxide in the solvent, so the chromaticity also increases with the increase of the dosage of the catalyst.
The existence of catalyst has adverse effects on the storage stability of crosslinking agent, and the storage period of B and C is significantly lower than that of other groups. The high degree of viscosity and chromaticity of crosslinking agent is caused by a large number of side reactions and oxidative reactions caused by prolonged heating.
From the microscopic analysis, the amount of catalyst has a great influence on the molecular weight. In this paper, the molecular weight distribution of crosslinking agents for different catalysts used in polyethylene glycol was detected, and the molecular weight (from left to right) was measured.
The average molecular weight of polyurethane crosslinking agent is between 600 and 1000. Excessive side reaction from excessive catalyst dosage leads to high production of large molecules, so B and C are too viscous and widely distributed. The cross-linking agent E, due to prolonged reaction time, causes the molecular weight distribution to widen. The function of F is longer, producing a large number of side reactions and large molecules, and the molecular weight distribution is very wide. Crosslinking agent is more suitable, the main molecular weight distribution is between 630 ~ 800, and the polymerization degree of the region is 6 ~ 7.
Effect of catalyst dosage on film performance. The crosslinking agent only forms the paint film with the hydroxyresins, which can be used to show the value of the crosslinking agent. The main paint used in the experiment was alkyd resin. It was diluted with the crosslinking agent and the paint film was formed in the form of spraying. The solvent is a mixture of butyl acetate, xylene and cyclohexanone.
A large number of catalysts can cause film hardness, mechanical impact and flexibility, and catalyst is one of the most important factors for coating aging. The dosage of the catalyst will not obviously affect the film performance, and the aging time will increase.
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