Common knowledge of coatings: the role of solvents in coatings

Core tips: ① low viscosity, adjusting rheology The viscosity of polymer solution is related to the properties of solvent It has been mentioned before that the viscosity of polymer solution in good solvent is lower than that in bad solvent with the same concentration because the coating is a solution with higher concentration There is a great relationship between the viscosity and hydrogen bond The viscosity of oligomer solution containing a lot of hydroxyl and carboxyl groups can be very high due to the interaction of hydrogen bond, but adding some solvents such as cyclohexanone can reduce the viscosity a lot The following formula shows the case of carboxylic acid itself and hydrogen bond in ketone solvent: Because ketones are hydrogen bonded receptors, not Which is the price of Dajin diatom mud Recommended brief introduction: which is the price of Dajin diatom mud? How to buy genuine diatom mud? Guangdong diatom mud agent suggests placing a basin of cold water in the air conditioning room, so that the diatom mud wall can breathe effectively The feature of the breathing wall is obvious When the indoor air is dry, the diatom mud wall will release the absorbed water quickly Put it out to help regulate the indoor dry humidity It is suggested to place a basin of cold water in the air conditioning room, so that the wall of diatom mud can breathe effectively The feature of the wall that can breathe is obvious When the indoor air is relatively dry, the wall of diatom mud will absorb the water Home of coatings: ① low viscosity, adjusting viscosity of rheological polymer solution is related to solvent properties It has been mentioned before that the viscosity of polymer solution in good solvent is lower than that in bad solvent with the same concentration because the coating is a solution with higher concentration There is a great relationship between the viscosity and hydrogen bond The viscosity of oligomer solution containing a lot of hydroxyl and carboxyl groups can be very high due to the interaction of hydrogen bond, but adding some solvents such as cyclohexanone can reduce the viscosity a lot The following formula shows the situation of carboxylic acid itself and hydrogen bond in ketone solvent: because ketone is a hydrogen bond acceptor, not a hydrogen bond donor, it can destroy the "network" structure formed by hydrogen bond between molecules, thus greatly reducing viscosity Due to the effect of hydrogen bond in polyurethane, it is easy to form gels, which can be recovered by adding ketone solvent When the solubility parameters of carboxyl containing oligomers are close to those of solvents, the viscosity of solutions is sometimes higher than that of the two Of course, when the solubility parameters are quite different, the viscosity will rise again The mechanism can also be explained by the above hydrogen bond The dissolving ability of solvent to paint, that is, the ability to reduce viscosity, is generally expressed by solvent index Solvent index = viscosity of paint diluted with standard solvent / viscosity of paint diluted with tested solvent is compared with that of tested solvent under equal weight condition If the solvent index is greater than 1, it means that the solubility of tested solvent is strong In addition, the solvent can also significantly affect the surface tension of the coating, which has a great impact on the coating performance ② The resistance electrostatic coating method of the control coating takes the coating as the anode and the coating atomizer as the cathode to generate a high-voltage electrostatic field between the two poles, and generate corona discharge at the cathode, so that the sprayed paint drops are electrified and further atomized, so as to effectively absorb the coating along the direction of the power line and complete the coating work Electrostatic coating has certain requirements on the electrical properties of the coating, in order to achieve the best effect The resistance of coating can be adjusted by solvent Polar solvent with low resistance and non-polar solvent with low resistance are added to high resistance coating ③ As a polymerization reaction solvent, it is used to control the molecular weight and distribution of the polymer When the solvent with suitable boiling point and chain transfer constant is used as the polymer medium, satisfactory molecular weight and molecular weight distribution can be obtained For example, xylene, benzyl alcohol, methyl amyl ketone, propyl acetate and heptyl ester can be used as polymerization solvent to prepare acrylate polymer with low molecular weight and narrow distribution ④ The improvement of coating and film properties can improve the fluidity of coating and the gloss of film by controlling the volatile speed of solvent, especially the volatile speed of different solvents in mixed solvent Choosing suitable solvent can improve the wetting of substrate and increase the adhesion of paint film The volatilization of solvent in the coating has a great influence on the performance of the film The solvent volatilizes from the coating in two stages The first stage is the wet stage The volatilization of the solvent mainly depends on the volatilization of the solvent itself With the volatilization of the solvent, the viscosity of the coating becomes larger and larger The second stage is the dry stage The solvent volatilization is mainly determined by the diffusion speed of the solvent in the coating It is related to the Tg of the polymer in the paint film and the size and shape of the solvent molecules, but not parallel to the volatility and solubility of the solvent For example, the order of volatility of n-butyl acetate and isobutyl acetate is opposite in the two stages In the first stage, isobutyl acetate volatilizes faster, while in the second stage, n-butyl acetate volatilizes faster In the second stage, the volatilization rate of solvent is very slow, and a small amount of solvent may exist in the film for a long time In the drying stage, vacuum drying is ineffective, because diffusion is not related to atmospheric pressure, vapor pressure, etc There is a transition between the wet and dry stages The bad choice of solvent can cause various disadvantages If volatilization is too fast, leveling is not good, but also easy to make the paint film white and bubbles The reason for whiteness is that the solvent volatilizes too fast When painting, the surface of the paint cools rapidly, making the surrounding temperature below the dew point The water vapor condenses into small drops and infiltrates into the paint film The surface becomes translucent white After the final moisture volatilizes, there is a small gap Due to scattering, the paint film has no luster Bubble is because the evaporation speed is too fast, the surface solidifies quickly, and the underlying solvent cannot escape When entering the oven, the residual solvent extrudes from the underlying surface, thus forming bubbles In addition, the good solution and the bad solution have a very important influence on the film structure and the dispersion stability of pigment, which need to be properly selected Considering the volatilization speed, the selection of coating solvent should balance the following requirements: (1) fast drying: fast volatilization (2) no sagging: fast volatilization (3) no shrinkage cavity: fast volatilization (4) good fluidity and leveling: slow volatilization (5) no edge thickening: fast volatilization (6) no bubble: slow volatilization (7) No whitening: the home of volatile slow coating is focused on coating, diatom mud, paint coating, coating process, news and coating of fire retardant coating, diatom mud, paint coating, coating process, decoration knowledge and decoration effect map of fire retardant coating,