The hydrophilicity of the resin is one of the main factors for whether the aqueous resin can be dispersed and stabilized in water. During this period, the molecular structure type of the aqueous resin, the type of the introduced group, the molecular weight, the molecular weight dispersion, and the neutralizer and co-solvent used are all capable. Factors affecting the stability of water-soluble resins.
1. The effect of hydrophilic group type on the hydrophilicity of water-based resin
There are many types of hydrophilic groups: mainly carboxyl groups, amino groups, ether bonds, hydroxyl groups and so on.
(1) The influence of ether groups: Take the linear polyester resin as an example, even if the degree of esterification is basically the same, its water solubility is also different. The more ether groups, the better the water solubility.
(2) Effect of high-functionality alcohols: Taking pentaerythritol and dimerized pentaerythritol as high-functionality alcohols as an example, using it to appropriately replace the polyol component in the polyester resin in the above example can produce different water-soluble polymers Ester resin.
(3) The influence of high-functionality acid: as high-functionality acid dehydration trimellitic acid and pyromellitic anhydride, it is used together with oxalic acid, and the dosage of each acid is adjusted accordingly, Keeping it with the same total functionality as the polyester in the previous example, it will eventually produce a different water-soluble resin.
2. The influence of molecular weight and molecular weight dispersion
The molecular weight of synthetic resin has a great influence on its water solubility. Compared with the same type of resin, the molecular weight is small and the water solubility is good, but the corrosion resistance of the coating film is poor; the resin with a larger molecular weight has better corrosion resistance, but the water solubility is poor. Therefore, on the premise of ensuring that the resin is soluble in water, the molecular weight of the resin should be made as large as possible to obtain a coating film with better functions.
The narrower the molecular weight dispersion of synthetic resin, the poorer the water solubility, but the function of the coating film is good. Especially for the paints constructed by the electrodeposition method, the narrower the molecular weight dispersion, the better, because the molecules of different sizes are under the action of the electric field , Showing a different electrical accumulation. When the molecular weight dispersion is wide, the mutual solubility effect between molecules is often conducive to the improvement of water solubility, but it is usually not easy to obtain a paint film with excellent functions and stability.
3. The effect of neutralizer
Different types of neutralizers can significantly affect the water solubility of the resin, the storage stability of the resin solution, the viscosity, the curing rate, and the yellowing of the coating film. Therefore, it is also very important to properly select the neutralizer. The type of resin is different, and the neutralizer used should be different.
4. The effect of cosolvent
In order to improve the water solubility of the resin, adjust the viscosity of the water-soluble resin liquid and the leveling property of the coating film, it is necessary for some water-soluble resins to participate in a small amount of co-solvents, such as low-molecular-weight hydrophilic alcohols and alcohol ether solvents. The choice of co-solvent also needs to consider the function of the neutralizer amine used. Generally, the solution obtained by using sec-butanol as a co-solvent has low viscosity and good stability. Correctly choose the type of co-solvent, maybe choose two types of co-solvent and increase the amount of co-solvent. It is useful to overcome the phenomenon of viscosity peak of water-based resin during dilution. However, for water-soluble paints for electrophoretic coating, usually more co-solvent is added, which is not good for electrodeposition.