The main role of amino resins (melamine-formaldehyde, benzoguanamine-formaldehyde and urea-formaldehyde (urea-formaldehyde) resins) in thermosetting coatings Yes, the main film-forming material molecules are cross-linked into a three-dimensional (three-dimensional) network structure through chemical reactions. This network structure is obtained through the reaction of amino resin molecules with functional groups on the film-forming material molecules, and simultaneous polycondensation reactions with other amino resin molecules. Amino resins react easily with polymers bearing primary and secondary hydroxyl, carboxyl, and amide groups, so amino resins are often used in paint systems based on acrylic, polyester, alkyd, or epoxy resins.
Amino resin is also used in polyurethane systems as a coating additive to improve the overall performance of certain uses of coatings.
Principle of amino resin:
Amino resin cross-linking agentThe importance of baking paint far exceeds its proportion in the coating. It is increasingly important to understand how to utilize the chemical properties of amino resins to design coating formulations. For example, if the paint formulator is not satisfied with certain properties of the coating film, he can adjust them through the following methods:
1. Improvement or reselection of the film-forming resin itself;
2. Selection of amino resin (methyl etherification or butyl etherification, and selection of etherification degree, etc.);
3. The matching ratio of film-forming resin and amino resin.
4. Selection of catalyst (whether to add or not, or how much to add.
The above 4 items except item 1 are all related to amino resin, and the performance of amino resin depends on its own functional groups and their activity, so understand the structure of amino resin Very important. But before understanding amino resin, we must first have a preliminary understanding of the host resin paired with amino resin.
As mentioned earlier, amino resin is mainly used with alkyd resin, acrylic resin, polyester resin, and epoxy resin. Alkyd resins are mainly synthesized from polyols and polyacid resins through an esterification reaction. During the synthesis process, alcohols are generally used in excess; there are also cases where the carboxyl groups of some polybasic acids are not fully reacted, so the final alkyd resin will contain a certain amount of amount of carboxyl and hydroxyl groups. The number of carboxyl groups and hydroxyl groups is usually characterized by acid value and hydroxyl value. The acid value refers to the number of milligrams of KOH required to neutralize 1g of solid resin with KOH titration.
The hydroxyl value refers to the number of milligrams of KOH required to convert the OH contained in 1g of solid resin into carboxyl groups and neutralize them completely with KOH titration. Similarly, polyester resin, acrylic resin, and amino resin also contain certain carboxyl and hydroxyl groups. It’s just that the raw materials used in synthetic resins are different. For example, the carboxyl groups in acrylic resin come from acrylic acid, and the hydroxyl groups come from hydroxyacrylic acid. The amounts of carboxyl groups and hydroxyl groups contained in amino resins are also different. Acid value, hydroxyl value, and viscosity are all important indicators of resin, which directly affect the performance of the resin.
