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CN-122011315-A - Full-aqueous melamine resin for metal baking varnish, preparation method and application thereof

CN122011315ACN 122011315 ACN122011315 ACN 122011315ACN-122011315-A

Abstract

The invention provides a preparation method of full-aqueous melamine resin for metal baking paint, which comprises the following steps of mixing melamine, formaldehyde donor, glyoxylic acid and cyclic urea, carrying out heating reaction under alkaline conditions to obtain a carboxyl-containing polymethyl intermediate, adding low-carbon alcohol, carrying out etherification reaction under acidic conditions to obtain etherified resin liquid, cooling the etherified resin liquid to 45-55 ℃, regulating the pH value of a system to 6.0-7.0, then adding an epoxy-containing silane coupling agent for thermal insulation grafting reaction to obtain grafted modified resin, carrying out decompression removal of small molecular byproducts on the grafted modified resin, then adding a neutralizing agent for regulating the pH value to weak alkaline, and adding deionized water for dispersion to obtain the full-aqueous melamine resin for metal baking paint. The invention has the advantages of ultra-low free formaldehyde, excellent storage stability, chemical bonding grade adhesion to metal substrates and excellent flexibility.

Inventors

  • YU HONGJIAN
  • HUANG ZIQIANG
  • LI JIAHAO
  • QIU YEXIA
  • XU SHAOLIN
  • JIANG XIAODI
  • JIANG HONGWEI
  • Pan Binxian
  • GU YAN
  • ZHAO ZHICHAO
  • ZHU JINJIE

Assignees

  • 浙江亚迪纳新材料科技股份有限公司

Dates

Publication Date
20260512
Application Date
20260309

Claims (9)

  1. 1. The preparation method of the full-aqueous melamine resin for the metal baking varnish is characterized by comprising the following steps of: S1, mixing melamine, formaldehyde donor, glyoxylic acid and cyclic urea, and performing heating reaction under alkaline conditions to obtain a polyhydroxy methyl intermediate containing carboxyl; s2, adding low-carbon alcohol into the polyhydroxy methyl intermediate containing carboxyl, and carrying out etherification reaction under an acidic condition to obtain etherified resin liquid; S3, cooling the etherified resin liquid to 45-55 ℃, regulating the pH value of a system to 6.0-7.0, and then adding a silane coupling agent containing epoxy groups for heat preservation grafting reaction to obtain grafted modified resin; s4, decompressing the grafted modified resin to remove small molecule byproducts, then adding a neutralizing agent to adjust the pH value to be alkalescent, and adding deionized water to disperse to obtain the full-aqueous melamine resin for metal baking paint.
  2. 2. The method for preparing the full-aqueous melamine resin for metal baking varnish according to claim 1, wherein the amount of the other raw material components is 1.2-2.0 mol based on 1 mol of melamine, 0.5-1.2 mol based on formaldehyde of the formaldehyde donor, 0.2-0.5 mol based on glyoxylic acid of the cyclic urea, 3.0-5.0 mol based on lower alcohols, and 0.05-0.15 mol based on epoxy group-containing silane coupling agents.
  3. 3. The preparation method of the full-aqueous melamine resin for metal baking varnish, which is disclosed in claim 1, is characterized in that in the step S1, the cyclic urea is ethylene urea or propenyl urea, the pH value of the alkaline condition is 8.0-9.0, the heating reaction temperature is 65-75 ℃, and the reaction time is 1-2 hours.
  4. 4. The preparation method of the full-aqueous melamine resin for metal baking varnish, which is disclosed in claim 1, is characterized in that in the step S2, the low-carbon alcohol is one or more of methanol, ethanol and butanol, the pH value of the acidic condition is 4.0-5.0, the etherification reaction temperature is 70-80 ℃, and the reaction time is 2-3 hours.
  5. 5. The method for preparing the full-aqueous melamine resin for metal baking varnish according to claim 1, wherein in the step S2, polycarbonate diol is added simultaneously with the low-carbon alcohol for a co-etherification reaction, the molar ratio of the polycarbonate diol to the melamine is 0.1-0.2:1, and the number average molecular weight of the polycarbonate diol is 1000-2000.
  6. 6. The preparation method of the full-aqueous melamine resin for metal baking varnish according to claim 1, wherein in the step S3, the epoxy group-containing silane coupling agent is gamma-glycidoxypropyl trimethoxy silane or gamma-glycidoxypropyl methyldiethoxy silane, and the heat-preservation grafting reaction time is 1-1.5 hours.
  7. 7. The method for preparing the full-aqueous melamine resin for metal baking varnish according to claim 1, wherein in the step S4, the neutralizing agent is one or more of N, N-dimethylethanolamine, triethylamine or ammonia water, and the weakly alkaline pH value is 7.5-8.5.
  8. 8. A full-aqueous melamine resin for metal baking varnish, which is characterized by being prepared by the preparation method of the full-aqueous melamine resin for metal baking varnish according to any one of claims 1 to 7.
  9. 9. Use of the all-aqueous melamine resin for metal baking varnish according to claim 8 in the field of metal surface coating.

Description

Full-aqueous melamine resin for metal baking varnish, preparation method and application thereof Technical Field The invention relates to melamine resin, a preparation method and application thereof, in particular to full-aqueous melamine resin for metal baking varnish, a preparation method and application thereof, and belongs to the technical field of high polymer resin materials. Background Melamine resins are widely used in metal baking paint coatings for their excellent hardness, abrasion resistance and chemical resistance. The high content of free formaldehyde is the first difficult problem faced by the traditional melamine resin and the water-based modification technology. The traditional melamine resin synthesis seriously depends on formaldehyde to carry out methylolation reaction, so that a large amount of free formaldehyde remains in the final product, which cannot meet the increasingly strict environmental protection regulation requirements, and is continuously released in the paint storage and coating process, thereby endangering the health of operators and polluting the environment. In the prior art, the water dispersibility is realized by externally adding an emulsifying agent or modifying a strong hydrophilic group, but the method often causes hydrolysis or self-polymerization of the resin in the storage process, the viscosity is rapidly increased or even gelled, the storage period is usually shorter, and the pressure is brought to the stock of a coating production enterprise, so that the industrialized application of the water-based melamine resin is limited. In addition, the traditional resin lacks active groups which form chemical bonding with the metal surface, is mainly adhered by physical adsorption, and when the metal plate is subjected to secondary processing such as deep drawing, bending and the like, a paint film is easy to peel off, so that the severe requirements of fields such as household appliances, automobile parts and the like on the coating processability can not be met. In addition, due to the rigidity characteristic of the melamine six-membered ring structure, the cured paint film is brittle and hard, and is easy to crack when the metal base material is subjected to thermal expansion and cold contraction or mechanical impact, so that the service life and the reliability of the product can be seriously influenced. Therefore, how to develop an all-aqueous melamine resin with ultralow free formaldehyde, excellent storage stability, chemical bonding grade adhesion to metal substrates and excellent flexibility is a technical problem to be solved in the field. Disclosure of Invention Based on the background, the invention aims to provide the full-aqueous melamine resin for the metal baking varnish, the preparation method and the application thereof, and the breakthrough of the performance of the aqueous melamine resin is realized through the molecular structure design and the process parameter control, so that the problems of high free formaldehyde content, poor storage stability, weak adhesive force to metal substrates and large brittleness of a paint film in the prior art are solved. In order to achieve the above object, the present invention provides the following technical solutions: the preparation method of the full-aqueous melamine resin for the metal baking varnish comprises the following steps: S1, mixing melamine, formaldehyde donor, glyoxylic acid and cyclic urea, and performing heating reaction under alkaline conditions to obtain a polyhydroxy methyl intermediate containing carboxyl; s2, adding low-carbon alcohol into the polyhydroxy methyl intermediate containing carboxyl, and carrying out etherification reaction under an acidic condition to obtain etherified resin liquid; S3, cooling the etherified resin liquid to 45-55 ℃, regulating the pH value of a system to 6.0-7.0, and then adding a silane coupling agent containing epoxy groups for heat preservation grafting reaction to obtain grafted modified resin; s4, decompressing the grafted modified resin to remove small molecule byproducts, then adding a neutralizing agent to adjust the pH value to be alkalescent, and adding deionized water to disperse to obtain the full-aqueous melamine resin for metal baking paint. Preferably, the melamine is used as 1 mole, and the dosage of each other raw material component is 1.2-2.0 moles of the formaldehyde donor, 0.5-1.2 moles of the glyoxylic acid, 0.2-0.5 moles of the cyclic urea, 3.0-5.0 moles of the low-carbon alcohol and 0.05-0.15 moles of the epoxy group-containing silane coupling agent are calculated as formaldehyde. Preferably, in the step S1, the cyclic urea is ethylene urea or propylene urea, the pH value of the alkaline condition is 8.0 to 9.0, the temperature of the heating reaction is 65 ℃ to 75 ℃, and the reaction time is 1 to 2 hours. Preferably, in the step S2, the lower alcohol is one or more of methanol, ethanol and butanol, the pH value of the acidic condition