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CN-122011318-A - Hydrophilic low-temperature-deblocking isocyanate curing agent, preparation method thereof and water-based coating composition containing curing agent

CN122011318ACN 122011318 ACN122011318 ACN 122011318ACN-122011318-A

Abstract

The invention discloses a hydrophilic low-temperature-seal isocyanate curing agent, a preparation method thereof and application thereof in water-based paint, and belongs to the technical field of functional paint. The preparation method of the curing agent comprises the steps of reacting organic polyisocyanate, polyol and polyol containing carboxyl to obtain a pre-polymer with a main chain containing the carboxyl-NCO end, blocking the-NCO group by using a chemical blocking agent, adding an organic alkali neutralizing agent to form salt with the carboxyl, and finally adding water to disperse to obtain the aqueous curing agent emulsion. The invention endows the curing agent with inherent water dilutability by copolymerizing built-in hydrophilic carboxyl on the main chain of polyurethane molecules and neutralizing to form salt, and does not need to add a small molecular surfactant. The curing agent prepared by the method has molecular-grade compatibility with similar water-based main resin, reduces VOC content, solves the problem of film defects such as shrinkage cavity, needle hole and the like caused by poor compatibility, and improves the hardness, glossiness, adhesive force and water resistance and corrosion resistance of the film.

Inventors

  • LIU ZHIWEN
  • ZHOU HAIYING
  • YIN LIPING

Assignees

  • 常州光辉化工有限公司

Dates

Publication Date
20260512
Application Date
20260303

Claims (10)

  1. 1. The preparation method of the aqueous low-temperature deblocking closed isocyanate curing agent is characterized by comprising the following steps of: (1) In a reaction vessel, reacting an organic polyisocyanate monomer, a polyol and a polyol monomer containing carboxyl in the presence of a catalyst and an organic solvent, wherein the total molar ratio of NCO to OH is 1.5:1-2.5:1, and generating a polyurethane prepolymer with a terminal group of-NCO group and carboxyl in a molecular main chain; (2) Dropwise adding a chemical blocking agent into the prepolymer prepared in the step (1) to enable the-NCO group at the tail end of the prepolymer to react with the blocking agent until the-NCO group is completely blocked, so as to obtain a blocked isocyanate prepolymer; (3) Adding an organic alkali neutralizer into the closed isocyanate prepolymer obtained in the step (2), and carrying out a neutralization reaction with carboxyl groups on a molecular chain of the prepolymer to generate carboxylate amine salt with self-emulsifying capability; (4) Slowly dripping deionized water into the neutralized product of the step (3) at a temperature lower than 40 ℃ under high-speed shearing (1000-2000 r/min) to disperse, so as to obtain the aqueous low-temperature sealing isocyanate curing agent emulsion.
  2. 2. The method for preparing the aqueous low-temperature-deblocking blocked isocyanate curing agent according to claim 1, wherein in the step (1), the organic polyisocyanate monomer is selected from one or more of isophorone diisocyanate (IPDI), hexamethylene Diisocyanate (HDI), toluene Diisocyanate (TDI) or a trimer thereof, and the organic solvent is selected from one or more of dibasic ester (DBE), N-methylpyrrolidone (NMP) or propylene glycol methyl ether acetate (PMA).
  3. 3. The method for preparing the aqueous low-temperature-deblocking-blocked isocyanate curing agent according to claim 1, wherein in the step (1), the polyol monomer containing carboxyl groups is selected from dimethylolpropionic acid (DMPA) or dimethylolbutyric acid (DMBA), and the amount of the polyol monomer is 4% -12% of the total mass of the solid.
  4. 4. The method for preparing an aqueous low-temperature deblocking blocked isocyanate curing agent according to claim 1, wherein in the step (2), the deblocking temperature of the chemical blocking agent is 80-120 ℃, and the specific chemical blocking agent is one or more selected from butanone oxime, caprolactam, diethyl malonate, 3, 5-dimethylpyrazole and phenol.
  5. 5. The preparation method of the aqueous low-temperature deblocking-sealing isocyanate curing agent according to claim 1, which is characterized by comprising, by mass, 55-70 parts of organic polyisocyanate, 0-10 parts of polyol, 5-8 parts of polyol monomer containing carboxyl, 18-25 parts of chemical sealing agent, 3.5-5 parts of organic alkali neutralizer, 15-25 parts of organic solvent and 110-140 parts of deionized water.
  6. 6. The method for preparing an aqueous low-temperature-deblocking-blocked isocyanate curing agent according to claim 1, wherein in the step (3), the organic base neutralizer is Triethylamine (TEA) or N, N-Dimethylethanolamine (DMEA), and the addition amount is 80% -110% of the number of moles of carboxyl groups.
  7. 7. An aqueous low temperature deblocked blocked isocyanate curing agent made by the method of any one of claims 1-6.
  8. 8. A water-based paint composition, which is characterized by comprising a component A, a component B and a component B, wherein the component A contains carboxylate hydrophilic groups and has hydroxyl-containing water-based main body resin, the component B is the water-based low-temperature-deblocking-blocked isocyanate curing agent as described in claim 7, and the carboxylate hydrophilic groups in the component A and carboxylate amine salts on the main chain of the component B have the same anionic hydrophilic groups.
  9. 9. The aqueous coating composition of claim 8, wherein the ratio of component B to component A is 0.8:1 to 1.5:1 in terms of the molar ratio of isocyanate groups (-NCO) to hydroxyl groups (-OH).
  10. 10. The aqueous coating composition of claim 8, wherein component A is one or more selected from the group consisting of anionic aqueous acrylic resins, anionic aqueous polyester resins and anionic aqueous polyurethane dispersions (PUDs).

Description

Hydrophilic low-temperature-deblocking isocyanate curing agent, preparation method thereof and water-based coating composition containing curing agent Technical Field The invention belongs to the technical field of polymer chemistry and functional coating, and particularly relates to a preparation method of an aqueous low-temperature deblocking blocked isocyanate curing agent for realizing inherent water dilutability by introducing hydrophilic groups into a molecular main chain, and a high-performance bi-component aqueous coating composition containing the curing agent. Background Blocked isocyanate curing agents are key components in two-component polyurethane coating systems. The core mechanism of action is that isocyanate groups (-NCO) are temporarily protected by a blocking agent at normal temperature, so that the isocyanate groups (-NCO) do not react with active hydrogen groups (such as hydroxyl groups, amino groups and the like) in the system, and therefore, the coating system has excellent storage stability (namely long pot life). When the coating is heated to a specific deblocking temperature, the blocking agent falls off to release high-activity-NCO groups, and the high-activity-NCO groups and active groups of the main resin undergo a crosslinking curing reaction to form the coating with excellent performance. The prior art blocked isocyanate curing agents are mainly divided into solvent-based and aqueous-based. Among them, the water-based coating is a trend of development in the coating industry. However, the water-based blocked isocyanate curing agent on the market has obvious technical defects that the molecular structure of the water-based blocked isocyanate curing agent is not substantially different from that of the traditional solvent-based curing agent, the water-based blocked isocyanate curing agent is usually diluted by adding a large amount of hydrophilic organic cosolvent (such as propylene glycol methyl ether acetate PMA, diethylene glycol butyl ether and the like), and then the forced and unstable emulsification and dispersion are carried out by the emulsification functional groups carried by the water-based main resin during use. This aqueous mode causes the problem that the curing agent molecules have a different hydrophilic mechanism than the aqueous main resin molecules and remain essentially in an oil/water two-phase system, with inherent limitations on compatibility. This tends to cause delamination and flocculation of the coating during storage or construction and eventually manifest as shrinkage cavities, pinholes, orange peel, uneven gloss, etc. in the coating film. In order to improve the compatibility problem, various wetting, dispersing and emulsifying aids have to be additionally added into the formula, which not only increases the complexity and cost of the formula design, but also can introduce new instability factors and even affect the water resistance of the final coating film. In order to realize dilution and dispersion of the oily curing agent, the addition amount of the hydrophilic organic cosolvent is generally high, so that the Volatile Organic Compound (VOC) content of the product is difficult to meet the increasingly strict environmental protection regulation requirements. Therefore, developing an aqueous blocked isocyanate curing agent with inherent self-dispersing ability, excellent compatibility with an aqueous main resin system, and improved overall properties of the final coating film is a technical problem to be solved in the art. Disclosure of Invention The primary aim of the invention is to overcome the defects of the prior art and provide a preparation method of a low-temperature sealing-off type isocyanate curing agent for realizing water-based modification from the molecular structure level. The curing agent prepared by the method has inherent water dilutability, does not need to be externally added with a surfactant, and has excellent compatibility with conventional water-based resin, so that the defect of a coating film is reduced, and the performance of the coating is improved. It is a further object of the present invention to provide an aqueous coating composition comprising the above curing agent. The composition has good storage stability, workability and comprehensive physical and chemical properties of the cured coating film, such as glossiness, adhesive force, hardness and water resistance, due to the compatibility between the curing agent and the main resin. In order to achieve the above purpose, the invention adopts the following technical scheme: The preparation method of the aqueous low-temperature deblocking closed isocyanate curing agent is characterized by comprising the following steps of: (1) Preparation of NCO-terminated hydrophilic prepolymers: in a reaction vessel, reacting an organic polyisocyanate monomer, an oligomer polyol and a polyol monomer containing carboxyl in the presence of a catalyst and an organic solvent, and con