The Formula Design of Waterborne High Corrosion Resistant Coating

Huang Yanyi, Chen Xinyao, Wei Xiaofei
(Guangzhou Human Chemical Co., Ltd., Guangzhou 511356, China)

Abstract: This paper mainly discusses the influencing factors of waterborne high corrosion resistant coating from the aspects of resin, monomer, curing agent,and coating additives, and discusses the coating application property.

1 Foreword
During the various heat treatment or mechanical processing of aluminum foil or aluminum plate, such as processing, rolling, cutting, the surface is inevitably oxidized to form an uneven aluminum oxide film, and it is mixed with various types of oil pollution or some impurities. , Oxidation layer is easy to fall off in later use, which causes aluminum to continue corroding and perforating. At present, there are many types of anti-corrosion coatings on the market, but most of them are solvent-based. During the construction process, the VOC is high and the smell is heavy, which is not good for the health of the construction workers. Water-based coil coating anticorrosive coatings have less room for improvement in corrosion resistance due to their wettability, wet adhesion, coating strength and chemical resistance after curing.
This article focuses on the synthesis of thermosetting silicone-modified acrylic emulsions, and uses hot melt, cold spell, and dispersion techniques commonly used in coatings to prepare thermosetting water-based high-resistance coatings. The main film-forming resin uses silicone to modify the acrylic resin. The surface energy of the silicone (siloxane) is low, the cohesive energy density is low, and the Si-Si bond energy is high (452 ​​kJ / mol). These structures make the silicone have Excellent weather resistance, air permeability, etc. Silicone is introduced into the acrylate main chain or side chain by chemical copolymerization modification. The prepared silicone-modified acrylic resin can combine the strengths of the two to improve the corrosion resistance of the coating. , Not only has good mechanical properties and adhesion properties, but also has good corrosion resistance.

2 Formulation design
The water-based high-resistance coating studied in this paper has synthesized a thermosetting silicone-modified acrylic emulsion as the main resin, and developed it with the formulation of a thermosetting water-based coating. The coating can be directly coated on the surface of aluminum foil after degreasing and cleaning treatment. Coating viscosity is 12 ~ 16 seconds (25 ℃, T4 cup), coating solid content is ≥26%. Appropriate coating viscosity and solid content help ensure coating thickness and appearance. The viscosity and solid content are too high or too low. When applied on a high-speed coating production line, the thickness of the coating is not easy to meet the requirements, thereby affecting the corrosion resistance of the coating.

2.1 Synthesis of Silicone Modified Acrylic Emulsion Resin
2.1.1 Resin Synthesis Process
Using monomer drop method to prepare silicone modified acrylic resin, the general process is:
Silicone monomer hydrolysis → chain extension → mixed solvents, emulsifiers, initiators, dispersion media → stirring and heating → polymerization → dropwise addition of acrylic monomers → heat preservation and stirring → detection of viscosity and solid content → cooling → filtration → packaging.

2.1.2 Selection of monomers

The vinyl siloxane-containing acrylate is used as the silicone monomer, and a hydroxy silicone oil with a molecular weight of 300 to 5000 and a methyl silicone oil with a molecular weight of 0 to 2000 are used to extend the chain and copolymerize with the methacrylic acid monomer. , Synthetic silicone modified acrylic resin emulsion. .

Mn = 0 ~ 2000 methyl silicone oil

During the synthesis of the emulsion resin, experiments have found that the total amount of silicone oil used for chain extension cannot exceed 15%, which is prone to incompatibility.
The resin design contains 40% solids. The higher the proportion of methacrylate in the resin, the smaller the particle size of the emulsion, and the finished product is a translucent blue phase. The higher the proportion of vinyl siloxane-containing acrylate, the larger the resin particle size. The storage stability of the finished paint, the proportion of vinyl siloxane-containing acrylate is recommended not to exceed 20%.

Monomer selection reference formula

2.2 Debugging of water-based coating formulations.
Based on the preparation of silicone-modified acrylic resin, materials such as silicone-modified acrylic resin, cross-linking agent, neutralizer, water, catalyst, leveling agent, and defoamer are used as impellers. A disc stirrer is mixed to produce a water-based high-resistance primer coating. The coating uses a full methyl etherified amino resin crosslinker to crosslink and cure with the resin, and a p-toluenesulfonic acid catalyst is introduced to increase the curing speed of the coating, thereby meeting the high-speed requirements of the coating for industrial roll coating.
The design solid content is 26%, and the reference formula is shown in Table 2 (in terms of mass fraction).

Reference formula of water-based high corrosion resistance coating

3 Discussion on physical and chemical properties of coatings and coating properties 

3.1 Physical and chemical properties of coatings

The test results of physical and chemical properties of coatings are shown in Table 3. The experiment found that when the proportion of curing agent is high, the storage stability of the coating decreases, and the curing agent addition ratio cannot be higher than 50. %.

Reference formula of water-based high corrosion resistance coating

3.2 Coating properties
The coating performance test results are as follows. The results show that Formula 3 has the best overall performance balance. In the aqueous silicone modified resin system studied in this paper, curing ratio screening is important. Too high a curing agent ratio will cause the molecular weight of the coating to crosslink. Low, affecting the corrosion resistance of the coating, too low curing agent ratio will also lead to insufficient crosslinking of the coating, reducing the corrosion resistance.

Performance comparison of different coatings

4 Conclusions
Through the above formulation tests, methacrylate was used as the main synthetic resin, acrylic monomer containing vinyl siloxane was used as the silicone segment, and silicone oil was used to extend the chain to synthesize an aqueous silicone-modified acrylic resin. Fully methyl etherified amino resin is used as curing agent, p-toluenesulfonic acid is used as catalyst, and suitable leveling agent and defoaming agent are used. The formulated water-based high-corrosion-resistant coating has uniform dispersion phase and moderate particle size, and good storage stability . In the case of a thin coating thickness, the prepared coating has a moderate curing temperature, the coating can achieve good leveling uniformity, excellent adhesion, good solvent resistance, acid and alkali corrosion resistance, and neutral salt spray resistance. Excellent performance, suitable for anti-corrosion treatment on the surface of aluminum foil or aluminum plate, which can effectively protect the surface of aluminum and prolong the life of aluminum.

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