Formulation Design of Waterborne Coatings for Steel Structure

Yu Shiguo (Suzhou Jiren High- Tech Materials Co., Ltd., Suzhou, Jiangsu215143,China)

Abstract : Based on the characteristics of coatings for steel structure, a type of waterborne fast drying primer -topcoat integral coating system for large -size steel structure has been prepared by using waterborne alkyd resin, acrylic emulsion, anti -rust pigment, corrosion inhibitor and film -forming additive, etc. The prepared coating system shows good comprehensive properties such as wetting, anti -rust, fast -drying, easy -to -use and water resistant performance, and has been industrialized for various steel structures and frameworks.

0 Introduction
At present, the country’s requirements for environmental protection are getting higher and higher, the coating industry and coatings are developing towards low pollution, water-based coatings are rising, anti-corrosion coatings for metal materials have attracted attention at home and abroad, and solvent-based coatings have air pollution, There are several issues such as toxicity and fire hazard. Therefore, the development of environmentally friendly water-based coatings has been valued. At present, most steel structure manufacturers are considering the following factors when using water-based paints: (1) low-cost oil-based rust-proof paints, the cost of using water-based rust-proof paints will greatly increase; (2) how to solve flash rust during construction Questions; (3) How to control temperature and humidity during construction; (4) Large steel structures generally do not treat the substrate in place, and the surface contains oil. How can water-based paint achieve sufficient wetting of the substrate and have considerable adhesion? (5) How to achieve a general film thickness, good initial water resistance, and a long-term anti-rust performance water-based paint; (6) Is it compatible with acrylic, polyurethane, fluorocarbon and other topcoats, and will not bite off? And other issues. In view of the above problems, in this research, different water-based alkyd resins, styrene-acrylic emulsions, pure acrylic emulsions, polyurethane emulsions, etc. were used for mutual improvement tests. Finally, the self-produced water-based alkyd resins and acrylic emulsions were selected to improve each other. Issues such as properties, hardness, and water resistance. The use of Tego’s KL245 and oil emulsifiers solves the problem of wetting and adhesion to substrates with slightly oily surfaces.

1 Experimental
1.1 Raw materials:
Water-based alkyd resin, acrylic emulsion: homemade; alcohol ester-12, benzyl alcohol, ethylene glycol butyl ether, pH adjuster: commercially available; substrate wetting agent 270, defoaming agent 810: Digao ; Corrosion inhibitor, water-based bentonite, dispersant 760W, water-based drier: commercially available; anti-flash rust additive 179: Hemmings; thickener, iron oxide red powder, precipitated barium sulfate, mica powder, zinc phosphate, three Aluminum polyphosphate, oil emulsifier (sodium dodecylbenzenesulfonate): commercially available.

1.2 Coating preparation process
Deionized water and water-based organic bentonite are pre-slurryed, and a certain amount of water-based alkyd resin, drier, dispersant, defoamer, and pH adjuster are added to the mixing tank. After low-speed mixing, add iron oxide red powder. 1. Precipitate barium sulfate, aluminum tripolyphosphate, mica powder, and zinc phosphate. Continue stirring for 20 to 30 minutes and grind to a fineness of <35 μm. During the grinding process, add deionized water to adjust the viscosity as appropriate. Finally, stir at low speed, and add acrylic resin, film-forming aid, anti-flash rust agent, substrate wetting agent, and thickener to adjust the viscosity.

1.3 Performance test

The sample was tested at room temperature for 24 hours and then tested for physical properties. After 7 days, type test items were tested. The test standards refer to national standards.

2 Results and discussion
2.1 Selection of water-based resins and dosages

The self-produced water-based alkyd resins with an oiliness of 53% to 56% were selected for testing. The experimental design was to use different amounts of water-based alkyd resins to formulate iron red paint on the bottom surface to the paint film. Testing of properties such as drying time, gloss and resistance. The formula of the iron red underside paint is shown in Table 1, and the performance test is shown in Table 2.

Iron red underside paint formula
Basic properties of paint film

It can be seen from Table 2 that when the water-based alkyd resin and acrylic resin are mixed, they can improve the dryness, water resistance and salt spray performance, and when the formula 3 is selected, that is, when the resin ratio is 1: 8, the paint films are different. The performance index is optimal, and the drying, corrosion resistance, water resistance and gloss are optimal.

2.2 Selection of corrosion inhibitors
In metal protective coatings of water-based coatings, flash corrosion often occurs during the drying process, so it is particularly important to choose a suitable corrosion inhibitor in the formula. Corrosion inhibitors are generally divided into 5 categories: (1) inorganic corrosion inhibitors and nitrites, which have low cost, high toxicity, and poor compatibility. (2) organic corrosion inhibitors, nitrogen-oxygen heterocyclic compounds, which are also highly toxic. There are also compatibility issues. (3) Silicates, which are added in large amounts, have an effect on the properties of the paint film. (4) Triethanolamine, etc., the corrosion inhibition effect of this type is not obvious. This kind of corrosion inhibitor not only has a corrosion inhibitory effect, but also enhances the adhesion and the stability of the coating. The test formulations of different corrosion inhibitors are shown in Table 3, and the performance comparison is shown in Table 4.

Iron red underside paint formula
Basic properties of paint film

It can be seen from Table 4 that in this water-based bottom-in-one paint system, the corrosion inhibitor 5 is the best raw material.

2.3 Selection of film-forming aids
When designing the formulation, the selection of film-forming aids is extremely critical, which affects the gloss, dryness, water resistance and corrosion resistance of the paint film, and is also critical to the storage state. In this paper, benzyl alcohol, dodecyl alcohol ester, ethylene glycol butyl ether, and propylene glycol methyl ether are used for comparison tests. Compatibility testing of film-forming auxiliaries with water-based acrylic emulsions shows that benzyl alcohol, ethylene glycol butyl ether, and propylene glycol methyl ether have good compatibility in styrene-acrylic emulsions, but they need to be added slowly, or flocculation will occur; Dicarbonate is very compatible in any emulsion, and it is easy to add, not easy to break, and has wide applicability.
Dodecyl alcohol ester is a strong solvent for emulsion polymers, and has very good hydrolytic stability and very good coalescence performance. It can effectively reduce the minimum film formation temperature (MFFT) and expand the polymerization for high glass transition temperature (Tg). The range of use of things. Compared with other film-forming aids, it is easy to be adsorbed by latex particles, easy to swell the rubber particles, and has a low volatility rate. It is retained in the paint film before film formation, and the film formation continuity is good, and it has a suitable volatility, without affecting Gloss and hardness of paint film. The properties of several film-forming additives are shown in Table 5.

Comparison of film forming additives

In the water-based paint using dodecyl alcohol ester as a film-forming aid, various indexes of the paint film reached a balance.

2.4 Selection of surfactant
There are many oil stains and fluxes on the surface of large steel structures. In order to reduce costs, some manufacturers do not properly handle the substrate and do not remove oil stains. For oily paint spraying, the problem is not big, but for waterborne paint spraying, it increases. Difficulty affects the wetting and adhesion of the coating to the substrate. Generally, a silicone-based leveling agent is selected to reduce the surface tension of the water-based coating to achieve the leveling effect, but it seriously affects the adhesion and recoating of the paint film. In this study, a surfactant (dodecylbenzenesulfonate) was used as an oil emulsifier, and the oil on the steel surface was directly emulsified, so that the paint film directly contacted the substrate. Oil-based emulsifier alone only solves the problem of oil staining, but the wetting of the substrate is not sufficient. In this experiment, we chose to mix with the Teco 270 substrate wetting agent to solve the problem of wetting and leveling of the paint film. Brings good substrate adhesion, the adhesion on oily substrates reaches level 1, and has excellent water resistance and salt spray resistance.

3 Concluding remarks
(1) The experiments compared different ratios of self-producing water-soluble alkyd resins and acrylic resins, which can improve the drying performance, water resistance and salt spray resistance. Moreover, when the resin ratio is 1: 8, the paint films are different. The performance index reached the best, and the drying, corrosion resistance, water resistance, and gloss were the best.
(2) The effects of different corrosion inhibitors on the performance of the paint film were compared. “It enables water-based coatings to be applied on rusted substrates and prevents the occurrence of flash rust.
(3) The experimental comparison and the use of dodecyl alcohol as a film-forming aid can effectively reduce the minimum film-forming temperature (MFFT). ). Expand the application range of polymers suitable for high glass transition temperature (Tg). It is easy to be adsorbed by latex particles, easy to swell the rubber particles, and has a low volatilization rate. It remains in the paint film before film formation and has good film formation continuity , have a suitable degree of evaporation does not affect the gloss and the hardness of the paint film;
(4) was chosen for oil emulsifier with a wetting agent Tego Blending substrate 270, the film of the wetting solution, leveling problems, while Good adhesion to the substrate, adhesion with the oil film reaches the substrate stage 1, and having excellent water resistance and salt spray resistance.
Through the above experiments, a wide range of water-based iron-red undercoats with one surface have been determined, and the cost is low, which can replace the solvent-based alkyd rust-proof paint and meet the requirements of environmental protection.

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