Steel drum water-based paint coating process

Steel Drum Water-Based Paint Coating Process

Wuhan Haiyuan Jiutian New Material Co., Ltd. – Liu Shengbo

Liu Shengbo gives a lecture during the fifth technical training session

I. Development and Current Status of Water-Based Paints

1. History of the Foreign Coating Industry

In July 1966, the United States introduced the 66 regulation to control photochemical volatile organic solvents due to environmental pollution concerns, marking the beginning of restrictions on volatile organic compounds (VOCs) in coatings.

By 1970, the Environmental Protection Agency was established, setting strict regulations for paint production and application. The U.S. also set an ozone concentration limit for all states, with a VOC upper limit of 420 g/L. Similar measures were adopted in Europe and other countries to regulate VOC emissions from paints.

Today, in developed countries in Europe and America, water-based wood lacquer accounts for 50%-80% of the market. In the decorative coating sector, the use of water-based products is becoming increasingly common, reaching up to 70% of total decorative coatings, largely due to the unique properties of waterborne coatings.

2. Current Situation of Domestic Water-Based Paints

With the continuous progress of China's reform and opening-up, both the government and the public have become more concerned about environmental protection and have gradually established environmental regulations aligned with international standards. As a result, research and development of eco-friendly coatings have gained more attention.

Over the past decade, China’s water-based industry has experienced significant growth. A wide range of water-based paint products are now available, including water-based wood lacquer, rust-proof paint, metal paint, UV paint, automotive paint, flooring-specific paint, and cabinet paint. However, the market share of water-based paints remains much lower than in many foreign countries, with solvent-based paints still dominating the market.

II. Characteristics of Water-Based Paints

Unlike traditional solvent-based coatings that use organic solvents as dispersants, water-based coatings use water as their main dispersant and diluent.

1. Water is harder to evaporate, which can lead to sagging under high humidity conditions.

2. The surface tension of water is higher than that of solvents. If not properly adjusted, it can affect the quality of the final film.

3. The viscosity of water changes significantly under shear force, which can greatly impact the performance of the paint system.

4. Water is highly corrosive to metal materials, potentially causing damage to equipment used in the coating process.

5. Water-based paints improve the working environment by using water as the main solvent. They allow for easier cleaning of tools with water, reducing the need for solvents, saving resources, minimizing fire risks, and lowering atmospheric pollution.

III. Performance Comparison Between Water-Based and Solvent-Based Paints

1. Performance

2. Quality

Some water-based paints offer excellent quality, even surpassing solvent-based ones in certain aspects.

IV. Water-Based Paint Construction Process

1. Methods

When switching from oil-based to water-based paints, it is essential to thoroughly clean the spray equipment. Start by cleaning the spray gun with a solvent, then rinse it with absolute ethanol, and finally wash it with tap water. Clean the outer wall of the oil inlet pipe and the filter on the spray machine as soon as possible.

Water-based paints must be stirred properly, especially the mixing tools should not be contaminated with dried oil paint, oil, or residue. It is recommended to rinse them with tap water before use. Ensure sufficient agitation to avoid issues like uneven spray gun performance or defects in the paint film. If the paint is not used for a short time or left overnight, seal the container tightly to prevent dust contamination and avoid surface cracking caused by drying.

Do not mix water-based paints from different manufacturers or different colors. Before applying water-based paint to steel drums, ensure there is no moisture or dew present to prevent issues such as sagging or color floating.

2. Process

(1) Phosphate-Free Process: Eliminate phosphating costs and reduce wastewater treatment.

(2) Monochrome Barrel: No change in painting process. Baking conditions: 120–150°C, 15–10 minutes.

(3) Color-Blocking Barrel: Pre-spray temperature of the barrel is 70–90°C, no need to change the painting process. Baking conditions: 120–150°C, 15–10 minutes.

V. Cost Comparison Between Water-Based and Solvent-Based Paints

1. Cost Comparison

2. Stability and Quality

A more stable workforce leads to better product quality. Employees with increased self-protection awareness contribute to a more stable team. An unstable painter team increases the risk of poor coating performance. Switching from oil to water-based paints reduces pressure on workers and improves overall safety.

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