Steel Drum Water-Based Paint Coating Process
Wuhan Haiyuan Jiutian New Material Co., Ltd. - Liu Shengbo
Liu Shengbo gives a lecture at the fifth technical training session
I. Development and Current Status of Water-Based Paint
1. The History of the Foreign Coating Industry
In July 1966, the United States introduced the 66 regulation to limit photochemical volatile organic solvents in response to environmental pollution issues, marking the beginning of restrictions on volatile organic compounds (VOCs) in coatings.
In 1970, the Environmental Protection Agency was established, introducing stricter regulations for paint production and application. The ozone concentration limits were set across all U.S. states, with an upper VOC limit of 420 g/L. Similar measures were adopted in Europe and other countries to control VOC emissions from paints.
Today, in developed countries in Europe and America, water-based wood lacquer accounts for 50% to 80% of the market. In the decorative coating sector, water-based products are increasingly popular, making up about 70% of total decorative coatings, largely due to the unique properties of waterborne coatings.
2. Current Status of Domestic Water-Based Paint
With the continuous development of reform and opening up, the Chinese government and people have become more concerned about environmental protection, gradually establishing environmental regulations aligned with international standards. Research and development of eco-friendly coatings are gaining more attention. China's water-based industry has developed significantly over the past decade, with a wide range of products such as water-based wood varnish, rust-proof paint, metal paint, UV paint, automotive paint, floor coatings, cabinet coatings, and more. However, the market share of water-based paints is still much lower than that of foreign countries, with solvent-based paints still dominating.
II. Characteristics of Water-Based Paint
Unlike traditional solvent-based coatings that use organic solvents as dispersants and diluents, water-based coatings rely on water as their main dispersion medium.
1. Water is harder to evaporate, which can lead to sagging in high humidity conditions.
2. The surface tension of water is higher than that of solvents. If not adjusted, it may affect the quality of the final film.
3. The viscosity of water changes significantly under shear force. High shear forces can cause a large drop in viscosity, affecting the overall paint system.
4. Water is highly corrosive to metal materials, potentially damaging equipment in contact with it.
5. Using water as the primary solvent improves the working environment. Tools can be cleaned with water, reducing the need for cleaning solvents, saving resources, eliminating fire hazards, and lowering atmospheric pollution.
III. Performance Comparison Between Water-Based and Solvent-Based Paint
1. Performance
Performance Item
Water-Based Paint
Solvent Paint
Surface Tension
High
Low
Vapor Pressure
High
Low
Evaporative Latent Heat
High
Low
Drying Process
Affected by Humidity
Less Affected
Film Formation
Cross-linking Reaction
Cross-linking Reaction
Flammability
Non-Flammable
Flammable
Safety
Safe
Toxic
VOC Content
Low or None
High
2. Quality
There are high-quality water-based paints that perform even better than solvent-based ones on certain indicators.
Indicator Name
Aqueous Amino Baking Varnish
Solvent-Based Amino Baking Varnish
Baking Condition
Opacity, g/m²
120°C, 15 min
≤75
120°C, 15 min
≤75
Gloss (60°), %
≥85
≥80
Hardness
2H
2H
Flexibility, mm
≤1
≤1
Adhesion (Circle Method), Level
≤1
≤2
Solvent Resistance (Butanone) Scrub
100 times without leakage, slight color loss
100 times without leakage, slight color loss
IV. Water-Based Paint Construction Process
1. Method
When switching from oil-based to water-based paint, it is essential to thoroughly clean the spray equipment. First, clean the spray gun with a solvent, then with absolute ethanol, and finally with tap water. Clean the outer wall of the oil inlet pipe and the filter as soon as possible.
Water-based paints should be stirred using a dedicated tool. Ensure that the mixing tool is not contaminated with dried oil paint, oil, or residue. It’s best to wash it with tap water before use. Only after sufficient mixing can the paint be applied to avoid issues like surface defects or problems with the spray gun. If not used for a short time or not fully consumed, the lid must be tightly sealed to prevent dust contamination and the formation of a crust on the paint surface, which can cause particles or clogging.
Do not mix water-based paints from different manufacturers or different colors.
Before applying water-based paint, ensure the steel drum is dry and free of moisture to prevent sagging or color floating.
2. Process
(1) Phosphate-Free Process: Reduces the cost of phosphating and minimizes wastewater.
(2) Monochrome Barrel: No changes to the painting process. Baking temperature: 120–150°C, baking time: 15–10 minutes.
(3) Color-Blocking Barrel: Preheat the barrel to 70–90°C before spraying, no changes to the painting process. Baking temperature: 120–150°C, baking time: 15–10 minutes.
V. Cost Comparison Between Water-Based and Solvent-Based Paint
1. Cost Comparison
Cost
Traditional Painting
New Coating
Original Paint Cost
-
Slightly Higher Unit Price
Thinner Cost
20%–40% of Paint Cost
Negligible
Labor Cost
Increases with Staff Changes
Stable Team, Limited Wage Increase
Energy Cost
High
Low
Fire Safety Cost
High
Low
Occupational Health Cost
High Risk of Injury and Disease
Minimal Labor Protection Costs
2. A more stable workforce leads to better product quality. Employees’ self-protection awareness increases, and a stable team reduces risks. Unstable painter teams can result in poor coating performance. Switching from oil to water-based paints helps reduce pressure on workers.
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