Introduction to New Steel Drum Coating Technologies
Hu Zongwei
1. Water-Based Drying Coating for Steel Drums
Composition: Water-based polyester resin, methyl etherified amino resin, pigments, functional fillers, additives, and water.
Application: Ideal for steel drums and metal components that can be baked.
Performance: Offers vibrant colors, high gloss, excellent weather and moisture resistance, good application tolerance, and is environmentally friendly and non-toxic.
Application Process: The steel drum must be phosphated, washed, and dried before spraying. The residual heat of the drum should meet the temperature requirements for water-based paint. It is suitable for color-filled drums and baking at 140°C for 17–20 minutes. After washing and drying, the steel drum must be free from any oil or sweat residue.
For dark-colored coatings, a higher viscosity is required, typically around 50 seconds ± 5 seconds.
Key Technical Parameters:
- Paint Film Color and Appearance: Smooth and even
- Fineness (μm): ≤ 20
- Viscosity (S): ≥ 90
- Drying Time (140°C, 30 min): ≤ 30 minutes
- Gloss (60° meter): ≥ 90
- Hardness (Pencil Method): ≥ H
- Impact Strength (cm): ≥ 50
- Adhesion (Level): ≤ 1
- Flexibility (mm): ≤ 2
- Water Resistance (40 ± 1°C): 24 hours without foaming; slight changes after 2 hours, which recover.
2. High-Solids Drying Coating for Steel Drums
Composition: High-solids polyester resin, high-solids methyl etherified amino resin, active solvents, pigments, functional fillers, and additives.
Features: This coating uses active solvents with solid content up to 80%. During baking, these solvents react with the resin to form a film without emitting volatile gases. The active solvents are difficult to evaporate, making the process eco-friendly and nearly non-toxic. It performs similarly to light-curing coatings and is encouraged by national policies in the coatings industry. Compared to traditional products, it offers better fullness, larger coverage area, lower cost than water-based paints, and can be applied using conventional solvent-based methods.
Key Technical Parameters:
- Gloss (60° meter): ≥ 90
- Solid Content: ≥ 80%
- Hardness (H): ≥ 1
- Coating Area (Dry Film Thickness 30μm): 20 m²/kg
- Impact (Vertical Drop Hammer Method): ≥ 50 kg/cm²
- Adhesion (Level): ≤ 1
- Weather Resistance (Tibet Areas, Light Loss and Color Change): ≤ 1
3. UV-Curable Coating for Steel Drums
Over the past decade, UV-curable coatings have been widely used in auto parts, metal components, plastics, and wood. These are environmentally friendly coatings supported by national policies.
The key feature is that the resin and reactive diluent in the coating rapidly crosslink under ultraviolet light from a high-pressure mercury lamp, forming a film without volatile emissions. The energy consumption during the curing process is low. The UV intensity of the high-pressure mercury lamp is between 296-300 nm, with a workpiece distance of 15-20 cm, and the coating is fully cured in 12 seconds.
UV-curable coatings are currently best suited for lighter colors. Dark colors like black, dark blue, and iron red are not ideal due to pigment interference with UV penetration, leading to incomplete curing and reduced hardness. However, they are suitable for most other colors. The current ex-factory price is about 40 yuan per kilogram. The coating provides excellent fullness, significantly improves the coating area compared to traditional paints, and offers good color retention and spray performance. This makes it a valuable product for the steel drum industry.
Key Technical Parameters:
- Solid Content: 100%
- Volatile Matter: ≤ 0.5%
- Hardness (H): ≥ 2H
- Impact Strength (Vertical Drop Method): ≥ 50 kg/cm²
- Coating Area (Dry Film Thickness 30μm): ≥ 20 m²/kg
- Gloss (60° Meter): ≥ 90
- Adhesion (Level): ≤ 1
- Weather Resistance (Light Loss in Tibet, 12 Months): ≤ 1
- Artificial Aging (QUV, 60h, Light Loss and Discoloration): ≤ 2
In summary, UV-curable coatings do not require changes to existing coating equipment. By installing two sets of high-pressure mercury lamps in the drying tunnel and removing the gas and fuel system, the curing source is switched from heat to ultraviolet light. This significantly reduces energy costs and eliminates environmental risks from volatile substances. These coatings are already widely used in the automotive and motorcycle industries, showing great potential for future applications in the steel drum sector.
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