Types and differences of color coated coil paint films

The zinc layer of galvanized coil is one of its core performance indicators, which directly determines the corrosion resistance, service life and application range of the product. The following is a detailed analysis of the importance of the zinc layer:

1. Anti-corrosion protection
Barrier effect: The zinc layer isolates the steel from oxygen and moisture, preventing the iron substrate from oxidation (rusting).

Sacrificial anode protection: Even if the zinc layer is partially damaged, the zinc will corrode preferentially (electrochemical protection) to protect the substrate from erosion.

Applicable environment: The thicker the zinc layer, the stronger the corrosion resistance in harsh environments such as humidity, salt spray (coastal areas), and industrial pollution.

2. Impact on product life
The thickness of the zinc layer is positively correlated with the life: For example, the corrosion resistance life of Z60 (zinc layer 60g/m²) is usually 2-3 times longer than that of Z20.

Economic trade-off: Although the thick zinc layer costs more, it can reduce the frequency of maintenance and replacement and is more economical in the long run (such as building roofs and bridge structures).

3. Application scenario requirements
Construction industry (roofs, wall panels): Z120-Z275 (high weather resistance) is required.

Home appliance panels (refrigerators, air conditioners): Z60-Z120 is commonly used, taking into account both aesthetics and rust prevention.

Auto parts: Galvanized sheets need to be matched with the coating process, and the zinc layer is usually thin (Z30-Z60).

Power facilities (transmission towers): Z150 or above is required to cope with long-term outdoor exposure.

4. Processing performance impact
Weldability: Too thick a zinc layer may cause welding pores, and the process needs to be adjusted (such as laser welding or reducing the thickness of the zinc layer).

Formability: The bonding strength between the zinc layer and the substrate affects the surface quality during stamping and bending (such as the risk of zinc layer falling off).

5. Zinc layer standards and classification
International standards:

ISO 3575 (commercial grade, stamping grade, etc.).

ASTM A653 (American standard, such as G60, G90, unit oz/ft²).

Zinc layer code:

DX51D+Z60: general use, zinc layer 60g/m² (double-sided).

DX53D+ZF80: for deep drawing, zinc-iron alloy layer 80g/m².

6. Zinc layer process selection
Hot-dip galvanizing (HDG): low cost, thicker zinc layer (commonly 10-50μm), suitable for heavy corrosion protection.

Electrogalvanizing (EG): thin zinc layer (3-20μm), uniform surface, suitable for precision machining.

Zinc alloy coating (such as Zn-Al, Zn-Mg): further improves corrosion resistance (2-4 times higher than pure zinc layer).

7. Risk of quality defects
Zinc layer detachment: caused by insufficient substrate cleanliness or process problems.

Uneven zinc flowers: affects appearance (such as home appliance panels require no zinc flowers or small zinc flowers).

White rust: caused by condensed water during transportation or storage, requiring oiling or chromate treatment.

Summary
The zinc layer is the soul of the performance of galvanized coils, and needs to be comprehensively selected according to the application scenario, cost budget and processing requirements. For example:

Building structure: give priority to thick zinc layer (Z180 or above).

Household appliance shell: balance the adhesion of zinc layer and surface coating (Z60-Z100).

Automotive plate: use alloy plating or composite process (such as galvanizing + phosphating).

Rational selection of zinc layer can significantly improve product competitiveness and avoid the risk of over-design or insufficient protection.

Types and differences of color-coated coil paint film
The types and performance of the paint film of color-coated coil (pre-coated color-coated steel plate) directly affect its appearance, durability and application scenarios. The following is a detailed analysis of common paint film types and their key differences:

1. Classification by resin base material

1. Polyester (PE, Polyester)

Features:

Low cost, rich colors, good flexibility (good T-bend performance).

Moderate weather resistance, suitable for indoor or mild climate environment.

Typical applications:

Home appliance panels (such as washing machines, air conditioner housings), indoor partitions, and general building materials.

Durability:

The service life is about 5-8 years (outdoor), and it is easy to powder under UV irradiation.

2. Silicone modified polyester (SMP, Siliconized Polyester)

Features:

Adding silicone resin to polyester improves weather resistance (UV resistance) and heat resistance (up to 120°C).

High hardness, but slightly lower flexibility than pure polyester.

Typical applications:

Building roofs/walls (medium and low corrosion areas), garage doors.

Durability:

Outdoor life is about 8-12 years.

3. High Durability Polyester (HDP, High Durability Polyester)

Features:

Through molecular structure optimization, the weather resistance is close to fluorocarbon (PVDF), and the cost is lower than PVDF.

Excellent anti-powdering and color retention (10-year color difference ΔE<5).

Typical applications:

High-end building curtain walls, solar panel backplanes.

4. Fluorocarbon (PVDF, Polyvinylidene Fluoride)
Features:

Contains more than 70% PVDF resin, and has strong weather resistance (UV, acid rain, salt spray resistance).

Good wear resistance and self-cleaning properties, but high cost, fewer color options (mainly metallic colors).

Typical applications:

Landmark buildings (such as airports, stadiums), coastal or industrially polluted areas.

Durability:

Outdoor life of 20-30 years, color retention (15 years ΔE <2).

5. Polyurethane (PU, Polyurethane)
Features:

Outstanding wear resistance and chemical corrosion resistance, often used in functional coatings.

Weather resistance is between polyester and PVDF.

Typical applications:

Industrial plants, refrigeration equipment, medical equipment.

6. Acrylic
Features:

Environmental protection (low VOC), strong adhesion, but poor weather resistance.

Typical applications:

Interior decorative panels, furniture veneers.

2. Classification by coating structure

1. Two-coat two-bake (2/2)

Structure: primer + topcoat (each layer is cured separately).

Advantages: uniform coating and good color stability.

Application: most common color-coated panels (such as PE, SMP).

2. Three-coat three-bake (3/3)

Structure: primer + intermediate paint + topcoat (or primer + topcoat + protective varnish).

Advantages: enhanced corrosion resistance (primer contains chrome/chrome-free passivation), weather resistance (varnish is UV-resistant).

Application: high-end PVDF coating, harsh environment (such as chemical plants).

3. Comparison of key performances
Paint film type Weather resistance Abrasion resistance Flexibility Cost Applicable environment
PE ★★☆ ★★☆ ★★★ Low Indoor/mild climate
SMP ★★★ ★★☆ ★★☆ Medium-low Ordinary outdoor buildings
HDP ★★★★ ★★★ ★★★ Medium-high Medium-high requirement buildings
PVDF ★★★★★ ★★★★ ★★☆ High Extreme climate/landmark building
PU ★★★☆ ★★★★ ★★☆ Medium-high Industrial wear-resistant scene
4. Special functional coating
Self-cleaning coating:

Add photocatalytic materials (such as TiO₂) to decompose surface organic matter, suitable for urban buildings.

Antibacterial coating:

Contains silver ions, used in hospitals and food factories.

Insulation/thermal insulation coating:

Reflects infrared rays (such as cool roof color panels) to reduce building energy consumption.

5. Selection suggestions
Architectural field:

Ordinary residential: SMP or HDP (high cost performance).

High-end curtain wall: PVDF (long-term maintenance-free).

Home appliance field:

Appearance priority: PE (colorful), HDP (durable).

Industrial field:

Chemical corrosion resistance: PU or PVDF + thick coating.

6. Common quality problems
Powdering: PE coating surface degradation after long-term exposure.

Fading: UV irradiation causes pigment decomposition (PVDF has the least effect).

Peeling: Insufficient primer adhesion or poor substrate pretreatment.

Rational selection of paint film requires balancing cost, environmental requirements and processing technology (such as bending requires high-flexibility paint film). For example, buildings in coastal areas should give priority to PVDF, while warehouse roofs can use SMP to reduce costs.