No.135: Phosphate treatment as a pre-painting process

Phosphate Treatment as a Paint Pre-treatment 

The phosphate film applied to metal surfaces not only improves the adhesion of the coating but also plays a vital role in preventing corrosion of the underlying metal when damaged. This treatment significantly enhances product durability and effectively mitigates the impacts of environmental conditions. 

When painting metal products, it is crucial to form a phosphate film on the metal surface beforehand. This film enhances the adhesion of the paint and effectively prevents corrosion of the underlying metal if the coating is damaged. Here are the main points explained: 

  • Thickness of the Phosphate Film: A relatively thin film is preferable. Excessively thick films can cause cohesive failure and potentially reduce the adhesion of the coating.
  • Chemical Stability: The environment under the coating may become acidic or alkaline, so the phosphate film needs to have high chemical stability.

Phosphate treatments commonly involve zinc phosphate and iron phosphate processes. The reasons for choosing each and their benefits are as follows: 

  • Reasons for Choosing Zinc Phosphate Treatment:
    • Chosen especially when corrosion resistance is crucial, as it offers excellent chemical stability.
    • Suitable for materials other than iron, providing adaptability to various materials.
  • Advantages of Iron Phosphate Treatment:
    • Low concentration of heavy metals in the treatment fluid, reducing environmental impact.
    • Generates less sludge and is compatible with degreasing processes due to its relatively neutral
  • Considerations for High-Temperature Environments: If the baking temperature of the paint exceeds 200°C, the crystal water in the zinc or iron phosphate films may be lost, causing the film to shrink and degrade adhesion. In such cases, zinc calcium phosphate treatment, which has excellent heat resistance, may be applied.

This concludes the basic information about phosphate treatment as a paint pre-treatment. For more detailed information, please refer to other documents provided by our company. 

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