Chromate-Free Coated Metal Plate Gloss Control
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Solution Overview
Problem
Chromate-free coated steel sheets experience severe corrosion in flat portions due to silica-based gloss adjusting agents, leading to issues like stain rust and coating film blistering before the intended service life, as the silica particles crack, collapse, or fall off from the overcoat coating film.
Innovation Solution
A chromate-free coated metal sheet with an overcoat coating film containing microporous particles as a gloss adjusting agent, where the content is between 0.01 to 15 vol % and satisfies specific particle diameter and film thickness ratios, ensuring the particles remain embedded and prevent corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If silica particles are used as gloss adjusting agent in the overcoat coating film, then the designability and appearance are improved, but the corrosion resistance in the flat portion deteriorates due to particle cracking, collapsing, or falling off
Solution Approach 1:
The patent changes the particle size parameter of the gloss adjusting agent from conventional 3-30 μm to a specific range of 0.5-5 μm. This parameter change ensures that particles remain embedded in the coating film without cracking or falling off, while still providing the desired gloss appearance. The controlled particle size prevents the harmful effects of large particles while maintaining the beneficial optical properties.
Solution Approach 2:
The patent applies different particle size characteristics to different functional requirements: small particles (0.5-5 μm) are used specifically for gloss adjustment in the overcoat coating film, while the undercoat coating film contains anti-corrosion pigments. This local differentiation of particle sizes allows each layer to optimize its specific function without compromising the other.
2Reliability
If chromate-based anti-rust components are used in coated metal sheets, then the corrosion resistance is improved, but the environmental compatibility deteriorates due to hexavalent chromium prohibition
Solution Approach 1:
The patent extracts and removes the harmful hexavalent chromium component from the coating system entirely. Instead of using chromate-based anti-rust treatments, the invention employs alternative non-chromium-based anti-corrosion pigments in the undercoat coating film, thereby eliminating environmental pollution while maintaining corrosion protection functionality.
Solution Approach 2:
The patent changes the chemical composition parameter of the anti-rust system from chromate-based to non-chromium-based pigments. This compositional change eliminates harmful environmental factors while preserving the essential corrosion resistance function through alternative pigment chemistry.
3Reliability
If the particle diameter of gloss adjusting agent is reduced to prevent corrosion, then the corrosion resistance is improved, but the gloss adjusting effectiveness may deteriorate
Solution Approach 1:
The patent optimizes the particle size parameter to a specific range of 0.5-5 μm, which is smaller than conventional sizes but carefully controlled to maintain effectiveness. This parameter optimization balances two competing requirements: small enough to prevent cracking and falling off (improving corrosion resistance), but large enough to provide adequate light scattering for gloss adjustment.
Data Source
AI summary
This coated metal plate is a chromate-free coated metal plate for exterior applications, which comprises a metal plate and a coating film that is arranged on the metal plate. The coating film contains 0.01-15% by volume of porous particles as a gloss control agent. If R (μm) is the number average particle diameter of the gloss control agent, T (μm) is the film thickness of the coating film, and σ is the standard deviation of the number-based particle size distribution of the gloss control agent, the coated metal plate satisfies the following formulae. (R+2σ)/T≤0.7 R≥2.0 9≤T≤19.