Multi-layer Coating Film Formation Method
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Solution Overview
Problem
Existing methods for forming multilayer coating films on metal substrates require a water-washing step after chemical conversion treatment, which complicates the process, increases equipment needs, and can affect the finished appearance and corrosion resistance if the electrical conductivity of the solution is too high.
Innovation Solution
A method that controls the electrical conductivity of the solution adhered to the metal substrate to less than 10,000 μS/cm, specifically between 60 μS/cm and 7,000 μS/cm, and reduces sodium, potassium, calcium, and magnesium ion concentrations to less than 500 ppm, allowing for electrodeposition coating without a water-washing step while maintaining excellent corrosion resistance and appearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If water-washing step is omitted after chemical conversion treatment, then process complexity and equipment requirements are reduced, but corrosion resistance and finished appearance may deteriorate due to high electrical conductivity solution remaining on substrate
Solution Approach 1:
The invention changes the electrical conductivity parameter of the chemical conversion treatment solution by controlling the concentration of ionic components (sodium, potassium, calcium, magnesium ions) to less than 500 ppm each, achieving electrical conductivity of less than 10,000 μS/cm. This parameter change allows the solution to remain on the substrate without causing deterioration in corrosion resistance or finished appearance, thereby eliminating the need for water-washing step and reducing process complexity
2Productivity
If water-washing step is omitted after chemical conversion treatment, then production time and processing efficiency are improved, but electrodeposition coatability may be affected by high electrical conductivity solution on substrate
Solution Approach 1:
The invention changes the electrical conductivity parameter of the chemical conversion treatment solution by controlling the concentration of ionic components (sodium, potassium, calcium, magnesium ions) to less than 500 ppm each, achieving electrical conductivity of less than 10,000 μS/cm. This parameter change prevents adverse effects on electrodeposition coatability even when the solution remains on the substrate, thereby eliminating the need for water-washing step and improving production time
3Strength
If chemical conversion treatment solution with high ionic concentration is used, then chemical conversion coating film properties are improved, but electrical conductivity increases requiring water-washing step
Solution Approach 1:
The invention changes the concentration parameters of ionic components (sodium, potassium, calcium, magnesium ions) in the chemical conversion treatment solution to less than 500 ppm each, achieving electrical conductivity of less than 10,000 μS/cm. This parameter change maintains sufficient coating film properties while reducing electrical conductivity to a level that does not require water-washing, thereby eliminating the need for extensive washing equipment and reducing capital investment
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables process-streamlining, space-saving, and improved corrosion resistance without compromising electrodeposition coatability, reducing the need for extensive water-washing and associated equipment, while ensuring a high-quality finished appearance.
Implementation Method 1
immersing a metal substrate in a chemical conversion treatment solution to form a chemical conversion coating film
Implementation Method 2
performing electrodeposition coating on the metal substrate by using a cationic electrodeposition coating composition to form an electrodeposition coating film
Data Source
AI summary
A problem to be solved by the present invention is to provide a method for forming a multilayer coating film, the method being capable of achieving excellent finished appearance and excellent corrosion resistance without affecting electrodeposition coatability even when a part or all of the water-washing step is omitted after chemical conversion treatment, and to provide a coated article. The invention provides a method for forming a multilayer coating film, comprising forming a chemical conversion coating film and an electrodeposition coating film on a metal substrate by Step 1 of immersing a metal substrate in a chemical conversion treatment solution to form a chemical conversion coating film, and Step 2 of omitting a part or all of the water-washing step, and performing electrodeposition coating on the metal substrate using a cationic electrodeposition coating composition to form an electrodeposition coating film, wherein when the electrodeposition coating is performed in Step 2, the solution adhered to and/or deposited on the metal substrate has an electrical conductivity of less than 10,000 μS/cm.