Black Chromium Resin Plating for Bluish Jet-Black Color
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Solution Overview
Problem
The existing black plating layers formed from trivalent chromium often exhibit a yellowish tone when viewed through a corrosion-resistant film, failing to meet the commercial demand for a non-yellowish, bluish jet-black color.
Innovation Solution
A black plated resin part with a black chromium plating layer composed of metallic chromium, chromium oxide, and chromium hydroxide, where the chromium is present in the form of these species in the surface region, and the b* value is reduced to 3.0 or less using a trivalent chromium plating bath containing thiocyanic acid and warm water immersion to adjust the compositional proportions and structural changes, achieving a bluish jet-black color.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a black chromium plating layer is formed using conventional trivalent chromium plating, then the plating layer provides corrosion resistance, but the plating layer exhibits a yellowish tone when viewed through the corrosion-resistant film
Solution Approach 1:
The invention changes the chemical composition parameters of the black chromium plating layer by controlling the ratios of metallic chromium, chromium oxide, and chromium hydroxide. Specifically, it maintains metallic chromium at 1-10 atomic%, chromium oxide at 70-90 atomic%, and chromium hydroxide at 10-20 atomic% in the surface region, which fundamentally alters the optical properties to eliminate the yellowish tone while preserving corrosion resistance through the chromium oxide and hydroxide phases.
Solution Approach 2:
The invention creates a composite plating layer structure combining multiple chromium species (metallic chromium, chromium oxide, and chromium hydroxide) in specific proportions. This composite structure leverages the different properties of each component: metallic chromium provides base structure, chromium oxide provides corrosion resistance and black color, and chromium hydroxide suppresses the yellowish tone, achieving a synergistic effect that satisfies both corrosion resistance and color requirements.
2Ease of manufacture
If the black chromium plating layer is formed to meet commercial demand for non-yellowish color, then the b* value is reduced, but the compositional control becomes more complex
Solution Approach 1:
The invention establishes specific parameter ranges for chromium species composition that directly correlate with achieving b* ≤ 3.0. By defining metallic chromium at 1-10 atomic%, chromium oxide at 70-90 atomic%, and chromium hydroxide at 10-20 atomic% in the surface region, the invention provides clear manufacturing targets that simplify process control while ensuring the desired non-yellowish color appearance.
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
The solution effectively conceals the underlying plating layer, achieving a non-yellowish and bluish jet-black color by reducing the b* value to −1.7 or less, meeting commercial color demands and providing improved corrosion resistance.
Implementation Method 1
electroplating a resin substrate provided with an underlying plating layer in a trivalent chromium plating bath containing thiocyanic acid, to thereby form a black chromium plating layer on the underlying plating layer
Implementation Method 2
immersing the resin substrate provided with the black chromium plating layer in warm water at 30° C. or higher for a predetermined time
Data Source
AI summary
A method for producing a black plated resin part includes the steps of electroplating a resin substrate provided with an underlying plating layer in a trivalent chromium plating bath containing thiocyanic acid, to thereby form, on the underlying plating layer, a black chromium plating layer composed of trivalent chromium and having a thickness of 0.15 μm or more; and immersing the resin substrate provided with the black chromium plating layer in warm water at 30° C. or higher for a predetermined time. In the method, the amount of thiocyanic acid contained in the trivalent chromium plating bath, the temperature of the warm water, and the time of immersion of the resin substrate in the warm water are adjusted so that the black chromium plating layer exhibits a b* value of −1.7 or less based on the L*a*b* color system.