Two-Color Molded Lens Corner R Control for Crack Prevention
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Solution Overview
Problem
The existing two-color molded lenses with hard coating films on the outer surface and anti-fogging coating films on the inner surface face issues of crack generation due to the hybrid type film forming step, leading to defective appearances, primarily because the anti-fogging coating material stagnates in groove-shaped gaps at the corner portions during the curing process, causing residual stress and visibility of cracks through the transparent lens body.
Innovation Solution
The two-color molded lens design sets the corner R at the corner portion between the inner surface of the primary molded product and the joining surface to a value of R0.2 mm or less, minimizing the groove-shaped gap and reducing the amount of anti-fogging coating material that stagnates, thereby preventing impregnation into the primary molded product and suppressing crack generation. Additionally, positioning the joining surface further from the connection position helps in preventing the anti-fogging coating material from spreading to the corner, and ensuring flush surfaces between the primary and secondary molded products to prevent coating material stagnation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the hybrid type film forming step is adopted to improve manufacturing efficiency, then operation efficiency is improved, but cracks are likely to be generated around the corner portion due to anti-fogging coating material impregnation
Solution Approach 1:
The patent applies local quality by creating a groove-shaped gap with specific dimensions (depth: 0.01-0.05mm, width: 0.05-0.15mm) only at the corner portion where the inner surface meets the joining surface. This localized structural modification prevents anti-fogging coating material from impregnating into the primary molded product at the critical corner region, while leaving other areas unchanged to maintain manufacturing efficiency of the hybrid film forming step.
Solution Approach 2:
The groove-shaped gap is formed preliminarily during the molding process before the film forming step. By pre-configuring the corner portion with this specific gap structure, the patent prevents coating material impregnation and subsequent crack generation before they can occur during the hybrid film forming process, thus maintaining both high productivity and product reliability.
2Ease of manufacture
If a typical molding machining with minimum corner R of about R0.3 mm is used, then manufacturing is easier, but a groove-shaped gap is formed at the corner portion causing coating material stagnation
Solution Approach 1:
The patent changes the corner R parameter from the typical minimum of R0.3mm to a smaller value that still allows standard end mill usage but creates the desired groove-shaped gap geometry. This parameter optimization enables the corner portion to have sufficient curvature for easy machining while simultaneously creating the gap structure that prevents coating material stagnation and impregnation.
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 configuration effectively suppresses the occurrence of cracks and defective appearances while maintaining improved manufacturing efficiency by minimizing the anti-fogging coating material's stagnation and impregnation, allowing for a more transparent and durable lens.
Implementation Method 1
curing the hard coating film by irradiation with ultraviolet rays
Implementation Method 2
curing the anti-fogging coating film by heat
Data Source
AI summary
A two-color molded lens includes: a lens body portion and a lens peripheral wall portion that rises toward an inner surface side of the two-color molded lens from a peripheral edge portion of the lens peripheral wall portion. The two-color molded lens is provided with a hard coating film on an outer surface thereof and an anti-fogging coating film on the inner surface thereof. The primary molded product is formed to wrap around from the lens body portion, the secondary molded product is formed to wrap around from the lens peripheral wall portion, a joining surface between the primary molded product and the secondary molded product is positioned on the lens body portion, and a corner R is set to a value of R0.2 mm or less in the primary molded product.