White Plastic Sheet Metamerism Control via Layered Brightener Segmentation
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Solution Overview
Problem
Existing white plastic sheets and paper substrates face challenges in maintaining consistent color across different lighting environments due to variations in optical brighteners and pigment loadings, leading to significant metamerism and yellowing, making it difficult to match the color of plastic and paper facings in signage applications.
Innovation Solution
A white plastic sheet is manufactured by coextruding an unpigmented thermoplastic resin print layer with dispersed optical brightener onto a pigmented base layer, allowing for separate control of opacity and brightness, which minimizes visual color shifts across various lighting conditions and reduces the need for high optical brightener concentrations, thereby reducing yellowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If high concentrations of optical brighteners are added to plastic sheets to achieve bright white color, then the brightness and whiteness are improved, but yellowing occurs over time and metamerism increases
Solution Approach 1:
The patent divides the plastic sheet into multiple layers with different functions: a base layer providing structural support and a top layer containing optical brighteners for brightness enhancement. This segmentation allows the optical brighteners to be concentrated in the top layer where they are most effective, reducing the overall concentration needed and minimizing yellowing while maintaining high brightness.
Solution Approach 2:
The patent applies optical brighteners locally in the top layer rather than uniformly throughout the entire sheet. This localized application concentrates the brightness-enhancing effect where it is most visible while reducing the total amount of optical brightener material, thereby decreasing yellowing and improving color consistency over time.
2Manufacturing precision
If optical brighteners are added to match the white color of plastic and paper substrates under one light source, then color matching is improved under that specific light source, but metamerism occurs when viewed under different lighting environments
Solution Approach 1:
The patent modifies the spectral characteristics of the white substrate by carefully selecting and formulating optical brighteners that emit light in specific wavelength ranges. This parameter change in the substrate's reflectance spectrum allows it to maintain consistent appearance across different illuminants, reducing metamerism while achieving precise color matching under standard lighting conditions.
3Adaptability or versatility
If different types of materials (paper and plastic) are used for signage substrates, then application versatility is improved, but color matching between materials becomes difficult
Solution Approach 1:
The patent creates a universal color matching system by formulating the plastic substrate with optical brighteners that replicate the spectral reflectance characteristics of clay-coated paper. This allows the plastic substrate to serve multiple functions: it provides the durability and flexibility of plastic while achieving color consistency with paper substrates, enabling versatile application across different signage types.
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 precise control over the white shade and minimal metamerism, ensuring consistent color appearance under different lighting conditions, achieving a cost-effective solution that matches the color of clay-coated paper stocks and reducing yellowing, thus maintaining the brightness and whiteness of the plastic sheet.
Implementation Method 1
Optical brighteners (hereinafter, OB) are also known as florescent whitening agents. These additives are put into almost all white papers and many white plastic consumer products to make them appear whiter and brighter. These optical brighteners absorb invisible ultraviolet light in the 300-400 nm range and make it re-emit or fluoresce in the blue region of the visible spectrum peaking at 435 nm.
Data Source
AI summary
A metamerism-resistant printable plastic sheet, especially white sheet, in which the desired shade of white can be easily specified or adjusted. This is achieved by separately controlling the opacity and the brightness. The opacity is controlled by the concentration of white pigment in a plastic base layer and the brightness is controlled by the concentration of an optical brightener in a plastic print layer bonded to, and preferably coextruded with, the base layer. Such a sheet can be bonded to one or both sides of a rigid core to create a graphics board, or used as a stand-alone flexible print sheet. Preferably, the plastic print layer comprises a polymer resin that is inherently resistant to a yellowing reaction from exposure to UV light.