Thermosensitive Recording Medium Light-Blocking Layer
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Solution Overview
Problem
Thermosensitive recording media using tungsten oxide compounds face issues with color change and increased absorbance in the near-infrared region when exposed to sunlight, leading to reduced image recording sensitivity and readability, as well as unerased portions due to excessive heating during repetitive use.
Innovation Solution
A thermosensitive recording medium with a support, an image recording layer containing a leuco dye, a color developer, and a metal oxide with near-infrared absorbance, along with an oxygen barrier layer and a light-blocking layer to prevent light-induced degradation and maintain sensitivity over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tungsten oxide compound is used as a photothermal converting material to improve image recording sensitivity and image erasing sensitivity, then the absorbance in the near infrared region is improved, but the color changes to blue and the absorbance increases when irradiated with sunlight for a long period, causing excessive heating and reduced readability
Solution Approach 1:
A light-blocking layer is introduced as an intermediary between the tungsten oxide compound and sunlight. This layer selectively blocks ultraviolet rays and blue light that cause the tungsten oxide to reduce to pentavalent tungsten (causing blue coloration), while allowing near-infrared laser light to pass through for image recording. The light-blocking layer uses materials like violet pigments or blue pigments with specific transmittance characteristics to achieve this selective filtering effect.
Solution Approach 2:
The invention changes the optical parameters of the system by controlling the transmittance of the light-blocking layer. Specifically, the light-blocking layer is designed to have a transmittance of 5% or less in the 300-400 nm (ultraviolet) range and 20% or less in the 380-495 nm (blue light) range, while maintaining high transmittance in the near-infrared region where laser recording occurs. This parameter control prevents coloration without affecting recording sensitivity.
2Stability of the object's composition
If a light-blocking layer with high ultraviolet and blue light blocking capability is added to prevent coloration of the tungsten oxide compound, then color stability is improved, but the device complexity increases due to additional layers
Solution Approach 1:
The light-blocking layer is designed to perform multiple functions simultaneously: (1) blocking ultraviolet rays to prevent photo-oxidation and coloration of the tungsten oxide compound, (2) blocking blue light to prevent reduction to pentavalent tungsten, (3) maintaining transparency to near-infrared laser light for recording, and (4) potentially serving as a protective layer for the underlying functional layers. This multi-functionality reduces the need for separate layers for each purpose.
3Reliability
If oxygen barrier layers are added to prevent deterioration of the leuco dye, then the leuco dye resistance to light is improved, but oxygen is not supplied to the tungsten oxide compound, preventing oxidation of pentavalent tungsten and causing permanent coloration
Solution Approach 1:
The light-blocking layer acts as an intermediary that allows selective light transmission. By positioning the light-blocking layer between the tungsten oxide compound and the environment, it provides a different mechanism for protection - optical filtering rather than oxygen barrier - thereby allowing oxygen access while preventing the specific wavelengths of light that cause irreversible coloration.
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 maintains excellent image recording and erasing sensitivity without color change or unerased portions, even when exposed to sunlight for extended periods, ensuring reliable repetitive use.
Implementation Method 1
a metal oxide having absorbance in the near infrared region
Implementation Method 2
particles of metal boride or metal oxide or both are used as a photothermal converting material
Implementation Method 3
a light-blocking layer... an average transmittance of the light-blocking layer to light in a wavelength range of 300 nm to 400 nm is 5% or less, and an average transmittance of the light-blocking layer to light in a wavelength range of 380 nm to 495 nm is 20% or less
Implementation Method 4
an oxygen barrier layer... to block not only ultraviolet rays but also oxygen to prevent deterioration of the leuco dye due to light
Data Source
Figure 1A~2A
Figure 2B~2D
Figure 2E~3B
AI summary
A thermosensitive recording medium, including: a support (101); an image recording layer (102), which is provided on the support, and contains a leuco dye, a color developer, and a metal oxide having absorbance in the near infrared region; an oxygen barrier layer (104); and a light-blocking layer (103), wherein the oxygen barrier layer (104) and the light-blocking layer (103) are provided on the surface of the image recording layer, which is on the opposite side to the surface thereof where the support is provided, and wherein an average transmittance of the light-blocking layer (103) to light in a wavelength range of 300 nm to 400 nm is 5% or less, and an average transmittance of the light-blocking layer (103) to light in a wavelength range of 380 nm to 495 nm is 20% or less.