JP2004020596A - Reversible image display medium and image forming method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reverse image display medium which enables color display and repeated use in image display and deletion, and to provide an image forming method including an emitting method which uses less light emission energy. <P>SOLUTION: The medium is constructed of photosensitive layers 2, 4 and 6 and light blocking layers 3 and 5, which are alternately stuck on a support substrate 1. The photosensitive layers have three kinds of photochromic compounds A, B and C of different color-development hues and threshold wavelengths, and the light-blocking layers block light for developing the colors of the photochromic compounds. The photosensitive layers 2, 4, and 6 have the threshold wavelength λ1, λ2, and λ3, respectively, and the relationship between the threshold wavelengths is λ1>λ2>λ3. The light-blocking layer 3 blocks light which has a wavelength shorter than λ2 but longer than λ3 whereas the light-blocking layer 5 blocks light which has a wavelength shorter than λ3. The photosensitive layers 2, 4, and 6 containing the photochromic compounds performing color display are subjected to the process of emitting light the quantity of which corresponds to the density of each pixel after color development. Images are formed with the photochromic compounds which respectively have maximum absorption wavelengths in color development which are in the range of 600 nm or more to less than 700 nm, in the range of 500 nm or more to less than 600 nm, and in the range of 400 nm or more to less than 500 nm. The process of decoloring the entire image display area from a colored state is provided, which allows the repeated use of the medium. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reversible image display medium capable of repeating writing and erasing of color image information by light irradiation, and an image forming method using the image display medium.
[0002]
[Prior art]
With the increase in paper consumption in offices, research on a reversible image display medium capable of repeatedly recording and erasing images has been attracting attention as a medium replacing paper. Among them, some proposals have been made on a color reversible image display medium capable of rewriting a multicolor image.
[0003]
For example, JP-A No. 11-24027 relates to a color image forming method using a cholesteric liquid crystal compound, and the cholesteric liquid crystal compound exhibits a selective reflection color caused by a helical molecular arrangement, so that various cholesteric liquid crystal compounds vary depending on a heating temperature. An image forming method by displaying colors has been proposed.
[0004]
Japanese Patent Application Laid-Open No. Hei 5-271649 relates to a color reversible image display medium using a photochromic compound which causes a reversible color change upon irradiation with light, and has three types of photochromic properties that emit yellow-orange, red and blue-violet colors. A method of displaying a color image by mixing a diarylethene compound and irradiating ultraviolet light has been proposed.
[0005]
Furthermore, Japanese Patent Application Laid-Open No. Hei 7-199401 proposes a color reversible image display medium using three types of photochromic fulgide compounds that emit yellow, magenta, and cyan.
[0006]
[Problems to be solved by the invention]
By the way, the method using a photochromic compound that displays a color by absorbing light proposed in JP-A-5-271649 and JP-A-7-199401 is disclosed in JP-A-11-24027. And has excellent characteristics in image display characteristics such as a high white reflectance and a high display color density, as compared with a system using a cholesteric liquid crystal compound which displays colors by selective reflection.
[0007]
However, the threshold wavelength at which light absorption occurs in the wavelength region where the photochromic compound changes from the decolored state to the colored state, ie, the light absorption in the decolored state of the photochromic compound, differs depending on the photochromic compound, and more than the threshold wavelength. In most cases, light of a short wavelength is colored by irradiation with light of any wavelength. Therefore, the image display system disclosed in JP-A-5-271649, which utilizes the fact that three types of photochromic compounds are independently colored only by ultraviolet light in a specific ultraviolet wavelength region, is not satisfactory.
[0008]
On the other hand, the image display system proposed in Japanese Patent Application Laid-Open No. 7-199401, in which all colors are developed with one kind of ultraviolet light and then selectively erased with visible light, is used in offices, for example, when used as a substitute for paper. Most of the documents created are written in black letters on a white background, and the average manuscript ratio (the ratio of the character area to the entire surface of the paper) is 10% or less. It will be decolored by irradiating light rays. Therefore, there is much waste of light irradiation energy for displaying an image.
[0009]
As a method of avoiding the waste of the energy described above, only pixels for displaying an image are selectively colored with ultraviolet rays instead of full-color coloring with ultraviolet rays, and thereafter, the color is erased for each pixel according to the color density of the pixels. A method of sequentially irradiating visible light with light in a sensitivity wavelength region for each photochromic compound is conceivable.
[0010]
However, even in this method, when the background of the image is set to a specific color and characters are displayed thereon, the entire area of the image display medium is colored, and then visible light other than the background color is applied to almost all areas. There is a drawback that light irradiation energy is wasted because it is necessary to erase the color.
[0011]
Therefore, the present invention has been made to solve the above-described problems, and is capable of displaying a color image, and a color reversible image display medium with low light irradiation energy for displaying an image, and a reversible image using a new light irradiation method. An object is to provide a forming method.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 provides a reversible image display in which a photosensitive layer individually containing three types of photochromic compounds having different coloring hues is laminated on a supporting substrate to perform multicolor display. In the medium, the three types of photochromic compounds in the decolored state have different threshold wavelengths for transitioning to the color-developed state, respectively, and are located between the laminated lowermost photosensitive layer and the photosensitive layer located thereon, and the uppermost photosensitive layer. The most main feature of the present invention is that a light-shielding layer for shielding light for coloring a photochromic compound is provided between the photosensitive layer and the photosensitive layer located thereunder.
[0013]
According to a second aspect of the present invention, the threshold wavelength of the photochromic compound having the longest threshold wavelength of the light that transitions to the colored state by light absorption in the decolored state is λ1, and then the light transitions to the colored state in the decolored state by light absorption. When the threshold wavelength of the photochromic compound having a long threshold wavelength for light is λ2, and the threshold wavelength of the shortest photochromic compound for transitioning to a colored state by light absorption in the decolored state is λ3, the reversible image display medium The lowermost photosensitive layer is a photochromic compound A having a threshold wavelength of λ1, the upper photosensitive layer is a photochromic compound B having a threshold wavelength of λ2, and the uppermost photosensitive layer has a threshold wavelength of λ3. The main feature is that it is a photochromic compound C.
[0014]
The light-shielding layer provided between the lowermost photosensitive layer and the photosensitive layer located above the lowermost photosensitive layer may have at least some wavelengths within a wavelength range shorter than λ1 and longer than λ2. And has a characteristic of blocking light of at least a part of the wavelength within a wavelength range shorter than λ2 and longer than λ3, and is provided between the uppermost photosensitive layer and the photosensitive layer located thereunder. The light-shielding layer provided has a characteristic of transmitting light of at least some wavelengths in a wavelength region shorter than λ1 and longer than λ3 and shielding light of at least some wavelengths in a wavelength region shorter than λ3. Characteristic.
[0015]
In the invention according to claim 4, the three types of photochromic compounds having different color hues are a photochromic compound A having a maximum absorption wavelength in a color development state of 600 nm or more and less than 700 nm, and a maximum absorption wavelength in a color development state of 500 nm or more. The main feature is that the photochromic compound B is in a range of less than 600 nm, and the photochromic compound С has a maximum absorption wavelength in a color-developed state of 400 nm or more and less than 500 nm.
[0016]
According to a fifth aspect of the present invention, in the colorless reversible image display medium, a photochromic compound having a threshold value of λ1 is irradiated with a light beam having a wavelength shorter than λ1 and longer than λ2 with an amount of light corresponding to a desired density after color development. Step I of irradiating each pixel of the reversible image display medium with a photochromic compound having a threshold value of λ2 by applying a light having a wavelength corresponding to a concentration after desired color development and having a wavelength shorter than λ2 and longer than λ3 to a pixel of the reversible image display medium. Image forming step of irradiating each pixel of the reversible image display medium with a step II of irradiating a photochromic compound having a threshold value of λ3 with a light amount corresponding to a desired density after color development and a wavelength shorter than λ3 for each pixel of the reversible image display medium Method is the main feature.
[0017]
According to a sixth aspect of the present invention, there is provided any one of the first to third aspects as a step of irradiating each pixel instead of performing the three steps I, II, and III of irradiating each pixel according to the fifth aspect. A step of irradiating each pixel of the reversible image display medium with light having a wavelength shorter than λ3 that passes through the two light-shielding layers of the reversible image display medium to simultaneously develop the three photosensitive layers. This is the main feature.
[0018]
The invention according to claims 7, 8, 9 and 10 mainly uses a fluorescent tube, a configuration of a fluorescent tube and an optical filter, a laser, a light emitting diode, or the like as a light source for irradiating light to a photosensitive layer containing a photochromic compound. It is a feature.
[0019]
According to an eleventh aspect of the present invention, as a pre-process of performing the step I of irradiating each pixel of the reversible image display medium according to the fifth or sixth aspect, white light is irradiated on the entire surface of the reversible image display medium. The main feature of the present invention is to provide a step of bringing the photosensitive layer containing the photochromic compound into a decolored state.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view of a layer constituting a reversible image display medium according to the present invention. A photosensitive layer 2 containing a photochromic compound A for holding a photosensitive layer is formed on a support substrate 1, and an upper portion of the photosensitive layer 2 is irradiated with light as described later. The light-shielding layer 3 for shielding the light having the wavelength of the step II is formed. Further, a photosensitive layer 4 containing the photochromic compound B is formed thereon, and a light-shielding layer 5 for shielding light having a wavelength of the irradiation step III to be described later is formed thereon. Further, a photosensitive layer 6 containing the photochromic compound C is formed thereon.
[0021]
A process of forming an image by selectively coloring the reversible image display medium having the above configuration will be described with reference to FIG. First, a step I of irradiating each pixel of the reversible image display medium with a light beam having a light amount corresponding to the concentration after the final color development of the photochromic compound A and having a wavelength shorter than λ1 and longer than λ2 is performed. The step I gives the photochromic compound A a desired coloring density. The photochromic compounds B and C do not develop color with respect to the light having the wavelength used in the step I because they do not have color development sensitivity.
[0022]
Next, a step II of irradiating each pixel of the image display medium with a light beam having a light amount corresponding to the density after the final color development of the photochromic compound B, shorter than λ2 and longer than λ3, and having a wavelength absorbed by the light shielding layer 3. I do. Step II provides the photochromic compound B with a desired color density. The photochromic compound C does not develop color with respect to the light having the wavelength used in the step II because it does not have color sensitivity. Further, the photochromic compound A does not develop color because the light in the step II is shielded by the light shielding layer 3.
[0023]
Finally, a step III of irradiating each pixel of the image display medium with a light beam having a light amount corresponding to the density of the photochromic compound C after the final coloring and shorter than λ3 and having a wavelength absorbed by the light shielding layer 5 is performed. Step III provides the photochromic compound C with a desired color density. The photochromic compounds A and B do not develop color because the light of step III is blocked by the light blocking layer 5.
[0024]
With the configuration of the photochromic compound having the above characteristics and the three steps of irradiating light for coloring the photochromic compound, photochromic compounds having three different hues can be selectively colored, and further image formation can be achieved. Since there is no need for the decoloring process at the time of performing, image formation without waste of light irradiation energy can be realized.
[0025]
For example, when forming an image of a black character document against a light blue background, in the present invention, in the three irradiation steps I, II, and III, only the pixels forming the characters are irradiated with strong ultraviolet rays. In the step I of irradiating a portion with a light blue background, a weak region is irradiated with weak light to irradiate the photochromic compound A with a light cyan concentration in the step I of irradiating, and in the step II of irradiating, weak light is irradiated to the region of the background. The photochromic compound B is colored at a light magenta density, thereby forming a light blue background image.
[0026]
On the other hand, when the method proposed in JP-A-7-199401 is used, first, the entire surface of the reversible image display medium is colored black. Thereafter, the photochromic compound C is decolored by irradiating light in a wavelength range of 400 nm or more and less than 500 nm to form an image of a blue background portion. However, since the background color is dark blue in this state, light of a wavelength range of 500 nm or more and less than 600 nm and light of a wavelength range of 600 nm or more and less than 700 nm are irradiated at an appropriate light intensity in order to make the background color light blue. The coloring density of the photochromic compound A and the photochromic compound B is reduced. Assuming that the original rate of black characters is 10% and the erasing sensitivity and the coloring sensitivity are equal, the energy required for image formation is 20 times or more as compared with the light irradiation method of the present invention.
[0027]
Also, as a method of avoiding the waste of light irradiation energy described above, only pixels for displaying an image are selectively colored with ultraviolet rays instead of full-color coloring with ultraviolet rays, and thereafter, each pixel is erased according to the color density of the pixels. In the method of sequentially irradiating the visible light with light in the sensitivity wavelength range of each photochromic compound, in order to obtain a light blue background, the background is colored light gray by weakly developing the photochromic compounds A, B and C together. After that, the photochromic compound C is decolorized by irradiating light in a wavelength range of 400 nm or more and less than 500 nm. Therefore, the light irradiation energy required for image formation is increased as compared with the present invention.
[0028]
In the above description, an example is given in which the steps from the step I of irradiating light to the step III of irradiating light are sequentially performed, but the steps I to III of irradiating light interchange the order of the steps of irradiating light. May be. In addition, many documents used in offices include only black and white characters or many black and white characters. In the case of such a document, the three light-sensitive layers were simultaneously colored in a single light irradiation step, rather than in the above-described three light irradiation steps I to III, which were sequentially superimposed to perform black light emission. In this case, the number of steps of irradiating light is small, and there is no fear of color shift of three colors. Therefore, by irradiating a light beam having a wavelength shorter than λ3 to the reversible image display medium for each pixel by transmitting light through the two light-shielding layers as a step of irradiating light different from the steps I to III of irradiating light. A step of simultaneously coloring three photosensitive layers may be performed.
[0029]
Further, even if the wavelength spectra of the photochromic compounds A, B, and C that cause light absorption in the color-developed state are largely overlapped, it is not necessary to perform selective decoloring as in the prior art, so that the spectral width of the photochromic compound in the color-developed state The desired hue can be obtained even when the color cannot be erased selectively.
[0030]
Hereinafter, the present invention will be described in more detail. For a white display having a high reflectance, the surface of the supporting substrate is preferably white, but may be colored according to the application. Further, the support substrate is preferably a relatively thin medium such as paper or film, but is not limited to this.
[0031]
The photosensitive layer on the supporting substrate contains a photochromic compound which becomes a colored state by irradiation with ultraviolet light and becomes a decolored state by irradiation with visible light. The photochromic compound includes a P-type compound whose color development state is stable to heat and changes color only by light, and a T-type compound whose color formation state is unstable to heat and changes color not only by light but also heat. However, in the present invention, it is particularly desirable to use a P-type compound.
[0032]
Typical P-type compounds include fulgide-based compounds and diarylethene-based compounds. To record and reproduce a full-color image, a photochromic compound that develops three primary colors, yellow, magenta, and cyan, is required. . Examples of the yellow coloring compound include "2- [1- (3,5-dimethyl-4-isoxazolyl) ethylidene] -3-isopropylidene succinic anhydride" and "2- [1- (5-methyl-2)". -Phenyl-4-oxazolyl) ethylidene] -3-isopropylidene succinic anhydride "," 2- [1- (2-phenyl-5-methyl-4-oxazolyl) stearylidene] -3-isopropylidene succinic anhydride And the like. The compound has a maximum absorption wavelength in a color-developing state of about 430 nm to 460 nm.
[0033]
Examples of the magenta coloring compound include "2- [1- (2,5-dimethyl-1-phenylpyrazolyl) ethylidene] -3-isopropylidene succinic anhydride" and "2- [1- (3-methoxy- 5-methyl-1-phenyl-4-pyrazolyl) ethylidene] -3-isopropylidenesuccinic anhydride "," 2- [1- (2-methyl-5-styryl-3-thienyl) ethylidene] -3-isopropylidene Ridensuccinic anhydride "and the like. The maximum absorption wavelength of the compound in a color-developing state is about 550 nm to 560 nm.
[0034]
Examples of the cyan coloring compound include “2- [1- (1,2,5-trimethyl-3-pyrrolyl) ethylidene] -3-isopropylidene succinic anhydride” and “2- [2,6-dimethyl- 3,5-bis (P-dimethylaminostyryl) benzylidene] -3-isopropylidene succinic anhydride ". The maximum absorption wavelength of the compound in the color development state is about 640 nm.
[0035]
The photochromic compound contained in the photosensitive layer may be dispersed in an acrylic resin, a vinyl chloride resin, a polyester resin, a polyamide resin, a polyolefin resin or a urethane resin, or may be encapsulated in microcapsules.
[0036]
Examples of the light-shielding layer provided between the photosensitive layers and the substance contained in the light-shielding layer include 2- (5-methyl-2-hydroxyphenyl) benzotriazole and 2- (3,5-di-t-butyl-2-). (Hydroxyphenyl) benzotriazole, indole dyes and the like. Further, if necessary, an image display medium may be provided in which a thin layer of polyvinyl alcohol is provided on the uppermost photosensitive layer as a protective film for preventing deterioration of the photosensitive layer.
[0037]
【Example】
Next, the present invention will be described more specifically with reference to examples.
(Example 1)
1,2-bis (6- (4-N, N-diethylaminophenylazo) -2-methylbenzo [B] thiophen-3-yl) -3,3,4,4,5,5-hexa as photochromic compound A Fluorocyclopentene (hereinafter abbreviated as PC1), 1,2-dicyano-1,2-bis (2,4,5-trimethyl-3-thienyl) ethene (hereinafter abbreviated as PC2) as photochromic compound B, and 1 as photochromic compound C , 2-bis (5-ethoxy-2-methylthiazole) -3,3,4,4,5,5-hexafluorocyclopentene [hereinafter abbreviated as PC3] was used.
[0038]
The maximum absorption wavelengths of PC1 to PC3 in the colored state were 610 nm, 540 nm, and 475 nm, respectively. When the photochromic compound was irradiated with light having a peak wavelength of 450 nm and a half width of 20 nm in the decolored state of the photochromic compound, PC3 showed a color-forming reaction, but PC1 and PC2 hardly showed a color-forming reaction. Further, when the photochromic compound was irradiated with light having a peak wavelength of 400 nm and a half width of 20 nm in the decolored state of the photochromic compound, PC1 and PC2 showed a coloring reaction, but PC3 hardly showed a coloring reaction. When irradiated with a 365-nm bright line from a mercury lamp, all the photochromic compounds showed a coloring reaction.
[0039]
As a light-shielding substance contained in the light-shielding layer 3, BONASORB UA-3901 (hereinafter abbreviated as S1) manufactured by Orient Chemical Industries, and as a light-shielding substance contained in the light-shielding layer 5, 2- (5-methyl-2-hydroxyphenyl) benzotriazole [hereinafter S2] Abbreviation]. Three types of photochromic compounds, PC1, PC2, and PC3, were each dispersed in polystyrene at 10 wt% to form a photosensitive solution. The photosensitive solution was formed by laminating a photosensitive solution containing PC1, followed by PC2 and then PC3 on a white polyethylene terephthalate support substrate (thickness: 0.5 mm) sequentially by spin coating to form a laminated photosensitive layer. The thickness of the laminated photosensitive layer was about 60 μm. Further, a thin film of polyvinyl alcohol (2 μm) was applied as a protective film on the surface of the uppermost photosensitive layer to prepare a reversible image display medium.
[0040]
(Example 2)
With respect to the decolored state of the reversible image display medium created in Example 1, light (1 mW / cm) having a peak wavelength of 450 nm and a half value width of 20 nm extracted from a xenon lamp and an interference filter was used. ² ) For 100 seconds, a deep cyan color was formed. This is presumed that PC1 has selectively developed color.
[0041]
(Example 3)
With respect to the decolored state of the reversible image display medium created in Example 1, light having a peak wavelength of 400 nm and a half-value width of 20 nm (1 mW / cm) extracted from a xenon lamp and an interference filter was used. ² ) For 100 seconds, a deep magenta color developed. This is presumed that PC2 selectively developed color.
[0042]
(Example 4)
With respect to the decolored state of the reversible image display medium manufactured in Example 1, a bright line of 365 nm (10 mW / cm) of a mercury lamp was used. ² ) For 10 seconds, a deep yellow color developed. This is presumed that the PC3 selectively developed color.
[0043]
(Example 5)
With respect to the decolored state of the reversible image display medium manufactured in Example 1, light having a peak wavelength of 450 nm and a half value width of 20 nm (1 mW / cm) extracted from a xenon lamp and an interference filter was used. ² ) For 100 seconds, and then a light having a peak wavelength of 400 nm and a half width of 20 nm (1 mW / cm) extracted from a xenon lamp and an interference filter. ² ) For 100 seconds, and finally a 365 nm bright line (10 mW / cm) of a mercury lamp. ² ) Was irradiated for 10 seconds to develop a black color. This is presumed that all three types of photochromic compounds developed color.
[0044]
(Example 6)
When a reversible image display medium containing the three types of photochromic compounds developed in Examples 2 to 5 was irradiated with light (100,000 lux) of a wavelength of 480 nm or more from a xenon lamp for 100 seconds, the reversible image display medium of Examples 2 to 5 In all examples, reversible image display media in which the photochromic compound was in the decolored state were obtained.
[0045]
【The invention's effect】
As described above, according to the first aspect, in a reversible image display medium that performs multicolor display by laminating photosensitive layers individually containing three types of photochromic compounds having different color hues on a supporting substrate, The photochromic compounds in the decolored state have different threshold wavelengths for transitioning to the colored state, and are located between the lowermost photosensitive layer and the photosensitive layer located thereon and between the lowermost photosensitive layer and the uppermost photosensitive layer. By providing a light-shielding layer for shielding light for coloring the photochromic compound between the photosensitive layer and the photosensitive layer, three types of photochromic compounds can be selectively colored to reduce light irradiation energy required for image formation. became.
[0046]
According to the second aspect, the threshold wavelength of the photochromic compound having the longest threshold wavelength of the light that transitions to the colored state by light absorption in the decolored state is λ1, and the threshold wavelength of the light that transits to the colored state by light absorption in the decolored state When the threshold wavelength of a photochromic compound having a long threshold wavelength is λ2, and the threshold wavelength of a photochromic compound having a shortest threshold wavelength of light that transitions to a colored state by light absorption in a decolored state is λ3, the lowermost photosensitive layer is λ1. By using a photochromic compound having a threshold wavelength and a photosensitive layer positioned thereon as a photochromic compound having a threshold wavelength of λ2, it is possible to use a material that absorbs all light of a specific wavelength or less as a light shielding layer. Was.
[0047]
According to the third aspect, the light-shielding layer provided between the lowermost photosensitive layer and the photosensitive layer located thereover emits light of at least a part of the wavelength within the wavelength range shorter than λ1 and longer than λ2. A light-shielding layer provided between the uppermost photosensitive layer and the photosensitive layer located therebelow, having a characteristic of blocking light of at least a part of the wavelength within a wavelength range shorter than λ2 and longer than λ3; Are three types of layers having a characteristic of transmitting light of at least a part of wavelength in a wavelength region shorter than λ1 and longer than λ3 and blocking light of at least part of wavelength in a wavelength region shorter than λ3. It has become possible to selectively develop the color of the photochromic compound.
[0048]
According to claim 4, the three types of photochromic compounds are a photochromic compound having a maximum absorption wavelength in a colored state in a range of 600 nm or more and less than 700 nm, a photochromic compound having a maximum absorption wavelength in a colored state in a range of 500 nm or more and less than 600 nm, By selecting a photochromic compound having a maximum absorption wavelength in the color-developing state in the range of 400 nm or more and less than 500 nm, a full-color reversible image display medium has become possible.
[0049]
According to the fifth aspect, a step I of irradiating a photochromic compound having a threshold value of λ1 with light having a wavelength corresponding to a desired density after color development and having a wavelength shorter than λ1 and longer than λ2 for each pixel of the reversible image display medium. Irradiating each pixel of the reversible image display medium with a photochromic compound having a threshold value of λ2 and irradiating light of a wavelength shorter than λ2 and longer than λ3 to each pixel with an amount of light corresponding to the density after desired color development. By performing the step III of irradiating each pixel of the reversible image display medium with the photochromic compound by irradiating each pixel of the reversible image display medium with light of a wavelength shorter than λ3 at a light amount corresponding to a desired density after color development, color is obtained. Light irradiation energy required for image formation can be reduced.
[0050]
According to claim 6, instead of the irradiation method of performing the steps I to III in the irradiation step according to claim 5, light having a wavelength shorter than λ3 is transmitted through the two light-shielding layers for each pixel of the reversible image display medium. Irradiating the three photosensitive layers at the same time, thereby reducing the number of steps in the case of a document having only black and white characters or a document having many black and white characters, and also reducing the color shift of three colors. It became possible.
[0051]
According to the seventh aspect, since the color density can be changed by changing the illuminance or irradiation time of light, it is possible to easily control the intermediate gradation.
[0052]
According to the eighth aspect, by configuring the light source with a fluorescent tube and an optical filter, it is possible to easily adjust the irradiation wavelength by forming conditions of the optical filter, replacing and installing the optical filter, and the like.
[0053]
According to the ninth and tenth aspects, by applying a laser or a light emitting diode to the light source, a light absorbing member such as a filter becomes unnecessary, and the light use efficiency is increased, thereby reducing the writing energy and the writing time. At the same time, a reversible image display method using a small, high-output light source has enabled high resolution, high-speed writing, and downsizing of the image forming apparatus.
[0054]
According to the eleventh aspect, separately from the light source for selectively coloring the photochromic compound, the white light is provided to the light source and the entire surface of the reversible image display medium is irradiated with the white light, so that the display is performed in a short time. It is now possible to delete all images.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a layer configuration of a reversible image display medium according to an embodiment of the present invention.
FIG. 2 is an absorption spectrum showing a state in which three types of photochromic compounds constituting a reversible image display medium according to one embodiment of the present invention have transitioned from a decolored state to a colored state by three light irradiation steps for image formation. is there.
[Explanation of symbols]
1 Support substrate
2 Photosensitive layer containing photochromic compound A
3 Shading layer D
4 Photosensitive layer containing photochromic compound B
5 Shading layer E
6. Photosensitive layer containing photochromic compound C
7 First light irradiation step I
8 Second light irradiation step II
9 Third light irradiation step III
Photochromic compound A having a threshold wavelength of 10 λ1
Photochromic compound B having a threshold wavelength of 11 λ2
Photochromic compound C having a threshold wavelength of 12 λ3

Claims (11)

In a reversible image display medium that performs multicolor display by laminating photosensitive layers individually containing at least three types of photochromic compounds having different color hues on a support substrate, the three types of photochromic compounds in a decolored state are in a colored state. The transition threshold wavelengths are different, respectively, and the photochromic compound is formed between the laminated lowermost photosensitive layer and the photosensitive layer located thereon, and between the uppermost photosensitive layer and the photosensitive layer located thereunder. A reversible image display medium, comprising a light-blocking layer that blocks light for coloring. In the decolored state of the photosensitive layer containing the photochromic compound, the threshold wavelength of the light that transitions to the colored state by light absorption in the decolored state is λ1, and the threshold wavelength of the photochromic compound is the longest. When the threshold wavelength of a photochromic compound having a long threshold wavelength of light is λ2, and the threshold wavelength of a photochromic compound having a shortest threshold wavelength of light that transits to a colored state by light absorption in a decolored state is λ3, the lowermost photosensitive layer is A photosensitive layer containing a photochromic compound having a threshold wavelength of λ1, a photosensitive layer located thereon is a photosensitive layer containing a photochromic compound having a threshold wavelength of λ2, and the uppermost photosensitive layer has a threshold wavelength of λ3. The reversible image display medium according to claim 1, wherein the medium is a photosensitive layer containing a photochromic compound. The light-shielding layer provided between the lowermost photosensitive layer and the photosensitive layer located thereon transmits light of at least some wavelengths in a wavelength region shorter than λ1 and longer than λ2 and transmits light of a wavelength shorter than λ2. The light-shielding layer provided between the uppermost photosensitive layer and the photosensitive layer located thereunder has a characteristic of blocking light of at least a part of the wavelength within a wavelength region shorter than λ3. 3. The light-emitting device according to claim 1, wherein the light-transmitting light has a characteristic of transmitting light of at least a part of the wavelength in a wavelength region shorter than λ3 and blocking light of at least a part of the wavelength in a wavelength region shorter than λ3. The reversible image display medium according to the above. The three types of photochromic compounds having different color hues are a photochromic compound A having a maximum absorption wavelength in a color development state of 600 nm or more and less than 700 nm, and a photochromic compound having a maximum absorption wavelength in a color development state of 500 nm or more and less than 600 nm. The reversible image display medium according to any one of claims 1 to 3, wherein the compound B is a photochromic compound C having a maximum absorption wavelength in a colored state of 400 nm or more and less than 500 nm. In a reversible image display medium in a decolored state, a photochromic compound having a threshold of λ1 is irradiated with a light beam having a wavelength corresponding to a desired density after color development and having a wavelength shorter than λ1 and longer than λ2 for each pixel of the reversible image display medium. Irradiating a photochromic compound having a threshold value of λ2 with light having a wavelength corresponding to a concentration after desired color development and having a wavelength shorter than λ2 and longer than λ3 for each pixel of the reversible image display medium. 5. The method according to claim 1, wherein a step III of irradiating a photochromic compound having a threshold value with a light beam having a wavelength corresponding to a desired color density and a wavelength shorter than λ3 to each pixel of the reversible image display medium is performed. An image forming method using the reversible image display medium according to any one of the above. The reversible image display medium according to any one of claims 1 to 3, wherein the step of irradiating each pixel is performed instead of the step of performing the three steps I, II, and III of irradiating each pixel according to claim 5. An image forming method, wherein a step of irradiating each pixel of a reversible image display medium with light having a wavelength shorter than λ3 transmitted through two light-shielding layers to simultaneously develop the three photosensitive layers is performed. The image forming method according to claim 5, wherein the light source that irradiates the photosensitive layer containing the photochromic compound with light includes a fluorescent tube. The image forming method according to claim 5, wherein the light source that irradiates the photosensitive layer containing the photochromic compound with light includes an optical element including a fluorescent tube and an optical filter. 7. The image forming method according to claim 5, wherein a laser is included as a light source for irradiating the photosensitive layer containing the photochromic compound with light. 7. The image forming method according to claim 5, wherein the light source for irradiating the photosensitive layer containing the photochromic compound with light includes a light emitting diode. A step of irradiating white light to the entire surface of the reversible image display medium to bring all the photosensitive layers containing the photochromic compound into a decolored state is performed as a pre-process before applying the step I of irradiating each pixel of the reversible image display medium. The image forming method according to claim 5 or 6, wherein:

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