JP2001001645A - Thermally reversible multiple color recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new reversible multiple color recording medium by which a more accurate, finer and clearer multiple color image can be expressed, and wherein a re-writing can be freely performed by deleting the image. SOLUTION: A writing is performed by using at least three laser beams, and this thermally reversible multiple color recording medium is constituted by laminating at least following three layers of respective thermally reversible color recording layers (A) to (C) on a base sheet 5. That is, the thermally reversible multiple color recording medium comprises (A) a thermally reversible color recording layer 1 comprising a first thermally reversible color developing layer 1a and a first laser beam absorbing layer 1b having a wavelength to develop a color of the color developing layer, (B) a thermally reversible color recording layer 2 comprising a second thermally reversible color developing layer 2a and a second layer beam absorbing layer 2b having a wavelength to develop a color of the color developing layer, and (C) a thermally reversible color recording layer 3 comprising a third thermally reversible color developing layer 3a and a third laser beam absorbing layer 3b having a wavelength to develop a color of the color developing layer. More preferably, a transparent heat insulating layer (glass bead or the like) is inserted between the recording layers 1 and 2, and 2 and 3. A multiple color recording/deletion is performed with colors of red, blue, green and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved thermoreversible multicolor recording medium particularly suitable for laser writing.
The recording medium itself can be used for various rewritable advertising media, or can be used in combination with various rewritable or reusable cards.

[0002]

2. Description of the Related Art Generally, reversible recording media are described in Journal of the Institute of Electrophotography, Vol. 35, No. 3 (1996), 148-15.
As described in the special feature on page 4 as "Recent Trends in Rewritable Marking Technology", an image is expressed in a single color of only turbidity based on physical change, and an image is expressed in multiple colors based on chemical change. There are two cases. The former single-color reversible (rewritable) recording medium,
This is a card type, which has already been put to practical use at a gas station or the like. However, at the present stage, the latter multicolor reversible recording medium is not yet in a practical stage. Since the need for colorization is high, it is considered that research will be promoted as a large theme in the future.

As a recent technology that can be seen in patent applications for reversible multicolor recording media, for example, Japanese Unexamined Patent Application Publication No. Hei 8-80682
Publication No. The basic technical idea of the publication is that a single colored layer containing a plurality of irreversible dyes (dyes or organic pigments generally used in printing inks) each of which absorbs light having a wavelength specific to the color and generates heat is provided below. hand,
On top of that, a specific temperature (temperature due to heat generation of the irreversible dye)
To form a reversible multicolor recording medium by laminating a rewritable layer that reversibly changes to transparent or non-transparent (cloudy).
Here, the one-layered colored layer is divided into each color layer, the rewritable layer is provided on each color layer, and the rewritable layers are laminated via a light-transmitting heat-insulating layer (air) to form the recording medium. It also states that it is good.

[0004]

The present inventors have made various studies from different angles different from those in the above-mentioned publication. As a result, a reversible multicolor recording medium having a clearer multicolor image and excellent durability has been found, and the present invention has been achieved.

[0005]

That is, according to the present invention, as described in claim 1, at least the following three thermoreversible color recording layers (A) to (C) are formed on a substrate (5). The main means is a thermoreversible multicolor recording medium in which layers are laminated. (A) a first thermoreversible color coloring layer (1a) and a first laser light absorbing layer (1) having a wavelength for coloring the coloring layer;
b) a thermoreversible color recording layer (1); (B) a second thermoreversible color coloring layer (2a) and a second laser light absorbing layer having a wavelength for coloring the coloring layer. (2
(C) a third thermoreversible color-developing layer (3a) and a third laser light absorbing layer having a wavelength for coloring the color-developing layer (3
b) a thermoreversible color recording layer (3)

The invention of claim 2 is also provided in connection with the main invention. It is a thermoreversible multicolor recording medium characterized in that a transparent heat insulating layer (4) is further laminated between at least three layers of the thermoreversible color recording layers (1, 2, 3) to be laminated. . Here, as a preferred form, the transparent heat insulating layer (4) is provided by a fine glass bead having a thickness of 5 to 100 μm and implanted in a dot shape (claim 3).

[0007] The invention according to claims 4, 5 and 6 is also provided dependent on claim 1 or 2. Hereinafter, the present invention will be described in detail in the following embodiments.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a thermoreversible multicolor recording medium (hereinafter referred to as an HRC medium) of the present invention freely writes certain information using at least three lasers (lights) having different wavelengths. The written information is quickly expressed (developed) with images of three or more colors. Conversely, if this is quenched or cooled at a certain temperature, the expression color image is maintained or erased as it is. It can be said that this expression and erasing operation can be repeated, that is, a rewritable color information recording medium is made possible by a new configuration.

[0009] In particular, the writing is specified to the laser light here, because a finer image is sharper than other writing methods using, for example, heat emission from a thermal head or a magnetism, electric field, pressure, or the like. This is because there is no danger of dirt, damage, and the like, because the information can be written quickly and can be arranged in a non-contact state.

The configuration of the HRC medium writable by at least three laser beams will be described based on claim 1.

First, the HRC medium is provided on the substrate 5 for safe and easy handling (manufacturing and use).
The use form (material, thickness, transparent to opaque, application, etc.) of the substrate is as follows, for example. For the material, for example, paperboard, synthetic paper, nonwoven fabric of synthetic fiber, polyethylene terephthalate, polyethylene naphthalate, polyether ketone, polycarbonate, polymethyl methacrylate, cyclic polyolefin, polyether sulfone,
Sheets made of a crystalline or amorphous thermoplastic resin such as polyarylate, sheets made of a thermosetting resin such as an epoxy-based, acrylic-based, urethane-based, or imide-based resin, and inorganic sheets such as ceramics and glass Things. Needless to say, a composite sheet in which two or more of these types are appropriately combined may be used. Their thickness is generally about 0.1 to 3 mm. In addition, as to transparency to (translucent) to opaque, this is determined particularly in relation to the use. For example, a transparent or translucent sheet is used for display applications such as posters, and an opaque sheet is used for merging with various cards. When they are transparent, they are preferably non-colored, and when they are translucent to opaque, they are preferably white. For whitening, there are methods such as kneading with titanium oxide, surface coating, and surface roughening. In order to impart adhesiveness to the sheet, pretreatment may be performed by a physical (corona discharge or the like) or chemical (surface oxidation with an oxidizing agent) method, or an anchor coat layer may be provided if necessary. Is also good.

On the substrate 5, at least (A)
The thermoreversible color recording layers (1), (2), and (3) of (C) are laminated independently, and this is achieved by using at least three laser beams having different wavelengths. This is for expressing an image by color. Therefore, in particular, (A) is the first,
(B) is called second and (C) is called third for the sake of convenience for distinguishing between at least three, and the order of lamination (the recording layer-hue) is called. It is not what it is. In addition, it is preferable that the recording layer is laminated in order that the dark color system is the lowermost layer and lighter colors are sequentially laminated on the lowermost layer in order to improve the visibility. For example, in the case of three hues of red, blue, green or yellow, red is the lowermost layer, blue is the middle layer, and green or yellow is the uppermost layer.

The at least first, second, and third thermoreversible color recording layers (1, 2, 3) correspond to the thermoreversible color coloring layers (1a, 2a, 3a) respectively. And the light absorbing layers (1b, 2b, 3b). Next, each of the coloring layer and the absorbing layer will be described in detail.

First, when each of the thermoreversible color-forming layers expresses a color with, for example, three hues of red, blue and green, precursors of electron-donating dyes as color-forming sources (hereinafter referred to as color-forming agents).
And an electron-accepting compound (hereinafter referred to as a color developer) having a color-reducing effect on the color former with temperature as a main component, which is mixed and dispersed in a binder resin to form each layer. I have. Here, the presence of the resin is preferably absent from the viewpoint of clearer and more faithful repetition of color development and decoloration.
However, in order to disperse the color former and the developer uniformly and to strengthen the adhesion to the substrate 5, it is desirable to use the resin in combination. However, the composition amount is desirably as small as possible.

Examples of the coloring agent include fluoran lactone compounds such as 2-chloro-6-diethylaminofluoran lactone and 3-methyl-6-diethylaminofluoran lactone for red. For blue color, 3- (4-diethylamino-2-methylphenyl) -3- (1-ethyl-2-methylindole-3-yl) -4-azaphthalide, 3- (4-diethylamino-6-ethoxyphenyl) -3- (1-hexyl-2-yl) -Methylindole-3
Phthalide compounds such as -yl) -4-azaphthalide. In green, fluoran lactone such as 7- (N, N-dibenzylamino) -3- (N, N-diethylamino) fluoran lactone and 7- (N-octylamino) -3- (N, N-diethylamino) fluoran lactone Oral lactone compounds. In addition, yellow is a fluoran lactone compound such as 3-methoxy-6-methoxyfluoran lactone, and black is 7- (2-chlorophenylamino) -3- (diethylamino) fluoran lactone, 6-methyl-7-
Fluorane lactone compounds such as (2,4-dimethylphenylamino) -3- (diethylamino) fluoran lactone can be exemplified. Of course, these are colorless or lightly colored in a normal state, and are different from ink dyes and pigments which are respectively colored in a normal state.

Further, the color developer is basically a compound having a structural portion exhibiting a color developing ability for coloring the color former and a long-chain aliphatic structural portion for controlling cohesion between molecules. There is no particular limitation. For example, in the structural part exhibiting the color developing ability, a phosphoric acid group, a carboxylic acid group, an aromatic group or the like is used, and in the structural part controlling the cohesive force, a long-chain alkyl group having C10 or more carbon atoms, preferably C12 to C24 is used. is there. Illustrating specific compounds, N
-Behenyloyl 4-aminophenol, p- (octadecylthio) phenol, p- (eicosyloxy) phenol, p-hexadecylcarbamoylphenyl,
Long-chain alkyl aromatic compounds such as 4- (N-behenoylamino) phenoxyacetic acid, α-hydroxyhexadecanoic acid, 2-bromohexadecanoic acid, 3-oxooctadecanoic acid, octadecylmalic acid, octadecylthiophosphoric acid, 2-octadecylpentanin Long-chain alkyl mono- or dicarboxylic acid compounds such as acids, octadecylphosphonic acid,
Long-chain alkyl phosphate compounds such as eicosylphosphonic acid can be exemplified.

The binder resin is firstly compatible with the color former and the developer, has excellent adhesion to the substrate 5, is dissolved in a solvent (water or organic solvent), and The resin is preferably selected in consideration of its excellent transparency, heat resistance and weather resistance. Although various resins suitable for the resin under such conditions are conceivable, it is more preferable to select among amorphous thermoplastic polymers.

The amorphous thermoplastic polymer as the binder resin is, for example, polyvinyl chloride, polyvinyl acetate, a copolymer of polyvinyl chloride and vinyl acetate, polystyrene or a copolymer of polystyrene and another vinyl monomer. Acryl-based copolymers or copolymers thereof with other vinyl monomers, maleic acid-based copolymers, polyvinyl alcohol-based polymers, cyclic olefin-based polymers such as vinyl-based polymers, phenoxy polymers, polyurethanes, polycarbonates, ester-based polymers ( (Amorphous), semi-synthetic cellulose (ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose), starch and the like. When a crystalline thermoplastic polymer is used, it is preferable to select a thermoplastic polymer having as low a crystallinity as possible and a low melting point.

The composition ratio of any one of the coloring agent, the developing agent and the binder resin constituting each of the thermoreversible color coloring layers is preferably determined by preliminary experiments in consideration of various conditions. , Roughly as follows. 15-40% by weight of color former,
85 to 60% by weight of the color developer and 1 to 10% by weight of the binder resin based on the total amount of the color former and the color developer. Incidentally, in order to improve the formation characteristics of the color-forming layer and the color-forming / decoloring characteristics, for example, a dispersant, a surfactant, a lubricant, an antioxidant, an ultraviolet absorber, a light stabilizer, a color-forming stabilizer, a decolorizing accelerator, Addition of trace amounts of additives such as sensitizers and sensitizers used in general thermal paper is acceptable.

The means for forming each of the thermoreversible color-developing layers on the substrate is generally as follows. First, a desired amount of a resin binder is dissolved in an organic solvent. Since the amount of dissolution differs depending on the solubility in the resin and the forming method, it cannot be uniquely determined, so it is preferable to determine the amount by a preliminary test. Next, a required amount of a predetermined color former and a required amount of a color developer are added to the dissolved solution separately or in advance. After the addition, the mixture is sufficiently stirred to uniformly disperse the whole. Here, there are no restrictions on the mixing conditions or the mixing order.
Then, it is applied to a predetermined thickness by a coating means (spin coating, roll coating, spray coating, screen printing, etc.) and dried.

Here, it is preferable that the layer thickness of each of the coloring layers coated is changed depending on whether it is the lowermost layer, the intermediate layer or the uppermost layer. This is because, if the upper layer is thick, the transmission of the laser beam is deteriorated, and as a result, the color density and the sharp difference of the displayed image are likely to be adversely affected. However, making it too thin will reduce the color density of the layer itself. Therefore, it is good to keep this in mind and decide by prior check.
Generally speaking, the range is 1 to 30 μm, preferably 5 to 20 μm.
μm, in which the optimum layer thickness for each color-forming layer is found.

Next, each of the thermoreversible color-forming layers (1a)
(2a) First, second and third lasers provided corresponding to (3a)
The light absorbing layers (1b), (2b) and (3b) will be described in detail.

Each of the absorbing layers has a first, a different wavelength.
It is necessary to quickly absorb the second or third laser light, convert it to heat (predetermined temperature), and transmit it to each of the color forming layers faithfully and with high efficiency. Therefore, the absorption layer is determined by the color of the coloring layer, and the laser light (wavelength) is also determined. On the contrary, if the wavelength of each laser beam to be used is determined, the absorption layer,
The color-forming layer corresponding thereto is also determined. It is preferable that the color of the absorbing layer and the color of the coloring layer match as much as possible.

The laser light used here is generally about 600 to 1000 nm, preferably 650 to 900 nm.
Is selected, and the wavelength determined within this wavelength range is preferably a single wavelength as much as possible. The source of the laser light may be a gas laser, a fixed laser, a semiconductor laser, or the like. Among them, a semiconductor laser having an optical output of about 20 mW is preferable.

The respective absorption layers for the determined laser beams have the following contents. First, the layer is mainly formed of a laser light absorbing agent capable of selectively absorbing a wavelength from a selected laser beam with high efficiency and converting it into a predetermined heat (temperature) energy as it is. . Here, a more effective selection of such an absorbent may have an effect on the color chromaticity of each of the determined color forming layers,
Of course, it is determined in consideration of durability (heat resistance against repeated heating and cooling), film forming property, adhesion to the coloring layer, and the like.
It is also preferable to consider the molar extinction coefficient.

The molar extinction coefficient (also referred to as molecular extinction coefficient) is generally expressed as the intensity of absorption of light by a dye molecule. In the present invention, the absorber molecule is emitted from a laser beam at 600 to 1000 nm. It means the intensity of absorption in the range (visible or infrared wavelength).
This can be measured by the absorbance measurement method described in JIS K0212. Taking this molar extinction coefficient into consideration, the absorber is numerically 10,000 or more laser light absorbers, more preferably 20,000 or more, and further absorbs the specified laser light. If the condition that the width of the wavelength peak is 200 nm or less is also included, a more preferable infrared absorbing agent can be selected.

Examples of the laser light absorbers to be used are, for example, generally known cyanine, phthalocyanine, indocyanine, naphthalocyanine, anthraquinone, polymethine, aminium, immonium. , Dithiol-based, metal complex-based, and the like, and further, based on the above conditions, the absorbent that absorbs only the heat conversion wavelength specific to the color development of the color-forming layer is selected.

The absorption layers (1b), (2b) and (3)
The means for forming each of the color forming layers (1a), (2a) and (3a) on b) is as follows. First, a predetermined amount of at least three selected laser light absorbers is dissolved in an organic solvent as it is or dissolved together with a small amount of the binder resin to prepare each coating solution. Next, each of the coating liquids is coated on the entire surface of each of the corresponding color forming layers by a coating method (any one of those exemplified in the case of the color forming layer). After the coating, the organic solvent is removed by evaporation by heating and drying, and the process is completed. Here, the thickness of each of the absorbing layers finally obtained by coating is determined under various conditions (laser light absorbing ability, strong adhesive strength and durability against impact, and influence of the coloring of the absorbing agent itself on the coloring layer. It is preferable to take this into consideration in consideration of the fact that it is small. As the organic solvent, ethers (interchain or cyclic), aliphatic alcohols, ketones (chain or cyclic), aliphatic esters, aliphatic nitriles, chlorinated methanes and the like are generally used. . In addition, the combined use of a binder resin generally tends to deteriorate the efficiency of absorption of laser light, the efficiency of heat conduction to the color-forming layer, the absorption peak width of the infrared absorbent (in the direction of spreading), and so on. It is better not to use it. When it is used, it is preferable that the amount is as small as possible, especially when the film strength or film formability cannot be obtained anymore.

Each of the thermoreversible color recording layers (1);
In (2) and (3), basically, the target thermoreversible recording medium is obtained by directly laminating the recording layer on the substrate 5 in order. Or the like, and these may be laminated to form the recording medium.

It is more desirable that the image can be recorded more quickly and efficiently with a clearer color image, and that the image can be erased. Therefore, claim 2 is provided as a means for this purpose. The recording means includes a thermoreversible color recording layer comprising at least three layers according to claim 1 (1), (2), (3), that is, between (1) and (2), and (2). That is, at least two transparent heat insulating layers (4) are interposed therebetween. Since the transparent heat insulating layer has a function of insulating the recording layer from heat, it is difficult for heat to be transmitted. That is, the heat independently received by the recording layers of the adjacent recording layers is used as it is for color development without escaping to the other. As a result, the influence on the coloring and decoloring of the adjacent recording layer is reduced, so that a clearer color image can be reproduced quickly and accurately. Also, the durability of repeated use is further improved.

The transparent heat insulation layer (4) is specifically
The layer thickness is about 100 μm, which is formed by an air layer, or a glass bead having a particle size of about 2 to 40 μm containing a transparent adhesive resin. Here, in the case of an air layer, for example, a space is provided around the periphery so as to leave a gap of 5 to 100 μm to make a complete air layer, or a dot (point) spacer (transparent binder) having a height of 5 to 100 μm. (By resin) to form an air layer. In particular, the latter case is preferable because the air layer is surely formed regardless of the size of the thermoreversible multicolor recording medium. The glass beads
In this case, the glass beads are mixed with an organic solvent using as little transparent adhesive resin as possible, and the glass beads are coated (planted) so as to be scattered over the entire surface or with fine dots. Among them, a method of forming the glass layer with a desired layer thickness irrespective of the size of the recording medium and facilitating the formation with the glass beads, and furthermore, a method of forming the glass beads in a scattered manner with dots is known. preferable.

The thermoreversible multicolor recording medium obtained above is
Although it is used as it is, it is preferable to protect at least the uppermost laser light absorbing layer (protection from environmental atmosphere such as air, water, temperature, damage during use, work process, etc.). Because of this, a material that is as transparent as possible and transmits (does not absorb) laser light as well as possible should have a film thickness of 0.1 to 1
It is also possible to cover the entire surface about 0 μm. The material is not specified, but when a resin is used, a photo-curable transparent resin, for example, acrylic, epoxy, urethane, acrylic / epoxy, acrylic / urethane, acrylic / silicone, etc., which binds silicone components, etc. Is coated and photocured. On the other hand, silicon oxide film by sol-gel method, silicon oxide film by sputtering method or IT
An O (indium tin oxide) film or the like can be used as the protective film. Of course, even if such a protective layer is provided, there is no effect on the developing / erasing action, but this is also because the present invention has a specific configuration.

[0033]

EXAMPLES The present invention will be described below with reference to examples together with comparative examples.
Will be described in more detail. The degree of color development in the example is determined by the following method.
Therefore, measure L^*a^*b^*It is expressed in a color system.
In other words, Mi manufactured based on JIS Z8729
Using a color difference meter "CR-200" manufactured by Norta Corporation
In each case, red, blue, and green obtained by laminating on a white substrate
The thermoreversible three-color recording plate (medium) of
Irradiate the light to develop red color and this L^*a^*b^*Measure
I do. After measurement, heat to 80 ° C to remove red color
You. Next, a laser beam corresponding to blue is irradiated, and color development and measurement are performed in the same manner.
Constant-decoloring. Finally, irradiate the laser light corresponding to green and
Color-measure-discolor. Where L ^*Is the lightness index of each color
The higher the number, the lighter and less dense (conversely, the lower the number, the darker
It becomes darker). a^*b^*Indicates hue and saturation
In chromaticity, L^*a^*b^*As is clear from the color system chromaticity diagram
a^*Is the red direction, -a^*Is green, and b^*Is the yellow direction,
-B^*Indicates the blue direction.

(Example 1) First, red, blue, and green compositions for thermoreversible color-forming layers were prepared according to the following formulation. For red coloring: 40 parts by weight of 2-chloro-6-diethylaminofluorolactone powder as a thermoreversible red coloring agent, and 2.
90 parts by weight of a 5% by weight aqueous solution of polyvinyl alcohol was added, and mixed and dispersed sufficiently (solution A). On the other hand, as a developer
100 parts by weight of N-behenyloylaminophenol powder and 400 parts by weight of a 2.5% by weight aqueous solution of polyvinyl alcohol were added thereto and sufficiently mixed and dispersed (solution B). Then, 65 parts by weight of the liquid A and 250 parts by weight of the liquid B were collected, and 100 parts by weight of a 10% by weight aqueous solution of polyvinyl alcohol and 200 parts by weight of water were collected.
A part by weight was added and mixed well to obtain a composition for red coloring (red coloring liquid). For blue coloring: 3- (4-diethylamino-2-methylphenyl) -3- as a reversible blue coloring agent instead of the red coloring agent
Each composition was prepared under the same conditions as above except that (1-ethyl-2-methylindol-3-yl) -4-azaphthalide was used to obtain a blue-coloring composition liquid (blue-coloring liquid). Green color development: The same conditions as described above, except that 7- (N, N-dibenzylamino) -3- (N, N-diethylamino) fluorolactone is used as a reversible green color developer instead of the red color former. To obtain a green coloring composition liquid (green coloring liquid).

On the other hand, a composition for a laser light absorbing layer corresponding to each of the color forming layers was prepared according to the following formulation. For red absorption: maximum absorption peak 83 with an absorption peak width of 50 nm
0.1 g of phthalocyanine-based absorbent absorbing 0 nm wavelength
Was dissolved in 20 g of ethyl acetate (red absorbing solution). For blue absorption: maximum absorption peak 65 at an absorption peak width of 50 nm
0.1 g of phthalocyanine-based absorbent absorbing 5 nm wavelength
Was dissolved in 20 g of ethyl acetate (blue absorption liquid). For green absorption: maximum absorption peak 78 with an absorption peak width of 50 nm
0.1 g of phthalocyanine-based absorbent absorbing 0 nm wavelength
Was dissolved in 20 g of ethyl acetate (green absorbing solution).

Next, a white opaque PET film having a thickness of 125 μm (L ^* = 99.44, a ^* = − 0.57, b ^* =
0.19) as the substrate 5, and the above-mentioned composition liquid for the thermoreversible color-forming layer and the composition liquid for the laser light-absorbing layer are sequentially coated and laminated according to the following procedure to obtain the desired composition. A three-color thermoreversible recording medium was prepared. On the entire surface of the PET film,
First, the red coloring liquid is applied and dried to provide a first thermoreversible red coloring layer 1a having a thickness of 10 μm. Then, the red absorbing liquid is applied on the first thermoreversible red coloring layer 1a and dried to absorb the first laser light having a thickness of 1 μm. The layer 1b was provided to form a first thermoreversible red recording layer 1. Next, the blue coloring liquid is coated on the thermoreversible red recording layer 1 and dried to form a second thermoreversible blue coloring layer 2a having a thickness of 10 μm. Subsequently, the blue absorbing liquid is coated on the 2a and dried to 1 μm. Second laser light absorbing layer 2b
To form a second thermoreversible red recording layer 2. Finally, the green coloring liquid is applied on the thermoreversible red recording layer 2 and dried to obtain 1
A 0 μm third thermoreversible blue coloring layer 3a is provided.
The above-mentioned green absorbing solution is applied on the substrate and dried to form a 1 μm third layer.
The third thermoreversible green recording layer 3 was provided with the light absorbing layer 3b.

With respect to the thermoreversible recording materials of the three colors prepared above, color development and decoloration tests were performed in the order of red, blue, and green to confirm the performance. The color development was carried out by separately irradiating semiconductor laser light having a maximum single wavelength at 830 nm for red color, 655 nm for blue color and 780 nm for green color from above the recording medium. Decoloration develops and develops color degree L ^* a
^After measuring ^* b ^* , the temperature was raised to 80 ° C before the next color development. As a result, each color was efficiently developed and decolored. Table 1 summarizes the coloring degree at that time. The color development degree L ^* a ^* b ^* of each color was measured at the time when color development and decoloration were repeated 100 times for each color, but there was no difference from the first (Table 1).

(Table 1)

(Example 2) (Example of Claim 2) First, under the same conditions as in Example 1, the red color developing solution, blue color developing solution, green color developing solution and red absorbing solution, blue absorbing solution, and green absorbing solution were used. Prepared.

On the other hand, the coating liquid for the transparent heat insulating layer has a particle size of 25.
A photocurable transparent acrylic resin precursor solution (solution for heat insulation layer) containing 20% by weight of a glass bead of 20 μm is prepared, and the heat insulation layer is interposed as described below using this. A three-color thermoreversible recording medium was prepared. Using the same white PET film as in Example 1 as a substrate, the red color developing solution and the red absorbing solution were sequentially applied and dried under the same conditions as in Example 1, and then dried.
A first thermoreversible red recording layer 1 was provided. Next, the liquid for the heat insulating layer is implanted in a grid pattern at a pitch of 5 mm by screen printing so as to have a layer thickness of 27 μm on the red recording layer, cured by irradiating ultraviolet rays, and cured by a glass bead dot. 4 were provided. Next, on the transparent heat-insulating layer, the blue-coloring liquid and the blue-absorbing liquid were sequentially applied and dried under the same conditions as in Example 1 to obtain a second liquid.
The thermoreversible blue recording layer 2 was provided. Then, the liquid for the heat insulating layer is applied again by screen printing so as to have a layer thickness of 27 μm on the blue recording layer, and is cured by irradiating ultraviolet rays to form the transparent heat insulating layer 4.
Was provided. Finally, the green color developing solution and the green absorbing solution were applied and dried on the transparent heat-insulating layer under the same conditions as in Example 1 to provide a third thermoreversible green recording layer 3, and the process was completed. The structure of the obtained thermoreversible recording medium is shown in FIG.

Then, the transparent insulating layers of the three colors obtained above are interposed.
Thermoreversible recording medium under the same conditions as in Example 1
Irradiates the semiconductor laser light to the surface to test for color development and decoloration
Was performed to confirm the heat insulating effect. As a result, first each color
When observing the situation with the eyes, each color is more colored than in Example 1.
It felt a little faster and slightly more vivid.
And the chromaticity L of each color^*a^*b^*And this is shown in Table 1.
I stopped again. This table can prove more clear.
The point at which color development and decoloration for each color was repeated 150 times
And the degree of color development L of each color^*a ^*b^*Was measured, but initially (Table
No difference was found between 1). And the three semiconductors
Irradiation with laser light at the same time
Three colors develop at the same time with vivid colors, and this is
It was also confirmed that all the colors were immediately erased when the temperature was changed to ° C.

(Comparative Example 1) 40 parts by weight of the thermoreversible red colorant, blue colorant and green colorant used in Example 1 mixed in equal amounts, and 2.5 parts by weight 90 parts by weight of an aqueous solution of polyvinyl alcohol was added and sufficiently mixed and dispersed (solution C). Then, the liquid C was applied to the white PET film used in Example 1 so as to have a layer thickness of 10 μm.
After drying, a three-color mixed thermoreversible recording layer consisting of one layer was provided.

Next, on the thermoreversible recording layer, the same red absorbing solution, blue absorbing solution and green absorbing solution as used in Example 1 were sequentially applied, dried, and dried to a thickness of 1 μm each. -The light (first, second, third) absorption layer was laminated.

In the obtained three-color thermoreversible recording medium,
655 nm, 780 nm, 830 nm as in Example 1.
Each color was developed using the laser light of the semiconductor and the color was erased, and the color development was observed. As a result, three colors were almost simultaneously formed for the laser beams of any wavelengths, and no single color was observed. At least a number of thermoreversible color recording layers corresponding to at least the number of colors to be formed are independently laminated, and the layers are colored with laser light having a wavelength specific to the coloring of the recording layers, and then cooled and erased. It can be clearly understood that there is a remarkable difference from the thermoreversible recording medium of the present invention, which is called color.

[0045]

As described above, the present invention has the following advantages.

First, by combining a thermoreversible multicolor recording medium having at least three layers of thermoreversible recording layers each as a single layer, and at least three laser beams having different wavelengths, the medium is extremely quickly combined. It was possible to develop multicolors with vivid colors, and it was possible to immediately erase the color by cooling.

Even after repeated use of coloring and decoloring a large number of times, the reduction in performance was small, and a great improvement in durability was observed.

Since writing is performed by using a laser beam, it is possible to express a color even to a finer portion. As a result, it can be used in a wider range, and there is a possibility that it can be replaced by hard copy.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a thermoreversible three-color recording medium of an example.

[Explanation of symbols]

 1 thermoreversible red recording layer 2 thermoreversible blue recording layer 3 thermoreversible green recording layer 4 transparent heat insulating layer (glass bead)

Claims (6)

[Claims] 1. The method according to claim 1, wherein at least the following (A) to
(C) A thermoreversible multicolor recording medium comprising three layers each of which is a thermoreversible color recording layer. (A) a first thermoreversible color coloring layer (1a) and a first laser light absorbing layer (1) having a wavelength for coloring the coloring layer;
b) a thermoreversible color recording layer (1); (B) a second thermoreversible color coloring layer (2a) and a second laser light absorbing layer having a wavelength for coloring the coloring layer. (2
(C) a third thermoreversible color-developing layer (3a) and a third laser light absorbing layer having a wavelength for coloring the color-developing layer (3
b) a thermoreversible color recording layer (3) 2. The method according to claim 1, wherein a transparent heat insulating layer (4) is further laminated between at least three layers of the thermoreversible color recording layers (1, 2, 3) to be laminated. Thermoreversible multicolor recording medium. 3. The transparent heat-insulating layer (4) has a thickness of 5 to 100.
3. The thermoreversible multicolor recording medium according to claim 2, comprising a fine glass bead implanted in a dot shape with a size of μm. 4. The thermoreversible color-forming layer (1a, 2a,
3. The thermoreversible multicolor recording medium according to claim 1, wherein the hue in 3a) comprises any one of three colors of red, blue and green. 5. The thermoreversible multicolor according to claim 1, wherein each of the laser beams is selected from light having a wavelength of 600 to 1000 nm emitted from a semiconductor laser. recoding media. 6. An absorption layer for each laser light (1b, 2b, 3).
5. The method according to claim 1, wherein b) is selected from infrared absorbing agents having a molar extinction coefficient of 10,000 or more.
Or the thermoreversible multicolor recording medium according to any one of the above items 5.