JP2000025338A - Thermal reversible multi-color recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal reversible multi-color recording medium, prominent in the quality of a picture and high in utility. SOLUTION: A heat reversible multi-color recording layer 2 of two colors or more (red, blue and green, for example) is arranged on a substrate 1 with a regular arraying pattern and a near infrared ray absorbing layer 3, absorbing near infrared ray from laser beam and whose principal constituent is a near infrared ray absorbing agent having a molar absorptivity of 20000 or more (preferably immonium base perchlorate), is laminated on the whole surface of the recording layer. Further, a transparent protecting layer 4 is provided on the whole surface of the absorbing layer 3 to protect the same from external hazard. Obtained thermal reversible multi-color recording medium is suitable especially for laser writing and is utilized practically in the form of combination with various kinds of advertisement mediums, various kinds of cards 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 a special feature on page 4 as "Recent Trends in Rewritable Marking Technology", it has recently begun to be used as one of marking technologies for recording on cards (thermal type, magnetic type) and the like. The technical content of this is that when energy is given to the recording medium by heat, light, magnetism, electric field, pressure, etc., a visible image corresponding to the energy can be obtained, and the visible image is maintained as it is. Is done. However, when the energy is applied again, the image is erased. In other words, a visible image is obtained when it is needed, and it is deleted when it is no longer needed, and it can be repeated. Therefore, it has both display and hard copy functions.

[0003] There are two types of visible images: transparent and opaque based on the principle of physical change, and colored images (color) based on the chemical change. The latter reversible recording medium of the colored image type lacks image quality and stability compared to the former, but it has become an indispensable condition in recent years to be able to perform color display like ordinary color prints. Is coming. However, the recording medium capable of color display is under intensive study by each company, and in reality, a practical level of technology has not yet been developed.

[0004]

SUMMARY OF THE INVENTION The present inventors have intensively studied a thermoreversible multicolor recording medium which repeatedly displays and erases a multicolor image. As a result, the image quality has been further improved, and a new means that can reach a practical level has been found, leading to the present invention. The solution is as follows.

[0005]

Means for Solving the Problems That is, the first invention which led to the invention
Is described in claim 1. That is, this is achieved by forming a recording layer (2) in which two or more thermoreversible thermosensitive recording compositions having different hues are arranged in a regular array pattern on the surface of the substrate (1) and the entire surface of the recording layer. A thermoreversible multi-layer comprising a near-infrared absorbing layer (3), which absorbs near-infrared rays from a laser beam and has a near-infrared ray absorbing agent having a molar extinction coefficient of 20,000 or more as a main component. It is a color recording medium.

A second aspect of the present invention is a second aspect of the present invention.
2. The thermoreversible multicolor recording according to claim 1, wherein a transparent protective layer (4) is further laminated on the entire upper surface of the near-infrared absorbing layer (3). Medium.

Further, the inventions according to claims 3 to 8 are provided as subordinate to the two inventions, and are provided as more preferable inventions.

One of them is that, in the third aspect, the recording layer (2) in the present invention is composed of three hues that emit red, blue and green, and is more preferable than a combination with other hues. A thermoreversible multicolor recording medium can be provided.

As two of them, in claim 4, 2
The present invention provides a thermoreversible multicolor recording medium in which the arrangement pattern of the thermoreversible thermosensitive recording composition of each color of a plurality of colors or more is formed on the substrate (1) surface in a striped or lattice regular pattern. is there.

In the present invention, a laser (light) is particularly used as a means for writing and recording information as the three. In the claims, a laser emitted by a semiconductor laser is used. The wavelength is 750-8
A thermoreversible multicolor recording medium using a near-infrared absorbing agent having a peak at 50 nm and having a molar extinction coefficient of 20,000 or more was used for the near-infrared absorbing layer (3).

[0011] Fourth, in claim 6, the immonium salt represented by Chemical Formula 1 embodied as the most effective compound is selected from among the near-infrared absorbing agents, and the thermoreversible polychrome using the same is used. A recording medium is provided.

[0012] Five of the above are described in claim 7, wherein the color and the light transmittance of the near-infrared absorbing layer (3) itself laminated on the entire upper surface of the recording layer (2) are expressed by:
An object of the present invention is to provide a thermoreversible multicolor recording medium which is transparent and achromatic and has a light transmittance at a wavelength of 750 to 850 nm in a range of 5 to 60%.

Finally, in claim 8, the near-infrared absorbing layer (3) is formed mainly of the near-infrared absorbing agent containing no binder resin, and has a layer thickness of 0.3 to 15 μm.
m is provided as a thermoreversible multicolor recording medium.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The above invention will be described in more detail below.

First, the thermoreversible multicolor recording medium (hereinafter referred to as HRC medium) of the present invention is a system in which certain information is freely written using a laser (light), and the written information is written in two colors. The above multi-color image is displayed as an image. Conversely, when the displayed multi-color image is heated at a certain temperature, it is erased.
The repetition of the multicolor image display and its erasure is used.

Regarding the writing means, other than the laser,
There are methods such as direct heat release from the thermal head, magnetism, electric field, pressure, etc.
Because finer images can be written more sharply and quickly, and can be arranged in a non-contact state with respect to the near-infrared absorbing layer (3), there is no danger of dirt or damage. In particular, the present invention employs a writing method using a laser.

Next, the configuration conditions of the HRC medium will be described. First, the substrate (1), which is used as the medium,
It is necessary for safe and easy handling (manufacturing and use), but its form differs depending on the method of use. In other words, what kind of material should be made and what kind of thickness it should be. If these are exemplarily shown, the thickness is about 0.1 to 3 mm, and it is inorganic or synthetic resin. Examples of the material include paperboard from pulp, synthetic paper with synthetic resin, and synthetic fiber. Non-woven fabric,
Polyethylene terephthalate, polyethylene naphthalate, polyether ketone, polycarbonate, polymethyl methacrylate, cyclic polyolefin, polyether sulfone, polyarylate and other crystalline or amorphous thermoplastic resin sheets, epoxy, acrylic,
A sheet made of a thermosetting resin such as a urethane-based or imide-based resin, or an inorganic sheet made of a ceramic, glass, or the like, or a composite sheet obtained by appropriately combining two or more of the above examples may be used.

Further, the substrate is not necessarily required to be transparent, and may be translucent to opaque, which is one of usage forms. 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, physical (corona discharge, etc.) and chemical (surface oxidation with an oxidizing agent, etc.)
Pretreatment may be performed by a method, or an anchor coat layer may be provided if necessary.

Next, the recording layer (2) will be described. When the information to be written is irradiated through a laser, the light is first converted into thermal energy (near-infrared absorbing layer (3)), and the written information is colored in a desired color. It is displayed as an image. When the colored image is rapidly cooled, the colored state is maintained, and when the colored image is gradually cooled, the image is erased. Further, when heating is performed from a state in which coloring is maintained at normal temperature (by another heating means), the coloring is performed again at a low heating temperature, but is erased when heated at a higher temperature.

The recording layer (2) comprises a precursor (hereinafter referred to as a color former) of an electron-donating dye, which is a source of coloring (coloring) of two or more colors, and develops a color with the color developing agent together with the temperature. And an electron-accepting compound (hereinafter referred to as a color developer) for causing a decoloring effect, but generally also contains a binder resin. The presence of the resin is preferably absent from the viewpoint of clearer and more faithful repetitive action of color development and decoloration, but it disperses the color former and the developer uniformly and makes it adhere to the substrate (1) surface. In order to enhance the properties, it is desirable to use the resin in combination. However, the composition amount is desirably as small as possible.

The color former is preferably colorless or lightly colored, but may be selected from generally known ones. For example, in a blue color,
3- (4-diethylamino-2-methylphenyl) -3
Phthalide compounds such as-(1-ethyl-2-methylindole-3-yl) -4-azaphthalide, 3- (4-diethylamino-6-ethoxyphenyl) -3- (1-hexyl-2-methylindole-3-yl) -4-azaphthalide . For red coloring, fluoran lactone compounds such as 2-chloro-6-diethylaminofluoran lactone and 3-methyl-6-diethylaminofluoran lactone. 7- (N, N-dibenzylamino) for green color
Fluoran lactone compounds such as -3- (N, N-diethylamino) fluoran lactone and 7- (N-octylamino) -3- (N, N-diethylamino) fluoran lactone. For black color development, 7- (2-chlorophenylamino) -3- (diethylamino) fluoran lactone,
6-methyl-7- (2,4-dimethylphenylamino)
Fluoran lactone compounds such as -3- (diethylamino) fluoran lactone; A yellow color is a fluoran lactone compound such as 3-methoxy-6-methoxy fluoran lactone.

The color developer is basically a compound having both 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. If there is, it is not limited. For example, the structural part showing the color developing ability is a phosphate group, a carboxylic acid group, an aromatic group or the like, and the structural part controlling the cohesive force has a carbon number of C ₁₀ or more, preferably a long chain of C _{12 to} C ₂₄ . It is an alkyl group. Specifically, for example, N-beheniroyl 4-aminophenol, p- (octadecylthio) phenol, p- (eicosyloxy) phenol, p-
Long-chain alkyl aromatic compounds such as hexadecylcarbamoylphenyl, α-hydroxyhexadecanoic acid, 2-bromohexadecanoic acid, 3-oxooctadecanoic acid, octadecylmalic acid, octadecylthiophosphoric acid, and long-chains such as 2-octadecylpentanoic acid Long-chain alkyl phosphate compounds such as alkyl mono- or dicarboxylic acid compounds, octadecylphosphonic acid, and eicosylphosphonic acid are exemplified.

When used in combination, the binder resin is compatible with the color former and the color developer, has excellent adhesion to the substrate (1), and is suitable for use in solvents (water or organic compounds). The polymer is selected because it dissolves and has excellent heat resistance and weather resistance. The polymer under such conditions is preferably selected from mainly amorphous thermoplastic polymers. Examples of the polymer include polyvinyl chloride, polyvinyl acetate, a copolymer of vinyl chloride and vinyl acetate, a copolymer of polystyrene, a copolymer of styrene and another vinyl monomer, and a copolymer of acrylic alone or with another vinyl monomer. Polymerized polymers, maleic acid-based copolymerized polymers, vinyl-based polymers such as polyvinyl alcohol and modified polymers thereof, phenoxine polymers, polyurethanes, polycarbonates, ester-based polymers (semi-aromatic or wholly aromatic homo- or copolymerized polymers), cellulose System (ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose), starch and the like.
Of course, a crystalline thermoplastic polymer can also be used, but in this case, it is more preferable to select from polymers having a low melting point in consideration of the melting point.

In the thermoreversible thermosensitive recording composition comprising the above-mentioned components, the composition ratio is determined in consideration of various conditions.
Although it is finally determined by preliminary experiments, it is generally common to each hue and is determined using the following range as a guide. Color former 1
5 to 40% by weight, 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. In addition, various additives may be added as needed to improve or suppress the coating characteristics and the coloring and decoloring characteristics of the recording layer. These additives include, for example,
Examples include dispersants, surfactants, lubricants, antioxidants, ultraviolet absorbers, light stabilizers, color stabilizers, decolorization accelerators, and sensitizers used in general thermal paper.

Next, a method of providing the thermoreversible thermosensitive recording layer (2) by disposing the compositions of the respective hues in a regular pattern on the surface of the substrate (1) will be described.

First, a desired amount of the binder resin is dissolved in a solvent. The amount of the solvent cannot be unambiguously determined because it depends on the solubility in the resin or the forming (coating) method, so it is better to determine the amount by a preliminary test. Next, the desired amounts of the color former and the developer are separately or preliminarily mixed in the dissolved solution. After the addition, the mixture is sufficiently stirred to uniformly disperse the whole. The mixing conditions (mixing means, temperature, etc.) here are not particularly limited. Of course,
The order of mixing the components is not limited.

Then, one surface of the substrate (1) is coated with the obtained solution composition having a coloring ability of at least two hues in a predetermined pattern. Here, the predetermined pattern is not particularly limited as long as the predetermined pattern forms a pixel, displays an image in multiple colors, and can be confirmed. In particular, it is desirable to display using a stripe-like or lattice-like pattern. This is because it is preferable to display the image accurately and easily. In the case of a stripe, the width is 0.03 for each hue.
Coating is repeatedly performed in order with two or more hues as one pixel at ２2 mm. For example, in the case of three hues of blue, green, and red, blue, green,
Separate from red and coat vertically or horizontally adjacently.
The three hues of blue, green and red are one pixel. On the other hand, in the lattice pattern, 0.03 to 2
Coat in mm square. In this case, for the pixel, for example, three grids of blue, green, and red become one pixel in three hues, and these are arranged vertically and horizontally and coated in a grid pattern.

The coating may be performed by a general printing means, such as screen printing, offset printing, gravure printing, pad printing, flexographic printing, or the like.

Since the layer thickness of the recording layer (2) greatly affects the color density of an image displayed in multiple colors, when viewed as a whole, the color density becomes a well-balanced color density for each color. It is important to be able to capture the whole image of the image, but the final image may be determined in consideration of coating properties and adhesion (strength). Usually 5-30μ
m, preferably 15 to 25 μm.

After coating, the coating is heated and dried to remove the solvent. In general, coating and heating and drying are repeated for each hue and sequentially performed.

Next, the near-infrared absorbing layer (3) laminated on the entire surface of the recording layer (2) obtained will be described. The absorption layer is particularly suitable for near-infrared rays from laser light,
It is necessary to selectively absorb wavelengths of ８850 nm, convert it to thermal energy, and transmit that energy to the underlying recording layer (2). In general, the presence of the absorbing layer lowers the efficiency of transferring heat energy to the recording layer with respect to the absorption of light and also lowers the image quality of a color image. Is preferred. However, on the other hand, when the absorbing layer is not provided, the durability of the recording layer is reduced. That is, since the HRC medium has an extremely short life and cannot be used practically, the presence of the absorbing layer is necessary.

The presence or absence of the absorption layer (3) is in a trade-off relationship as described above, and the present invention particularly absorbs near-infrared light from the laser light with extremely high efficiency and converts it into thermal energy. The problem was solved by finding a near-infrared absorbing agent having a molar extinction coefficient of 20,000 or more, preferably 22,000 or more. That is, an HRC medium having extremely high quality and a multicolor image and excellent durability can be obtained by the absorbent having such characteristics.

Here, the molar extinction coefficient (also referred to as a molecular extinction coefficient) is generally expressed as the intensity of absorption of light by a dye molecule. In the present invention, the near-infrared absorbing agent molecule emits near-infrared light emitted from laser light. It means the strength to absorb infrared rays. This is represented by Equation 1 and JIS
It can be measured by the absorbance measurement method described in K0212.

[0034]

(Equation 1) (In Equation 1, A is the absorbance, ε is the molar extinction coefficient, C is the transmission thickness of the solution containing the near-infrared absorbent in the cell (cm), and d is the molar concentration of the solution (mol / l).)

The near-infrared absorbing agent is not particularly limited as long as it has a molar absorption coefficient of 20,000 or more. This covers generally known infrared absorbers, for example, cyanine, phthalocyanine, naphthalocyanine, naphthaloquinone, anthraquinone, polymethine, aminium, immonium, dithiol, metal complex and the like.

The absorber is specified as a compound having a molar extinction coefficient of 20,000 or more. In addition, the absorber has sufficient absorption characteristics in the wavelength range of 750 to 850 nm in laser light, Properties (heat resistance against repeated heating and cooling, weather resistance), film forming properties of the absorbing layer and the recording layer (2)
It is also desirable that the adhesiveness of the recording layer (2) be satisfactory, as well as strong adhesion to the recording layer (2).

Regarding the coloring chromaticity of the recording layer (2) under the incidental conditions, the color characteristics of the near-infrared absorbing layer (3) further formed are as transparent and achromatic as possible, and the wavelength is 750 to 750. Light transmittance at 850 nm of 5 to 60%,
Preferably 10 to 40%, more preferably 15 to 30%
%, A greater effect can be obtained. Here, since the transparent achromatic color of the absorption layer is mainly provided by the near-infrared absorbing agent itself, it is more preferable that the transparent achromatic color be as transparent as possible. In addition, the transmittance is related to the efficiency of heat generation caused by laser beam absorption, and the efficiency is higher in a range of 5 to 60%. Therefore, information is displayed quickly in multiple colors, and the coloring of the color becomes clearer. The light transmittance was specified as 5 to 60% for the following reason. In other words, the near-infrared absorbing agent which is less than 5% generally increases the absorption in the visible light region and enhances the coloring of the near-infrared absorbing layer (3), thereby lowering the color saturation of the recording layer (2), On the other hand, if it exceeds 60%, the heat generation due to the absorption of the laser beam becomes weak, and it takes a long time to develop the color of the recording layer (2) or the color does not develop.

A near-infrared absorbing agent that satisfies the above conditions is more effective, and among these generally known, an immonium-based or aminium-based absorbing agent is preferable.

Here, the immonium-based compound has a structural formula represented by the following chemical formula 1.

[0040]

(In the formula R is, H, or an alkyl group of C ₁ ~ _12, X
Is SbF ₆ , ClO ₄ , BF ₄ , NO ₃ , F, Cl, B
r or I)

With respect to specific compounds of the immonium salt,
For example, N, N, N ', N'-tetrakis (p-di-n
-Butylaminophenyl) -p-benzoquinone-bis (immonium perchlorate), N, N, N ', N'-tetrakis (p-diethylaminophenyl) -p-benzoquinone-bis (immonium hexafluoroantimonate ), N, N, N ', N'-tetrakis (p-di-n
-Hexyfuraminophenyl) -p-benzoquinone-bis (fluoromonate boronate), N, N, N ',
N'-tetrakis (p-di-n-isopropylaminophenyl) -p-benzoquinone-bis (immonium nitrate), N, N, N ', N'-tetrakis (p-di-n-
Octylaminophenyl) -p-benzoquinone-bis (hexafluoroantimonate of immonium), N,
N, N ', N'-tetrakis (p-diethylaminophenyl) -p-benzoquinone-bis (immonium bromide).

The aminium-based compound has a structural formula represented by the following chemical formula 2.

[0043]

Embedded image (Wherein R is, H, or an alkyl group of C ₁ ~ _12, X is SbF
₆ , ClO ₄ , BF ₄ , NO ₃ , F, Cl, Br or I
Is one of

For specific aminium-based compounds,
For example, N, N, N ', N'-tetrakis (p-di-n
-Butylaminophenyl) -p-phenylenediaminium perchlorate, N, N, N ', N'-tetrakis (p
-Dimethylaminophenyl) -p-phenylenediaminium chloride, N, N, N ', N'-tetrakis (p-
Hexafluoroantimonate of di-n-dodecylaminophenyl) -p-phenylenediaminium, N, N,
N ', N'-Tetrakis (p-diethylaminophenyl) -p-phenylenediaminium fluoride borate, N, N, N', N'-tetrakis (p-di-n-butylaminophenyl) -p-phenylene Diaminium fluorine salt; N, N, N ′, N′-tetrakis (p-diethylaminophenyl) -p-phenylenediaminium perchlorate;

Further, among the above-mentioned immonium-based and aminium-based, the immonium-based is more preferable.

The thickness of the laminated near-infrared absorbing layer (3) containing the above-mentioned near-infrared absorbing agent as a main component is determined by the laser light absorbing performance of the absorbing agent, the adhesion to the recording layer (2), and the resistance. It is determined in consideration of the impact properties and the degree of coloring of the absorbing layer. For example, the absorbent, which is excellent in the absorbing performance and excellent in the adhesion and the impact resistance, can be made thinner. As a result, even if the absorbent itself has some coloring,
The adverse effect on the multicolor image is extremely small. In consideration of the above, the layer thickness may be set to about 0.3 to 15 μm as a guide. In particular, in the case of the above-mentioned immonium salt, it is preferable to set the thickness to 1 to 8 μm, preferably 2 to 6 μm, so that the coloring chromaticity (red: x = 0.37 to 0.4)
2, y = 0.36-0.41, blue: x = 0.31-0.
36, y = 0.35-0.40, green: x = 0.33-
0.38, y = 0.38-0.43, preferably red: x
= 0.38-0.41, y = 0.37-0.40, blue:
x = 0.32 to 0.35, y = 0.36 to 0.39,
Green: x = 0.34 to 0.37, y = 0.39 to 0.4
2, more preferably red: x = 0.39-0.40, y
= 0.38 to 0.39, blue: x = 0.33 to 0.34,
y = 0.37-0.38, green: x = 0.35-0.3
6, a colored image of y = 0.40 to 0.41) is obtained.

The source of the laser light is any one of a gas laser, a solid laser, and a semiconductor laser, and is more effective in the present invention.
A semiconductor laser having an optical output of about 00 mW, having a maximum wavelength in the range of 750 to 850 nm, and enabling compactness as an apparatus is preferable.

Next, a method of laminating the absorbing layer (3) will be described. First, a predetermined amount of the selected near-infrared absorbing agent is dissolved in an organic solvent of the absorbing agent as it is or dissolved together with a small amount of the binder resin to prepare a coating solution. Next, the coating liquid is coated on the entire upper surface of the recording layer (2) by commonly used coating means such as spin coating, dipping coating, roll coating, spray coating and the like. After the coating, the organic solvent is evaporated and removed by heating and drying, and a near-infrared absorbing layer (3) having a desired thickness is laminated. As the organic solvent, ethers (chain or cyclic), aliphatic alcohols, ketones (chain or cyclic), aliphatic esters, aliphatic nitriles, chlorinated methanes and the like are generally used. .

It is preferable not to use the binder resin because it deteriorates the laser light absorption efficiency of the near-infrared absorbing layer (3) itself and the efficiency of heat transfer to the recording layer (2). Whether or not this binder resin is used depends on the film forming property of the selected near-infrared absorbing agent itself, strength, etc., but in the case of the aminium-based or immonium-based materials mentioned as preferable as described above, it is necessary to use the binder resin. This is one of the features.

Next, further lamination of the transparent protective layer (4) according to claim 2 will be described. The transparent protective layer (4) functions particularly for the maintenance of the near-infrared absorbing layer (3) (environmental atmosphere such as air, moisture, temperature, damage during use or work process, etc.), so that it is efficient. It is not always preferable from the viewpoint of coloring and decoloring. In other words, there is a trade-off relationship. Therefore, ideally, it is desirable that the protective layer satisfies both of them. However, this is a near-infrared absorbing agent which does not need the binder resin, and the above-mentioned aminium-based absorbing agent is particularly preferable. This is the case of the near-infrared absorbing layer (3) using the immonium-based absorber. That is, in the case of the absorbent, the near-infrared absorbing layer (3) using the binder resin is more
It is better to form the absorbing layer (3) with the absorbing agent alone and to separately (independently) overcoat the protective layer (4),
This is because the effect is large also in terms of decoloring.

The transparent protective layer (4) may be a non-hydrophilic one among the polymers exemplified as the binder resin, but is preferably a photo-curable transparent resin, generally a perfect binder for binding an acrylic component. Acrylic-epoxy-based, acrylic-urethane-based, acrylic-based resins that also combine acrylic resins, epoxy components, urethane components, silicone components, etc.
A precursor of each resin such as a silicone resin is coated on the entire upper surface of the near-infrared absorbing layer (3) (according to the above-described coating method), and is formed by UV exposure. On the other hand, thin film forming means, such as silicon dioxide, indium oxide, tin oxide or the like by a sputtering method,
The protective layer (4) can be used, or a protective layer (4) can be formed by coating a polyalkoxysilane or perhydropolysilazane and chemically decomposing to form a silicon dioxide film.

The thickness of the transparent protective layer (4) varies depending on the material to be coated, but it is preferable that the thickness is as thin as possible. Generally, it is better to set the thickness to 0.1 to 10 μm as a standard. Also, a small amount of additives such as a weathering agent, a light-proofing agent and a heat-resistant material can be added to the transparent protective layer (4).

[0053]

The present invention will be described in more detail with reference to the following examples together with comparative examples. Incidentally, transmittance in the text and the examples,
The coloring chromaticity was measured by the following method, but these are not specified by the present method.

The light transmittance at a wavelength of 750 to 850 nm is an average value of the light transmittance measured at a wavelength of 750 to 850 nm using an automatic recording spectrophotometer U-3410 (with an integrating sphere) manufactured by Hitachi, Ltd.

The chromaticity of the color development is determined by positioning the part to be tested on the XY table with respect to each hue pattern, positioning each of the patterns with an optical lens system for a beam diameter of 300 μm, and setting each of the patterns. Is irradiated with a semiconductor laser (laser light having an oscillation wavelength of 830 nm at 100 mW) whose beam is narrowed down by an optical lens system, and the color is recorded.
The xy chromaticity of each of the recording colors was determined using a color luminance meter (BM-7 manufactured by Topcon).

(Example 1) (corresponding to claim 1) First, thermoreversible thermosensitive compositions which develop the following three hues of red, blue and green were prepared.

Red coloring: First, 2-chloro-6-diethylaminofluoran lactone 2 as a thermoreversible red coloring agent.
8.3% by weight and 71.7% by weight of N-behellouyl 4-aminophenol as a developer were mixed to form a mixture. On the other hand, 8.6% by weight of polyvinyl alcohol as a binder resin is dissolved in pure water (3 times the total amount of the three components) with respect to the total amount of the mixture, and the mixture is added thereto.
The mixture was uniformly mixed and dispersed using a ball mill. Hereinafter, it is referred to as a red composition.

Blue color development: As a thermoreversible blue color former, 3
-(4-Diethylamino-2-methylphenyl) -3- (1-ethyl-2-methylindole-3-yl) -4
28.3% by weight of azaphthalide, the other color developer, binder resin, and pure water were mixed at the same mixing ratio as in the case of the red color development, and finally mixed and dispersed uniformly by a ball mill. Hereinafter, it is referred to as a blue composition.

Green color development: As a thermoreversible green colorant, 7
28.3% by weight of-(N, N-dibenzylamino) -3- (N, N-diethylamino) fluoran lactone, and other developers, binder resin, and pure water are the same as in the case of the above red coloration. The materials were mixed at the same mixing ratio, and finally mixed and dispersed uniformly by a ball mill. Hereinafter, it is referred to as a green composition.

Next, each of the above compositions was coated with a thickness of 120 μm,
A biaxially stretched PET film (polyethylene terephthalate film) having a width of 100 × 200 mm was coated by the following method to provide a three-color thermoreversible thermosensitive recording layer (2) in a stripe pattern. First, the red composition was printed by screen printing in the vertical direction at a pitch of 900 μm on a stripe having a width of 300 μm and a length of 8 cm at a pitch of 900 μm, and dried by heating to form a recording layer having a layer thickness of 21 μm (hereinafter referred to as R1). Call). Next, using a blue composition, a stripe having a width of 300 μm and a length of 8 cm is similarly screen-printed at a pitch of 900 μm adjacent to R1 and dried by heating to obtain a recording layer having a layer thickness of 21 μm (hereinafter referred to as B1).
Then, using a green composition, a stripe having a width of 300 μm and a length of 8 cm is formed adjacent to B1 at a pitch of 90 μm.
Screen printing was performed at 0 μm in the same manner, followed by drying by heating to provide a recording layer (hereinafter referred to as G1) having a layer thickness of 21 μm.

Next, a near infrared absorbing agent was coated on the entire surface of the recording layer provided by the following method to provide a near infrared absorbing layer (3). N, N, N ', N'-tetrakis (p-di-n-butylaminophenyl) -p-benzoquinone-bis (immonium perchlorate) having a molar extinction coefficient of 22000 was used as the near infrared absorber. Was dissolved in tetrahydrofuran (THF), coated with a spin coater, and dried by heating. The layer thickness of the obtained absorption layer (3) was 4.8 μm.

Then, the obtained recording medium was cut in half, and using one of the sheets, the chromaticity of color development of three hues was measured, and this was shown in the chromaticity diagram of FIG. R1, blue is B
1, green is indicated as G1). At the same time as the irradiation of the laser beam, each color immediately developed a color, and the color was the same as the size of the beam, and the color was developed clearly. This means
This indicates that multicolor display can be performed with sharp image quality.

Further, after the recording medium was colored (irradiated with a laser beam) and heated to 80 ° C., the color was immediately erased. The coloring and decoloring were repeated 100 times, but there was no difference in the coloring and decoloring characteristics between the first and 100th times.

In order to measure the light transmittance of the near-infrared absorbing layer (3) itself at a wavelength of 750 to 850 nm, the following experiment was separately conducted to confirm the transmittance of the absorbing layer. First, the transmittance of the PET film itself was measured,
88% was obtained. Next, the PET film was spin-coated with a 0.01% by weight THF solution of the near-infrared absorber in the same manner, and dried by heating to provide an absorption layer having a layer thickness of 4.8 μm. The transmittance was measured to be 20%. Therefore, the transmittance of the absorbing layer itself is the quotient of this value and the transmittance of the substrate, which means that it is 22.7%.

Example 2 (corresponding to claim 1) Instead of the near-infrared absorbing agent used in Example 1, a thickness of 12
A perchlorate of N, N, N ', N'-tetrakis (p-dibutylaminophenyl) -p-phenylenediamineaminium with a molar extinction coefficient of 21,000 is used for a PET film of 0 μm, length × width = 100 × 200 mm. except,
Others form each layer under the same conditions, striped red,
A thermoreversible recording medium having three hues of blue and green was obtained.

Then, the chromaticity of the color development was measured in the same manner as in Example 1, and this was shown in the xy chromaticity diagram of FIG. In each hue, red is indicated as R2, blue is indicated as B2, and green is indicated as G2. It can be seen that the chromaticity of the color development is slightly shifted to the yellowish direction as compared with the immonium-based color of Example 1, but it is clear that the color development is much clearer and higher in quality than in the comparative example described later. . Note that the repetition characteristics of color development and decoloration are described in Example 1.
No significant difference was observed between the first and 100th runs up to 100 runs.

(Example 3) (corresponding to claim 2) Using the remaining half of the recording medium obtained in Example 1, a photocurable acrylic-based A resin precursor (liquid) (diabeam part number UR6530, manufactured by Mitsubishi Rayon Co., Ltd.) was coated with a bar coater, cured by irradiating ultraviolet rays, and provided with an acrylic transparent resin protective layer (4). The thickness of the protective layer was 5 μm.

The chromaticity of each color was measured for the obtained recording medium with a transparent protective layer by the same measurement method as that of Example 1, and the chromaticity diagram of FIG. 2 is shown in FIG.
In each hue, red is indicated as R3, blue is indicated as B3, and green is indicated as G3.

A repetition test of coloring and decoloring was performed in the same manner as in Example 1. The results were as follows, along with coloring at the same size as the laser beam, degraded color saturation, and the response speed of coloring and decoloring. No substantial difference from 1 was found. This means that the molar extinction coefficient of the present invention is particularly 20,000.
As long as the above-mentioned absorption layer of the near-infrared absorber is combined with the recording layer composed of multicolor hues, even if the transparent protective layer is provided, the color saturation of the color is reduced or the response speed of the color development and decoloration is reduced. This means that high-quality and multi-color display can be performed without performing. The configuration of the recording medium in this example is shown in FIG.
FIG.

Example 4 A fluorinated phthalocyanine-based near-infrared absorbent having a molar extinction coefficient of 101,000 (EEX Color IR1 manufactured by Nippon Shokubai Co., Ltd.) was used in place of the near-infrared absorbent in Example 1, except that Each layer was laminated under the same conditions to produce a recording medium having each color of red, blue and green.

The recording medium thus obtained was irradiated with a semiconductor laser beam to each color. As a result, for each hue, the speed of color development and the shape (sharpness) of the color development point were slightly better than in Example 1. Next, the xy chromaticity of each hue was calculated in the same manner as in the first embodiment.
2, B4 and G4 are shown in FIG.

It can be seen that all the hues are shifted toward the bluish gray as compared with the hue of Example 1. That is, a slight decrease in saturation is observed. In other words, these results indicate that the molar extinction coefficient needs to be as large as possible in terms of color developability, but the addition of another color to the original color emitted from the recording layer does not reduce the saturation. This indicates that it is more preferable to consider the achromatic color as much as possible in addition to the molar extinction coefficient when selecting the near-infrared absorbing agent.

(Comparative Example 1) (Near-infrared absorber having a molar extinction coefficient of less than 20,000) Instead of the near-infrared absorber in Example 1, a cyanine-based near-infrared absorber having a molar extinction coefficient of 3500 (manufactured by Fuji Photo Film Co., Ltd.) Each layer was laminated under the same conditions except that the recording medium was used for IRF700) to produce a recording medium having red, blue, and green hues.

When each color of the recording medium was irradiated with a semiconductor laser beam, no color development from each recording layer was visually recognized. On the other hand, the transmittance of the near-infrared absorbing layer was measured to be 75%. The above results indicate that the absorber did not substantially absorb laser light, especially semiconductor laser light, and as a result, it was not possible to obtain the heat energy required for color development, leading to the color development referred to in the present invention. It was not.

(Comparative Example 2) (Color Development by Thermal Head) First, under the same conditions as in Example 1, a recording layer and a near-infrared absorbing layer corresponding to red, blue and green stripes were laminated on a PET film. Further, an acrylic transparent resin protective layer was laminated under the same conditions as in Example 3 to obtain a recording medium with the protective layer.

With respect to the recording medium obtained above, thermal energy was directly emitted from the thermal head under the following conditions, and the state of color development was examined. The recording medium was set in a thermal transfer printer for printing with a thermal head, and the entire surface was printed. Each hue pattern developed color, but turbidity due to slight bleeding was observed at the boundary between the adjacent patterns. This is considered to be because the thermal energy from the thermal head dissipates more in the film plane direction than the thermal energy locally absorbing from the near infrared absorber by absorbing the laser beam. In addition, coloring and decoloring were repeatedly performed, and the state of damage to the protective layer and the state of remaining decoloring were checked. As a result, after repeating the coloring and decoloring 100 times, the remaining decoloring was observed, and a damaged portion was observed in the protective layer.

[0077]

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

First, a thermoreversible multicolor recording medium capable of displaying a high-quality multicolor image with excellent coloring can be obtained in combination with a writing means using a laser beam.

The durability (deterioration of image quality) was improved with respect to repeated use of writing and coloring by laser light and decoloring by heating.

Even if the transparent protective layer is provided, there is almost no difference in the response speed of color development and decoloration, and there is no effect on image quality. Therefore, the protection of the near-infrared absorbing layer by the protective layer is added, and a more practical thermoreversible recording medium can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a recording medium obtained in Example 3.

FIG. 2 is an xy chromaticity diagram showing chromaticity of color development in each example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 PET film 2 Recording layer consisting of three hues 3 Near-infrared absorbing layer 4 Transparent protective layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B41M 5/18 E 101C F-term (Reference) 2H026 AA07 AA09 AA14 AA24 BB02 BB21 DD01 DD45 DD56 FF09 FF11 FF13 FF22

Claims (8)

[Claims] 1. A recording layer (2) in which two or more thermoreversible thermosensitive recording compositions each having a different hue are arranged in a regular array pattern on a surface of a substrate (1), and on a whole surface of the recording layer. A thermoreversible multi-layer comprising a near-infrared absorbing layer (3), which absorbs near-infrared rays from a laser beam and has a near-infrared ray absorbing agent having a molar extinction coefficient of 20,000 or more as a main component. Color recording medium. 2. The thermoreversible multicolor recording medium according to claim 1, wherein a transparent protective layer (4) is further laminated on the entire upper surface of the near-infrared absorbing layer (3). 3. The thermoreversible multicolor recording medium according to claim 1, wherein the hue comprises three colors of red, blue and green. 4. The method according to claim 1, wherein the regular array pattern is a stripe or lattice pattern.
Item 19. The thermoreversible multicolor recording medium according to Item 1. 5. The thermoreversible multicolor recording medium according to claim 1, wherein the near infrared light from the laser light is light having a wavelength of 750 to 850 nm emitted from a semiconductor laser. 6. The near-infrared absorbing agent has a general formula: (Alkyl group wherein R is H or C ₁ ~ _12, X is Sb
_{F 6, ClO 4, BF 4} , NO 3, F, Cl, claims 1-5 are immonium salt represented by Br or I)
The thermoreversible multicolor recording medium according to any one of the above items. 7. The near-infrared absorbing layer (3) is transparent and achromatic and has a light transmittance of 5 to 850 nm.
The thermoreversible multicolor recording medium according to any one of claims 1 to 6, wherein the content is 60%. 8. The method according to claim 1, wherein the near-infrared absorbing layer (3) has a layer thickness of 0.3 to 15 μm containing a near-infrared absorbing agent containing no binder resin as a main component. Thermoreversible multicolor recording medium.