JP2007118204A - Reversible multi-color thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reversible multi-color thermal recording medium with high sensitivity of color development/color erasability and excellent image unifomity. <P>SOLUTION: This reversible multi-color thermal recording medium has a reversible thermal recording layer, formed on a support, which contains an electron-donative coloring compound and an electron-acceptive compound and can relatively create a black color development state and a color erasability state, depending on the difference in heating temperature and/or cooling rate after heating. In addition, the thermal recording layer contains a fine zinc oxide particle with 10 nm or above to 100 nm or below particle diameter. Further, the thermal recording layer and a coloring layer with repeating units each representing a three different primary color, are laminated sequentially, and the three primary color divisions of the coloring layer contain a photothermal conversion material which absorbs a light of respectively different wavelength and generates heat. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention uses a reversible multicolor thermosensitive coloring composition that utilizes a coloring reaction between an electron-donating color-forming compound and an electron-accepting compound, and can control the formation of a color image and erase it by controlling thermal energy. The present invention relates to a reversible multicolor thermosensitive recording medium and a recording method using the same.

  2. Description of the Related Art Conventionally, heat-sensitive recording media using a color developing reaction between an electron donating color developing compound (hereinafter also referred to as a color former or a leuco dye) and an electron accepting compound (hereinafter also referred to as a developer) are widely known. With the progress of OA, it is widely used as an output sheet for facsimiles, word processors, scientific measuring instruments, etc., and recently as a magnetic thermal card such as prepaid cards and point cards. However, these conventional recording media that have been put to practical use are being reviewed for recycling and reduced usage due to environmental problems. However, since they are irreversible colors, once recorded images are erased. It cannot be used repeatedly, and the area of the recordable part is limited because new information is added to the part where no image is recorded. Therefore, the actual situation is that the amount of information to be recorded is reduced or the card is remade when the recording area runs out. Therefore, it has been desired to develop a reversible thermosensitive recording medium that can be rewritten any number of times, against the background of the dust problem and forest destruction problem that have been actively discussed in recent years.

  By the way, various reversible thermosensitive recording media have been proposed from these requirements. For example, polymer-type reversible thermosensitive recording media using physical changes such as transparency and cloudiness are disclosed (see Patent Documents 1 and 2). In addition, a dye-type reversible thermosensitive recording medium utilizing a chemical change has been newly proposed. Specifically, those using a combination of gallic acid and phloroglucinol as the developer (for example, see Patent Document 3), those using compounds such as phenolphthalein and thymolphthalein as the developer (for example, patents) Reference 4), a recording layer containing a homogeneous solution of color former, developer, and carboxylic acid ester (see, for example, Patent Documents 5, 6, and 7), and an ascorbic acid derivative used as the developer (For example, refer to Patent Document 8), and those using a salt of bis (hydroxyphenyl) acetic acid or gallic acid and a higher aliphatic amine as a developer (for example, refer to Patent Documents 9 and 10).

  Furthermore, the present inventors previously used an organic phosphate compound, aliphatic carboxylic acid compound or phenol compound having a long-chain aliphatic hydrocarbon group as a developer in Patent Document 11, and this and a leuco dye which is a color former. In combination, the color development and decoloring can be easily performed under heating and cooling conditions, and the color development state and the color erasure state can be stably maintained at room temperature, and the color development and color erasure are repeated. A reversible thermosensitive coloring composition and a reversible thermosensitive recording medium using the same for a recording layer have been proposed. Thereafter, it has been proposed to use a phenolic compound having a long chain aliphatic hydrocarbon group having a specific structure (see, for example, Patent Documents 12 and 13).

However, a recording medium using such a material has problems such as a slow erasing speed and a long time for rewriting, insufficient erasing, or low thermal stability of a color image.
Therefore, the present inventors further proposed a recording medium having a high contrast between color development and decoloration, capable of high-speed erasing, and excellent in color stability of the image area by using the phenol compound described in Patent Document 14. . The recording medium using this phenol compound can be erased by a heating member such as a hot stamp, a heat roller, or a ceramic heater, and has excellent practicality.

  On the other hand, with the diversification of methods for using recording media, the demand for colorization has increased in recent years. In Patent Document 15 and Patent Document 16, a plurality of reversible recording layers having different color tones are laminated using a light absorbing dye having a specific wavelength, or a plurality of reversible recording layers each having an adjacent photothermal conversion layer are provided. There have been proposed a method of performing laser recording using a laminated reversible recording layer recording medium and a method of performing laser recording using a recording medium having a recording layer surface divided for each color tone. However, these methods have a problem that the sensitivity of recording and erasing is not sufficient or is not uniform.

JP 63-107584 A JP-A-4-78573 Japanese Patent Laid-Open No. 60-193691 Japanese Patent Laid-Open No. Sho 61-237684 JP-A-62-138556 JP-A-62-138568 JP-A-62-140881 Japanese Patent Laid-Open No. 63-173684 JP-A-2-188293 JP-A-2-188294 JP-A-5-124360 Japanese Patent Laid-Open No. 6-210954 JP-A-10-95175 JP-A-10-67177 Japanese Patent Laid-Open No. 2003-266941 JP 2003-266842 A

  Accordingly, the present invention is to provide a reversible multicolor thermosensitive recording medium having high color developing / decoloring sensitivity and excellent image uniformity.

The present inventors consider that the above problem is a problem that the temperature distribution width becomes large due to the slow rate of diffusion of heat generated by laser irradiation into the recording layer, and a uniform heating state is not achieved. In particular, improvement was studied by improving the heat conduction inside the recording layer and making the inside of the layer uniform.
As a result of examining various materials for improving the heat conduction, it was found that the coloring / decoloring sensitivity and the uniformity of the image can be remarkably improved by including the zinc oxide fine particles in the recording layer.

That is, the said subject is solved by the following (1)-(6) of this invention.
(1) “On the support, an electron-donating color-forming compound and an electron-accepting compound are used, and a relatively black-colored state and a decolored state are caused by a difference in heating temperature and / or cooling rate after heating. In a reversible thermosensitive recording medium having a reversible thermosensitive recording layer that can be formed, the recording layer contains zinc oxide fine particles having a particle diameter of 10 nm or more and 100 nm or less, and is further divided into three primary colors of the recording layer and light. And a colored layer having units are sequentially laminated, and the portion of the colored layer divided into three primary colors contains a photothermal conversion material that absorbs light of different wavelengths and generates heat. Multicolor thermal recording media "
(2) “Reversible multicolor recording medium according to item (1), wherein a light-transmitting heat insulating layer is formed between the recording layer and the colored layer”
(3) “Reversible multicolor recording medium according to item (1) or (2), wherein a protective layer is formed on the outermost surface”
(4) “Items (1) to (3), wherein the electron-accepting compound is a phenol compound having a saturated aliphatic group having 8 or more carbon atoms represented by the following formula (1)”: A reversible multicolor thermosensitive recording medium according to any one of

式中、Ｘ_１及びＸ_２は直接結合手、または−ＮＨ−，−ＣＯ−，−Ｏ−，−ＳＯ_２−，−Ｓ−からなる２価の基を示す。ただし、Ｘ_１及びＸ_２は同時に直接結合手であることはない。Ｒ_１は炭素数１から２２の２価の炭化水素基を表わし、Ｒ_２は炭素数８から３０の炭化水素基を表わす。また、ｐは０から４の整数を表わし、ｐが２から４のとき繰り返されるＲ_１およびＸ_２は同一でも異なっていても良い。また、ｐが０のときＸ_１は直接結合手ではない。さらに、ｑは１から３の整数を表わす」
（５）「前記第（１）項乃至第（４）項のいずれかに記載の可逆性多色感熱記録媒体を用いた記録方法であって、画像情報に応じて選択された波長の光を照射して露光し、記録層の特定領域を発色させて、画像表示を行なうことを特徴とする記録方法」
（６）「前記第（１）項乃至第（４）項のいずれかに記載の可逆性多色感熱記録媒体を用いた記録方法であって、全面を発色させた後、画像情報に応じて選択された波長の光を照射して露光し、記録層の特定領域を消色させて、画像表示を行なうことを特徴とする記録方法」

In the formula, X ₁ and X ₂ represent a direct bond or a divalent group consisting of —NH—, —CO—, —O—, —SO ₂ —, —S—. However, X ₁ and X ₂ are not simultaneously direct bonds. R ₁ represents a divalent hydrocarbon group having 1 to 22 carbon atoms, and R ₂ represents a hydrocarbon group having 8 to 30 carbon atoms. P represents an integer of 0 to 4, and when p is 2 to 4, R ₁ and X _{2 that} are repeated may be the same or different. When p is 0, X ₁ is not a direct bond. Furthermore, q represents an integer from 1 to 3. "
(5) “A recording method using the reversible multicolor thermosensitive recording medium according to any one of (1) to (4), wherein light having a wavelength selected according to image information is emitted. A recording method characterized by performing image display by irradiating and exposing to color a specific area of the recording layer "
(6) “A recording method using the reversible multicolor thermosensitive recording medium according to any one of (1) to (4), wherein the entire surface is colored, and then in accordance with image information. A recording method characterized by irradiating with light of a selected wavelength and exposing, decoloring a specific area of the recording layer, and displaying an image "

  Here, zinc oxide is an organic substance such as a leuco dye, a developer and a polymer used in the recording layer, and an inorganic filler such as silica, talc and calcium carbonate added to this type of recording material. The heat conductivity is high, and the addition to the recording layer improves the heat conduction in the layer, and is expected to reduce the heating temperature unevenness. However, when conventionally known zinc oxide is added to the recording layer, it is difficult to uniformly add zinc oxide into the recording layer because the particle size is as coarse as several microns, Due to the distribution of zinc oxide particles, uneven temperature distribution may occur, resulting in poor erasure, or the color density of the recording layer may be reduced by light scattering by the zinc oxide particles, or the recording layer itself may be colored. .

In the present invention, by using zinc oxide fine particles having a particle diameter of 10 to 100 nm, the zinc oxide fine particles become substantially transparent in the visible region, and there is no adverse effect on the decrease in image density as described above. It has been found that, by miniaturization, the recording layer can be uniformly added, and the temperature distribution in the layer becomes uniform.
On the other hand, when the particle size is less than 10 nm, it is found that there is a problem that stable dispersion is difficult because the particles are easily aggregated. Therefore, in the present invention, the zinc oxide fine particles have a particle size of 10 nm to 100 nm. Are preferably used, and more preferably 10 nm to 70 nm.
When zinc oxide fine particles exceeding 100 nm are used, light scattering occurs in the recording layer and the color density is lowered. On the other hand, when the particle size is less than 10 nm, the stability of the primary particles is poor, and there is a possibility of causing light scattering as in the case of coarse particles in an aggregated state.
Furthermore, in the case of such coarse particles (including the case where the particles become agglomerated as a result of aggregation), a high density part and a low density part are formed without being uniformly contained in the recording layer. It is considered that the diffusion of the color becomes non-uniform and adversely affects color development / decoloration.

  The addition amount of the zinc oxide fine particles used in the present invention is preferably 5 to 40% by weight in the recording layer, and if it is less than 5%, the effect of improving erasability is not seen, and more than 40%. In such a case, problems such as a decrease in the strength of the recording layer occur.

  From the following detailed and specific description, the reversible multicolor thermosensitive recording medium of the present invention reversibly develops color and emits light at an arbitrary place by irradiating light (including infrared rays) of a specific wavelength selected. It can be seen that the material can be erased and has excellent color development and decoloring characteristics that can be erased by light irradiation even during rewriting.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. However, the reversible multicolor recording medium of the present invention is not limited to the following examples.
FIG. 1 shows a reversible multicolor recording medium according to a first example of the present invention. In this reversible multicolor recording medium (1), a recording layer (11) and a colored layer (12) having repeating units divided into three primary colors of light are sequentially laminated on a support (10). It has the structure by which the protective layer (13) was formed in the uppermost layer.

  As the support (10), a conventionally known material used for this type of recording material can be used. For example, a white polyester film is preferably used.

The recording layer (11) contains fine zinc oxide particles, a leuco dye, a reversible developer compound, and a resin. In addition, the recording layer has a color disappearance for improving the color stability and the decoloring speed. A color control agent or the like may be added.
Further, the leuco dye used in the recording layer is a leuco dye that develops a black color, which is used alone or in combination, and is a known dye precursor such as a phthalide compound, an azaphthalide compound, or a fluorane compound. Examples of these compounds include black leuco dyes described in JP-A-5-124360, JP-A-6-210594, JP-A-10-230680, and the like.

  In the present invention, a phenol compound having an aliphatic group having 8 or more carbon atoms represented by the following formula (1) is particularly preferably used as the developer.

式中、Ｘ_１及びＸ_２は直接結合手、または−ＮＨ−，−ＣＯ−，−Ｏ−，−ＳＯ_２−，−Ｓ−からなる２価の基を示す。ただし、Ｘ_１及びＸ_２は同時に直接結合手であることはない。Ｒ_１は炭素数１から２２の２価の炭化水素基を表わし、Ｒ_２は炭素数８から３０の炭化水素基を表わす。また、ｐは０から４の整数を表わし、ｐが２から４のとき繰り返されるＲ_１およびＸ_２は同一でも異なっていても良い。また、ｐが０のときＸ_１は直接結合手ではない。さらに、ｑは１から３の整数を表わす。

In the formula, X ₁ and X ₂ represent a direct bond or a divalent group consisting of —NH—, —CO—, —O—, —SO ₂ —, —S—. However, X ₁ and X ₂ are not simultaneously direct bonds. R ₁ represents a divalent hydrocarbon group having 1 to 22 carbon atoms, and R ₂ represents a hydrocarbon group having 8 to 30 carbon atoms. P represents an integer of 0 to 4, and when p is 2 to 4, R ₁ and X _{2 that} are repeated may be the same or different. When p is 0, X ₁ is not a direct bond. Furthermore, q represents an integer of 1 to 3.

Specifically, R ₁ and R ₂ represent an optionally substituted hydrocarbon group, which may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and is composed of both of them. It may be a hydrocarbon group. The aliphatic hydrocarbon group may be linear or branched and may have an unsaturated bond. Examples of the substituent attached to the hydrocarbon group include a hydroxyl group, a halogen, and an alkoxy group. R ₁ may be a direct bond.

Since the carbons of R ₂ is a 7 or less lowers the stability and color erasing of color, the number of carbon atoms is preferably 8 or more, more preferably 11 or more. X ₁ and X ₂ each represent a divalent group containing a direct bond or a hetero atom, and preferably represents a divalent group having at least one group represented below.

その具体例としては、以下に示すものが挙げられる。

Specific examples thereof include those shown below.

  Specific examples of the phenol compound in the present invention are listed below, but the present invention is not limited to these. Moreover, a phenol compound can also be used individually or in mixture.

（式中のｒ，ｓは前記のＲ_１およびＲ_２の炭素数を満足する整数を表わす。）

(R and s in the formula represent integers satisfying the carbon number of R ₁ and R ₂ described above.)

  Besides these, for example, JP-A-5-124360, JP-A-6-210554, JP-A-10-95175, JP-A-9-290563, JP-A-11-188969, Developers described in, for example, Kaihei 11-99749 can be used.

Hereinafter, the coloring and decoloring of the recording layer will be described.
This recording layer can form a relatively colored state and a decolored state depending on the heating temperature and / or the cooling rate after heating. This basic coloring / decoloring phenomenon will be described.
FIG. 3 shows the relationship between the color density of this recording medium and the temperature. When the temperature of the recording medium initially in the decolored state (A) is raised, the leuco dye and the developer are melted and mixed at the temperature (T ₁ ) at which melting begins, and color development occurs and the molten color state (B) is obtained. . When rapidly cooled from the melt color state (B), the color state can be lowered to room temperature and a fixed color state (C) is obtained. Whether or not this color development state is obtained depends on the rate of temperature decrease from the molten state, and in slow cooling, the color disappears during the temperature decrease, and the same color disappearance state (A) or rapid color development state (C ) A relatively low concentration state is formed. On the other hand, when the rapid color development state (C) is raised again, decoloration occurs at a temperature (T ₂ ) lower than the color development temperature (D to E). Return. The actual color developing temperature and color erasing temperature vary depending on the combination of the developer and color former used, and can be selected according to the purpose. Further, the density of the melt coloring state and the coloring density when rapidly cooled are not necessarily the same and may be different.

  In the recording medium of the present invention, the color development state (C) obtained by quenching from the molten state is a state in which the developer and the color former are mixed in a state where they can contact each other and form a solid state. Often doing. This state is a state where the developer and the color former are aggregated to maintain the color development, and it is considered that the color development is stabilized by the formation of this aggregated structure. On the other hand, the decolored state is a state in which both phases are separated. This state is a state in which molecules of at least one compound aggregate to form a domain or crystallize, and the color former and developer are separated and stabilized by aggregation or crystallization. It is done. In many cases, in the present invention, more complete color erasure occurs due to phase separation of the two and crystallization of the developer. In both the decolorization by slow cooling from the melted state and the decolorization by raising the temperature from the colored state shown in FIG. 3, the aggregation structure changes at this temperature, and phase separation and crystallization of the developer occur.

  Further, as the resin used in the recording layer, a resin in a crosslinked state is preferably used. Specifically, an acrylic polyol resin, a polyester polyol resin, a polyurethane polyol resin, a phenoxy resin, a polyvinyl butyral resin, a cellulose acetate propionate, Examples thereof include resins having a group that reacts with a crosslinking agent such as cellulose acetate butyrate, or resins obtained by copolymerizing a monomer having a group that reacts with a crosslinking agent and other monomers, but the present invention is limited to these compounds. It is not something.

  Further, in the present invention, an acrylic polyol resin is preferably used because the coloration stability is particularly good and the decoloring property is good. The hydroxyl value is 70 (KOHmg / g) or more, and particularly preferably 90 (KOHmg / g) or more. Moreover, as a hardening | curing agent, conventionally well-known isocyanates, amines, phenols, an epoxy compound, etc. are mentioned. Of these, isocyanate curing agents are preferably used. In addition to these crosslinkable resins, conventionally known thermoplastic resins can also be used. Examples thereof include polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, ethyl cellulose, polystyrene, styrene copolymer, Phenoxy resin, polyester, aromatic polyester, polyurethane, polycarbonate, polyacrylic acid ester, polymethacrylic acid ester, acrylic acid copolymer, maleic acid polymer, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, carboxymethyl cellulose, starch Etc.

  The recording layer (11) can be formed by applying a coating material prepared by dispersing materials such as the zinc oxide fine particles, leuco dye, and developer in the resin using a solvent.

  It is assumed that the colored layer (12) has repeating units divided into three primary colors of light, and these three primary colors (RGB) are painted with fine dots that are invisible. This colored layer (12) can be formed by photolithography or a printing method usually used for liquid crystal displays. As the coloring material, in the pigment system, it represents red (R), diaminoanthraquinonyl, dibavirturoisoindoline, green (G), nanobromidodrichlorocopper phthalocyanine, dibavirulu isoindoline, An example of blue (B) is copper phthalocyanine. The color material is not limited to these, and various color materials used in the fields of ink, paint, printing, and printer can be applied.

  The unit of the pixels constituting the colored layer (12), that is, the size of the image dot, is appropriately adjusted to a size that cannot be visually recognized according to the viewing distance of the user of the reversible multicolor recording medium (1). . Further, it is assumed that the portion of the colored layer (12) divided into the three primary colors contains a photothermal conversion material that generates heat by absorbing light of different wavelengths (λ1, λ2, and λ3 in FIG. 1). As this photothermal conversion material, a phthalocyanine dye, a cyanine dye, a metal complex dye, a diimmonium dye or the like generally used as an infrared absorbing dye having no absorption peak in the visible region can be applied.

  The protective layer (13) can be formed using a conventionally known ultraviolet curable resin or thermosetting resin, and has a film thickness of about 0.1 to 20 μm, more preferably about 0.5 to 5 μm.

Next, another example of the reversible multicolor recording medium of the present invention will be described with reference to FIG.
In the reversible multicolor recording medium (2) in this example, a recording layer (11), a heat insulating layer (14), a colored layer (12), and a protective layer (13) are sequentially laminated on a support (10). It shall have the composition.

  The support (10), recording layer (11), colored layer (12) and protective layer (13) are the same as in the first example.

  The heat insulating layer (14) is formed using a material that transmits visible light. The heat insulating layer is preferably a transparent layer so as not to shield the recording layer on the lower side, and examples thereof include a thermosetting resin and a thermoplastic resin used in the recording layer. The required thickness of the heat insulating layer varies depending on the thermal conductivity of the material constituting the layer, but is preferably about 3 to 50 μm.

Next, a recording method for the recording medium will be described.
A light beam having a selected wavelength and output, for example, infrared light is irradiated to an arbitrary location of the recording medium described above by a semiconductor laser or the like.
The red (R), green (G), and blue (B) regions in the colored layer (12) contain photothermal conversion materials that absorb light of wavelengths λ1, λ2, and λ3, respectively.
As a first method, recording on a recording medium includes a method in which a colorless recording layer is colored according to image information.
For example, by irradiating light having a wavelength of λ1, the photothermal conversion material in the red portion generates heat, and the recording layer is colored black. Thereby, a cyan image is displayed by photosynthesis of green and blue. Further, by irradiating with light rays of λ1 and λ2, the photothermal conversion layers in the red and green portions are blackened and a blue image is displayed.
For erasing the image, there is a method in which the irradiation of λ1 is performed so that the heat generation of the photothermal conversion material is in the color erasing temperature region, or a method in which the entire surface is uniformly heated to the color erasing temperature region by a ceramic heater or a heat roller. However, decoloring by light irradiation is preferable in view of the complexity of the apparatus.

Next, as a second method, there is a method in which the entire surface of the recording medium is colored and erased according to image information.
After heating to a color development temperature or higher with a ceramic heater or a heat roller, the entire surface is blackened by rapid cooling, and then, for example, a light beam having a wavelength λ1 is irradiated to the extent of heating to the decoloring temperature range, and the red recording layer By decoloring (11), a red image is displayed. Further, the recording layers (11) in the red and green portions are decolored by irradiating light beams of λ1 and λ2. As a result, yellow, which is color-combined with red and green, is displayed.
For erasing the image, the entire surface of the recording layer (11) may be colored black, and there are a method of color development by irradiation with light of a corresponding wavelength, a method of using a ceramic heater or a heat roller, and the like.
At this time, the recording layer is heated to a temperature lower than the recording temperature in advance from the back surface or the like, thereby enabling recording with lower energy.

Next, specific examples of the reversible multicolor recording medium of the present invention will be described. However, the reversible multicolor recording medium of the present invention is not limited to the following examples.
[Example 1]
A reversible multicolor thermosensitive recording medium having a structure in which a recording layer (11), a colored layer (12) and a protective layer (13) were sequentially laminated on a support (10) was produced.

[Preparation of recording layer]
N- (4-hydroxyphenyl) -N'-octadecyl urea 4 parts Acrylic polyol resin (LR503, 50% solid content solution manufactured by Mitsubishi Rayon Co., Ltd.) 12 parts Tetrahydrofuran (THF) 70 parts Average particle size of the above composition using a ball mill It was pulverized and dispersed to a diameter of about 1 μm. To the obtained dispersion, 10 parts of a zinc oxide fine particle dispersion (Sumitomo Osaka Cement Co., Ltd., ZS-303 solid concentration 30%) having a particle size of 30 nm (manufacturer value), 2-anilino-3-methyl-6-dibutylaminofur 1.5 parts of Oran (color tone: black) and 2.5 parts of Coronate HL (Adduct type hexamethylene diisocyanate 75% ethyl acetate solution) manufactured by Nippon Polyurethane were added in order and stirred well to prepare a recording layer coating solution.
The thermosensitive recording layer coating solution having the above composition was applied to white PET having a thickness of 188 μm using a wire bar, dried at 100 ° C. for 2 minutes, and then heated at 60 ° C. for 24 hours to obtain a first film having a thickness of about 8.0 μm. Recording layer (11) was provided.

On the recording layer (11) formed as described above, a colored layer (12) having a film thickness of about 1 μm was formed using photoresists for three color filters of RGB. One stroke has a size of about 500 μm × 166 μm. In addition, the following phthalocyanine-based infrared absorbing dyes were contained in each region of R (red), G (green), and B (blue) constituting the colored layer (12).
Red portion: YKR-1010 (manufactured by Yamamoto Kasei, absorption wavelength peak 687 μm)
Green part: YKR-3071 (manufactured by Yamamoto Kasei, absorption wavelength peak 788 μm)
Blue part: YKR-3070 (manufactured by Yamamoto Kasei, absorption wavelength peak 830 μm)

[Create protection layer]
40% solution of UV-absorbing polymer (UV-G300 manufactured by Nippon Shokubai Co., Ltd.) 10 parts Isocyanate-based crosslinking agent (manufactured by Nippon Polyurethane Co., Ltd., Coronate HX) 1.4 parts Silicone-based acrylic resin (GS-1015 manufactured by Toagosei Co., Ltd.) 0 .5 parts Methyl ethyl ketone 10 parts The above composition was well stirred to prepare a protective layer coating solution.
A protective layer coating solution having the above composition is applied onto the colored layer (12) using a wire bar, dried at 100 ° C. for 2 minutes, and then heated at 60 ° C. for 24 hours to form a protective layer having a thickness of about 3.5 μm The reversible thermosensitive recording medium of the present invention was produced.

  A semiconductor laser having a wavelength of 685 nm and a power of 30 mW was irradiated to an arbitrary place of the reversible multicolor thermosensitive recording medium produced as described above so as to have a spot diameter of 20 μm. The photothermal conversion material generated heat in the red irradiated portion of the colored layer (12), and the adjacent recording layer (11) was colored black. As a result, green and blue of the colored layer (12) were synthesized and displayed, and a cyan image was recorded.

  Next, the same place was irradiated with a semiconductor laser having a wavelength of 784 nm and a power of 30 mW so as to have a spot diameter of 20 μm. Then, the photothermal conversion material generated heat in the green irradiated portion of the colored layer (12), and the adjacent recording layer (11) was colored black. As a result, a blue image was displayed.

Next, a semiconductor laser with a wavelength of 685 nm and a power of 30 mW was irradiated to the same spot so as to have a spot diameter of 150 μm, and a semiconductor laser with a wavelength of 784 nm and a power of 30 mW was irradiated so as to have a spot diameter of 150 μm. The light-to-heat conversion material in the green part generated heat, and the adjacent recording layer (11) was decolored, and the display image was erased. The erased portion was in a uniform state with no erase residue.
When this image display / erasure was repeated, the image was in a good state with no damage to the recording medium, no decrease in image display density, no erasure residue, and the like.

[Example 2]
The entire surface of the reversible multicolor thermosensitive recording medium prepared in Example 1 was heated with a ceramic heater, and then rapidly cooled with a metal roller to develop a color on the entire surface.
An arbitrary place of this recording medium was irradiated with a semiconductor laser having a power of 30 mW and a spot diameter of 150 μm at 784 nm. The photothermal conversion material generated heat in the green irradiated portion of the colored layer (12), and the adjacent recording layer (11) was decolored, so that the green color of the colored layer (12) was displayed. When other arbitrary portions were separately irradiated with wavelengths of 680 nm and 830 nm, respectively, red and blue were displayed, respectively.
In addition, when the same place was sequentially irradiated with wavelengths of 784 nm and 830 nm, green and blue photosynthesized cyan were displayed.
In addition, these images were all uniform with no color mixing for each dot.

Next, when the recorded image portion was irradiated three times at a wavelength of 680 nm, 784 nm, and 830 nm under the conditions of 30 mW and a spot diameter of 20 μm, the photothermal conversion material of the colored layer (12) corresponding to each generated heat, The adjacent recording layer (11) was colored to black and the image was erased.
When the above image display / erasure was repeated, it was in a good state with no damage to the recording medium, a decrease in image display density, and no erasure residue.

[Comparative Example 1]
Except not using the zinc oxide fine particles, a semiconductor laser having a wavelength of 685 nm and a power of 30 mW was irradiated to an arbitrary place produced in the same manner as in Example 1 so as to have a spot diameter of 20 μm. The photothermal conversion material generated heat in the red irradiated portion of the colored layer (12), and the adjacent recording layer (11) was colored black. As a result, green and blue of the colored layer (12) were synthesized and displayed, and a cyan image was recorded.

  Next, the same place was irradiated with a semiconductor laser having a wavelength of 784 nm and a power of 30 mW so as to have a spot diameter of 20 μm. Then, the photothermal conversion material generated heat in the green irradiated portion of the colored layer (12), and the adjacent recording layer (11) was colored black. As a result, a blue image was displayed.

Next, the same part was irradiated with a semiconductor laser with a wavelength of 685 nm and a power of 30 mW so as to have a spot diameter of 150 μm, and further irradiated with a semiconductor laser with a wavelength of 784 nm and a power of 30 mW so as to have a spot diameter of 150 μm. The green portion of the photothermal conversion material generated heat, causing the adjacent recording layer (11) to be decolored and the display image to be erased. However, there was uneven erasing residue in the erasing part.
When this image was repeatedly displayed / erased, non-uniform erasure was continuously confirmed.

It is a figure which shows the 1st structural example of the reversible multicolor thermosensitive recording medium of this invention. It is a figure which shows the 2nd structural example of the reversible multicolor thermosensitive recording medium of this invention. It is a figure which shows the color development and decoloring characteristic of the reversible thermosensitive coloring composition used for this invention.

Explanation of symbols

1: reversible multicolor thermosensitive recording medium 2: reversible multicolor thermosensitive recording medium 10: support 11: recording layer 12: colored layer 13: protective layer 14: heat insulating layer

Claims (6)

A reversible that can form a relatively black-colored state and a decolored state on the support using an electron-donating color-forming compound and an electron-accepting compound, depending on the heating temperature and / or the cooling rate after heating. In a reversible thermosensitive recording medium having a heat-sensitive recording layer, the recording layer contains zinc oxide fine particles having a particle diameter of 10 nm or more and 100 nm or less, and further has a repeating unit divided into three primary colors of the recording layer and light Layers are sequentially laminated, and the portion of the colored layer divided into the three primary colors contains a photothermal conversion material that absorbs light of different wavelengths and generates heat. recoding media. The reversible multicolor recording medium according to claim 1, wherein a translucent heat insulating layer is formed between the recording layer and the colored layer. The reversible multicolor recording medium according to claim 1, wherein a protective layer is formed on the outermost surface. 4. The reversible multicolor thermosensitive according to claim 1, wherein the electron accepting compound is a phenol compound having a saturated aliphatic group having 8 or more carbon atoms represented by the following formula (1). recoding media.

In the formula, X ₁ and X ₂ represent a direct bond or a divalent group consisting of —NH—, —CO—, —O—, —SO ₂ —, —S—. However, X ₁ and X ₂ are not simultaneously direct bonds. R ₁ represents a divalent hydrocarbon group having 1 to 22 carbon atoms, and R ₂ represents a hydrocarbon group having 8 to 30 carbon atoms. P represents an integer of 0 to 4, and when p is 2 to 4, R ₁ and X _{2 that} are repeated may be the same or different. When p is 0, X ₁ is not a direct bond. Furthermore, q represents an integer of 1 to 3. A recording method using the reversible multicolor thermosensitive recording medium according to claim 1, wherein the recording layer is exposed by irradiation with light having a wavelength selected according to image information, and a specific area of the recording layer A recording method characterized in that the image is displayed by coloring. A recording method using the reversible multicolor thermosensitive recording medium according to any one of claims 1 to 4, wherein the entire surface is colored and then exposed to light having a wavelength selected according to image information. And displaying the image by erasing a specific area of the recording layer.

Images