JP4879853B2 - Reversible thermosensitive recording medium - Google Patents

Description

  The present invention uses a reversible thermosensitive coloring composition utilizing 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 thermosensitive recording medium, an image processing method using the same, and an image processing apparatus.

  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 development of OA, it is widely used as output paper for facsimiles, word processors, scientific measuring instruments, etc., and recently, as magnetic heat sensitive cards 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, the 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.

Furthermore, when producing a reversible thermosensitive recording medium using these phenolic compounds, a coloring / decoloring control agent aimed at improving decoloring property and improving image stability for enhancing practicality, Accelerators have been studied, and by using the long-chain alkyl compounds described in Patent Documents 15, 16, 17 and the like, the erasability is improved and almost no unerased residue is generated. By using the long-chain alkyl compound, improved color erasability and a stable color image were obtained.
Furthermore, in recent years, there has been an increasing demand for downsizing and energy saving of the rewriting device, thermal head erasing that does not require an erasing heat source other than the thermal head, and thermal head overwrite that performs image recording and erasing in one pass. For example, a recording medium compatible with thermal head rewriting has been required.

  Even when the above-mentioned phenolic compounds, color development / decoloration control agents, and decolorization accelerators are used, decoloration is not sufficient, resulting in unerased residue, or increased unerased during high-speed erasure. There was a problem.

  Further, Patent Document 18 discloses that a thermal control layer that controls heat conduction using inorganic ceramics as a main material is provided above or below the recording layer, thereby widening the decoloring temperature range and improving the decoloring property. Are listed. Although this thermal control layer widened the erasing temperature range by heating the hot stamp, it could not cope with erasing with an extremely short heating time of several milliseconds such as thermal head erasing.

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. 9-48175 Japanese Patent Laid-Open No. 9-290563 Japanese Patent Laid-Open No. 11-70731 JP 2004-255625 A

An object of the present invention is to provide a reversible thermosensitive recording medium excellent in high-speed erasability that can be adapted to thermal head rewriting.
Still another object of the present invention is to provide an image processing method and an image processing apparatus using the reversible thermosensitive recording medium.

In the case of erasing in a very short time of several milliseconds such as thermal head overwriting, the temperature distribution inside the thermal recording layer becomes large depending on the distance from the thermal head and the distance from the center of the heating dot. The erasability may be caused by non-uniform heating, and erasability may be generated, especially by improving the heat conduction inside the thermal recording layer and heating the thermal recording layer uniformly. .
In the specification, the reversible thermosensitive recording layer and the thermosensitive recording layer may be simply referred to as a recording layer.

  As a result of various studies for improving the heat conduction in the recording layer, it was found that the thermal head erasability is improved by improving the heat conductivity on the support side of the recording layer. This is presumably because the heating temperature of the entire recording layer becomes more uniform and the decoloring property is improved by increasing the thermal conductivity of the lower part of the recording layer away from the thermal head.

As a means for increasing the thermal conductivity, there is a method using inorganic particles having high thermal conductivity. However, when these inorganic fine particles are added to the recording layer coating solution and applied and dried, convection occurs in the recording layer solution coated on the support during the drying process, and the inorganic fine particles are relatively As a result of TEM observation, it was found that a large amount was contained on the surface side. Therefore, in the present invention, as a preferable method for producing a recording medium, the recording layer is divided and multi-stage coated, and the heat-sensitive recording layer coating liquid is made to have a high thermal conductivity toward the support side, whereby the support side In addition, a reversible thermosensitive recording medium having a recording layer with high thermal conductivity is provided. The number of divisions of the recording layer produced by multi-stage coating is not particularly limited, but about 2 to 4 layers are preferable from the viewpoint of productivity.
Furthermore, in the present invention, it has been found that the erasability is further improved by providing an under layer containing a hollow filler between the recording layer and the support.

  This is because the lower part of the recording layer contains, for example, zinc oxide ultrafine particles with high density and high density, so that it is good to the lower part of the recording layer that could not be heated sufficiently by heating in a short time such as thermal head heating. It is considered that heat conduction is achieved and the decoloring property is improved.

That is, the said subject is solved by following (1)-(10) of this invention.
(1) “Using an electron-donating color-forming compound and an electron-accepting compound on a support, a relatively colored state and a decolored state depending on the difference in heating temperature and / or cooling rate after heating. A reversible thermosensitive recording medium having a reversible thermosensitive recording layer that can be formed, wherein the thermosensitive recording layer on the support side has higher thermal conductivity than the thermosensitive recording layer on the display surface side;
(2) “The heat-sensitive recording layer has a multi-layered structure formed by multi-step coating, and each heat-sensitive recording layer has high thermal conductivity from the display surface side toward the support side. Reversible thermosensitive recording medium according to (1) ";
(3) “Reversible thermosensitive recording medium according to (1) or (2) above, wherein an under layer containing hollow particles is provided between the support and the thermosensitive recording layer”;
(4) In any one of (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): The reversible thermosensitive recording medium described.

（式中、Ｘ_１及びＸ_２は直接結合手または−ＮＨ−、−ＣＯ−、−Ｏ−、−ＳＯ_２−、−Ｓ−から選ばれる２価の基、或いはこれら２価の基を２個以上組み合わせた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１〜２２の２価の炭化水素基を表わし、Ｒ_２は炭素数８〜３０の炭化水素基を表わす。また、ｐは０〜４の整数を表わし、ｐが２〜４のとき繰り返されるＲ_１およびＸ_２は同一でも、異なっていてもよい。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１〜３の整数を表わす。）」；
（５）「情報記憶部を設けたことを特徴とする前記（１）乃至（４）のいずれかに記載の可逆性感熱記録媒体」；
（６）「記録媒体の表示面もしくは裏面の少なくとも１つに、接着剤層又は粘着剤層を設けたことを特徴とする前記（１）乃至（５）のいずれかに記載の可逆性感熱記録媒体」；
（７）「前記（１）乃至（６）のいずれかに記載の可逆性感熱記録媒体を用いて、画像の形成及び／又は消去を行なうことを特徴とする画像処理方法」；
（８）「サーマルヘッドを用いて前記可逆性感熱記録媒体の表示部に画像を形成することを特徴とする前記（７）に記載の画像処理方法」；
（９）「サーマルヘッドを用いて画像を消去することを特徴とする前記（７）に記載の画像処理方法」；
（１０）「前記（８）又は（９）の少なくともいずれか１項に記載の画像処理方法により、画像の形成及び／又は消去を行なうことを特徴とする画像処理装置」。

(In the formula, X ₁ and X ₂ represent a direct bond or a divalent group selected from —NH—, —CO—, —O—, —SO ₂ —, and —S—, or 2 of these divalent groups. A divalent group in combination of two or more, wherein X ₁ and X ₂ are not directly a direct bond, R ₁ represents a divalent hydrocarbon group having 1 to 22 carbon atoms, and R ₂ represents Represents a hydrocarbon group having 8 to 30 carbon atoms, p represents an integer of 0 to 4, and R ₁ and X ₂ repeated when p is 2 to 4 may be the same or different. when p is 0, X ₁ is not a direct bond, and q represents an integer of 1 to 3) ";
(5) “Reversible thermosensitive recording medium according to any one of (1) to (4) above, wherein an information storage unit is provided”;
(6) “Reversible thermosensitive recording according to any one of (1) to (5) above, wherein an adhesive layer or a pressure-sensitive adhesive layer is provided on at least one of the display surface and the back surface of the recording medium. Medium ";
(7) “An image processing method comprising forming and / or erasing an image using the reversible thermosensitive recording medium according to any one of (1) to (6)”;
(8) “The image processing method according to (7), wherein an image is formed on a display unit of the reversible thermosensitive recording medium using a thermal head”;
(9) “The image processing method according to (7), wherein the image is erased using a thermal head”;
(10) “An image processing apparatus that forms and / or erases an image by the image processing method according to at least one of (8) and (9)”.

The reversible thermosensitive recording medium of the present invention has good color development sensitivity and image density, and is highly practical with excellent thermal head erasability.
The image processing method and the image processing apparatus using the reversible thermosensitive recording medium of the present invention can form an image having a good image density and excellent thermal head erasability.

In the present invention, as a method for increasing the thermal conductivity, there is a method using high thermal conductive inorganic fine particles such as alumina, zinc oxide, boron nitride, silicon nitride, aluminum nitride. Among these highly heat conductive inorganic fine particles, particularly preferable results are obtained with ultrafine zinc oxide particles. Further, as a method for increasing the thermal conductivity on the support side relative to the surface side of the heat sensitive layer, there is a method such as laminating a recording layer in which the content of the high thermal conductive fine particles is changed.
Preferred thermal conductivity of the highly thermally conductive inorganic particles used in the present invention is preferably not more ^{20Wm -1 K} -1 or higher, and more preferably is ^{30Wm -1 K} -1 or higher. The upper limit of the preferred range is not particularly limited, but the material having a high thermal conductivity exceeding 500 Wm ⁻¹ K ⁻¹ is limited to diamond or the like, and its practicality is low. Therefore, the preferred thermal conductivity range is 20 to 500 Wm ⁻¹ K. ⁻¹ , more preferably 30 to 500 Wm ⁻¹ K ⁻¹ .
Here, for example, the thermal conductivity (Wm ⁻¹ K ⁻¹ ) of the high thermal conductive inorganic fine particles used in the present invention is 20 to 40 for alumina, 54 for zinc oxide, 60 for boron nitride, and 30 to 90 for silicon nitride. Aluminum nitride 70-270.
In the following, a case where zinc oxide is used as the highly thermally conductive inorganic fine particles will be described as an example.

  Zinc oxide has a higher thermal conductivity than organic substances such as leuco dyes, developers and polymers used in the recording layer, and inorganic fillers such as silica, talc and calcium carbonate added to this type of recording material. The heat conduction in the layer is improved by the addition to the recording layer, and it 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. .

Therefore, in the present invention, by using zinc oxide fine particles having a particle diameter of preferably 10 to 100 nm, the zinc oxide fine particles become substantially transparent in the visible region, and the above-described adverse effect on the decrease in image density is eliminated. Further, the finer particles are more uniformly distributed, and the temperature distribution unevenness in the recording layer is reduced.
On the other hand, when the particle size is less than 10 nm, aggregation tends to occur, so that there is a problem that stable dispersion becomes difficult. Therefore, in the present invention, zinc oxide fine particles having a particle diameter of 10 to 100 nm are preferably used, and those having a particle diameter of 10 to 70 nm are more preferably used.

The addition amount of the high thermal conductive inorganic 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% by weight, the effect of improving erasability is small, and more than 40% by weight. In the case where the amount is too large, the strength of the recording layer may be reduced, and problems such as deformation of the recording medium and reduction in image density may occur during repeated use.
In addition, when zinc oxide fine particles are added to the recording layer coating liquid as described above, and coated and dried, the zinc oxide fine particles are recorded by the convection phenomenon of the solvent in the recording layer coating liquid during the drying process. It moves to the upper part of the layer and is distributed at a higher density than the lower part of the recording layer. This is confirmed by TEM (transmission electron microscope) observation of the recording layer cross section.

That is, when the zinc oxide fine particles are added to the recording layer coating solution and applied and dried as in the conventional known recording layer production method, the content of zinc oxide fine particles at the bottom of the recording layer of the present invention is It is not relatively higher than the upper part. Therefore, in the present invention, as a preferable method for producing a recording medium, the recording layer is divided and subjected to multi-stage coating, and the recording layer coating solution on the support side has a high thermal conductivity, whereby heat conduction is performed on the support side. A reversible thermosensitive recording medium having a highly recording layer is provided.
In addition, when zinc oxide fine particles are contained in the recording layer, the recording layer may be colored due to the interaction with the leuco dye in the recording layer, and in particular, the tendency of coloring during dispersion by a paint shaker or a ball mill. Is seen.

This is considered to be due to the surface activity of the refined zinc oxide particles. As a method for reducing the surface activity of the zinc oxide fine particles, it is preferable to carry out a surface treatment, and as a modification method, modification by coating, topological modification, modification by microencapsulation, modification by precipitation reaction, etc. There is. Among these, those whose surface has been modified with an alumina, titanium-based or zirconia-based compound are particularly preferably used.
The above is the same for not only zinc oxide particles but also other highly thermally conductive inorganic particles.

Furthermore, in the present invention, an under layer containing hollow particles is provided on the support, a reversible thermosensitive recording layer is provided on the under layer, and a protective layer or the like is further formed on the thermosensitive recording layer as necessary. A reversible thermosensitive recording medium is provided.
At this time, by using an under layer containing hollow particles, it is possible to prevent diffusion of heat to the support and the like, and heat from the thermal head can be used with high efficiency.
In the present invention, extremely good erasability is exhibited by the uniformization of the temperature in the recording layer by the zinc oxide fine particles used in the recording layer and the heat insulating effect of the under layer.

Here, the under layer used in the present invention will be described.
The hollow particles to be contained in the under layer are those obtained by microencapsulating a low boiling point liquid such as butane or pentane with a polymer or copolymer such as polyvinylidene chloride, polyacrylonitrile, or polymethyl methacrylate. Pre-foamed hollow particles and non-foamed hollow particles are added, but when added in an unfoamed state and foamed by heat during reversible thermosensitive recording medium production or printing, uniform foaming is difficult and the image quality is poor. A better image quality can be obtained by adding foamed hollow particles.

The hollow particles preferably have a particle size of 0.2 to 50 μm, and if it is less than 0.2 μm, it is difficult to obtain sufficient cushioning properties and heat insulation properties. On the other hand, when the thickness exceeds 50 μm, the smoothness of the coating film is lowered, and the uniform cushioning property is impaired, and image omission and non-uniform erasure are likely to occur.
Further, the volume hollowness of the hollow particles is preferably 50% or more, and if the volume hollowness is lower than this, sufficient cushioning properties and heat insulation properties are difficult to obtain. Moreover, the thing with a hollow rate of 70%-95% is especially preferable.
The hollow ratio is a volume ratio calculated from the specific gravity, and is represented by the following formula.
Hollow ratio (%) = [1-1 / (A / B)] × 100
(Where, A = specific gravity of shell material, B = true specific gravity of hollow particles)
Moreover, since hollow particles have a small specific gravity and are difficult to handle in operation, hollow particles having a high specific gravity coated with an inorganic pigment may be used. Inorganic pigments for coating the hollow particles include calcium carbonate, talc, and titanium oxide, and those in which these are coated on the hollow particles by heat fusion or the like can be used.

  Further, the thickness of the partition walls of the hollow particles is preferably 0.05 to 3 μm. When the thickness is less than 0.05 μm, the strength of the particles is low, and the hollow particles are destroyed when printing / erasing is repeated, and cushioning properties and heat insulation properties are reduced. On the other hand, when the thickness is larger than 3 μm, the particles become hard, so that the cushioning property is lowered or the heat insulating property is lowered, which is not preferable.

The present invention is described in detail below.
The reversible thermosensitive recording medium of the present invention 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. 1 shows the relationship between the color density and temperature of this reversible thermosensitive recording medium. Introduction gradually heated the recording medium in the decolored state (A), leuco dye and the developer are mixed melt at temperatures T ₁ begins to melt, coloring occurs a molten color developed state (B). 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, rapidly cooled colored state (C) is again raised gradually and discoloring occurs at a lower temperature T ₂ than the coloring temperature (E from D), returns the beginning when the temperature decreases from here to the same decolored state (A). 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 reversible thermosensitive recording medium of the present invention, the colored state (C) obtained by quenching from the molten state is a state in which the developer and the color former (leuco dye) are mixed in a state where they can be contacted with each other. This often forms a solid state. 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 decoloring by slow cooling from the molten state and the decoloring by raising the temperature from the colored state shown in FIG. 1, the aggregation structure changes at this temperature, and phase separation and crystallization of the developer occur.

  As the leuco dye used in the reversible thermosensitive recording layer, one or more compounds commonly used in this type of reversible thermosensitive recording medium can be used. For example, phthalide compounds, azaphthalide compounds, fluorane compounds It is a known dye precursor. Examples of these compounds are leuco dyes described in JP-A-5-124360, JP-A-6-210594, JP-A-10-230680 and the like.

  Of these, particularly preferred examples include 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-di (n-butylamino) fluorane, 2-anilino-3-methyl-6. -(Nn-propyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-isopropyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N- Isobutyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-ethyl-p-) Toluidino) fluoran, 3- (1-ethyl-2-methylindol-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -4-azaphthalide, 3- ( - ethyl-2-methylindole-3-yl) -3- (2-ethoxy-4-diethylaminophenyl) -7-azaphthalide, 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−から選ばれる２価の基、或いはこれら２価の基を２個以上組み合わせた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１〜２２の２価の炭化水素基を表わし、Ｒ_２は炭素数８〜３０の炭化水素基を表わす。また、ｐは０〜４の整数を表わし、ｐが２〜４のとき繰り返されるＲ_１およびＸ_２は同一でも、異なっていてもよい。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１〜３の整数を表わす。）

(In the formula, X ₁ and X ₂ represent a direct bond or a divalent group selected from —NH—, —CO—, —O—, —SO ₂ —, and —S—, or 2 of these divalent groups. A divalent group in combination of two or more, wherein X ₁ and X ₂ are not directly a direct bond, R ₁ represents a divalent hydrocarbon group having 1 to 22 carbon atoms, and R ₂ represents Represents a hydrocarbon group having 8 to 30 carbon atoms, p represents an integer of 0 to 4, and R ₁ and X ₂ repeated when p is 2 to 4 may be the same or different. when p is 0, _{X 1} is not a direct bond. further, q is an integer of 1-3.)

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 has 1 to 22 carbon atoms, and if the carbon number exceeds 22, it becomes difficult to obtain raw materials and it is difficult to synthesize, which is not preferable.

The carbon number of R ₂ is 8 to 30, and when the carbon number is 7 or less, the stability of color development and decoloring properties are lowered. Therefore, the carbon number is preferably 8 or more, and more preferably 11 or more. When the number of carbon atoms exceeds 30, it is difficult to obtain raw materials and it is difficult to synthesize, which is not preferable.
X ₁ and X ₂ represent a direct bond or a divalent group containing a hetero atom shown in Table 1 below,

  Preferably, it represents a divalent group having at least one group represented by Table 1. Specific examples thereof include the following.

  Specific examples of the phenol compound in the present invention are listed below, but the present invention is not limited thereto. 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）等が挙げられる。

(Wherein, r and s represent integers satisfying the carbon number of R ₁ and R ₂ described above).

  In addition to 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.

  In the present invention, as the resin for forming the reversible thermosensitive recording layer, a resin in a crosslinked state is preferably used. Specifically, acrylic polyol resin, polyester polyol resin, polyurethane polyol resin, phenoxy resin, polyvinyl butyral resin, cellulose acetate Resin having a group that reacts with a cross-linking agent such as propionate and cellulose acetate butyrate, or a resin obtained by copolymerizing a monomer having a group that reacts with a cross-linking agent and other monomers, and the like. It is not limited to compounds.

  Further, in the present invention, a resin having a hydroxyl value of 70 (KOHmg / g) or more is preferably contained (initially used). Examples of the resin having a hydroxyl value of 70 (KOHmg / g) or more include acrylic polyol resins and polyester polyols. Resins, polyurethane polyol resins, and the like are used, and acrylic polyol resins are preferably used because they have particularly good color stability and good decoloring properties. The hydroxyl value is 70 (KOHmg / g) or more, particularly preferably 90 (KOHmg / g) or more. The magnitude of the hydroxyl value affects the crosslink density and thus affects the chemical resistance and physical properties of the coating film. The inventors of the present invention are particularly preferably used because the hydroxyl value is 70 (KOHmg / g) or more and durability, coating film surface hardness and crack resistance are improved.

  In addition, acrylic polyol resins have different characteristics depending on the structure. Hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate ( HPMA), 2-hydroxybutyl monoacrylate (2-HBA), 1,4-hydroxybutyl monoacrylate (1-HBA), etc. are used, but it is particularly preferable to use a monomer having a primary hydroxyl group. Since the crack resistance and durability are good, 2-hydroxyethyl methacrylate is preferably used.

  Examples of the crosslinking agent used in the present invention include conventionally known isocyanates, amines, phenols, epoxy compounds and the like. Among these, an isocyanate type crosslinking agent is preferably used. The isocyanate compound used here is selected from known modified urethane monomers, allophanate-modified, isocyanurate-modified, burette-modified, carbodiimide-modified, blocked isocyanate and the like. The isocyanate monomer that forms the modified product includes tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), naphthylene diisocyanate NDI), paraphenylene diisocyanate (PPDI). ), Tetramethylxylylene diisocyanate (TMXDI), hexamethylene diisocyanate (HDI), dicyclohexylmethane diisocyanate (HMDI), isophorone diisocyanate (IPDI), lysine diisocyanate (LDI), isopropylidenebis (4-cyclohexylisocyanate) (IPC) Cyclohexyl diisocyanate (CHDI), tolidine diisocyanate (TODI), and the like. However, the present invention is not limited to these compounds.

  Furthermore, you may use the catalyst used for this kind of reaction as a crosslinking accelerator. Examples of the crosslinking accelerator include tertiary amines such as 1,4-diaza-bicyclo [2,2,2] octane, and metal compounds such as organic tin compounds. The total amount of the crosslinking agent added may or may not undergo a crosslinking reaction.

  That is, an unreacted curing agent may be present. Since this type of crosslinking reaction proceeds over time, the presence of an unreacted curing agent does not indicate that the crosslinking reaction has progressed at all, but an unreacted curing agent is detected. However, this does not mean that there is no resin in a crosslinked state. Further, as a method for distinguishing whether the polymer in the present invention is in a crosslinked state or in a non-crosslinked state, it can be distinguished by immersing the coating film in a highly soluble solvent. That is, since the polymer in the non-crosslinked state dissolves in the solvent and does not remain in the solute, the presence or absence of the polymer structure of the solute may be analyzed.

  Furthermore, according to the present invention, the recording layer contains a color development / decoloration control agent having a linear hydrocarbon group, a hydrogen bond group such as an amide group or a urea group, and the like together with the developer and the leuco dye. As a result, the storage stability of the color image is good, and the erasability at the time of erasing is also improved to obtain good erasability.

Further, according to the present invention, an intermediate layer can be provided between the recording layer and the protective layer in order to improve adhesion.
As the resin used for the intermediate layer, conventionally known thermoplastic resins and thermosetting resins are widely used, and examples thereof include polyester resins and polyurethane resins.
Furthermore, according to the present invention, a protective layer containing a resin in a crosslinked state can be provided on the reversible thermosensitive recording layer. As the resin used for the protective layer, the same thermosetting resin, ultraviolet curable resin, electron beam curable resin and the like as those of the recording layer described above are used.
As the resin used in the protective layer, an ultraviolet absorbing polymer having an ultraviolet absorbing group in the molecular structure is particularly preferably used.
As the ultraviolet absorbing polymer, a monomer having an ultraviolet absorbing group and a polymer having a monomer having a crosslinkable functional group are preferably used. As the monomer having an ultraviolet absorbing group, (2 '-Hydroxy-5'-methacryloxyethylphenyl) -2H-benzotriazole, 2- (2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3'-ω-butyl- A monomer having a benzotriazole skeleton such as 5′-methylphenyl) -5-chlorobenzotriazole is particularly preferably used.

  Examples of the monomer containing a functional group include 2-isopropenyl-2-oxazoline, 2-aziridinylethyl (meth) acrylate, methacrylic acid, glycidyl (meth) acrylate, hydroxylethyl (meth) acrylate, hydroxyl Propyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, and the like, among them, hydroxylethyl (meth) ) Acrylate, hydroxylpropyl (meth) acrylate and the like are particularly preferably used.

  Furthermore, in order to increase the strength of the coating film and improve heat resistance, the following monomers may be copolymerized with a copolymer of a monomer containing an ultraviolet absorbing group and a monomer containing a functional group. For example, monomer groups such as styrene, styrene-butadiene, styrene-isobutylene, ethylene vinyl acetate, vinyl acetate, methacrylonitrile, vinyl alcohol, vinyl pyrrolidone, acrylonitrile, methacrylonitrile; acrylic acid, methyl (meth) acrylate, ethyl (meth ) Acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, ethylhexyl (meth) acrylate, octyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) ) Acrylate, lauryl tridecyl (meth) acrylate, tridecyl (meth) acrylate, cetyl stearyl (meth) acrylate, stearyl (meth) acrylate (Meth) acrylic acid ester groups not containing functional groups such as cyclohexyl (meth) acrylate and benzyl (meth) acrylate; ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene Glycol di (meth) acrylate, decaethylene glycol di (meth) acrylate, pentacontahector ethylene glycol (meth) acrylate, butylene di (meth) acrylate, pentaerythritol tetra (meth) acrylate, trimethylolpropane tri (meth) acrylate, penta Decaethylene glycol di (meth) acrylate, phthalic acid diethylene glycol di (meth) acrylate, etc. have two or more polymerizable double bonds in one molecule Although it is mentioned from a monomer group etc., it is not particularly limited, among them, styrene, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, Particularly preferred is t-butyl (meth) acrylate. Moreover, 2 or more types can also be used together as needed.

  From the above, specific preferred examples of the polymer having an ultraviolet absorption structure used in the present invention include 2- (2′-hydroxy-5′-methacryloxyethylphenyl) -2H-benzotriazole and 2-hydroxy methacrylate. Examples include a copolymer composed of ethyl and styrene, and a copolymer composed of 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2-hydroxypropyl methacrylate and methyl methacrylate. Is not to be done.

Furthermore, according to the present invention, the protective layer can contain inorganic fine particles having ultraviolet absorbing ability.
The inorganic pigment used in the present invention is arbitrary as long as it has an average particle size of 0.1 μm or less. Examples of such inorganic pigments include zinc oxide, indium oxide, alumina, silica, zirconium oxide, tin oxide, cerium oxide, iron oxide, antimony oxide, barium oxide, calcium oxide, bismuth oxide, nickel oxide, magnesium oxide, chromium oxide, Manganese oxide, tantalum oxide, niobium oxide, thorium oxide, hafnium oxide, molybdenum oxide, iron ferrite, nickel ferrite, cobalt ferrite, barium titanate, metal oxides such as potassium titanate and complex oxides thereof, zinc sulfide, Metal sulfides such as barium sulfate or sulfate compounds, titanium carbide, silicon carbide, molybdenum carbide, tungsten carbide, metal carbides such as tantalum carbide, aluminum nitride, silicon nitride, boron nitride, nitride Rukoniumu, vanadium nitride, titanium nitride, niobium nitride, and metal nitrides such as gallium nitride.
Among these, a pigment having an absorption edge in a wavelength region of 400 nm or less is particularly preferable.

  Such a pigment includes a pigment (A) having an absorption edge in the ultraviolet UV-A region, that is, an ultraviolet UV-A region having a wavelength of 320 to 400 nm, and an inorganic pigment having an absorption edge on the shorter wavelength side than the ultraviolet UV-A region ( B) can be classified into two groups. In the present invention, the inorganic pigment (A) or the inorganic pigment (B) can be used alone, but the effect of the present invention becomes more remarkable by using the inorganic pigment (A) and the inorganic pigment (B) in combination. When the inorganic pigment (A) or the inorganic pigment (B) is used alone, these pigments can be contained in either the intermediate layer or the protective layer. In the case where the inorganic pigment (A) and the inorganic pigment (B) are used in combination, these pigments can be simultaneously contained in the intermediate layer or the protective layer, but the inorganic pigment (A) and the inorganic pigment (B) are included in the intermediate layer. And can be contained separately in the protective layer. In this case, when the inorganic pigment (A) is contained in the intermediate layer and the inorganic pigment (B) is contained in the protective layer, the effect of the present invention is more remarkably exhibited.

  Specific examples of the inorganic pigment (A) include zinc sulfide, titanium oxide, indium oxide, cerium oxide, tin oxide, molybdenum oxide, zinc oxide, and gallium nitride.

Specific examples of the inorganic pigment (B) include silica, alumina, silica-alumina, antimony oxide, magnesium oxide, zirconium oxide, barium oxide, calcium oxide, strontium oxide, silicon nitride, aluminum nitride, boron nitride, and barium sulfate. Can be mentioned.
Further, in the present invention, inorganic / organic fillers, lubricants and the like used for this type of recording medium may be used in the protective layer.

The support for the reversible thermosensitive recording medium of the present invention is paper, resin film, PET film, synthetic paper, metal foil, glass or a composite thereof, and the like, as long as it can hold the thermosensitive recording layer. Moreover, the thing of the thickness as needed can be used individually or by bonding. That is, it is preferably 60 to 150 μm, and a support having an arbitrary thickness from about several μm to about several mm is used.
Moreover, when providing the said under layer on these support bodies, crack generation | occurrence | production prevention and generation | occurrence | production of a burr | flash are improved by providing through an contact bonding layer.
The adhesive layer can be formed by the same coating method as that for each of the above layers.

The reversible thermosensitive recording label of the present invention is one in which an adhesive layer or a pressure-sensitive adhesive layer is provided on the surface opposite to the surface of the support constituting the reversible thermosensitive recording medium described above.
This reversible thermosensitive recording label includes an adhesive layer or a pressure-sensitive adhesive layer (non-peeling paper type), and a release paper attached under the adhesive layer or pressure-sensitive adhesive layer (peeling paper type). As a material constituting the adhesive layer, a hot melt type material is usually used.

Commonly used materials can be used for the adhesive layer or the pressure-sensitive adhesive layer.
For example, urea resin, melamine resin, phenol resin, epoxy resin, vinyl acetate resin, vinyl acetate-acrylic copolymer, ethylene-vinyl acetate copolymer, acrylic resin, polyvinyl ether resin, vinyl chloride-vinyl acetate Copolymer, polystyrene resin, polyester resin, polyurethane resin, polyamide resin, chlorinated polyolefin resin, polyvinyl butyral resin, acrylic ester copolymer, methacrylic ester copolymer, natural rubber , Cyanoacrylate resins, silicon resins, and the like, but are not limited thereto.

  The reversible thermosensitive recording medium of the present invention functions as a reversible display unit that functions as at least a thermosensitive recording layer constituting the reversible thermosensitive recording medium, and information produced by combining it with a member (information storage unit) having an information storage function. It can be used as a display storage member.

Next, the information display storage member will be described.
The members having the information storage unit and the reversible display unit can be roughly classified into the following three items.
(1) A part of a member having an information storage function is used as a support for a reversible thermosensitive recording medium, and a thermosensitive recording layer is directly formed thereon.
(2) A member having an information storage function, wherein a support surface of a reversible thermosensitive recording medium which is separately formed and has a thermosensitive recording layer on the support is bonded.
(3) The reversible thermosensitive recording label bonded to a member having an information storage function via an adhesive layer or an adhesive layer.
In these cases (1), (2), and (3), it is necessary to set the functions of the information storage unit and the reversible display unit so that the functions can be performed. Can be arbitrarily selected according to the purpose, and can be provided on the opposite surface of the support in the reversible thermosensitive recording medium, between the support and the thermosensitive recording layer, or in the thermosensitive recording. It can also be provided on a part of the layer.
The member having the information storage function is not particularly limited, and a general card, disk, disk cartridge, or tape cassette can be used.

Examples of these include thick cards such as IC cards and optical cards, flexible disks, magneto-optical recording disks (MD), disk cartridges with built-in disks that can rewrite storage information, such as DVD-RAM, CD-RWs, etc. Examples thereof include a disc that does not use a disc cartridge, a write-once disc such as a CD-R, an optical information recording medium (CD-RW) that uses a phase-change storage material, and a video tape cassette.
The information display storage member having both the reversible display function and the information storage function will be described in the case of a card, for example, by displaying a part of the information stored in the information storage unit on the reversible thermosensitive recording layer. The owner or the like can confirm information by looking at the card without a special device, and the convenience is greatly improved compared to a card to which the reversible thermosensitive recording medium is not applied.

The information storage unit is not particularly limited as long as it can store necessary information. For example, magnetic recording, contact IC, non-contact IC, or optical memory is useful.
The magnetic recording layer is formed by coating the support using a commonly used metal compound such as iron oxide or barium ferrite and a resin such as vinyl chloride, urethane or nylon, or without using a resin. It forms by methods, such as vapor deposition and sputtering, using the said metal compound. Further, the reversible thermosensitive recording layer in the reversible thermosensitive recording medium used for display can also be used as a storage unit in a manner such as a barcode or a two-dimensional code.

In addition, as an example of using the reversible thermosensitive recording label of (3) above, when the reversible thermosensitive recording layer is difficult to apply as a support, such as a vinyl chloride card with a magnetic stripe, An adhesive layer or a pressure-sensitive adhesive layer can be provided on the entire surface or a part thereof.
By doing so, the convenience of this medium can be improved, such as being able to display a part of the information stored in the magnetism.
The reversible thermosensitive recording label provided with the adhesive layer or the pressure-sensitive adhesive layer is applicable not only to the above-described magnetic PVC card but also to a thick card such as an IC card or an optical card.

The reversible thermosensitive recording label can be used in place of a display label on a disk cartridge having a built-in rewritable disk such as a flexible disk, MD or DVD-RAM (see FIGS. 2 and 3). ).
Further, in the case of a disc that does not use a disc cartridge such as a CD-RW, a reversible thermosensitive recording label can be directly attached to the disc, or a reversible thermosensitive recording layer can be provided directly on the disc. By doing so, it is possible to apply to applications such as automatically changing display contents in accordance with changes in the stored contents.

The reversible thermosensitive recording label of the present invention can also be displayed by rewriting a part of the stored information added to the CD-R by sticking the reversible thermosensitive recording label on a write-once disc such as a CD-R.
Further, it may be used as a display label for a video tape cassette (see FIG. 4).
As a method of providing a thermoreversible recording function on a thick card, a disc cartridge, and a disc, in addition to the method of applying the reversible thermosensitive recording label, a method of directly applying a reversible thermosensitive recording layer on them, There is a method of forming a reversible thermosensitive recording layer on the support and transferring the thermosensitive recording layer onto a thick card, a disc cartridge, or a disc.

When transferring, an adhesive layer such as a hot melt type or an adhesive layer may be provided on the reversible thermosensitive recording layer.
When attaching a reversible thermosensitive recording label or providing a reversible thermosensitive recording layer on a rigid object such as a thick card, disk, disk cartridge, tape cassette, etc., improve the contact with the thermal head. In order to form an image uniformly, it is preferable to provide a cushioning layer or sheet between the rigid substrate and the label or the reversible thermosensitive recording layer.

Furthermore, FIG. 5 shows a schematic diagram of an example relating to an image processing method and an image processing apparatus using the reversible thermosensitive recording medium of the present invention.
FIG. 5 shows rewriting of a reversible thermosensitive recording medium having a magnetic recording portion on the back surface. First, the magnetic recording portion on the back surface of the recording medium is rewritten with the magnetic head 34 and then heated to the erasing temperature. The reversible thermosensitive recording part on the surface side of the recording medium is erased by the ceramic heater 38. Then, after writing in the reversible thermosensitive recording part with the thermal head 53, a card is carried out in the left direction of a figure.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist. In the text, “part” or “%” is based on weight unless otherwise specified.

Example 1
[Preparation of under layer liquid]
10 parts of hollow particles
Average particle size: 4 μm
Hollow rate: 90%
Main component of wall material: 150 parts of 10% aqueous solution of acrylonitrile, methacrylonitrile polyvinyl alcohol
Kuraray PVA618
Water 20 parts A coating solution obtained by stirring and dispersing the mixture having the above composition was applied and dried on a 100 μm white PET using a wire bar so as to have a thickness of about 15 μm.

[Preparation of Thermosensitive Recording Layer 1-1]
N- (4-Hydroxyphenyl) -N'-octadecyl urea 4 parts Acrylic polyol resin
(LR503 manufactured by Mitsubishi Rayon Co., Ltd., 50% solid concentration solution) 12 parts Methyl ethyl ketone 70 parts The above composition was pulverized and dispersed to a mean particle size of about 1 µm using a ball mill. Zinc oxide fine particle dispersion (Sumitomo Osaka Cement Co., Ltd., ZS-303, solid content concentration 30%, particle size 30 nm) 7 parts, 2-anilino-3-methyl-6-dibutylaminofluorane 1.5 parts Then, 2.5 parts of Coronate HL (Adduct type hexamethylene diisocyanate 75% ethyl acetate solution) manufactured by Nippon Polyurethane Co., Ltd. were sequentially added and stirred well to prepare a thermal recording layer coating solution.
The thermal recording layer coating solution having the above composition was applied onto the under layer using a wire bar and dried at 100 ° C. for 2 minutes to provide a thermal recording layer 1-1 having a thickness of about 5.0 μm.

[Preparation of thermosensitive recording layer 1-2]
Next, a thermal recording layer coating solution was prepared in the same manner except that 4 parts of the zinc oxide fine particle dispersion used in the production of the thermal recording layer 1-1 was used, and this was used as the thermal recording layer 1-1. A wire bar was used for coating, dried at 100 ° C. for 2 minutes, and then heated at 60 ° C. for 24 hours to provide a thermal recording layer 1-2 having a thickness of about 5.0 μm.

[Preparation of protective 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 or more of the composition was thoroughly stirred to prepare a protective layer coating solution.
A protective layer coating solution having the above composition is applied onto the recording layer using a wire bar, dried at 100 ° C. for 2 minutes, and then heated at 60 ° C. for 24 hours to provide a protective layer having a thickness of about 3.5 μm. The reversible thermosensitive recording medium of the invention was produced.

Example 2
In Example 1, except that the zinc oxide fine particle dispersion used in the production of the thermosensitive recording layer 1-1 was changed to 10 parts, the thermosensitive recording layer 2-1 was produced, and the thermosensitive recording layer 1-2. The heat-sensitive recording layer 2-2 was prepared in the same manner except that the zinc oxide fine particle dispersion used in the preparation of 7 was changed to 7 parts. Otherwise, the reversible heat-sensitive recording medium of the present invention was the same as in Example 1. Was made.

Comparative Example 1
A reversible thermosensitive recording medium was prepared in the same manner as in Example 1 except that the zinc oxide fine particle dispersion liquid of the recording layers 1-1 and 1-2 used in Example 1 was not used.

Comparative Example 2
In Example 1, except that the zinc oxide fine particle dispersion used in the production of the thermosensitive recording layer 1-1 was changed to 1 part, the thermosensitive recording layer 2′-1 was produced in the same manner, and the thermosensitive recording layer 1− A heat-sensitive recording layer 2′-2 was prepared in the same manner except that the zinc oxide fine particle dispersion used in the preparation of 2 was changed to 4 parts. Otherwise, the reversible heat-sensitive recording medium was prepared in the same manner as in Example 1. Produced.

The following tests were conducted on the reversible thermosensitive recording medium produced as described above.
<Color test>
Using a thermal printing apparatus manufactured by B.COM, printing was performed at a voltage of 13, 14 and 15 V under the condition of 2 msec, and the developed image density and background density were measured with a Macbeth densitometer RD914.
<Decoloration test>
The image produced by the color development test was heated at 120 ° C. for 1 second with a thermal inclination tester manufactured by Toyo Seiki Co., Ltd., and the decoloring density was measured.
<Thermal head decoloring test>
With a thermal printing device manufactured by BCOM, erase the 8-16V in 0.5V increments under the condition of 2msec by changing the energy on the part that is solidly printed under the condition of 21V, 2msec. It was measured with a densitometer, and the density of the most decolored portion was selected to obtain the thermal head decoloration density.
The results are shown in Table 4.

It is a figure which shows the color development and decoloring characteristic of the reversible thermosensitive coloring composition of this invention. It is a figure which shows the example which affixed the reversible thermosensitive recording label in this invention on the disk cartridge of MD. It is a figure which shows the example which affixed the reversible thermosensitive recording label in this invention on CD-RW. It is a figure which shows the example which used the reversible thermosensitive recording label in this invention as a display label of a videotape cassette. It is a figure which shows the example of the image processing apparatus of this invention.

Explanation of symbols

34 Magnetic head 38 Ceramic heater 40 Transport roller 47 Transport roller 53 Thermal head

Claims (10)

  Reversible that can form a relatively 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. A reversible heat-sensitive recording medium having a heat-sensitive recording layer, wherein the heat-sensitive recording layer on the support side has higher thermal conductivity than the heat-sensitive recording layer on the display surface side.   The heat-sensitive recording layer has a multi-layered structure formed by multi-stage coating, and each heat-sensitive recording layer has high thermal conductivity from the display surface side to the support side. Reversible thermosensitive recording medium.   The reversible thermosensitive recording medium according to claim 1, wherein an under layer containing hollow particles is provided between the support and the thermosensitive recording layer. The reversible thermosensitive recording medium according to any one of claims 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). .

(In the formula, X ₁ and X ₂ represent a direct bond or a divalent group selected from —NH—, —CO—, —O—, —SO ₂ —, and —S—, or 2 of these divalent groups. A divalent group in combination of two or more, wherein X ₁ and X ₂ are not directly a direct bond, R ₁ represents a divalent hydrocarbon group having 1 to 22 carbon atoms, and R ₂ represents Represents a hydrocarbon group having 8 to 30 carbon atoms, p represents an integer of 0 to 4, and R ₁ and X ₂ repeated when p is 2 to 4 may be the same or different. when p is 0, _{X 1} is not a direct bond. further, q is an integer of 1-3.)   5. The reversible thermosensitive recording medium according to claim 1, further comprising an information storage unit.   The reversible thermosensitive recording medium according to any one of claims 1 to 5, wherein an adhesive layer or a pressure-sensitive adhesive layer is provided on at least one of the display surface and the back surface of the recording medium.   An image processing method comprising forming and / or erasing an image using the reversible thermosensitive recording medium according to claim 1.   The image processing method according to claim 7, wherein an image is formed on a display unit of the reversible thermosensitive recording medium using a thermal head.   The image processing method according to claim 7, wherein the image is erased using a thermal head.   An image processing apparatus for forming and / or erasing an image by the image processing method according to claim 8.

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