JPH0725151A - Reversuble thermal recording medium, production thereof and production of molten mixture of color former and coupler - Google Patents

Abstract

PURPOSE:To enhance high developed color recording density from the initial stage of use and hold the same even after many-time repeated use. CONSTITUTION:In a reversible thermal recording medium obtained by providing a thermal recording layer wherein fine particles of a molten mixture of a color former and a coupler are dispersed in a resin matrix on a support, the color former and the coupler are bonded through a binder resin and dispersed in the resin matrix in a fine granular state to form the recording layer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a reversible thermosensitive recording medium utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound and a method for producing the same, an electron-donating color-forming compound and an electron. The present invention relates to a method for producing a molten mixture with a receptive compound.

[0002]

2. Description of the Related Art Conventionally, heat-sensitive recording utilizing a color-forming reaction between an electron-donating color-forming compound (hereinafter also referred to as a color-developing agent) and an electron-accepting compound (hereinafter also referred to as a color-developing agent). The medium is widely known, and the output of electronic calculators, facsimiles, vending machines, printers of scientific measuring machines, C
Widely used in RT medical measurement printers. However, all the conventional products have irreversible color development, and it is not possible to repeat the color development and the color erasing alternately.

On the other hand, according to the patent publication, there has been proposed a reversible color developing and decoloring method. For example, a combination of gallic acid and phloroglucinol is used as a color developing agent. No. 193691, Japanese Patent Application Laid-Open No. 61-237684, which uses a compound such as phenolphthalein or thymolphthalein as a developer, and a recording layer containing a homogeneous compatible solution of a color former, a developer and a carboxylic acid ester. JP-A-62-138556, JP-A-62-138
568 and JP-A-62-140881, JP-A-2-188294 in which a salt of gallic acid and a higher aliphatic amine is used as a color developer, and bis (hydroxyphenyl) acetic acid or butyric acid and a higher level as color developers. JP-A-2-188293, which uses a salt with an aliphatic amine, is disclosed. However, various problems remain in the conventional reversible thermosensitive recording medium described above, and it is not yet satisfactory.

The present inventors previously used a compound such as an organic phosphoric acid having a long-chain aliphatic group, a carboxyl compound, a phenol compound, or a hydroxyphosphonic acid as a color developer, which was used as a color-developing agent. By combining with, the coloring and decoloring can be easily performed only by heating, and the coloring and decoloring states can be maintained at room temperature, and the decoloring temperature is higher than the coloring temperature. A reversible thermochromic composition which is low and which can be repeatedly formed and erased by changing the temperature.
And a reversible thermosensitive recording medium containing the same in a recording layer has been proposed (Japanese Patent Application No. 3-355078). This reversible thermosensitive recording medium does not cause problems such as a decrease in color recording density and defective erasing even when it is repeatedly used a number of times, and can be used a number of times that is unthinkable from the prior art. However, in this recording medium, the initial color recording density is often low, and the color recording density gradually increases with repeated color development and erasing. It is desired to develop a reversible thermosensitive recording medium with high efficiency.

[0005]

SUMMARY OF THE INVENTION The present invention provides a reversible thermosensitive recording medium having a high color recording density from the beginning of use and capable of retaining a high color recording density even after repeated use many times, and a method for producing the same. It is an object of the present invention to provide a method for producing a molten mixture of an electron-donating color-forming compound and an electron-accepting compound.

[0006]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, a thermosensitive recording layer containing an electron-donating color-developing compound and an electron-accepting compound dispersed in a resin base material is provided on a support, and a color is formed when the recording layer is heated and melted. In a reversible thermosensitive recording medium in which a recording state is formed, and when it is heated to a temperature lower than the color recording temperature, a decolored state in which the recording disappears, the electron-donating color-forming compound and the electron-accepting compound are melt-mixed with each other. Provided is a reversible thermosensitive recording medium characterized by being contained as a body in a resin matrix and a method for producing the same.

Further, according to the present invention, a thermosensitive recording layer containing an electron-donating color-developing compound and an electron-accepting compound dispersed in a resin matrix is provided on a support, and the recording layer is heated.
In a reversible thermosensitive recording medium, a color recording state is formed when melted, and a decolored state where the recording disappears when heated to a temperature lower than the color recording temperature, in the reversible thermosensitive recording medium, the fine particles of the electron-donating colorable compound and the electron-accepting compound. A reversible thermosensitive recording medium and a method for producing the same are provided, in which the fine particles of (1) are present as fine particles bonded to each other via a binder resin. Furthermore, according to the present invention, in a method for producing a molten mixture of an electron-donating color-forming compound and an electron-accepting compound, which develops color when heated and melted and can be decolorized when heated to a temperature lower than the color development temperature. To evaporate and remove the organic solvent by heating an organic solvent solution in which both the electron-donating color-developing compound and the electron-accepting compound are dissolved to a temperature equal to or higher than the color development start temperature of the molten mixture. Provided is a method for producing a melt mixture of a characteristic electron-donating color-forming compound and an electron-accepting compound.

The reversible thermosensitive recording medium of the present invention is one in which a color former and a color developer are melted and mixed by heating to develop a color, and when the color developer separates from the color former and crystallizes, the color disappears. A more detailed examination of the mechanism for forming the color-developing body in the recording medium reveals that the color-developing agent is dissolved in the melted developer to form the color-developing body. The mechanism for generating a coloring material and the mechanism for erasing the color in the reversible thermosensitive recording medium of the present invention are the same as those of the reversible thermosensitive recording medium shown in the above-mentioned prior application of the present inventors. The reason why the initial color recording density is often low in the prior application is presumed to be that the generation of color bodies upon application of heat is not sufficiently large in the recording medium in the early stage of use. That is, in the recording layer forming method with high practicality in the recording medium of the prior application, the recording layer forming coating solution using a solvent that dissolves the resin base material and the color developing agent but does not dissolve the color developing agent is applied to the support and dried. However, it cannot be said that almost all of the color-developing agent and the color-developing agent in the recording layer are close to each other. Therefore, in the initial stage of use of the recording medium, even if heat is applied to the recording layer, some of the color former particles cannot come into contact with the melted developer, and as a result, the amount of color former generated when heat is applied is small. It seems to be. The present invention has been made for the purpose of solving such a problem.

The present invention provides a recording medium in which a color developing agent is disposed in the vicinity of the color developing agent in the recording layer. Therefore, the color developing agent and the color developing agent are contained in the resin base material forming the recording layer. The molten mixture of the agent is dispersed in the form of fine particles, or fine particles in which the fine color developer particles and the fine developer particles are bonded to each other through a binder resin (fine particles of bonded body) are dispersed. In this recording layer, since the color developing agent is present in the vicinity of the color developing agent, almost all of the color developing agent can be dissolved in the color developing agent melted by heat application from the initial use of the recording medium. It is possible to obtain a recording medium having a higher color recording density at the beginning of use than a recording medium having a recording layer in which a color former and a color developer are simply dispersed. Further, in the present invention, in order to prevent the color former and the developer from escaping into the resin base material from the above-mentioned melted mixture or bonded fine particles, at least a part of the surface of the fine particles is used as a recording layer forming resin. It is also one of the features to coat with a resin that is not compatible, and this coating prevents the color former and developer from escaping into the resin base material during recording layer formation and image formation / erasure. It is possible to prevent a decrease in color recording density due to multiple use.

The molten mixture of the color-developing agent and the color-developing agent used in the present invention is a method in which a predetermined amount of the finely-pulverized color-developing agent and the color-developing agent are mixed well and heated to a temperature above the melting point of the color-developing agent. Alternatively, it can be easily obtained by a method in which a finely pulverized color developing agent is added to and dissolved in a developer which is in a molten state by being heated to a temperature equal to or higher than the melting point. Then, if the molten mixture in the molten state obtained by the above method is cooled to a temperature below the melting point of the developer, it becomes solid, but if the cooling in this case is rapid cooling, the molten mixture in the colored state is gradually cooled. In the case of, a decolored molten mixture is obtained. Comparing the obtained molten mixture in the colored state with the molten mixture in the decolored state, the addition of the molten mixture in the colored state to the recording layer has a higher effect of improving the initial color density. It is also a preferable method to use a solvent in which both the color former and the developer are soluble in order to mix them well. That is, a mixed solution in which both a color former and a developer are dissolved is prepared, the solution is heated to evaporate and remove the solvent, and then the mixture is heated to a temperature equal to or higher than the melting point of the developer to form a molten mixture. The initial color density is further improved by this method.

More specifically, a method for producing a molten mixture using a solvent will be described. After coating a solution containing a color former and a developer on a heat-resistant substrate having a smooth surface, the coating layer is melted. An example is a method of obtaining a molten mixture in the form of a dry film by drying the mixture at a temperature not lower than the color development start temperature. Alternatively, the solution may be sprayed onto a substrate heated to a temperature not lower than the color development start temperature of the molten mixture to form a dry film. The dry film-like molten mixture thus obtained may be peeled off from the substrate and finely pulverized to a desired particle size, and then added as it is or after adding a binder resin or the like to the recording layer forming coating liquid. . The substrate used here is preferably a metal plate whose surface is coated with Teflon, a stainless buffing plate, or the like. When a melt mixture is produced by the above method, a solvent insoluble for the color former and / or the developer may be used, and the dispersion may be applied to or sprayed onto the substrate to form a dry film. The method for producing the body is not limited to the above method.

Various solvents can be used as a solvent for dissolving both the color-developing agent and the color-developing agent. The specific type of the solvent is selected depending on the type of the color-developing agent used. It is desirable to use a cyclic ether solvent. As the cyclic ether solvent, tetrahydrofuran, 2-methyltetrahydrofuran, 1,
3-dioxolane, 2-methyl-1.3-dioxolane, tetrahydropyran, 2-methyltetrahydropyran, 3,4-dihydro-2H-pyran, 1,3-dioxane, 1,4-dioxane, 4-methyl-1 , 3-dioxane and the like. In addition, toluene, methyl ethyl ketone, etc. heated to 50 to 60 ° C. are also preferably used as the solvent for producing the melt mixture.

If necessary, the melt mixture may contain a binder resin and an additive for the purpose of improving the decoloring / coloring temperature and the decoloring speed. Such a molten mixture is
The additive and the binder resin may be dissolved or dispersed in the solvent used for producing the melted mixture, and the melted mixture may be produced by the same method as the method for producing the melted mixture. The binder resin used here is a vinyl chloride-vinyl acetate copolymer, polyvinyl chloride, polyvinyl acetate, polystyrene, alkyd resin, polyurethane, polycarbonate, polyacrylate, polyvinyl alcohol, nitrocellulose resin, etc. Thermoplastic or thermosetting resins can be used. The addition amount of the binder resin is 0 to 250% of the weight of the molten mixture, preferably 2
It is preferable to set it to 0 to 100%, and if the addition amount is too large, the content of the molten mixture is lowered, so that the color recording density is lowered. If the amount of addition is too small, at least a part of the melted mixture will be eluted if a solvent in which the melted mixture or the color former or developer forming the mixture is soluble is used as the recording layer forming solvent. .

The binder resin contained in the melted mixture makes it possible to optimize the erasing / coloring temperature and accelerate the erasing speed, and also to melt the mixture into the resin base material forming the recording layer. Has various roles such as improving the dispersibility of As one of them, when forming the recording layer by dispersing the molten mixture in a solvent together with the resin base material, if the molten mixture contains a solvent-insoluble binder resin, the color former and the developer are dissolved. Even if a solvent is used, the melted mixture is solidified with a binder resin, so the elution of the color former and developer is suppressed, and even if the above-mentioned solvent in which the color former or developer is soluble is melt mixed. It is possible to form a recording layer in which the body is uniformly dispersed. Therefore, it can be said that this method increases the degree of freedom in forming the recording layer. The binder resin added to the molten mixture may or may not be compatible with the resin base material for forming the recording layer.

In the reversible thermosensitive recording medium of the present invention, the recording layer is formed by dispersing fine particles (hereinafter, also referred to as fine particle joined body) in which the fine particles of the molten mixture are joined together through a binder resin, in a resin base material. Can be formed. In this method, if a solvent-insoluble resin is used as the binder resin for forming the fine particle conjugate, the recording layer-forming solvent can be recorded even if the melted mixture or a solvent in which its constituent components (color former and developer) are soluble. They do not elute at the time of layer formation, and therefore the selection range of the recording layer forming solvent can be expanded. Further, in the reversible thermosensitive recording medium obtained by dispersing the fine particle bonded body in the resin base material, it is possible to simultaneously improve both the erasing / coloring characteristics and the life as described below. In the reversible thermosensitive recording medium of the present invention, the erasing / developing density, thermal sensitivity, erasing / developing characteristics such as erasing speed are greatly influenced by the type of the color former or the resin around the developer and the additives. In many cases, both the color former and the developer exhibit good erasing / coloring characteristics in a system that is easy to move, but if the erasing / coloring is repeated in this system, the color former and the developer migrate / aggregate. It becomes unusable because it causes uneven density. Therefore, a resin base material for forming a recording layer in which the fine particle conjugate is dispersed is used by using a resin that easily moves the color former or the developer as the binder resin for forming the fine particle conjugate around the color former or the developer. If a resin that is difficult to move is used, an excellent recording medium can be obtained in terms of erasing / coloring characteristics and life.

The fine particle joined body is produced by a method in which a finely pulverized melt mixture is kneaded in a molten binder resin, and then the kneaded product is cooled and pulverized. The melt mixture used here is used. May contain a binder resin,
The binder resin and the binder resin for bonding may or may not be compatible with each other. The fine particle joined body can be manufactured by various methods other than the above. For example, a method of using a solvent that dissolves the binder resin without dissolving the melt mixture, and evaporating and removing the solvent from a liquid in which the fine particles of the melt mixture are well dispersed in the solvent in which the binder resin is dissolved, or a method of melt mixing A binder resin having a melting point lower than the melting point of the body is melted, and fine particles of the melted mixture are well mixed and dispersed in the binder resin, followed by cooling. It can be obtained by a method of finely pulverizing with a known pulverizer such as a mill or an attritor.

The binder resin for joining the fine particles of the melt mixture is a vinyl chloride-vinyl acetate copolymer, a phenol resin, polyvinyl acetate, polystyrene, an alkyd resin,
Polyurethanes, polyesters, polyacrylates, nitrocellulose resins, styrene-maleic anhydride copolymers, etc., and known thermosetting resins as well as thermosetting and ultraviolet curable resins can be used. If the amount of the binder resin added for joining the melted mixture particles is too large, the concentration of the melted mixture will decrease, and the color development / recording density will decrease.
If the amount is too small, the fine particles of the melted mixture cannot be joined. Therefore, if the addition amount of the binder resin for joining is B, the sum of the binder resin amounts A and B added to the melted mixture is (A
It is desirable to add 20 to 70%, preferably 40 to 70% of (weight + B weight + molten mixture weight). The binder resin for bonding the molten mixture particles may or may not be compatible with the resin base material forming the recording layer. In addition to this, the addition effect of the binder resin for joining the melt mixture fine particles has many similarities to the addition effect of the binder resin added to the melt mixture. It is possible to improve the dispersibility of the molten mixture particles.

In the present invention, the recording layer can be formed by coating the molten mixture fine particles and the fine particle bonded body with a resin that is incompatible with the recording layer forming resin base material and dispersing the resin in the resin base material. . In such a recording medium, since the color former and the developer do not escape into the resin base material even if the melted mixture or the fine particle bonded body does not contain the binder resin which is incompatible with the resin base material, It is possible to suppress the occurrence of image density unevenness and the decrease in color recording density due to repeated use. The coating resin used here is insoluble in the recording layer forming solvent, and a curable resin such as a thermosetting resin, an ultraviolet curable resin, or an electron beam curable resin is preferable, but repeated application of heat many times. However, any resin that is incompatible with the resin forming the recording layer and insoluble in the recording layer forming solvent can be used. The thickness of the coating layer is preferably as thin as 2 μm or less.
The coating layer does not dissolve the molten mixture or the molten mixture containing the binder resin, and uses a solvent that dissolves the coating resin, and the fine particles containing the molten mixture are dissolved in a solution in which the coating resin is dissolved. In addition to the dipping method of drying after dipping, it may be formed by a known method such as a method of applying a coating technique such as a spray coating method.

In the recording medium of the present invention, the color former and the color developer in the recording layer do not necessarily have to form a molten mixture, and the color former and the color developer in the recording layer interpose a binder resin. The particles may be bonded particles (bonded particles). The joined fine particles formed of the color former, the developer and the binder resin can be produced by various methods. For example, a dispersion liquid containing a color former, a developer, a binder resin, and a solvent is applied on a substrate having a smooth surface, and then the temperature lower than the temperature at which the color former and the developer form a molten mixture. The resulting dried film-like material is peeled off from the substrate and finely pulverized to obtain fine particles of a joined body. Further, the use of a solvent that dissolves both the color former and the developer improves mixing, which is preferable. In this case, if a liquid in which the color former, the developer and the binder resin are dissolved is used instead of the dispersion liquid. good. These methods are the same as the method for producing melt mixture fine particles using the above solvent except for the drying temperature of the coating layer, and the type of solvent and substrate used is the same as that described above when producing the melt mixture. is there. In addition to the above, the conjugate fine particles may be produced from a dispersion liquid using a solvent in which one or two of the color former, the developer and the binder resin are dissolved, or the color former, the developer and the binder resin. The block-shaped material obtained by evaporating the solvent from the liquid containing the may be finely pulverized to produce the joined fine particles. It is also possible to produce the joined fine particles by a method of kneading a fine particle color developer and a developer in a molten binder resin and then finely pulverizing them, and the method for producing the joined fine particles is not particularly limited.

The binder resin for joining the color former and the developer is a vinyl chloride-vinyl acetate copolymer, a phenol resin, polyvinyl acetate, polystyrene, an alkyd resin,
Polyurethane, polycarbonate, polyester, polyvinyl alcohol, nitrocellulose resin, styrene-
It is a maleic anhydride copolymer or the like, and in addition to known thermoplastic resins, thermosetting or ultraviolet curable curable resins are used. If the amount of the binder resin used is too large, it impairs the proximity of the color-developing agent and the color-developing agent, which is the object of the present invention, and since the color-forming density decreases due to the decrease in the content of the color-developing agent and the color-developing agent,
70% or less, preferably 20 to 4 of the total weight of the joined fine particles.
It is good to set it to 0%. In addition, the binder resin in the fine particles of the joined body joins the color former and the developer, and also has various functions similar to those of the binder resin added to the molten mixture. -Coloring temperature and decoloring speed have been improved. If desired, additives having various roles may be added to the fine particles of the joined body, and the addition method is the same as the method for adding the additives to the molten mixture described above. The binder resin for joining the color former and the developer may or may not be compatible with the resin base material forming the recording layer, but if the binder resin is not compatible with the resin base material. As in the case of the binder resin added to the molten mixture, the decrease in color recording density and the occurrence of image unevenness that occur when the recording medium is repeatedly used are suppressed.

In the present invention, the fine particles of the joined body of the color former and the developer are coated with a resin that is incompatible with the recording layer forming resin base material,
This can be dispersed in a resin base material to form a recording layer. In such a recording medium, even if a binder resin compatible with the resin base material is used to bond the color former and the developer, the color former and the developer do not escape into the resin base material. It is possible to suppress the occurrence of image density unevenness and the decrease in color recording density due to repeated use. The coating resin used here is insoluble in the recording layer forming solvent, and a curable resin such as a thermosetting resin, an ultraviolet curable resin, or an electron beam curable resin is preferable, but repeated application of heat many times. However, any resin that is incompatible with the resin forming the recording layer and insoluble in the recording layer forming solvent can be used. The thickness of the coating layer is preferably as thin as 2 μm or less. The coating layer uses a solvent that does not dissolve the conjugate particles and dissolves the coating resin, and uses a dipping method in which the conjugate particles are immersed in a solution in which the coating resin is dissolved and then dried, as well as a spray coating method. It may be formed by a known method such as a method applying a coating technique. When the binder resin forming the joined fine particles is incompatible with the recording layer forming resin and insoluble in the recording layer forming solvent, the coating layer may not be formed on the joined fine particles. Since the fine particles of the bonded body are not destroyed, the particles may be dispersed as they are in the resin for forming the recording layer to form the recording layer.

The molten mixture or the fine particles of the joined body of the color-developing agent and the color-developing agent which have been described in detail above are used in the present invention by the conventional method of dispersing them in water or an organic solvent together with the resin base material. Can be In this case, it is preferable to add the molten mixture in the color-developed state, but the addition in the decolored state exhibits a sufficient initial color-developing effect, and therefore the addition is not limited to the addition in the color-developed state. Further, the fine particles of the melted mixture and the fine particles of the joined body of the color-developing agent and the developer in the coating liquid for forming the recording layer have a particle diameter of 5 to 0.1 μm, preferably 0.8
It is desirable that the thickness be about 0.2 μm. The fine particles having such a particle diameter are usually obtained by finely pulverizing the powder of the molten mixture or the bonded body of the color-developing agent and the developer by a pulverizing / dispersing machine such as a ball mill or an attritor in a solvent that does not dissolve the fine particles. It can be easily obtained by law.

In the present invention, the mixing ratio of the color-developing agent and the color-developing agent used for forming the molten mixture needs to be selected at an appropriate ratio depending on the physical properties of the compound used. The range is about 1 to about 1 to 1 for the color developer in a molar ratio.
It is in the range of 4, preferably in the range of 1.5 to 2.5. Similarly, the mixing ratio of the color-developing agent and the color-developing agent in the case of forming the conjugate fine particles of the color-developing agent and the color-developing agent needs to be appropriately selected depending on the physical properties of the compound to be used. In this case, the mixing ratio is a molar ratio of the color developer to the developer of 2 to 2.
It is in the range of 5, preferably in the range of 2-3. If the amount of the developer is less or more than this range, the density of the color-developed state becomes low, which is a practical problem. Further, even in the above preferable range, the decoloring property changes depending on the ratio of the color developing agent and the color developing agent. When the color developing agent is relatively large, the decoloring start temperature is low, and when it is relatively small. Decolorization becomes sharp with respect to temperature.
Therefore, this ratio must be appropriately selected according to the application and purpose. The color-developing agent and the color-developing agent used here may be used alone or in combination of two or more kinds.

As described above, the reversible thermosensitive recording medium of the present invention has a recording layer on a support, and the recording layer is a molten mixture of a color former and a developer in a resin matrix. It is formed by dispersing fine particles of a joined body of a color former and a developer. The resin base material used here has a role to stably disperse the above-mentioned molten mixture or bonded fine particles on the support, and does not dissolve even when dissolved in the recording layer forming solvent. Is also good. Although the resin base material in the recording layer has various roles, one of the important roles is to protect the thermochromic fine particles such as the molten mixture from the high heat when heat is applied. It is desirable to use a high heat resistant resin. As such resin base material, polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polystyrene, styrene copolymer, phenoxy resin, polyester, aromatic polyester, polyurethane, polycarbonate, polyacrylic ester And polymethacrylic acid esters, acrylic acid copolymers, maleic acid copolymers, polyvinyl alcohol, ethyl cellulose, chlorinated vinyl chloride resins, and mixtures of the above resins.

The reversible thermosensitive recording medium of the present invention instantly develops color upon heating, and the color development state thereof is stable even at room temperature, but the recording layer in the color development state is decolored by heating below the color development temperature, and the color disappears. The color state is stable even at room temperature. The principle of color development and color erasure of the reversible thermosensitive recording medium of the present invention, that is, image formation and image erasure will be described with reference to the graph shown in FIG. The vertical axis of the graph represents the color density and the horizontal axis represents the temperature. The solid line 1 represents the image forming process by heating and the broken line 3 represents the image erasing process by heating. A is the density in the completely erased state, B is the density in the saturated coloring state when heated to a temperature of T ₁ or higher, C is the density at the temperature of T ₀ or lower in the saturated coloring state, and D is T _0. It shows the concentration when erased by heating at a temperature between T _{1 and} T ₁ .

The reversible thermosensitive recording medium of the present invention is in a colorless state (A) at a temperature of T ₀ or lower. To record
It may be heated to a temperature of T ₁ or higher with a thermal head or the like,
Color development (B) is performed to form a recorded image. Even if the recorded image is returned to the temperature of T ₀ or less according to the solid line 2, the state (C) is maintained as it is, and the recording memory property is not lost. Next, in order to erase the recorded image, the formed recorded image may be heated to a temperature between T _{0 and} T _{1, which} is lower than the coloring temperature, and the state becomes colorless (D). This state is maintained as it is even if the temperature is returned to T ₀ or lower (A). That is, the process of forming the recorded image reaches C by the path of the solid line ABC and the recording is held. During the process of erasing the recorded image, the erased state is maintained up to A by the path of the broken line CDA. The behavioral characteristics of formation and erasure of the recorded image are reversible and can be repeated many times.

FIG. 2 is an explanatory view showing an example of image formation and image erasing. 1 is a support, 2 is a reversible thermosensitive recording layer, and 3 is
Is a colored image. In the image forming process (A) → (B), the image forming heat source, for example, the thermal head 4 is used to perform the T of FIG.
Recording and printing may be performed at a temperature of ₁ or higher. The image erasing step (B) → (A) is achieved by heating the image erasing heat source, for example, the heating roller 5 to a temperature between T _{0 and} T ₁ . The reversible thermosensitive recording medium of the present invention contains a color former and a developer as essential components. The color development of the reversible thermosensitive recording medium is obtained by cooling the color former composition formed by heating and melting the color former and the developer in the recording layer to room temperature. Since this color-forming material composition has an erasing temperature region on the lower temperature side than the melting temperature, rapid cooling is preferable when cooling from the melt-colored state to room temperature while maintaining the color development. In the case of gradual cooling, some bleaching occurs when passing through the erasing temperature range, and the density often decreases.

It is considered that in the color former composition, the molecules of the color former and the developer interact with each other to open the lactone ring of the color former to develop a color. The composition in the melted state and the rapidly cooled state contains, in addition to the chromophore molecule, the chromophore molecule and the developer molecule which are not directly involved in the formation of the chromophore. In the reversible thermosensitive recording medium of the present invention, the color former composition at room temperature is in a solidified state due to the cohesive force between these molecules. Further, although the aggregate structure of the color former composition shows some regularity, it may be very regular or not very regular. This depends on the combination of the color former and the developer, the amount ratio, and the cooling conditions. Such an aggregation structure is a cohesive force that acts between the alkyl chain structure part of the developer molecule forming the color former and the excess alkyl chain structure part of the developer molecule not forming the color former. Is presumed to be formed on the basis of. The formation of such an aggregate structure is associated with the decoloring phenomenon of the color former composition.

The color-forming material composition can be decolored by heating its color-developed state to a specific temperature range.
In this decoloring process, the aggregate structure of the color developing state changes, and finally the developer molecule is separated and crystallized from the color former composition to form crystals of the developer alone, resulting in a stable decolored state. Is confirmed by X-ray. As described above, in the reversible thermosensitive recording medium of the present invention, it is clear that the alkyl chain portion of the color developer plays a large role in the formation of the color-developed state and the decoloring process thereof. It is a characteristic of the formed colorant composition. Therefore, the decolorization temperature can be controlled by the length of the alkyl chain portion of the color developer, and the longer the chain length, the more often the color development and decolorization temperature shifts to the high temperature side. This is because the cohesiveness and motility of the developer molecules change depending on the length of this portion.

The reversible thermochromic composition formed in the recording layer of the reversible thermosensitive recording medium of the present invention is basically a composition in which a developer having an alkyl chain structure and a color former are combined. , There are preferred color formers for each developer.
The combination of the color-developing agent and the color-developing agent used in this reversible thermochromic composition is a color-developing state composition obtained by heating both of the color-developing state compositions obtained by heating both to a temperature lower than the melting temperature. It is appropriately selected depending on the characteristics such as ease of erasing (decoloring property) and color tone of the coloring state. Among these, the decoloring property can be judged by the presence or absence of an exothermic peak appearing in the temperature rising process in the differential thermal analysis (DTA) or the differential scanning calorimetry (DSC) of the color-developed state composition obtained by the combination. This exothermic peak corresponds to the decoloring phenomenon that characterizes the composition, and serves as a criterion for selecting a combination having a good decoloring property. In the reversible thermosensitive recording medium of the present invention, the third substance may be present in the recording layer, and, for example, even if a high molecular compound is present, its reversible decoloring behavior can be maintained.

In the reversible thermosensitive recording medium of the present invention, the color developing agent used in combination with the color developing agent has a structure exhibiting color developing ability capable of developing the color developing agent in the molecule and a cohesive force between the molecules. A compound having an alkyl chain structure part to be controlled, which is an organic phosphoric acid compound, an aliphatic carboxylic acid compound or a phenol compound having an aliphatic group having 12 or more carbon atoms, or a mercaptoacetic acid having an aliphatic group having 10 to 18 carbon atoms Or an acidic organic phosphoric acid ester having a long-chain aliphatic group having 16 or more carbon atoms, and an alkyl ester of caffeic acid having an alkyl group having 5 to 8 carbon atoms. The aliphatic group includes a linear or branched alkyl group and alkenyl group, and may have a substituent such as halogen, an alkoxy group and an ester group. The reversible thermochromic composition constituting the recording medium of the present invention is constituted by combining the above-mentioned color developer and color former. The color former is a colorless or light-colored dye precursor exhibiting an electron donating property, and is not particularly limited, and conventionally known triphenylmethanephthalide compounds, fluorane compounds, phenothiazine compounds,
A leuco auramine-based compound, an indinophthalide-based compound and the like are used. Specific examples of the color-developing agent and the color-developing agent used in the present invention include Japanese Patent Application No. 3-355078, Japanese Patent Application No. 4-191643, Japanese Patent Application No. 4-207604 and Japanese Patent Application No. 5-85375. Etc.

The reversible thermosensitive recording medium of the present invention has a basic constitution in which a lowermost layer is provided with a support and a recording layer and a protective layer are sequentially laminated thereon. The support used here is
Paper, synthetic paper, plastic film or composites thereof, glass plate and the like may be used as long as they can hold the recording layer. Since the protective layer prevents surface deformation and discoloration due to heat and pressure when heat is applied, it is extremely effective to install the protective layer when used many times. The protective layer also has chemical resistance,
It can also have a role of improving water resistance, abrasion resistance, head matching property, and the like. Therefore, it is preferable that the protective layer forming material has high heat resistance and high strength, and silicone rubber, silicone resin, polysiloxane graft polymer, ultraviolet curable resin, electron beam curable resin and the like are used. By forming such a protective layer, heat resistance is improved, and resistance to contact with organic solvent, plasticizer, oil, sweat, water, etc. is also increased, and image formation and deletion can be repeated without problems even in a bad environment. A recording medium is obtained. In addition, if a light stabilizer is contained in the protective layer, the light resistance of the image and the background is remarkably improved, and the addition of a polymeric cationic conductive agent prevents electrification, and the addition of an organic or inorganic filler and a lubricant. Thus, the sticking development can be reduced. The protective layer may be formed by uniformly dispersing or dissolving the components of the protective layer in water or an organic solvent as in the case of forming the recording layer, and then uniformly coating and drying this on the recording layer. The thickness is preferably about 0.5 to 10 μm.

The reversible thermosensitive recording medium used in the present invention may be provided with an undercoat layer or an intermediate layer having various purposes. The undercoat layer is provided for the purpose of improving heat insulation and adhesion between the support and the recording layer.
One of the important roles of the undercoat layer is to improve heat insulation so that the applied heat energy can be used for recording formation and erasure without waste. Coloring and decoloring can be performed sharply by installing the heat insulation undercoat layer. be able to. The undercoat layer for heat insulation may be formed by coating fine hollow particles of an organic or inorganic material on a support. The method for forming and erasing a recorded image is not particularly limited as long as the temperature conditions for coloring and erasing are given, and a thermal head, laser heating, a hot pen, etc. may be used for image formation, and a heating roller or surface may be used for image erasing. A heating element, a heating lamp, etc. are generally used. It is also possible to erase the recorded image with the thermal head set to the erasing temperature and to form the recorded image on the recording medium from which the recording has been erased with another thermal head set to the recording temperature.

[0034]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. All the following percentages are weight percentages. Also, the recorded image's erasing and coloring densities are Macbeth reflection densitometer RD
It was measured at 914.

Example 1 33 g of 2- (o-chloroanilino) -6-dibutylaminofluorane and 100 g of stearylphosphonic acid were well ground in separate mortars and uniformly mixed to obtain an average particle size of 1.0 to 1 The mixed powder of 0.5 μm was placed in an aluminum container and heated at 120 ° C. for 2 seconds to melt and develop color, and this was left at 23 ° C. to obtain a melted mixture (solid a) in a decolored state. Further, the melted mixture which was colored at 120 ° C. was brought into contact with ice water and rapidly cooled to obtain a melted mixture (solid b) in a colored state.

Example 2 To 133 g of a powdery mixture of a color former and a developer having the same composition as in Example 1 (average particle size 1.0 to 1.5 μm) was added Super Beckasite 1001 (Phenol manufactured by Dainippon Ink and Chemicals, Inc.). Resin brand name) 50g powder is added and mixed uniformly,
This was heated and melted at 100 ° C. and then cooled to obtain a solid, decolorized composition in which a joined body of the color former and the developer was formed (solid C). Also, instead of Super Becca site 1001, Super Becca site 3011
(Dainippon Ink and Chemicals, Inc. phenol resin trade name) was used, and while heating and melting 50 g of this resin at 130 ° C., 133 g of a powdery mixture having the same composition as in Example 1 was added,
After mixing and stirring, the mixture was gradually cooled to obtain a solid of a molten mixture containing a binder resin in a decolored state (solid d). Furthermore,
When slowly cooled, the melt forming solid d was brought into contact with ice water to be rapidly cooled, and a solid of a molten mixture containing a binder resin in a colored state was obtained (solid e).

Example 3 The solid a produced in Example 1 was crushed with a mortar and a jet mill to obtain 100 g of powder having an average particle size of 6 μm. 25g of Unidick 5502 (Dainippon Ink and Chemicals, Inc. UV curable resin) was added and mixed, and 40m was added to this mixture.
A solid (a joined body of fine particles of a molten mixture) cured by irradiation with ultraviolet rays having an energy of w / cm ² was obtained (solid f).

Example 4 Tetrahydrofuran (THF) was added to a powdery mixture of a color former and a developer having the same composition as in Example 1 and heated to 45 ° C. to obtain a THF solution containing 15% of solid content. . Immediately after coating this solution on a stainless steel buffing plate heated to 45 ° C., it was heated and dried in a constant temperature bath at 120 ° C. to prepare a dry film-like melt mixture. This was scraped from the substrate and pulverized to obtain a molten mixture powder in a colored state (solid g).

Example 5 A mixture of a color developer and a developer having the same composition as in Example 1 was used, and the mixture was pulverized to have an average particle size of the developer of 6 μm. -Vinyl acetate copolymer (manufactured by Union Carbide: product code VYHH)
100 g of powder, and toluene and methyl ethyl ketone (M
An equal weight mixed solvent of EK) was added to prepare a mixed / dispersed liquid having a solid content concentration of 20%. This solution is applied to a metal plate whose surface is coated with Teflon with a wire bar.
It is dried at 0 ° C. for 1 minute and then heat-treated at 120 ° C. for 20 seconds to form a colored molten mixture, and then cooled at 5 ° C. is blown onto the back surface of the metal plate to rapidly cool the binder resin in the colored state. A molten mixture containing was obtained as a dry film. This was scraped off from the metal plate and pulverized to obtain a solid powder (solid h).

Example 6 3,4-Dihydro-2 was added to a solvent which dissolves the color former and the developer.
A mixed solution of a color former and a developer (solid content concentration 15%) was obtained in the same manner as in Example 4 except that H-pyran was used.
Spray this solution into the air maintained at 135 ° C,
A molten mixture powder in a colored state was obtained (solid i).

Example 7 The solid a produced in Example 1 was jet milled to have an average particle size of 6
The powder was pulverized to have a size of μm, and 10 g of this powder was polyvinyl alcohol [Kuraray Co., Ltd .: product code PVA205].
80 g of 10% aqueous solution of was added and well stirred to prepare a dispersion liquid of solid a. This dispersion was treated with a hydrophilic treatment on the surface of 100 μm thick polyethylene terephthalate (P
ET) film with a wire bar and apply this at 60 ° C
And dried for 10 minutes to form a coating layer (recording layer) having a thickness of 6 μm. Printing was performed on the above recording layer with a thermal head at a printing energy of 30 mj / mm ² , and the color image density was measured and found to be 1.60. Next, the colored image was pressed against a heat roll having a surface temperature of 74 ° C. for 5 seconds to erase the color, and heat was applied to the recording layer after the color erasing by the thermal head as described above to form a colored image. . When the density of the color image was measured after repeating such an operation 20 times, the image density was 1.78.

Example 8 A recording layer was prepared in the same manner as in Example 7 except that the solid b prepared in Example 1 was used in place of the solid a, and the same erasing / color developing test as in Example 7 was conducted. The first developed image density was 1.82 and the 20th developed image density was 1.85.

Example 9 The solid C produced in Example 2 was subjected to jet milling to have an average particle size of 2
It is pulverized to have a particle size of ˜3 μm, and 10 g of this powder is used as a polymerization initiator (manufactured by Ciba Geigy: trade name Irgacure 651).
0.24 g and 80% ethyl acetate solution of UV curable resin (manufactured by Dainippon Ink and Chemicals, Inc .: trade name Unidick 422
0) Add 10 g, stir and mix well, then add 100
It is applied to a PET film of μm with a casting blade, and after application, it is dried at 60 ° C. for 1 minute to give a dry film thickness of 15 μm.
m coating layer was formed. 40 mw / cm in this coating layer
^The recording layer was formed by irradiating with an ultraviolet ray having energy of ² to cure it. When the same erasing / coloring test as in Example 7 was conducted on this recording layer, the first color image density was 1.45.
The 20th color image density was 1.75.

Example 10 A recording layer was prepared in the same manner as in Example 9 except that the solid d prepared in Example 2 was used instead of the solid C, and the same erasing / color developing test as in Example 7 was conducted. The first developed image density was 1.56, and the 20th developed image density was 1.81.

Example 11 A recording layer was prepared in the same manner as in Example 9 except that the solid e prepared in Example 2 was used instead of the solid C, and the same erasing / color developing test as in Example 7 was conducted. The first developed image density was 1.85, and the 20th developed image density was 1.82.

Example 12 The solid f produced in Example 3 was jet milled to have an average particle size of 3
The powder was pulverized to have a size of μm, and 10 g of this powder was polyvinyl butyral (manufactured by Denki Kagaku: product code # 3000-2).
8.5 g and an equal weight mixed solvent of toluene and MEK were added to prepare a dispersion liquid having a solid content concentration of 16%. This dispersion was applied to a PET film having a thickness of 100 μm by a wire bar so that the dry thickness was 7 μm, and then dried at 60 ° C. for 3 minutes to form a recording layer. When this recording layer was subjected to the same erasing / coloring test as in Example 7, the color density of the first image was 1.63 and that of the 20th time was 1.87.

Example 13 10 g of the solid (solid g) produced in Example 4, 16 g of acrylic polyol (manufactured by Dainippon Ink and Chemicals, Inc .: trade name Acridic BU-927) and a curing agent (manufactured by Dainippon Ink and Chemicals: product) 16 g of the name Barnock DN990) was added to an aliphatic hydrocarbon solvent (manufactured by Esso Corporation: trade name Swazol 31).
0) and well dispersed and mixed in a beaker to obtain a dispersion liquid having an average particle size of solid g of 0.9 μm and a solid content concentration of 50%.
This dispersion was applied onto a 100 μm-thick easily-adhesive PET film (Type HPJ manufactured by Teijin Ltd.) with a wire bar to give a dry film thickness of 6 μm, and then dried at 70 ° C. for 20 minutes to form a recording layer. Let When the same erasing / color developing test as in Example 7 was carried out on this recording layer, the color image density of the first time was 1.84 and that of the 20th time was 1.88.

Example 14 A recording layer was prepared in the same manner as in Example 13 except that the solid h prepared in Example 5 was used in place of the solid g.
When the same erasing / coloring test was conducted, the first developed image density was 1.72 and the 20th developed image density was 1.68.

Example 15 A recording layer was prepared in the same manner as in Example 13 except that the solid i prepared in Example 6 was used in place of the solid g.
When the same erasing / coloring test was conducted, the first developed image density was 1.77 and the 20th developed image density was 1.80.

Comparative Example 1 Vinyl chloride-vinyl acetate copolymer (manufactured by Union Carbide: product code VYHH) 100 g of powder was mixed with toluene and M.
It is dissolved in an equal weight mixed solvent of EK, 100 g of stearylphosphonic acid is added to this solution, and the mixture is pulverized and dispersed in a ball mill so that the average particle size of the developer is 6 μm. 33 g of -chloroanilino) -6-dibutylaminofluorane was dissolved to obtain a mixed dispersion liquid having a solid content concentration of 20%, and this was used as a coating liquid for forming a recording layer to prepare a recording layer. That is, the coating liquid was applied onto a PET film having a thickness of 100 μm by a wire bar so that the dry film thickness was 6 μm, and the coating layer was dried at 70 ° C. for 3 minutes to form a recording layer. When the same erasing / coloring test as in Example 7 was conducted on this recording layer, the first colored image density was 0.62 and 2
The 0th time was 1.81.

From the results of the erasing / coloring test of the recording layer shown in Examples 7 to 15 and Comparative Example 1, it is clear that the recording layer of the Example has a much higher initial color density than that of the Comparative Example. Is. Further, comparing the case where the recording layer contains the melted mixture in the decolored state and the case where the recording layer contains the conjugate of the color former and the developer (comparison between Examples 9 and 10), the former It can be seen that the initial color density of is high. However, the difference is not so large, and if the recording layer is configured so that the developer is present in the vicinity of the color developer in the recording layer, the color developer and the developer form a bonded body in the recording layer. Even if it does, it is recognized to be effective. In addition, comparing the case where the molten mixture was colored and added to the recording layer and the case where it was added in the decolored state (Comparison of Examples 7 and 8 and 10 and 11), the addition in the colored state was considerably higher. It can be seen that the initial color density is high.

[0052]

According to the reversible thermosensitive recording medium of claim 1, since the recording layer is formed by dispersing the molten mixture of the color-developing agent and the color-developing agent in the resin base material, the recording layer is formed in the recording layer. Since the color developing agent is disposed in the vicinity of the color forming agent, the initial color recording density can be significantly increased as compared with that of the reversible thermosensitive recording medium prepared by the conventional manufacturing method. The reversible thermosensitive recording medium produced by the method according to claim 2 is obtained by thoroughly dispersing and mixing a melted mixture of a color former and a developer formed by melting and mixing and a resin base material in a solvent. Since the dispersion is prepared, and the recording layer is formed by coating and drying the dispersion on the support, the developer is disposed in the vicinity of the coloring agent in the recording layer.
The initial color recording density can be significantly increased over that of the reversible thermosensitive recording medium prepared by the conventional manufacturing method.
In the reversible thermosensitive recording medium according to claim 3, fine particles of a molten mixture of a color former and a developer are bonded via a binder resin, and therefore, a solvent for forming a recording layer at the time of producing the recording medium is selected. The range can be expanded, and at the same time, the recording medium can achieve both improvement of the erasing / color-developing characteristics and increase of the life.

The reversible thermosensitive recording medium according to claim 4 has a recording layer formed by dispersing a bonded body, in which a color former and a developer are bonded with a binder resin, in a resin matrix. Since the color developing agent is disposed in the vicinity of the color developing agent in the layer, the initial color recording density can be significantly increased as compared with that of the reversible thermosensitive recording medium prepared by the conventional manufacturing method. A reversible thermosensitive recording medium produced by the method according to claim 5 is obtained by well dispersing and mixing a resin base material and a joined body of both formed by joining a color former and a developer with a binder resin. Since the dispersion is prepared, and the recording layer is formed by applying the dispersion on a support and drying the dispersion, the developer is disposed in the vicinity of the color developer in the recording layer. Can be significantly increased over that of the reversible thermosensitive recording medium produced by the conventional production method. Since the molten mixture of the color former and the developer prepared by the method of claim 6 is sufficiently mixed with the color former and the developer, the above-described effect of increasing the recording density of the initial color development is obtained. Is an elevated melt mixture,
The initial color recording density of the reversible thermosensitive recording medium having the molten mixture in the recording layer is further increased. Since the melted mixture of the color former and the developer prepared by the method of claim 7 contains a binder resin, in the reversible thermosensitive recording medium having the melted mixture in the recording layer, decoloring / coloring is performed. It is possible to optimize the temperature, accelerate the color erasing speed, and prevent the occurrence of image unevenness and the decrease in color recording density due to repeated use many times.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between color density and temperature of a reversible thermosensitive recording medium of the present invention.

FIG. 2 is an explanatory diagram of an image forming process and an image erasing process of the reversible thermosensitive recording medium of the present invention.

[Explanation of symbols]

 1 Support 2 Recording Layer 3 Colored Image 4 Thermal Head 5 Heating Roller

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location 6956-2H B41M 5/18 108 9121-2H 5/26 102

Claims (7)

[Claims] 1. A heat-sensitive recording layer containing an electron-donating color-developing compound and an electron-accepting compound dispersed in a resin matrix on a support, and when the recording layer is heated and melted, a color-recorded state is obtained. And a reversible thermosensitive recording medium which forms a decolored state in which recording disappears when heated to a temperature lower than the color recording temperature, in which the electron-donating color-forming compound and the electron-accepting compound form a molten mixture of both. A reversible thermosensitive recording medium characterized by being contained in a resin base material. 2. A thermosensitive recording layer containing an electron-donating color-developing compound and an electron-accepting compound dispersed in a resin matrix on a support, and when the recording layer is heated and melted, a color-recorded state is obtained. In the method for producing a reversible thermosensitive recording medium, which forms a decolored state in which recording disappears when heated to a temperature lower than the color recording temperature, a molten mixture of the electron-donating color-forming compound and the electron-accepting compound. And a resin base material, and a recording layer-forming coating liquid comprising a solvent that does not dissolve the molten mixture, and the coating liquid is dried on a support to form a recording layer. Production method. 3. A thermosensitive recording layer containing an electron-donating color-developing compound and an electron-accepting compound dispersed in a resin matrix on a support, and a color-recorded state is obtained by heating and melting the recording layer. And a reversible thermosensitive recording medium which forms a decolored state in which recording disappears when heated to a temperature lower than the color recording temperature, a fine particle of a molten mixture of the electron-donating color-forming compound and the electron-accepting compound is a binder. A reversible thermosensitive recording medium characterized by being present as fine particles bonded via a resin. 4. A thermosensitive recording layer containing an electron-donating color-developing compound and an electron-accepting compound dispersed in a resin matrix on a support, and when the recording layer is heated and melted, a color-recorded state is obtained. In the reversible thermosensitive recording medium in which the recorded color disappears when heated to a temperature lower than the color recording temperature, the fine particles of the electron-donating color-forming compound and the fine particles of the electron-accepting compound are separated from each other. A reversible thermosensitive recording medium, characterized in that it is present as fine particles bonded via a binder resin. 5. A thermosensitive recording layer containing an electron-donating color-developing compound and an electron-accepting compound dispersed in a resin matrix on a support, and when the recording layer is heated and melted, a color-recorded state is obtained. In the method for producing a reversible thermosensitive recording medium, which forms a decolored state in which the recording disappears when heated to a temperature lower than the color recording temperature, the electron-donating color-forming compound and the electron-accepting compound form a binder resin. A reversible method, characterized in that a recording layer-forming coating liquid comprising a fine particle bonded via an adhesive, a resin base material, and a solvent that does not dissolve the fine particle is applied on a support and dried to form a recording layer. Manufacturing method of thermal recording medium. 6. A method for producing a molten mixture of an electron-donating color-forming compound and an electron-accepting compound, which develops a color when heated and melted and can be decolored when heated to a temperature lower than the color development temperature. An organic solvent solution in which both an electron-donating color-forming compound and an electron-accepting compound are dissolved is heated to a temperature above the color development start temperature of the molten mixture to evaporate and remove the organic solvent. A method for producing a molten mixture of an electron-donating color-forming compound and an electron-accepting compound. 7. A method for producing a molten mixture according to claim 6, wherein a binder resin is added to an organic solvent solution in which both the electron-donating color developing compound and the electron-accepting compound are dissolved. .