JPH10109477A - Multicolor thermosensible recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fine particle-like decoloring agent composition adapted to multicolor thermosensible sheet without obstructing color developing and decoloring each other on the same support by allowing fine particle color erasing agent containing reactive product of guanidine compound with polyhydric isocyanate compound to exist in a leuco dye color developing layer. SOLUTION: A high temperature leuco dye color developing layer 2 containing leuco dye and developer is provided on a support such as woodfree paper or polyester resin film. Then, a low temperature leuco dye color developing layer 3 containing leuco dye and developer different in hue from that of the high temperature color developing layer as well as sensitizer as desired is provided on the layer 2. At this time, fine particle-like decoloring agent or microcapsule enclosing the decoloring agent is uniformly dispersed in the low temperature color developing layer and existed and/or a decoloring layer 4 containing decoloring agent or microcapsule enclosing the agent as another layer adjacent to the low temperature color developing layer is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material having a heating element such as a thermal head and used in a recording apparatus for forming a thermal image by applying heat. The present invention relates to a multicolor heat-sensitive recording material having at least two or more heat-sensitive coloring layers that develop different hues depending on the difference in applied heat energy and forming a color image of two or more colors.

[0002]

2. Description of the Related Art Thermal paper using a light-colored or colorless leuco dye which develops color by application of heat from a heating element such as a thermal head and a developer thereof is well known. This thermal paper is used as a recording material for facsimile, printer, etc.
The paper is widely used because the apparatus can be made compact, maintenance is easy, and the paper itself is inexpensive and its usage is simple.

Conventionally, recording with thermal paper has been mainly performed in a single color such as black color or blue color. However, with the expansion of the use of a recording apparatus, there is a demand for a multi-color and further full-color image recording material. Recently, it has been increasing. Recently, technologies such as electrostatic recording with a laser, ink jet, and transfer thermal film have been applied for multi-color and full-color applications. There is an increasing demand for multicolor image recording materials that can be used. In order to achieve such a requirement, two or more types of leuco dyes having different coloring hues contained in the thermal paper and a developer corresponding thereto are used, and the degree of energy applied from a thermal head or the like depends on the degree of energy applied. Attempts have been made to change the color hue.

[0004] One of the above-mentioned attempts is to form two layers of a low-temperature coloring layer and a high-temperature coloring layer having different hues on a support and heat them at a low temperature or at a high temperature to change the hue. There is a way to try. In this method, only the hue that depends on the low-temperature coloring layer is obtained in the portion where the low-temperature heat-applied energy is applied, but in the portion where the high-temperature heat-applying energy is applied, the low-temperature coloring layer also simultaneously generates color, and is thus obtained. As for the coloring hue, the hue depending on each layer cannot be separated and the hue of the low-temperature coloring layer and the hue of the high-temperature coloring layer are mixed, so that only the hue depending on the high-temperature coloring layer cannot be obtained.

In order to improve this point, an image in the low-temperature coloring layer has been erased recently by using a decoloring agent which exerts a decoloring effect on the color-forming body of the low-temperature coloring layer when heated at a high temperature. Many methods have been proposed for obtaining an image record of only the high-temperature coloring layer. Regarding a multicolor heat-sensitive recording material using a decoloring agent, for example, JP-B-51-292024, JP-B-54-36864
No., JP-A-56-40588, JP-A-62-73990, JP-A-2-175186, JP-A-2-84380, JP-A-2-362
No., JP-A No. 2-9680, JP-B-6-431 and the like, and as the decoloring agent described therein, amines or quaternary ammonium salts, guanidine derivatives, Examples include morpholine derivatives, amidine derivatives, amine derivatives, acid amides, fatty acid esters, urea derivatives, piperidinyl esters, and the like. However, these color erasing agents are generally compounds having a polar group, and when the solubility in water is slight, accompanied by the deterioration of the recording material, fogging, poor color development upon heating, and the like. The recorded image has a serious defect such as disappearance over time. Further, in the case of a compound which is completely insoluble in water, its decoloring function becomes insufficient, and it is impossible to completely separate the respective color hues of the low-temperature coloring layer and the high-temperature coloring layer. There was a disadvantage that clear recording could not be obtained with color mixing and bleeding.

Further, some of the above publications disclose that this type of decoloring agent is microencapsulated or dispersed in water, an organic solvent, oil or the like. However, no specific procedures and methods for microencapsulation are described. In addition to the above, JP-A-54-139742,
JP-A-60-105584, JP-A-1-125276, JP-A-4-29839
In No. 1 etc., a heat-sensitive recording material or a multicolor heat-sensitive recording paper using microcapsules containing a decoloring agent is described, but the microencapsulation methods used in these are all conventionally known. It just adopts the method.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a multicolor heat-sensitive recording material comprising a plurality of coloring layers having different coloring hues due to a difference in heat application energy. In particular, the present invention can achieve both the contradictory functions of coloring and decoloring of a heat-sensitive recording material, which have been impossible in the past, as well as the stability of heat-sensitive recording paper and thermal image recording, color mixing of image recording, and bleeding. And a multicolor heat-sensitive recording material to which the decoloring agent is applied. In other words, the present invention provides a novel fine particulate decolorizer composition which does not hinder the contradictory properties of color development and decoloration on the same support at all and is useful for multicolor thermal paper. Is what you do.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that two or more thermosensitive coloring layers formed on a support (where each layer has a different coloring hue). And at least one of the layers is a leuco dye coloring layer.) In the presence of a non-volatile hydrophobic organic solvent, A fine particle decolorant containing a reaction product of a guanidine compound and a polyvalent isocyanate compound which are insoluble or hardly soluble in the leuco dye coloring layer and / or in another layer adjacent to the layer. As a result, it has been found that an excellent multicolor heat-sensitive recording material which is extremely stable and free from color mixing and bleeding can be obtained. Furthermore, the present invention
The present invention provides a multicolor color thermosensitive image recording material using the above-mentioned particulate decolorizer, particularly, a particulate decolorizer microcapsule containing the above-mentioned decolorant by a specific microencapsulation method which has not been known before. Is what you do.

The present invention relates to (a) a support, and (b) two or more thermosensitive coloring layers having different coloring hues formed on the support, and at least one of the thermosensitive coloring layers.
One is a multicolor heat-sensitive recording material comprising a leuco dye coloring layer and containing a particulate decoloring agent in the leuco dye coloring layer and / or in another layer adjacent to the leuco dye coloring layer. Wherein the decoloring agent contains a reaction product of a guanidine compound insoluble or hardly soluble in the nonvolatile hydrophobic organic solvent and a polyvalent isocyanate compound in the presence of the nonvolatile hydrophobic organic solvent. It relates to a characteristic recording material.

In the present invention, the leuco dye coloring layer (b)
Is a colorless or light-colored leuco dye, a colorless or light-colored developer for the leuco dye, and contains a decolorizing agent that inhibits the color development of the leuco dye or microcapsules containing the decoloring agent. It is contained in the coloring layer and / or in another layer adjacent to the coloring layer. The leuco dye coloring layer develops a color when an applied energy higher than a certain reference temperature is applied, and when an applied energy higher than the temperature at which the leuco dye coloring layer develops is applied, the contained particulate decolorizing agent Is melted or the decoloring agent is released from the decolorizing agent-containing microcapsules, thereby decolorizing the hue of the leuco dye coloring layer or eliminating the function of the coloring layer itself.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A two-color thermosensitive recording paper (10) which is an example of a typical structure of the present invention will be described with reference to FIG.
In FIG. 1, first, a high-temperature leuco dye coloring layer (2) containing a leuco dye and a developer is provided on a support (1) such as a high-quality paper or a polyester resin film. Next, a low-temperature leuco dye coloring layer (3) containing a leuco dye and a developing agent having a hue different from that of the high-temperature coloring layer and, if desired, a sensitizer is placed on the high-temperature leuco dye coloring layer (2). Provide. At this time, the decolorizing agent in the form of fine particles, or microcapsules containing the decoloring agent, is uniformly dispersed and present in the low-temperature coloring layer, and / or as another layer adjacent to the low-temperature coloring layer. And a decoloring layer containing a decoloring agent or microcapsules containing the decoloring agent. FIG. 1 shows a case where the decoloring layer (4) exists between the high-temperature coloring layer (2) and the low-temperature coloring layer (3). Alternatively, in order to sufficiently exert the function of the decoloring agent and prevent the coloring of the high-temperature coloring layer from occurring due to the decoloring agent, the color is formed between the high-temperature coloring layer and the low-temperature coloring layer or between the high-temperature coloring layer and the decoloring layer. An intermediate blocking layer (not shown) may be provided between the layers.

When low heat application energy is applied to the surface of the thermal recording paper (10), only the hue of the uppermost low-temperature coloring layer (3) develops a color. Alternatively, when higher heat applied energy is applied to the surface of the recording paper (10), the decolorizing agent present in the low-temperature coloring layer or a layer adjacent to the low-temperature coloring layer is melted, or the decolorizing agent is removed from the microcapsules. Is released, the color-forming function of the low-temperature coloring layer is lost, or the colored image recording is decolorized, and at the same time, the high-temperature coloring leuco dye coloring layer (2) is colored. Only the image recording of the high-temperature coloring layer (2) having a different hue can be obtained. In this case, the temperature relating to the decoloring function of the decoloring agent does not exert any decoloring effect at a temperature at which the low-temperature coloring layer develops color, and does not impair the color-forming function of the low-temperature coloring layer. When the high-temperature coloring layer is colored, it must be set so that only the low-temperature coloring image recording is erased. Therefore, the portion where the thermal energy is not applied remains unchanged on a white background (color of the support), and the portion where the low thermal energy is applied records an image in which only the hue of the low-temperature coloring layer (3) is developed. Alternatively, an image record in which only the hue of the high-temperature coloring leuco dye layer (2) develops in a portion to which high heat energy is applied can be obtained. FIG. 1 shows a two-color coloring structure for the purpose of explanation. Naturally, a multicolor thermosensitive recording material of two or more colors can be obtained by laminating the coloring structural elements excluding the support. Combination with other heat-sensitive recording materials such as heat-sensitive recording and sublimation transfer heat-sensitive recording materials is also possible.

In the present invention, a guanidine compound which is insoluble or hardly soluble in a nonvolatile hydrophobic organic solvent is dispersed in the nonvolatile hydrophobic organic solvent as a decoloring agent in the multicolor heat-sensitive recording material. Solid fine particles of a reaction product of a guanidine compound and a polyvalent isocyanate compound obtained by adding a solution of the polyvalent isocyanate compound and mixing with stirring are used.

Further, in the present invention, the guanidine compound is dispersed in a nonvolatile hydrophobic organic solvent, a polyvalent isocyanate compound solution is added thereto, and the mixture is stirred and reacted until a transparent solution is obtained. The transparent solution is dispersed in fine particles having a diameter of 0.1 to 10 μm in a hydrophilic medium containing a substance forming a capsule wall by reacting with the remaining isocyanate in the solution, and then formed by heating as necessary. A microcapsule decoloring agent containing the resinous reaction product thus obtained can also be used.

The guanidine compound used in the present invention is:
The following general formula:

Embedded image (Wherein, R ^{1 to} R ⁵ are each independently hydrogen, carbon atom 1
Represents an alkyl group having up to 7 carbon atoms, a cyclic alkyl group having up to 10 carbon atoms, an aryl group having up to 10 carbon atoms, an aralkyl group having up to 10 carbon atoms, and / or a phenyl group. ) Is selected from guanidine compounds which are insoluble or hardly soluble in a nonvolatile hydrophobic organic solvent. Preferred compounds include guanidine compounds that are hardly soluble or insoluble in the organic solvent, such as diphenylguanidine and di-o-tolylguanidine.

Japanese Patent Publication No. 51-29202 on multicolor heat-sensitive paper
No. 4, JP-B-51-37542, various guanidine compounds described in JP-A-50-147736, guanidine compounds insoluble in the above organic solvents can also be used, the disclosure of which is hereby incorporated by reference. I do.

The polyvalent isocyanate compound used in the present invention includes, for example, m-phenylene diisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,5-diisocyanate , 4,4'-diphenylmethane-
Diisocyanate, 3,3'-dimethyldiphenylmethane-4,
4'-diisocyanate, xylylene-1,4-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1 , 2-Diisocyanate, cyclohexylene-1,4-diisocyanate, 4,4 ', 4 "-triphenylmethane triisocyanate,
Toluene-2,4,6-triisocyanate, 4,4'-dimethyldiphenylmethane-2,2 ', 5,5'-tetraisocyanate, adduct of hexamethylene diisocyanate with trimethylolpropane, 2,4-tolylenediene Adducts of isocyanate and trimethylolpropane, and adducts of xylylene diisocyanate and trimethylolpropane are exemplified. Furthermore, a mixture of two or more of the above compounds can be used, and it is particularly preferable to use a mixture of an aliphatic isocyanate compound and an aromatic isocyanate.

The nonvolatile hydrophobic organic solvent used in the reaction between the guanidine compound and the polyvalent isocyanate compound for producing the decoloring agent of the present invention includes, for example, phosphoric acid such as tricresyl phosphate and octyl diphenyl phosphate. Esters; phthalic esters such as dibutyl phthalate and dioctyl phthalate; maleic esters such as dibutyl maleate and dioctyl maleate; alkylated naphthalenes such as monoisopropyl naphthalene and diisopropyl naphthalene; diisopropyl biphenyl and diisobutyl biphenyl Alkylated biphenyls; 1-
Phenyl-1-xylylethane, 1-methyl-1-dimethylphenyl-1-phenylmethane, 1-ethyl-1-dimethylphenyl
1-phenylmethane, 1-propyl-1-dimethylphenyl-1
Diarylalkanes such as -phenylmethane; chlorinated paraffins, and mixtures thereof. In the present invention, in addition to the organic solvent, if necessary, ethyl acetate,
A low boiling organic solvent such as isopropyl acetate or butyl acetate may be mixed as a solubilizing agent in an amount of 30% by weight or less of the nonvolatile hydrophobic organic solvent.

As a first embodiment of the present invention, a method for producing a solid color decoloring agent will be described. First, a guanidine compound is added to a nonvolatile hydrophobic organic solvent and mixed. Since the guanidine compound is insoluble or hardly soluble in a non-volatile hydrophobic organic solvent as a reaction solvent, it is sufficiently stirred and mixed to form a uniform dispersion. Next, the isocyanate compound is added to the dispersion at room temperature. When the stirring and mixing are continued, the guanidine compound and the isocyanate compound gradually react and gradually dissolve in the nonvolatile hydrophobic organic solvent. When the transparent solution is formed, stirring is stopped and the mixture is left to stand. The reaction further proceeds to obtain a resinous reaction product containing a solid nonvolatile hydrophobic organic solvent.
The obtained solid resinous reaction product is pulverized using a conventionally known technique to obtain a decoloring agent.

In the above reaction, the weight ratio of the guanidine compound to the isocyanate compound is in the range of 1: 1 to 1: 4. The amount of the nonvolatile hydrophobic organic solvent used is about 70% of the total weight of the guanidine compound and the isocyanate compound.
Amounts ranging from wt% to about 120 wt% are used.

The details of the reaction between the guanidine compound and the polyvalent isocyanate compound in the present invention have not been elucidated. However, first of the guanidine compounds-
When an addition polymerization reaction proceeds between the NH- group and the -NCO group of the polyvalent isocyanate compound to form a prepolymer, the prepolymer is formed, the polymer becomes soluble in the organic solvent, and the polymerization proceeds to form an insoluble resinous solid. It is presumed to be formed. The molecular weight of the insoluble resinous solid is desirably in the range of 1,200 to 6,000 from the viewpoint of softening melting temperature and thermal stability in a coated state.

The decolorizing agent powder obtained by finely pulverizing the solid resinous reaction product obtained by the above reaction is roughly dispersed in water in an amount of 5 to 30% by weight, and then appropriately dispersed in a suitable dispersing machine (for example, Using a ball mill, a sand mill, an attritor, or the like), the dispersion is finely dispersed to a diameter of about 0.1 to 10 μm to obtain a decolorizer dispersion. When the dispersion itself is used as the decoloring agent of the present invention, the material for forming the low-temperature leuco dye coloring layer contains 10
It may be mixed in an amount of up to 30% by weight. When a decoloring agent is present in the decoloring layer formed as another layer adjacent to the low-temperature leuco dye coloring layer, a binder (for example, polyvinyl alcohol, starch, styrene-butadiene latex) is added to the decoloring agent dispersion. Acrylate emulsion), finely disperse to a diameter of about 0.1 to 10 μm in the same manner as described above, and use a conventionally known coating method to make it exist as an overcoat or undercoat above or below the low-temperature leuco dye coloring layer. This is achieved by: In this case, preferably, 5 to 20% by weight of a binder is added to the decolorizing agent dispersion, and the obtained decolorizing layer forming coating solution is applied in an amount of 2
It is applied and dried in the range of 1515 g / m ² to form a decoloring layer having a thickness of 2 to 5 μm. In the present invention, the decolorizing agent dispersion may be contained both in the low-temperature leuco dye coloring layer and in another layer adjacent to the layer.

In the second embodiment of the present invention, in order to further improve both the decoloring effect and the stability of the coloring function of the multicolor heat-sensitive recording material, a microcapsule wall forming material (here, wall) suitable for a decoloring agent is used. Decoloring agent microcapsules encapsulated in the composition) can also be used. Less than,
A method for producing the decolorizer microcapsules will be described. First, a guanidine compound is added to the above-mentioned nonvolatile hydrophobic organic solvent and mixed. Since the guanidine compound used in the present invention is insoluble or hardly soluble in the above-mentioned organic solvents, the guanidine compound is sufficiently mixed and stirred in the solvent to convert it into a uniform dispersion. Next, the isocyanate compound is added at room temperature, and stirring is continued at a stirring speed of 100 to 1,000 rpm for 3 to 10 minutes, whereby the guanidine compound and the isocyanate compound gradually react and gradually dissolve in the nonvolatile hydrophobic organic solvent. Begin to. When the reaction solution became transparent, the stirring was stopped once, and this was added to an aqueous solution containing a protective colloid such as polyvinyl alcohol, and further emulsified and dispersed under stirring conditions of about 5,000 to about 10,000 rpm for 10 to 60 minutes. After emulsification, the stirring speed is 3,000-5,000rp
m, the temperature is raised to 40 ° C. to 80 ° C., and stirring is continued for 60 to 180 minutes, and the interfacial polymerization reaction between the residual polyvalent isocyanate compound and water in the nonvolatile hydrophobic organic solvent causes the guanidine compound / isocyanate A microcapsule coating (wall) is formed around the reaction product in which the compound is emulsified and dispersed. Microcapsules having a diameter of about 0.1 to 10 μm and containing a resinous material containing a nonvolatile hydrophobic organic solvent are obtained.

In the microencapsulation of the decoloring agent in the present invention, it is also possible to add other known microcapsule wall-forming materials such as polyvalent amines and polyols for microencapsulation. What is important here is that the reaction between the polyvalent isocyanate compound and the guanidine compound is not completely terminated in the emulsification / dispersion step and is liquid, and at the end of microencapsulation, the reaction product is a prepolymer, That is, the state of the resinous material is maintained. Unlike the case where the prepolymer is used as a solid reaction product, the molecular weight of the prepolymer is preferably in the range of 400 to 3,000, since the prepolymer is softened and melted by heat and elutes from the capsule wall to cause a decoloring reaction. Is desirable.

The heat-sensitive microcapsules using the conventionally known interfacial polymerization method can encapsulate only a liquid substance such as a hydrophobic liquid or a hydrophobic organic solvent solution. By the encapsulation method, it was possible to obtain, for the first time, a heat-sensitive microcapsule containing a resinous material insoluble in a hydrophobic organic solvent. Also,
Conventionally, mechanically dispersing an insoluble resinous material in water to a diameter of 0.1 to 10 μm is extremely inefficient because a long time is required, and it has been difficult to obtain a uniform dispersion. By the microencapsulation method of the present invention described above,
A uniform decolorant dispersion can be obtained at once and easily, and the inclusions can be chemically and / or physically separated in the low-temperature leuco dye coloring layer and / or in another layer adjacent to said layer. It has become possible to stably hold it.

The microcapsule wall-forming material (that is, wall-forming agent) suitable for the method for microencapsulating a decoloring agent according to the second embodiment of the present invention includes polyurethane, polyurea, polyamide, polyester, urea-formalin resin, melamine Resins, gelatin and the like can be mentioned, and in particular, polyurea-polyurethane, polyurea, and polyurethane resin are preferable because of excellent heat sensitivity. In the above second embodiment of the present invention, a guanidine compound insoluble in a nonvolatile hydrophobic organic solvent is reacted with a polyvalent isocyanate compound to make the guanidine compound soluble in the organic solvent. It is emulsified and dispersed in an aqueous protective colloid solution such as alcohol, and furthermore, the reaction product of the guanidine compound and the polyvalent isocyanate compound is microencapsulated, and at the same time, the polymerization in the reaction product is advanced to form a nonvolatile hydrophobic organic solvent. A generally known method of microencapsulation can be referred to except for obtaining a resinous insoluble solid containing the solid. For example, the details thereof are described in JP-A-59-222716, the disclosure of which is incorporated herein by reference.

The microcapsules produced as described above are:
When heat is applied, the decolorizing agent contained therein is released to the outside by breaking the microcapsules or through the capsule coating without breaking the microcapsules. By using such heat-sensitive microcapsules, the decoloring agent is stably isolated from the high-temperature coloring layer, and the decoloring agent is present in the low-temperature leuco dye coloring layer or in another layer adjacent to the layer. However, the stability of the coloring function before coloring and the stability with time of the recording of the coloring image after coloring can be guaranteed.

A binder such as polyvinyl alcohol, starch, styrene-butadiene latex, acrylate emulsion and the like, and various auxiliaries as needed are added to the microcapsule solution containing the above-described decoloring agent, After conversion to the decolorizing agent microcapsule dispersion, the dispersion is directly mixed with the low-temperature leuco dye coloring layer coating solution and used. Preferably, for the microcapsule liquid,
The above various additives can be added in a total amount of 5 to 50% by weight. When a decoloring agent is present in another layer adjacent to the low-temperature leuco dye coloring layer as the decoloring layer, the decolorizing agent microcapsule dispersion liquid is overlaid on or below each low-temperature leuco dye coloring layer. Achieved by being present as a coat or undercoat. In this case, it is preferable to apply and dry the above-mentioned decolorizing agent microcapsule dispersion in a coating amount of ^{2 to} 15 g / m ² ,
A decoloring layer of ~ 10 µm is formed. In the present invention, the microcapsule dispersion liquid of the decoloring agent may be contained both in the low-temperature leuco dye coloring layer and in another layer adjacent to the layer.

Leuco dyes suitable for use in the low-temperature leuco dye coloring layer of the present invention include triarylmethane, diphenylmethane, xanthene, thiazine, and spiropyran compounds. For example, Japanese Patent Publication No. 6-431, Japanese Patent Application Laid-Open No. 2-9680, Japanese Patent Application Laid-Open No. 2-1362, and Japanese Patent Publication No. 51-37542 discloses a number of leuco dyes, and in the present invention, Any of these known colorless or pale leuco dyes can be used,
These disclosures are incorporated herein by reference. The present invention
Of course, the present invention is not limited to the leuco dyes described in the above publication, and two or more of the above dyes may be mixed and used as necessary in consideration of hue and decoloring effect. The coloring temperature of the low-temperature leuco dye can be controlled by using a sensitizer (a heat-fusible substance). In the case of FIG. 1 described above as an example, the low-temperature leuco dye coloring layer (3)
It is desirable to use a dye that develops a color between 80 and 95 ° C. Specifically, as a blue coloring component, leuco dye
Examples include a mixture of 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (CVL) with various known sensitizers (eg, dibenzyl oxalate). On the other hand,
The high temperature leuco dye coloring layer (2) is preferably 105 to 120 ° C.
It is preferable that the difference in coloration temperature between the dye used in the low-temperature leuco dye coloring layer (3) and the dye used in the high-temperature leuco dye coloring layer (2) is 10 to 40 ° C. Specific examples of leuco dyes include 3-diethylamino-6-methylfluoran, 3-diethylamino-5-ethyl-7-chlorofluoran, and the like. Sensitizers (thermofusible substances) that adjust the sensitivity of the heat energy to develop color include stearic acid amide, methylene bisamide stearate, 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 4,4 '
Many substances are already known, such as -butylidenebis (6-tert-butyl-3-methylphenol) and 4,4'-ethylenedioxy-bis-benzoic acid diphenylmethyl ester, and these substances should be appropriately selected and used. For example, the above-mentioned JP-B 6-431, JP-A 2-9680, JP-A 2-1
There are many examples in Japanese Patent Publication No. 362, Japanese Patent Publication No. 51-37542, etc., which are cited here.

The developer used in combination with the low-temperature and high-temperature leuco dyes also includes phenol, triphenylmethane, sulfur-containing phenol, carboxylic acid, sulfone, urea or thiourea compounds. Numerous substances are known. For example, the above publications, and the Pulp and Paper Times (1985), pp. 49-54 and
Examples of a large number of color developers are described on pages 65 to 70 and the like, and any of these color developers can be similarly used as the color developer in the present invention. To quote.

The coating solution for the low-temperature and high-temperature leuco dye coloring layers is first prepared by separately adding the above-mentioned leuco dye and the developing agent separately to an aqueous solution containing a dispersion-protecting polymer such as polyvinyl alcohol or polyacrylamide by a ball mill or an atomizer. Finely disperse into fine particles of several μm or less using a lighter, sand mill or the like. Thereafter, the two are mixed, and if necessary, a binder, an inorganic pigment, a sensitizer, a lubricant, and other auxiliaries are added to prepare the coating solution for a thermosensitive coloring layer.

Examples of the binder used in the thermosensitive coloring layer coating solution include starch, methylcellulose,
Polyvinyl alcohol, carboxy-modified polyvinyl alcohol, polyacrylamide and the like, as the inorganic pigment, for example, kaolin, clay, calcium carbonate,
Examples of the fine particles include anhydrous silica, and examples of the sensitizer include fatty acid amides, aromatic carboxylic acid esters, fatty acid esters, and aromatic ethers. As a binder, an inorganic pigment, a sensitizer, a lubricant, and other auxiliaries that can be used in the present invention, various known materials can be used.

In the present invention, the types and amounts of the leuco dye, the developer, the sensitizer, and other various components used in the coating solution for the leuco dye coloring layer are determined by the hue required for each heat-sensitive layer, Although determined by heat energy sensitivity and recording suitability, usually, 1 part of leuco dye, 3 to 12 parts of developer, 0 to 12 parts of sensitizer, 1 to 20 parts of inorganic pigment
Parts and binder are used in an amount of 10 to 25 parts (solids).

The thus obtained coating solution for leuco dye coloring layer is coated with a known coating method such as a wire bar, an air knife, a roll, a gravure screen or a blade in order to produce the multicolor heat-sensitive recording material of the present invention. To a suitable support such as, for example, base paper, woodfree paper, condenser paper, cellophane, polyethylene film or polyester film. The coating amount of each coating solution is determined by the color density (ie, “color tone”) of each color forming layer,
It is determined experimentally depending on the heat sensitivity, the degree of the decoloring effect, and the like. The leuco dye coloring layer: ^{2 to} 12 g / m ² , preferably 3 to 7 g / m ² , and the decoloring agent layer: ^{2 to} 15 g / m m ² . Each coating solution is coated and dried on or under the support, or each leuco dye coloring layer, or the decoloring layer or the intermediate blocking layer, and each leuco dye coloring layer is formed in a thickness of 2 to 10 μm, respectively. The multicolor heat-sensitive recording material of the present invention is produced.

In the multicolor heat-sensitive recording material of the present invention, as described above, in order to guarantee the function of the decoloring agent and to prevent the coloring of the high-temperature coloring layer from occurring due to the decoloring agent, the intermediate blocking layer is formed. They may be provided as needed. The intermediate barrier layer suitable in the present invention includes a binder (for example, a water-soluble resin liquid such as polyvinyl alcohol, a water-soluble polyester resin, an epoxy dispersion water-soluble polyester resin, or a shellac resin), an extender, titanium oxide, zinc oxide, and the like. The binder: extender pigment: white pigment may be mixed with a solvent in a weight ratio of 5 to 30: 5 to 10: 5 to 10 to obtain a solid content of 10 to 40% by weight. A solution is prepared, and the solution is applied by a conventionally known application method at an application amount of ² to 10 g / cm ² and dried to form a film having a thickness of 1 to 5 μm.

Further, in the present invention, an intermediate layer can be provided so as to give an appropriate temperature gradient to the cross section of the recording paper so that the thermal energy given by the thermal head or the like gives desired different colors. As this intermediate layer, in addition to the decoloring agent layer and / or the intermediate blocking layer having the same function, another polyethylene wax emulsion or the like having no decoloring function or blocking effect is applied to reduce the thickness. It can be varied to control the temperature gradient.

In a further embodiment of the present invention,
Optionally by laminating one or more hot leuco dye coloring layers and low temperature leuco dye coloring layers, and optionally a decoloring layer and / or an intermediate blocking layer or intermediate layer.
It is also possible to form a multicolor heat-sensitive recording material of two or more colors or full color.

[0038]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. Example 1 Decolorant Dispersion A guanidine dispersion was prepared by adding 1.5 parts by weight of di-o-tolylguanidine to 8.0 parts by weight of diisopropylnaphthalene at room temperature and stirring. Next, a solution prepared by adding 0.2 parts by weight of butyl acetate to 4.6 parts by weight of 2,4-tolylene diisocyanate was prepared and added to the guanidine dispersion. When stirring was continued at room temperature, a reaction gradually occurred between guanidine and the isocyanate, and the reaction product began to dissolve in diisopropylnaphthalene, a nonvolatile hydrophobic organic solvent. Stop stirring when it becomes a clear solution, 40 ℃
And left for 1 to 3 hours, the reaction further proceeded to obtain a resin-like solid decoloring agent containing diisopropylnaphthalene. This was crushed by a grinder, and a 20% oxidized starch aqueous solution was added to 10.0 parts by weight of the crushed decoloring agent.
0 parts by weight were added and finely dispersed by a sand mill until the average diameter became 3 μm, whereby a decolorizing agent dispersion was obtained.

Example 2: Dispersing agent microcapsule dispersion 30 parts by weight of the prepolymer clear solution obtained in the course of the reaction in Example 1 was added to 40 parts by weight of a 10% aqueous polyvinyl alcohol solution at about 12,000 rpm. The guanidine solution was emulsified into microdroplets having a diameter of about 1 to 5 μm by gradually adding while stirring. 0.5 parts by weight of a 20% aqueous solution of hexamethylenediamine is added to the emulsion, and the temperature is raised to 60 ° C.
It lasted for 3 hours. An interfacial polycondensation reaction occurs between the isocyanate and the diamine remaining in the guanidine solution, a microcapsule coating is formed around the microspherical guanidine / isocyanate reaction product, and a resinous material containing diisopropylnaphthalene is formed. An encapsulated microcapsule dispersion was obtained. To this, 50 parts by weight of water was added to obtain a dispersion in water.

Example 3: High-temperature thermosensitive recording layer dispersion 3- (N-cyclohexyl-N-methylamino) -6-methyl-7-
A color former dispersion was prepared by finely dispersing 10 parts of phenylaminofluorane, 5 parts of a 5% aqueous solution of polyvinyl alcohol, 15 parts of calcium carbonate, and 25 parts of water by a sand mill until the average particle diameter became 3 μm.

Separately, 30 parts of 4,4'-isopropylidene diphenol, 30 parts of a 5% aqueous solution of polyvinyl alcohol, 15 parts of calcium carbonate, and 70 parts of water are finely dispersed by a sand mill until the average particle diameter becomes 3 μm. A developer dispersion was obtained.

40 parts of the above-prepared colorant dispersion and 130 parts of the developer dispersion were mixed with a 20% aqueous solution of polyvinyl alcohol 7
The mixture was stirred and mixed with 5 parts and 70 parts of water to obtain a high-temperature coloring heat-sensitive recording layer dispersion liquid.

Example 4: Low-Temperature Coloring Thermosensitive Layer 10 parts by weight of 3-diethylamino-7,8-benzofluoran, 20 parts by weight of dibenzyl terephthalate, 15 parts by weight of calcium carbonate, 15 parts by weight of a 5% aqueous solution of polyvinyl alcohol, and water 80 parts by weight were finely dispersed by a sand mill until the average particle diameter became 3 μm to prepare a color former dispersion.

125 parts by weight of this color former dispersion, 130 parts by weight of the developer dispersion described in Example 3, 150 parts by weight of a 20% aqueous solution of polyvinyl alcohol, and 55 parts by weight of water were stirred and mixed to produce a low-temperature color thermosensitive recording. This was a layer dispersion.

Example 5: Preparation of two-color heat-sensitive paper-1 A high-temperature color heat-sensitive dispersion of Example 3, a decolorizer dispersion of Example 1, and a low temperature of Example 4 were weighed on a high-quality paper of 50 g / m ^2. The coating amount after drying of the color dispersion was 6 g / m ² , 4 g / m ² ,
g / m ^2, and then dried.
A heat-sensitive paper capable of color development was obtained.

[0046] Example 6: woodfree paper creation -2 basis weight 50 g / m ² of 2-color thermal paper, a high temperature color developing thermal dispersion of Example 3, decolorizer microcapsule dispersion of Example 2, Example Each of the low-temperature coloring dispersions of No. 4 and 6 was dried in an amount of 6
^{g / m 2, 4g / m} 2, 4g / m 2 and so as to successively coated and dried to give 2-color development that can be thermal paper with three layers.

Example 7 Preparation of Two-Color Thermal Paper— The high-temperature color heat-sensitive dispersion of Example 3 was applied to high-quality paper of 50 g / m ² basis weight and dried. Next, 10 parts by weight of the decolorizing agent microcapsule dispersion of Example 2 and 10 parts by weight of the low-temperature coloring dispersion of Example 4 were mixed, stirred, applied, and dried to form a two-layer thermosensitive paper. Produced. Coating amount after drying is ^{6g / m 2, 4g / m} 2 in order respectively, to obtain a 2-color development that can be thermal paper.

Example 8: Preparation of two-color heat-sensitive paper-4 High-temperature color heat-sensitive dispersion of Example 3 and 10 parts by weight of the decolorizer dispersion of Example 1 on 40 g / m ² high quality paper % Microcrystalline wax emulsion (“Emaster 042X” manufactured by Nippon Seiro Co., Ltd.) 10 parts by weight of a decolorizing agent / wax dispersion mixed and stirred, 10 parts by weight of the decolorizing agent dispersion of Example 1 and the low temperature of Example 4 A mixture obtained by mixing and stirring 10 parts by weight of the color dispersion was sequentially applied and dried to prepare a two-layer heat sensitive paper having a three-layer structure. The coating amount after drying was 6 g /
m ² , 4 g / m ² and 4 g / m ² .

Comparative Example 1 As a decolorizing agent dispersion, 1.0 part by weight of a 20% aqueous starch oxide solution was added to 5.0 parts by weight of di-o-tolylguanidine in place of the microcapsule dispersion of the decolorizing agent of Example 2, and a sand mill was used. A two-color heat-sensitive paper was obtained in the same manner as in Example 6, except that a decolorizing agent dispersion finely dispersed until the average diameter became 3 μm was used.

The two-color heat-sensitive recording materials obtained by the above Examples and Comparative Examples can obtain red color images at a temperature of about 90 ° C. and black color images at a temperature of about 140 ° C. For these, printing was performed by using a thermal printer PW-PR01-02 manufactured by NEC Corporation and applying heat application energy changed corresponding to each temperature of about 90 ° C. and about 140 ° C. The results are summarized in Table 1.

[0051]

[Table 1]

As is evident from Table 1, an extremely vivid and excellent two-color heat-sensitive recording material was obtained.

[0053]

According to the present invention, in a multicolor heat-sensitive recording material, a low-temperature leuco dye coloring layer containing a particulate decoloring agent or a decolorizing agent microcapsule, or a particulate decoloring agent or a decolorizing agent The decoloring layer containing the capsule,
By providing the layer in combination with the high-temperature leuco dye coloring layer and, if necessary, the intermediate blocking layer, it is possible to obtain a clear image recording which is excellent in the stability of the coloring / decoloring mechanism and free from color mixing and bleeding.

[Brief description of the drawings]

FIG. 1 shows a schematic cross-sectional view of one embodiment of the multicolor thermal paper of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Support, 2 ... High temperature leuco dye coloring layer, 3 ... Low temperature leuco dye coloring layer, 4 ... Decoloring layer, 10 ... 2-color thermosensitive recording paper.

Claims (3)

[Claims] 1. (a) a support, and (b) two or more thermosensitive coloring layers having different coloring hues formed on the support, and at least one of the thermosensitive coloring layers is a leuco dye coloring layer. A multicolor heat-sensitive recording material comprising a leuco dye coloring layer and / or a layer containing a particulate decoloring agent in another layer adjacent to the layer, wherein the decoloring agent is Is, in the presence of a non-volatile hydrophobic organic solvent,
A recording material comprising a reaction product of a guanidine compound insoluble or hardly soluble in a nonvolatile hydrophobic organic solvent and a polyvalent isocyanate compound. 2. The method according to claim 1, wherein the particulate decoloring agent is present in the form of microcapsules having a diameter of 0.1 to 10 μm and enclosed by a wall material selected from the group consisting of polyurea, polyurethane and polyurea-polyurethane. The multicolor heat-sensitive recording material as described above. 3. A decoloring agent, wherein a guanidine compound insoluble or hardly soluble in a nonvolatile hydrophobic organic solvent is first dispersed in a nonvolatile hydrophobic organic solvent, and then a polyvalent isocyanate compound is added thereto. Stir until homogenized to react, emulsify to a diameter of 0.1 to 10 μm in a protective colloid-containing aqueous solution or a protective colloid aqueous solution containing a wall-forming agent capable of reacting with the remaining isocyanate in solution before the reaction is completed. The multicolor heat-sensitive recording material according to claim 1, which is microparticles dispersed and optionally heated and microencapsulated.