JPH0450919B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a thermosensitive coloring material capable of producing beautiful dyes with excellent fastness and good sensitivity by heating, and a thermosensitive recording medium using the same. BACKGROUND ART In recent years, non-impact printer systems have been put into practical use as a method for recording information and obtaining visible images. Among these recording methods, thermal recording systems that use dot-line thermal heads have the following characteristics: they are essentially maintenance-free, noiseless, consume little energy, and can be miniaturized. It is becoming widely used in fields such as measuring instrument recorders, computer terminal output records, data communication terminal records, and ticket issuing for station operations. However, as such heat-sensitive recording methods become more widespread, problems with the heat-sensitive recording media currently in use, particularly drawbacks caused by heat-sensitive materials, such as poor light resistance, oil resistance, solvent resistance, and storage stability. etc. are becoming a problem. In other words, due to these drawbacks, thermal recording media are not suitable for promissory notes, checks, etc.
It is not suitable for recording cash certificates such as commuter passes, coupon tickets, and gift certificates, as well as important documents that will be stored for a long time. In addition, even in disposable applications, when it comes into contact with materials containing plasticizers, such as hair styling products, wraps for food packaging, and soft vinyl pass cases used for commuter pass holders, the image may disappear due to migration of the pigment, making it difficult to read. There are problems such as impossibility, and there are restrictions in terms of usage. The disadvantage of such heat-sensitive recording media is that many commercially available heat-sensitive recording materials are composed of leuco dyes such as crystal violet lactone and leucomethylene blue, aromatic compounds having phenolic hydroxyl groups, or acidic substances. ing. In addition, recently, heat-sensitive recording media using iron salt-based heat-sensitive materials have been on the market for applications such as horse racing tickets, but the developed colors are poor and the physical properties are not excellent. In order to improve the drawbacks of the conventional dye-type thermosensitive coloring materials, a pigment-type thermosensitive coloring material has been developed (Japanese Unexamined Patent Publication No. 16781/1981).
That is, this thermosensitive coloring material essentially consists of a coloring agent represented by the following general formula (). [Here, X represents a hydrogen atom or a halogen atom, n is an integer of 0 to 4, R is a hydrogen atom, and the number of carbon atoms is 1
-4 alkyl group or aromatic group, Y is =
CO, =CS, = _SO2 , =C=NH or,

[Formula], R ₁ is −CN, −COC ₆ H ₅ , −COOCH ₃ ,
-Represents COOC ₂ H ₅ or a benzimidazole group. ] and a color developer represented by the following general formula () [However, R ₂ and R ₃ in the above formula are a C ₁ to C ₄ alkyl group, a phenyl group, or (CH ₂ ) _n X ₁ (m is 1
-4 integer, _X1 represents a halogen atom, hydroxyl group or alkylsulfamoyl group), or may be a cyclic group in which _R2 and _R3 are connected directly or through O or S. , R ₄ is a hydrogen atom C ₁ to C ₁₈ alkyl group, alkoxy group,
or an amino group, and HA represents an inorganic or organic acid. ], and is characterized by the formation of a dye with improved solvent resistance, weather resistance, water resistance, etc., especially compared to dyes formed using conventional heat-sensitive color formers. do. However, there are several problems with this heat-sensitive coloring material, and the biggest one is the thermal sensitivity of the heat-sensitive recording medium obtained by dispersing these color formers and color developers in a common binder. There is a problem in that the sensitivity is considerably inferior compared to conventional methods using leuco dyes or iron salts. For this reason, the reality is that it is still insufficient in terms of practical use. OBJECTS OF THE INVENTION In view of the above-mentioned circumstances, an object of the present invention is to provide a thermosensitive color-forming material that combines various fastness properties and thermal sensitivity, and a thermosensitive recording medium using the same. Summary of the Invention For the above-mentioned purposes, the present inventors conducted research to increase the thermal sensitivity of a system consisting of a combination of a color forming agent of the above formula () and a color developer of the formula () to a practical level. As a result, we found that by introducing a nitro group as at least one of the groups X ₁ to _{X 4} in the color forming agent of the above formula (), it is possible to significantly improve the thermal sensitivity while maintaining the characteristics of this system. I found it. The thermosensitive color forming material of the present invention is based on such knowledge, and more specifically, the thermosensitive color forming material of the present invention is based on the following general formula (1).
It is characterized by consisting of a combination of a color forming agent represented by the formula (2) and a color developer represented by the general formula (2). [However, in the above formula, X ₁ , X ₂ , X _{3 ,} and It represents a tertiary amino group or a halogen atom, and they may be the same or different, but at least one of X ₁ to X ₄ is a nitro group, and R is hydrogen. They are atoms, alkyl groups having 1 to 18 carbon atoms, and aromatic groups. Y is =
CO, =CS, = _SO2 , =C=NH or,

[Formula] represents, R ₁ is CN, COC ₆ H ₅ , COOCH ₃ ,
COOC ₂ H ₅ represents a benzimidazole group. ] [However, R ₂ and R ₃ in the above formula are a C ₁ to C ₁₈ alkyl group, a phenyl group, or C _n H _(2n+1-o) X _o (m is an integer of 1 to 4, n is an integer of 1 to 9, X represents a halogen atom, a hydroxyl group, or an alkylsulfamoyl group), or a cyclic group in which R ₂ and R ₃ are connected directly or through O or S. Preferably, R ₄ represents a hydrogen atom C ₁ to C ₁₈ alkyl group, alkoxy group, or amino group,
HA represents an inorganic or organic acid. ] Further, the heat-sensitive recording medium of the present invention is formed by forming a heat-sensitive coloring layer on a support, and the heat-sensitive coloring layer contains a coloring agent represented by the above general formula (1) and a color former represented by the general formula (2). It is characterized in that it contains a color developer represented by the following in a state that it can be contacted with the color developer separately under heating. The thermosensitive coloring material of the present invention has excellent thermal sensitivity,
The reason why a dye with excellent durability can be produced is not necessarily clear, but it is thought that the fastness of the produced dye is due to the stability of the azomethine dye formed in the following manner. That is, the reaction between the color forming agent of formula (1) above and the color developer of (2) yields an addition product as shown in structural formula (3) below, which is
By heating at about 100 to 300℃, ammonia is dissociated to produce inorganic or organic acids and salts, and the formula (4)
It is thought that stable azomethine dyes such as the following are formed. In addition, when the group R ₄ in the color developer of formula (2) above is an amino group, this amino group also has the same effect as the NH group of the color former of formula (1), as in formula (3) above. An addition reaction is carried out. That is, in this case, addition of 2 moles of color former and subsequent condensation will occur to 1 mole of color developer. The present invention will be explained in more detail below. In the following description, "parts" and "%" expressing quantitative ratios are as follows:
Unless otherwise specified, measurements are based on weight. DETAILED DESCRIPTION OF THE INVENTION The thermosensitive color-forming material of the present invention comprises a combination of a color former represented by general formula (1) and a color developer represented by formula (2). The group of compounds (color formers) represented by the general formula (1) is itself known as an intermediate for azomethine pigments, and a large number of compounds are known. As mentioned earlier, in the present invention, by using a compound in which a nitro group is introduced as a substituent to be introduced into the aromatic ring of formula (1) among these known compound groups,
It has excellent thermal sensitivity and constitutes a thermosensitive coloring system that can develop color with relatively low energy. Specific examples of color formers suitable for use in the present invention include the following compounds. 1,3-diimino-4(or-5)-nitroisoindoline, 1,3-diimino-2,4-dinitroisoindoline, 3-imino-4(or-
5) Nitroisoindoline-1one, 1-imino-3thio-4 (or -5) nitroisoindoline, 1-dicyanomethylene-3-imino-4 (or -5)-nitroisoindoline, 1-cyanocarbo Methoxymethylene-3-imino-4(or-5)-nitroisoindoline, 1-cyanobenzoylmethylene-3-imino-4(or-5)
-Nitroisoindoline, 1-(cyanobenzimidazole-2')-methylene-3imino-4(or -5)-nitroisoindoline, 1-(cyanocarbonialidomethylene)-3imino-4,5-dinitro Isodrine, 1-cyanocarbomethoxymethylene-3-imino-4,5-dinitroisoindoline, 3-imino-4,5-dinitroisoindolin-1-one, 1,3-diimino-4,5,
6-trinitroisoindoline, 3-imino-
4,5,6-trinitroisoindolin-1-one and the like. The color developer represented by general formula (2), which is the other component constituting the thermosensitive coloring material of the present invention, is an amine salt, and specific examples thereof include the following compounds. N,N-dimethyl-p-phenylenediamine hydrochloride, N,N-diethyl-p-phenylenediamine hydrochloride, 4-amino-N,N-diethylamino-m-toluidine hydrochloride, 4-amino-N- Ethyl-N-(β-methylsulfamidoethyl)-m-
Toluidine sulfate, 4-amino-N-(β-hydroxyethyl)-N-ethylaniline sulfate 4-amino-N-ethyl-N-chloroethylamino-m-toluidine hydrochloride, P-morpholinoaniline hydrochloride , 4-morpholino-2,5-diethoxyaniline hydrochloride, P-(N-methyl-N-
phenylamino)-aniline hydrochloride, 4-amino N(β-hydroxyethyl)-m-toluidine sulfate, 4-amino-N-ethyl N-hydroxyethyl-m-toluidine hydrochloride, N-1-naphthyl-
Examples include N'-diethylethylenediamine hydrochloride. In addition, although all the above examples are inorganic hydrochlorides and sulfates, depending on the purpose of use, organic acid salts such as acetate, formate, oxalate, stearate, and laurate may also be used. It can also be used as The thermosensitive color-forming material of the present invention is basically obtained by combining the above-described color former and color developer in a stoichiometric ratio. That is, when the color developer represented by formula (2) is a monoamine salt, the color developer and color forming agent are used in an approximately equimolar ratio, and the diamine salt (R ₄ in formula (2)) is used as the color developer. is an amino group),
Approximately 1 mole of color developer is used per 2 moles of color former, but it is also possible to use these two types of color developer in combination and adjust the amount ratio with the color former accordingly. The heat-sensitive recording medium of the present invention is formed by forming a heat-sensitive color-forming layer on a support, using the heat-sensitive color-forming material, and containing the color former and color developer in a separated state, which can come into contact with each other under heating. Such a heat-sensitive recording medium is produced by independently dispersing a coloring agent represented by general formula (1) and a coloring agent represented by general formula (2) in a binder that melts at a desired temperature, and By separately coating the top layer to form a heat-sensitive coloring layer having a multilayer structure of a color former layer and a color developer layer, or by mixing and applying both, it is essentially a single layer, but inside it can be obtained by forming a heat-sensitive coloring layer containing a color former and a color developer separated via a binder. Further, if necessary, one or both of the color former and the color developer can be microencapsulated with a heat-melting or thermoplastic material. A heat sensitizer can also be used in combination with the heat-sensitive color forming material of the present invention to further improve the heat sensitivity. According to the research of the present inventors, in the combination of the color former and color developer, a specific compound, namely a benzophenone derivative, exhibits a unique heat sensitizing effect,
Preferably used. In other words, the benzophenone derivative also functions as a melting point depressant for the binder used, melting preferentially and not only promoting mutual contact between the color former and color developer, but also inhibiting the reaction between the two. It is thought that it also acts as a catalyst. By using a benzophenone derivative, a thermosensitive recording medium can be obtained which has a thermal sensitivity improved by 25 to 50% compared to a case where no benzophenone derivative is used. Specific examples of preferred benzophenone derivatives include the following compounds. 2,4-dihydroxybenzophenone, 2-hydroxy4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-dodecyloxybenzophenone,
2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, 2-hydroxy- 4-methoxy-2-carboxybenzophenone and the like can be used. These heat sensitizers are used per mole of the addition reaction product to be produced by the reaction between the color former and the color developer.
It is preferable to use it in a proportion of 0.1 to 2 moles. When using a heat sensitizer in a multi-layer thermal recording medium, the heat sensitizer is either included in the color developer layer provided on the color former layer, or placed between the color former layer and the color developer layer. Preferably, a separate heat sensitizer layer is formed. Regarding the configuration of each part of the thermosensitive recording medium of the present invention,
To explain in more detail, the material of the support can be any material, including ordinary paper such as coated paper, art paper, and high-quality paper, as well as plastics such as polyester, polyolefin, polyvinyl chloride, triacetate, and other films or sheets. It can be selected from those commonly used as base materials. It goes without saying that these can be used by adding various fillers and other additives, or by coloring them. In addition, flexible sheet materials such as cloth and metal foil are preferably used, and any solid material on which a heat-sensitive coloring layer can be formed by coating or the like can be used. The binder used for dispersing the color forming agent, developer, or heat sensitizer to form a heat-sensitive color forming layer may be any one of the following, as long as it can fix these components on the support and does not interfere with their action. Any material can be used. Common binders include:
It is a synthetic or natural resin. For example, acrylic resins such as polyacrylates and polymethacrylates, cellulose resins such as nitrocellulose, cellulose acetate, cellulose acetate butyrate, ethylcellulose, and hydroxyethylcellulose, polyvinyl acetate, polyvinyl alcohol, polyvinyl formal, and polyvinyl butyral. Thermoplastic resins such as vinyl acetate resins such as, vinyl polymer resins such as polyvinylpyrrolidone and polyvinyl carbazole, polyester resins, polycarbonate resins, polyamide resins, polyurethane resins, and ethylene vinyl acetate copolymer resins are preferred. Various photosensitive resins can also be used as binders. Examples are polyvinyl cinnamate,
Cinnamate ester of ethylene-vinyl alcohol copolymer, cinnamate ester of glyptal resin,
Cinnamate ester of epoxy resin, cinnamate ester of polyether resin, cinnamoyl type polymer with styrene backbone, cinnamoyl type polymer of acrylic, cinnamate ester of styrene-maleic anhydride copolymer, polyvinyl cinnamyl Denacetate, polyvinylbenzalacetophenone, polyvinyl styryl ketone, polyvinyl-
These include p-azidobenzoate, polyvinyl-p-azidobenzal, and a condensation polymer of m-nitrobenzaldehyde and phenol. When using such a photosensitive resin, it is preferable to use a sensitizer such as a benzophenone type or anthraquinone type in combination. The binder described above may be used in an amount of about 30 to 600 parts per 100 parts of the total weight of the color former and color developer. Suitable amounts are usually in the range of about 100 to 300 parts. Even when the color forming agent layer, color developing agent layer, or heat sensitizer layer is provided as separate layers, it is appropriate to use the binder in the above ratio for each component. It is recommended that a lubricant and a mold release agent be added to the thermosensitive coloring layer, particularly in the uppermost layer when a multilayer structure is adopted, in order to prevent the layer from adhering to the recording head during use. In particular, dot line type thermal printers apply pressure during thermal printing, causing strong friction between the recording material and the thermal head, so it is effective to use lubricants and release agents in thermal recording materials intended for such applications. be. Metal soaps, ie, metal salts of fatty acids such as lauric acid and stearic acid, are representative of substances that serve as lubricants, but there are also the following substances: Organotin fatty acids, such as dibutyl-tin-dilaurate, dibutyl-tin-dinonylate, fatty acid amides, such as stearylamide, palmitylamide, oleylamide, bis-fatty acid amides, higher ketones, such as stearone, higher alcohols and their derivatives, such as myristyl alcohol. , cetyl alcohol, stearyl alcohol, polyethylene glycol, polyglycerol, hydrocarbons such as liquid paraffin, paraffin wax, micro wax, polyethylene with a low degree of polymerization, and natural waxes such as carnauba wax, candelilla wax, beeswax, spermaceti wax , Ibotarou, Montaro. Mold release agents generally refer to those used for the purpose of improving mold release during the processing of rubber and plastics. Many kinds of substances are useful, but the main ones are as follows. Mineral oils, such as petroleum ethers, Vegetable oils, such as olive oil, castor oil, petrolatum or lanolin, Fatty acids, especially alkanoic or alkenoic acids having 11 to 24 carbon atoms and their esters, especially C ₆ -
Esters with alkyl or alkenyl of C ₂₄ , phosphites, especially phenyl or C ₈
Esters of ~ _C13 alkyls, fatty acid esters of glycerin-sorbitan condensates, alkenoyl ( _C7 - _C21 ) amino acid esters, fluorocarbons such as Teflon, and silicones. In order to form a heat-sensitive coloring layer comprising the above-mentioned components on a support, known techniques may be followed. For example, the color forming agent and the color developing agent are preferably contained separately in an inert organic solvent together with waxes, binders, and, if necessary, gum arabic, casein, clay, talc, titanium oxide, and other organic pigments. After dissolution or dispersion, they are applied as individual or mixed coatings to the support by conventional coating or printing methods. The above-mentioned mixed coating solution containing a color former and a color developer in a dispersed state, or the combination of a coating solution containing a color former and a coating solution containing a color developer, is a specific example of the heat-sensitive color forming material of the present invention. This is one product aspect. The application method of the above-mentioned coating liquid is gravure coating,
roll coat, air knife coat, kiss coat,
Spray coating, continuous coating, dip coating, spinner coating, wheeler coating, wire bar coating, brush coating, solid printing by silk screen, gravure printing, gravure offset printing, lithographic offset printing, dilithography, letterpress printing, intaglio printing, digital printing. Includes a wide range of printing methods such as etching and electrostatic printing. The amount of heat-sensitive color forming layer applied on the support is determined by the color density,
2 to 30 on dry weight basis, considering resolution etc.
Select from the g/ ^m2 range. A particularly suitable amount is usually 2 to 5 g/m ² . In addition to the above-mentioned essential components, the thermosensitive recording medium of the present invention may include an adhesive layer or a protective layer between the support and the recording layer, or may use both together. The adhesive layer enables adhesion between the support and the recording layer when they do not adhere as they are, or improves adhesion when it is difficult to do so. Resin-based products such as ethylene-vinyl acetate copolymer, acrylic resin, polyvinyl chloride, epoxy resin, polyester, phenol resin, cyanoacrylate, urea resin, polyurethane, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, and neoprene, styrene. You can select from rubber-based materials such as butadiene rubber and nitrile rubber. The protective layer that provides moisture resistance to the heat-sensitive recording medium and improves the running performance of the thermal head is made of materials with a thermal softening temperature among the materials used as the binder for the recording layer.
It can be provided using a paint whose main component is a thermoplastic resin having a temperature of 150° C. or higher, or a resin curable by a two-component addition reaction of an OH group-containing component and a polyisocyanate. The thermal head for recording on the thermosensitive recording medium of the present invention may be of any type, such as a line or matrix dot type, a segment type, a thermal type type, or a thermal pen type. By setting a predetermined temperature and time with these heating elements and heating and scanning, desired colors, designs, letters, numbers, etc. can be developed. The thermal energy required for color development of the thermosensitive recording medium according to the present invention is in the range of 0.5 to 5 mJ/dot. Effects of the Invention As described above, according to the present invention, due to the combination of a specific originating agent and a color developer, it has a thermal sensitivity comparable to that of conventional thermosensitive coloring materials, and has a higher thermal sensitivity than conventional thermosensitive coloring materials. Thus, a heat-sensitive coloring material capable of providing a stable azomethine-type skeleton dye with dramatically improved water resistance, solvent resistance, oil resistance, light resistance, storage stability, etc. is provided, and this material can be used to improve sensitivity and durability. A thermosensitive recording medium is also provided. Furthermore, the thermosensitive color-forming material according to the present invention can produce yellow, orange, red,
Another advantage is that the color hue can be easily changed over a wide range of colors such as green, blue, purple, brown, and black. Because of these characteristics, the thermochromic organic material according to the present invention can be applied not only to the thermosensitive recording medium described above, but also to coloring and patterning various polymer molded products, and moreover, it can be applied to the final stage of the manufacturing process. Since it is possible to create any color or pattern at any stage, it has the advantage of streamlining the process and diversifying products at the same time. Therefore, its application fields are not limited to heat-sensitive recording media, but also include vinyl tiles, synthetic leather, coated electric wires,
It can also be applied to industrial materials such as plastics and metal coating paints for coloring and patterning. Next, the present invention will be explained in more detail with reference to Examples. Example 1 The following composition was coated on the surface of a milky white polyester sheet "X-24" (manufactured by Toray Industries, Ltd., thickness 188 .mu.m) by a rod coating method so that the thickness after drying was 1 .mu.m to form an adhesive layer. (Adhesive layer composition) Polyester resin (manufactured by Toyobo, Vylon 200#)
18 parts partially saponified vinyl chloride-vinyl acetate copolymer resin (UCC's Vinyrite VAGH) 15 parts toluene 90 parts MEK (methyl ethyl ketone) 45 parts XDI type isocyanate (Takeda Pharmaceutical's Takenate)
D110N) 10 parts total 160 parts The following color former composition and color developer composition were separately prepared, and the first layer was coated onto the polyester sheet by roll coating so that the dry weight was approximately 3 g/ ^m2 . The color-forming composition, then the second layer, and the color-developing composition were applied in this order, and after drying at 60°C for 20 seconds, a protective layer was applied using a gravure printing method to a dry weight of 1 g/
A thermosensitive recording medium was created by overprinting to a size of m ² . (Color former composition) 1,3-diimino-4-nitroisoindoline
20 parts Vinyrite VAGH 20 parts MEK 50 parts Toluene 40 parts Total 130 parts (Developer composition) 4-Amino-N-(β-hydroxyethyl)-N-
Ethylaniline sulfate 20 parts Vinyltoluene-butadiene copolymer resin (Pryolite VT, Gutduyer) 20 parts Ethylcyclohexane 80 parts Total 120 parts (protective layer composition) Vinyltoluene-butadiene copolymer resin (Pryolite VT, Gutduyer) Light VT) 20 parts polyethylene wax (manufactured by Adeka Argus)
FC113) 2 parts fluorocarbon thermal mold release agent (Moldbits F-57 manufactured by Axel Plastics) 2 parts dimethylpolysiloxane type silicone oil (KF-96 manufactured by Shin-Etsu Chemical) 2 parts Ethylcyclohexane 100 parts Cyclohexane 20 parts Total 146 parts This When the thus obtained thermal recording medium was printed with a thermal printer having a dot line type thermal head, a clear high density blue-black image was obtained under the condition of 1.2 mJ/dot. In addition, in order to investigate the static coloring characteristics, when the material was heated at 140° C. for 5 seconds using a thermal press machine (manufactured by Sakata Kiko), it was colored a highly concentrated blue-black color. This colored product showed excellent resistance to organic solvents, plasticizers in erasers, sunlight, etc. Example 2 Railway ticket paper (manufactured by Tokushu Paper Co., Ltd., Kent paper 230g/m ² ) was used as a support, and no adhesive layer was provided on the surface.
A heat-sensitive recording medium was obtained using the following heat-sensitive recording composition and in the same manner as in Example 1 except for the following conditions. (Color former composition) 1,3-diimino-4,5-dinitroisoindoline 20 parts Vinyrite VAGH 20 parts MEK 50 parts Toluene 40 parts Total 130 parts (Color developer composition) 4-Amino-N-(β- hydroxyethyl)-m-
Toluidine sulfate 20 parts 2,4-dihydroxybenzophenone 10 parts Priorite VT 30 parts Ethylcyclohexane 120 parts Total 180 parts This heat-sensitive recording paper has excellent storage stability, and Example 1
When printed in the same manner as above, a clear black-brown image was obtained. The thermal sensitivity at this time was 1.0 mJ/dot. Example 3 The following thermal recording composition and protective layer composition were used, except that a sensitizer composition was formed as an intermediate layer between the color former layer and the color developer layer so that the dry weight was 1 g/m ² A thermosensitive recording medium was produced in the same manner as in Example 1. (Color former composition) 3-imino-4 nitroisoindolin-1one
20 parts colored pigment yellow (manufactured by Hoechst Permanent Yellow)
HR) 0.5 parts Cellulose acetate propionate resin (CAP504-02 manufactured by Eastman Kodak) 20 parts Isopropyl alcohol 160 parts Water 40 parts Total 240.5 parts (Developer composition) N,N dimethyl P-phenylenediamine hydrochloride Silylated hydrophobic silica (Sideroid 162 manufactured by Fuji Davison) 2 parts Ethylene vinyl acetate copolymer resin (Sumitate KC-10 manufactured by Sumitomo Chemical) 20 parts Cyclohexane 200 parts Total 242 parts (sensitizer composition) 2 , 2'-dihydroxy-4-methoxybenzophenone 20 parts Ethylene vinyl acetate copolymer resin (Sumitate KC-10 manufactured by Sumitomo Chemical Co., Ltd.) 10 parts Toluene 80 parts N-hexane 20 parts Total 130 parts (protective layer composition) Single dimethylsiloxane type silicone oil (KF-96 manufactured by Shin-Etsu Chemical Co., Ltd.) This heat-sensitive recording medium is colored pale yellow, and when printed in the same manner as in Example 1, the image develops in reddish-purple color and has excellent contrast. gave an image.
The thermal sensitivity at this time was 1.2 mJ/dot. Example 4 Next, for the purpose of developing images other than black, the following heat-sensitive recording composition was used, and the other conditions were as in Example 1.
A thermosensitive recording medium was obtained in the same manner as above. (Color former composition) 3-imino-4-nitroisoindoline-1-one 20 parts Vinyrite VAGH 20 parts MEK 50 parts Toluene 40 parts Total 130 parts (Color developer composition) m-phenylenediamine-hydrochloride
20 parts Vinyltoluene-butadiene copolymer resin 20 parts Ethylcyclohexane 80 parts Total 120 parts When this heat-sensitive recording medium was heated at 160° C. for 5 seconds using a thermal press, it developed a bright yellow color. Example 5 A heat-sensitive recording medium was obtained using the following heat-sensitive recording composition and following the same conditions as in Example 4 except for the following conditions. (Color former composition) 1-[(cyano-benzimidazolyl-2')-methylene]-3-imino-4-nitroisoindolin-1 20 parts Vinylite VAGH 20 parts MEK 50 parts Toluene 40 parts Total 130 parts ( Color developer composition) 3-3'-dimethyldiphenylenediamine hydrochloride 20 parts Vinyltoluene-butadiene copolymer resin 20 parts Ethylene cyclohexane 80 parts Total 120 parts This heat-sensitive recording medium was heated in the same manner as in Example 4. As a result, the color turned bright red. Example 6 1,3-diiminoisoindoline (hereinafter referred to as Dii
) or 3-iminoisoindoline-1-
The performance of color formers obtained by introducing various electron-withdrawing functional groups into the 4th, 5th, and 6th positions of the isoindoline skeleton based on ion (hereinafter referred to as iiD) was compared. That is, for each of the color formers listed in Table 1 below, a color former composition was prepared in the same manner as in Example 1, and the other conditions were the same as in Example 1 to obtain a thermosensitive recording medium. The evaluation results of each thermal recording medium are
Shown in the table.

[Table] [Evaluation Method] The evaluation results of the heat-sensitive recording media in Table 1 above and the table below were evaluated using the following methods and criteria. Hot temperature static characteristics: using Sakata Kiko's Thermic Press machine, 5
Optical density (OD) by Macbeth reflection densitometer (using Ratten filter #106) in seconds is 1.0
Indicates the temperature reached (initial color development temperature). Dynamic characteristics: Using a Toshiba thermal printer, O.
Indicates the coloring energy required to give D.1.0. **The following measurements were all performed on samples that were heated and colored on a hot plate at 180°C for 5 minutes. Developed color: Visual lightfastness: The time until color fading occurs was measured using a food meter, and evaluated based on the following criteria. 10 hours or less 40 hours or less 160 hours or more × △ ○ Chemical resistance Water resistance: Discoloration and fading after immersion in tap water at 20°C for 80 hours was evaluated. Alcohol resistance: To primary ethyl alcohol at 20℃
After 80 hours of immersion, discoloration and fading were evaluated. Plasticizer resistance: Place an office eraser on the colored image.
The sample was kept at 20°C for 8 hours, and discoloration due to bleeding was evaluated. Regarding water resistance, alcohol resistance, and plasticizer resistance, those whose OD decrease width after testing is within 0.1 based on the optical density OD value of the untested product are ○, those from 0.3 to 0.4 are △, and 0.8 or more. The results were evaluated as ×. Comparative Example 1 Using commercially available thermosensitive recording media, the performance was compared based on the above evaluation method, and the results are shown in Table 2 below.

[Table] From the above evaluation results, it can be seen that the heat-sensitive recording medium obtained using the color former in which at least one nitro group is introduced into the aromatic ring in the formula (1) according to the present invention has no other functional group introduced into the aromatic ring. It is proven that the thermal sensitivity is significantly superior to that using a color former. It can also be easily understood that the various fastness properties of the heat-sensitive recording medium according to the present invention are significantly superior to those of commercially available heat-sensitive recording media. Example 7 1,3-diiminoisoindoline (Dii) or 1,3-diimino-4-nitroisoindoline (abbreviated as Dii- _NO2 ), 1,3-diimino-4-bromoisoindoline (abbreviated as Dii-Br) ), a color former composition was prepared in the same manner as in Example 1, and additives such as melting point depressants or PH varying agents listed in Table 3 below were added to the following color developer composition. A thermosensitive recording medium was obtained under the same conditions as in Example 1 except for the combination. The thermal sensitivity evaluation results of each thermal recording medium are shown in Table 3. (Developer composition) 4-amino-N-(β-hydroxyethyl)-N ethylaniline sulfate 10 parts Vinyltoluene-butadiene copolymer resin 15 parts Ethylcyclohexane 70 parts Additives (each substance shown in Table 3) ) 5 copies total 100 copies

【table】

[Table] According to the performance evaluation in Table 3 above, it is recognized that an outstanding heat sensitizing effect can be obtained when a benzophenone-based substance is used in combination.

Claims (1)

[Scope of Claims] 1. A heat-sensitive color forming material comprising a combination of a color former represented by the following general formula (1) and a color developer represented by the general formula (2). [However, in the above formula, X ₁ , X ₂ , X _{3 ,} and It represents a tertiary amino group or a halogen atom, and they may be the same or different, but at least one of X ₁ to X ₄ is a nitro group, and R is hydrogen. They are atoms, alkyl groups having 1 to 18 carbon atoms, and aromatic groups. Y is =
Represents CO, =CS, =SO ₂ , =C=NH or [Formula], R ₁ is CN, COC ₆ H ₅ , COOCH ₃ ,
COOC ₂ H ₅ represents a benzimidazole group. ] [However, R ₂ and R ₃ in the above formula are a C ₁ to C ₁₈ alkyl group, a phenyl group, or C _n H _(2n+1-o) X _o (m is an integer of 1 to 4, n is an integer of 1 to 9, X represents a halogen atom, a hydroxyl group, or an alkylsulfamoyl group), or a cyclic group in which R ₂ and R ₃ are connected directly or through O or S. Preferably, R ₄ represents a hydrogen atom C ₁ to C ₁₈ alkyl group, alkoxy group, or amino group,
HA represents an inorganic or organic acid. ] 2 The color former of general formula (1) is 1,3-diimino-4
(or -5)-nitroisoindoline or 1,
The heat-sensitive color forming material according to claim 1, which is 3-diimino-4,6 (or -5,6)-dinitroisoindoline. 3. The heat-sensitive color-forming organic material according to claim 1 or 2, wherein the color developer of general formula (2) is a P-phenylenediamine derivative. 4. The thermochromic organic material according to claim 1, 2 or 3, which uses a benzophenone derivative as a heat sensitivity improver. 5 A heat-sensitive color forming layer is formed on a support, and in the heat-sensitive color forming layer, a color former represented by the following general formula (1) and a color developer represented by the general formula (2) are heated. A heat-sensitive recording medium characterized in that the heat-sensitive recording medium is contained separately and in a contactable state at the bottom. [However, in the above formula, X ₁ , X ₂ , X _{3 ,} and It represents a tertiary amino group or a halogen atom, and they may be the same or different, but at least one of X ₁ to X ₄ is a nitro group, and R is hydrogen. They are atoms, alkyl groups having 1 to 18 carbon atoms, and aromatic groups. Y is =
CO, =CS, = _SO2 , =C=NH or,
[Formula] represents, R ₁ is CN, COC ₆ H ₅ , COOCH ₃ ,
COOC ₂ H ₅ represents a benzimidazole group. ] [However, R ₂ and R ₃ in the above formula are a C ₁ to C ₁₈ alkyl group, a phenyl group, or C _n H _(2n+1-o) X _o (m is an integer of 1 to 4, n is an integer of 1 to 9, X represents a halogen atom, a hydroxyl group, or an alkylsulfamoyl group), or a cyclic group in which R ₂ and R ₃ are connected directly or through O or S. Preferably, R ₄ represents a hydrogen atom C ₁ to C ₁₈ alkyl group, alkoxy group, or amino group,
HA represents an inorganic or organic acid. 6. The heat-sensitive recording medium according to claim 5, wherein the heat-sensitive color forming layer contains a color former and a color developer dispersed in a binder. 7. The heat-sensitive recording medium according to claim 5 or 6, wherein the heat-sensitive coloring layer contains a benzophenone derivative as a heat sensitivity improver. 8. Claim 5, wherein the heat-sensitive coloring layer has a laminated structure of a coloring agent layer containing the coloring agent of the formula (1) and a color developer layer containing the color developer of the formula (2). 7. The heat-sensitive recording medium according to any one of items 7 to 7. 9. The heat-sensitive recording medium according to claim 8, wherein the heat sensitivity improver is contained in the color developer layer. 10. The heat-sensitive recording medium according to claim 8, wherein a layer containing a heat sensitivity improver is inserted between the color former layer and the color developer layer.