JPH04325285A - Thermal recording material - Google Patents

Abstract

PURPOSE:To reduce the damage of a thermal head in a thermal recording material wherein at least one color erasing type transparent thermal layer is provided on a support. CONSTITUTION:In a thermal recording material consisting of a support and the thermal layer containing a dye and a color erasing agent capable of erasing the color of the dye formed on the support, the thermal layer is formed by coating the support with a coating solution containing microcapsules including said dye or color erasing agent and an emulsified dispersion having the other component not contained in the microcapsules emulsified and dispersed therein and the total amount of the sodium and potassium ions contained in the coating film is set to 10mg/1m<2> or less.

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, and more particularly to a heat-sensitive recording material that can reduce damage to a thermal head.

0002

BACKGROUND OF THE INVENTION Thermal recording methods (1) do not require development, (2) are easy to handle, (3) have high color density, (4) use a simple and inexpensive recording device; 5) Because it has advantages such as no noise during recording, it has become rapidly popular in the field of facsimiles and printers in recent years.

[0003] In these heat-sensitive recording materials, measures are taken to reduce damage to the thermal head used for recording, but in this case, the total amount of sodium ions and potassium ions contained in the heat-sensitive recording material is reduced. method is adopted.

That is, in the thermal head, the surface of the heating element is
It is covered with a thin inorganic protective film (e.g. aluminum oxide, ruthenium oxide, silicon carbide, silicon oxide, etc.), and this protective film withstands temperatures of 400°C to 700°C during printing, and protects the heat-sensitive layer of the heat-sensitive recording material. It has been thought that the thermal head is protected not only from physical damage caused by the highly hard inorganic powder present in the thermal head but also from damage caused by the presence of sodium ions (Na+) and potassium ions (K+). From this point of view, conventionally, sodium ions and potassium ions contained in thermal paper have been reduced to a predetermined amount (Japanese Patent Publication No. 59-25672).

[0005] In addition, as a heat-sensitive recording material suitable for the image forming method that can be used in the above-mentioned facsimile printers, the present applicant has previously developed a dye that is colored by contacting and reacting a leuco dye with an acidic compound. A heat-sensitive recording material obtained by coating a decoloring agent on the same side of a support (Japanese Patent Laid-Open No. 63-22
No. 7375) was proposed.

When such a color-erasing type heat-sensitive recording material is used, it is not only possible to send and receive images for an overhead projector directly over a telephone line using a widely used facsimile printer, but also to send and receive images for an overhead projector even on a dark background. Since it is possible to obtain a bright and high-contrast image on the screen, there is very little eye fatigue even when used for a long time, and it has the advantage that the contents of the overhead projector sheet can be easily seen with the naked eye.

[0007]

[Problems to be Solved by the Invention] Recently, decolorable heat-sensitive recording materials having the above-mentioned heat-sensitive layer have been
It is expected to be used not only for P but also for medical purposes, plotters, and multicolor recording, and as these uses expand, there is a need to further prevent damage to thermal heads. There is.

[0008] The present inventors have proceeded with studies on reducing head damage in the above-mentioned color erasable heat-sensitive recording material, and found that damage to the thermal head is caused by the total ion content of the sodium ions and potassium ions in the coating layer. They have discovered that the process progresses significantly when the amount exceeds a certain level, and have completed the present invention.

[0009] Accordingly, an object of the present invention is to provide a heat-sensitive recording material having at least one decolorable transparent heat-sensitive layer on a support, which can reduce damage to a thermal head. It is in.

0010

[Means for Solving the Problems] The above objects of the present invention are as follows:
A heat-sensitive recording material comprising a support and a heat-sensitive layer containing a dye formed on the support and a decolorizing agent capable of decolorizing the dye, the heat-sensitive layer comprising a dye formed on the support and a decolorizing agent capable of decolorizing the dye. It is formed by coating a coating liquid containing microcapsules to be encapsulated and an emulsified dispersion in which the other component not encapsulated in the microcapsules is emulsified and dispersed onto a support, and also The total amount of sodium ions and potassium ions contained in
This was achieved using a heat-sensitive recording material characterized by a concentration of 0 mg or less.

In the color erasable heat-sensitive recording material according to the present invention, the unheated portion is colored with a dye (preferably a reaction product of a colorless or light-colored electron-donating dye precursor and a color developer), In the heated area, the aforementioned coloring is bleached by the decoloring agent that has passed through the heat-responsive capsule wall, so when an image sheet obtained using the heat-sensitive recording material of the present invention is applied to an overhead projector (OHP), it becomes white. On the screen, the background is colored and the heated image area appears colorless or light colored.

[0012] The support used in the present invention may be transparent or opaque. When an opaque support is used, a so-called negative type thermal paper is obtained. Transparent supports preferably used in the present invention include polyester,
Examples include acrylic resin, styrene/acrylic copolymer, cellulose acetate, etc., but are not particularly limited.

Next, the heat-sensitive layer according to the present invention will be explained in detail. The heat-sensitive layer in the present invention includes a dye and a decoloring agent capable of decolorizing the dye, and either or both of the components of the dye and the decolorizing agent are encapsulated in separate microcapsules, In addition, the components that are not microencapsulated are made into an emulsified dispersion.

The above dye used in the heat-sensitive layer of the present invention is
There is no particular limitation as long as the color can be erased by the color erasing agent described below, but from the viewpoint of image clarity, it must be a coloring reaction product of an electron-donating dye precursor and a color developer. is preferred.

[0015] The electron-donating dye precursor preferably used in the present invention is a colorless or light-colored one selected from known compounds that develop color by donating electrons or accepting protons such as acids. do it. Such compounds include lactones, lactams, sultones, spiropyrans, esters,
It has a partial skeleton such as amide, and these partial skeletons ring-open or cleave when contacted with a color developer. Preferred compounds include, for example, triarylmethane compounds, diphenylmethane compounds, xanthene compounds, and thiazine. Examples include spiropyran-based compounds and spiropyran-based compounds.

The color developer that causes a color-forming reaction with the electron-donating dye precursor used in the present invention can be appropriately selected from known ones. For example, color developers for leuco dyes include phenolic compounds, triphenylmethane compounds, sulfur-containing phenolic compounds, carboxylic acid compounds, sulfone compounds, urea or thiourea compounds, and the like. For more information on these compounds,
For example, Paper and Pulp Technology Times (1985) 49-5
Reference may be made to pages 4 and 65-70.

Among the color developers used in the present invention, particularly preferred ones are represented by the following general formulas (1) to (5).

[Chemical formula 1]

embedded image R1 is an alkyl group, an aryl group or an aralkyl group, with methyl, ethyl and/or butyl groups being particularly preferred.

embedded image R2 is an alkyl group, particularly preferably a butyl group, a pentyl group, a heptyl group and/or an octyl group.

[0018]

[C4] R3 is an alkyl group or an aralkyl group.

embedded image R4 and R5 each independently represent hydrogen, halogen, hydroxyl group, nitro group, alkyl group, allyl group, aralyl group, or alkylaryl group.

The color erasing agent used in the present invention has a color erasing effect on dyes. Specific examples of such decolorizing agents are illustrated below. a) Alkylene oxide adducts of bisphenols (see Japanese Patent Application No. 53-46689)

[C6] A here represents methylene or alkylidene.

b) Methylolamides and bisamides with a melting point of 110°C or higher (Japanese Patent Application No. 53-80557), c) Long-chain 1,2-glycol (Japanese Patent Application No. 53-99563), d) Ethylene oxide of terephthalic acid. Additives (patent application 1973-
No. 96666),

e) Solid alcohols such as stearyl alcohol, tripropyl carbinol, polyethylene glycol, polypropylene glycol, 1,8-octanediol, dimethylpentaglycerin, 1,2,3,4-tetraoxybutane Publication No. 17865)
,

f) Polyoxydecamethylene, polyoxymethylene, polyethylene oxide, trimethylene oxide polymer, 1,3-dioxolane polymer, polyoxyethylene alkylamine, sorbitan monostearate, polyoxyethylene oleyl ether, Polyethers or polyethylene glycol derivatives such as polyethylene glycol monostearate, polyoxyethylene alkylamide, oxyethylene alkylamine (Japanese Patent Publication No. 17867-1982 and Japanese Patent Publication No. 17868-1987),

g) Acetamide, stearamide, phthalonitrile, m-nitroaniline, β-naphthylamine (Japanese Patent Publication No. 19991/1983), h) 1,3-dicyclohexyl-2-phenylguanidine, 1,3-dicyclohexyl-2 - Guanidine derivatives such as naphthylguanidine, 2,3-dicyclohexyl-1-phenylguanidine, 1,2,3-triphenylguanidine (Japanese Patent Publication No. 51-29024),

002
4]i) Hexadecylamine, tribenzylamine, N
, N,N',N'-tetrabenzylethylenediamine,
Tricyclohexylamine, dioctadecylamine, 2
-Amine or quaternary ammonium salt such as aminobenzoxazole, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride (
(Japanese Unexamined Patent Publication No. 18048/1983).

The decoloring agent is applied in an amount sufficient to erase the color of the dye. This amount can be determined experimentally, but is usually 0.
It is preferable to use it in the range of 0.05 to 8 g/m2. In the present invention, by encapsulating at least one of the above-mentioned dye and decoloring agent in microcapsules, decolorization during the production of heat-sensitive recording materials is prevented, and at the same time, the raw and archival properties of the heat-sensitive recording materials are improved. It can be further increased. In this case, by selecting the wall material and manufacturing method of the microcapsules, it is possible to increase the image density during recording.

In the present invention, photofading inhibitors described in, for example, JP-A No. 61-283589, JP-A No. 61-283590, and JP-A No. 61-283591 may be appropriately added to the heat-sensitive layer, if necessary. can.

In the present invention, at least one of a dye (preferably a color-forming reaction product of an electron-donating dye precursor and a color developer) or a decolorizer is dissolved in an organic solvent that is sparingly soluble or insoluble in water. After that, the dye or decolorizer that is not microencapsulated is microencapsulated using the method described below.The dye or decolorizer that is not microencapsulated is dissolved in an organic solvent that is sparingly soluble or insoluble in water, and then a surfactant is added. A transparent heat-sensitive layer can be formed by mixing it with an aqueous phase containing a water-soluble polymer as a protective colloid and using it in the form of an emulsified dispersion.

[0028] The organic solvent for dissolving the dye or decolorizer can be appropriately selected from those commonly used as pressure-sensitive oils, but especially those having two or more benzene rings and containing a hetero atom. Oils whose number is less than or equal to the fundamental constant are preferred. Such oils have the following general formulas (Chemical formula 7) to (Chemical formula 9)
and triallylmethane (e.g. tritolylmethane, tolyldiphenylmethane), terphenyl compounds (e.g. terphenyl), alkylated diphenyl ethers (e.g. propyl diphenyl ether), hydrogenated terphenyl (e.g. hexahydro terphenyl), diphenyl ether, etc.

[0029]

embedded image In the formula, R1 is hydrogen or an alkyl group having 1 to 18 carbon atoms,
R2 represents an alkyl group having 1 to 18 carbon atoms. p1
and q1 represents an integer of 1 to 4, and the total number of alkyl groups is 4 or less. In addition, the alkyl group of R1 and R2 is preferably a C1-C8 alkyl group.

[0030]

embedded image In the formula, R3 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, R4 represents an alkyl group having 1 to 12 carbon atoms, and n represents 1 or 2. p2 and q2 each independently represent an integer of 1 to 4. When n=1, the total number of alkyl groups is 4 or less, and when n=2, the total number of alkyl groups is 6 or less.

[0031]

[Image Omitted] In the formula, R5 and R6 are hydrogen atoms or have 1 to 1 carbon atoms
8 represents the same or different alkyl group. m is 1~
Represents an integer of 13. p3 and q3 are each independently 1
represents an integer of ~3, and the total number of alkyl groups is 3 or less. In addition, it is especially preferable that the alkyl group of R5 and R6 is a C2-C4 alkyl group.

Examples of the compound represented by formula (7) include dimethylnaphthalene, diethylnaphthalene, and diisopropylnaphthalene. Examples of the compound represented by (Chemical formula 8) include dimethylbiphenyl, diethylbiphenyl, diisopropylbiphenyl, and diisobutylbiphenyl.

Examples of compounds represented by (Chemical formula 9) include 1
-Methyl-1-dimethylphenyl-1-phenylmethane, 1-ethyl-1-dimethylphenyl-1-phenylmethane, and 1-propyl-1-dimethylphenyl-1-phenylmethane. The above-mentioned oils may be used alone, or may be used in combination with each other or with other oils, if necessary.

In the present invention, an auxiliary solvent may be added to the above-mentioned organic solvent as a low boiling point solubilizing agent. Particularly preferred examples of such co-solvents include, for example, ethyl acetate, isopropyl acetate, butyl acetate and methylene chloride.

In the present invention, the water-soluble polymer contained as a protective colloid in the aqueous phase mixed with the oil phase in which the dye or decolorizer is dissolved is a known anionic polymer, nonionic polymer, or amphoteric polymer. Although it can be appropriately selected from among them, it is particularly preferable to use polyvinyl alcohol, gelatin, cellulose derivatives, and the like.

[0036] Also, as the surfactant to be contained in the aqueous phase, from among anionic and nonionic surfactants,
Those that do not cause precipitation or aggregation when acting with the above-mentioned protective colloids can be appropriately selected and used. Preferred surfactants include alkylbenzene sulfonates (e.g., ammonium dodecylbenzene sulfonate), alkyl sulfates (e.g., ammonium lauryl sulfate), dioctyl ammonium sulfosuccinates, polyalkylene glycols (e.g., polyoxyethylene nonylphenyl ether), and the like. can be mentioned.

[00037] The emulsified dispersion of the dye or decolorizer in the present invention is prepared by mixing an oil phase containing the dye or decolorizer and an aqueous phase containing a protective colloid and a surfactant using a conventional method such as high-speed stirring or ultrasonic dispersion. It can be easily obtained by mixing and dispersing using the means used for fine particle emulsification. At this time, the oil droplet size (diameter) of the emulsified dispersion has a haze of 4
When the objective is to obtain a transparent heat-sensitive layer with a thickness of 0% or less, the thickness is preferably 7 μm or less. More preferably 0
．． It is within the range of 1 to 5 μm.

The ratio of the oil phase to the aqueous phase (oil phase weight/aqueous phase weight) is preferably from 0.023 to 0.6. More preferably, it is 0.1 to 0.4. If it is less than 0.02, the water phase will be too large and diluted, resulting in insufficient image clarity;
．． If it is 6 or more, the viscosity of the liquid increases, resulting in inconvenience in handling and a decrease in transparency.

[0039] A melting point depressing agent such as a decolorizing agent may be appropriately added to this emulsified dispersion, if necessary. Some of these melting point depressants also have the function of a glass transition point modifier for microcapsule walls, which will be described later. Examples of such compounds include hydroxy compounds, carbamate ester compounds, sulfonamide compounds, and aromatic methoxy compounds. For details of these regulators, reference may be made to, for example, Japanese Patent Application No. 59-244190.

These melting point depressants are used in an amount of 0.1 to 2 parts by weight, more preferably 0.1 to 2 parts by weight, per 1 part by weight of the decolorizer that lowers the melting point.
It is preferable to use it in a range of 5 to 1 part by weight as necessary. Further, it is preferable that the melting point depressant and the decolorizing agent, which lowers the melting point, be used at the same location. When adding to different locations, it is preferable to add 1 to 3 times the above amount.

When used in the form of an emulsified dispersion, the dye is preferably coated on the support in an amount ranging from 0.05 to 15 g/m 2 . The microcapsules used in the present invention can be appropriately selected from known capsules such as capsules that are destroyed by heat or pressure and capsules that pass through substances only when heated.

[0042] At room temperature, preferred microcapsules:
The substance isolation effect of the microcapsule wall prevents contact between the substance inside and outside the capsule, and the permeability of the substance increases only while it is heated above a certain temperature. In this case, the permeation start temperature can be freely controlled by appropriately selecting the capsule wall material, capsule core material, and additives, and the permeation start temperature in this case corresponds to the glass transition temperature of the capsule wall. (For example, Japanese Patent Application Laid-Open No. 59-91
No. 438, JP-A-59-190886, JP-A-60-
242094, etc.).

In order to control the glass transition point specific to the capsule wall, it is necessary to change the type of capsule wall forming agent. Wall materials for microcapsules include polyurethane, polyurea, polyester, polycarbonate,
Urea-formaldehyde resin, melamine resin, polystyrene, styrene methacrylate copolymer, styrene-
Examples include acrylate copolymers, gelatin, polyvinylpyrrolidone, polyvinyl alcohol, and the like.

In the present invention, two or more of these polymeric substances can be used in combination, if necessary. Among the above polymer materials, polyurethane, polyurea, polyamide,
Polyester, polycarbonate, etc. are preferred, and polyurethane and polyurea are particularly preferred.

The microcapsules used in the present invention are produced by emulsifying a core material containing a dye or decolorizer and other additives added as necessary, and then forming a wall of a polymer material around the oil droplets. It is preferred to form and microencapsulate, in which case a reactant forming a polymeric substance is added inside the oil droplets and/or outside the oil droplets. For details about microcapsules that can be preferably used in the present invention, such as a preferred method for producing microcapsules, see
For example, it is described in JP-A-59-222716.

When making microcapsules, they can be made from an emulsion containing 0.2% by weight or more of the component to be microencapsulated. Moreover, an organic solvent can be added to the core material of the microcapsules in addition to the dye or decolorizing agent.

Furthermore, in order to increase the transparency of the thermally printed portion, it is preferable that the refractive index of the core material of the microcapsule be close to the refractive index of the microcapsule wall and the material outside the microcapsule. In the present invention, the size of the microcapsules is, for example,
The volume average particle size measured by the measurement method described in No. 90 is preferably 2 μm or less, particularly preferably 1 μm or less.

The preferred microcapsules produced as described above are not destroyed by heat or pressure as used in conventional recording materials, but are destroyed by the application of heat.
Those that allow the core of the microcapsule and the substance contained outside to permeate the microcapsule wall (
thermoresponsive capsule wall).

The heat-sensitive layer obtained as described above is substantially transparent. Substantially transparent herein means that the haze (%) (measured with an integrating sphere HTR meter manufactured by Nippon Seimitsu Kogyo Co., Ltd.) is 40% or less. However, the transparency of an actual heat-sensitive layer test sample is greatly influenced by light scattering due to minute irregularities on the surface of the heat-sensitive layer. Therefore, the inherent transparency of the heat-sensitive layer, which is a problem in the present invention,
That is, when measuring the transparency inside the heat-sensitive layer using a haze meter, a simple method is to attach a transparent adhesive tape onto the heat-sensitive layer and evaluate the measured value by substantially excluding surface scattering.

The heat-sensitive recording material of the present invention can be coated with a suitable binder, if necessary. The binder may be water-soluble or water-insoluble, but when the heat-sensitive layer is to be transparent, polyvinyl alcohol, methylcellulose, carboxymethylcellulose, hydroxypropylcellulose, gum arabic, gelatin, polyvinylpyrrolidone, and casein are particularly suitable. , styrene-butadiene latex, acrylonitrile-butadiene latex, polyvinyl acetate, polyacrylic acid ester,
It is necessary to use various emulsions such as ethylene-vinyl acetate copolymer. The amount of binder used is preferably 0.5 to 5 g/m2 in terms of solid content. When the dye or decolorizer is used as an emulsified dispersion, it is not necessary to use the binder described above.

In the present invention, a coating solution containing microcapsules containing a dye or a decolorizing agent, a dispersion in which the dye or a decolorizing agent is emulsified and other additives such as a binder is prepared, On a support such as a film,
After coating and drying using coating methods such as bar coating, blade coating, air knife coating, gravure coating, roll coating, spray coating, and dip coating, the solid content is 2.5.
A heat-sensitive recording material is produced by forming a heat-sensitive layer of ~25 g/m2.

In the present invention, a protective layer may be provided on top of the heat-sensitive layer. Specific examples of polymers used as binders for the protective layer include methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, starches, gelatin, gum arabic, casein, styrene-maleic anhydride copolymer hydrolyzate, and styrene-maleic anhydride copolymer. Water-soluble polymers such as combined half ester hydrolyzate, polyvinyl alcohol, silica-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, polyacrylamide derivatives, polyvinylpyrrolidone, sodium polystyrene sulfonate, sodium alginate, styrene-butadiene rubber latex, acrylonitrile-bra Examples include water-insoluble polymers such as diene rubber latex, methyl acrylate-butadiene rubber latex, and polyvinyl acetate emulsion.

[0053] Additives such as pigments, metal soaps, waxes, crosslinking agents, etc. may be added to the protective layer as necessary for the purpose of improving matching with the thermal head during thermal printing and improving the water resistance of the protective layer. It may also be added. Pigments include colloidal silica, zinc oxide, calcium carbonate, barium sulfate, titanium oxide, lithopone, talc, waxite, kaolin, aluminum hydroxide, amorphous silica, etc., and the amount of these added is 0.00% of the total weight of the polymer. It is preferable that it is 0.05 to 2 times.

[0054] Metal soaps include emulsions of higher fatty acid metal salts such as zinc stearate, calcium stearate, and aluminum stearate.
．． It is added in a proportion of 5 to 20% by weight, preferably 1 to 10% by weight. Waxes include emulsions such as paraffin wax, microcrystalline wax, carnauba wax, methylolstearamide, polyethylene wax, silicone, etc., and the amount is 0.5 to 4% of the total weight of the protective layer.
It is added in a proportion of 0% by weight, and more preferably 1 to 20% by weight.

Further, in order to uniformly form a protective layer on the heat-sensitive layer, it is preferable to add a surfactant to the coating solution for forming the protective layer. Examples of the surfactant include sulfosuccinic acid-based alkali metal salts, fluorine-containing surfactants, and more specifically, sodium sulfosuccinic acid such as di-(2-ethylhexyl)sulfosuccinic acid and di-(n-hexyl)sulfosuccinic acid. Examples include salts and ammonium salts.

[0056] Furthermore, a surfactant, a polymer electrolyte, etc. may be added to the protective layer to prevent charging of the heat-sensitive recording material, if necessary. The solid content coating amount of the protective layer is usually 0.
Preferably 2 to 5 g/m2, more preferably 1 to 3 g
/m2.

[0057] When two or more heat-sensitive layers are provided on a support to form a multicolor heat-sensitive recording material, a layer having the same composition as the protective layer may be provided as an intermediate layer. As the intermediate layer, in particular, as disclosed in JP-A-1-301282,
It is preferable to use a layer formed by gelling a water-soluble polyanionic polymer with polyvalent cations.

The heat-sensitive recording material of the present invention can be coated on a support such as paper or a synthetic resin film by bar coating, blade coating, air knife coating, gravure coating, roll coating, or
It is manufactured by coating and drying using a coating method such as spray coating or dip coating. In this case, a transparent support or an opaque support is used depending on the purpose and use.

As the support, polyesters such as polyethylene terephthalate and polybutylene terephthalate,
Examples include cellulose derivatives such as cellulose triacetate, polyolefins such as polystyrene, polypropylene, and polyethylene, and these may be transparent or opaque. These can be used alone or in combination.

In the present invention, an undercoat layer may be provided between the synthetic resin support and the heat-sensitive layer in order to improve the adhesion between the two layers. Gelatin, synthetic polymer latex, nitrocellulose, etc. are used as the material for the undercoat layer. The coating amount of the undercoat layer is preferably in the range of 0.1 g/m2 to 2.0 g/m2, particularly 0.2 g/m2 to 1
．． A range of 0 g/m2 is preferred.

If the coating amount is less than 0.1 g/m2, the adhesion between the support and the heat-sensitive layer will not be sufficient;
Even if the thickness is increased beyond m2, the adhesive force between the support and the heat-sensitive layer reaches saturation, which is disadvantageous in terms of cost.

The undercoat layer may swell due to the water contained in the heat-sensitive layer when the heat-sensitive layer is applied thereon. Since image quality may deteriorate, it is desirable to harden the heat-sensitive layer using a hardening agent.

[0063] As hardeners that can be used in the present invention, the following can be mentioned. (1) Divinylsulfone N,N'-ethylenebis(vinylsulfonylacetamide), 1,3-bis(vinylsulfonyl)-2-propanol, methylenebismaleimide, 5-acetyl-1,3-diacryloyl-hexahydro -s-triazine, 1,3,5-triacryloyl-
Active vinyl compounds such as hexahydro-s-triazine, 1,3,5-trivinylsulfonyl-hexahydro-s-triazine.

(2) 2,4-dichloro-6-methoxy-
s-triazine, 2,4-dichloro-6-(2-sulfoethylamino)-s-triazine, N-N'-bis(2
-Activated halogen compounds such as chloroethylcarbamyl)piperazine.

(3) Bis(2,3-epoxypropyl)
Methylpropylammonium p-toluenesulfonate, 1,4-bis(2',3'-epoxypropyloxy)butane, 1,3,5-triglycidyl isocyanurate, 1,3-diglycidyl-5-(γ -acetoxy-
Epoxy compounds such as β-oxypropyl) isocyanurate.

(4) Ethyleneimino compounds such as 2,4,6-triethylene-s-triazine, 1,6-hexamethylene-N,N'-bisethyleneurea, and bis-β-ethyleneiminoethylthioether.

(5) Methanesulfonic acid ester compounds such as 1,2-di(methanesulfonoxy)ethane, 1,4-di(methanesulfonoxy)butane, and 1,5-di(methanesulfonoxy)pentane.

(6) dicyclohexylcarbodiimide,
1-Cyclohexyl-3-(3-trimethylaminopropyl)carbodiimide-p-trienesulfonate, 1
- Carbodiimide compounds such as ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride.

(7) Isoxazole such as 2,5-dimethylisoxazole perchlorate, 2-ethyl-5-phenylisoxazole-3'-sulfonate, 5,5'-(paraphenylene)bisisoxazole system compound.

(8) Inorganic compounds such as chromium alum and chromium acetate. (9) N-carboethoxy-2-isopropoxy-1,
Dehydrated condensed peptide reagents such as 2-dihydroquinoline, N-(1-morpholinocarboxy)-4-methylpyridinium chloride; N,N'-adipoyldioxydisuccinimide, N,N'-terephthaloyldioxydi Active ester compounds such as succinimide.

(10) Isocyanates such as toluene-2,4-diisocyanate and 1,6-hexamethylene diisocyanate. (11) Dialdehydes such as glutaraldehyde, glyoxal, dimethoxyurea, and 2,3-dihydroxy-1,4-dioxane.

Among these, it is particularly preferable to use dialdehydes such as glutaraldehyde and 2,3-dihydroxy-1,4-dioxane, and/or boric acid. The amount of these hardeners to be added is 0.00% based on the weight of the heat-sensitive layer.
An appropriate addition amount can be selected from a range of 0.01% to 10% by weight depending on the coating method and desired degree of curing. If the amount added is more than 0.01% by weight, thermal sensitivity and image density will decrease, which is not preferable.

The undercoat layer may further contain waxes similar to those added to the protective layer in a range of 1 to 10% by weight. Pigments can also be added. In this case, it is particularly preferable that the pigment has an oil absorption of 40 cc/100 g or more as defined by JIS-K5101. Furthermore,
Before applying the undercoat layer, it is desirable to activate the surface of the support by a known method.

As a method of activation treatment, etching treatment with acid, flame treatment with gas burner, corona discharge treatment, glow discharge treatment, etc. are used, but from the point of view of cost or simplicity, US Pat. ,715,0
No. 75, No. 2,846,727, No. 3,549,
The corona discharge treatment described in No. 406, No. 3,590,107, etc. is most preferably used.

As the paper used for the support, if a heat-extracted neutral paper (described in JP-A-55-14281) sized with a neutral sizing agent such as an alkyl ketene dimer and has a pH of 6 to 9 is used, it is possible to It is advantageous in terms of storage stability. In order to prevent the coating liquid from penetrating the paper and to improve the contact between the thermal recording head and the thermal recording layer, Japanese Patent Application Laid-Open No. 57-116
The paper described in No. 687 and having a Bekk smoothness of 90 seconds or more is advantageous.

[0076] Also, as described in JP-A-58-136492, the engineering surface roughness is 8 μm or less and the thickness is 40 to 75 μm.
m paper, density 0.9 g as described in JP-A No. 58-69097
/cm3 or less and has an optical contact rate of 15% or more, Canadian standard freeness (JI) described in JP-A-58-69097
Paper made from pulp beaten to 400 cc or more using S P8121) to prevent penetration of the coating liquid, the glossy side of base paper made by a Yankee machine described in JP-A No. 58-65695 as the coated surface. Materials that improve color density and resolution, such as paper in which base paper is subjected to corona discharge treatment to improve coating suitability, as described in JP-A-59-35985, can also be used in the present invention and give good results. In addition to these, any support commonly used in the field of heat-sensitive recording paper can be used as the support of the present invention.

The total amount of Na+ and K+ ions in the heat-sensitive recording material of the present invention must be 10 mg/m2 or less. For this purpose, materials that contain sodium ions (Na+) and potassium ions (K+) or materials that easily release them should not be used, or if used, the amount used should be reduced as much as possible. preferable.

That is, for example, water used in an aqueous solution or dispersion contains Na+ or K+, and polyvinyl alcohol (
Na+ for water-soluble polymers such as PVA), Na+ and K+ for surfactants, and Na+ for pigments such as kaolin.
are included, so the total amount of these ions is 10 mg.
/m2 More preferably, it needs to be 5 mg/m2 or less.

Therefore, in the present invention, ion-exchanged water is used as the water contained in the coating solution, and N is used as the water-soluble polymer.
In addition to using products with low a+ or K+ content, if it is absolutely necessary to use materials that produce the above Na+ and K+, either sufficiently reduce the amount used or remove Na+ and K+ ions through ion exchange treatment. This is necessary.

[0080] The ions in the heat-sensitive recording material are determined by subjecting the heat-sensitive material to hot water extraction for 4 hours, filtering the extract through a microfilter, and measuring the filtrate by ion chromite or atomic absorption spectrometry. be able to.

[0081]

Effects of the Invention As detailed above, the heat-sensitive recording material having a decolorable transparent heat-sensitive layer of the present invention has sodium ions,
Since it contains only 10 mg/m2 or less of potassium ions in total, damage to the thermal head is reduced when recording is performed using this thermal head, and the life of the thermal head can be significantly extended.

[0082]

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto. In addition, in the following examples, "ion exchange water" was used as water in all cases.

Example 1. [Preparation of dye emulsion dispersion] 2 g of color developer (Chemical formula 10), 1 g of (Chemical formula 11), 8 g of (Chemical formula 12) represented by the following structural formula, and 2 g of the electron-donating dye (Chemical formula 13) were mixed with diethyl maleate. 5 g and 10 g of ethyl acetate.

The obtained solution was mixed with 8% polyvinyl alcohol (PVA217C: trade name manufactured by Kuraray Co., Ltd.).
VA217C is a grade with low content of Na+ and K+ ions. ), 50 g of water, and 0.5 g of dodecylbenzenesulfonic acid triethanolamine salt.
After mixing with an aqueous solution consisting of, using an Ace homogenizer manufactured by Nippon Seiki Co., Ltd.,
Emulsification was carried out for 5 minutes at room temperature to obtain an emulsified dispersion with a particle size of 0.5μ.

[Chemical formula 10]

[Chemical formula 11]

[Chemical formula 12]

[Chemical formula 13]

[Preparation of decolorizing agent capsule liquid] The following decolorizing agent (
Chemical formula 14) 10g, 1-phenyl-1-xylylethane 2
0g, ethyl acetate 10g, and Takenate D-11
0N (manufactured by Takeda Pharmaceutical Co., Ltd., capsule wall material product name) 25
8% polyvinyl alcohol (P
VA217C (product name manufactured by Kuraray Co., Ltd.) 60g and water 2
After emulsifying for 5 minutes at 10,000 rpm using an Ace homogenizer manufactured by Nippon Seiki Co., Ltd., 150 g of water was added and the mixture was reacted at 40°C for 3 hours to form a microorganism with a capsule size of 0.7 μm. A decolorizer capsule solution containing capsules was produced.

[Chemical formula 14]

[Preparation of heat-sensitive material] 5.0 g of the above decolorizer capsule liquid, 10 g of electron-donating dye precursor color developer emulsion dispersion
．． 0g and 5.0g of water were stirred and mixed, coated on a transparent polyethylene terephthalate (PET) support with a thickness of 70μ so that the solid content was 7g/m2, and dried at 40°C. A thermosensitive layer was formed.

Next, a coating solution prepared by dissolving a protective layer composition having the composition shown below (Table 1) in 20 parts by weight of ion-exchanged water is used to coat the heat-sensitive recording layer so that the solid content is 2.5 g/m2. A protective layer was formed by coating as described above, and a heat-sensitive recording material was obtained. The following Kaobrite was used after ion exchange treatment of a liquid dispersed in 16 parts by weight of water using an ion exchange resin Amberlite MB3 (trade name, manufactured by Organo Co., Ltd.).

[0088]

[Table 1] ──────────────────────────
────────────Polyvinyl alcohol (PVA124C manufactured by Kuraray Co., Ltd.)
2 parts by weight Kaobrite (Thiele)
4 parts by weight boric acid
0.1 part by weight Zn stearate dispersion (Chukyo Yushi)
0.2 parts by weight ammonium lauryl sulfate
0.05 parts by weight────────────
──────────────────────────

Regarding the heat-sensitive recording material obtained above, the sample was extracted with hot water for 4 hours, the extract was filtered through a microfilter, and the filtrate was subjected to an atomic absorption spectrometer to determine Na +
When the total content of K+ and K+ was measured, it was found to be 2.8m
g/m2. When a straight line was recorded on the above heat-sensitive recording material with a thermal head, the head did not break even at a distance of 4,000 m, and very good results were obtained.

Example 2. Thermal recording was carried out in exactly the same manner as in Example 1, except that the same amount of polyvinyl alcohol (PVA217, trade name manufactured by Kuraray Co., Ltd.) was used instead of the polyvinyl alcohol (PVA217C) used in the dye emulsion dispersion in Example 1. The material was prepared. The total amount of Na+ and K+ ions contained in the obtained heat-sensitive recording material was 4.5 mg/m2. Next, a durability test of the head was conducted in the same manner as in Example 1, and the result was 4.0.
No head damage occurred even after continuous recording for 00 m or more.

Example 3. A heat-sensitive recording material was prepared in exactly the same manner as in Example 2, except that PVA124 was used instead of polyvinyl alcohol PVA124C used in the protective layer, and the total amount of Na+ and K+ ions was measured.
It was 6.8 mg/m2. As a result of conducting a running test of the thermal head in the same manner as in Example 1, it was confirmed that the head did not break down up to 3,000 m.

Example 4. PV instead of PVA217C
A217 is used, and in place of ammonium lauryl sulfate in the protective layer.

A heat-sensitive recording material was produced in the same manner as in Example 1 except that the following was used, and the total ion content of Na+ and K+ was measured to be 7.9 mg/m2. A thermal head running test was carried out using this heat-sensitive recording material in the same manner as in Example 1, and it was confirmed that the head did not break down up to 2,500 m.

Example 5. PV instead of PVA217C
Using A217 and also instead of dodecylbenzenesulfonic acid triethanolamine salt used in the emulsified dispersion,
A heat-sensitive recording material was prepared in the same manner as in Example 1 except that sodium dodecylbenzenesulfonate was used, and the total amount of Na+ and K+ ions was measured to be 8.8 mg/
It was m2. Using the obtained heat-sensitive recording material, a thermal head running test was conducted in the same manner as in Example 1, and the results were as follows.
It was confirmed that head failure did not occur up to 2,500 m.

Comparative Example 1. KOH was added to the coating solution for the protective layer in Example 2 so that the solid content coating amount was 10 mg/m2.
A heat-sensitive recording material was produced in the same manner as in Example 2 except that . The total ion amount of Na+ and K+ is 11.5
mg/m2. Using this heat-sensitive recording material, a running test of a thermal head was conducted in the same manner as in Example 1, and as a result, the head broke after 250 m.

Comparative Example 2. PV instead of PVA217C
A217 was used, sodium dodecylbenzenesulfonate was used instead of triethanolamine salt of dodecylbenzenesulfonate used in the emulsion, sodium lauryl sulfate was used instead of ammonium lauryl sulfate used in the protective layer, and ion exchange treatment of kaobrite was performed. without doing
Furthermore, a heat-sensitive recording material was prepared in the same manner as in Example 1 except that tap water was used instead of ion-exchanged water.
The total ion amount of K + was 13 mg/m2. A running test of a thermal head was conducted in the same manner as in Example 1 using the obtained heat-sensitive recording material, and as a result, the head broke at 450 m. A summary of the above results is shown below (Table 2).

[0096]

[Table 2] ──────────────────────────
──────────
Na+ +K+ amount
Head destruction occurred
(mg/m2) ──────
──────────────────────────
────── Example 1
2.8 4,
000m or more Example 2
4.5 4
,000m or more Example 3
6.8
3,000m Example 4
7.9 2
,500m Example 5
8.8 2,
500m Comparative example 1 1
1.5
250m Comparative example 2 1
3.0
450m────────────────────
──────────────

[0097] Above (Table 2
) results show that Na + and K + ions greatly affect damage to the thermal head, and if the total ion amount is 10 mg/m2 or less, the durability of the thermal head is extremely good; It has been demonstrated that it is even better if it is less than m2.

Claims (3)

[Claims] Claim 1: A support; formed on the support;
A heat-sensitive recording material having a heat-sensitive layer containing a dye and a color-erasing agent capable of erasing the dye, the heat-sensitive layer comprising microcapsules containing the dye or color-erasing agent and encapsulated in the microcapsules. It is formed by coating on a support a coating solution containing an emulsified dispersion in which the other component is emulsified and dispersed, and all the sodium ions and potassium ions contained in the coating film. A heat-sensitive recording material characterized in that the amount is 10 mg or less per m2. 2. The heat-sensitive recording material comprises an undercoat layer provided between the support and the heat-sensitive layer, an intermediate layer provided between the heat-sensitive layer and another heat-sensitive layer, and a protection layer provided on the heat-sensitive layer. 2. The heat-sensitive recording material according to claim 1, wherein the heat-sensitive recording material has at least one of the layers and the total amount of sodium ions and potassium ions contained in all the coating layers on the recording surface side of the heat-sensitive recording material is 10 mg or less per m2. material. 3. The heat-sensitive recording material according to claim 1, wherein the dye is a dye produced by a color-forming reaction between a colorless or light-colored electron-donating dye precursor and a color developer.