JP2005313478A - Thermosensitive recording material and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosensitive recording material, which has a thermosensitive recording layer and an intermediate layer on a support and in which the density change of an image after recording is little and which is excellent in thermal preservation resistance. <P>SOLUTION: In the thermosensitive recording material, in which at least the thermosensitive recording layer comprising a thermosensitive recording raw material and a binder and the intermediate layer including a water-soluble binder are provided on the support, the intermediate layer is formed by being added with a polymer latex. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording material and a method for producing the same, and more particularly relates to a heat-sensitive recording material suitable for medical recording media and the like and having good heat-resistant storage stability of recorded images and a method for producing the same.

In the thermal recording method, (1) development is unnecessary, (2) when the support is paper, the material is close to general paper, (3) easy to handle, (4) high color density, (5 ) The recording device has advantages such as simple, reliable and inexpensive, (6) low noise during recording, (7) no maintenance, etc. In recent years, the application has been expanded to a wide range of fields. We also provide transparent thermal recording materials that are suitable for dealing with multiple colors, for example, projecting images with an overhead projector, or observing directly on a light table such as medical recording media, etc. Has been.
As the heat-sensitive recording material used for such heat-sensitive recording, those using a reaction between an electron-donating dye precursor and an electron-accepting compound and materials using a reaction between a diazo compound and a coupler are well known. It has been.

In general, a thermal recording material is a thermal recording material in which component A and component B that react with each other to develop a color are dispersed in the form of fine particles, or one of component A and component B is encapsulated in a microcapsule and the other as an emulsion. A layer is provided on the support. In particular, a transparent thermosensitive recording material using a transparent support such as a synthetic polymer film as a support is also provided.
This transparent heat-sensitive recording material has a problem that sticking and noise are likely to occur during printing, and particularly when used as a medical recording medium, a high transmission density is required. Tended to be more conducive. Therefore, from the viewpoint of improving such problems, a protective layer is generally provided on the thermosensitive recording layer.

  When used as a medical transmission film, it is required that the color of the image portion is close to pure black. Since it is difficult to obtain a pure black color with a single leuco dye, a plurality of leuco dyes are used, and the absorption region is complemented to obtain a pure black color. The leuco dye develops color by interacting with the developer, but since this reaction is a reversible reaction, the leuco dye ring-closing product, which was not originally colored during storage at high temperatures, acts with the developer. As a result, the phenomenon of new coloring often occurred.

  In recent years, various forms of imaging technology have been provided, and the thermal recording material is often used under various conditions. For example, in a relatively high temperature environment such as overseas, the image density after printing is increased. In other words, there is a so-called “image density change” state in which the image quality increases, and the image quality required for medical use cannot be maintained. The failure to maintain high image quality includes two phenomena: image quality deterioration in which dots change, and highlights that are important for medical diagnosis collapse due to an increase in density. Thus, further improvement in storage stability is demanded along with improvement in image quality.

As described above, the method for preventing the change in the density of the image as described above is not disclosed at present, particularly in the case of forming an image by applying thermal energy by printing such as a medical image. is there.
An object of the present invention is to provide a heat-sensitive recording material having a heat-sensitive recording layer and an intermediate layer on a support, in particular, in order to solve the above-described conventional problems. The object is to provide an excellent thermal recording material.

<1> A heat-sensitive recording material having at least a heat-sensitive recording layer formed of a heat-sensitive recording material and a binder and an intermediate layer containing a water-soluble binder on a support, wherein the intermediate layer is added with a polymer latex. A heat-sensitive recording material characterized in that it is formed.
<2> The heat-sensitive recording material according to <1>, wherein the binder of the heat-sensitive recording layer contains polyvinyl alcohol as a main component.

<3> The thermosensitive recording material according to <1> or <2>, wherein the thermosensitive recording layer is formed by further adding a polymer latex.
<4> A thermosensitive recording material comprising at least a thermosensitive recording layer formed of a thermosensitive recording material and a binder and an intermediate layer containing a water-soluble binder on a support, wherein the thermosensitive recording layer is added with a polymer latex. A heat-sensitive recording material characterized by being formed as described above.

<5> The heat-sensitive recording material according to <4>, wherein the binder of the heat-sensitive recording layer contains polyvinyl alcohol as a main component.
<6> The heat-sensitive recording material according to any one of <1> to <5>, wherein the water-soluble binder contains gelatin as a main component.

<7> The above <1> to <6, wherein the thermosensitive recording material has a protective layer on the thermosensitive recording layer, and the intermediate layer is provided between the thermosensitive recording layer and the protective layer. > The heat-sensitive recording material according to any one of
<8> The heat-sensitive recording material according to <7>, wherein the binder forming the protective layer contains polyvinyl alcohol.

<9> The heat-sensitive recording material as described in <7> or <8> above, wherein the hardener used for the protective layer is 2,3-dihydroxy-1,4-dioxane.
<10> The heat-sensitive recording material according to any one of <1> to <9>, wherein the support is polyethylene terephthalate.

<11> A method for producing a heat-sensitive recording material, comprising: a step of applying a heat-sensitive recording layer coating solution containing a heat-sensitive recording material and a binder; and a step of coating an intermediate layer coating solution containing a water-soluble binder. The method for producing a heat-sensitive recording material according to claim 1, wherein the intermediate layer coating solution contains a polymer latex.
<12> Production of a heat-sensitive recording material comprising a step of coating a support with a heat-sensitive recording layer coating solution containing a heat-sensitive recording material and a binder, and a step of coating an intermediate layer coating solution containing a water-soluble binder. A method for producing a heat-sensitive recording material, wherein the heat-sensitive recording layer coating solution contains a polymer latex.

  According to the present invention, it is possible to provide a heat-sensitive recording material excellent in heat-resistant storage with little change in image density after recording, and further to provide a production method thereof.

The heat-sensitive recording material of the present invention will be described below.
≪Thermal recording material≫
As an aspect of the heat-sensitive recording material of the present invention, first, a heat-sensitive recording provided with at least a heat-sensitive recording layer formed of a heat-sensitive recording material and a binder and an intermediate layer containing a water-soluble binder on a support. In the material, there is an embodiment (first embodiment) in which the intermediate layer is a heat-sensitive recording material formed by adding a polymer latex, and secondly, the intermediate layer is formed of a heat-sensitive recording material and a binder on a support. A mode (second mode) in which the heat-sensitive recording layer is formed by adding a polymer latex to the heat-sensitive recording material provided with at least a heat-sensitive recording layer and an intermediate layer containing a water-soluble binder. is there.

-First embodiment-
Hereinafter, the first aspect of the heat-sensitive recording material of the present invention will be described.
As a first aspect, in a heat-sensitive recording material in which a heat-sensitive recording layer formed of a heat-sensitive recording material and a binder and an intermediate layer containing a water-soluble binder are provided on a support, the intermediate layer is a polymer. It is formed by adding latex.
Furthermore, in the first aspect, a heat-sensitive recording material obtained by adding a polymer latex to the heat-sensitive recording layer is preferable.

The heat-sensitive recording material of this embodiment has a layer structure having a heat-sensitive recording layer and an intermediate layer on a support, but preferably has a protective layer and a back layer. Furthermore, if necessary, an arbitrary layer such as a hue adjusting layer or an ultraviolet absorbing layer can be provided on the color development surface or the back surface.
A heat-sensitive recording material obtained by adding a polymer latex to the intermediate layer can obtain a heat-sensitive recording material excellent in heat-preserving storage property that there is little change in image density after image recording even when heat-printed with high energy. Can do.

(Middle layer)
In the heat-sensitive recording material of the first aspect, the heat-sensitive recording layer of the support is used in order to prevent mixing of each layer and to block the components contained in the protective layer, such as gases harmful to image storability (oxygen, ozone, etc.). An intermediate layer containing a water-soluble binder is provided on the color development surface side having the above.
The intermediate layer is a layer provided between two layers and does not include a heat-sensitive recording layer. Specifically, when two or more different heat-sensitive recording layers are provided on the color-forming surface side of the support having the heat-sensitive recording layer, the heat-sensitive recording layer, and further, a heat-sensitive recording layer (in the case of having a plurality of heat-sensitive recording layers) Means a thermosensitive recording layer farthest from the support) and a protective layer and the like.
The intermediate layer is preferably formed between the heat-sensitive recording layer and the protective layer.
The intermediate layer is obtained by adding a polymer latex. Furthermore, in addition to the binder, the intermediate layer can contain a crosslinking agent, a lubricant, a surfactant, other additives, and the like, depending on the purpose and necessity.

  As described above, by adding a polymer latex to the intermediate layer, the heat-resistant storage stability after recording by thermal printing is remarkably improved, and the density change of the image (image density) even under high-temperature environmental conditions that are not preferable as a storage environment. Can be significantly suppressed.

The polymer latex is an emulsion of a monomer polymer (including a copolymer), and the monomer composition includes alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate, methyl methacrylate, and ethyl. Examples thereof include alkyl methacrylates such as methacrylate, propyl methacrylate, and butyl methacrylate, hydroxyethyl methacrylate, acrylic acid, and styrene. Other examples include polyester-based, styrene-butadiene-based, and synthetic rubber-based latexes (for example, styrene-butadiene, chloroprene, polyisoprene, vinyl acetate, nitrile-butadiene, ethylene-vinyl acetate, acrylamide, and the like).
Among these, alkyl acrylates and alkyl methacrylates are preferable from the viewpoint of heat-resistant storage stability of images.
As the alkyl acrylates, methyl acrylate and ethyl acrylate are particularly preferable. Further, as the alkyl methacrylates, methyl methacrylate, ethyl methacrylate, and hydroxyethyl methacrylate are particularly preferable.
These can be used alone as a polymer, or as a copolymer using two or more monomers. Furthermore, a polymer latex may be formed using a plurality of polymers (or copolymers).

  The particle size distribution of the dispersed particles is not particularly limited, and may have a wide particle size distribution or a monodispersed particle size distribution. It is preferable to use two or more types having a monodispersed particle size distribution in order to control coating properties.

Although the preferable example of the copolymer of the said polymer latex is shown below using a raw material monomer, this invention is not limited to these.
Latex of EA (100) (solid content 20% by mass), Latex of EA-AA (95: 5) (solid content of 20% by mass), St-MMA-BA-HEMA-AA (57.2: 8.7: 27.7: 4.8: 1.6) latex (solid content 20% by mass) and the like. The abbreviations indicate monomers of EA: ethyl acrylate, MMA: methyl methacrylate, BA: butyl acrylate, HEMA: hydroxyethyl methacrylate, AA: acrylic acid, St: styrene.
The polymer latex described above may be commercially available, or may be synthesized by a conventionally known method.

As the water-soluble binder for the intermediate layer, gelatin, polyvinyl alcohol, or the like can be used, and it is particularly preferable to use gelatin as a main component. When gelatin is used, the ability to separate the protective layer and the heat-sensitive recording layer is excellent, so that inter-layer mixing during simultaneous multilayer coating is prevented, and the coating suitability is excellent.
That is, the gelatin has an aqueous solution at a high temperature, but has a property of losing fluidity and gelling at a low temperature (for example, 35 ° C. or lower) (set property). In order to form a layer, each coating solution is applied and dried to provide two adjacent layers, either by applying and drying a plurality of layers sequentially, or by applying and drying multiple layers at once by an extrusion die method or the like. The two layers are effectively prevented from mixing with each other, and the surface shape of the resulting thermal recording material is improved, and a thermal recording material capable of forming a high-quality image can be obtained. It is suitable for a medical diagnostic recording material that needs to be formed. Further, even when dried at a high wind speed, the surface condition is not deteriorated, so that the production efficiency is improved.

  As the gelatin, unmodified (untreated) gelatin or modified (treated) gelatin can be used without any problem. Examples of modified gelatin include lime-processed gelatin, acid-processed gelatin, phthalated-processed gelatin, deionized-processed gelatin, and enzyme-processed low-molecular-weight gelatin. Of these, alkali-processed gelatin having a low isoelectric point (for example, lime-processed gelatin) and derivative gelatin (for example, phthalated gelatin) in which an amino group is reacted are preferable.

In the intermediate layer, the coating amount of the water-soluble binder comprising the polymer latex, usually, it is preferably used in the range of 0.2 to 10 g / m ^2. As content as solid content (mass%) of this water-soluble binder and polymer latex, it is preferable that it is 80 mass%-100 mass%, and it is more preferable to set it as 90 mass%-99 mass%.
A water-soluble binder other than gelatin can be used together with gelatin as the water-soluble binder, but when used in combination with gelatin, the content of the other water-soluble binder is preferably 20% by mass or less.
The solid content ratio of the water-soluble binder and polymer latex is preferably 3: 1 to 1: 3, and more preferably 2: 1 to 1: 2.
By setting it within this range, it becomes possible to prevent mixing of coloring components, adjust the sensitivity between recording layers, and the like, and the heat-resistant recording material has good heat-resistant storage stability.

The water-soluble binder for the intermediate layer is not particularly limited in addition to the gelatins described above, and water-soluble binders such as polyvinyl alcohol, polyvinyl pyrrolidone, and cellulose derivatives can be added. For example, vinyl acetate-acrylamide copolymer , Polyvinyl alcohol, silicon-modified polyvinyl alcohol, starch, modified starch, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, gum arabic, casein, styrene-maleic acid copolymer hydrolyzate, styrene-maleic acid copolymer half ester hydrolyzate And water-soluble polymers such as hydrolysates of isobutylene-maleic anhydride copolymer, polyacrylamide derivatives, polyvinyl pyrrolidone, polystyrene sulfonate soda and sodium alginate.
When a water-soluble binder other than the gelatin is added, the total amount of these binders is preferably within the above range.

  For the purpose of further improving the water resistance, it is effective to use a crosslinking agent and a catalyst for promoting the reaction in combination. Examples of the crosslinking agent include epoxy compounds, blocked isocyanates, vinyl sulfone compounds, aldehyde compounds. , Methylol compounds, boric acid, carboxylic acid anhydrides, silane compounds, chelate compounds, halides and the like. Moreover, in order to accelerate | stimulate a crosslinking reaction, you may use a well-known acid, a metal salt, etc. as a catalyst. What can adjust pH of the coating liquid for intermediate | middle layer formation to 6.0-7.5 is preferable. Examples of the catalyst include known acids and metal salts, and those that can adjust the pH of the coating solution to 6.0 to 7.5 as described above are preferable.

Suitable examples of the lubricant include zinc stearate, calcium stearate, paraffin wax, polyethylene wax and the like.
Preferred examples of the surfactant include sulfosuccinic acid-based alkali metal salts and fluorine-containing surfactants so that an intermediate layer can be uniformly formed on the heat-sensitive recording layer. Examples thereof include sodium salts such as (2-ethylhexyl) sulfosuccinic acid and di- (n-hexyl) sulfosuccinic acid, and ammonium salts.

The intermediate layer forming coating solution (intermediate layer coating solution) is obtained by mixing the above-described components. Furthermore, you may add a mold release agent, a wax, a water repellent, etc. as needed.
The heat-sensitive recording material of the present invention can be formed, for example, by applying an intermediate layer coating solution on a heat-sensitive recording layer formed on a support by a known coating method. Examples of the known coating method include a method using a bar coater, an air knife coater, a blade coater, a curtain coater and the like.

(Thermosensitive recording layer)
The heat-sensitive recording layer provided on the color development surface of the heat-sensitive recording material of the first aspect contains at least a heat-sensitive recording material and a binder, but it is preferable to add a polymer latex from the viewpoint of heat-resistant storage of images. Furthermore, other components can be contained as required, such as use. In the present invention, the heat-sensitive recording material refers to a dye precursor that develops color by thermal printing.

<Coloring component>
The heat-sensitive recording layer in the present invention can be used in any composition as long as it has excellent transparency when not processed and has a property of rapidly coloring when heated. As such a heat-sensitive recording layer, a so-called two-component heat-sensitive recording layer containing a substantially colorless coloring component A and a substantially colorless coloring component B that reacts with the coloring component and colors. However, from the viewpoint of storage stability and background fogging, the color developing component A or the color developing component B is preferably in the form of being encapsulated in a microcapsule. Examples of the combination of the two components constituting the two-component heat-sensitive recording layer include the following (a) to (m).

(A) a combination of an electron-donating dye precursor and an electron-accepting compound (b) a combination of a photodegradable diazo compound and a coupler (c) an organometallic salt such as silver behenate or silver stearate and protocatechinic acid (D) Combination of long-chain aliphatic salts such as ferric stearate and ferric myristate with phenols such as gallic acid and ammonium salicylate (e) Acetic acid Organic acid heavy metal salts such as salts with nickel, cobalt, lead, copper, iron, mercury, silver, etc., and alkaline earth metal sulfides such as calcium sulfide, strontium sulfide, potassium sulfide, etc. Or a combination of the organic acid heavy metal salt and an organic chelating agent such as s-diphenylcarbazide or diphenylcarbazone (f) Silver sulfide, lead sulfide, sulfide A combination of a (heavy) metal sulfate such as silver or sodium sulfide and a sulfur compound such as Na-tetrathionate, sodium thiosulfate or thiourea (g) an aliphatic ferric salt such as ferric stearate; A combination with an aromatic polyhydroxy compound such as 3,4-dihydroxytetraphenylmethane (h) an organic noble metal salt such as silver oxalate and mercury oxalate, and an organic polyhydroxy compound such as polyhydroxy alcohol, glycerin and glycol (I) Combination of an aliphatic ferric salt such as ferric pelargonate and ferric laurate and a thiocesylcarbamide or isothiocecilcarbamide derivative (j) Lead caproate, lead pelargonate, behen Combinations of organic acid lead salts such as lead acid and thiourea derivatives such as ethylenethiourea and N-dodecylthiourea (k) ferric stearate, steer A combination of a higher fatty acid heavy metal salt such as copper acid and a zinc dialkyldithiocarbamate (l) a compound that forms an oxazine dye such as a combination of resorcin and a nitroso compound (m) a formazan compound and a reducing agent and / or a metal salt Combination with

  Among the above, the heat-sensitive recording material of the present invention includes (a) a combination of an electron donating dye precursor and an electron accepting compound, (b) a combination of a photodegradable diazo compound and a coupler, and (c) an organic material. A combination of a metal salt and a reducing agent is preferably used, and the combination of (a) or (b) is particularly preferable.

  Further, the heat-sensitive recording material of the present invention is excellent in transparency by constituting the heat-sensitive recording layer so as to reduce the haze value calculated from (diffuse transmittance / total light transmittance) × 100 (%). An image can be obtained. The haze value is an index representing the transparency of the material, and is generally calculated from the total transmitted light amount, diffuse transmitted light amount, and parallel transmitted light amount using a haze meter.

In the present invention, for example, (1) the 50% volume average particle size of both the color forming components A and B contained in the heat-sensitive recording layer is 1.0 μm or less, preferably 0. 6 μm or less, and a method of containing a binder in the range of 30 to 60% by mass of the total solid content of the heat-sensitive recording layer, or (2) either one of the color developing components A and B is microencapsulated and the other is coated and dried The method of using it as what substantially comprises a continuous layer (for example, emulsified dispersion) etc. are mentioned. It is also effective to make the refractive index of the component used for the thermosensitive recording layer as close as possible to a constant value.
Here, the 50% volume average particle diameter is, for example, an average of pigment particles corresponding to 50% volume in the pigment measured by a laser diffraction particle size distribution measuring device “LA700” manufactured by Horiba, Ltd. This means the particle size (hereinafter, sometimes simply referred to as “average particle size”), and the same applies hereinafter.

Next, the combination (a, b, c) of the color forming components preferably used for the heat-sensitive recording layer in the invention will be described in detail below.
(A) Combination of electron-donating dye precursor and electron-accepting compound The electron-donating dye precursor preferably used in the present invention is not particularly limited as long as it is substantially colorless. Or has a property of accepting a proton such as an acid to develop a color, in particular, having a partial skeleton such as lactone, lactam, sultone, spiropyran, ester, amide, Those which are colorless compounds in which these partial skeletons are opened or cleaved upon contact are preferred.

  Examples of the electron-donating dye precursor include triphenylmethane phthalide compounds, fluoran compounds, phenothiazine compounds, indolyl phthalide compounds, leucooramine compounds, rhodamine lactam compounds, and triphenylmethane compounds. Examples thereof include compounds, triazene compounds, spiropyran compounds, fluorene compounds, pyridine compounds, pyrazine compounds.

Specific examples of the phthalides include compounds described in U.S. Reissue Patent No. 23024, U.S. Pat. Nos. 3,491,111, 3,491,112, 3,491,116, and 3,509,174. .
Specific examples of the fluorans are described in U.S. Pat. Nos. 3,624,107, 3,627,787, 3,410,411, 3,462,828, 3,681,390, 3,920,510, 3,959,571, and the like. Compounds.
Specific examples of the spiropyrans include compounds described in US Pat. No. 3,971,808.
Examples of the pyridine-based and pyrazine-based compounds include compounds described in US Pat. Nos. 3,775,424, 3,853,869 and 4,246,318.
Specific examples of the fluorene compound include compounds described in Japanese Patent Application No. 61-240989.
Among these, black-colored 2-arylamino-3- [H, halogen, alkyl, or alkoxy-6-substituted aminofluorane] is particularly preferably used.

  Specifically, for example, 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-N-cyclohexyl-N-methylaminofluorane, 2-p-chloroanilino-3- Methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6-dioctylaminofluorane, 2-anilino-3-chloro-6-diethylaminofluorane, 2-anilino-3-methyl-6-N- Ethyl-N-isoamylaminofluorane, 2-anilino-3-methyl-6-N-ethyl-N-dodecylaminofluorane, 2-anilino-3-methoxy-6-dibutylaminofluorane, 2-o-chloroanilino -6-dibutylaminofluorane, 2-p-chloroanilino-3-ethyl-6-N-ethyl-N-isoamylaminophen Oran, 2-o-chloroanilino-6-p-butylanilinofluorane, 2-anilino-3-pentadecyl-6-diethylaminofluorane, 2-anilino-3-ethyl-6-dibutylaminofluorane, 2-o -Toluidino-3-methyl-6-diisopropylaminofluorane, 2-anilino-3-methyl-6-N-isobutyl-N-ethylaminofluorane, 2-anilino-3-methyl-6-N-ethyl-N -Tetrahydrofurfurylaminofluorane, 2-anilino-3-chloro-6-N-ethyl-N-isoamylaminofluorane, 2-anilino-3-methyl-6-N-methyl-N-γ-ethoxypropylamino Fluorane, 2-anilino-3-methyl-6-N-ethyl-N-γ-ethoxypropylaminofluorane, 2-anilino 3-methyl -6-N-ethyl--N-.gamma. propoxypropyl aminofluoran like.

Examples of the electron-accepting compound that reacts with the electron-donating dye precursor include acidic substances such as phenol compounds, organic acids or metal salts thereof, and oxybenzoic acid esters, and examples thereof include those disclosed in JP-A-61-291183. And compounds described in Japanese Patent Publication No.
Specifically, 2,2-bis (4′-hydroxyphenyl) propane (generic name: bisphenol A), 2,2-bis (4′-hydroxyphenyl) pentane, 2,2-bis (4′-hydroxy) -3 ', 5'-dichlorophenyl) propane, 1,1-bis (4'-hydroxyphenyl) cyclohexane, 2,2-bis (4'-hydroxyphenyl) hexane, 1,1-bis (4'-hydroxyphenyl) ) Propane, 1,1-bis (4′-hydroxyphenyl) butane, 1,1-bis (4′-hydroxyphenyl) pentane, 1,1-bis (4′-hydroxyphenyl) hexane, 1,1-bis (4′-hydroxyphenyl) heptane, 1,1-bis (4′-hydroxyphenyl) octane, 1,1-bis (4′-hydroxyphenyl) -2-methyl-pentane, 1, -Bis (4'-hydroxyphenyl) -2-ethyl-hexane, 1,1-bis (4'-hydroxyphenyl) dodecane, 1,4-bis (p-hydroxyphenylcumyl) benzene, 1,3-bis Bisphenols such as (p-hydroxyphenylcumyl) benzene, bis (p-hydroxyphenyl) sulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, bis (p-hydroxyphenyl) acetic acid benzyl ester;

Salicylic acid derivatives such as 3,5-di-α-methylbenzylsalicylic acid, 3,5-di-tertiarybutylsalicylic acid, 3-α-α-dimethylbenzylsalicylic acid, 4- (β-p-methoxyphenoxyethoxy) salicylic acid; Or a polyvalent metal salt thereof (in particular, zinc or aluminum is preferable); p-hydroxybenzoic acid benzyl ester, p-hydroxybenzoic acid-2-ethylhexyl ester, β-resorcinic acid- (2-phenoxyethyl) ester, etc. Oxybenzoates; phenols such as p-phenylphenol, 3,5-diphenylphenol, cumylphenol, 4-hydroxy-4'-isopropoxy-diphenylsulfone, 4-hydroxy-4'-phenoxy-diphenylsulfone Is mentioned.
Among these, bisphenols are particularly preferable from the viewpoint of obtaining good color development characteristics. Moreover, these electron-accepting compounds may be used individually by 1 type, and may use 2 or more types together.

(B) Combination of photodegradable diazo compound and coupler This photodegradable diazo compound causes a coupling reaction with a coupler, which will be described later, and develops a desired hue, and is specified before the reaction. It is a photodegradable diazo compound that decomposes when receiving light in the wavelength range and no longer has a coloring ability even when a coupling component is present.
The hue in this color developing system is determined by a diazo dye formed by the reaction of a diazo compound and a coupler. Therefore, by changing the chemical structure of the diazo compound or coupler compound, the color hue can be easily changed, and an arbitrary color hue can be obtained depending on the combination.

Examples of the photodegradable diazo compound preferably used in the present invention include aromatic diazo compounds, and specifically include aromatic diazonium salts, diazosulfonate compounds, diazoamino compounds and the like.
Preferred examples of the aromatic diazonium salt include compounds represented by the following structural formulas, but the aromatic diazonium salt is not limited thereto. The aromatic diazonium salt is preferably used because it is excellent in photofixability, generates little colored stain after fixing, and has a stable color developing portion.
Ar-N ₂ ⁺ · X ⁻
In the above formula, Ar represents a substituted or unsubstituted aromatic hydrocarbon ring group, N ₂ ⁺ represents a diazonium group, and X ⁻ represents an acid anion.

  As the diazo sulfonate compound, a large number of diazo sulfonate compounds have been known in recent years, and each diazonium salt can be obtained by treating with a sulfite and can be suitably used for the heat-sensitive recording material of the present invention.

The diazoamino compound can be obtained by coupling a diazo group with dicyandiamide, sarcosine, methyltaurine, N-ethylanthranic acid-5-sulfonic acid, monoethanolamine, diethanolamine, guanidine, etc. It can be suitably used for the heat-sensitive recording material of the invention.
Details of these diazo compounds are described in detail, for example, in JP-A-2-136286.

  On the other hand, examples of the coupler compound that undergoes a coupling reaction with the diazo compound described above include those described in JP-A No. 62-146678, including 2-hydroxy-3-naphthoic acid anilide, resorcin, and the like. Can be mentioned.

When using a combination of a diazo compound and a coupler in the above heat-sensitive recording layer, these coupling reactions are carried out in a basic atmosphere so that the reaction can be further promoted. It is preferable to add a sex substance.
Examples of the basic substance include water-insoluble or hardly soluble basic substances and substances that generate alkali by heating, such as inorganic or organic ammonium salts, organic amines, amides, urea, thiourea or derivatives thereof, Nitrogenous compounds such as thiazoles, pyrroles, pyrimidines, piperazines, guanidines, indoles, imidazoles, imidazolines, triazoles, morpholines, piperidines, amidines, forimazines or pyridines. .
Specific examples thereof include those described in JP-A No. 61-291183.

(C) Combination of organometallic salt and reducing agent As the organometallic salt, specifically, a long chain such as silver laurate, silver myristate, silver palmitate, silver stearate, silver aralate or silver behenate Silver salt of aliphatic carboxylic acid; Silver salt of organic compound having imino group such as benzotriazole silver salt, benzimidazole silver salt, carbazole silver salt or phthalazinone silver salt; Silver salt of sulfur-containing compound such as s-alkylthioglycolate Silver salt of aromatic carboxylic acid such as silver benzoate and silver phthalate; silver salt of sulfonic acid such as silver ethanesulfonate; silver salt of sulfinic acid such as silver o-toluenesulfinate; silver silver phosphate Silver salt of phosphoric acid; silver barbiturate, silver saccharinate, silver salt of salicylasdoxime or any mixture thereof.
Of these, long-chain aliphatic carboxylic acid silver salts are preferable, and silver behenate is more preferable. Further, behenic acid may be used together with silver behenate.

The reducing agent can be appropriately used based on the description in JP-A 53-1020, page 227, lower left column, line 14 to page 229, upper right column, line 11. Among them, mono, bis, tris or tetrakisphenols, mono or bisnaphthols, di or polyhydroxynaphthalenes, di or polyhydroxybenzenes, hydroxy monoethers, ascorbic acids, 3-pyrazolidones, pyrazolines, pyrazolones It is preferable to use reducing sugars, phenylenediamines, hydroxylamines, reductones, hydroxamic acids, hydrazides, amide oximes, N-hydroxyureas and the like.
Of the above, aromatic organic reducing agents such as polyphenols, sulfonamidophenols or naphthols are particularly preferred.

  In order to ensure sufficient transparency in the heat-sensitive recording material of the present invention, (a) a combination of an electron-donating dye precursor and an electron-accepting compound, or (b) a photodegradable diazo compound and a coupler in the heat-sensitive recording layer. It is preferable to use a combination of In the present invention, it is preferable to use one of the color developing component A and the color developing component B in a microcapsule, and the electron donating dye precursor or the photodegradable diazo compound is contained in the microcapsule. It is more preferable to encapsulate and use.

<Microcapsule>
Next, a method for producing microcapsules will be described in detail.
There are an interfacial polymerization method, an internal polymerization method, an external polymerization method and the like in the production of microcapsules, and any method can be adopted.
As described above, the heat-sensitive recording material of the present invention is preferably microencapsulated with an electron-donating dye precursor or a photodegradable diazo compound, and in particular, an electron-donating dye precursor or photodegradable used as the core of the capsule. An oil phase prepared by dissolving or dispersing a diazo compound in a hydrophobic organic solvent is put into an aqueous phase in which a water-soluble polymer is dissolved, and emulsified and dispersed by a stirring means such as a homogenizer, and then heated. It is preferable to adopt an interfacial polymerization method in which a polymer forming reaction is caused at the oil droplet interface to form a microcapsule wall made of a polymer substance.

  The reactant that forms the polymer substance is added inside the oil droplet and / or outside the oil droplet. Specific examples of the polymer substance include polyurethane, polyurea, polyamide, polyester, polycarbonate, urea-formaldehyde resin, melamine resin, polystyrene, styrene methacrylate copolymer, styrene-acrylate copolymer, and the like. Among these, polyurethane, polyurea, polyamide, polyester, and polycarbonate are preferable, and polyurethane and polyurea are particularly preferable.

  For example, when polyurea is used as a capsule wall material, polyisocyanates such as diisocyanate, triisocyanate, tetraisocyanate and polyisocyanate prepolymer, polyamines such as diamine, triamine and tetraamine, two or more amino acids A microcapsule wall can be easily formed by reacting a prepolymer having a group, piperazine or a derivative thereof, a polyol, or the like in the aqueous phase by an interfacial polymerization method.

  Further, for example, the composite wall made of polyurea and polyamide or the composite wall made of polyurethane and polyamide is made of, for example, polyisocyanate and a second substance (for example, acid chloride, polyamine, or polyol) that reacts therewith to form a capsule wall. It can be prepared by mixing in a water-soluble polymer aqueous solution (aqueous phase) or an oily medium to be encapsulated (oil phase), emulsifying and dispersing them, and then heating. Details of the method for producing the composite wall comprising polyurea and polyamide are described in JP-A-58-66948.

The polyisocyanate compound is preferably a compound having a trifunctional or higher functional isocyanate group, but a bifunctional isocyanate compound may be used in combination.
Specifically, diisocyanates such as xylene diisocyanate and hydrogenated products thereof, hexamethylene diisocyanate, tolylene diisocyanate and hydrogenated products thereof, isophorone diisocyanate and the like, and dimers thereof. Alternatively, in addition to a trimer (burette or isocyanurate), a polyfunctional adduct of a polyol such as trimethylolpropane and a bifunctional isocyanate such as xylylene diisocyanate, a polyol such as trimethylolpropane and a xylylene Examples thereof include a compound in which a high molecular weight compound such as polyether having active hydrogen such as polyethylene oxide is introduced into an adduct with a bifunctional isocyanate such as range isocyanate, and a formalin condensate of benzene isocyanate.
The compounds described in JP-A-62-212190, JP-A-4-26189, JP-A-5-317694, and Japanese Patent Application No. 8-268721 are also preferable.

  The polyisocyanate is preferably added so that the average particle size of the microcapsules is 0.3 to 12 μm and the thickness of the capsule wall is 0.01 to 0.3 μm. The dispersed particle size is generally about 0.2 to 10 μm.

Specific examples of polyols and / or polyamines added to the aqueous phase and / or oil phase as one of the components that react with the polyisocyanate to form the microcapsule wall include propylene glycol, glycerin, and trimethylolpropane. , Triethanolamine, sorbitol, hexamethylenediamine and the like. When a polyol is added, a polyurethane wall is formed. In the above reaction, it is preferable to keep the reaction temperature high or to add an appropriate polymerization catalyst from the viewpoint of increasing the reaction rate.
These polyisocyanates, polyols, reaction catalysts, and polyamines for forming a part of the walling agent are described in detail in “Polyurethane Handbook” (Nikkan Kogyo Shimbun, 1987) edited by Keiji Iwata.

  Further, a metal-containing dye, a charge control agent such as nigrosine, or any other additive substance can be added to the microcapsule wall as necessary. These additives can be contained in the capsule wall at the time of forming the capsule wall or at any time. Further, a monomer such as a vinyl monomer may be graft-polymerized in order to adjust the chargeability of the capsule wall surface as necessary.

Furthermore, it is also preferable to use a plasticizer suitable for the polymer used as the wall material in order to make the microcapsule wall excellent in material permeability even under a low temperature condition and rich in color development sensitivity. The plasticizer preferably has a melting point of 50 ° C. or higher, and more preferably has a melting point of 120 ° C. or lower. Among these, those that are solid at room temperature can be suitably selected and used.
For example, when the wall material is made of polyurea or polyurethane, a hydroxy compound, a carbamic acid ester compound, an aromatic alkoxy compound, an organic sulfonamide compound, an aliphatic amide compound, an arylamide compound, or the like is suitably used as the plasticizer.

In preparing the oil phase, the organic solvent having a boiling point of 100 to 300 ° C. is used as the hydrophobic organic solvent used when the electron donating dye precursor or the photodegradable diazo compound is dissolved to form the core of the microcapsule. preferable.
Specifically, in addition to esters, dimethylnaphthalene, diethylnaphthalene, diisopropylnaphthalene, dimethylbiphenyl, diisopropylbiphenyl, diisobutylbiphenyl, 1-methyl-1-dimethylphenyl-2-phenylmethane, 1-ethyl-1-dimethylphenyl -1-phenylmethane, 1-propyl-1-dimethylphenyl-1-phenylmethane, triallylmethane (eg, tritoluylmethane, toluyldiphenylmethane), terphenyl compound (eg, terphenyl), alkyl compound, alkylated diphenyl ether (For example, propyl diphenyl ether), hydrogenated terphenyl (for example, hexahydroterphenyl), diphenyl ether, and the like. Among these, it is particularly preferable to use esters from the viewpoint of emulsion stability of the emulsion dispersion.

  Examples of the esters include phosphate esters such as triphenyl phosphate, tricresyl phosphate, butyl phosphate, octyl phosphate, and cresyl phenyl phosphate; dibutyl phthalate, 2-ethylhexyl phthalate, ethyl phthalate, Phthalic acid esters such as octyl phthalate and butyl benzyl phthalate; Dioctyl tetrahydrophthalate; Benzoic acid esters such as ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate and benzyl benzoate; Ethyl abietic acid, abietic acid Abietic acid esters such as benzyl; dioctyl adipate; isodecyl succinate; dioctyl azelate; oxalic acid esters such as dibutyl oxalate and dipentyl oxalate; diethyl malonate; dimethyl maleate, diethyl maleate, di maleate Maleic acid esters such as chill; Tributyl citrate; Sorbic acid esters such as methyl sorbate, ethyl sorbate, and butyl sorbate; Sebacic acid esters such as dibutyl sebacate and dioctyl sebacate; Formic acid monoesters and diesters, butyric acid monoester And ethylene glycol esters such as diester, lauric acid monoester and diester, palmitic acid monoester and diester, stearic acid monoester and diester, oleic acid monoester and diester; triacetin; diethyl carbonate; diphenyl carbonate; ethylene carbonate; propylene carbonate And boric acid esters such as tributyl borate and tripentyl borate.

  Among these, in particular, when tricresyl phosphate is used alone or in combination, the stability of the emulsion is most favorable, which is preferable. It is also possible to use the above oils in combination with other oils.

  When the solubility of the electron donating dye precursor or photodegradable diazo compound to be encapsulated in the hydrophobic organic solvent is inferior, a low-boiling solvent having high solubility can be used in combination. Preferred examples of such a low boiling point solvent include ethyl acetate, isopropyl acetate, butyl acetate, and methylene chloride.

The content of the heat-sensitive recording material in the present invention is not particularly limited, and is preferably appropriately selected according to the heat-sensitive recording material to be used and the application, for example, an electron-donating dye precursor or a photodegradable diazo compound. When is used, it is preferably used as follows.
When the electron donating dye precursor or the photodegradable diazo compound is contained in the heat sensitive recording layer of the heat sensitive recording material, the content of the electron donating dye precursor is 0.1 to 5.0 g / m ^2. 1.0 to 4.0 g / m ² is more preferable. Moreover, as content of a photodegradable diazo compound, 0.02-5.0 g / m < ² > is preferable and 0.10-4.0 g / m < ² > is more preferable from the point of coloring density.
When the content of the electron donating dye precursor is within the above range, a sufficient color density is obtained, and when the content of both is within 5.0 g / m ² , a sufficient color density is obtained. And the transparency of the heat-sensitive recording layer can be maintained.

  On the other hand, an aqueous solution in which a water-soluble polymer is dissolved as a protective colloid is used for the aqueous phase to be used, and after the oil phase is added thereto, emulsification and dispersion are performed by stirring means such as a homogenizer. , It functions as a dispersion medium that makes the dispersion uniform and easy and stabilizes the emulsified and dispersed aqueous solution. Here, in order to more uniformly emulsify and disperse and stabilize, a surfactant may be added to at least one of the oil phase and the aqueous phase. As the surfactant, a well-known emulsifying surfactant can be used. 0.1-5% is preferable with respect to the mass of an oil phase, and, as for the addition amount of this surfactant, 0.5-2% is more preferable.

As the surfactant to be contained in the aqueous phase, an anionic or nonionic surfactant that does not act on the protective colloid to cause precipitation or aggregation can be appropriately selected and used. .
Preferable surfactants include, for example, sodium alkylbenzene sulfonate, sodium alkyl sulfate, dioctyl sulfosuccinate sodium salt, polyalkylene glycol (for example, polyoxyethylene nonyl phenyl ether) and the like.

  Emulsification / dispersion is a means used for normal fine particle emulsification, such as a high-speed stirrer and an ultrasonic dispersion device, for example, a homogenizer, a manton, and the oil phase containing the above components and an aqueous phase containing a protective colloid and a surfactant. It can be easily carried out using other known emulsifying dispersion devices such as a Golie, an ultrasonic disperser, a dissolver, and a Keddy mill. After emulsification and dispersion, the emulsion is preferably heated to 30 to 70 ° C. in order to promote the capsule wall formation reaction. Further, during the reaction, in order to prevent aggregation between the capsules, it is preferable to add water to reduce the collision probability between the capsules or to perform sufficient stirring.

  Further, a dispersing agent for preventing aggregation may be added again during the capsule formation reaction. As the polymerization reaction proceeds, the generation of carbon dioxide gas is observed, and the end of the generation can be regarded as the end point of the capsule formation reaction. Usually, the target microcapsule can be obtained by reacting for several hours.

<Emulsified dispersion>
When an electron donating dye precursor or a photodegradable diazo compound is encapsulated as a core substance, the electron accepting compound or coupler compound to be used is, for example, a water-soluble polymer and an organic base, other coloring aids, etc. In addition, it can be used after being solid-dispersed by a mixing means such as a sand mill. However, after previously dissolving in a high-boiling organic solvent that is hardly soluble or insoluble in water, this is used as a protective colloid with a surfactant and / or a water-soluble polymer. It is more preferable to use it as an emulsion mixed with an aqueous polymer solution (aqueous phase) and then emulsified and dispersed with a homogenizer or the like. In this case, a low boiling point solvent can be used as a dissolution aid, if necessary.
Further, the coupler compound and the organic base can be emulsified and dispersed separately, or mixed and then dissolved in a high boiling point organic solvent to be emulsified and dispersed. A preferable emulsified dispersion particle size is 1 μm or less.

  The high boiling point organic solvent used in this case can be appropriately selected from, for example, high boiling point oils described in JP-A-2-141279. Among them, it is preferable to use esters from the viewpoint of emulsion stability of the emulsion dispersion, and among these, tricresyl phosphate is particularly preferable. The above oils can be used together with other oils.

  The water-soluble polymer contained as the protective colloid can be appropriately selected from known anionic polymers, nonionic polymers, and amphoteric polymers, and is soluble in water at the temperature at which emulsification is attempted. Is preferably 5% or more water-soluble polymer, and specific examples thereof include polyvinyl alcohol or a modified product thereof, polyacrylic acid amide or a derivative thereof, ethylene-vinyl acetate copolymer, styrene-maleic anhydride copolymer, Ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, polyvinylpyrrolidone, ethylene-acrylic acid copolymer, vinyl acetate-acrylic acid copolymer, carboxymethylcellulose, cellulose derivatives such as methylcellulose, casein, gelatin , Starch derivatives, arabic gum, sodium alginate And the like. Among these, polyvinyl alcohol, gelatin, and cellulose derivatives are particularly preferable.

  Moreover, 0.02-0.6 are preferable and, as for the mixing ratio (oil phase mass / aqueous phase mass) with respect to the water phase of an oil phase, 0.1-0.4 are more preferable. When the mixing ratio is in the range of 0.02 to 0.6, an appropriate viscosity can be maintained, the production suitability is excellent, and the stability of the coating solution over time is excellent.

When an electron-accepting compound is used in the heat-sensitive recording material of the present invention, the electron-accepting compound is preferably 0.5 to 30 parts by mass with respect to 1 part by mass of the electron-donating dye precursor. 10 mass parts is more preferable.
Further, when a coupler compound is used in the heat-sensitive recording material of the present invention, the coupler is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 10 parts by mass with respect to 1 part by mass of the diazo compound. .
Examples of the polymer latex used for forming the heat-sensitive recording layer in the present invention include the polymer latex exemplified in the intermediate layer, and suitable examples are also the same. The content of the polymer latex is the same as that in the intermediate layer when a binder is substituted for the water-soluble binder.
The polymer latex can be added when adjusting the emulsion in addition to adjusting the coating solution for the thermal recording layer described later.

<Coating solution for thermal recording layer>
The thermosensitive recording layer coating solution can be prepared, for example, by mixing the microcapsule solution, the emulsified dispersion, and the polymer latex prepared as described above. Here, the water-soluble polymer used as the protective colloid in the preparation of the microcapsule liquid and the water-soluble polymer used as the protective colloid in the preparation of the emulsified dispersion function as a binder in the thermosensitive recording layer. To do. In addition to these protective colloids, a binder may be added and mixed to prepare a thermal recording layer coating solution.

As the binder to be added, a water-soluble binder is generally used, and it is preferable to add polyvinyl alcohol as a main component from the viewpoints of coating uniformity and ensuring the strength of the coating film. Furthermore, modified polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, epichlorohydrin modified polyamide, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic salicylic anhydride copolymer, polyacrylic acid, polyacrylamide , Methylol-modified polyacrylamide, starch derivatives, casein, gelatin and the like can be added.
The addition amount of the binder is not particularly limited, but is preferably 3 to 20% by mass with respect to the total solid content (mass) of the thermosensitive recording layer from the viewpoint of coating film strength. More preferably, it is -15 mass%, and it is especially preferable that it is 8-12 mass%.
In order to apply the thermal recording layer coating liquid onto the support, known coating means used for aqueous or organic solvent based coating liquids are used. In this case, the thermal recording layer coating liquid is applied safely and uniformly. In addition, in order to ensure the strength of the coating film, in the heat-sensitive recording material of the present invention, methyl cellulose, carboxymethyl cellulose, polystyrene or a copolymer thereof, polyester or a copolymer thereof, polyethylene or a copolymer thereof, an epoxy resin An acrylate resin or a copolymer thereof, a methacrylate resin or a copolymer thereof, a polyurethane resin, a polyamide resin, a polyvinyl butyral resin, or the like can be used.

  In addition, a water resistance improver is added for the purpose of imparting water resistance to these binders, and emulsions of hydrophobic polymers other than the polymer latex, specifically, styrene-butadiene rubber latex, acrylic resin emulsion, etc. are added. You can also

<Other ingredients>
Hereinafter, other components that can be used in the thermosensitive recording layer will be described.
There is no restriction | limiting in particular as said other component, Although it can select suitably according to the objective or necessity, For example, a well-known thermofusible substance, a ultraviolet absorber, antioxidant, etc. are mentioned.
The coating amount of the other components, preferably about ^{0.05~1.0g / m 2, 0.1~0.4g / m} 2 is more preferable. The other components may be added inside the microcapsule or outside the microcapsule.

  The heat-fusible substance can be contained in the heat-sensitive recording layer for the purpose of improving thermal response. Examples of such heat fusible substances include aromatic ethers, thioethers, esters, aliphatic amides, ureidos, and the like. Examples of these are disclosed in JP-A Nos. 58-57989, 58-87094, 61-58789, 62-109682, 62-132673, 63-151478, and 63-235961. It is described in Japanese Laid-Open Patent Publication Nos. 2-184289 and 2-215585.

  Preferred examples of the UV absorber include benzophenone UV absorbers, benzotriazole UV absorbers, salicylic acid UV absorbers, cyanoacrylate UV absorbers, and oxalic acid anilide UV absorbers. Examples of these are disclosed in JP-A-47-10537, 58-111942, 58-21284, 59-19945, 59-46646, 59-109555, 63-53544, JP-A 36-10466, 42-26187, 48-30492, 48-31255, 48-41572, 48-54965, 50-10726, U.S. Pat. 3707375, 3754919, and 4220711.

  Preferable examples of the antioxidant include hindered amine antioxidants, hindered phenol antioxidants, aniline antioxidants, and quinoline antioxidants. Examples of these are described in JP-A Nos. 59-155090, 60-107383, 60-107384, 61-137770, 61-139481, 61-160287, and the like. Yes.

The heat-sensitive recording layer in the present invention is used for obtaining a saturated transmission density (D _T-max ) in order to obtain a high-quality image by suppressing density unevenness caused by a slight difference in thermal conductivity of the thermal head. A thermal recording layer having a wide required energy amount, that is, a wide dynamic range is preferable. The heat-sensitive recording material of the present invention has a heat-sensitive recording layer as described above, and has a characteristic capable of obtaining a transmission density (D _T-max ) of 3.0 with a heat energy amount in the range of 90 to 150 mJ / mm ^2. A heat-sensitive recording layer is preferable.

The heat-sensitive recording layer in the present invention is applied so that the solid content after coating and drying is 1 to 25 g / m ² , and the thickness of the recording layer is 1 to 25 μm. It is preferable. In addition, two or more heat-sensitive recording layers can be laminated and used. In this case, the solid coating amount after application and drying of the entire thermosensitive recording layer is preferably 1 to 25 g / m ² .
More preferred.

(Support)
The support used in the heat-sensitive recording material of the present invention has a heat shrinkage rate of less than 1%, preferably 0.5% or less in the longitudinal and transverse directions in order to effectively prevent deformation such as curling. Is preferred. By selecting a support having a low thermal shrinkage rate, the thermal contraction of the support itself can be suppressed even when used in applications where high thermal energy is applied, such as when used for medical recording, and curling after recording is possible. It is possible to prevent problems such as deformation.

  The support in the present invention can be used without particular limitation as long as it has a low thermal shrinkage as described above, and can be appropriately selected from known supports. Among them, a transparent support is preferable, and as the transparent support, a synthetic polymer film such as a polyester film such as polyethylene terephthalate, polybutylene terephthalate, or polyethylene naphthalate, a cellulose triacetate film, or a polyolefin film such as polypropylene or polyethylene is used. A support of polyethylene terephthalate (PET) is particularly preferable. These can be used alone or in combination. As thickness of the said synthetic polymer film, 25-250 micrometers is preferable and 50-200 micrometers is more preferable.

  The synthetic polymer film may be colored in an arbitrary hue. As a method for coloring the synthetic polymer film, a method of forming a film by kneading a dye into a resin before forming the resin film, a coating solution in which the dye is dissolved in an appropriate solvent, and preparing this as a colorless transparent A known coating method such as a gravure coating method, a roller coating method, a wire coating method, or the like may be used on such a resin film. Of these, a polyester resin such as polyethylene terephthalate (PET) or polyethylene naphthalate kneaded with a blue dye is preferably formed into a film and subjected to heat treatment, stretching treatment, antistatic treatment or the like.

  In particular, when observing from the support on the Schaukasten, the Schaukasten light transmitted through the transparent non-image portion may cause illusion and make the image difficult to see. In such a case, in order to avoid the above-mentioned illusion, A (x = 0.2055, y = 0.3005), B on the chromaticity coordinates defined by the method described in JIS-Z8701 (1999). (X = 0.2820, y = 0.2970), C (x = 0.2885, y = 0.015), and D (x = 0.2870, y = 0.040). It is particularly preferable to use a synthetic polymer film colored blue in a rectangular region.

(Back layer)
In the heat-sensitive recording material of the present invention, a back containing at least one water-soluble binder on the opposite side (back surface) of the coloring surface having the heat-sensitive recording layer and the intermediate layer of the support in order to improve the curl balance. Preferably a layer is provided.
As the water-soluble binder, gelatin, polyvinyl alcohol and the like are preferable, and gelatin is particularly preferable.
As the gelatin, alkali-processed gelatin having a low isoelectric point, derivative gelatin reacted with an amino group (for example, phthalated gelatin) and the like are particularly preferable.
As said water-soluble binder, 1 type may be used independently and 2 or more types may be used together. When the back layer is composed of two or more layers, at least two layers preferably contain gelatin and may contain other water-soluble binder together with gelatin.
Water-soluble binder coated amount of the back surface, from the viewpoint of further improving the curl balance, is preferably 1 to 5 g / m ^2, and most preferably 2 to 4 g / m ^2.

When the water-soluble binder coating amount on the back surface is less than 1 g / m ² , the curl balance with the color developing side having the thermosensitive recording layer cannot be maintained, and curling deformation after thermal recording is avoided. It can be very difficult to do. On the other hand, when the coating amount of the water-soluble binder exceeds 5 g / m ² , the balance with the side having the thermosensitive recording layer may not be maintained, such as curl deformation on the back layer side.

The heat-sensitive recording material of the present invention can further contain a latex on the back surface in order to improve the curl balance. In this case, the amount of latex applied is less than or equal to the amount of water-soluble binder applied on the back surface. It is preferable. Furthermore, in order to further improve the curl balance, the latex coating amount on the back surface is preferably 50% by mass or less of the water-soluble binder coating amount on the back surface. Here, the latex is preferably used in the form of an aqueous dispersion.
The latex is considered to act as a filler for the water-soluble binder, and has a function of suppressing thermal expansion and contraction of the water-soluble binder film and improving dimensional stability. On the other hand, when the application ratio of latex to water-soluble binder is increased, the water-soluble binder film is plasticized, thereby deteriorating adhesion resistance. In particular, if the coating weight after latex coating and drying exceeds the gel coating weight on the back surface, the adhesion between the back surface and the color development surface will increase, and it will be easy to cause film peeling when peeling both of them. Not suitable. In order to avoid this, the latex coating amount is preferably not more than the water-soluble binder coating amount on the back surface, and particularly preferably not more than 50% by mass of the water-soluble binder coating amount on the back surface.

  The latex used in the present invention is preferably a copolymer of various monomers. Specific examples of the monomer composition include alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate; methyl methacrylate, ethyl Examples thereof include alkyl methacrylates such as methacrylate, propyl methacrylate, and butyl methacrylate; hydroxyethyl methacrylate, acrylic acid, styrene, and the like. These monomers can be used alone or in combination.

  The back layer in the present invention may be composed of one layer or may be composed of two or more layers. In particular, it is preferably composed of two or more layers from the viewpoint that a coating film can be formed satisfactorily while increasing the coating amount of a water-soluble binder containing gelatin without causing any other problems. Moreover, you may contain other components, such as a hardening agent, a mat agent, a ultraviolet absorber, dye, a pH adjuster, antiseptic | preservative, and surfactant, as needed or the objective.

  Examples of the water-soluble binder used for the back layer in the present invention include, in addition to gelatins, polyvinyl alcohols such as vinyl acetate-acrylamide copolymer, silicon-modified polyvinyl alcohol, acetyl-modified polyvinyl alcohol, and fluorinated acetyl-modified polyvinyl alcohol. , Starch, modified starch, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, gum arabic, casein, styrene-maleic acid copolymer hydrolyzate, styrene-maleic acid copolymer half ester hydrolysate, isobutylene-maleic anhydride copolymer Water-soluble polymers such as coalescent hydrolysates, polyacrylamide derivatives, polyvinyl pyrrolidone, polystyrene sulfonate soda, sodium alginate and the like.

  As another component, a hardener may be contained for the purpose of hardening the coated film by acting with a water-soluble binder (particularly gelatin) and imparting water resistance. Examples of the hardener include those described on pages 77 to 87 of “THE THEORY OF THE PHOTOGRAPHIC PROCESS; FORTH EMOTION” (by TH James), and vinyl sulfone compounds are preferable.

Further, a matting agent may be contained for the purpose of improving transportability and preventing light reflection.
Examples of the matting agent include fine particles such as starch obtained from barley, wheat, corn, rice, beans, cellulose fiber, polystyrene resin, epoxy resin, polyurethane resin, urea formalin resin, poly (meth) acrylate resin, Polymethyl (meth) acrylate resin, copolymer resin such as vinyl chloride or vinyl acetate, fine particles of synthetic polymer such as polyolefin, inorganic substances such as calcium carbonate, titanium oxide, kaolin, smectite clay, aluminum hydroxide, silica, zinc oxide Fine particles.
From the viewpoint of improving the transparency of the heat-sensitive recording material, a particulate material having a refractive index of 1.45 to 1.75 is preferable, and the average particle diameter is 1 to 20 μm (particularly 1 to 10 μm). preferable.

Moreover, it is preferable to add a fluorine-type surfactant to the back layer used as an outermost layer seeing from a support body as a coating adjuvant or an antistatic agent.
Examples of the fluorosurfactant include potassium perfluorooctane sulfonate, sodium N-propyl-N-oxyethylene perfluorooctanesulfonamidobutyl sulfonate, trimethyl (propyleneaminosulfonylperfluorooctane) ammonium chloride, N- And propyl-N-oxyethylene perfluorooctane sulfonate sodium.

  A thickening agent that adjusts the viscosity of the coating solution may be added to the back layer for the purpose of smoothly applying the back layer. An ultraviolet absorber may be added for the purpose of increasing the light resistance of the image after recording. The above thickener and ultraviolet absorber can be appropriately selected from known ones.

  From the viewpoint of improving the hue of the heat-sensitive recording material, various dyes such as C.I. I. Pigment Blue 60, C.I. I. Pigment Blue 64, C.I. I. Pigment Blue 15: 6 or the like may be added.

  For the purpose of maintaining the stability of the coating solution for forming the back layer, a pH adjusting agent capable of adjusting pH, such as sodium hydroxide, may be added. Further, a preservative may be added for the purpose of preventing deterioration of the coating solution for forming the back layer and the heat-sensitive recording material. The preservative can be appropriately selected from known ones.

When the back layer is composed of a plurality of layers, the other components described above may be contained in any layer. Further, other components can be appropriately contained within a range not impairing the effects of the present invention.
As a coating method for coating and forming the back layer, a known coating method such as a blade coating method, an air knife coating method, a gravure coating method, a roll coating coating method, a spray coating method, a dip coating method, or a bar coating method is applied. it can. When the back layer is composed of a plurality of layers, multiple layers may be applied.

  On the side of the support that does not have a heat-sensitive recording layer and a protective layer, in addition to the back layer, it is adjacent to the back layer in that the behavior of the curl before it reaches equilibrium in a short time after printing can be adjusted. And you may have the layer (henceforth a "PVA layer") containing polyvinyl alcohol. The layer may be provided on the back layer surface farthest from the support on the side having the back layer of the support, or may be provided between the support and the back layer. When it consists of a plurality of layers, it may be provided between the back layer and the back layer. A plurality of the PVA layers may be formed.

Suitable examples of the polyvinyl alcohol include fully saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, and silica-modified polyvinyl alcohol.
As content in the PVA layer of the said polyvinyl alcohol, 50-100 mass% of solid content (mass) of this layer is preferable.

  The PVA layer may further contain a surfactant. Examples of the surfactant include sodium alkylbenzene sulfonate, sodium alkyl sulfate, dioctyl sulfosuccinate sodium salt, polyalkylene glycol, and the like.

  Similarly to the back layer, the PVA layer can be formed by applying a coating solution prepared containing polyvinyl alcohol, and the layer thickness is preferably 0.5 to 10 μm.

-Second aspect-
The heat-sensitive recording material according to the second aspect of the present invention will be described in detail below.
As the heat-sensitive recording material of the second aspect of the present invention, a heat-sensitive recording material comprising at least a heat-sensitive recording layer formed of a heat-sensitive recording material and a binder and an intermediate layer containing a water-soluble binder on a support. The heat-sensitive recording layer is formed by adding a polymer latex.
The heat-sensitive recording material in the second aspect is the same as the layer structure of the first aspect, and the preferred aspect is also the same.
The heat-sensitive recording material obtained by adding the polymer latex to the heat-sensitive recording layer is to obtain a heat-sensitive recording material excellent in heat-resistant storage stability that is not affected by the temperature environment and has little change in image density after image recording. Can do.

(Thermosensitive recording layer)
The heat-sensitive recording layer in this embodiment is the same as that of the first embodiment except that it is formed by further adding a polymer latex, and particularly described, and the preferred range is also the same.
The polymer latex may be added to the heat-sensitive recording layer coating solution, or may be added, for example, when preparing an emulsion in which the electron accepting compound or coupler compound is emulsified and dispersed.
The polymer latex is the same as the polymer latex used in the intermediate layer formation of the first aspect, and preferred examples, ranges, and the like are also the same.

(Middle layer)
The intermediate layer in the second aspect is the same as the intermediate layer described in the first aspect except that the polymer latex used in the first aspect is not added.

In the intermediate layer, the coating amount of the water-soluble binder is usually in the range of 0.2 to 10 g / m ² . The content of gelatin in the water-soluble binder as solid content (% by mass) is preferably 80% by mass to 100% by mass, and more preferably 90% by mass to 99% by mass. The water-soluble binder other than gelatin is the same as in the first embodiment.
By setting it within this range, it becomes easy to prevent mixing of coloring components and adjust sensitivity between recording layers.

  Further, the support, the back layer, and the like are the same as those in the first aspect, and the same applies to preferable examples, ranges, and the like.

(Protective layer)
In the heat-sensitive recording material of the present invention, the protective layer is preferably formed as an upper layer of the heat-sensitive recording layer and the intermediate layer on the color developing surface side.
The protective layer is usually prepared and applied as a protective layer coating solution, and the protective layer coating solution is used as a binder in order to maintain a good head matching property over a wide recording energy range. A form containing at least polyvinyl alcohol as a main component and further containing a pigment and a liquid or solid lubricant is preferable.

<Pigment>
The pigment used in the protective layer in the heat-sensitive recording material of the present invention is usually used for the purpose of making thermal recording with a thermal head suitable, that is, for the purpose of suppressing the occurrence of sticking, abnormal noise, etc. Both pigments and inorganic pigments can be used and are not particularly limited.

  The pigment used for the protective layer in the present invention has an average particle diameter, specifically, a 50% volume average particle diameter measured by a laser diffraction method (by a laser diffraction particle size distribution measuring apparatus “LA700” manufactured by Horiba, Ltd.). The measured average particle diameter of the pigment particles corresponding to 50% volume in the pigment, hereinafter referred to simply as “average particle diameter”) is preferably 0.10 to 5 μm. In particular, when performing thermal recording with a thermal head, the 50% volume average particle size is in the range of 0.20 to 0.50 μm from the viewpoint of suppressing the occurrence of sticking or abnormal noise between the thermal head and the thermal recording material. More preferably. When the 50% volume average particle size is in the range of 0.10 to 5.0 μm, the effect of reducing friction against the thermal head is great, and as a result, the thermal head and the protective layer of the heat-sensitive recording material adhere to each other during printing. In other words, the so-called sticking phenomenon can be effectively prevented.

  The kind of pigment that can be used for the protective layer in the present invention is not particularly limited, and can be appropriately selected from known organic and inorganic pigments. Inorganic pigments such as titanium, kaolin, aluminum hydroxide, amorphous silica, and zinc oxide, and organic pigments such as urea formalin resin and epoxy resin are preferable. Of these, kaolin, aluminum hydroxide, and amorphous silica are particularly preferable. These pigments may be used alone or in combination of two or more. Among the above pigments, a pigment whose surface is coated with at least one selected from the group consisting of higher fatty acids, higher fatty acid metal salts, and higher alcohols can be suitably used. Examples of the higher fatty acid used for the surface treatment include stearic acid, palmitic acid, myristic acid, lauric acid, and the like.

  The above pigments include, for example, sodium metametaphosphate, partially saponified or fully saponified polyvinyl alcohol, polyacrylic acid copolymer, various surfactants and other dispersing aids, preferably partially saponified or fully saponified polyvinyl alcohol, polyacrylic. In the presence of an acid copolymer ammonium salt, it is preferably used after being dispersed to the average particle size by a known disperser such as a dissolver, a sand mill, or a ball mill. That is, the pigment is preferably used after being finely dispersed until the 50% volume average particle size of the pigment is in the range of 0.1 to 5.0 μm.

<Lubricant>
The lubricant used for the protective layer in the present invention is usually liquid at room temperature or a lubricant having a melting point of less than 40 ° C. and a melting point of 40 ° C. or higher in order to reduce the printing torque and to make thermal recording with a thermal head suitable. Although the form containing this lubricant is preferable, it is not particularly limited.
Examples of the lubricant that is liquid at room temperature include silicone oil, liquid paraffin, and lanolin, and silicone oil is particularly preferable. These silicone oils may have a substituent such as a carboxyl group or a polyoxyethylene group, and the viscosity of the silicone oil is preferably 100 to 100,000 cps.

  Examples of the lubricant having a melting point of less than 40 ° C. include polyoxyethylene alkyl ether, polyoxyethylene alkyl ether acetate, polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether phosphate, etc. A polyoxyethylene alkyl ether phosphate represented by the following structural formula [001] is preferred.

上式［００１］中、Ｒはアルキル基を表し、該アルキル基は置換基によって置換されていてもよい。ｎは２〜２０の整数を表す。
上記の常温で液体の潤滑剤及び融点が４０℃以下の潤滑剤は、単独で使用ないし２種以上を併用してもよい。

In the above formula [001], R represents an alkyl group, and the alkyl group may be substituted with a substituent. n represents an integer of 2 to 20.
The above-mentioned lubricant that is liquid at normal temperature and the lubricant having a melting point of 40 ° C. or less may be used alone or in combination of two or more.

  The lubricant having a melting point of 40 ° C. or higher is desirably a melting point of 160 ° C. or lower, preferably 140 ° C. or lower, stearic acid amide (melting point 100 ° C.), methylol stearic acid amide (101 ° C.), polyethylene Wax (melting point 110 ° C. or less), paraffin wax with melting point 50 to 90 ° C., glycerin tri-12-hydroxystearate (melting point 88 ° C.), oleic acid amide (melting point 73 ° C.), zinc oleate (melting point 75 ° C.), laurin Acid amide (melting point 84 ° C.), aluminum stearate (melting point 102 ° C.), manganese stearate (melting point 112 ° C.), zinc stearate (melting point 125 ° C.), calcium stearate (melting point 160 ° C.), ethylene bisstearamide (melting point) 140 ° C), magnesium stearate (melting point 132 ° C), Palmiti Magnesium acid (melting point 122 ° C.), magnesium myristate (melting point 131 ° C.), and the like. These lubricants having a melting point of 40 ° C. or higher may be used alone or in combination of two or more.

  When the lubricant used in the present invention is insoluble in water, it is preferably added to the protective layer in the form of dispersion or emulsion. In the case of a solid, (1) an aqueous dispersion dispersed with a known disperser such as a homogenizer, dissolver or sand mill in the presence of a water-soluble polymer such as polyvinyl alcohol or a dispersant such as various surfactants. (2) Emulsified after being dissolved in a solvent and then emulsified and dispersed with a known emulsifying device such as a homogenizer, dissolver or colloid mill in the presence of a dispersing agent such as a water-soluble polymer or various surfactants Used in the form of In the case of a liquid, it is used in the form of an emulsion as described above. A preferable average particle size of the dispersion or emulsion is 0.1 to 5.0 μm, and more preferably 0.1 to 2.0 μm. Here, the average particle diameter refers to, for example, a 50% volume average particle diameter measured at a transmittance of 71 ± 1% using a laser diffraction particle size distribution measuring device “LA-700” manufactured by Horiba, Ltd. .

  On the other hand, water-soluble lubricants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl ether acetate, polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl ether phosphate, etc. are optional in consideration of solubility. And can be added to the protective layer.

  Further, the protective layer of the heat-sensitive recording material of the present invention has a surface scratch resistance of 40 g or more as defined in JIS K6718 on the surface thereof in order to prevent coating film peeling during cutting and damage during handling. Preferably. In the present invention, as a test method for the above-mentioned surface scratch hardness, a continuous load type scratch strength tester is used, and a sapphire cone-shaped scratching needle (tip R: 0.1 mm) is used for a movement distance of 100 mm. Scratching the surface of the protective layer by changing the weight continuously in the range of 0 to 200 g, and observing the color developed to a transmission density of 1.2 under transmitted light. The scratch hardness was sought from.

<Binder etc.>
In the protective layer in the present invention, polyvinyl alcohol can be used as a binder from the viewpoint of improving transparency, and examples thereof include modified PVA such as carboxy-modified polyvinyl alcohol and silica-modified polyvinyl alcohol.

Further, the protective layer in the present invention preferably contains a known hardener or the like. Examples of the hardener include inorganic compounds such as boric acid, borax, and colloidal silica, aldehyde derivatives, and dialdehyde derivatives.
It is preferable to add 2,3-dihydroxy-1,4-dioxane as a hardener to the protective layer from the viewpoint of increasing the film strength and improving the water resistance of the protective layer. Examples of 2,3-dihydroxy-1,4-dioxanes include 2,3-dihydroxy-5-methyl-1,4-dioxane (a compound represented by the following structural formula [002]), 2,3-dihydroxy-1 , 4-dioxane, 2,3-dihydroxy-5,6-dimethyl-1,4-dioxane, 2,3-dihydroxy-2,5,6-trimethyl-1,4-dioxane, 2,3-dihydroxy-2 -Methyl-1,4-dioxane.

  In the present invention, a surfactant can be added to the coating solution for forming the protective layer in order to form the protective layer uniformly on the heat-sensitive recording layer or the intermediate layer. As the surfactant, sulfosuccinic acid-based alkali metal salts, fluorine-containing surfactants, and the like are preferable. Specific examples include di- (2-ethylhexyl) sulfosuccinic acid and di- (n-hexyl) sulfosuccinic acid. Examples include sodium salts, potassium salts, or ammonium salts, acetylene glycol derivatives, sodium perfluoroalkyl sulfate, potassium salts, ammonium salts, perfluoroalkyl betaine compounds, and the like.

Furthermore, metal oxide fine particles, inorganic electrolytes, polymer electrolytes, and the like may be added to the protective layer for the purpose of preventing charging of the thermosensitive recording material. The protective layer may have a single layer structure or a laminated structure of two or more layers.
Dry coating amount of the protective layer is preferably ^{0.2~7g / m 2, 1~4g / m} 2 is more preferable.

(Other layers)
In the present invention, an ultraviolet filter layer may be provided at any position on the support for the purpose of preventing image fading. The ultraviolet filter layer contains an ultraviolet absorber such as benzotriazole, benzophenone, or hindered amine.
Moreover, you may have further a light reflection prevention layer. The light reflection preventing layer can be constituted by containing fine particles suitable for a matting agent usable for the back layer.

  In order to prevent the heat-sensitive recording layer from peeling off from the support, an undercoat layer may be formed on the support in advance before applying the heat-sensitive recording layer, the protective layer or the like. The undercoat layer is made of an acrylate copolymer, polyvinylidene chloride, SBR, aqueous polyester, or the like, and the thickness of the layer is preferably 0.05 to 0.5 μm.

  When applying the heat-sensitive recording layer on the undercoat layer, the undercoat layer may swell due to moisture contained in the heat-sensitive recording layer coating solution, and the image recorded on the heat-sensitive recording layer may deteriorate. It is preferable to harden using dialdehydes such as glutaraldehyde, 2,3-dihydroxy-1,4-dioxane, or a hardener such as boric acid. The addition amount of the hardener can be appropriately added in accordance with the desired degree of curing in the range of 0.2 to 3.0% by mass with respect to the dry mass of the undercoat layer.

(Method for producing thermosensitive recording material)
The method for producing a heat-sensitive recording material of the present invention comprises a step of coating a heat-sensitive recording layer coating solution containing a heat-sensitive recording material and a binder on a support to form a heat-sensitive recording layer, a water-soluble binder, and an intermediate layer containing a polymer latex. In this method, a coating solution is applied to form an intermediate layer, and it is preferable to form a protective layer using a protective layer coating solution.
A step of coating a thermal recording material coating solution containing a thermal recording material and a binder on a support; and a step of coating an intermediate layer coating solution containing a water-soluble binder; By adopting a production method containing a polymer latex, it is possible to suppress changes in image density after recording, thereby improving the heat resistant storage stability of the heat-sensitive recording material.

Furthermore, as another aspect, the method for producing a heat-sensitive recording material of the present invention comprises applying a heat-sensitive recording layer coating solution containing a heat-sensitive recording material, a binder, and a polymer latex on a support to make the heat-sensitive recording layer water-soluble. It is a method of forming an intermediate layer by coating an intermediate layer coating solution containing a conductive binder, and it is preferable to form a protective layer using a protective layer coating solution. Furthermore, other layers can be formed as necessary.
A heat-sensitive recording layer coating solution comprising a step of coating a heat-sensitive recording material containing a heat-sensitive recording material and a binder, and a step of coating an intermediate layer coating solution containing a water-soluble binder; However, by using a production method that further contains a polymer latex, it is possible to suppress changes in the image density after recording, thereby improving the heat-resistant storage stability of the thermosensitive recording material.

These supports, heat-sensitive recording materials, binders, water-soluble binders, polymer latexes, etc. are the already described supports, heat-sensitive recording materials, binders, water-soluble binders, polymer latexes, etc. used in the heat-sensitive recording material of the present invention. The preferred examples are also the same.
Examples of the heat-sensitive recording layer coating solution, the intermediate layer coating solution, and the protective layer coating solution to be used include the above-described heat-sensitive recording layer coating solution, intermediate layer coating solution, and protective layer coating solution, and preferred examples are also the same.
Examples of other layers include other layers such as an undercoat layer.

The method for producing the heat-sensitive recording material of the present invention will be specifically described below, but the present invention is not limited thereto.
The heat-sensitive recording material of the present invention is formed, for example, by applying a heat-sensitive recording layer-forming coating liquid on one side of a support to form a heat-sensitive recording layer, on which the intermediate-layer coating liquid and protective layer are formed. A layer coating solution is applied and formed on the side opposite to the side, as described above, a back layer coating solution is applied to form a single layer or a plurality of layers. Accordingly, another layer is formed on the one and the other. As a specific coating method on the one side, a known coating method, a coating method similar to the case of coating and forming a back layer, and the like can be applied.
Here, the heat-sensitive recording layer, the intermediate layer and the protective layer may be formed at the same time. In this case, the heat-sensitive recording layer coating solution, the intermediate layer and the protective layer coating solution are simultaneously coated on the support. Can be formed.

  The heat-sensitive recording material of the present invention can preferably record an image with a heating element such as a thermal head. As the thermal head, a protective layer is formed on a heating element having a heating resistor and an electrode on a glaze layer using a known film forming apparatus so that the carbon ratio of the uppermost layer in contact with the heat-sensitive recording material is 90% or more. Those provided with are preferably used. Two or more head protective layers may be used, but at least the uppermost layer preferably has a carbon ratio of 90% or more.

  Examples of the present invention are shown below, but the present invention is not limited to these examples. In the following, “%” means “mass%”.

(Example 1)
(Preparation of coating solution for first back layer)
Water was added to the following composition to prepare a total amount of 21.03 liters to obtain a first back layer coating solution (hereinafter referred to as “BC layer coating solution”). Here, the gelatin content in the present back layer is the total amount of “lime-processed gelatin” in the following composition and gelatin in “gelatin dispersion containing 12% spherical PMMA matting agent”. The polymer content of the latex is the solid content in the “polyethyl acrylate latex (20% liquid)” in the following composition.

<Composition of coating solution for BC layer>
・ Lime-treated gelatin (water-soluble binder): 1000g
Gelatin dispersion containing 12% spherical PMMA matting agent (average particle size: 5.7 μm)
……… 180g
-An emulsion of an ultraviolet absorber containing the compounds represented by the following structural formulas [1] to [5] in the following content: 1028 g
[The content of the ultraviolet absorber per kg of the emulsion is 14.9 g of the compound represented by the structural formula [1], 12.7 g of the compound represented by the structural formula [2], and represented by the structural formula [3]. 14.9 g of the compound, 21.1 g of the compound represented by the structural formula [4], and 44.5 g of the compound represented by the structural formula [5]. ]
・ 1,2-Benzisothiazolin-3-one… 0.98g
・ Sodium poly-p-vinylbenzenesulfonate: 16.4g
(Molecular weight: about 400,000)
-Compound represented by the following structural formula [6] ... 3.79 g
・ Latex of polyethyl acrylate (20% solution) ……… 1448 ml
・ N, N-ethylene-bis (vinylsulfonylacetamide) ... 52.2g
・ 1,3-Bis (vinylsulfonylacetamide) propane ………… 17.4g

(Preparation of coating solution for second back layer)
Water was added to the following composition to prepare a total amount of 26.59 liters to obtain a second back layer coating solution (hereinafter referred to as “BPC layer coating solution”). Here, the gelatin content in the present back layer is the total amount of “lime-processed gelatin” in the following composition and gelatin in “gelatin dispersion containing 15% spherical PMMA matting agent”.

<Composition of coating solution for BPC layer>
・ Lime-treated gelatin (water-soluble binder): 1000g
Gelatin dispersion containing 15% spherical PMMA matting agent (average particle size: 0.7 μm)
……… 1015g
・ 1,2-Benzisothiazolin-3-one ……… 2.09g
・ Pt-octylphenoxy sodium polyoxyethylene ethylsulfonate
......... 9.53g
・ Sodium polyacrylate (Molecular weight: approx. 100,000) ... 57.9g
・ Sodium poly-p-vinylbenzenesulfonate (molecular weight: about 400,000)
......... 22.9g
・ N-propyl-N-polyoxyethylene-perfluorooctane sulfonate sodium amidobutyl sulfonate …… 0.37g
・ Hexadecyloxy-nonyl (ethyleneoxy) -ethanol
......... 8.97 g
・ 1N sodium hydroxide aqueous solution …… 28.1g
・ Latex of polyethyl acrylate (20% solution) ... 2087ml
・ N, N-ethylene-bis (vinylsulfonylacetamide) ............ 18.0g
・ 1,3-Bis (vinylsulfonylacetamide) propane …… 6.0g

(Preparation of support with back layer)
A transparent PET support (thickness: 175 μm) dyed blue with x = 0.2850 and y = 0.2995 with chromaticity coordinates defined by the method described in JIS-Z8701 (1999) was obtained from the above. The BC layer coating solution and the BPC layer coating solution were applied on the transparent PET support in the order of the BC layer coating solution and the BPC layer coating solution in the order of 51.37 ml / The layers were applied simultaneously by a slide bead method so as to be m ² and 14.70 ml / m ² and dried. Here, the coating and drying conditions are as follows.

The coating speed was 160 m / min, the gap between the coating die tip and the support was 0.10 to 0.30 mm, and the pressure in the decompression chamber was set lower by 196 to 882 Pa than the atmospheric pressure. The support was previously charged with ion wind before application. Subsequently, in the chilling zone, the coating solution is cooled with wind at a dry bulb temperature of 10 to 20 ° C., then conveyed in a non-contact manner, and a dry bulb temperature of 23 to 45 ° C. and a wet bulb with a helical contactless dryer. It dried with the drying wind of temperature 15-21 degreeC.
As described above, a back layer composed of two layers was formed on one side of the transparent PET support. The total coating amount of gelatin contained in the backing layer of the two layers is 3.05 g / m ^2, the coating amount of the latex is 0.94 g / m ^2.

(Preparation of coating solution for protective layer)
(1) Preparation of pigment dispersion After adding 280 g of aluminum hydroxide (trade name “Hijilite H42S” manufactured by Showa Denko KK) surface-treated with stearic acid as a pigment to 900 g of water, the mixture was stirred for 3 hours. The dispersion aid (trade name “Poise 532A” manufactured by Kao Corporation) 8.5 g, 10% polyvinyl alcohol aqueous solution (trade name “PVA105” manufactured by Kuraray Co., Ltd.) 300 g, 2% adjusted to the following 75 g of an aqueous solution of the compound represented by the structural formula [100] was added and dispersed with a sand mill to an average particle size of 0.33 μm, and water was added to adjust the concentration to 18% to obtain a pigment dispersion for protective layer. .

  Here, the average particle size is obtained by dispersing the test solution in which the pigment to be used is dispersed in the presence of a dispersant and diluted to 0.5% by adding water to the pigment dispersion immediately after the dispersion. Was added to warm water and adjusted so that the light transmittance was 72 ± 1%, and then subjected to ultrasonic treatment for 30 seconds. A laser diffraction particle size distribution measuring apparatus (trade name “ The average particle diameter of pigment particles corresponding to 50% volume of all pigments measured by LA700 "), and the average particle diameters described below all represent average particle diameters measured by the same method.

(2) Preparation of Lubricant Dispersion To 280 g of water, 110 g of glycerin tri-12-hydroxystearate (trade name “K3 Wax 500” manufactured by Kawaken Fine Chemical Co., Ltd.) as a lubricant was added and stirred for 3 hours. Dispersion aid (trade name “Poise 532A” manufactured by Kao Corporation) 3 g, 10% polyvinyl alcohol aqueous solution (trade name “MP103” manufactured by Kuraray Co., Ltd.) 340 g, and the above structural formula adjusted to 2% [ 100] of an aqueous solution of a compound represented by [100] was added and dispersed with a sand mill to an average particle size of 0.26 μm, and water was added thereto to adjust to 18% to obtain a lubricant dispersion for protective layer. Here, the concentration of glycerin tri-12-hydroxystearate, which is a lubricant, is 13.6%.

(3) Preparation of coating solution for protective layer 430 g of 5% polyvinyl alcohol (trade name “PVA124C” manufactured by Kuraray Co., Ltd.), 5 g of 72% aqueous sodium dodecylbenzenesulfonate, acetylene glycol surfactant (Nisshin Chemical ( Co., Ltd. product name “Surfinol 104”) 50% liquid 5.5 g, “Surflon S131S” (Asahi Glass Co., Ltd.) 10 g, melting point 35 ° C. polyoxyethylene alkyl ether phosphate (Daiichi Kogyo Seiyaku) "Plysurf A217E" manufactured by KK) 2 g, 245 g of the 18% pigment dispersion obtained above, 10 g of the 18% glycerol tri-12-hydroxystearate dispersion obtained above, 20.5% stearic acid Zinc dispersion (trade name “F115” manufactured by Chukyo Yushi Co., Ltd.) 21 g, 18% stearic acid dispersion (Chukyo Yushi ( Co., Ltd., trade name “Cerosol 920”) 31 g, 35% silicone oil aqueous dispersion (trade name “BY22-840”, manufactured by Toray Dow Corning Co., Ltd.) 41.5 g, 5% styrene maleic acid copolymer 110 g of ammonium salt aqueous solution (trade name “Polymaron 385” manufactured by Arakawa Chemical Co., Ltd.), 53 g of 20% colloidal silica (trade name “Snowtex” manufactured by Nissan Chemical Co., Ltd.), 70 g of 4% aqueous solution of boric acid, 2% acetic acid 30 g of an aqueous solution and 22 g of a 50% aqueous solution of the compound represented by the structural formula [002] were mixed. Water was added to this to adjust the concentration to 12% to obtain the intended protective layer coating solution.

(Preparation of coating solution for thermosensitive recording layer)
According to the following procedure, a microcapsule liquid and an electron-accepting compound emulsified dispersion each containing an electron-donating dye precursor as a core substance were prepared.
(1) Preparation of Microcapsule A Solution As an electron-donating dye precursor, 63.7 g of a compound represented by the following structural formula [201], 21 g of a compound represented by the following structural formula [202], and the following structural formula [203 10.8 g of the compound represented by the following structural formula [204], 5.8 g of the compound represented by the following structural formula [205], represented by the following structural formula [206] 2.7 g of the compound and 2.6 g of the compound represented by the following structural formula [207] were added to 110 g of ethyl acetate, heated to 70 ° C. and dissolved, and then cooled to 45 ° C. To this, 70 g of capsule wall material (trade name “Takenate D140N” manufactured by Mitsui Takeda Chemical Co., Ltd.) was added and mixed.
This solution was added to an aqueous phase of 300 g of a 5.9% aqueous polyvinyl alcohol solution (trade name “MP-103” manufactured by Kuraray Co., Ltd.), and then rotated using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.). Emulsification and dispersion were performed at 15000 rpm. After adding 275 g of water and 6.5 g of tetraethylenepentamine to the obtained emulsion, an encapsulation reaction was performed at a temperature of 60 ° C. for 4 hours, and finally the concentration was adjusted to 25% with water to obtain an average particle size. A microcapsule solution A having a diameter of 0.8 μm was obtained.

(2) Preparation of microcapsule B solution As an electron-donating dye precursor, 54.5 g of a compound represented by the following structural formula [201], 14.8 g of a compound represented by the following structural formula [202], and the following structural formula 10.5 g of a compound represented by [203], 6.4 g of a compound represented by the following structural formula [204], 3.4 g of a compound represented by the following structural formula [205], and represented by the following structural formula [206] 0.5 g of the compound obtained and 2.1 g of the compound represented by the following structural formula [207] were added to 110 g of ethyl acetate, heated to 70 ° C. and dissolved, and then cooled to a temperature of 45 ° C. To this, 65.5 g of capsule wall material (trade name “Takenate D127N” manufactured by Mitsui Takeda Chemical Co., Ltd.) was added and mixed.
This solution was added to a 275 g aqueous phase of a 5.9% aqueous polyvinyl alcohol solution (trade name “MP-103” manufactured by Kuraray Co., Ltd.), and then rotated using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.). Emulsification and dispersion were performed at 15000 rpm. After adding 275 g of water and 5.70 g of tetraethylenepentamine to the obtained emulsified liquid, an encapsulation reaction was performed at a temperature of 60 ° C. for 4 hours, and finally the concentration was adjusted to 28% with water. A microcapsule solution B having a diameter of 0.3 μm was obtained.

(3) Preparation of an electron-accepting compound emulsion dispersion As an electron-accepting compound, 220 g of a compound represented by the following structural formula [301], 80 g of a compound represented by the following structural formula [302], and the following structural formula [303] A compound 26g represented by the following structural formula [304], a compound 4.8g represented by the following structural formula [305], and a compound 41g represented by the following structural formula [306]. It was added to 160 g of ethyl acetate together with 10 g of resilfofate and 5 g of diethyl maleate and dissolved by heating to 70 ° C. This solution is represented by 1340 g of water, 43.5 g of polyvinyl alcohol (trade name “PVA217C” manufactured by Kuraray Co., Ltd.), 29 g of polyvinyl alcohol (trade name “PVA205C” manufactured by Kuraray Co., Ltd.), represented by the following structural formula [401]. 110 g of a 2% aqueous solution of the compound and 110 g of a 2% aqueous solution of the compound represented by the following structural formula [402] are added to the mixed aqueous phase, and then rotated using an ace homogenizer (manufactured by Nippon Seiki Co., Ltd.). The mixture was emulsified and dispersed to an average particle size of 0.7 μm at several 10000 rpm, and adjusted with water to a concentration of 22% to obtain an emulsified dispersion of an electron-accepting compound.

(4) Preparation of coating liquid A for thermosensitive recording layer 160 g of the microcapsule A liquid (solid content concentration 25%), 30 g of the microcapsule B liquid (solid content concentration 28%), and the electron-accepting compound emulsion dispersion (solid 710 g (concentration 22%), 7.2 g of 50% aqueous solution of the compound represented by the structural formula [002], and 25.5 g of colloidal silica (trade name “Snowtex O” manufactured by Nissan Chemical Co., Ltd.) Then, the concentration was adjusted to 21.5% with water to prepare the desired thermal recording layer coating solution (A).

(5) Preparation of coating liquid B for thermosensitive recording layer 60 g of the above microcapsule A liquid (solid content concentration 25%), 110 g of the above microcapsule B liquid (solid content concentration 28%), and the above-mentioned electron-accepting compound emulsion dispersion (solid 725 g, concentration of 22%), 6.5 g of 50% aqueous solution of the compound represented by the structural formula [002], and 23.5 g of colloidal silica (trade name “Snowtex O” manufactured by Nissan Chemical Co., Ltd.) Then, the concentration was adjusted to 21.5% with water to prepare the desired thermal recording layer coating solution (B).

(Preparation of coating solution A for intermediate layer)
After adding 9766 g of water to 1000 g of lime-processed gelatin and dissolving, 5% solution of di-2-ethylhexylsulfosuccinate Na salt (“Nissan Rapizol B90” manufactured by NOF Corporation) (water / methanol = 1 / 206 g of 1 volume mixed solvent) and 4998 g of polymer latex having a monomer composition of 100% ethyl acrylate (solid content: 20%) were added to prepare the target intermediate layer coating solution A.

(Preparation of intermediate layer coating solution B)
After 14500 g of water was added to 1000 g of lime-processed gelatin and dissolved, a 5% solution of di-2-ethylhexylsulfosuccinate Na salt (“Nissan Rapizol B90” manufactured by NOF Corporation) (water / methanol = 1 / 137 g of 1 volume mixed solvent), 25 g of 3.5% 1,2-benzisothiazolin-3-one aqueous solution, 1080 g of 3.0% poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000) Was added to prepare a target intermediate layer coating solution B.

(Preparation of thermal recording material)
On the surface opposite to the back layer of the support coated with the back layer, from the side close to the support, the thermal recording layer coating solution (A), the thermal recording layer coating solution (B), and the intermediate layer. Coating solution (A) and the coating solution for the protective layer in this order so that the coating amount becomes 41.3 mL / m ² , 22.5 mL / m ² , 24.7 mL / m ² , 27.5 mL / m ² , respectively. A transparent heat-sensitive recording material of the present invention having a heat-sensitive recording layer (A), a heat-sensitive recording layer (B), an intermediate layer (A), and a protective layer on a support is obtained by simultaneously applying multiple layers by the slide bead method and drying. It was.
The coating solution for each layer was adjusted to a temperature range of 33 ° C to 37 ° C. The drying conditions are as follows. The coating speed was set to 160 m / min, the distance between the coating die tip and the support was set to 0.10 to 0.30 mm, and the pressure in the decompression chamber was set to 200 to 1000 Pa lower than the atmospheric pressure. The support was neutralized with an ion wind before coating. In the subsequent initial drying zone, after drying with wind at a temperature of 45 ° C. to 55 ° C. and a dew point of 0 to 5 ° C., it is transported in a non-contact manner, and the dry bulb temperature is 30 to 45 ° C. It dried with the dry wind of wet-bulb temperature 17-23 degreeC, and humidity was adjusted at 40 to 60% of humidity at 25 degreeC after drying.
Here, the gelatin coating amount of the intermediate layer on the heat-sensitive recording layer side (coloring surface) is 1.50 g / m ² .

(Example 2)
In the preparation of the intermediate layer coating solution (A) of Example 1, from 4998 g of a polymer latex having a monomer composition of 100% ethyl acrylate, 4998 g of a polymer latex of ethyl acrylate: acrylic acid = 95: 5 (%) (solid content mass) The thermal recording material of the present invention was produced in the same manner as in Example 1 except for changing to 20%).

(Example 3)
In preparation of the intermediate layer coating solution (A) of Example 1, from 4998 g of a polymer latex having a monomer composition of 100% ethyl acrylate, styrene: methyl methacrylate: butyl acrylate: hydroxyethyl methacrylate: acrylic acid = 57.2: 8 .7: 27.7: 4.8: 1.6 (%) The polymer latex was changed to 4998 g (solid content: 20%), except that the heat sensitive recording material of the present invention was produced in the same manner as in Example 1. .

Example 4
In the preparation of the thermal recording layer coating liquid B of Example 1, 316 g of polymer latex (solid content: 20%) having a monomer composition of 100% ethyl acrylate was further added to the mixed component, and the intermediate layer coating liquid was changed from A to A. A heat-sensitive recording material of the present invention was produced in the same manner as in Example 1 except that B was changed.

(Example 5)
In the preparation of the thermal recording layer coating liquid B of Example 4, the monomer composition was changed from 316 g of a polymer latex consisting of 100% ethyl acrylate (solid content 20%) to ethyl acrylate: acrylic acid = 95: 5 (%). Except for this, the same procedure as in Example 4 was followed to produce a heat-sensitive recording material of the present invention.

(Example 6)
In the preparation of the thermal recording layer coating liquid B of Example 4, the monomer composition was styrene: methyl methacrylate: butyl acrylate: hydroxyethyl methacrylate: acrylic acid = 57.2: 8.7: 27.7: 4.8: 1. A heat-sensitive recording material of the present invention was produced in the same manner as in Example 4 except that the polymer latex was changed to 316 g (solid content mass 20%).

(Example 7)
In the preparation of the thermal recording layer coating liquid B of Example 1, the same as Example 1 except that 316 g of polymer latex (solid content: 20%) having a monomer composition of 100% ethyl acrylate was further added to the mixed component. The heat-sensitive recording material of the present invention was produced.

(Comparative Example 1)
A heat-sensitive recording material of a comparative example was prepared in the same manner as in Example 1 except that the intermediate layer coating solution B to which no polymer latex was added was used in the adjustment of the intermediate layer coating solution in Example 1.

(Image preservation test and evaluation method)
Each heat-sensitive recording material obtained above was printed with a thermal head (trade name: KGT, 260-MPH8, manufactured by Kyocera Corporation) at a head pressure of 10 kg / cm ² to prepare samples. After the prepared sample was stored in an oven at 60 ° C. for 5 hours, the density change at each printing density was confirmed with a Macbeth densitometer TD904 type (orthomatic filter, manufactured by Macbeth Co., Ltd.).
Table 1 shows ΔOD values (changes in image density) at the density having the largest change in image density in the 24-step printing. Here, the density change of the image represents the amount of change in the OD value before and after storage under the temperature condition, and the smaller the value, the less the density change of the image and the better the heat resistant storage stability of the image. The evaluation criteria are shown in Table 1 with ◯ being ΔOD = 0.2 or less, Δ being ΔOD = 0.2 to 0.4, and x being ΔOD = 0.4 or more.

  As is clear from the results in Table 1 above, it can be seen that, in all of the examples using polymer latex as compared with the comparative example, the density change of the image is small under any of the above storage conditions.

Claims (12)

A heat-sensitive recording material comprising at least a heat-sensitive recording layer formed of a heat-sensitive recording material and a binder and an intermediate layer containing a water-soluble binder on a support, and the intermediate layer is formed by adding a polymer latex. A heat-sensitive recording material characterized by that. The heat-sensitive recording material according to claim 1, wherein the binder of the heat-sensitive recording layer contains polyvinyl alcohol as a main component. The heat-sensitive recording material according to claim 1 or 2, wherein the heat-sensitive recording layer is further formed by adding a polymer latex. A heat-sensitive recording material comprising at least a heat-sensitive recording layer formed of a heat-sensitive recording material and a binder and an intermediate layer containing a water-soluble binder on a support. The heat-sensitive recording layer is formed by adding a polymer latex. A heat-sensitive recording material characterized by the above. The heat-sensitive recording material according to claim 4, wherein the binder of the heat-sensitive recording layer contains polyvinyl alcohol as a main component. The heat-sensitive recording material according to any one of claims 1 to 5, wherein the water-soluble binder contains gelatin as a main component. The thermal recording material has a protective layer on the thermal recording layer, and the intermediate layer is provided between the thermal recording layer and the protective layer. The heat-sensitive recording material described in 1. The heat-sensitive recording material according to claim 7, wherein the binder forming the protective layer contains polyvinyl alcohol. The heat-sensitive recording material according to claim 7 or 8, wherein the hardener used for the protective layer is 2,3-dihydroxy-1,4-dioxane. The heat-sensitive recording material according to claim 1, wherein the support is polyethylene terephthalate. In a method for producing a heat-sensitive recording material, the method comprises: applying a heat-sensitive recording material coating solution containing a heat-sensitive recording material and a binder on a support; and applying an intermediate layer coating solution containing a water-soluble binder. A method for producing a heat-sensitive recording material, wherein the intermediate layer coating solution contains a polymer latex. In a method for producing a heat-sensitive recording material, comprising a step of applying a heat-sensitive recording material coating solution containing a heat-sensitive recording material and a binder on a support, and a step of applying an intermediate layer coating solution containing a water-soluble binder. A method for producing a heat-sensitive recording material, wherein the heat-sensitive recording layer coating solution contains a polymer latex.