JP2006035594A - Thermal recording material and image recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording material which has inconspicuous density irregularities even when a platen roller with a partial difference in rubber hardness is used, in recording an image using a thermal head and improves the yield of equipment components, and an image recording method for recording an image in the thermal recording material. <P>SOLUTION: This thermal recording material has at least a thermal recording layer, a single or more than one intermediate layer formed on the same surface of a support. At least one intermediate layer shows not more than 3×10<SP>9</SP>storage elastic modulus E' at 120°C. Also, the image recording method for recording an image in the thermal recording material using the thermal head is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording material and an image recording method, and in particular, in a heat-sensitive recording material such as a medical recording medium, a good heat-sensitive recording material obtained by adjusting the image hue after recording, and the heat-sensitive recording material. The present invention relates to an image recording method for recording an image.

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 (film) is required to have a high transmission density, particularly when used as a medical recording medium, and a heat-sensitive recording material corresponding to this is proposed (for example, see Patent Documents 1 to 3). .) A heat-sensitive recording material produced by simultaneous multilayer coating has also been proposed (see, for example, Patent Document 4).

  Furthermore, as a technique for compensating the surface defects of the heat sensitive film, a surface sensitive film is introduced by introducing a specific surfactant (see, for example, Patent Document 5), defoaming the liquid and homogenizing the dispersion. A method for improving the level has been proposed (see, for example, Patent Document 6).

However, the unevenness due to the transport of the equipment is rattling of the member itself, and it is well known that the unevenness can be reduced by improving the accuracy of the feed parts, but there was almost no improvement knowledge from the media being transported .
Patent No. 318225 specification JP-A-8-90916 JP 2000-355164 A Japanese Patent Laid-Open No. 4-97886 JP 2002-283730 A JP 2002-248859 A

  The present invention relates to a heat-sensitive recording material in which density unevenness is not noticeable even when a platen roll having a partial difference in rubber hardness is used when an image is recorded using a thermal head, and the yield of equipment parts is improved. And an image recording method for recording an image on the thermosensitive recording material.

As a result of intensive studies in order to solve the above problems, the present inventors have defined the storage elastic modulus E ′ of at least one of the intermediate layers, so that regardless of the rubber hardness of the platen roll used for image recording by the thermal head. The present inventors have found that a heat-sensitive recording material in which density unevenness is inconspicuous can be obtained, thereby completing the present invention.
That is, the present invention
<1> A thermosensitive recording material having at least a thermosensitive recording layer and one or more intermediate layers on the same surface of the support, wherein at least one of the intermediate layers is at 120 ° C. A heat-sensitive recording material having a storage elastic modulus E ′ of 3 × 10 ⁹ or less.

<2> The heat-sensitive recording material according to <1>, wherein at least one of the intermediate layers contains gelatin.
<3> A protective layer is provided as the uppermost layer on the side having the thermosensitive recording layer, and at least one of the intermediate layers is provided between the thermosensitive recording layer and the protective layer. <1> to <3> The heat-sensitive recording material according to any one of 3.

<4> The heat-sensitive recording material according to <3>, wherein the protective layer contains 5% by mass or more of a dispersed water-insoluble material with respect to the total solid content in the protective layer. is there.
<5> The heat-sensitive recording material according to any one of <1> to <4>, wherein the support is made of a polymer film.

<6> The heat-sensitive recording material according to <5>, wherein the support is made of a polyethylene terephthalate film and has a thickness of 100 μm or more.
<7> An image recording method, wherein an image is recorded on the heat-sensitive recording material according to any one of <1> to <6> using a thermal head.

  According to the present invention, when an image is recorded using a thermal head, density unevenness is not noticeable even when a platen roll having a partial difference in rubber hardness is used, and the heat sensitivity that improves the yield of equipment parts. A recording material and an image recording method can be provided. By employing the heat-sensitive recording material and / or image recording method of the present invention, the yield can be further improved and the cost can be further reduced.

The heat-sensitive recording material of the present invention is a heat-sensitive recording material having at least a heat-sensitive recording layer and one or more intermediate layers on the same surface of a support, wherein at least one of the intermediate layers. Has a storage elastic modulus E ′ at 120 ° C. of 3 × 10 ⁹ or less.
The heat-sensitive recording material of the present invention preferably has a protective layer as the uppermost layer on the side having the heat-sensitive recording layer. On the other hand, a back layer may be provided on the side opposite to the surface having the heat-sensitive recording layer (back surface), and other optional layers may be provided on the color development surface or the back surface as necessary or necessary. Can do.
Here, the storage elastic modulus E ′ at 120 ° C. is a value obtained by the following measuring method.
An intermediate layer to be measured is peeled off from the heat-sensitive recording material, and a sample having a sample length of 30 mm and a sample width of 4 mm is cut out from the peeled intermediate layer, and an automatic dynamic viscoelasticity measuring apparatus (apparatus name: Rheobibron DDV-II). -EA, manufactured by Toyo Baldwin Co., Ltd.), the storage elastic modulus E ′ was measured at a frequency of 110 Hz and a heating rate of 2 ° C./min, and the measured value at 120 ° C. was determined as the storage elastic modulus at 120 ° C. E '.

<Intermediate layer>
The heat-sensitive recording material of the present invention has one or more intermediate layers in order to prevent mixing of each layer and to block gases (oxygen, ozone, etc.) harmful to image storage stability. The intermediate layer is a layer provided between two layers and does not include a heat-sensitive recording layer. Specifically, on the surface side of the support having the heat-sensitive recording layer, when two or more different heat-sensitive recording layers are provided between the support and the heat-sensitive recording layer, the heat-sensitive recording layer, and further a protective layer Can be appropriately provided between the heat-sensitive recording layer (in the case of having a plurality of heat-sensitive recording layers, the heat-sensitive recording layer farthest from the support) and the protective layer.

In the heat-sensitive recording material of the present invention, when the intermediate layer in the present invention is a single layer and has a protective layer, the intermediate layer (the storage elastic modulus E ′ at 120 ° C. is 3 × 10 ⁹ or less) The intermediate layer to be filled is preferably provided between the heat-sensitive recording layer (in the case of having a plurality of heat-sensitive recording layers, the heat-sensitive recording layer farthest from the support) and the protective layer.
Further, when the intermediate layer in the present invention is at least two layers and has a protective layer, at least one intermediate layer is a thermal recording layer (in the case of having a plurality of thermal recording layers, the thermal recording farthest from the support). And an intermediate layer provided between the heat-sensitive recording layer and the protective layer has a storage elastic modulus E ′ at 120 ° C. of 3 ×. More preferably, the condition of 10 ⁹ or less is satisfied, and it is more preferable that all the intermediate layers satisfy the condition that the storage elastic modulus E ′ at 120 ° C. is 3 × 10 ⁹ or less.

Further, as described above, the heat-sensitive recording material of the present invention requires that the storage elastic modulus E ′ at 120 ° C. of at least one intermediate layer is 3 × 10 ⁹ or less. The storage elastic modulus E ′ is preferably 2 × 10 ⁹ or less, and more preferably 1 × 10 ⁹ or less.
When the storage elastic modulus E ′ at 120 ° C. of all the intermediate layers exceeds 3 × 10 ⁹ , when a platen roll having a difference in rubber hardness is used when recording an image using a thermal head, the density is increased. Unevenness is conspicuous and the yield of equipment parts decreases. This is presumably because the contact area between the thermal recording material and the thermal head cannot be maintained at a constant amount.
On the other hand, the storage elastic modulus E ′ at 120 ° C. is preferably 0.1 × 10 ⁹ or more. When the storage elastic modulus E ′ at 120 ° C. is 0.1 × 10 ⁹ or more, the contact area with the thermal head is not increased excessively, the transportability is further improved, the transport torque is increased during printing, and sticking is performed. It is preferable that the printing failure such as the above does not occur.

As described above, examples of the method for setting the storage elastic modulus E ′ at 120 ° C. to 3 × 10 ⁹ or less include a method of containing a binder having a low glass transition point (low Tg binder). The glass transition point of the low Tg binder is preferably 120 ° C. or lower, and more preferably 100 ° C. or lower. The low Tg binder is preferably an acrylic, urethane, or synthetic rubber water-insoluble polymer binder; non-modified polyvinyl alcohol is preferred, and specifically, styrene-butadiene rubber latex, polyurethane latex, ethylene acrylate. Latex, alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate; and hydroxyethyl methacrylate, acrylic acid, and styrene. Of these, styrene-butadiene rubber latex, polyurethane latex, and ethylene acrylate latex are preferable.

The storage elastic modulus E ′ at 120 ° C. can also be adjusted by the amount of the low Tg binder added, and can also be adjusted by including a crosslinking agent and a hardener together with the low Tg binder.
Examples of the cross-linking 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, metal salts, and the like, and those that can adjust the pH of the coating solution to 6.0 to 7.5 as described above are preferable.

In the heat-sensitive recording material of the present invention, at least one of the intermediate layers preferably contains gelatin as a binder, and all the intermediate layers more preferably contain gelatin as a binder. By containing gelatin in the intermediate layer, gases (oxygen, ozone, etc.) harmful to mixing prevention and image storability of each layer are blocked.
In general, when gelatin is used alone as a binder, the storage elastic modulus E ′ at 120 ° C. exceeds 3 × 10 ⁹ . In order to make the storage elastic modulus E ′ at 120 ° C. of the intermediate layer containing gelatin 3 × 10 ⁹ or less, it is necessary to further contain the low Tg binder.

  Gelatin has fluidity at high temperatures, but it loses fluidity at low temperatures (for example, 35 ° C or less) and has excellent gelling properties (setability), so multiple layers are formed on the support. In order to achieve this, each coating solution is applied and dried, and if an intermediate layer containing gelatin is provided, multiple layers can be applied at once by an extrusion die method, etc. Even in the drying method, the adjacent two layers are effectively prevented from being mixed with each other, the surface shape of the resulting heat-sensitive recording material is improved, and a heat-sensitive recording material capable of forming a high-quality image is obtained. Therefore, it is suitable for a recording material for medical diagnosis that needs to form a clear image in detail. Further, even when dried at a high wind speed, the surface condition is not deteriorated, so that the production efficiency is improved.

  The intermediate layer in the present invention may further contain another binder as long as the effects of the present invention are not impaired. The other binder is not particularly limited, and a water-soluble binder is preferable. Specifically, vinyl acetate-acrylamide copolymer, silicon-modified polyvinyl alcohol, starch, modified starch, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose, gum arabic, casein, styrene-maleic acid copolymer hydrolyzate, styrene-malein Examples thereof include water-soluble polymers such as acid copolymer half ester hydrolysates, isobutylene-maleic anhydride copolymer hydrolysates, polyacrylamide derivatives, polyvinyl pyrrolidone, polystyrene sulfonate soda, and sodium alginate.

The coating amount of the intermediate layer in the present invention is preferably 0.2~5.0g / m ^2, more preferably from 0.5~3.0g / m ^2, 0.7~2.0g further preferably / m ^2. When the coating amount of the intermediate layer containing gelatin is 0.2 to 5.0 g / m ^2, it is excellent in balance from the viewpoint of thermal sensitivity and prevention of layer mixing, and is preferable.

In addition, a lubricant may be added to the intermediate layer, and examples of the lubricant include zinc stearate, calcium stearate, paraffin wax, polyethylene wax, silicone emulsion, and the like. Change.
Further, a surfactant may be added to the intermediate layer, and the surfactant includes a sulfosuccinic acid-based alkali metal salt and a fluorine-containing compound so that the intermediate layer can be uniformly formed on the thermosensitive recording layer. Surfactants and the like are preferably mentioned, and specific examples include sodium salts such as di- (2-ethylhexyl) sulfosuccinic acid and di- (n-hexyl) sulfosuccinic acid, and ammonium salts.

A coating solution for forming an intermediate layer (intermediate layer coating solution) is obtained by mixing the components described above. Furthermore, you may add a viscosity modifier, a mold release agent, 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. As the known coating method, for example, a method using a bar coater, an air knife coater, a blade coater, a curtain coater, etc., as described above, an intermediate layer coating solution is extruded and overlapped with other layers adjacent at once by a die method or the like. The method of apply | coating is mentioned.

  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.

<Thermal recording layer>
The heat-sensitive recording layer in the heat-sensitive recording material of the present invention contains at least a color forming component and a binder, and may further contain other components as necessary. The thermosensitive recording layer may be provided in one layer or in two or more layers.

(Coloring component)
As the color-forming component, any composition can be used as long as it has excellent transparency when not processed and has a property of rapidly coloring when heated. Examples of such a coloring component include a so-called two-component coloring component that contains a substantially colorless coloring component A and a substantially colorless coloring component B that reacts with the coloring component and develops color. 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. The following (a) to (m) are mentioned as the combination of the two components constituting the two-component thermosensitive recording layer.

(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, as the heat-sensitive recording layer in the present invention, as the color forming component, (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) It is preferable to use any combination of an organic metal salt and a reducing agent, and it is particularly preferable to use the combination (a) or (b).

  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 particle diameter 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 diameter (hereinafter, sometimes simply referred to as “average particle diameter”), and the same applies hereinafter.

Next, (a), (b), and (c), which are preferable combinations of coloring components, 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 when contacted 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, 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. 3491111, 3491112, 3491116, 3509174, and the like. .
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 U.S. 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 compounds 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 the diazo dye produced by the reaction of the photodegradable diazo compound and the coupler. Therefore, by changing the chemical structure of the photodegradable diazo compound or coupler compound, the color hue can be easily changed, and depending on the combination, any color hue can be obtained.

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, but are not limited to, compounds represented by the following structural formula. 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 recently, and each diazonium salt is 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 above-described photodegradable diazo compound include, for example, 2-hydroxy-3-naphthoic acid anilide, resorcin, and JP-A No. 62-146678. The thing that is.

When using a combination of a photodegradable diazo compound and a coupler in the heat-sensitive recording layer, these coupling reactions are carried out in a basic atmosphere, from the viewpoint that the reaction can be further promoted, and sensitization. It is preferable to add a basic substance as an agent.
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 Specifically, the organometallic salt is 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 these, aromatic organic reducing agents such as polyphenols, sulfonamidophenols, and naphthols are particularly preferred.

  In order to ensure sufficient transparency of the heat-sensitive recording material, (a) a combination of an electron-donating dye precursor and an electron-accepting compound, or (b) a combination of a photodegradable diazo compound and a coupler is used in the heat-sensitive recording layer. It is preferable to use it. 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.

(Micro capsule)
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 with an interfacial polymerization method in the aqueous phase.

  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.

As the polyisocyanate compound, a compound having a trifunctional or higher isocyanate group is preferable, but a compound having a trifunctional or higher isocyanate group may be used in combination with a bifunctional isocyanate compound. An isocyanate compound may be used alone.
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 compounds in which a high molecular weight compound such as polyether having active hydrogen such as polyethylene oxide is introduced into an adduct with bifunctional isocyanate such as range isocyanate, formalin condensate of benzene isocyanate, and the like.
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.

  In addition, a metal-containing dye, a charge control agent such as nigrosine, or any other additive 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 preferably 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, cresyl phenyl phosphate; dibutyl phthalate, 2-ethylhexyl phthalate, ethyl phthalate, Phthalic acid esters such as octyl phthalate and butyl benzyl phthalate; Dioctyl tetrahydrophthalate; Ethyl benzoate, propyl benzoate, butyl benzoate, isopentyl benzoate, benzoic acid esters such as benzyl benzoate; 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 oils in combination with other oils or 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.
In order to realize a high concentration with a small coating amount, only a low boiling point solvent can be used as the capsule solvent as described in JP-A-4-101858. As the low boiling point solvent in this case, the same low boiling point solvents that can be used in combination as described above can be preferably used.

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 can be 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 a stirring means such as a homogenizer. As the water-soluble polymer, , 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), acetylene glycol and the like.

  Emulsification / dispersion is a means used for normal fine particle emulsification such as a high-speed stirrer, ultrasonic dispersion device, etc., for example, a homogenizer, a manton, and the oil phase containing the above components and the 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 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 and dispersed 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 preferable, and polyvinyl alcohol is 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.
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 weight, and 0.5 to 10 parts by weight with respect to 1 part by weight of the photodegradable diazo compound. Is more preferable.

(Coating solution for thermal recording layer)
The thermal recording layer coating liquid can be prepared, for example, by mixing the microcapsule liquid prepared as described above and an emulsified dispersion. 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. It is also a preferred embodiment to prepare a thermal recording layer coating solution by adding and mixing a binder separately from these protective colloids.

As the binder contained in the heat-sensitive recording layer, hydroxyethyl cellulose, hydroxypropyl cellulose, epichlorohydrin-modified polyamide, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic salicylic acid copolymer, Examples thereof include polyacrylic acid, polyacrylic amide, methylol-modified polyacrylamide, starch derivatives, casein, and gelatin.
Further, for the purpose of imparting water resistance to these binders, a water resistance improver may be added, or an emulsion of a hydrophobic polymer, specifically, an acrylic resin emulsion, a styrene-butadiene latex or the like may be added.

  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, hydroxyethyl cellulose, starches, gelatin, polyvinyl alcohol, polyacrylamide, polystyrene or a copolymer thereof, polyester or The copolymer, polyethylene or copolymer thereof, epoxy resin, acrylate resin or copolymer thereof, methacrylate resin or copolymer thereof, polyurethane resin, polyamide resin, polyvinyl butyral resin, styrene-butadiene latex, etc. It can also be used.

(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 the above-mentioned heat-sensitive recording layer, and has a characteristic that a transmission density (D _T-max ) of 3.0 can be obtained with a heat energy amount in the range of 70 to 130 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, it is preferable that the solid coating amount after application and drying of the entire thermosensitive recording layer is 1 to 25 g / m ² .

<Protective layer>
The heat-sensitive recording material of the present invention preferably has a protective layer as the uppermost layer on the side having the heat-sensitive recording layer. The protective layer is usually formed by applying a coating solution prepared as a protective layer coating solution. The protective layer coating solution covers a wide recording energy region and has good head matching properties. It is preferable to contain polyvinyl alcohol as a water-soluble binder. The heat-sensitive recording material of the present invention preferably contains 5% by mass or more of a dispersed water-insoluble material with respect to the total solid content in the protective layer. The content of the dispersed water-insoluble material with respect to the total solid content in the protective layer is more preferably 6% by mass or more, and further preferably 7% by mass or more.

  Examples of the dispersed water-insoluble material include dispersed pigments added to prevent head gas adhesion, sticking / fusing, and abnormal noise; dispersed or emulsified and dispersed lubricants, release agents Examples thereof include a mold agent, a sliding agent, and a dispersed matting agent added for the purpose of adjusting the surface gloss.

(Pigment)
As the pigment used in the protective layer, either an organic pigment or an inorganic pigment can be used.
The pigment used in the protective layer has an average particle diameter, specifically, a 50% volume average particle diameter measured by a laser diffraction method (measured by a laser diffraction particle size distribution measuring apparatus “LA700” manufactured by Horiba, Ltd.). In addition, the average particle diameter of pigment particles corresponding to 50% volume in the pigment, which is hereinafter simply referred to as “average particle diameter”) is preferably 0.10 to 5.0 μm. In particular, when performing thermal recording with a thermal head, the average particle size may be 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 preferred. When the average particle size is in the range of 0.10 to 5.0 μm, the effect of reducing friction with respect to the thermal head is large, and as a result, the thermal head and the protective layer of the heat-sensitive recording material adhere to each other during printing. The so-called sticking phenomenon can be effectively prevented.

  The type of pigment that can be used in the protective layer is not particularly limited, and can be appropriately selected from known organic and inorganic pigments. Among them, calcium carbonate, titanium oxide, Inorganic pigments such as kaolin, aluminum hydroxide, amorphous silica, and zinc oxide, and organic pigments such as urea formalin resin and epoxy resin are preferred. 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 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 pigment may be, for example, sodium metametaphosphate, partially or fully saponified polyvinyl alcohol, modified polyvinyl alcohol, polyacrylic acid copolymer, various surfactants, and the like, preferably partially or fully saponified polyvinyl. Used in the presence of alcohol, itaconic acid-modified polyvinyl alcohol, terminal alkyl-modified polyvinyl alcohol, and polyacrylic acid copolymer ammonium salt, dispersed to the average particle size with a known disperser such as a dissolver, sand mill, or ball mill. It is preferable. 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, mold release agent and slip agent)
Lubricants, mold release agents and slip agents (hereinafter sometimes referred to as “lubricants etc.”) used for the protective layer are usually for reducing printing torque and making thermal recording with a thermal head suitable. A form containing a lubricant which is liquid at room temperature or has a melting point of less than 40 ° C. and a lubricant having a melting point of 40 ° C. or more is preferable.
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 preferable.

In the above formula [001], R represents an alkyl group, and the alkyl group may be substituted with a substituent. n represents 1 or 2.
The above-mentioned lubricants that are liquid at normal temperature and lubricants having a melting point of 40 ° C. or less may be used alone or in combination of two or more.

  As the lubricant having a melting point of 40 ° C. or higher, a melting point of 160 ° C. or lower, preferably 140 ° C. or lower is desirable, stearic acid amide (melting point 100 ° C.), methylol stearic acid amide (101 ° C.), Polyethylene wax (melting point 110 ° C. or lower), paraffin wax with melting point 50-90 ° C., glycerin tri-12-hydroxystearate (melting point 88 ° C.), oleic acid amide (melting point 73 ° C.), zinc oleate (melting point 75 ° C.), Lauric 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.), palmi Magnesium phosphate (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 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. The average particle diameter of the dispersed lubricant or the emulsified lubricant is preferably 0.1 to 5.0 μm, 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.

(Matting agent)
As the matting agent contained in the protective layer, for example, 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, calcium carbonate, titanium oxide, kaolin, smectite clay, aluminum hydroxide, Examples thereof include fine particles of inorganic substances such as silica and zinc oxide. 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.

  The protective layer preferably has a surface hardness of 40 g or more as defined in JIS K6718 on the surface of the protective layer in order to prevent film peeling at the time of cutting and damage during handling. In the present invention, as a method for testing the 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 moving 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.)
As the binder used in the protective layer, polyvinyl alcohol is preferably used as the binder from the viewpoint of improving transparency, and modified PVA such as carboxy-modified polyvinyl alcohol and silica-modified polyvinyl alcohol can also be used.

The protective layer 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.
In the present invention, 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.
These 2,3-dihydroxy-1,4-dioxanes are preferably used in an amount of 0.1 to 200% by weight, more preferably 1 to 100% by weight, still more preferably 10 to 50% by weight based on the binder of the layer. %, Particularly preferably 20 to 40% by mass.

  In the present invention, in order to form a protective layer uniformly on the heat-sensitive recording layer or the intermediate layer, it is preferable to add a surfactant to the protective layer forming coating solution. 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, more preferably 1 to 4 g / m ^2.

<Support>
The support used in the heat-sensitive recording material of the present invention preferably has a heat shrinkage rate of less than 1% in the vertical and horizontal directions in order to effectively prevent deformation such as curling, and is 0.5% or less. It is more preferable that 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.

  As the support in the present invention, a support having a low heat shrinkage rate is preferable as described above, and can be appropriately selected from known supports. Among them, a support made of a polymer film is preferable, Examples of the transparent support include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, cellulose triacetate films, and synthetic polymer films such as polyolefin films such as polypropylene and polyethylene. Particularly, polyethylene terephthalate. A support of (PET) is preferred. These can be used alone or in combination. The thickness of the synthetic polymer film is preferably 100 μm or more, more preferably 120 μm or more, and further preferably 150 μm or more. It is preferable that the thickness of the synthetic polymer film is 100 μm or more because it is easy to insert and remove when observing the Schaukasten particularly for medical diagnosis. The synthetic polymer film preferably has a thickness of 250 μm or less. When the thickness of the synthetic polymer film is 250 μm or less, the mass of the film itself can be light.

  The synthetic polymer film is preferably transparent, and may be further 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. As the support in the present invention, a polyethylene terephthalate film having a thickness of 100 μm or more is particularly preferable.

  On the other hand, in the case of transmission observation on the Schaukasten, illusion may occur due to the Schaukasten light transmitted through the transparent non-image portion, resulting in a difficult-to-see image. In such a case, in order to avoid the dazzling, 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 or intermediate layer of the support in order to improve the curl balance. A layer is preferably provided. The coating amount of the water-soluble binder on the back surface is preferably 0.5 to 5 g / m ² , and most preferably 1.5 to 4 g / m ² from the viewpoint of further improving the curl balance.
Among the water-soluble binders used in the back layer in the present invention, gelatins are most preferable. Examples of the gelatin include alkali-treated gelatin having a low isoelectric point, derivative gelatin reacted with an amino group (for example, phthalated). Gelatin etc.) are preferred.
The said water-soluble binder used for the back layer in this invention may be used individually by 1 type, and may use 2 or more types 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.

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 latex coating amount should be less than the gelatin coating amount on the back surface. 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 gelatin 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 gelatin filler, and has a function of suppressing thermal expansion and contraction of the gelatin film and improving dimensional stability. On the other hand, when the coating ratio of latex to gelatin is increased, the gelatin film is plasticized, so that the adhesion resistance is deteriorated. 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. May not be suitable. In order to avoid this, the latex coating amount is preferably not more than the gelatin coating amount on the back surface, and particularly preferably not more than 50% by mass of the gelatin 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 in 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 acetyl-fluorinated 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 combined hydrolysates, polyacrylamide derivatives, polyvinyl pyrrolidone, sodium polystyrene sulfonate, sodium alginate, and styrene-butadiene rubber latex, Ronitoriru - butadiene rubber latex, methyl acrylate - butadiene rubber latex, water-insoluble polymers such as vinyl acetate emulsion.

  As another component used in the back layer in the present invention, 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.

The back layer may contain a matting agent for the purpose of improving transportability and preventing light reflection.
As the matting agent used in the back layer in the present invention, for example, 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, calcium carbonate, titanium oxide, kaolin, smectite clay, aluminum hydroxide, Examples thereof include fine particles of inorganic substances such as silica and zinc oxide.
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.

Further, it is preferable to add a fluorosurfactant as a coating aid or antistatic agent to the back layer which is the outermost layer on the side opposite to the thermosensitive recording layer as viewed from the support.
Examples of the fluorosurfactant include potassium perfluorooctane sulfonate, N-propyl-N-oxyethylene perfluorooctanesulfonamidobutyl sulfonate, trimethyl (propyleneaminosulfonylperfluorooctane) ammonium chloride, N- Examples thereof include sodium propyl-N-oxyethylene perfluorooctane sulfonate.

  A thickener for adjusting 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 thickener and ultraviolet absorber can be appropriately selected from known ones.

From the viewpoint of improving the hue of the heat-sensitive recording material, it is preferably formed by adding a dye to the back layer. As the dye, a cyan dye or a blue dye can be used, and a cyan dye is particularly suitable for preparing a hue according to the intended use.
Examples of the cyan dye include C.I. I. Pigment Blue 60, C.I. I. Pigment Blue 64, C.I. I. Pigment Blue 15: 6 and the like.

  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 component 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 by an extrusion die method or the like.

  On the side of the support that does not have a heat-sensitive recording layer, in addition to the back layer, the behavior before curl reaches equilibrium in a short time after printing can be adjusted. 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.

As the polyvinyl alcohol in the PVA layer, for example, fully saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silica-modified polyvinyl alcohol and the like are suitable.
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 sodium sulfosuccinate, polyalkylene glycol, and the like.

  Similar 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.

<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 configured to contain 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 a 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 relative to the dry mass of the undercoat layer.

The heat-sensitive recording material of the present invention can be produced, for example, as follows, but is not limited thereto. On one side of the support in the present invention, a thermal recording layer forming coating liquid (hereinafter referred to as “thermal recording layer coating liquid”) is applied to form a thermal recording layer, and the thermal recording layer is formed on the thermal recording layer. Apply the intermediate layer coating solution and the protective layer coating solution, and apply the back layer coating solution on the opposite side to the back layer consisting of a single layer or multiple layers as described above. Further, if necessary, another layer is formed on the one side and the other side. In addition, as a specific coating method on the one side, the same coating method as that for coating and forming the back layer can be applied.
Here, the thermosensitive recording layer, the intermediate layer and the protective layer may be formed at the same time. In this case, the thermosensitive recording layer coating solution, the intermediate layer and the protective layer coating solution are simultaneously coated on the support. Can be formed.

The image recording method of the present invention is a method for suitably recording an image on the above-described heat-sensitive recording material of the present invention using 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 thermal recording material is 90% or more. Those provided with are preferably used. Further, the head protective layer may be two or more layers. In this case, the carbon ratio of the uppermost layer is preferably 90% or more.
According to the image recording method of the present invention, even when a platen roll having a difference in rubber hardness is used, density unevenness is not conspicuous, and the yield of equipment parts is improved, so that the yield is further improved and the cost is further reduced. Is possible.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. In the examples, “parts” and “%” represent “parts by mass” and “% by mass” unless otherwise specified.

[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 1 kg of the emulsion is represented by 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 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 = 0.29995 at the 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.

(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 K.K.) 2g, 245g of 18% pigment dispersion obtained above, 10g of 18% glycerin tri-12-hydroxystearate dispersion obtained above, 20.5% stearic acid Zinc dispersion (trade name “Hydrin F115” manufactured by Chukyo Yushi Co., Ltd.) 21 g, 18% stearic acid dispersion ( 31g, trade name “Cerosol 920” manufactured by Chukyo Yushi Co., Ltd., 35% silicone oil aqueous dispersion (trade name “BY22-840” manufactured by Toray Dow Corning Co., Ltd.) 41.5g, 5% styrene maleic acid 110 g of copolymer aqueous ammonium salt 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, 30 g of 2% acetic acid aqueous solution and 22 g of 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 thermosensitive recording layer coating liquid (A) 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 content 22%) 710 g, 7.2 g of 50% aqueous solution of the compound represented by the structural formula [002], and colloidal silica (trade name “Snowtex O” manufactured by Nissan Chemical Co., Ltd.) 25.5 g Were mixed and adjusted to a concentration of 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 content 22%) 725 g, a 50% aqueous solution of the compound represented by the structural formula [002] 6.5 g, and colloidal silica (trade name “Snowtex O” manufactured by Nissan Chemical Co., Ltd.) 23.5 g Were mixed and adjusted to a concentration of 21.5% with water to prepare the desired thermal recording layer coating solution (B).

(Preparation of intermediate layer coating solution (C1))
After adding 12538 g of water to 1000 g of lime-processed gelatin, 5% solution of di-2-ethylhexylsulfosuccinate Na salt (“Nissan Rapizol B90” manufactured by NOF Corporation) (water / methanol = 1 / 13.7 g of 1 volume mixed solvent), SBR latex (trade name: SN-307, manufactured by Sumika ABS Latex Co., Ltd., Tg: -27 ° C.) 2083 g, 3.5% 1,2-benzisothiazoline- 25 g of 3-one aqueous solution and 648 g of 3.0% sodium poly (p-vinylbenzenesulfonate) (molecular weight: about 400,000) were added to prepare a target intermediate layer coating solution (C1).

(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. The coating liquid (C1) and the protective layer coating liquid were sequentially slid so that the coating amounts were 41.3 ml / min, 22.5 ml / min, 12.4 ml / min, and 27.5 ml / min, respectively. Four layers are simultaneously applied by the bead method and dried to obtain the transparent heat-sensitive recording material of the present invention having the heat-sensitive recording layer (A), the heat-sensitive recording layer (B), the intermediate layer (C1) and the protective layer on the support. It was.

  In addition, the coating liquid of each layer was adjusted to the temperature range of 33 degreeC-37 degreeC. The drying conditions are as follows. The coating speed was 160 m / min, the distance between the coating die tip and the support was 0.10 to 0.30 mm, and the pressure in the decompression chamber was set 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.

[Example 2]
A thermosensitive recording material of the present invention was produced in the same manner as in Example 1 except that the intermediate layer coating solution (C1) was changed to the following intermediate layer coating solution (C2).
(Preparation of intermediate layer coating solution (C2))
After dissolving 10076 g of water in 1000 g of lime-processed gelatin, a 5% solution of di-2-ethylhexyl sulfosuccinic acid Na salt (“Nissan Rapizol B90” manufactured by NOF Corporation) (water / methanol = 1 / 13.7 g of 1 volume mixed solvent), polyurethane latex (trade name: AP-40, manufactured by DIC Corporation, Tg: 49 ° C.) 4545 g, 3.5% 1,2-benzisothiazolin-3-one aqueous solution 25 g , 648 g of 3.0% poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000) was added to prepare the intended intermediate layer coating solution (C2).

[Example 3]
A thermosensitive recording material of the present invention was produced in the same manner as in Example 1 except that the intermediate layer coating solution (C1) was changed to the following intermediate layer coating solution (C3).
(Preparation of intermediate layer coating solution (C3))
After 9621 g of water was added to 1000 g of lime-processed gelatin and dissolved, di-2-ethylhexyl sulfosuccinate Na salt (“Nissan Rapizol B90” manufactured by Nippon Oil & Fats Co., Ltd.) 5% solution (water / methanol = 1 / 13.7 g of 1 volume mixed solvent), polyurethane latex (trade name: AP-70, manufactured by DIC Corporation, Tg: −7 ° C.) 5000 g, 3.5% 1,2-benzisothiazolin-3-one aqueous solution 25 g of 648 g of 3.0% poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000) was added to prepare a target intermediate layer coating solution (C3).

[Example 4]
A thermosensitive recording material of the present invention was produced in the same manner as in Example 1, except that the intermediate layer coating solution (C1) was changed to the following intermediate layer coating solution (C4).
(Preparation of intermediate layer coating solution (C4))
After 9621 g of water was added to 1000 g of lime-processed gelatin and dissolved, di-2-ethylhexyl sulfosuccinate Na salt (“Nissan Rapizol B90” manufactured by Nippon Oil & Fats Co., Ltd.) 5% solution (water / methanol = 1 / 13.7 g of 1 volume mixed solvent), 5000 g of polyurethane latex (trade name: HW-350, manufactured by DIC Corporation, Tg: 57 ° C.), 25 g of 3.5% 1,2-benzisothiazolin-3-one aqueous solution , 648 g of 3.0% poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000) was added to prepare the intended intermediate layer coating solution (C4).

[Example 5]
A thermosensitive recording material of the present invention was produced in the same manner as in Example 1 except that the intermediate layer coating solution (C1) was changed to the following intermediate layer coating solution (C5).
(Preparation of intermediate layer coating solution (C5))
After 9621 g of water was added to 1000 g of lime-processed gelatin and dissolved, di-2-ethylhexyl sulfosuccinate Na salt (“Nissan Rapizol B90” manufactured by Nippon Oil & Fats Co., Ltd.) 5% solution (water / methanol = 1 / 13.7 g of 1 volume mixed solvent), polyethyl acrylate latex (EA ratio: 100%, designed Tg: −20 ° C., solid content concentration adjusted to 20%) 5000 g, 3.5% 1,2-benzisothiazoline— 25 g of 3-one aqueous solution and 648 g of 3.0% poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000) were added to prepare a target intermediate layer coating solution (C5).

[Example 6]
A thermosensitive recording material of the present invention was produced in the same manner as in Example 1 except that the intermediate layer coating solution (C1) was changed to the following intermediate layer coating solution (C6).
(Preparation of intermediate layer coating solution (C6))
After 12121 g of water was added to 1000 g of lime-processed gelatin and dissolved, a 5% solution of di-2-ethylhexyl sulfosuccinic acid Na salt (“Nissan Rapizol B90” manufactured by NOF Corporation) (water / methanol = 1 / 13.7 g of 1 volume mixed solvent), polyethyl acrylate latex (EA ratio: 100%, designed Tg: −20 ° C., adjusted to 20% solid content) 2500 g, 3.5% 1,2-benzisothiazoline— 25 g of 3-one aqueous solution and 648 g of 3.0% poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000) were added to prepare a target intermediate layer coating solution (C6).

[Comparative Example 1]
In Example 1, the intermediate layer coating solution (C1) was changed to the following intermediate layer coating solution (C7), and the intermediate layer coating solution (C7) was applied to the surface opposite to the back layer of the support. A comparative heat-sensitive recording material was produced in the same manner as in Example 1 except that the coating amount was changed to 24.7 ml / min.
(Preparation of intermediate layer coating solution (C7))
After 14621 g of water was added to 1000 g of lime-processed gelatin and dissolved, a 5% solution of di-2-ethylhexylsulfosuccinic acid Na salt (“Nissan Rapizol B90” manufactured by NOF Corporation) (water / methanol = 1 / 1 volume mixed solvent) 13.7 g, 3.5% 1,2-benzisothiazolin-3-one aqueous solution 25 g, 3.0% poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000) 648 g of was added, and the target intermediate layer coating solution (C7) was prepared.

[Comparative Example 2]
A thermosensitive recording material of the present invention was produced in the same manner as in Example 1, except that the intermediate layer coating solution (C1) was changed to the following intermediate layer coating solution (C8).
(Preparation of intermediate layer coating solution (C8))
After 12121 g of water was added to 1000 g of lime-processed gelatin and dissolved, a 5% solution of di-2-ethylhexyl sulfosuccinic acid Na salt (“Nissan Rapizol B90” manufactured by NOF Corporation) (water / methanol = 1 / 13.7 g of 1 volume mixed solvent), polystyrene-acrylic acid latex (PS (polystyrene): BA (butyl acrylate): MMA (methyl methacrylate) (molar ratio)) = 57:28:15, Tg: 50 ° C., solid content (Concentrated 20% adjusted product) 2500 g, 3.5% 1,2-benzisothiazolin-3-one aqueous solution 25 g, 3.0% poly (sodium p-vinylbenzenesulfonate) (molecular weight: about 400,000) 648 g Was added to prepare a target intermediate layer coating solution (C8).

<Evaluation>
The following evaluation was performed on the above heat-sensitive recording materials.
(Measurement of deformation under heating load)
An intermediate layer was peeled off from each of the obtained heat-sensitive recording materials, and a sample having a sample length of 30 mm and a sample width of 4 mm was cut out from the peeled intermediate layer, and an automatic dynamic viscoelasticity measuring device (device name: Rheobibron DDV-II). -EA, manufactured by Toyo Baldwin Co., Ltd.), the storage elastic modulus E ′ was measured at a frequency of 110 Hz and a heating rate of 2 ° C./min, and the measured value at 120 ° C. was determined as the storage elastic modulus at 120 ° C. E '. The results are shown in Table 1.

(Evaluation of stamped screen)
First, a platen roll having a normal part hardness of 64 degrees and a joint part of 66 degrees (having a rubber hardness difference of 2 degrees) is attached to “Imager Drypix 1000” manufactured by Fuji Photo Film Co., Ltd.
Next, using “Imager Drypix 1000” equipped with a platen roll having a rubber hardness difference of 2 degrees, the printing energy is set to each obtained thermal recording material so as to have a density of OD1.2. Was printed. The heat-sensitive recording material on which the obtained image was printed was visually evaluated on a medical Schaukasten according to the following criteria. The results are shown in Table 1. The rubber hardness was measured by the method defined by JIS K6301 (Scale A, type JA) manufactured by Kobunshi Keiki Co., Ltd.

<Evaluation criteria>
A: The density unevenness is hardly visible.
○: Thin density unevenness is visible.
Δ: Density unevenness is visible, but there is no practical problem.
X: Density unevenness is seen even in a practical image, and is a level that causes a practical problem.

From Table 1, the heat-sensitive recording materials of Examples 1 to 6 having an intermediate layer having a storage elastic modulus E ′ at 120 ° C. of 3 × 10 ⁹ or less are image forming apparatuses equipped with platen rolls having different rubber hardness depending on the part. It can be seen that even when an image is printed using this, the stamp screen shape is good.

Claims (7)

A thermosensitive recording material having at least a thermosensitive recording layer and one or more intermediate layers on the same surface of the support,
At least one of the intermediate layers has a storage elastic modulus E ′ at 120 ° C. of 3 × 10 ⁹ or less.   The heat-sensitive recording material according to claim 1, wherein at least one of the intermediate layers contains gelatin.   2. The protective layer is provided as the uppermost layer on the side having the thermosensitive recording layer, and at least one of the intermediate layers is provided between the thermosensitive recording layer and the protective layer. The heat-sensitive recording material according to any one of 1 to 3.   The heat-sensitive recording material according to claim 3, wherein the protective layer contains 5% by mass or more of a dispersed water-insoluble material with respect to the total solid content in the protective layer.   The thermosensitive recording material according to claim 1, wherein the support is made of a polymer film.   6. The heat-sensitive recording material according to claim 5, wherein the support is made of a polyethylene terephthalate film and has a thickness of 100 μm or more.   An image recording method, wherein an image is recorded on the heat-sensitive recording material according to claim 1 using a thermal head.