JP2011183799A - Thermosensitive recording material and image recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosensitive recording material having excellent light resistance, water resistance and high whiteness and to provide an image recording method using the thermosensitive recording material. <P>SOLUTION: The thermosensitive recording material 1 includes a support 2 and further at least one undercoat layer 3, a thermosensitive coloring layer 4 which comes into contact with the undercoat layer and includes a leuco dye and a developer and at least one protective layer including a water-soluble resin and a fluorescent whitening agent in this order on the support. The undercoat layer which comes into contact with the thermosensitive coloring layer includes the water-soluble resin and has air permeance of 150 mL/minute or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a heat-sensitive recording material having a protective layer containing a fluorescent brightening agent on a heat-sensitive coloring layer, and an image recording method using the heat-sensitive recording material.

  Thermal recording materials are POS field for fresh foods, lunch boxes and prepared foods; Copy field for books and documents; Communication field such as facsimiles; Ticketing field for ticket machines, receipts and receipts; Tags for baggage in the aircraft industry As the application spreads, there is an increasing demand for improved whiteness and light resistance.

As such a heat-sensitive recording material, conventionally, a material that improves the whiteness of the appearance by arranging a protective layer containing a fluorescent brightening agent on the heat-sensitive coloring layer is known.
For example, a heat-sensitive recording material containing 0.1 to 10 parts by weight of a fluorescent brightening agent in the protective layer has been proposed (see Patent Document 1). Further, a heat-sensitive recording material containing a naphthalimide-based cationic fluorescent dye in the protective layer has been proposed (see Patent Document 2).
However, in these proposals, since the content of the fluorescent brightening agent in the protective layer is small, there is a problem that the light resistance is not sufficient although the effect of improving the whiteness of the appearance is recognized.
It is known that the light resistance is improved when a fluorescent brightening agent is contained. For example, a dry weight of 0.1 to 0.5 g of a stilbene fluorescent dye is contained in a protective layer disposed on a thermosensitive coloring layer. A heat-sensitive recording material that is contained so as to be / m ² has been proposed (see Patent Document 3).
According to this proposal, although it is recognized that the light resistance is improved to a certain degree, sufficient light resistance has not been obtained. In other words, it has been pointed out that when the amount of fluorescent whitening agent (fluorescent dye) attached is increased in order to obtain light resistance, the background becomes yellow. In this proposed configuration, the amount of fluorescent whitening agent attached is increased. There is a problem that it is difficult to increase the value further.
Further, as with this proposal, for the purpose of improving the light resistance, a method of adding a fluorescent whitening agent to the protective layer has been proposed (see Patent Document 4), but similarly, sufficient light resistance cannot be obtained. There's a problem.

On the other hand, in a heat-sensitive recording material using a near-infrared absorbing material as a color former, it has also been proposed to obtain light resistance by including a fluorescent whitening agent in the protective layer (see Patent Document 5). Here, as an example, in a thermosensitive recording material in which a protective layer is formed using a protective layer dispersion prepared by adding 40 parts by mass of an aqueous solution of 50% fluorescent dye to 100 parts by mass of the dispersion, the required light resistance is required. It has been proposed that the characteristics can be obtained.
However, with the amount of the fluorescent whitening agent attached in this proposed example, the light fastness of the image area is improved, but as described in Patent Document 3, the background is yellowed and the background whiteness is satisfactory. There is a problem that cannot be obtained.
In addition, another method in which a fluorescent whitening agent is contained in a protective layer in a heat-sensitive recording material using a near-infrared absorbing material as a color former has been proposed (see Patent Document 6). However, this proposal also has a problem that the whiteness of the appearance is the main effect, and the light resistance has not been improved.
Therefore, in these proposals, there is a problem that it is difficult to achieve both improvement of light resistance and background whiteness.
In addition, if the desired amount of fluorescent whitening agent is to be obtained by reducing the amount of fluorescent whitening agent and increasing the amount of protective layer deposited, it is necessary to significantly increase the amount of protective layer deposited. There is a problem that the color developability of the thermosensitive coloring layer is reduced.

For this reason, there has been proposed a method for reducing the amount of fluorescent whitening agent used in combination with an ultraviolet absorber and a fluorescent whitening agent, and achieving both light resistance and background whiteness (for example, (See Patent Documents 7 to 11).
However, ultraviolet absorbers may cause deterioration in storage stability such as heat resistance and color developability when placed in a heat-sensitive color developing layer, and problems such as sticking and head-casing adhesion may deteriorate when placed in a protective layer. is there.
Although the reason for the deterioration due to light is not clear, when exposed to light such as sunlight in a state where oxygen has entered the thermosensitive coloring layer, the leuco dye contained in the thermosensitive coloring layer becomes sunlight. It has been experimentally confirmed that deterioration occurs due to the reaction between ultraviolet rays and oxygen contained in the heat-sensitive recording material, causing discoloration of the background of the heat-sensitive recording material and fading of the image.
Therefore, in order to dramatically improve the light resistance, not only the blocking of ultraviolet rays but also the blocking of oxygen is an important factor. In particular, oxygen penetrates not only from the upper side of the thermosensitive coloring layer (the side exposed to light such as sunlight) but also from the lower layer side of the thermosensitive coloring layer, so it is necessary to block from the lower layer side. is there.

In this regard, in the conventional technology, a protective layer is provided on the upper side of the thermosensitive coloring layer to block oxygen from the upper side, but blocking oxygen from the lower side has not been studied. . That is, the conventional under layer is provided for the purpose of improving the color development sensitivity and the fineness of the printed image. Therefore, functionally, the void in the layer is increased and the adhesion and heat insulation of the heat-sensitive recording material are improved. Designed to improve.
Since the resin added to the under layer will inhibit the above-mentioned function when added in a large amount, only the minimum amount for imparting interlayer adhesion is used. The ability to block light is low, and satisfactory light resistance cannot be obtained.
For example, Patent Documents 7 to 9 also propose to provide underlayers (undercoat layers). These underlayers have the functions of enhancing the color development sensitivity and blocking ultraviolet rays, but are described above. In order to increase the color development sensitivity, it is designed to reduce the amount of resin and increase the gap, which increases the air permeability, resulting in a low ability to block oxygen and insufficient light resistance. There is.
Accordingly, the present situation is that there are not enough heat-sensitive recording materials having excellent light resistance and water resistance and high whiteness.

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, an object of the present invention is to provide a heat-sensitive recording material having excellent light resistance and water resistance and high whiteness, and an image recording method using the heat-sensitive recording material.

Means for solving the problems are as follows. That is,
<1> a support, at least one under layer on the support, a heat-sensitive color developing layer in contact with the under layer and containing a leuco dye and a developer, at least a water-soluble resin and a fluorescent brightening agent Having one protective layer in this order,
The heat-sensitive recording material, wherein the under layer is a layer in contact with the heat-sensitive color-developing layer containing a water-soluble resin, and the air permeability of the under layer is 150 mL / min or less.
<2> The heat-sensitive recording material according to <1>, wherein the under layer includes hollow particles.
<3> Any one of <1> to <2>, wherein a content of the water-soluble resin contained in the under layer is 50% by mass to 80% by mass with respect to a total amount of the hollow particles and the water-soluble resin. The heat-sensitive recording material described in 1.
<4> In the above <1>, the under layer has a first under layer containing a water-soluble resin and a second under layer containing hollow particles in this order from the surface in contact with the thermosensitive coloring layer to the support side. The heat-sensitive recording material described.
<5> A first protective layer in which the protective layer contains a water-soluble resin and a fluorescent whitening agent, and a second protection that contains the water-soluble resin on the first protective layer and does not contain the fluorescent whitening agent. The heat-sensitive recording material according to any one of <1> to <4>, further comprising a layer.
<6> The thermosensitive recording material according to any one of <1> to <5>, wherein the optical brightener is a stilbene compound.
<7> An image recording method, wherein an image is recorded on the heat-sensitive recording material according to any one of <1> to <6> by any one of a thermal head and a laser image recording means. is there.
<8> The image recording method according to <7>, wherein the laser is a CO ₂ laser having a wavelength of 9.3 μm to 10.6 μm.

  According to the present invention, the conventional problems can be solved, the object can be achieved, the heat-sensitive recording material has excellent light resistance and water resistance and high whiteness, and image recording using the heat-sensitive recording material A method can be provided.

FIG. 1 is a schematic sectional view showing a layer structure of a thermosensitive recording material according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a layer structure of a heat-sensitive recording material according to another embodiment of the present invention.

(Thermal recording material)
The heat-sensitive recording material of the present invention comprises a support, and at least one under layer, a heat-sensitive color-developing layer, and at least one protective layer in this order on the support. Accordingly, other layers are provided.

<Support>
There is no restriction | limiting in particular as said support body, According to the objective, it can select suitably, For example, the support body (uses 50% or more of used paper pulp) which consists of high-quality paper and a used paper pulp, a synthetic paper, a polyethylene film, a laminate Any of paper or the like can be used.

<Under layer>
The under layer has an air permeability of 150 mL / min or less.
When the air permeability exceeds 150 mL / min, the ability to block oxygen entering from the support side necessary for light resistance becomes insufficient, and the intended light resistance cannot be obtained.
From such a viewpoint, the air permeability of the under layer is preferably 50 mL / min or less, and ideally 0 mL / min.

The structure of the under layer is not particularly limited as long as it contains a water-soluble resin in the layer in contact with the thermosensitive coloring layer, and can be appropriately selected according to the purpose. One layer or two or more layers May be laminated.
That is, the under layer may be the first under layer itself when the layer containing the water-soluble resin is in contact with the thermosensitive coloring layer and the water-soluble resin is used as the first under layer. If necessary, a second under layer and a third under layer may be laminated on the surface of the under layer on the support side.

-First under layer-
The first under layer is in contact with the thermosensitive coloring layer and is a layer containing the water-soluble resin, and may be the under layer itself.

  The water-soluble resin is not particularly limited and may be appropriately selected depending on the intended purpose. For example, polyvinyl alcohol, modified polyvinyl alcohol, starch or derivatives thereof, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, etc. Cellulose derivatives, polyacrylic acid soda, polyvinylpyrrolidone, acrylamide-acrylic acid ester copolymer, acrylamide-acrylic acid ester-methacrylic acid terpolymer, arikari salt of styrene-maleic anhydride copolymer, isobutylene- Alikari salt of maleic anhydride copolymer, polyacrylamide, modified polyacrylamide, methyl vinyl ether-maleic anhydride copolymer, carboxy modified polyethylene, polyvinyl alcohol Le - acrylamide block copolymers, melamine - formaldehyde resins, urea - formaldehyde resin, sodium alginate, gelatin, casein, and the like. These may be used individually by 1 type and may use 2 or more types together. Among these, polyvinyl alcohol resin is particularly preferable.

The first under layer can be formed by applying and drying as an aqueous dispersion of the water-soluble resin, but is added to the aqueous dispersion and included in the first under layer. As the component, for example, an inorganic filler, hollow particles, a water-soluble emulsion resin, and other components as necessary can be contained. In particular, when an image is formed using a thermal head, it is preferable to use hollow particles from the viewpoint of improving the color development sensitivity and fineness.
There is no restriction | limiting in particular as content of the said water-soluble resin in a said 1st under layer, Although it can select suitably according to the objective, 20 mass%-80 mass% are preferable, 30 mass%-70 The mass% is more preferable.
When the content is less than 20% by mass, it is difficult to obtain a predetermined air permeability, and when it exceeds 80% by mass, it is difficult to obtain sufficient color sensitivity when an image is generated using a thermal head. is there.

  The inorganic filler is not particularly limited and may be appropriately selected depending on the intended purpose. For example, aluminum hydroxide, calcium carbonate, aluminum oxide, zinc oxide, titanium dioxide, silica, barium sulfate, talc, kaolin, alumina, clay Etc. These may be used individually by 1 type and may use 2 or more types together. Among these, aluminum hydroxide, calcium carbonate, kaolin, and clay are particularly preferable from the viewpoints of liquidity when used as a coating solution, stability of dispersed particles, and water solubility.

The hollow particles preferably have a hollow ratio of 80% or more, more preferably 90% or more. When the hollow ratio is less than 80%, the heat insulation and cushioning properties are insufficient, so when forming an image using a thermal head, the thermal energy from the thermal head is released to the outside of the thermal recording material through the support. In addition, since the adhesiveness with the thermal head becomes weaker, the effects of improving sensitivity and definition may be small. In addition, the hollow ratio of the fine hollow particles obtained is 98% or less.
Here, the said hollow rate is ratio of the outer diameter of a hollow particle, and an internal diameter, and is represented by the following numerical formula.

The hollow particles are made of a thermoplastic resin as a shell, contain air or other gas inside, and are fine hollow particles that are already in a foamed state, and have a volume average particle diameter of 2 μm to 10 μm. It is done.
When the volume average particle diameter (particle outer diameter) is smaller than 2 μm, there are production problems such as it is difficult to obtain an arbitrary hollow ratio. Conversely, when the volume average particle diameter is larger than 10 μm, the surface after coating and drying is smooth. As a result, the adhesiveness with the thermal head is lowered and the effect of improving the sensitivity is lowered. Therefore, it is preferable that such particle distribution has a uniform distribution peak with a small variation and a particle diameter in the above range.

  As the hollow particles, the thermoplastic resin is used as a shell. Examples of the thermoplastic resin include polystyrene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polyacrylate ester, Examples thereof include polyacrylonitrile, polybutadiene, and copolymer resins thereof. Among these, a copolymer resin mainly composed of vinylidene chloride and acrylonitrile is particularly preferable.

  There is no restriction | limiting in particular as said water-soluble emulsion resin, According to the objective, it can select suitably, For example, latex, such as a styrene / butadiene copolymer and a styrene / butadiene / acrylic copolymer; Vinyl acetate resin, Examples include vinyl acetate / acrylic acid copolymers, styrene / acrylic acid ester copolymers, emulsions of acrylic acid ester resins, polyurethane resins, and the like. These may be used individually by 1 type and may use 2 or more types together.

The adhesion amount of the hollow particles after drying is preferably 0.2 g or more, more preferably 0.4 g to 5 g per 1 m ² of the support.
The amount of the water-soluble resin relative to the hollow particles is preferably 60% by mass to 80% by mass with respect to the total amount of the hollow particles and the water-soluble resin. When the content is less than 60% by mass, it is difficult to obtain a predetermined air permeability, and when it exceeds 80% by mass, sufficient color development sensitivity may be difficult to obtain.

As the coating weight of the heat-sensitive recording material of the first under layer is not particularly limited, as appropriate may be ^{selected, 0.4g / m 2 ~10g / m} 2 are preferred according to the purpose, 0. more preferably ^{6g / m 2 ~7g / m 2} .
When the adhesion amount is less than 0.4 g / m ² , it may be difficult to obtain a predetermined air permeability, and when it exceeds 10 g / m ² , the binding property of the layer may be lowered. .

-Second under layer-
The under layer is not particularly limited as long as it has the first under layer, and can be appropriately selected according to the purpose. From the viewpoint of improving the color development sensitivity of the thermosensitive color developing layer, the first under layer is not limited. A second underlayer containing hollow particles can be provided on the support side of the layer.
The second under layer contains hollow particles and a binder, and further contains other components as necessary.

The hollow particles preferably have a hollow ratio of 80% or more, more preferably 90% or more. When the hollow ratio is less than 80%, the heat insulating property and cushioning property are insufficient. Therefore, when an image is formed using a thermal head, the thermal energy from the thermal head passes through the support to the outside of the thermal recording material. Since it is released and the adhesion to the thermal head is weakened, the effect of improving sensitivity and definition may be small. In addition, the hollow ratio of the fine hollow particles obtained is 98% or less.
Here, the said hollow rate is ratio of the outer diameter of a hollow particle, and an internal diameter, and is represented by the following numerical formula.

The hollow particles are made of a thermoplastic resin as a shell, contain air or other gas inside, and are fine hollow particles that are already in a foamed state, and have a volume average particle diameter of 2 μm to 10 μm. It is done.
When the volume average particle diameter (particle outer diameter) is smaller than 2 μm, there are production problems such as it is difficult to obtain an arbitrary hollow ratio. Conversely, when the volume average particle diameter is larger than 10 μm, the surface after coating and drying is smooth. As a result, the adhesiveness with the thermal head is lowered and the effect of improving the sensitivity is lowered. Therefore, it is preferable that such particle distribution has a uniform distribution peak with a small variation and a particle diameter in the above range.

  As the hollow particles, the thermoplastic resin is used as a shell. Examples of the thermoplastic resin include polystyrene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polyacrylate ester, Examples thereof include polyacrylonitrile, polybutadiene, and copolymer resins thereof. Among these, a copolymer resin mainly composed of vinylidene chloride and acrylonitrile is particularly preferable.

The binder is not particularly limited and is appropriately selected from at least one of conventionally known water-soluble polymers and water-soluble polymer emulsions.
Examples of the water-soluble polymer include cellulose derivatives such as polyvinyl alcohol, starch or derivatives thereof, methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose; polyacrylic acid soda, polyvinylpyrrolidone, acrylamide / acrylic acid ester copolymer Acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, casein, etc. It is done.
Examples of the aqueous polymer emulsion include latex such as styrene / butadiene copolymer and styrene / butadiene / acrylic copolymer; vinyl acetate resin, vinyl acetate / acrylic acid copolymer, styrene / acrylic acid ester copolymer, Examples thereof include emulsions such as acrylic ester resins and polyurethane resins. These may be used individually by 1 type and may use 2 or more types together.

The second under layer is formed by dispersing the hollow particles and the binder in water, coating and drying the same.
In this case, the adhesion amount of the hollow particles after drying is preferably 0.2 g or more and more preferably 0.4 g to 5 g per 1 m ² of the support.
The amount of the binder applied may be an amount that strongly bonds the second under layer to the adjacent layer, and is usually 2% by mass to 50% by mass with respect to the total amount of the hollow particles and the binder resin. Is preferred.

<Thermosensitive coloring layer>
The thermosensitive coloring layer contains a leuco dye and a developer, and further contains other components as necessary.

-Leuco dye-
The leuco dye is a compound exhibiting electron donating properties, and is applied singly or in combination of two or more. However, the leuco dye is a colorless or light-colored dye precursor, and is a conventionally known one such as triphenyl. Methanephthalide, triallylmethane, fluorane, phenothiocyan, thioferolane, xanthene, indophthalyl, spiropyran, azaphthalide, chromenopyrazole, methine, rhodamine anilinolactam, rhodamine lactam In addition, leuco compounds such as quinazoline-based, diazaxanthene-based, and bislactone-based compounds can be used.
Considering the color development characteristics, the discoloration of the image area due to moisture and heat resistance and the quality of the background fogging of the background area, specific examples of such compounds include, for example, 2-anilino-3-methyl-6-diethylaminofluorane, 2 -Anilino-3-methyl-6- (di-n-butylamino) fluorane, 2-anilino-3-methyl-6- (di-n-pentylamino) fluorane, 2-anilino-3-methyl-6- ( N-n-propyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-isopropyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-isobutyl- N-methylamino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-se) -Butyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-ethylamino) fluorane, 2-anilino-3-methyl-6- (N-iso-amyl) -N-ethylamino) fluorane, 2-anilino-3-methyl-6- (N-cyclohexyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-ethyl-p-toluidino) fluorane 2-anilino-3-methyl-6- (N-methyl-p-toluidino) fluorane, 2- (m-trichloromethylanilino) -3-methyl-6-diethylaminofluorane, 2- (m-trifluoro) Methylanilino) -3-methyl-6-diethylaminofluorane, 2- (m-trifluoromethylanilino) -3-methyl-6- (N-cyclohexyl-N) Methylamino) fluorane, 2- (2,4-dimethylanilino) -3-methyl-6-diethylaminofluorane, 2- (N-ethyl-p-toluidino) -3-methyl-6- (N-ethylanilino) Fluorane, 2- (N-methyl-p-toluidino) -3-methyl-6- (N-propyl-p-toluidino) fluorane, 2-anilino-6- (Nn-hexyl-N-ethylamino) fluorane 2- (o-chloroanilino) -6-diethylaminofluorane, 2- (o-bromoanilino) -6-diethylaminofluorane, 2- (o-chloroanilino) -6-dibutylaminofluorane, 2- (o-fluoroanilino) ) -6-dibutylaminofluorane, 2- (m-trifluoromethylanilino) -6-diethylaminofluorane, 2- (p-a Cetylanilino) -6- (Nn-amyl-Nn-butylamino) fluorane, 2-benzylamino-6- (N-ethyl-p-toluidino) fluorane, 2-benzylamino-6- (N-methyl) -2,4-dimethylanilino) fluorane, 2-benzylamino-6- (N-ethyl-2,4-dimethylanilino) fluorane, 2-dibenzylamino-6- (N-methyl-p-toluidino) Fluorane, 2-dibenzylamino-6- (N-ethyl-p-toluidino) fluorane, 2- (di-p-methylbenzylamino) -6- (N-ethyl-p-toluidino) fluorane, 2- (α -Phenylethylamino) -6- (N-ethyl-p-toluidino) fluorane, 2-methylamino-6- (N-methylanilino) fluorane, 2-methylamino- -(N-ethylanilino) fluorane, 2-methylamino-6- (N-propylanilino) fluorane, 2-ethylamino-6- (N-methyl-p-toluidino) fluorane, 2-methylamino-6- ( N-methyl-2,4-dimethylanilino) fluorane, 2-ethylamino-6- (N-methyl-2,4-dimethylanilino) fluorane, 2-dimethylamino-6- (N-methylanilino) fluorane, 2-dimethylamino-6- (N-ethylanilino) fluorane, 2-diethylamino-6- (N-methyl-p-toluidino) fluorane, benzoleucomethylene blue, 2- [3,6-bis (diethylamino)]-6 (O-Chloranilino) xanthylbenzoate lactam, 2- [3,6-bis (diethylamino)]-9- (o-chloro) Anilino) xanthyl benzoate lactam, 3,3-bis (p-dimethylaminophenyl) phthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3,3-bis (p-dimethyl) Aminophenyl) -6-diethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide, 3- (2-methoxy-4-) Dimethylaminophenyl) -3- (2-hydroxy-4,5-dichlorophenyl) phthalide, 3- (2-hydroxy-4-dimethylaminophenyl) -3- (2-methoxy-5-chlorophenyl) phthalide, 3- (2-hydroxy-4-dimethoxyaminophenyl) -3- (2-methoxy-5-chlorophenyl) phthalide, 3 (2-hydroxy-4-dimethylaminophenyl) -3- (2-methoxy-5-nitrophenyl) phthalide, 3- (2-hydroxy-4-diethylaminophenyl) -3- (2-methoxy-5-methylphenyl) ) Phthalide, 3,6-bis (dimethylamino) fluorene spiro (9,3 ′)-6′-dimethylaminophthalide, 6′-chloro-8′-methoxy-benzoindolino-spiropyran, 6′-bromo- And 2'-methoxy-benzoindolino-spiropyran. These may be used individually by 1 type and may use 2 or more types together.
The content of the leuco dye in the thermosensitive coloring layer is preferably 5% by mass to 20% by mass, and more preferably 10% by mass to 15% by mass.

-Developer-
As the developer, various electron-accepting substances that react with the leuco dye when heated to develop color are applied. Specific examples thereof include phenolic compounds, organic or Examples include inorganic acidic compounds, and esters or salts thereof.
Specific examples of the developer include, for example, bisphenol A, tetrabromobisphenol A, gallic acid, salicylic acid, 3-isopropylsalicylic acid, 3-cyclohexylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3,5- Di-α-methylbenzylsalicylic acid, 4,4′-isopropylidenediphenol, 1,1′-isopropylidenebis (2-chlorophenol), 4,4′-isopropylidenebis (2,6-dibromophenol), 4,4′-isopropylidenebis (2,6-dichlorophenol), 4,4′-isopropylidenebis (2-methylphenol), 4,4′-isopropylidenebis (2,6-dimethylphenol), 4 , 4′-isopropylidenebis (2-tert-butylphenol), 4,4′-sec-butylidene Phenol, 4,4′-cyclohexylidenebisphenol, 4,4′-cyclohexylidenebis (2-methylphenol), 4-tert-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, α-naphthol, β -Naphthol, 3,5-xylenol, thymol, methyl-4-hydroxybenzoate, 4-hydroxyacetophenone, novolac phenol resin, 2,2'-thiobis (4,6-dichlorophenol), catechol, resorcin, hydroquinone Pyrogallol, phloroglycine, phloroglysin carboxylic acid, 4-tert-octylcatechol, 2,2′-methylenebis (4-chlorophenol), 2,2′-methylenebis (4-methyl-6-tert-butylphenol), 2 , 2'-dihydroxy Sidiphenyl, ethyl p-hydroxybenzoate, propyl p-hydroxybenzoate, butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate, p-hydroxybenzoic acid-p-chlorobenzyl, p-hydroxybenzoic acid-o- Chlorobenzyl, p-hydroxybenzoic acid-p-methylbenzyl, p-hydroxybenzoic acid-n-octyl, benzoic acid, zinc salicylate, 1-hydroxy-2-naphthoic acid, 2-hydroxy-6-naphthoic acid, 2- Zinc hydroxy-6-naphthoate, 4-hydroxydiphenylsulfone, 4-hydroxy-4'-chlorodiphenylsulfone, bis (4-hydroxyphenyl) sulfide, 2-hydroxy-p-toluic acid, 3,5-di-tert -Zinc butylsalicylate, 3,5-di-tert-butylsalicy Stannic acid, tartaric acid, oxalic acid, maleic acid, citric acid, succinic acid, stearic acid, 4-hydroxyphthalic acid, boric acid, thiourea derivative, 4-hydroxythiophenol derivative, bis (4-hydroxyphenyl) acetic acid, Bis (4-hydroxyphenyl) ethyl acetate, bis (4-hydroxyphenyl) acetate-n-propyl, bis (4-hydroxyphenyl) acetate-n-butyl, bis (4-hydroxyphenyl) acetate phenyl, bis (4- Hydroxyphenyl) benzyl acetate, bis (4-hydroxyphenyl) phenethyl acetate, bis (3-methyl-4-hydroxyphenyl) acetic acid, bis (3-methyl-4-hydroxyphenyl) acetic acid methyl, bis (3-methyl-4) -Hydroxyphenyl) acetic acid-n-propyl, 1,7-bis (4-hydroxypheny Thio) 3,5-dioxaheptane, 1,5-bis (4-hydroxyphenylthio) 3-oxapentane, dimethyl 4-hydroxyphthalate, 4-hydroxy-4'-methoxydiphenylsulfone, 4-hydroxy-4 '-Ethoxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-propoxydiphenylsulfone, 4-hydroxy-4'-butoxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenyl Sulfone, 4-hydroxy-4′-sec-butoxydiphenylsulfone, 4-hydroxy-4′-tert-butoxydiphenylsulfone, 4-hydroxy-4′-benzyloxydiphenylsulfone, 4-hydroxy-4′-phenoxydiphenylsulfone 4-hydroxy 4 ′-(m-methylbenzyloxy) diphenylsulfone, 4-hydroxy-4 ′-(p-methylbenzyloxy) diphenylsulfone, 4-hydroxy-4 ′-(o-methylbenzyloxy) diphenylsulfone, 4-hydroxy -4 '-(p-chlorobenzyloxy) diphenyl sulfone, 4-hydroxy-4'-allyloxydiphenyl sulfone, and the like. These may be used individually by 1 type and may use 2 or more types together.
The mixing ratio of the leuco dye and the developer in the thermosensitive coloring layer is preferably 0.5 parts by mass to 10 parts by mass with respect to 1 part by mass of the leuco dye, and 1 part by mass to 5 parts by mass. Is more preferable.

In the thermosensitive coloring layer, in addition to the leuco dye and the developer, a thermosensitive material such as a binder, a filler, a thermofusible substance, a crosslinking agent, a pigment, a surfactant, a fluorescent whitening agent, and a lubricant. Various materials conventionally used for constituting the recording material can be appropriately used in combination.
The binder is used as necessary for improving the coatability and binding properties of the layer. Specific examples thereof include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, arabic gum, polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic. Examples thereof include acid copolymer salts, styrene / acrylic copolymer salts, and styrene / butadiene copolymer salt emulsions.
The filler is not particularly limited and may be appropriately selected depending on the intended purpose. For example, calcium carbonate, aluminum oxide, zinc oxide, titanium dioxide, silica, aluminum hydroxide, barium sulfate, talc, kaolin, alumina, clay Inorganic pigments such as the above, or known organic pigments. Among these, silica, alumina, and kaolin which are acidic pigments (showing acidity in an aqueous solution) are preferable, and silica is particularly preferable from the viewpoint of color density.

  It is also preferable to use the thermofusible substance in combination. Examples of the thermofusible substance include fatty acids such as stearic acid and behenic acid; fatty acid amides such as stearic acid amide, erucic acid amide, palmitic acid amide, behenic acid amide, and palmitic acid amide; N-lauryl laurin N-substituted amides such as acid amide, N-stearyl stearamide, N-oleyl stearamide; methylene bis stearamide, ethylene bis stearamide, ethylene bis laurate, ethylene biscapric amide, ethylene bis Bisfatty acid amides such as behenic acid amides; Hydroxy fatty acid amides such as hydroxystearic acid amide, methylene bishydroxystearic acid amide, ethylene bishydroxystearic acid amide, hexamethylene bishydroxystearic acid amide; Fatty acid metal salts such as zinc oxide, aluminum stearate, calcium stearate, zinc palmitate, zinc behenate; p-benzylbiphenyl, terphenyl, triphenylmethane, benzyl p-benzyloxybenzoate, β-benzyloxynaphthalene, β-naphthoic acid phenyl, 1-hydroxy-2-naphthoic acid phenyl, 1-hydroxy-2-naphthoic acid methyl, diphenyl carbonate, benzyl terephthalate, 1,4-dimethoxynaphthalene, 1,4-diethoxynaphthalene, 1, 4-dibenzyloxynaphthalene, 1,2-diphenoxyethane, 1,2-bis (4-methylphenoxyethane), 1,4-diphenoxy-2-butene, 1,2-bis (4-methoxyphenylthio) Ethane, dibenzoylmethane, 1,4-diphe Ruthiobutane, 1,4-diphenylthio-2-butene, 1,3-bis (2-vinyloxyethoxy) benzene, 1,4-bis (2-vinyloxyethoxy) benzene, p- (2-vinyloxyethoxy) Biphenyl, p-aryloxybiphenyl, dibenzoyloxymethane, dibenzoyloxypropane, dibenzyl disulfide, 1,1-diphenylethanol, 1,1-diphenylpropanol, p-benzyloxybenzyl alcohol, 1,3-phenoxy-2 -Propanol, N-octadecylcarbamoyl-p-methoxycarbonylbenzene, N-octadecylcarbamoylbenzene, 1,2-bis (4-methoxyphenoxy) propane, 1,5-bis (4-methoxyphenoxy) -3-oxapentane, Oxalic acid dibenge , Oxalic acid bis (4-methylbenzyl) oxalate bis (4-chlorobenzyl), and the like. These may be used individually by 1 type and may use 2 or more types together.

Further, when diacetone-modified polyvinyl alcohol is contained in the thermosensitive coloring layer, a crosslinking reaction is likely to occur when N-aminopolyacrylamide is contained as a crosslinking agent in the protective layer or the thermosensitive coloring layer and the protective layer. This is preferable because the water resistance can be improved without adding other cross-linking agents that cause inhibition.
The heat-sensitive coloring layer can be formed by a generally known method. For example, a leuco dye or a developer, together with a binder and other components, respectively, by a dispersing machine such as a ball mill, an attritor, or a sand mill. Then, after pulverizing and dispersing until the dispersed particle size becomes 1 μm to 3 μm, if necessary, mixing with a filler, a heat-fusible substance (sensitizer) dispersion, etc., and mixing with a predetermined formulation to prepare a thermosensitive coloring layer coating solution And it can form by apply | coating on a support body.
The thickness of the heat-sensitive coloring layer varies depending on the composition of the heat-sensitive coloring layer and the application of the heat-sensitive recording material, and cannot be defined unconditionally.

<Protective layer>
The protective layer contains at least a water-soluble resin and a fluorescent brightening agent. By having this protective layer, further improvement in light resistance can be expected while maintaining the whiteness of the background.
The layer structure of the protective layer may be one layer or two layers, and includes a first protective layer containing the water-soluble resin and the fluorescent whitening agent on the thermosensitive coloring layer, and the water-soluble resin. It is preferable to have the 2nd protective layer which does not contain a fluorescent whitening agent in this order.
In this case, even if the fluorescent whitening agent is added in a large amount in the entire protective layer, the whiteness of the background can be maintained while suppressing yellowness, and the light resistance is improved by the fluorescent whitening agent. In addition, water resistance can be improved.

-First protective layer-
The first protective layer contains a fluorescent brightening agent and a water-soluble resin, and if necessary, contains a crosslinking agent.

--Fluorescent whitening agent--
There is no restriction | limiting in particular as said fluorescent whitening agent, Although it can select suitably according to the objective, From a viewpoint which has the outstanding light resistance, a stilbene compound is preferable.

The stilbene compound is not particularly limited and may be appropriately selected depending on the intended purpose. For example, 4,4′-bis (2-amino-4-anilino-1,3,5-triazinyl-6-amino ) Stilbene-2,2′-disulfonic acid, 4,4′-bis (2,4-dianilino-1,3,5-triazin-6-yl-amino) stilbene-2,2′-disulfonic acid disodium, 4,4′-bis (2-anilino-4-hydroxyethylamino-1,3,5-triazinyl-6-amino) stilbene disulfonic acid, 4,4′-bis {2-anilino-4-di (hydroxyethyl) ) Amino-1,3,5-triazinyl- (6) -amino} stilbene-2,2′-disulfonic acid sodium salt, 4,4′-bis [2- (2-methylanilino) -4-bis (hydroxyethyl) Amino-1,3,5-to Azinyl-6-amino] stilbene-2,2′-disulfonate sodium, 4,4′-bis {2- (m-sulfophenylamino) -4- (2-hydroxypropyl) amino-1,3,5- Triazinyl-6-amino} stilbene-2,2′-disulfonate sodium, 4- [2-p-sulfoanilino-4-bis (hydroxyethyl) amino-1,3,5-triazinyl-6-amino] -4 ′ -[2-m-sulfoanilino-4-bis (hydroxyethyl) amino-1,3,5-triazinyl-6-amino] stilbene-2,2'-disulfonate, 4,4'-bis {2-so Sodium sulfanyl-4-di (hydroxyethyl) amino-1,3,5-triazinyl- (6) -amino} stilbene-2,2′-disulfonate, 4,4′-bis [4- [3-acetyla] NO-4- (4,8-Disulfo-2-naphthylazo)] anilino-6- (3-carboxypyridinio) -1,3,5-triazin-2-ylamino] -2,2′-disulfostilbene -Dihydroxide = hexasodium salt, 4,4'-bis [4- [3-acetylamino-4- (4,8-disulfo-2-naphthylazo)] anilino-6-chloro-1,3,5-triazine -2-ylamino] -2,2′-stilbene disulfonic acid = hexasodium salt, 4,4′-bis [4- [3- [3-carboxy-5-hydroxy-1- (p-sulfophenyl) -4] -Pyrazolylazo] -4-sulfoanilino] -6-chloro-1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid = octasodium salt, 4,4'-bis [4-chloro -6- [3- [1- (2-chloro-5 Sulfophenyl) -5-hydroxy-3-methyl-4-pyrazolylazo] -4-sulfoanilino] -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid = hexasodium salt, 4 , 4′-bis [6- [N- (2-cyanoethyl) -N- [2- (2-hydroxyethoxy) ethyl] amino] -4- (2,5-disulfoanilino) -1,3,5-triazine -2-ylamino] -2,2′-stilbene disulfonic acid = hexasodium salt, 4,4′-bis [4-bis (2-hydroxypropyl) amino-6- (4-sulfoanilino) -1,3,5 -Triazin-2-ylamino] -2,2'-stilbene disulfonic acid = tetrasodium salt, 4- (4 amino-6-anilino-1,3,5-triazin-2-ylamino) -4 '-(4 6-Diamino-1,3,5- Riazin-2-ylamino) -2,2'-stilbene disulfonic acid, 4- (2,4-diamino-1,3,5-triazin-6-yl) amino-4 '-(4-amino-2-chloro) -6-yl) amino-2,2′-stilbene disulfonate calcium, 4,4′-bis (4-amino-6-anilino-1,3,5-triazin-2-ylamino) -2,2′- Stilbene disulfonic acid, 4,4′-bis (4-amino-6-anilino-1,3,5-triazin-2-ylamino) -2,2′-stilbene disulfonic acid, 4,4′-bis ( 4-amino-6-anilino-1,3,5-triazin-2-ylamino) -2,2′-stilbenedidisulfonic acid potassium potassium salt, 4,4′-bis (4-amino-6-chloro-1, 3,5-triazin-2-ylamino) -2,2′-stil Benzodisulfonic acid, 4,4′-bis (4-amino-6-chloro-1,3,5-triazin-2-ylamino) -2,2′-stilbene disulfonic acid, 4,4′-bis ( 6-amino-4-chloro-1,3,5-triazin-2-ylamino) -2,2′-stilbene disulfonate, 4,4′-bis (4-amino-6-chloro-1,3, 5-triazin-2-ylamino) -2,2′-stilbene disulfonic acid potassium hydrogen salt, 4,4′-bis (4-amino-6-chloro-1,3,5-triazin-2-ylamino) -2, Sodium 2′-stilbene disulfonate, disodium 4,4′-bis (4-amino-6-chloro-1,3,5-triazin-2-ylamino) -2,2′-stilbene disulfonate, 4, 4'-bis [4-anilino-6- (p- Sulfoanilino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid = potassium salt (monosalt, disalt, trisalt or tetrasalt), 4,4′-bis [4- Anilino-6- (2-hydroxyethylamino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′-bis [4-anilino-6- (2- Hydroxyethylamino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonate, 4,4′-bis [4-anilino-6- (2-hydroxyethylamino)- 1,3,5-Triazin-2-ylamino] -2,2′-stilbene disulfonate potassium 4,4′-bis (4-anilino-6-methylamino-1,3,5-triazine-2- Ilamino) -2,2'-stilbe Disodium disulphonate, 4,4′-bis [4- (2,5-disulfoanilino) -6- (2-hydroxypropylamino) -1,3,5-triazin-2-ylamino] -2,2′- Stilbene disulfonic acid, 4,4′-bis [6- (m-sulfoanilino) -4- (2-hydroxydiethylamino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′-bis [6- (m-sulfoanilino) -4- (2-hydroxypropylamino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4 '-Bis [6- (2-hydroxyethylamino) -4-anilino-1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid, 4,4'-bis [4-bis (2-Hydroxyethyl) a Nor-6-chloro-1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid sodium salt, 4,4′-bis (4-methylamino-6-phenylamino-1,3 , 5-Triazin-2-ylamino) -2,2′-stilbene disulfonic acid, 4- [4-chloro-6-bis (2-hydroxyethyl) amino-1,3,5-triazin-2-ylamino]- 4 ′-[4,6-bis [bis (2-hydroxyethyl) amino] -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′bis [4- Anilino-6-bis (2-hydroxyethyl) amino-1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′bis [4-anilino-6-bis (2 -Hydroxyethyl) amino-1, , 5-Triazin-2-ylamino] -2,2′-stilbene disulfonate, 4,4′bis [4-anilino-6-bis (2-hydroxyethyl) amino-1,3,5-triazine- 2-ylamino] -2,2′-stilbene dihydrogen potassium potassium salt, 4,4′bis [4-anilino-6- [N- (2-hydroxyethyl) -N-methylamino] -1,3,5- Triazin-2-ylamino] -2,2′-stilbene disulfonate, 4,4′bis [4-anilino-6- [N- (2-hydroxyethyl) -N-methylamino] -1,3 5-Triazin-2-ylamino] -2,2′-stilbene disulfonic acid potassium potassium salt, 4,4′-bis [4- (diethylamino) -6- (2,5-disulfoanilino) -1,3,5-triazine -2-ylamino ] -2,2′-stilbene disulfonic acid = sodium salt (mono-, di-, tri-, tetra-, penta- or hexa-salt), 4,4′-bis [6- (p-sulfamoylphenylamino) ) -4-Bis (2-hydroxyethyl) amino-1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid, 4,4'-bis [4-bis (2-hydroxyethyl) ) Amino-6- (p-sulfamoylanilino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′-bis [4-bis (2- Hydroxyethyl) amino-6-chloro-1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′-bis [6-bis (2-hydroxyethyl) amino -4- (2,5-disulfoanilino) -1,3,5-tri Azin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′-bis [4-bis (2-hydroxyethyl) amino-6- (m-sulfoanilino) -1,3,5-triazine- 2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′-bis [4-bis (2-hydroxyethyl) amino-6- (p-sulfoanilino) -1,3,5-triazine-2- Ylamino] -2,2′-stilbene disulfonic acid, 4,4′-bis [4-bis (2-hydroxyethyl) amino-6- (m-sulfoanilino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid potassium salt (mono, di, tri or tetra), 4,4'-bis [4-bis (2-hydroxyethyl) amino-6- (p-sulfophenoxy) -1,3,5-triazin-2-yl No] -2,2′-stilbene disulfonic acid, 4- [4-bis (2-hydroxyethyl) amino-6- (p-sulfoanilino) -1,3,5-triazin-2-ylamino] -4 ′ [ 4-bis (2-hydroxyethyl) amino-6- (m-sulfoanilino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4- [4-bis (2- Hydroxyethyl) amino-6- (p-sulfonilino) -1,3,5-triazin-2-ylamino] -4 '-[4-bis (2-hydroxyethyl) amino-6- (m-sulfoanilino) -1 , 3,5-Triazin-2-ylamino] -2,2′-stilbene disulfonic acid = sodium salt (mono-, di-, tri- or tetra-salt), 4- [4-bis (2-hydroxyethyl) amino -6-methoxy-1,3,5-triazine 2-ylamino] -4 '-(4-methoxy-6-morpholino-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonic acid, 4- [4-bis (2-hydroxyethyl) ) Amino-6-methoxy-1,3,5-triazin-2-ylamino] -4 '-[4- (2-hydroxysulfonylethylamino) -6-methoxy-1,3,5-triazin-2-ylamino ] -2,2'-stilbene disulfonic acid, 4- (4-anilino-6-methoxy-1,3,5-triazin-2-ylamino) -4 '-(4-chloro-6-methoxy-1,3) , 5-Triazin-2-ylamino) -2,2′-stilbene disulfonate, 4- (4-anilino-6-methoxy-1,3,5-triazin-2-ylamino) -4 ′-(4 , 6-Dimethoxy-1,3,5- Triazin-2-ylamino) -2,2′-stilbene disulfonic acid, 4- (4-anilino-6-methoxy-1,3,5-triazin-2-ylamino) -4 ′-(4,6-dimethoxy-) 1,3,5-triazin-2-ylamino) -2,2′-stilbene disulfonate, 4- (4-anilino-6-methoxy-1,3,5-triazin-2-ylamino) -4 ′ -(4,6-dimethoxy-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonic acid potassium hydrogen salt, 4- (4-anilino-6-methoxy-1,3,5-triazine 2-ylamino) -4 '-(4,6-dimethoxy-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonic acid sodium salt, 4- (4-anilino-6-methoxy) -1,3,5-triazi -2-ylamino) -4 ′-(4,6-dimethoxy-1,3,5-triazin-2-ylamino) -2,2′-stilbene disulfonate, 4,4′-bis [6- ( 1-hydroxy-1-methylethylamino) -4-methoxy-1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4- (4-chloro-6-methoxy-1, 3,5-triazin-2-ylamino) -4 '-(4,6-dimethoxy-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonic acid, 4- (4-chloro- 6-methoxy-1,3,5-triazin-2-ylamino) -4 ′-(4,6-dimethoxy-1,3,5-triazin-2-ylamino) -2,2′-stilbene disulfonate 4- (4-Chloro-6-methoxy-1,3 5-triazin-2-ylamino) -4 '-(4,6-dimethoxy-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonic acid potassium potassium salt, 4- (4-chloro- 6-methoxy-1,3,5-triazin-2-ylamino) -4 '-(4,6-dimethoxy-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonic acid sodium hydrogen salt 4- (4-Chloro-6-methoxy-1,3,5-triazin-2-ylamino) -4 '-(4,6-dimethoxy-1,3,5-triazin-2-ylamino) -2, Disodium hydrogen 2′-stilbene disulfonate, 4,4′-bis (4-anilino-6-methoxy-1,3,5-triazin-2-ylamino) -2,2′-stilbene disulfonic acid, 4,4 '-Bis [4-chloro-6- (p Sulfophenyloxy) -1,3,5-triazin-2-ylamino] -2,2 ′ stilbene disulfonic acid, 4,4′-bis [4-chloro-6- (p-sulfophenoxy) -1,3, 5-Triazin-2-ylamino] -2,2′-stilbene disulfonic acid disodium salt, 4,4′-bis [4-chloro-6- (p-sulfophenoxy) -1,3,5-triazine-2 -Ylamino] -2,2'-stilbene disulfonic acid sodium salt (mono-, di-, tri- or tetra-salt), 4,4'-bis [4-chloro-6-phenoxy-1,3,5- Triazin-2-ylamino) -2,2'-stilbene disulfonic acid sodium salt (mono- or di-salt), 4,4'-bis [4-chloro-6-methoxy-1,3,5-triazine-2- Ylamino) -2,2'-stilbene disulfonic acid, 4, '-Bis (4-chloro-6-methoxy-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonate, 4,4'-bis (4-chloro-6-methoxy) -1,3,5-Triazin-2-ylamino) -2,2′-stilbene disulfonic acid potassium hydrogen salt, 4,4′-bis (4-chloro-6-methoxy-1,3,5-triazine-2- Ylamino) -2,2′-stilbene disulfonic acid sodium salt (mono- or di-salt, 4,4′-bis [4- (2-hydroxyethylamino) -6-phenoxy-1,3,5-triazine-2) -Ylamino] -2,2'-stilbene disulfonic acid, 4,4'-bis [4- (2-hydroxyethylamino) -6-methoxy-1,3,5-triazin-2-ylamino] -2,2 '-Stilbene disulfonic acid, 4,4'-bi (4-anilino-6-chloro-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonic acid, 4,4'-bis (4-anilino-6-chloro-1,3 5-triazin-2-ylamino) -2,2′-stilbene disulfonate, 4,4′-bis (4-anilino-6-chloro-1,3,5-triazin-2-ylamino) -2, Potassium hydrogen 2'-stilbene disulfonate, 4,4'-bis (4-anilino-6-chloro-1,3,5-triazin-2-ylamino) -2,2'-sodium hydrogen hydrogen stilbene disulfonate, 4, 4'-bis (4-anilino-6-chloro-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonate, 4,4'-bis (4-anilino-6) -Chloro-1,3,5-triazine- 2-ylamino) -2,2′-stilbene disulfonate potassium sodium, 4,4′-bis [4-chloro-6- (p-chloroanilino) -1,3,5-triazin-2-ylamino] -2, 2′-stilbene disulfonic acid, sodium 4,4′-bis [4-chloro-6- (p-chloroanilino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid sodium salt, 4,4′-bis [4-chloro-6- (p-chloroanilino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonate, 4,4′-bis [4-Chloro-6- (2,5-disulfoanilino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′-bis [4-chloro-6 (2,5-disulfoanilino)- , 3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid sodium salt (mono-, di-, tri-, tetra-, penta- or hexa-salt), 4,4′-bis [4 -Chloro-6- (p-sulfamoylanilino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonate, 4,4'-bis [4-chloro- 6- (m-sulfoanilino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′-bis [4-chloro-6- (p-sulfoanilino) -1 , 3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid, 4,4'-bis [4-chloro-6- (m-sulfoanilino) -1,3,5-triazine-2- Ylamino] -2,2′-stilbene disulfonic acid potassium salt (monosalt, disyl Salt, trisalt or tetrasalt), 4,4′-bis [4-chloro-6- (p-sulfoanilino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonic acid Potassium salt (mono-, di-, tri- or tetra-salt), 4,4'-bis [4-chloro-6- (2,5-disulfoanilino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid hexapotassium salt, 4,4'-bis [4-chloro-6- (p-sulfoanilino) -1,3,5-triazin-2-ylamino] -2,2'- Stilbene disulfonic acid sodium salt (mono-, di-, tri-, or tetra-salt), 4,4'-bis [4-chloro-6- (m-sulfoanilino) -1,3,5-triazin-2-ylamino ] -2,2'-stilbene disulfonic acid sodium salt (mono salt, di salt, tri salt or tetra salt), 4, '-Bis [4-chloro-6- (2-sulfoethylamino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid, 4,4'-bis [4-chloro -6- (2-sulfoethylamino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid potassium salt (mono salt, di salt, tri salt or tetra salt), 4, 4'-bis [4-chloro-6- (2-sulfoethylamino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid sodium salt (monosalt, disalt, tris Salt) or 4,4′-bis [4-chloro-6- (o-toluidino) -1,3,5-triazin-2-ylamino] -2,2′-stilbenesulfonic acid, 4,4 '-Bis [4-chloro-6- (o-toluidino) -1,3,5-triazin-2-ylamino Dipotassium 2,2′-stilbene disulfonate, 4,4′-bis [4-chloro-6- (o-toluidino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene Potassium hydrogen disulfonate, sodium 4,4′-bis [4-chloro-6- (o-toluidino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonate, 4, 4′-bis [4-chloro-6- (o-toluidino) -1,3,5-triazin-2-ylamino] -2,2′-stilbene disulfonate, 4,4′-bis [4 -Chloro-6- (2-hydroxyethylamino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid sodium salt, 4,4'-bis [4-chloro-6 (2-hydroxyethylamino) -1 , 3,5-Triazin-2-ylamino] -2,2′-stilbene disulfonate, 4,4′-bis [4-chloro-6- (2-hydroxyethylamino) -1,3,5- Triazin-2-ylamino] -2,2′-stilbene disulfonic acid, 4,4′-bis [4-chloro-6- (7-phenylazo-8-disulfo-1-naphthylamino) -1,3,5- Triazin-2-ylamino] -2,2′-stilbene disulfonic acid sodium salt (mono-, di-, tri-, tetra-, penta- or hexa-salt), 4,4′-bis [4-chloro-6] -(7-phenylazo-8-hydroxy-2,5-disulfo-1-naphthylamino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid sodium salt (mono-salt, di-salt Salt, trisalt, tetrasalt, pentasalt, or hexasalt), 4,4 '-Bis [4-chloro-6- (o-methylanilino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonate, 4,4'-bis (4,6 -Dichloro-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonic acid, 4,4'-bis (4,6-dichloro-1,3,5-triazin-2-ylamino) -2,2'-calcium stilbene disulfonate, sodium 4,4'-bis (4,6-dichloro-1,3,5-triazin-2-ylamino) stilbene-2,2'-disulfonic acid sodium salt, 4, 4'-bis [4-morpholino-6- (p-sulfoanilino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid, 4,4'-bis [4-morpholino- 6- (2-sulfoethylamino) -1, , 5-Triazin-2-ylamino] -2,2′-stilbene disulfonic acid kaurim salt (mono-, di-, tri- or tetra-salt), 4,4′-bis [4-morpholino-6- (o -Toluidino) -1,3,5-triazin-2-ylamino] -2,2'-stilbene disulfonic acid, 4,4'-bis [4-morpholino-6- (o-toluidino) -1,3,5 -Triazin-2-ylamino] -2,2'-stilbene disulfonate, 4,4'-bis [4-morpholino-6- (o-toluidino) -1,3,5-triazin-2-ylamino] Potassium hydrogen-2,2′-stilbene disulfonate, 4- (4-chloro-6-methoxy-1,3,5-triazin-2-ylamino) -4 ′-(4-methoxy-6-morpholino-1, 3,5-triazin-2-ylamino) -2,2′-su Disodium tilrubene disulfonate, 4,4′-bis [4-chloro-6-morpholino-1,3,5-triazin-2-ylamino) -2,2′-stilbene disulfonic acid, 4,4′-bis [4-chloro-6-morpholino-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonic acid sodium salt, 4,4'-bis [4-chloro-6-morpholino-1, 3,5-triazin-2-ylamino) -2,2′-stilbene disulfonic acid disodium, 4,4′-bis (4,6-dimorpholino-1,3,5-triazin-2-ylamino) -2, Examples include 2'-stilbene disulfonic acid, 4,4'-bis [4,6-dimorpholino-1,3,5-triazin-2-ylamino) -2,2'-stilbene disulfonic acid. These may be used individually by 1 type and may use 2 or more types together.

The heat-sensitive recording material, the content of the fluorescent brightening agent in the first protective layer is ^{0.5g / m 2 ~1.5g / m 2} , and the fluorescent brightening in the first protective layer The content of the agent is preferably 20% by mass or more.
If the content is less than 0.5 g / m ² , sufficient light resistance cannot be obtained, and even if it exceeds 1.5 g / m ² , the degree of light resistance does not change, and conversely yellowing of the background In order to prevent this, it is necessary to increase the adhesion amount of the entire protective layer, and the color developability may be lowered.
At the same time, if the content is less than 20% by mass, it is necessary to increase the adhesion amount of the first protective layer in order to obtain a predetermined fluorescent brightening agent, resulting in a decrease in color developability as a heat-sensitive recording material. Sometimes. From such a viewpoint, the content is particularly preferably 30% by mass or more.
The upper limit of the content is preferably 80% by mass or less from the viewpoint of water resistance of the thermosensitive recording material.
The content and content of the fluorescent brightening agent in the first protective layer are determined by peeling the first protective layer from the heat-sensitive recording material and dissolving the first protective layer in a solvent. It can be measured by performing component analysis by HPLC analysis, IR analysis, mass spectrometry, or the like.

-Water-soluble resin-
There is no restriction | limiting in particular as said water-soluble resin, According to the objective, it can select suitably, For example, polyvinyl alcohol and its modified material, starch and its derivative, a cellulose derivative, poly (meth) acrylic acid, and those Alkali salt, poly (meth) acrylamide or alkali salt thereof, (meth) acrylamide copolymer or alkali salt thereof, styrene / maleic anhydride copolymer alkali salt, polyvinylpyrrolidone, polyethyleneimine, sodium alginate, gelatin, casein, etc. Is mentioned. These may be used individually by 1 type and may use 2 or more types together.
An aqueous emulsion resin may be used as the water-soluble resin. Specific examples of the aqueous emulsion resin include acrylic copolymer, acrylic acid copolymer, (meth) acrylic acid ester copolymer, urethane resin, epoxy resin, vinyl acetate (co) polymer, vinylidene chloride. Examples thereof include emulsions such as (co) polymers and vinyl chloride (co) polymers, and latexes such as styrene / butadiene copolymers and styrene / butadiene / acrylic copolymers. These may be used individually by 1 type and may use 2 or more types together.
Among these, polyvinyl alcohol and diacetone modified polyvinyl alcohol are particularly preferable from the viewpoints of barrier properties, head matching properties, and mechanical strength.

-Crosslinking agent-
The crosslinking agent is not particularly limited and may be appropriately selected depending on the intended purpose.For example, a polyvalent amine compound such as ethylenediamine, a polyhydric aldehyde compound such as glyoxal, glutaraldehyde, and dialdehyde, adipic acid dihydrazide, Dihydrazide compounds such as phthalic acid dihydrazide, polyamide epichlorohydrin compounds, water-soluble methylol compounds (urea, melamine, phenol), polyfunctional epoxy compounds, polyvalent metal salts (Al, Ti, Zr, Mg, etc.), titanium lactate, boric acid, etc. Is mentioned. These may be used individually by 1 type and may use 2 or more types together.

  Although there is no restriction | limiting in particular as content rate in the 1st protective layer of the said crosslinking agent, Although it changes also with the modification amount and kind of the functional group of a crosslinking agent, 0.1 mass with respect to 100 mass parts of said binder resin. Part to 100 parts by weight is preferable, and 1 part to 50 parts by weight is more preferable.

-Second protective layer-
The second protective layer contains the water-soluble resin, does not contain the fluorescent whitening agent, and contains a crosslinking agent, an inorganic filler, a lubricant, and the like as necessary.

-Water-soluble resin-
There is no restriction | limiting in particular as said water-soluble resin, According to the objective, it can select suitably, For example, the said water-soluble resin used for a said 1st protective layer is mentioned. However, the water-soluble resin of the second protective layer may be the same as or different from the water-soluble resin used for the first protective layer.
As the water-soluble resin used in the second protective layer, a polyvinyl alcohol-based resin is preferable as in the first protective layer.

-Crosslinking agent-
There is no restriction | limiting in particular as said crosslinking agent, According to the objective, it can select suitably, For example, the said crosslinking agent used for a said 1st protective layer is mentioned. However, as the crosslinking agent for the second protective layer, the same or different one as the crosslinking agent used for the first protective layer may be used.

  Although there is no restriction | limiting in particular as content rate in the 2nd protective layer of the said crosslinking agent, Although it changes also with the modification amount and kind of the functional group of a crosslinking agent, 0.1 mass with respect to 100 mass parts of said binder resin. Part to 100 parts by weight is preferable, and 1 part to 50 parts by weight is more preferable.

--Inorganic filler--
Examples of the inorganic filler include aluminum hydroxide, calcium carbonate calcium carbonate, aluminum oxide, zinc oxide, titanium dioxide, silica, aluminum hydroxide, barium sulfate, talc, kaolin, alumina, and clay. These may be used individually by 1 type and may use 2 or more types together.
Among these, aluminum hydroxide and calcium carbonate are particularly preferable in that they have good wear resistance with respect to the thermal head when printing is performed over a long period of time.

  There is no restriction | limiting in particular as content rate in the 2nd protective layer of the said inorganic filler, Although it can select suitably according to the objective, Although it changes also with kinds etc. of a filler, with respect to 100 mass parts of said binder resin 50 parts by mass to 500 parts by mass is preferable.

--Lubricant--
The lubricant is not particularly limited and may be appropriately selected depending on the purpose.For example, higher fatty acids such as zinc stearate, calcium stearate, montanic ester wax, polyethylene wax, carnauba wax, paraffin wax, ester wax, or the like Examples thereof include various waxes such as metal salts, higher fatty acid amides, higher fatty acid esters, animal waxes, vegetable waxes, mineral waxes, and petroleum waxes. These may be used individually by 1 type and may use 2 or more types together.

The thermosensitive recording material comprises the fluorescent whitening agent in a total amount of the fluorescent whitening agent contained in the first protective layer and the water-soluble resin contained in the first protective layer and the second protective layer. The content of the agent is preferably 55% by mass or less.
When the content exceeds 55% by mass, the water resistance of the heat-sensitive recording material is deteriorated and peeling may occur.
In addition, as a minimum of the said content, 20 mass% or more is preferable from the point of the coloring property fall by the increase in the total adhesion amount of each said protective layer.
Further, the content of the fluorescent whitening agent in the total amount of the fluorescent whitening agent contained in the first protective layer and the water-soluble resin contained in the first protective layer and the second protective layer. Remove the first protective layer and the second protective layer from the heat-sensitive recording material, dissolve each protective layer in a solvent, and then analyze the components by HPLC analysis, IR analysis, mass spectrometry, etc. It can be measured by doing.

  There is no restriction | limiting in particular as a formation method of a said 1st protective layer and a said 2nd protective layer, According to the objective, it can select suitably, For example, a blade coating method, a roll coating method, a wire bar coating method, It can be formed by a die coating method or a curtain coating method.

<Other layers>
-Back layer-
The heat-sensitive recording material preferably has a back layer containing a pigment, a water-soluble resin (binder resin), and a crosslinking agent on the opposite side of the support from the under layer.
The back layer may further contain other components such as a filler, a lubricant, and an antistatic agent.

As the binder resin, either a water-dispersible resin or a water-soluble resin is used, and specific examples include conventionally known water-soluble polymers and aqueous polymer emulsions.
Examples of the water-soluble polymer include polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylate ester copolymer Polymer, acrylamide / acrylic ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, casein, etc. It is done. These may be used individually by 1 type and may use 2 or more types together.

Examples of the aqueous polymer emulsion include latex such as acrylic acid ester copolymer, styrene / butadiene copolymer, styrene / butadiene / acrylic copolymer, vinyl acetate resin, vinyl acetate / acrylic acid copolymer, Examples thereof include emulsions such as styrene / acrylic acid ester copolymers, acrylic acid ester resins, and polyurethane resins. These may be used individually by 1 type and may use 2 or more types together.
As said crosslinking agent, the thing similar to the case of the 2nd protective layer mentioned above can be used.
As the filler, an inorganic filler or an organic filler can be used.
Examples of the inorganic filler include carbonates, silicates, metal oxides, and sulfate compounds.
Examples of the organic filler include silicone resin, cellulose resin, epoxy resin, nylon resin, phenol resin, polyurethane resin, urea resin, melamine resin, polyester resin, polycarbonate resin, styrene resin, acrylic resin, polyethylene resin, formaldehyde Resin, polymethyl methacrylate resin and the like.

There is no restriction | limiting in particular as a formation method of the said back layer, Although it can select suitably according to the objective, The method of apply | coating and forming a back layer coating liquid on a support body is suitable.
The coating method can also be appropriately selected according to the purpose. For example, a blade coating method, a roll coating method, a wire bar coating method, a die coating method, a curtain coating method, or the like can be used.
There is no restriction | limiting in particular in the thickness of the said back layer, Although it can select suitably according to the objective, 0.1 micrometer-10 micrometers are preferable, and 0.5 micrometer-5 micrometers are more preferable.

A configuration example of the heat-sensitive recording material will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a layer structure of a thermosensitive recording material 1 according to one embodiment of the present invention.
The heat-sensitive recording material 1 comprises, on a support 2, an under layer 3 containing a water-soluble resin, a heat-sensitive coloring layer 4, a first protective layer 5 containing a water-soluble resin and a fluorescent whitening agent, and a water-soluble resin. And a second protective layer 6 that does not contain the fluorescent brightening agent.
In the thermosensitive recording material 1, the under layer 3 that suppresses the air permeability to a predetermined value or less is disposed between the support 2 and the thermosensitive coloring layer 4, so that deterioration of the thermosensitive coloring layer 4 due to light is suppressed. In addition, the first protective layer 5 and the second protective layer 6 can further improve the light resistance while maintaining the whiteness of the background.

The layer structure of the heat-sensitive recording material 1 relates to one embodiment, and the present invention is not limited to this embodiment. Another embodiment of the present invention will be described with reference to FIG. FIG. 2 is a schematic sectional view showing a layer structure of a thermosensitive recording material 10 according to another embodiment of the present invention.
The heat-sensitive recording material 10 includes a second under layer 7 containing hollow particles, a first under layer 3 containing a water-soluble resin, a heat-sensitive coloring layer 4, a water-soluble resin, and a fluorescent enhancement material. A first protective layer 5 containing a whitening agent and a second protective layer 6 containing a water-soluble resin and not containing the fluorescent whitening agent are arranged in this order.
In the heat-sensitive recording material 10, in addition to the first under layer 3 containing a water-soluble resin, a second under layer 7 containing hollow particles is laminated. The color development sensitivity of the layer 4 can be improved.

(Image recording method)
In the image recording method of the present invention, an image is recorded on the heat-sensitive recording material of the present invention by any one of a thermal head and a laser image recording means.

  There is no restriction | limiting in a shape, a structure, a magnitude | size, etc. as said thermal head, According to the objective, it can select suitably.

As the laser is not particularly limited and may be appropriately selected depending on the purpose, CO ₂ laser preferably has a wavelength of 9.3Myuemu～10.6Myuemu.
When a CO ₂ laser having a wavelength of 9.3 μm to 10.6 μm is used, a sufficient laser printed image can be obtained without using a photothermal conversion agent such as a phthalocyanine dye.

  Hereinafter, the present invention will be described in detail based on examples and comparative examples. The idea of the present invention is not limited to the examples and comparative examples illustrated here. In the examples, “parts” and “%” represent “parts by mass” and “% by mass” unless otherwise specified.

Example 1
(1) Preparation of under layer coating solution [Part A]
-10% aqueous solution of polyvinyl alcohol-100 parts-Aluminum hydroxide dispersion (solid content 30%)-30 parts-Water-90 parts [Liquid A] was prepared.
(2) Preparation of thermosensitive coloring layer coating solution [B solution]
・ 2-anilino-3-methyl-6- (di-n-butylamino) fluorane: 20 parts ・ 10% aqueous solution of itaconic acid-modified polyvinyl alcohol: 20 parts ・ Water: 60 parts [solution C ]
· 4-hydroxy-4'-allyloxydiphenyl sulfone ··· 20 parts · 10% aqueous solution of itaconic acid-modified polyvinyl alcohol · · 20 parts · Silica (Mizusawa Chemical Co., Ltd., Mizukacil P-527) · · · 10 Part: Water: 50 parts Disperse each of [Liquid B] and [Liquid C] having the above composition using a sand mill so that the average particle diameter of the contained particles is 1.0 μm or less. Liquid [Liquid B] and developer dispersion liquid [Liquid C] were prepared.
Subsequently, [Liquid B] and [Liquid C] were mixed at a ratio of 1: 3, the solid content was adjusted to 25%, and stirred to prepare a thermosensitive coloring layer coating liquid [Liquid D].

(3) Preparation of protective layer forming coating solution [E solution]
-10% aqueous solution of diacetone-modified polyvinyl alcohol-100 parts-10% aqueous solution of adipic acid dihydrazide-20 parts-Aluminum hydroxide dispersion (solid content 30%)-50 parts-Montanate ester wax ( 3.3 parts of solid content) ... 3.3 parts-Brightening agent (stilbene compound, Tinopal UP (solid content 45%), manufactured by CIBA) ... 14.4 parts (6.5 parts of solid content)
-Water ... 90 parts The material of the said composition was mixed and stirred and the 2nd coating liquid for protective layer formation [E liquid] was prepared.

Next, apply [Liquid A] uniformly on the surface of the base paper support (high-quality paper with a basis weight of about 60 g / m ² ) so that the adhesion amount after drying is 0.6 g / m ^2, and then dry. Thus, an under layer was formed. On top of that, [D liquid] was uniformly applied so as to have an adhesion amount after drying of 3.0 g / m ² and dried to form a thermosensitive coloring layer.
On top of that, the protective layer forming coating solution [E solution] was uniformly applied so that the amount of adhesion after drying was 4.0 g / m ² and dried to form a protective layer. Surface treatment was performed with a render to produce the thermosensitive recording material in Example 1. The air permeability of the under layer of the thermosensitive recording material in Example 1 was 150 mL / min.

(Example 2)
In the formation of the under layer in Example 1, the heat-sensitive recording material in Example 2 was prepared in the same manner as in Example 1 except that the condition of the adhesion amount was changed from 0.6 g / m ² to 1.0 g / m ^2. Manufactured. The air permeability of the under layer of the heat-sensitive recording material in Example 2 was 50 mL / min.

(Example 3)
Example 2 is the same as Example 2 except that the first protective layer and the second protective layer are formed as follows using [F solution] and [G solution] instead of [E solution] in Example 2. Thus, the heat-sensitive recording material in Example 3 was produced.
(1) Preparation of first protective layer-forming coating solution [F solution]
・ 10% aqueous solution of diacetone modified polyvinyl alcohol ・ ・ ・ 100 parts ・ 10% aqueous solution of adipic acid dihydrazide ・ ・ ・ 20 parts ・ Fluorescent whitening agent (stilbene compound, Tinopal UP (solid content 45%), manufactured by CIBA) ・..21.1 parts (solid content: 9.5 parts)
-Water: 100 parts A material having the above composition was mixed and stirred to prepare a first protective layer-forming coating solution [F solution].

(2) Preparation of coating solution for forming second protective layer [G solution]
-10% aqueous solution of diacetone-modified polyvinyl alcohol-100 parts-10% aqueous solution of adipic acid dihydrazide-20 parts-Aluminum hydroxide dispersion (solid content 30%)-50 parts-Montanate ester wax ( (Solid content 30%) ... 3.3 parts Water ... 90 parts The materials having the above composition were mixed and stirred to prepare a second protective layer forming coating solution [G solution].
The first protective layer forming coating solution [F solution] and the second protective layer forming coating solution [G solution] on the heat-sensitive color developing layer have an adhesion amount after drying of 1.7 g / m ² , 2 0.0 g / m ² uniformly applied and dried, and after the first protective layer and the second protective layer are formed in this order on the heat-sensitive color developing layer, surface treatment is performed with a super calender. The heat-sensitive recording material of Example 3 was manufactured.

Example 4
A heat-sensitive recording material of Example 4 was produced in the same manner as Example 3 except that [Liquid H] was used instead of [Liquid A] of Example 3 and an under layer was formed as described below. . The air permeability of the under layer of the heat-sensitive recording material of Example 4 was 30 mL / min.
(1) Preparation of under layer coating liquid [H liquid] Materials of the following composition were mixed and stirred and dispersed to prepare an under layer coating liquid [H liquid].
[H liquid]
・ Plastic spherical hollow particles (hollow rate 90%, solid content 33%) 15.15 parts ・ Polyvinyl alcohol 10% aqueous solution 100 parts Water 50 parts Under the surface of the base paper support The undercoat layer was formed by uniformly applying and drying the layer coating solution [Liquid H] so that the adhesion amount after drying was 3.0 g / m ² .

(Example 5)
The second under layer containing hollow particles between the base paper support and the first under layer as described below using the under layer formed on the base paper support in Example 3 as the first under layer. A heat-sensitive recording material of Example 5 was produced in the same manner as in Example 3 except that was formed. The air permeability of the under layer of the heat-sensitive recording material of Example 5 was 10 mL / min.
(1) Preparation of second under layer coating liquid [I liquid] Materials of the following composition were mixed, stirred and dispersed to prepare second under layer coating liquid [I liquid].
[Liquid I]
-Plastic spherical hollow particles (hollow rate 90%, solid content 33%) ... 15.15 parts -Styrene / butadiene copolymer latex (solid content 50%) ... 20 parts -Water ... 115 parts Base paper The second under layer coating liquid [I liquid] is uniformly applied to the surface of the support so that the adhesion amount after drying is 3.0 g / m ² and dried to form the second under layer. Then, the first under layer was formed on the second under layer.

(Comparative Example 1)
In Example 3, a thermosensitive coloring layer was formed on a base paper support without forming an under layer, and a fluorescent brightening agent was added in the preparation of the first protective layer forming coating solution [F solution] Without applying, the first protective layer forming coating solution [F solution] was uniformly applied so that the adhesion amount after drying was 2.0 g / m ^2, and dried to obtain the first protective layer. A thermosensitive recording material of Comparative Example 1 was produced in the same manner as in Example 3 except that was formed. The air permeability of the base paper support of the heat-sensitive recording material of Comparative Example 1 was 500 mL / min.

(Comparative Example 2)
In Example 3, in the preparation of the first protective layer forming coating solution [F solution], the fluorescent whitening agent was not added, and this first protective layer forming coating solution [F solution] was dried. A thermosensitive recording material of Comparative Example 2 was produced in the same manner as in Example 3 except that the amount of adhesion was uniformly applied to be 2.0 g / m ² and dried to form the first protective layer. . The air permeability of the under layer of the heat-sensitive recording material of Comparative Example 2 was 50 mL / min.

(Comparative Example 3)
In Example 3, a thermosensitive recording material of Comparative Example 3 was produced in the same manner as in Example 3 except that the thermosensitive coloring layer was formed on the base paper support without forming an under layer. The air permeability of the base paper support of the heat-sensitive recording material of Comparative Example 3 was 500 mL / min.

(Comparative Example 4)
In the formation of the under layer of Example 3, the heat-sensitive recording material of Comparative Example 4 was prepared in the same manner as in Example 3 except that the condition of the adhesion amount was changed from 1.0 g / m ² to 0.4 g / m ^2. Manufactured. The air permeability of the under layer of the heat-sensitive recording material of Comparative Example 4 was 200 mL / min.

(Comparative Example 5)
In Example 5, the thermal recording of Comparative Example 5 was performed in the same manner as in Example 5 except that the thermosensitive coloring layer was formed without forming the first under layer on the second under layer containing hollow particles. The material was manufactured. The air permeability of the under layer of the heat-sensitive recording material of Comparative Example 5 was 250 mL / min.

  Next, the manufacturing conditions of the heat-sensitive recording materials of Examples 1 to 5 and Comparative Examples 1 to 5 are shown in Tables 1 and 2 below.

* In Table 1, the air permeability of Comparative Examples 1 and 3 represents the air permeability of the base paper support, not the under layer.

<Image recording>
With respect to the heat-sensitive recording materials of Examples 1 to 5 and Comparative Examples 1 to 5, a head printing power of 0.45 W / dot and a line recording time of 20 msec / L were performed using a thermal printing experimental apparatus having a thin film head manufactured by Matsushita Electric Parts Co. Images were printed and recorded at a pulse width of 1.2 msec every 1 msec under conditions of a scanning density of 8 × 385 dots / mm.

For the heat-sensitive recording materials of Example 3 and Comparative Example 3, using a CO ₂ laser marker device (manufactured by SUNX, LP-400 40W machine), a scanning speed of 1,500 mm / s and a setting power of 11.5% The image was printed and recorded.

(Measurement method and evaluation method)
<Measurement method of air permeability>
The air permeability was measured with a BENDTSEN tester manufactured by MESSMER according to ISO 5636 (Bendtsen method).

<Measurement method of light resistance>
Using a light resistance test apparatus (manufactured by ATLAS, SUNTEST CPS +), before and after irradiation with Xe light for 15 hours, the image density of the image recording portion, and the image density of the background portion where no image is recorded Was measured with a Macbeth densitometer (GRETAG MACBETH, DensiEye700). During the measurement with the Macbeth densitometer, the image density of the image recording portion was measured with a black measurement filter, and the image density of the background portion was measured with a yellow measurement filter. The results are shown in Table 3.

<Measurement of background whiteness>
The background whiteness was measured according to ISO 2470 using Elrepho 3000 manufactured by Datacolor.

<Water resistance measurement method and evaluation method>
Each thermosensitive recording material was immersed in water for 30 minutes, and the surface was rubbed 10 times with a finger to observe the presence or absence of peeling, and water resistance was measured and evaluated. The results are shown in Table 3.

From the results of Table 3, the thermal recording materials in Comparative Examples 1 and 2 had a low whiteness value, and were inferior in whiteness as compared with the thermal recording materials in Examples 1 to 5.
In the heat-sensitive recording materials in Comparative Examples 1 to 5, the background image density after irradiation with Xe light for 15 hours is higher than that in the initial state before irradiation with the light. The heat-sensitive recording materials 1 to 5 can suppress a change in the image density of the background portion before and after the light irradiation, and can maintain whiteness.
Therefore, the heat-sensitive recording materials in Examples 1 to 5 have excellent results in both whiteness and light resistance, and can achieve both whiteness and light resistance.
Further, as a result of printing and recording an image with the thermal head and the CO ₂ laser on the heat-sensitive recording material in Example 3, in both cases, excellent whiteness and light resistance can be obtained.

  Since the heat-sensitive recording material of the present invention has excellent whiteness, light resistance and water resistance, for example, POS field such as for fresh foods, lunch boxes and side dishes; copy field for books and documents; communication field such as facsimile; It can be used in various fields such as ticket vending machines, receipts, receipts, etc .;

1,10 Thermal recording material 2 Support 3 Under layer (first under layer)
4 thermosensitive coloring layer 5 first protective layer 6 second protective layer 7 second under layer

Japanese Unexamined Patent Publication No. 62-184880 Japanese Patent No. 3446092 Japanese Patent No. 3463080 Japanese Patent Laid-Open No. 10-44609 Japanese Patent No. 3156401 Japanese Patent Laid-Open No. 06-48038 Japanese Patent No. 3829426 Japanese Patent No. 3635388 JP-A-10-235996 Japanese Patent Laid-Open No. 08-282114 Japanese Patent No. 2936556

Claims (8)

A support, at least one under layer on the support, a thermosensitive coloring layer in contact with the under layer and containing a leuco dye and a developer, and at least one layer containing a water-soluble resin and a fluorescent brightening agent With protective layers in this order,
The heat-sensitive recording material, wherein the under layer includes a water-soluble resin in a layer in contact with the heat-sensitive coloring layer, and the air permeability of the under layer is 150 mL / min or less.   The heat-sensitive recording material according to claim 1, wherein the under layer contains hollow particles.   The heat-sensitive recording material according to claim 1, wherein the content of the water-soluble resin contained in the under layer is 50% by mass to 80% by mass with respect to the total amount of the hollow particles and the water-soluble resin. .   2. The thermal recording according to claim 1, wherein the under layer has a first under layer containing a water-soluble resin and a second under layer containing hollow particles in this order from the surface in contact with the thermosensitive coloring layer to the support side. material.   The protective layer includes a first protective layer containing a water-soluble resin and a fluorescent whitening agent, and a second protective layer containing the water-soluble resin and not containing the fluorescent whitening agent on the first protective layer. The heat-sensitive recording material according to any one of claims 1 to 4.   The heat-sensitive recording material according to any one of claims 1 to 5, wherein the optical brightener is a stilbene compound.   7. An image recording method, wherein an image is recorded on the heat-sensitive recording material according to claim 1 by any one of a thermal head and a laser image recording means. The image recording method according to claim 7, wherein the laser is a CO ₂ laser having a wavelength of 9.3 μm to 10.6 μm.