JP2003182242A - Heat sensitive recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat sensitive recording material, with which a highly sensitive high density is obtained under the condition that a ground white is kept unchanged, which is especially excellent in light resistance and image preservability, has a fitness for inkjetting and favorable thermal head matchability and which develops small head wear and a few head staining. <P>SOLUTION: In the heat sensitive recording material having a heat sensitive recording layer including an electron donative colorless dye and an electron acceptive compound developing color through its reaction with the electron donative colorless dye on a support, 4-hydrobenzene sulfonanilide is employed as the electron acceptive compound, at the same time, the support has a priming layer including an oil absorbent pigment and the heat sensitive layer includes an image stabilizer, which is at least one kind selected from the group consisting of 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane and 1,1,3-tris (2- methyl-4-hydroxy-5-cyclohexylphenyl) butane. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more specifically, it has excellent apparatus suitability without deterioration of apparatus durability such as head wear, and has printing suitability and stability as a recording medium. The present invention relates to a heat-sensitive recording material that is suitable as a plain paper-like recording medium and is suitable for printing suitability, printing suitability, environment suitability, and the like.

[0002]

2. Description of the Related Art Thermal recording technology has historically been used in 1960's.
In the 1980s, NCR developed a dye-based thermal paper using a colorless leuco dye and a phenolic acidic substance, and this system has become the mainstream of the current thermal recording system. After that, a thermal head was developed against the background of semiconductor technology,
Due to significant improvements in performance, downsizing of the device,
It has become possible to reduce the price, and along with this, the quality of the thermal paper (thermal recording material) itself has been improved (higher sensitivity, improved head matching, etc.), and
Thermal recording method is electrostatic recording, inkjet recording, PP
Thermal paper (hereinafter referred to as "thermosensitive recording material") was evaluated as being advantageous in terms of convenience, that is, convenience, low cost, maintenance-free, etc., as compared with each recording method such as C recording. ) Demand has grown dramatically.

However, as thermal recording materials have been used in fax machines and various printers due to their convenience and become familiar to daily life, the drawbacks of thermal recording materials have become well known. That is, for example: -Discoloration due to light-Discoloration when stored under high temperature (such as leaving in an automobile) -Chemicals (plasticizer in plastic film, oils and fats, organic solvent in marker pen, inkjet printer) The recorded image is discolored by ink for printing, etc. ・ Plain paper-like feeling (good stamping suitability such as dryness and no blurring, good readability with a matte recording surface, and writability with pencil etc.) Has been pointed out that there is no such thing as "good", that it is less likely to cause rubbing stains; and so on; hereinafter the same). Therefore, there has been a demand for the development and provision of a heat-sensitive recording material which eliminates the above-mentioned drawbacks of conventional heat-sensitive recording materials and enhances the added value.

In recent years, heat-sensitive recording materials have been used widely because they are generally relatively inexpensive and their recording equipment is compact and maintenance-free. Under such circumstances, sales competition of thermal recording materials has intensified recently, and further higher functionality that can be differentiated from conventional functions, especially color density, background whiteness, sharpness, stability during storage In addition, there is a high demand for a heat-sensitive recording material that has good hue and vividness for a full-color image recorded by an inkjet method, etc., and in order to meet these demands, the color-forming property and storability of the heat-sensitive recording material are high. Studies on various performances such as the above are being conducted earnestly.

The various performances that a thermal recording material should have are:
(1) High sensitivity (high density can be obtained), (2) High whiteness of the background area (non-image area) (low background fog), (3) Image storability after printing Excellent, (4) excellent light resistance, (5) excellent chemical resistance, (6) sharp and high image quality, (7) each hue even when recording a full-color image with an inkjet method. Good and vivid, (8) Good thermal head matching, and good head resistance with little thermal head wear.
(9) Having a plain paper-like feel, (10) having printability capable of being printed on a heat-sensitive recording layer and imprintability without bleeding,
(11) Applicability to high-performance printers such as high-speed printers, (12)
For example, it is required to have environmental suitability. Under the above-mentioned circumstances, it is required to satisfy all of these performances at the same time without impairing any performance.
However, at present, a thermal recording material capable of satisfying all of the above-mentioned various properties at the same time has not yet been provided.

In particular, in recent years, image stability capable of holding a formed image for a long period of time has been required, and it is also applicable to a field where image reliability is required for a long period of time due to the simplicity of the apparatus and recording. Is desired. On the other hand, 2,2-bis (4-hydroxyphenyl) propane (so-called "bisphenol A") has been widely used as an electron-accepting compound that reacts with an electron-donating colorless dye used in a heat-sensitive recording material to develop a color. Although it has been used, satisfactory results have not yet been obtained with this system in terms of sensitivity, background fog, and image storability.

Further, there is a problem in (13) suitability for ink jet as described below. That is, when full-color information is recorded on a heat-sensitive recording material, recording may be performed using an inkjet ink.
When ink-jet recording is performed on the recording surface of a normal thermosensitive recording material using, the hue of the ink cannot be faithfully reproduced and a vivid hue cannot be obtained, or the fading of a recorded image that has already been thermosensitively recorded. Could cause Further, when the above-mentioned ordinary heat-sensitive recording material is placed in contact with the medium recorded by the ink jet printer, the background fog may occur and the recorded image may be discolored.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the various problems in the prior art and achieve the following objects. That is, the present invention can form a high-sensitivity and high-density image while suppressing the fog density in the background part (background fog) (good printability), and light resistance after printing,
A high-performance printer with excellent image storability and chemical resistance, inkjet suitability that does not cause image color fading or bleeding of inkjet images, and image fading caused by inkjet inks, and has high speed and a partial glaze structure. Even when applied to, it is possible to provide a thermal recording material having good thermal head matching properties and less head wear and head stains (good head suitability), and in addition to these, a sharp and high-quality image can be obtained. The obtained image has excellent light resistance, printing and imprinting can be performed on the heat-sensitive recording layer or protective layer without bleeding, and it can be formed at a low cost with a small coating amount (environmental suitability). An object of the present invention is to provide a thermal recording material having a paper-like feeling.

[0009]

Means for Solving the Problems The inventors of the present invention have made the following findings as a result of extensive studies on a technique for simultaneously satisfying various performances that a thermal recording material should have at a high level. . <Higher sensitivity> The following points (1) to (3) are important for higher sensitivity. That is, firstly, (1) it is important to improve the heat transfer from the thermal head to the thermal recording layer. For this purpose, the surface smoothness of the recording surface of the thermal recording material is improved, and the cushion to the recording surface is improved. It is effective to impart sex. Secondly, (2) it is important to effectively utilize the heat transferred from the thermal head, and for this purpose, it is effective to make the support heat insulating and slim the heat-sensitive recording layer. Third, (3) It is important to improve the dissolution rate of the electron-donating colorless dye and the electron-accepting compound with respect to the sensitizer. For this purpose, the solubility is improved, the melt viscosity is reduced, and the material particle size is reduced. Is effective. The details will be described below.

(1) Improving heat transfer from the thermal head to the heat-sensitive recording layer A certain amount of heat is required to develop a color in the heat-sensitive recording layer to a certain density. How efficiently the heat from the head is transferred to the recording layer is important. Here, the thermal conductivity of a solid is significantly higher than that of a gas, and the conduction heat is much higher than the radiation heat. Therefore, it is effective to increase the contact rate between the surface of the thermal recording layer (hereinafter, also referred to as “recording surface”) and the thermal head during printing, and the heat from the thermal head is transferred to the thermal recording layer. It can be transmitted efficiently. In order to increase the contact rate between the recording surface and the thermal head, the physical properties required for the thermal recording material are:
It is particularly effective to enhance the smoothness of the recording surface in advance and enhance the cushioning property of the heat-sensitive recording material.

In order to improve the smoothness of the recording surface, it is effective to improve the flatness of the support. Specifically, it is desirable to use a base paper having a high flatness, and to provide an undercoat layer containing an oil-absorbing pigment as a main component to fill the irregularities of the pulp. In addition, it is also effective to apply a thermal recording layer or a supercalendering process after coating and drying the heat-sensitive recording layer to enhance smoothness. In addition, the cushioning property of the heat-sensitive recording material is enhanced (giving cushioning property).
Is effective based on the following findings. That is, when thermally printing on a thermal recording material using a thermal head, an appropriate pressure is applied using a platen roll, but in order to increase the contact rate between the thermal head and the recording surface under pressure, the thermal recording It is good if the material is easily deformed. Therefore,
As a specific means for imparting cushioning properties, it is effective to provide an undercoat layer containing an oil-absorbing pigment as a main component or to contain a pigment having a high oil absorption (for example, amorphous silica) in the heat-sensitive recording layer. . The concept of giving the cushioning property is particularly effective for high sensitivity when recording is performed using a thermal head having a partial glaze structure. here,
The partial glaze structure refers to a structure in which the cross-sectional shape of the glaze layer of the heating element portion is convex (mountain-shaped) on the substrate.

(2) Effective Utilization of Heat Transferred from Thermal Head In order to effectively utilize the heat transferred from the thermal head, it is effective to impart a heat insulating property to the support. It is effective to provide voids in the support as much as possible. In the case of a heat-sensitive recording material, for example, an undercoat layer containing a pigment having a high oil absorption is provided, the amount of binder used in the undercoat layer is reduced as much as possible, and hollow particles are contained in the undercoat layer. Further, in order to effectively use heat, it is also effective to slim the heat-sensitive recording layer. Considering that the heat capacity of the heat-sensitive recording layer contributes to the sensitivity, the heat-sensitive recording layer contains many components that do not contribute to color development, and the heat capacity is wasted. Examples of the component include release agents and waxes that suppress scratches between the thermal head and the recording layer, oil-absorbing pigments that absorb molten components, binders that impart dispersion of the material and coating strength, and the like. To do. The amount of heat consumed by these amounts to about 20 to 30%.
An improvement in sensitivity of 5% can be expected.

According to the results of studies by the present inventors, the sensitivity can be improved by reducing the content of the pigment and the binder in the recording layer. Since the sensitivity can be increased more than expected by reducing the amount of binder, contributions other than heat capacity are possible, but the cause is unknown. However, if the content of the binder is simply reduced, the head matching property of the thermal head and the coating strength will deteriorate, so the material should be distributed as efficiently as possible, that is, the necessary components should be used in the minimum amount in the required layers. Is important.

(3) Improvement of dissolution rate of electron-donating colorless dye and electron-accepting compound in sensitizer At the initial stage of technological development of a heat-sensitive recording material, the sensitizer is an electron-donating colorless dye and an electron-accepting compound. It has been selected as a melting point depressant for organic compounds for the purpose of developing color at lower temperatures. However, with this idea, there is a limit to increase the sensitivity while maintaining the color development start temperature, and it was difficult to achieve both background fog and sensitivity. Therefore, the present inventors regard the sensitizer as a material for dissolving an electron-donating colorless dye or an electron-accepting compound, and do not lower the eutectic point more than necessary, that is, keep the background fog low. As a result of investigating a sensitizer that realizes high sensitivity, it was found that the faster diffusion of an electron-donating colorless dye or an electron-accepting compound in a molten sensitizer is advantageous for higher sensitivity. I got the knowledge of. That is, it is preferable to select a sensitizer having not only high solubility but also low melt viscosity and to reduce the dispersed particle size of the electron-donating colorless dye or the electron-accepting compound, which are effective in increasing the sensitivity. If the dispersed particle size is too small, the background fog will worsen, so it is important to set it in an appropriate range.

<Providing Matching Property with Thermal Head and Head Durability> In the heat-sensitive recording material, the recording surface (the surface of the heat-sensitive recording layer) is brought into direct contact with the thermal head, which is a heating element, and the surface is rubbed to print ( Printed). Therefore, the melted component in the recording layer may adhere to the head and be deposited as dirt. Further, the life of the head itself may be shortened due to physical wear or corrosion of the surface of the thermal head. Therefore, it is desirable to apply the following means. That is, 1) From the viewpoint of preventing head contamination, it is important to absorb and retain substances such as dyes, developers and sensitizers, which are melted by heat, on the material side. It is effective to use a pigment having a high property or to provide an undercoat layer using a pigment having a high oil absorption property. 2) Further, it is important to suppress the content of ions (Na ⁺ , K ^+, etc.), which are likely to cause head corrosion, in the constituents of the recording material. 3) From the viewpoint of reducing physical wear as much as possible, it is important to consider the hardness, shape, particle size, etc. of the pigment.

<Compatibility of image storability (and chemical resistance) and background fog> In a color image, a chemical reaction caused by contact between a leuco dye and a color developer, which is a coloring principle of a heat-sensitive recording material, is melted by heat. Since it is a reaction, a reverse reaction easily occurs due to chemicals such as oils and fats and plasticizers. Therefore, hand creams and other cosmetics, or products with fats and oils on hands, plastic products containing plasticizers, products containing organic solvents, leather products (eraser, vinyl chloride desk mats and food packaging films, marker pens, etc. , Inkjet ink, wallet, commuter pass, etc.) Color images disappear in everyday life when placed in contact with
Problems tend to occur in terms of image storability and chemical resistance.

Various studies have been conducted in order to overcome the phenomenon (image disappearance, fading) resulting from the above coloring principle, for example, forming a protective layer on the recording layer for the purpose of physical shielding. The so-called overcoat type, the addition of a crosslinkable additive to the recording layer, and the like have been performed. However, even if a protective layer is provided, it is unavoidable that the oil and plasticizer will gradually permeate and the fading will progress over time, and as a result, it will not be possible to use the product for a short period of time, such as a measurement label attached to fresh food in supermarkets. There is a problem that it is limited to applications, it takes a considerable time from coloring to the effect even if a cross-linking substance is added, etc. Didn't.

Therefore, as a result of the investigations by the present inventors regarding the improvement of the storage stability, a specific electron-accepting compound is useful for improving the image storage stability, and the background fog can be compatible with it. Further, it was found that the background fog can be further improved by combining a specific sensitizer and an electron-donating colorless dye. Further, they have also found that by combining a specific image stabilizer, the image storability and the light resistance can be further improved without substantially deteriorating the background fog. According to these findings, it is possible to impart a high level of not only image storability but also stampability and handleability, which is difficult with the conventional storability imparting technology that relies on the overcoat. As described above, it is possible to achieve both printing suitability and image storability.

<Improvement of light resistance> Depending on the application, a heat-sensitive recording material having excellent light resistance may be required. However, since the leuco dye carrying an image is easily decomposed by ultraviolet rays or the like, long-time natural light is required. There was a problem in terms of light resistance, such as fading even when exposed to light. In order to improve the light resistance, it is important to provide a means for preventing the decomposition of the leuco dye by light. For this purpose, it is particularly effective to add an ultraviolet absorber (image stabilizer) for preventing ultraviolet rays, which is a high energy, to the thermosensitive recording layer or the protective layer, especially before ultraviolet rays reach the thermosensitive recording layer. From the viewpoint of efficiently blocking, it is more effective to wrap the liquid ultraviolet absorber in microcapsules and to contain it in the protective layer.

<Providing printability> Offset printing may be performed on the recording surface (surface of the thermosensitive recording layer) of the thermosensitive recording material depending on the application. For such an application, it is necessary to have a surface strength capable of withstanding a printing speed of 100 m / min of a rotary foam printing machine and a dampening water absorption property, and to prevent the formation of pigments or binders in the heat-sensitive recording layer. It is important to optimize the compounding ratio. For this purpose, an oil absorbing pigment such as calcium carbonate is preferred as the pigment, and polyvinyl alcohol (PVA) is preferred as the binder, and sulfo-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol are particularly preferred.

<Giving Plain Paper-Like Feeling> As a result of widespread use of heat-sensitive recording materials as recording paper for facsimiles in offices and homes, and for various printers,
I feel a sense of incongruity compared to the paper around me (PPC paper, notebook, report paper, etc.), that is, the surface is slippery, the writing is bad, and it does not rub when held by a thin hand. The point has come to be actively made. These are one of the reasons why office facsimiles have recently moved to the PPC type, which uses plain paper. From this point of view, the base paper as a support is made thicker to make it stronger, and by providing a protective layer, it gives a low gloss surface property, writability, and imprintability, etc. It is important to get closer to.

Here, the heat-sensitive recording material having a plain paper-like feeling eliminates the disadvantages of the conventional heat-sensitive paper as a processed paper, has a matte surface, has no slimy feel to the touch, and is less likely to be rubbed and smeared. It is considered that the recording image has a performance such as fading of the recorded image, and so far, it has been proposed that a protective layer is provided on the recording layer for the purpose of making it like plain paper. However, the conventional protective layer has not been given much attention to touchability, appearance (matte tone), writability, etc., so that the suitability for printing has not been taken into consideration. However, in view of the customs of Japan, it was considered that imprinting aptitude (no bleeding, good drying of stamps, etc.) is particularly important, and an improvement of the protective layer for a thermal recording material having plain paper-like properties was examined. .

As a result, it was found that the following pigments and binders are useful for the protective layer in order to obtain a plain-paper-like feel including imprintability. As the pigment, a pigment having an appropriate particle size and an oil absorption amount is preferable in order to give importance to imprintability, appearance (matte tone) and writability. If the particle size is too large, the image quality may deteriorate, and if it is too small, the writability and appearance may deteriorate. On the other hand, if the oil absorption is too large, the opacity of the protective layer increases and the recording density decreases, and if the oil absorption is too small, the imprintability (dryness) tends to deteriorate. As the binder,
A mixture of PVA and starch in an appropriate ratio is particularly preferable for the purpose of preventing imprinting suitability (bleeding). The PVA is a so-called fully saponified type (saponification degree of about 93% or more) from the viewpoint of imparting imprintability (dryness).
Are preferred.

<Higher Sensitivity and Head Matching Property in Combination with Device> In recent years, heat-sensitive recording materials have been adopted in many fields and applications, and heat-sensitive recording such as downsizing, low running cost and maintenance-free is a background. Not only was there an advantage of the system, but there have also been improvements in technology for both printers (hardware) and recording paper (media).
On the hardware side, for example, the recording speed is 10 inches (about 25 cm) per second, and the recording width is the maximum A0 size (about 90 cm).
0 mm), resolution is 600 dpi (24 dots / mm)
As such, high-performance printers that are not inferior to conventional dot printers and laser printers have emerged, and therefore,
It is important to combine each technology according to the application and to configure it so as to have an optimum design and control method.

That is, as the high-performance printer, a high-speed printer having a recording speed of 10 cm / sec or more, a printer having a thermal head having a partial glaze structure, and the like are preferable. In a high-speed printer with a speed of 10 cm / sec or more, the sensitivity of the conventional thermal recording material may be insufficient, and in a printer equipped with a thermal head having a partial glaze structure, head contamination tends to occur.

Therefore, as a result of studying design optimization on the side of the heat-sensitive recording material, when a specific developer (electron-accepting compound) is selected and used, a high-speed printer, a recording speed especially at a recording speed of 10 cm / sec or more, Even when combined with a printer equipped with a thermal head having a glaze structure, it has been found that high sensitivity and good head matching can be achieved while satisfying the performance required for the above-mentioned thermal recording material at a high level. Obtained.

<Improvement of image quality> In some hardware (apparatus) using the heat-sensitive recording material, the recording image quality may be important, such as in a facsimile when receiving a photograph. In order to improve the recording image quality, it is effective to improve the image quality by applying an undercoat layer mainly containing an oil-absorbing pigment, especially by applying the undercoat layer by curtain coating method or blade coating method (particularly blade coating method). We obtained the knowledge that

<Reduction of environmental load> In recent years, there has been a social demand for a system having a smaller environmental load, and the field of heat-sensitive recording materials is no exception. In order to reduce the environmental load, it is important to meet the required performance with less material usage and less energy usage. To this end, it is effective to apply a thermal recording layer or the like by the curtain coating method from the viewpoint of improving the color density, and to simultaneously coat a plurality of layers is an energy saving method for drying and handling. We have found that it is effective in reducing consumption. In other words, if the color density is the same, it is possible to obtain a material with a smaller amount of material than before and with low energy.

The present invention is based on the above findings,
The specific means for solving the above problems are as follows. <1> In a heat-sensitive recording material having a heat-sensitive recording layer containing, on a support, an electron-donating colorless dye and an electron-accepting compound that reacts with the electron-donating colorless dye to develop a color, the electron-accepting compound is , Which is a compound represented by the following general formula (1) (excluding 2,4-bis (phenylsulfonyl) phenol), and the density residual ratio of the printing portion after irradiation with a fluorescent lamp of 500,000 Lux · h Of 80% or more is a heat-sensitive recording material.

General formula (1): R ¹ -Ph-SO ₂ R ^{2 In the} above formula, R ¹ represents a hydroxyl group or an alkyl group. R ² is
-Ph, -NH-Ph, -Ph- OR 3, -NH-CO
Represents —NH—Ph, and R ³ represents an alkyl group. Ph
Represents a phenyl group, which may be substituted with a substituent containing —SO ₂ R ² .

According to the heat-sensitive recording material described in the above item <1>, since the electron-accepting compound represented by the general formula (1) is used as one of the color-developing components, the sensitivity is improved while keeping the background fog low. It is possible to improve the long-term storability of the formed image (image storability; hereinafter the same), chemical resistance, and head matching property of the thermal head. Moreover, after thermal printing, the density residual ratio of the printed area after irradiation with a fluorescent lamp of 500,000 Lux · h is 80% or more, so that a robust image can be obtained and light resistance is excellent.

<2> The thermosensitive recording layer is coated, and the dry coating amount after coating is less than 6 g / cm ² <1>
The heat-sensitive recording material described in 1. According to the heat-sensitive recording material as described in <2> above, the heat-sensitive recording layer is formed with a coating amount of the coating liquid for forming the layer of less than 6 g / cm ² .
Since a thin film is formed, the drying load is small, the whiteness of the background and the image storability are not impaired, and a plain paper-like feeling can be imparted.

<3> The thermosensitive recording material according to <1> or <2>, wherein the compound represented by the general formula (1) is 4-hydroxybenzenesulfonanilide. According to the heat-sensitive recording material as described in <3> above, since it contains 4-hydroxybenzenesulfonanilide as an electron-accepting compound, it is possible to more effectively improve the sensitivity, improve the image storability, and improve the head matching property. Also, there is no increase in the background fog in the background part (fogging density in the background part).

<4> The heat-sensitive recording layer contains an image stabilizer,
The image stabilizer is 1,1,3-tris (2-methyl-4).
-Hydroxy-5-tert-butylphenyl) butane and at least one of 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane <1> to <3> The heat-sensitive recording material described in 1. According to the heat-sensitive recording material as described in <4> above, since the heat-sensitive recording layer contains a specific image stabilizer, the transfer of the color reaction (forward reaction) to the reverse reaction is suppressed, and the image storability is further improved. be able to. At the same time, it contributes to the improvement of light resistance.

<5> The heat-sensitive recording layer contains an inorganic pigment, and the inorganic pigment is at least one selected from calcite (light) calcium carbonate, amorphous silica, and aluminum hydroxide. To <4>, which is the heat-sensitive recording material. According to the heat-sensitive recording material as described in <5> above, since the heat-sensitive recording layer contains a specific inorganic pigment, it is possible to further improve the head matching property with the thermal head in contact, and at the same time, impart the printing suitability. can do.

<6> The thermosensitive recording layer contains an adhesive, and the adhesive is at least one selected from sulfo-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol. The heat-sensitive recording material according to any one of 5>. According to the heat-sensitive recording material described in <6> above, since the heat-sensitive recording layer contains a specific water-soluble resin as an adhesive, it is possible to achieve both higher sensitivity at a higher level and further reduction of background fog. be able to. Also, with this configuration, printability can be imparted at the same time. Furthermore,
Water resistance can also be imparted by combining with a crosslinking agent.

<7> The heat-sensitive recording material according to any one of <1> to <6>, wherein the support contains waste paper pulp. According to the heat-sensitive recording material as described in <7> above, since waste paper pulp is used for the support, resource reuse and resource saving can be realized.

<8> A thermosensitive recording layer having a protective layer on the thermosensitive recording layer, the protective layer containing at least one inorganic pigment selected from aluminum hydroxide, kaolin and amorphous silica, and a water-soluble polymer. The heat-sensitive recording material according to any one of the above items <1> to <7>. According to the heat-sensitive recording material as described in <8> above, since a protective layer containing a specific inorganic pigment is provided on the heat-sensitive recording layer, the oil-absorbing property and the like can improve the storability, and at the same time, the handleability and the aptitude for printing. Can also be realized (giving a feeling of plain paper).

<9> The above <1> to <8, wherein the total ion concentration of Na ⁺ ions and K ⁺ ions is 1500 ppm or less.
> The heat-sensitive recording material according to any one of the above items. <9>
According to the heat-sensitive recording material described in (1), as a result of selectively using a material having a low ion content, the total ion concentration in the whole of the support, layers, etc. constituting the heat-sensitive recording material can be suppressed to be low, so that the ions attached to the head The amount can be suppressed, and the corrosion resistance (durability) of the thermal head can be improved.

<10> The thermosensitive recording material according to any one of <1> to <9>, wherein the contact angle is 20 ° or more after 0.1 second has passed after dropping distilled water on the surface of the thermosensitive recording layer. Is. According to the heat-sensitive recording material as described in <10> above, since the contact angle of the surface of the heat-sensitive recording layer is 20 ° or more, ink bleeding at the time of inkjet recording or marking is effectively suppressed, and inkjet suitability is imparted. It is possible to improve the suitability for printing.

<11> The formed image after printing is printed at a temperature of 60.
The heat-sensitive recording material according to any one of <1> to <10>, which has a density residual ratio of 65% or more in the formed image after being left for 24 hours under an environmental condition of ° C and a relative humidity of 20%. . According to the heat-sensitive recording material as described in <11> above, since the formed image can be maintained at a high density for a long period of time, image reliability can be maintained for a long period of time such as storing important documents, advance tickets, receipts, cash vouchers, etc. It can be applied in the required fields.

<12> The heat-sensitive recording layer contains a sensitizer, and the sensitizer is 2-benzyloxynaphthalene, dimethylbenzyl oxalate, m-terphenyl, ethylene glycol tolyl ether, p-benzyl biphenyl, 1, Two
-The thermosensitive recording material according to any one of <1> to <11>, which is at least one selected from diphenoxymethylbenzene, 1,2-diphenoxyethane, and diphenylsulfone. According to the heat-sensitive recording material described in the above <12>, since the heat-sensitive recording layer contains a specific sensitizer, the dissolution viscosity can be lowered to allow the color-forming component to be well diffused, and the background fog is not deteriorated. The sensitivity can be effectively increased.

<13> The content of the sensitizer is 75 to 2 with respect to 100 parts by mass of the compound represented by the general formula (1).
The heat-sensitive recording material as described in <12> above, which is 100 parts by mass. According to the heat-sensitive recording material as described in <13> above, since the sensitizer is contained in a range suitable for the amount of the electron-accepting compound, it does not impair other performances and is effectively high. It is possible to increase sensitivity.

<14> The electron-donating colorless dye is 2-anilino-3-methyl-6-diethylaminofluorane,
2-anilino-3-methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6- (N-ethyl-
N-isoamylamino) fluorane, 2-anilino-3
-Methyl-6- (N-ethyl-N-propylamino) fluorane, 2-anilino-3-methyl-6-di-n-amylaminofluorane, and 2-anilino-3-methyl-6- (N- <Ethyl-N-p-tolylamino) fluorane, which is at least one selected from the above <1> to <
13> The heat-sensitive recording material according to any one of 13>.

According to the heat-sensitive recording material described in the above <14>, since the heat-sensitive recording layer contains a specific electron-donating colorless dye, the sensitivity is improved at a higher level, the background fog is reduced, and the storage stability is improved. Can be satisfied at the same time.

<15> At least one layer on the support is coated and formed by a curtain coating method.
> The heat-sensitive recording material according to any one of the above items. <15
According to the heat-sensitive recording material described in <1>, at least one of the plurality of layers, particularly the heat-sensitive recording layer, is applied by the curtain coating method, so that the constituent components can be concentrated on the recording surface, and less material is used. The color density can be increased by the amount, and the image quality (image quality) can be improved. Further, when a plurality of layers are simultaneously coated by the curtain coating method, it is possible to reduce energy consumption during manufacturing.

[0047]

BEST MODE FOR CARRYING OUT THE INVENTION In the heat-sensitive recording material of the present invention
Combines an electron-donating colorless dye and an electron-accepting compound
And a thermosensitive recording layer of a coloring system
As a mixture, R ¹-Ph-SO₂R²The compound represented by
Included and heat-printed in the printing section
The concentration residual rate after Lux · h irradiation is set to 80% or more. Since
The thermal recording material of the present invention will be described in detail below.

The heat-sensitive recording material of the present invention has one or more heat-sensitive recording layers on the support, and preferably has a protective layer. Moreover, you may have other layers, such as an intermediate | middle layer as needed. <Heat-sensitive recording layer> The heat-sensitive recording layer contains at least an electron-donating colorless dye and an electron-accepting compound that reacts with the electron-donating colorless dye to develop a color, and is preferably an image stabilizer (UV inhibitor). ), An inorganic pigment, an adhesive, a sensitizer, and optionally other components.

-Electron-donating colorless dye-The heat-sensitive recording layer according to the invention contains at least one electron-donating colorless dye as a color-forming component. The electron-donating colorless dye can be appropriately selected from conventionally known ones, for example, 2-anilino-3-methyl-6-diethylaminofluorane and 2-anilino-3-.
Methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6- (N-ethyl-N-isoamylamino) fluorane, 2-anilino-3-methyl-6- (N
-Ethyl-N-propylamino) fluorane, 2-anilino-3-methyl-6-di-n-amylaminofluorane, and 2-anilino-3-methyl-6- (N-ethyl-Np-tolylamino) ) Fluoran, 2-anilino-
3-Methyl-6-N-ethyl-N-sec-butylaminofluorane, 3-di (n-pentylamino) -6-methyl-7-anilinofluorane, 3- (N-isoamyl-N-ethyl) Amino) -6-methyl-7-anilinofluorane, 3- (Nn-hexyl-N-ethylamino)
-6-Methyl-7-anilinofluorane, 3- [N-
(3-Ethoxypropyl) -N-ethylamino] -6-
Methyl-7-anilinofluorane, 3-di (n-butylamino) -7- (2-chloroanilino) fluorane, 3
-Diethylamino-7- (2-chloroanilino) fluorane, 3- (N-cyclohexyl-N-methylamino)
-6-methyl-7-anilinofluorane and the like can be mentioned.

Among the above, 2-anilino-3-methyl-6-diethylaminofluorane and 2-anilino-3-
Methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6- (N-ethyl-N-isoamylamino) fluorane, 2-anilino-3-methyl-6- (N
-Ethyl-N-propylamino) fluorane, 2-anilino-3-methyl-6-di-n-amylaminofluorane, and 2-anilino-3-methyl-6- (N-ethyl-Np-tolylamino) ) It is particularly preferable to contain at least one selected from the group consisting of fluoran. Further, the electron-donating colorless dye may be used singly in a single heat-sensitive recording layer, or may be used in combination of two or more kinds.

By containing at least one selected from the above group as an electron-donating colorless dye, in particular, the color density is increased while the background fog is kept low, and the image storability of the image area formed at the same time is also improved. It can be further improved.

In preparing a coating solution for forming a heat-sensitive recording layer (hereinafter sometimes referred to as "coating solution for heat-sensitive recording layer"), the particle diameter of the electron-donating colorless dye is a volume average particle diameter. 1.0 μm or less is preferable, and 0.4 to 0.7
μm is more preferable. If the volume average particle size exceeds 1.0 μm, the thermal sensitivity may decrease, and if it is less than 0.4 μm, background fog may worsen. The volume average particle diameter is a laser diffraction type particle size distribution measuring device (for example,
It can be easily measured by LA500 (manufactured by Horiba Ltd.) or the like.

[0053] The coating amount of the electron-donating colorless dye is preferably from 0.1 to 1.0 g / m ^2, in terms of color density and background fogging, and more preferably 0.2-0.5 g / m ² .

—Electron-Accepting Compound— In the heat-sensitive recording layer according to the present invention, a compound represented by the following general formula (1) is used as an electron-accepting compound that reacts with the electron-donating colorless dye under heat to develop a color. Containing at least one of By containing the compound as an electron-accepting compound, it is possible to increase the sensitivity while keeping the background fog low, and to maintain the formed image for a long time (image storability), chemical resistance, ink jet suitability and thermal head. The head matching property can be improved at the same time.

General formula (1): R ¹ -Ph-SO ₂ R ^{2 In the} above formula, R ¹ represents a hydroxyl group or an alkyl group. R ² is
-Ph, -NH-Ph, -Ph- OR 3, -NH-CO
Represents —NH—Ph, and R ³ represents an alkyl group. Ph
Represents a phenyl group, which may be substituted with a substituent containing —SO ₂ R ² . However, 2,4-bis (phenylsulfonyl) phenol is not included.

The alkyl group represented by R ¹ is
An alkyl group having 1 to 3 carbon atoms is preferable, and a methyl group, an ethyl group, an isopropyl group and the like are preferable. Among them, as R ¹ , a hydroxyl group is particularly preferable.

R ³ represents an alkyl group, and the alkyl group is preferably an alkyl group having 1 to 4 carbon atoms,
An isopropyl group and the like are particularly suitable. Further, Ph can be a substituted phenyl group the phenyl group is substituted with "substituent comprising -SO ₂ R ^2", R ² of said substituents are further substituted by a methyl group, a halogen atom, etc. May be. As the _{substituent, -CH 2 -C 6 H 5 -NHCONH} -SO 2
_{-C 6 H 5, -SO 2 -C} 6 H 4 -CH 3, -SO 2 -C 6 H 4
-Cl, etc. are mentioned. Above all, as R ² ,
-NH-Ph is preferred, -NH-C ₆ H ₅ are especially preferred.

Preferred specific examples of the compound represented by the general formula (1) include 4-hydroxybenzenesulfonanilide (= p-N-phenylsulfamoylphenol) and p-N- (2-chlorophenyl) sulfin. Famoylphenol, p-N-3-tolylsulfamoylphenol, p-N-2-tolylsulfamoylphenol,
p-N- (3-methoxyphenyl) sulfamoylphenol, p-N- (3-hydroxyphenyl) sulfamoylphenol, p-N- (4-hydroxyphenyl) sulfamoylphenol, 2-chloro-4 -N-
Phenylsulfamoylphenol, 2-chloro-4-
N- (3-hydroxyphenyl) sulfamoylphenol, 4'-hydroxy-p-toluenesulfoneanilide, 4,4'-bis (p-toluenesulfonylaminocarbonylamino) diphenylmethane (= BTUM), 4
-Hydroxy-4'-isopropoxydiphenyl sulfone, and the like. However, the present invention is not limited to these.

Among the electron-accepting compounds represented by the general formula (1), 4-hydroxybenzenesulfonanilide is most preferable from the viewpoint of the balance between image storability and background fog.

The content of the electron-accepting compound in the single heat-sensitive recording layer is preferably 50 to 400% by mass, and 100 to 30% by mass based on the mass of the electron-donating colorless dye.
0 mass% is more preferable.

With the electron-accepting compound represented by the general formula (1), the effects of the present invention (in particular, reduction of background fog,
Other publicly known electron-accepting compounds may be used in combination within the range of not increasing the sensitivity and improving the image storability, chemical resistance, and head matching property. The known electron-accepting compound can be appropriately selected and used,
In particular, a phenolic compound, or a salicylic acid derivative and a polyvalent metal salt thereof are preferable from the viewpoint of suppressing background fog.

Examples of the phenolic compound include 2,2'-bis (4-hydroxyphenol) propane (bisphenol A), 4-t-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, 1,1. '-Bis (4-hydroxyphenyl) cyclohexane, 1,1'-bis (3-chloro-4-hydroxyphenyl) cyclohexane, 1,1'-bis (3
-Chloro-4-hydroxyphenyl) -2-ethylbutane, 4,4'-sec-isooctylidene diphenol, 4,4'-sec-butylylene diphenol, 4-
tert-octylphenol, 4-p-methylphenylphenol, 4,4'-methylcyclohexylidenephenol, 4,4'-isopentylidenephenol, 4
-Hydroxy-4-isopropyloxydiphenyl sulfone, benzyl p-hydroxybenzoate, and the like.

Examples of the salicylic acid derivative include:
4-pentadecylsalicylic acid, 3-5-di (α-methylbenzyl) salicylic acid, 3,5-di (tert-octyl) salicylic acid, 5-octadecylsalicylic acid, 5-α
-(P-α-methylbenzylphenyl) ethylsalicylic acid, 3-α-methylbenzyl-5-tert-octylsalicylic acid, 5-tetradecylsalicylic acid, 4-hexyloxysalicylic acid, 4-cyclohexyloxysalicylic acid, 4-decyloxysalicylic acid, 4-dodecyloxysalicylic acid, 4-pentadecyloxysalicylic acid, 4
-Octadecyloxysalicylic acid and the like, and zinc, aluminum, calcium, copper and lead salts thereof.

When the known electron-accepting compound is used in combination, the content of the electron-accepting compound represented by the general formula (1) is as follows, based on the total mass of the electron-accepting compound.
50 mass% or more is preferable, and 70 mass% or more is particularly preferable.

When preparing a coating liquid for forming a heat-sensitive recording layer,
The particle size of the electron-accepting compound is preferably 1.0 μm or less in volume average particle size, and more preferably 0.4 to 0.7 μm. When the volume average particle diameter exceeds 1.0 μm,
The thermal sensitivity may decrease. If it is less than 0.4 μm, the background fog may worsen. The volume average particle size is also measured by a laser diffraction type particle size distribution measuring device (for example, LA50
0 (manufactured by Horiba Ltd.) and the like can be easily measured.

—Sensitizer— The heat-sensitive recording layer according to the invention preferably contains a sensitizer. In particular, in that the sensitivity can be greatly improved, 2
-Benzyloxynaphthalene, dimethylbenzyl oxalate, m-terphenyl, ethylene glycol tolyl ether, p-benzyl biphenyl, 1,2-diphenoxymethylbenzene, 1,2-diphenoxyethane, and diphenyl sulfone (hereinafter , Sometimes referred to as "sensitizer according to the present invention").

The total content of the selected sensitizers in the heat-sensitive recording layer is the electron-accepting compound (preferably 4-hydroxybenzenesulfonanilide) 10
75 to 200 parts by mass is preferable with respect to 0 parts by mass, and 1
More preferably, it is from 00 to 150 parts by mass. When the content is within the above range, the effect of improving the sensitivity is large and the image storability can be improved.

In addition to the sensitizer selected from the above group, other sensitizers appropriately selected from conventionally known ones may be used in combination as long as the effects of the present invention are not impaired. When the other sensitizer is used in combination, the amount of the sensitizer selected from the group is preferably 50% by mass or more, and more preferably 70% by mass or more of the total amount of the sensitizer contained in the layer. preferable.

Examples of the other sensitizers include aliphatic monoamide, aliphatic bisamide, stearyl urea,
Di (2-methylphenoxy) ethane, di (2-methoxyphenoxy) ethane, β-naphthol- (p-methylbenzyl) ether, α-naphthylbenzyl ether,
1,4-butanediol-p-methylphenyl ether, 1,4-butanediol-p-isopropylphenyl ether, 1,4-butanediol-p-tert-
Octyl phenyl ether, 1-phenoxy-2- (4
-Ethylphenoxy) ethane, 1-phenoxy-2-
(Chlorophenoxy) ethane, 1,4-butanediol phenyl ether, diethylene glycol bis (4-methoxyphenyl) ether, 1,4-bis (phenoxymethyl) benzene and the like can be mentioned.

-Image Stabilizer (Ultraviolet Absorber) -It is preferable that the heat-sensitive recording layer according to the present invention contains an image stabilizer (including an ultraviolet absorber). The UV absorber may be microencapsulated. By containing the image stabilizer, the storability of the formed color image (image storability) can be further improved.

As the image stabilizer, for example, a phenol compound, particularly a hindered phenol compound is effective, and for example, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane. ,
1,1,3-tris (2-methyl-4-hydroxy-5)
-Cyclohexylphenyl) butane, 1,1,3-tris (2-ethyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (3,5-di-
tert-butyl-4-hydroxyphenyl) butane,
1,1,3-tris (2-methyl-4-hydroxy-5)
-Tert-butylphenyl) propane, 2,2'-methylene-bis (6-tert-butyl-4-methylphenol), 2,2'-methylene-bis (6-tert-
Butyl-4-ethylphenol), 4,4'-butylidene-bis (6-tert-butyl-3-methylphenol), 4,4'-thio-bis- (3-methyl-6-te).
(rt-butylphenol) and the like. The image stabilizers may be used alone or in combination of two or more.

Among others, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexyl) Phenyl) butane is preferred.

The total content of the image stabilizer in the single heat-sensitive recording layer is from the viewpoint of suppressing the background fog and effectively improving the image storability.
10 to 100 parts by mass is preferable with respect to 0 parts by mass, and 2
0 to 60 parts by mass is more preferable. Further, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane and / or 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) When the above-mentioned image stabilizer other than these is used in combination with butane, in the single heat-sensitive recording layer,
1,3-tris (2-methyl-4-hydroxy-5-t
ert-butylphenyl) butane and / or 1,1,3
The content of -tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane is preferably 50% by mass or more, and more preferably 70% by mass or more, based on the total mass of the image stabilizer.

Examples of the ultraviolet absorber include the following ultraviolet absorbers.

[Chemical 1]

The content of the ultraviolet absorber in the single heat-sensitive recording layer is from the viewpoint of effectively improving the image storability, with respect to 100 parts by mass of the electron-donating colorless dye.
10 to 300 parts by mass is preferable, and 30 to 200 parts by mass is more preferable.

-Inorganic Pigment- In the heat-sensitive recording layer according to the present invention, as an inorganic pigment, at least one selected from calcite-based calcium carbonate, amorphous silica, and aluminum hydroxide (the inorganic pigment according to the present invention is used. ) Is preferably contained. By containing these, the head matching property with the thermal head in contact can be further improved, and at the same time, printability and plain paper-like property can be imparted.

(Light) calcium carbonate generally has crystal forms such as calcite, aragonite and vaterite.
Calcite-based (light) calcium carbonate is preferred from the viewpoints of color density when recording with a thermal head, prevention of head stains, absorption, hardness, etc. Among them, in particular, the particle shape is spindle-shaped or uneven. A triangular surface is preferable. Calcite-based (light) calcium carbonate can be produced by a known production method. The calcite-based (light) calcium carbonate preferably has a volume average particle diameter of 1 to 3 μm. The volume average particle size is
It can be measured in the same manner as the electron-donating colorless dye.

The content of the above-mentioned "inorganic pigment according to the present invention" in a single heat-sensitive recording layer is 100 parts by mass of the electron-accepting compound from the viewpoint of improving the color density and preventing the deposition of dust on the thermal head. 50 to 500 parts by mass, more preferably 70 to 350 parts by mass, 90 to 2 parts by mass
50 parts by mass are particularly preferred.

Further, other inorganic pigments may be used in combination with the above-mentioned inorganic pigment according to the present invention within a range that does not impair the effects of the present invention (in particular, improvement of head matching property, printability and plain paper-like property). . Examples of the other inorganic pigments include calcium carbonate excluding calcite (light) calcium carbonate, barium sulfate, lithopone, wax, kaolin, calcined kaolin, amorphous silica, kaolin, magnesium carbonate, magnesium oxide, and the like. To be The volume average particle size of the other inorganic pigment (by a laser diffraction particle size distribution measuring device (for example, LA500 (manufactured by Horiba Ltd.)) is preferably 0.3 to 1.5 μm, and 0.5 to 0.9
μm is more preferable.

When the inorganic pigment according to the present invention and the other inorganic pigment are used in combination, the ratio of the total weight (v) of the "inorganic pigment according to the present invention" to the total weight (w) of the other inorganic pigment. (V /
As w), 100/0 to 60/40 is preferable, and 1
00/0 to 80/20 are more preferable.

From the viewpoint of suppressing the wear of the thermal head, an inorganic pigment having a Mohs hardness of 3 or less is preferable.
“Mohs hardness” means the Mohs hardness described in “English-Plastic Industry Dictionary, 5th Edition, p.616” (Shin Ogawa, published by Industrial Research Institute Co., Ltd.). Inorganic pigments having a Mohs hardness of 3 or less include calcium carbonate, aluminum hydroxide and the like.

When the inorganic pigment according to the present invention is used in combination with magnesium carbonate or magnesium oxide, it is preferable in that it is effective in reducing background fog, and the content of magnesium carbonate and / or magnesium oxide in that case is preferable. , 3 to 50 mass% of the total mass of the inorganic pigment, especially 5 to 30
It is preferably set to mass%.

—Adhesive— At least one selected from sulfo-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol as an adhesive (or protective colloid during dispersion) in the heat-sensitive recording layer according to the present invention. It is preferable to contain one kind (that is, modified polyvinyl alcohol (hereinafter sometimes referred to as “specific modified PVA”)). By containing the specific modified PVA as an adhesive in the heat-sensitive recording layer, it is possible to give a plain paper-like feeling and to increase the adhesive force between the heat-sensitive recording layer and the support, which is generated during offset printing. Trouble such as peeling can be prevented, and printability can be improved. Further, it is possible to increase the color density when recording with the thermal head while suppressing the background fog to a lower level.

The specific modified PVA may be used alone or in combination, and may be used in combination with other modified PVA or polyvinyl alcohol (PVA). When the other modified PVA or PVA is used in combination, the specific modified PVA is used.
The ratio of 1 to the total mass of the adhesive component
0 mass% or more is preferable, and 20 mass% or more is more preferable.

The specific modified PVA preferably has a saponification degree of 85 to 99 mol%. When the saponification degree is less than 85 mol%, water resistance to the fountain solution used during offset printing may be insufficient, and so-called paper peeling may easily occur. To avoid this, the amount of modified PVA added If the color density is increased to prevent peeling of the paper, the color density may decrease. On the other hand, when the saponification degree exceeds 99 mol%, undissolved substances are likely to be produced during the preparation of the coating liquid, which may cause defective coating. In order not to impair the effects of the present invention, even when other modified PVA or PVA is used in combination, the saponification degree of the other modified PVA or PVA is preferably within the above range.

Further, the polymerization degree of the specific modified PVA is preferably 200 to 2000. The degree of polymerization is 200
If the amount is less than the above range, it may be easy to cause the paper peeling during offset printing, and if the addition amount is increased to avoid the paper peeling, the color density may decrease. Also,
When the degree of polymerization exceeds 2000, the modified PVA is difficult to dissolve in a solvent (water) and the viscosity of the liquid during preparation increases, so that it becomes difficult to prepare and apply a coating liquid for forming a heat-sensitive recording layer. is there. Further, in order not to impair the effects of the present invention, even when other modified PVA or PVA is used in combination, it is preferable that the degree of polymerization of the other modified PVA or PVA is within the above range. The degree of polymerization here means J
The average degree of polymerization determined by the method described in IS-K6726 (1994).

The content of the specific modified PVA in the heat-sensitive recording layer is an electron-donating colorless dye 10 from the viewpoint of improving the color density and imparting offset printability (paper peeling prevention, etc.).
30 to 300 parts by mass is preferable with respect to 0 parts by mass, and 7
0 to 200 parts by mass is more preferable, and 100 to 170 parts by mass is particularly preferable. The specific modified PVA has a function as a dispersant, a binder, and the like, as well as a function as an adhesive that enhances interlayer adhesion.

Next, each of the specific modified PVA, that is, the sulfo-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol will be described in detail.

The sulfo-modified polyvinyl alcohol is
A polymer obtained by polymerizing an olefin sulfonic acid such as ethylene sulfonic acid, allyl sulfonic acid, or methallyl sulfonic acid or a salt thereof and a vinyl ester such as vinyl acetate in an alcohol or an alcohol / water mixed solvent is saponified. Method, a method of copolymerizing amide sodium salt and vinyl ester such as vinyl acetate, and saponifying the obtained copolymer, after treating PVA with bromine, iodine, etc., and then in an acidic sodium sulfite aqueous solution. It can be produced by a method of heating, a method of heating PVA in a concentrated aqueous solution of sulfuric acid, a method of acetalizing PVA with an aldehyde compound containing a sulfonic acid group, and the like.

The diacetone-modified polyvinyl alcohol is a partially or completely saponified product of a copolymer of a monomer having a diacetone group and a vinyl ester, and is obtained by copolymerizing a monomer having a diacetone group and a vinyl ester. It can be produced by saponifying the resin thus obtained. In the diacetone-modified polyvinyl alcohol, the ratio of the diacetone group-containing monomer (repeating unit structure) is not particularly limited.

The acetoacetyl-modified polyvinyl alcohol is generally a solution of polyvinyl alcohol resin,
It can be produced by adding and reacting liquid or gaseous diketene to the dispersion or powder. The degree of acetylation of the acetoacetyl-modified polyvinyl alcohol can be appropriately selected depending on the quality of the intended heat-sensitive recording material.

-Other Components-In the heat-sensitive recording layer according to the invention, in addition to the above-mentioned components, a crosslinking agent, other pigments, metal soaps, waxes, surfactants, binders, antistatic agents may be added, if desired or necessary. Other components such as agents, defoamers and fluorescent dyes may be contained.

[Crosslinking Agent] The heat-sensitive recording layer may contain a crosslinking agent which acts on the specific modified PVA used as the adhesive (or protective colloid) and other modified PVA. By containing the crosslinking agent, the water resistance of the heat-sensitive recording material can be improved. As the cross-linking agent,
It can be appropriately selected as long as it can crosslink the specific modified PVA (and preferably other modified PVA etc.), and among them, an aldehyde compound such as glyoxal and a dihydrazide compound such as adipic acid dihydrazide are particularly preferable. As the content of the crosslinking agent in the heat-sensitive recording layer, the specific modified PVA and other modified PVA to be crosslinked, etc. 10
1 to 50 parts by mass is preferable with respect to 0 parts by mass, and 3 to 2
0 mass part is more preferable. When the content of the crosslinking agent is within the above range, water resistance can be effectively improved.

[Mordant] The heat-sensitive recording layer may contain a mordant for the purpose of preventing bleeding during inkjet recording. The mordant is at least selected from an amide group, an imide group, a primary amino group, a secondary amino group, a tertiary amino group, a primary ammonium base, a secondary ammonium base, a tertiary ammonium base and a quaternary ammonium base. There may be mentioned a compound containing one kind of chaos group.

Specific examples thereof include polyamide epichlorohydrin, polyvinylbenzyltrimethylammonium chloride, polydiallyldimethylammonium chloride, polymethacryloyloxyethyl-β-hydroxyethyldimethylammonium chloride, polydimethylaminoethylmethacrylate hydrochloride, polyethyleneimine, polyallylamine, Examples thereof include polyallylamine hydrochloride, polyamide-polyamine resin, chaotic starch, dicyandiamide formalin condensate, dimethyl-2-hydroxypropylammonium salt polymer, and the like.

Besides the above, cationic polymers are also suitable. Examples of the cationic polymer include polyethyleneimine, polydiallylamine, polyallylamine, polydiallyldimethylammonium chloride, polymethacryloyloxyethyl-β-hydroxyethyldimethylammonium chloride, polyallylamine hydrochloride, polyamide-polyamine resin, cationized starch. , Dicyandiamide formalin condensate, dimethyl-2
-Hydroxypropyl ammonium salt polymer, polyamidine, polyvinylamine and the like can be mentioned.

The molecular weight of the mordant is from 1,000 to
About 200,000 is preferable. If the molecular weight is less than 1000, water resistance tends to be insufficient, and 200
If it exceeds 000, the viscosity may be high and the handling may be poor. The cationic polymer is
It may be added to either the heat-sensitive recording layer or the protective layer described later.

[Metal Soap, Wax, Surfactant] Examples of the metal soap include higher fatty acid metal salts, and specific examples include zinc stearate, calcium stearate, aluminum stearate and the like. Examples of the wax include paraffin wax, microcrystalline wax, carnauba wax, methylol stearamide, polyethylene wax, polystyrene wax,
And fatty acid amide wax, etc. may be used alone or in a mixture of two or more. As the surfactant, for example, a sulfosuccinic acid-based alkali metal salt,
Fluorine-containing surfactants and the like can be mentioned.

[Binder] The electron-donating colorless dye described above,
Dispersion of the electron-accepting compound, the inorganic pigment, the adhesive and the sensitizer, and other components can be suitably carried out in a water-soluble binder. As the binder used here, a compound that is soluble in 5% by mass or more in water at 25 ° C. is preferable. Specifically, for example, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose,
Examples thereof include starches (including modified starch), gelatin, gum arabic, casein, and saponified products of styrene-maleic anhydride copolymer.

The binder has a function of improving the film strength of the heat-sensitive recording layer as well as at the time of dispersion, and in order to exhibit this function, a styrene-butadiene copolymer, a vinyl acetate copolymer, an acrylonitrile- A synthetic polymer latex binder such as a butadiene copolymer, a methyl acrylate-butadiene copolymer, or polyvinylidene chloride can also be used in combination.

-Others- The electron-donating colorless dyes, electron-accepting compounds, inorganic pigments, adhesives and sensitizers described above include ball mills, attritors,
It can be prepared as a coating solution by simultaneously or separately dispersing with a stirring / crushing machine such as a sand mill. In the coating liquid, if necessary, the above-mentioned other components, that is, a crosslinking agent,
A mordant, metal soap, wax, surfactant, binder, antistatic agent, defoaming agent, fluorescent dye and the like are added.

After prepared as a coating solution as described above,
The coating liquid is applied on the surface of the support to form a heat-sensitive recording layer. The coating method for applying the coating liquid is not particularly limited, and may be appropriately selected from the coating methods using an air knife coater, roll coater, blade coater, curtain coater, etc., and is dried after coating. After drying, it is preferably subjected to a smoothing treatment by a calendar treatment before use. The dry coating amount of the coating liquids in the case of applying and forming a heat-sensitive recording layer, preferably less than ^{6g / m 2, 5g / m} 2 or less is particularly preferred.

In the present invention, high density (high sensitivity) can be obtained with a smaller amount of material used, and at the same time image quality (image quality) can be obtained.
The curtain coating method using a curtain coater is particularly preferable in that it can also improve Further, as will be described later, when a protective layer and the like are laminated in addition to the heat-sensitive recording layer, the energy consumption during manufacturing can be further reduced by simultaneously coating a plurality of layers by the curtain coating method. Specifically, it is as follows.

The heat-sensitive recording material preferably comprises a single layer or a part or all of a plurality of layers provided on a support.
A single or a plurality of types of coating solutions are curtain coated on the surface of a support and then dried to produce the coating. The type of layer formed by curtain coating is not particularly limited, and examples thereof include an undercoat layer, a thermosensitive recording layer, and a protective layer.
A preferred mode is that these adjacent series of layers are simultaneously coated in multiple layers by curtain coating.

Specific examples of the combination of layers in the case of simultaneous multi-layer coating include a combination of an undercoat layer and a heat-sensitive recording layer, a combination of a heat-sensitive recording layer and a protective layer, a combination of an undercoat layer, a heat-sensitive recording layer and a protective layer, and a type thereof. Examples include, but are not limited to, a combination of two or more undercoat layers different from each other, a combination of two or more thermal recording layers different from each other, a combination of two or more protective layers different from each other, and the like.

The curtain coating device used for curtain coating is not particularly limited, but examples include an extrusion hopper type curtain coating device and a slide hopper type curtain coating device, among which a photographic light-sensitive material is used. The slide hopper type curtain coating device described in JP-B-49-24133 is particularly preferable. By using this slide hopper type curtain coating device, it is possible to easily perform multi-layer simultaneous coating.

In the heat-sensitive recording material of the present invention, the heat-printed image area has a density residual ratio (light resistance) of 80% or more even when irradiated with a fluorescent lamp of 500,000 Lux · h. The density remaining ratio is the ratio of the density D ² of the printed area after irradiation to the density D ¹ of the printed area before irradiation (D ² / D ¹ × 1).
00). Each density is Macbeth reflection densitometer (RD-
918, manufactured by Macbeth) or the like. When the density residual ratio is less than 80%, the light resistance is insufficient, and the printing density decreases during storage after printing, resulting in a decrease in commercial value. Above all, 90% or more is desirable. In order to make the image residual ratio 80% or more, in particular, an image stabilizer (particularly an ultraviolet absorber) is contained in the heat-sensitive recording layer or the protective layer,
Electron-donating colorless dyes, types and formulations of electron-accepting compounds,
In addition, microencapsulation of the color-developing component can be performed by appropriately selecting it in a suitable mode.

<Protective Layer> At least one protective layer is preferably provided on the thermosensitive recording layer, and the protective layer contains organic or inorganic fine powder, a binder, a surfactant, a heat-fusible substance and the like. It can be comprised by containing. Examples of the fine powders include inorganic fine powders of calcium carbonate, silicas, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, kaolin, clay, talc, surface-treated calcium and silica, etc. Besides,
Examples thereof include urea-formalin resin, styrene / methacrylic acid copolymer, and organic fine powder such as polystyrene.

Examples of the binder contained in the protective layer include polyvinyl alcohol, carboxy-modified polyvinyl alcohol, vinyl acetate-acrylamide copolymer,
Silicon-modified polyvinyl alcohol, starch, modified starch, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, gelatins, arabic gum, casein, styrene-maleic acid copolymer hydrolyzate, polyacrylamide derivative, polyvinylpyrrolidone, and styrene-butadiene rubber latex, Examples thereof include acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, and latexes such as vinyl acetate emulsion.

A preferred mode is one in which a binder component in the protective layer is crosslinked to add a waterproofing agent for further improving the storage stability of the heat-sensitive recording material. Examples of the water-proofing agent include water-soluble initial condensation products such as N-methylol urea, N-methylol melamine, and urea-formalin, glyoxal, dialdehyde compounds such as glutaraldehyde, and inorganic materials such as boric acid, borax, and colloidal silica. Examples include a system cross-linking agent and polyamide epichlorohydrin.

Among the above, a particularly preferable protective layer is preferably an embodiment containing at least one inorganic pigment selected from aluminum hydroxide, kaolin and amorphous silica, and a water-soluble polymer. By configuring in this mode, the storability can be improved, and at the same time, the handleability and the suitability for printing can be imparted. Further, a surfactant, a heat-fusible substance, etc. may be further contained.

The volume average particle diameter of the inorganic pigment contained in the protective layer is preferably 0.5 to 3 μm, and 0.7 to 2.5.
μm is more preferable. Among them, aluminum hydroxide having a thickness of 0.5 to 1.2 μm is preferable from the viewpoint of improving the suitability for printing, and amorphous silica is preferably used from the viewpoint of improving suitability for inkjet. The volume average particle size here can be measured in the same manner as that of the electron-donating colorless dye described above.

The total content of inorganic pigments selected from aluminum hydroxide, kaolin and amorphous silica is 10 based on the total solid content (mass) of the coating liquid for forming the protective layer.
-90 mass% is preferable, and 30-70 mass% is more preferable. Further, other pigments such as barium sulfate, zinc sulfate, talc, clay and colloidal silica may be used in combination within a range that does not impair the effects of the present invention (in particular, improvement of storage stability and imparting of handleability and imprintability). Good.

Examples of the water-soluble polymer include polyvinyl alcohol or modified polyvinyl alcohol (hereinafter collectively referred to as “polyvinyl alcohol”), starch or oxidized starch, urea phosphate esterified starch, and the like among the binders. Modified starch, styrene-maleic anhydride copolymer, styrene-maleic anhydride copolymer alkyl ester compound, carboxyl group-containing polymer such as styrene-acrylic acid copolymer, and the like. Among them, from the viewpoint of imprintability, polyvinyl alcohol, oxidized starch and urea phosphate esterified starch are preferable, and polyvinyl alcohol (x) and oxidized starch and / or urea phosphate esterified starch (y) are 90/10 to 10 Mass ratio of 10/90 (x /
It is particularly preferable to use a mixture of y). In particular, when all of the polyvinyl alcohol, the oxidized starch and the urea phosphate esterified starch are used in combination, the mass ratio (y ¹ / y) of the oxidized starch (y ¹ ) and the urea phosphate esterified starch (y ² ). ² ) is preferably 10/90 to 90/10.

As the modified polyvinyl alcohol,
Acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, and amide-modified polyvinyl alcohol are preferable,
In addition, sulfo-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol and the like are used. By combining these cross-linking agents that react with polyvinyl alcohol, it is possible to further improve the storability, handleability, and imprintability.

The content ratio of the water-soluble polymer is 10 to 10 based on the total solid content (mass) of the coating liquid for forming the protective layer.
90 mass% is preferable and 30-70 mass% is more preferable.

Examples of the cross-linking agent for cross-linking the water-soluble polymer include polyhydric amine compounds such as ethylenediamine, polyhydric aldehyde compounds such as glyoxal, glutaraldehyde and dialdehyde, dihydrazide such as adipic acid dihydrazide and phthalic acid dihydrazide. Compounds, water-soluble methylol compounds (urea, melamine, phenol), polyfunctional epoxy compounds, polyvalent metal salts (Al, T
(i, Zr, Mg, etc.) and the like are preferable. Of these, polyvalent aldehyde compounds and dihydrazide compounds are preferable.

The content ratio of the crosslinking agent is preferably about 2 to 30% by mass, more preferably 5 to 20% by mass, based on the mass of the water-soluble polymer. By containing the cross-linking agent, the film strength and water resistance can be further improved. The mixing ratio of the inorganic pigment selected from aluminum hydroxide, kaolin and amorphous silica and the water-soluble polymer in the protective layer may be the type of the inorganic pigment, its particle size, the type of the water-soluble polymer. Etc., but
The amount of water-soluble polymer is 50 to 4 with respect to the mass of the inorganic pigment.
The amount is preferably 00% by mass, more preferably 100 to 250% by mass. The total mass of the inorganic pigment and the water-soluble polymer in the protective layer is preferably 50% by mass or more of the total mass of the solid content of the protective layer.

From the viewpoint of improving the suitability of the inkjet ink, a surfactant is added to the protective layer, that is, the coating liquid for forming the protective layer (hereinafter, may be referred to as "protective layer coating liquid"). Aspects are also preferred. Examples of the surfactant include alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, sulfosuccinic acid alkyl ester salts such as dioctyl sodium sulfosuccinate, polyoxyethylene alkyl ether phosphates, sodium hexametaphosphate, perfluoroalkylcarboxylic acid. Acid salts and the like are preferable, and among them, sulfosuccinic acid alkyl ester salts are more preferable. The content ratio of the surfactant is preferably 0.1 to 5 mass% with respect to the total solid content (mass) of the coating liquid for forming the protective layer, and is 0.1.
5 to 3 mass% is more preferable.

The coating liquid for forming the protective layer contains the above-mentioned inorganic pigment selected from aluminum hydroxide, kaolin and amorphous silica, a water-soluble polymer, and, if necessary, a crosslinking agent, a surfactant and the like. It can be prepared by dissolving or dispersing in a desired aqueous solvent. Here, in the coating liquid, a lubricant, a defoaming agent, a fluorescent whitening agent, a colored organic pigment, or the like is impaired in the effects of the present invention (in particular, improvement of storage stability, and handling property and imprintability). It can be added in the range not present. Examples of the lubricant include metal soaps such as zinc stearate and calcium stearate, paraffin wax, microcrystalline wax, waxes such as carnauba wax and synthetic polymer wax, and the like.

-Support-As the support, a conventionally known support can be applied. Specific examples thereof include paper supports such as high-quality paper, coated paper obtained by coating paper with resin or pigment, resin-laminated paper, high-quality paper having an undercoat layer, synthetic paper, plastic film, and the like. It is also possible to use a support which contains mainly waste paper pulp, i.e. waste paper pulp accounts for 50% by weight of the support.

From the viewpoint of dot reproducibility, the support is preferably a smooth support having a smoothness defined by JIS-P8119 within the range of 300 seconds to 500 seconds. Furthermore, for the same reason as above, it is more preferable that the smoothness defined by JIS-P8119 is 100 seconds or more,
Those of 150 seconds or more are particularly preferable.

The waste paper pulp generally has the following 1) to 3).
It is made from a combination of 3 steps. 1) Disaggregation: Waste paper is treated with mechanical force and chemicals using a pulper to disintegrate it into fibers, and the printing ink is separated from the fibers. 2) Dust removal ... Foreign matter contained in used paper (plastic, etc.)
And remove dust. 3) Deinking: The printing ink separated from the fibers is removed from the system by flotation or washing. If necessary, bleaching can be performed at the same time as deinking or in another step. A support for a thermal recording material is formed by a conventional method using 100% by mass of the waste paper pulp thus obtained or a mixture of the waste paper pulp and the virgin pulp having a content of less than 50% by mass.

An undercoat layer may be provided on the support. In this case, the undercoat layer has a Steckigt size of 5
It is preferably provided on the surface of the support for a second or more, and a material containing a pigment and a binder as main components is preferable. As the pigment for the undercoat layer, all general inorganic and organic pigments can be used, but in particular, an oil absorbing pigment having an oil absorption of 40 ml / 100 g (cc / 100 g) or more specified by JIS-K5101 is preferable. Specific examples of the oil absorbing pigment include calcined kaolin, aluminum oxide, magnesium carbonate, calcined diatomaceous earth, aluminum silicate, magnesium aluminosilicate, calcium carbonate, barium sulfate, aluminum hydroxide, kaolin, calcined kaolin, amorphous silica and urea. Formalin resin powder and the like can be mentioned. Among them, calcined kaolin having an oil absorption of 70 ml / 100 g to 80 ml / 100 g is particularly preferable.

When an undercoat layer is formed by coating on a support,
The coating amount of the pigment is preferably 2 g / m ² or more, 4g / m ² or more preferably, 7~12g / m ² is particularly preferred.

Examples of the binder for the undercoat layer include water-soluble polymers and aqueous binders. These may be used alone or in combination of two or more. Examples of the water-soluble polymer include starch, polyvinyl alcohol, polyacrylamide, carboxymethyl cellulose, methyl cellulose, and casein, and examples of the aqueous binder include synthetic rubber latex and synthetic resin emulsions. Examples thereof include styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex and vinyl acetate emulsion.

The amount of the binder used for the undercoat layer is determined in consideration of the film strength and the thermal sensitivity of the thermosensitive color developing layer, but is 3 to 10 relative to the mass of the pigment for the undercoat layer.
0 mass% is preferable, 5 to 50 mass% is more preferable,
8-15 mass% is especially preferable. Also, in the undercoat layer,
Wax, anti-fading agent, surfactant and the like may be added.

The coating liquid for forming the undercoat layer can be coated by a known coating method. Specific examples include a coating method using an air knife coater, a roll coater, a blade coater, a gravure coater, a curtain coater, etc. Among them, a coating method using a curtain coater or a blade coater is preferable, and a blade coater is used. The coating method is more preferable. After coating and drying, it may be further subjected to a smoothing treatment with a calender or the like before use.

The method using the blade coater is not limited to the coating method using a bevel type or bent type blade, but includes the rod blade coating method and the bill blade coating method, and is limited to the off-machine coater. The coating may be performed by an on-machine coater installed in the paper machine instead of the one. In order to obtain excellent smoothness and surface state by imparting fluidity during blade coating, the etherification degree of 0.6 to 0.8 is added to the coating liquid for forming the undercoat layer (coating liquid for the undercoat layer). , Weight average molecular weight 20000-200
1 to 5% by weight, preferably 1 to 3% by weight, may be added to the pigment amount.

The coating amount of the undercoat layer is not particularly limited, but is preferably ² g / m ² or more, more preferably 4 g / m ² or more, and 7 to 12 g depending on the characteristics of the heat-sensitive recording material.
/ M ² is particularly preferred.

In the present invention, an undercoat layer (particularly preferably, an undercoat layer having a high oil absorption, a heat insulating effect and a high flatness) is provided in order to improve the head matching property of the thermal head and to achieve high sensitivity and high image quality. An undercoat base paper having a base coat having an oil-absorbing pigment using a blade coater is particularly preferable.

The total ion concentration of Na ⁺ ions and K ⁺ ions contained in the thermal recording material is preferably 1500 ppm or less, more preferably 1000 ppm or less, from the viewpoint of preventing head corrosion of the thermal head in contact with the thermal recording material. It is preferably 800 ppm or less, and particularly preferably.
The measurement of the ion concentration of the Na ⁺ ion and K ⁺ ion is
It can be carried out by extracting the heat-sensitive recording material with hot water and measuring the ion mass of Na ⁺ ion and K ⁺ ion in the extracted water by an ion quantitative analysis method by an atomic absorption method. The total ion concentration is expressed in ppm with respect to the total mass of the thermosensitive recording material.

In the heat-sensitive recording material of the present invention, the wettability of the surface of the heat-sensitive recording layer, that is, the contact angle after the lapse of 0.1 seconds after dropping distilled water on the surface of the heat-sensitive recording layer is 20 ° or more. It is preferably present, and more preferably 50 ° or more. By setting the contact angle in the above range, it is possible to prevent bleeding of the print when printing with an inkjet printer (giving inkjet printability and improving it). The electron-accepting compound represented by the general formula (1) (preferably 4)
-Hydroxybenzenesulfonanilide), the above contact angle can be obtained, and in addition, the sensitizer and paraffin wax according to the present invention can be used as a material capable of maintaining a high contact angle of distilled water on the recording surface. It is also preferable to use a method such as inclusion in the recording layer.

The contact angle was measured by dropping distilled water on the surface (recording surface) of the heat-sensitive recording layer of the heat-sensitive recording material, and then measuring 0.1.
It can be performed by measuring the contact angle after a lapse of seconds by a conventional method. For example, the FIBRO system (DA
It can be measured by a dynamic contact angle absorption tester such as T1100 (manufactured by ab) or the like.

The heat-sensitive recording material of the present invention is useful in that it is excellent in image storability, and preferably, the formed image after printing is left for 24 hours under an environmental condition of a temperature of 60 ° C. and a relative humidity of 20%. The density residual ratio in the formed image is set to 65% or more. As described above, by containing the electron-accepting compound represented by the general formula (1) (particularly preferably 4-hydroxybenzenesulfonanilide), preferably containing an image stabilizer, the concentration residual ratio Can be within the above range. As a result, the formed image can be maintained at a high density for a long period of time, and can be applied to fields requiring image reliability for a long period of time, such as storage of important documents, advance tickets, receipts, and cash vouchers.

The density residual ratio of the image is calculated by the following formula, in an atmosphere of 60 ° C. and a relative humidity of 20% when printed under the same conditions as the image density measured by a Macbeth reflection densitometer (for example, RD-918) immediately after printing. It is represented by the ratio (%) of the image density after standing for 24 hours. Remaining density = [(image density after leaving) / (image density immediately after printing)] x 100

[0137]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Hereinafter, "parts" and "%" in the examples mean "parts by mass" and "mass%", respectively.

(Example 1) <Preparation of coating liquid for thermosensitive recording layer> -Preparation of dispersion liquid A (containing an electron-donating colorless dye) -The following components were dispersed and mixed in a ball mill to give a volume average particle diameter. To obtain a dispersion A having a particle size of 0.7 μm. The volume average particle size is
Laser diffraction particle size analyzer LA500 (HORIBA CORPORATION)
Manufactured). [Composition of Dispersion A] 2-anilino-3-methyl-6-diethylaminofluorane 10 parts (electron-donating colorless dye) Polyvinyl alcohol 2.5% solution 50 parts (PVA-105, Co., Ltd.) (Made by Kuraray)

-Preparation of Dispersion B (containing electron-accepting compound) -The following components were dispersed and mixed in a ball mill to obtain Dispersion B having a volume average particle diameter of 0.7 µm. The volume average particle size is
The measurement was performed in the same manner as in the case of Dispersion A. [Composition of Dispersion B] 4-Hydroxybenzenesulfonanilide 20 parts (electron-accepting compound represented by the general formula (1)) Polyvinyl alcohol 2.5% solution 100 parts (PVA-105, ( Made by Kuraray Co., Ltd.)

-Preparation of Dispersion C (with sensitizer) -The following components were dispersed and mixed in a ball mill to obtain Dispersion C having a volume average particle size of 0.7 µm. The volume average particle size is
The measurement was performed in the same manner as in the case of Dispersion A. [Composition of Dispersion C] 2-benzyloxynaphthalene (sensitizer) 20 parts Polyvinyl alcohol 2.5% solution 100 parts (PVA-105, manufactured by Kuraray Co., Ltd.)

-Preparation of Dispersion Liquid D (containing pigment) -The following components were dispersed and mixed in a sand mill to obtain Dispersion Liquid D having a volume average particle diameter of 2.0 µm. The volume average particle size is
The measurement was performed in the same manner as in the case of Dispersion A. [Composition of Dispersion D] Calcite light calcium carbonate ... 40 parts (Unibar 70, manufactured by Shiraishi Industry Co., Ltd.)-Sodium polyacrylate ... 1 part-Water ... 60 parts

-Preparation of coating liquid for thermosensitive recording layer- The following compositions were mixed to obtain a coating liquid for thermal recording layer. [Composition of coating liquid for thermal recording layer]   ・ Dispersion A ... 60 parts   ・ Dispersion B ... 120 parts   ・ Dispersion C ... 120 parts   Dispersion D ... 101 parts   ・ Zinc stearate 30% dispersion ... 15 parts   ・ Paraffin wax (30%): 20 parts   ・ Sodium dodecylbenzenesulfonate (25%)… 3 parts

<Preparation of Support Undercoat Layer Coating Liquid> The following components were stirred and mixed with a dissolver to obtain a dispersion liquid. -Calcined kaolin (oil absorption of 75 ml / 100 g) ... 100 parts-Sodium hexametaphosphate ... 1 part-Water ... 110 parts Subsequently, 20 parts of SBR (styrene-butadiene rubber latex) and oxidized starch (25 parts) were added to the resulting dispersion. %)
And 25 parts were added to obtain a coating solution for a support undercoat layer.

<Preparation of Thermosensitive Recording Material> As a support, J
A high-quality paper having a smoothness of 150 seconds according to IS-P8119 was prepared, and the coating liquid for a support undercoat layer obtained above was applied to the surface of the high-quality paper with a blade coater so that the coating amount was 8 g / m ^2. Was applied to form an undercoat layer. By applying the undercoat layer, the smoothness of the support according to JIS-P8119 was 350 seconds.

Then, the coating solution for heat-sensitive recording layer obtained above was coated on the undercoat layer by a curtain coater so that the coating amount after drying was 4 g / m ^2, and dried to obtain the heat-sensitive recording layer. Was formed. Then, the surface of the formed thermosensitive recording layer was subjected to a calendering treatment to obtain a thermosensitive recording material (1) of the present invention. With respect to the obtained thermal recording material (1), the applied energy of the thermal head was measured by the same conditions and methods as in the following (evaluation), 15.2 mJ / m.
The color density at m ² (by Macbeth reflection densitometer RD-918) was 1.28.

(Example 2) -Preparation of dispersion E-The following components were dispersed and mixed by a ball mill to obtain a dispersion E having a volume average particle size of 0.7 µm. The volume average particle size is
The measurement was performed in the same manner as in Example 1. [Composition of Dispersion E] 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane (image stabilizer) 5 parts Polyvinyl alcohol 2.5% solution 25 parts (PVA-105, manufactured by Kuraray Co., Ltd .; adhesive)

-Preparation of coating liquid for thermosensitive recording layer-Dispersions A, B, C and D were prepared in the same manner as in Example 1 and mixed with Dispersion E obtained above in the following composition to prepare a thermosensitive recording layer. A coating solution was prepared, and the same procedure as in Example 1 was carried out to obtain a heat-sensitive recording material (2) of the present invention. [Composition of coating liquid for thermosensitive color developing layer] Dispersion A ... 60 parts Dispersion B ... 120 parts Dispersion C ... 120 parts Dispersion E ... 30 parts Dispersion D ... 101 parts Zinc stearate 30% Dispersion: 15 parts Paraffin wax (30%): 20 parts Sodium dodecylbenzene sulfonate (25%): 3 parts

(Example 3) In Example 2, the dispersion E
Used in the preparation of 1,1,3-tris (2-methyl-4-
Instead of hydroxy-5-tert-butylphenyl) butane (image stabilizer), 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl)
Dispersion E was prepared in the same manner as in Example 2 except that butane was used, and further in the same manner as in Example 2 to obtain a thermosensitive recording material (3) of the present invention.

(Examples 4 to 5) In place of 40 parts of the calcite-based light calcium carbonate (Unibar 70; inorganic pigment) used in the preparation of the dispersion D in Example 1, amorphous silica (Mizukasil P832, Mizusawa Chemical Co., Ltd.) 2
0 parts or aluminum hydroxide (Hidilite H42,
Thermal recording materials (4) to (4) of the present invention were prepared in the same manner as in Example 1 except that 40 parts of Showa Denko KK were used.
(5) was obtained.

Example 6 Polyvinyl alcohol used in the preparation of dispersions A, B and C in Example 1.
Example 1 except that a 2.5% aqueous solution of sulfo-modified polyvinyl alcohol (Goselan L3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was used instead of the 5% aqueous solution (adhesive).
The thermal recording material (6) of the present invention was obtained in the same manner as described above.

(Example 7) Polyvinyl alcohol used in the preparation of dispersions A, B and C in Example 1.
The 5% aqueous solution (adhesive) was replaced with a 2.5% aqueous solution of diacetone-modified polyvinyl alcohol (D500, manufactured by Unitika Ltd.), and the resulting dispersions A, B and C were mixed in the same manner as in Example 1. A thermosensitive recording material (7) of the present invention was obtained in the same manner as in Example 1 except that 13 parts of a 5% aqueous solution of adipic dihydrazide (crosslinking agent) was further added to the coating liquid for thermosensitive recording layer.

(Example 8) Polyvinyl alcohol used in the preparation of dispersions A, B and C in Example 1.
A 5% aqueous solution (adhesive) was replaced with a 2.5% aqueous solution of acetoacetyl-modified polyvinyl alcohol (Gosefimer Z210, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), and the resulting dispersions A, B and C were used as examples. In the same manner as in Example 1 except that 13 parts of a 5% aqueous solution of glyoxal (crosslinking agent) was further added to the coating liquid for heat-sensitive recording layer prepared by mixing in the same manner as in 1, the heat-sensitive recording material of the present invention (8 ) Got.

Example 9 Instead of the high-quality paper used as the support in Example 1, 70% recycled pulp and 30% LBKP were used.
The smoothness according to JIS-P8119 is 1
A thermal recording material (9) of the present invention was obtained in the same manner as in Example 1 except that recycled paper (50 g / m ² ) for 70 seconds was used.

Example 10 In place of <Preparation of Thermosensitive Recording Material> of Example 1, instead of coating, drying and calendering the coating solution for the thermal recording layer, which was carried out after the undercoat layer was formed on the support. Then, after forming the undercoat layer, the coating liquid for thermal recording layer obtained in Example 1 and the coating liquid for protective layer consisting of the following are simultaneously multilayer coated using a curtain coater and dried to form a laminated protective layer. A thermal recording material (10) of the present invention was obtained in the same manner as in Example 1 except that the surface of the above was subjected to a calendering treatment. The dry coating amount of the protective layer was 2.0 g / m ² .

—Preparation of Coating Liquid for Protective Layer— The following composition was dispersed by a sand mill to prepare a pigment dispersion having a volume average particle diameter of 2 μm. The volume average particle diameter was measured in the same manner as in Example 1.・ Aluminum hydroxide (average particle size 1 μm) 40 parts (Hidilite H42, Showa Denko KK) ・ Sodium polyacrylate 1 part ・ Water 60 parts

Separately, 200 parts of urea phosphate esterified starch 15% aqueous solution (MS4600, manufactured by Nippon Shokuhin Kako Co., Ltd.) and polyvinyl alcohol 15% aqueous solution (PVA-10
5, manufactured by Kuraray Co., Ltd.), 60 parts of water was added to 200 parts of the mixture, the pigment dispersion obtained above was mixed, and the zinc stearate emulsion dispersion having a volume average particle diameter of 0.15 μm was further prepared. (Hydrin F115, manufactured by Chukyo Yushi Co., Ltd.) and 25 parts were mixed with 125 parts of a 2% sulfosuccinic acid 2-ethylhexyl ester sodium salt aqueous solution to obtain a coating liquid for a protective layer.

(Examples 11 to 13) Instead of 40 parts of aluminum hydroxide (Hydrite H42; inorganic pigment) used in the preparation of the coating solution for protective layer of Example 10, aluminum hydroxide (Hydlite H43, volume) was used. Average particle size 0.7μ
m, manufactured by Showa Denko KK 40 parts, kaolin (caobrite, volume average particle diameter 2.5 μm, manufactured by Shiraishi Industry Co., Ltd.) 40
Parts or 20 parts of amorphous silica (Mizukasil P707, volume average particle size 2.2 μm, manufactured by Mizusawa Chemical Co., Ltd.), respectively, were used in the same manner as in Example 10 to obtain the thermosensitive recording material of the present invention. (11) to (13) were obtained.

(Examples 14 to 20) Dispersion C of Example 1
In place of 2-benzyloxynaphthalene (sensitizer) used in the preparation of dimethyl oxalate (HS352
0R-N, Dainippon Ink and Chemicals, Inc., m-terphenyl, ethylene glycol tolyl ether, p-benzyl biphenyl, 1,2-diphenoxymethylbenzene, diphenyl sulfone, or 1,2-diphenoxyethane. The thermal recording materials (14) to (20) of the present invention were obtained in the same manner as in Example 1 except that each was used.

(Examples 21 to 25) Dispersion A of Example 1
In place of 2-anilino-3-methyl-6-diethylaminofluorane (electron donating colorless dye) used in the preparation of
2-anilino-3-methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6- (N-ethyl-
N-isoamylamino) fluorane, 2-anilino-3
-Methyl-6- (N-ethyl-N-propylamino) fluorane, 2-anilino-3-methyl-6-di-n-amylaminofluorane, or 2-anilino-3-methyl-6- (N- The thermal recording materials (21) to (25) of the present invention were obtained in the same manner as in Example 1 except that ethyl-Np-tolylamino) fluorane was used.

(Example 26) The heat-sensitive material of the present invention was prepared in the same manner as in Example 1 except that an air knife coater was used instead of the curtain coater used for coating the coating liquid for heat-sensitive recording layer. A recording material (26) was obtained.

(Examples 27 to 29) Dispersion B of Example 1
In place of 4-hydroxybenzenesulfonanilide (electron-accepting compound) used in the preparation of N-benzyl-4-
Hydroxybenzenesulfonamide (= p-N-benzylsulfamoylphenol), BTUM, or 4-hydroxy-4'-isopropoxydiphenylsulfone,
Thermal recording materials (27) to (29) of the present invention were obtained in the same manner as in Example 1 except that each of the above was used.

(Comparative Examples 1-2) Instead of 4-hydroxybenzenesulfonanilide (electron-accepting compound) used in the preparation of the dispersion B of Example 1, 2,2'-bis (4-) was used.
Comparative thermal recording materials (30) to (31) were obtained in the same manner as in Example 1 except that (hydroxyphenol) propane (bisphenol A) or 4,4′-dihydroxydiphenylsulfone was used.

Comparative Example 3 The same procedure as in Example 1 was repeated except that 20 parts of 4-hydroxybenzenesulfonanilide (electron-accepting compound) used in the preparation of the dispersion B of Example 1 was changed to 4 parts. Thus, a comparative heat-sensitive recording material (32) was obtained.

(Evaluation) The heat-sensitive recording materials (1) to (29) of the present invention and the heat-sensitive recording material (30) for comparison, obtained as described above.
For (32) to (32), the following measurements and evaluations were performed. still,
The results of measurement and evaluation are shown in Table 1 below. (1) Sensitivity measurement part Thermal head having a glaze structure (KF200
Printing was performed using a thermal printing device equipped with 3-GD31A, manufactured by ROHM Co., Ltd. The printing is head voltage 24V,
Printing cycle 0.98ms / line (printing speed 12.8c
m / sec), the pulse width was 0.375 ms (applied energy 15.2 mJ / mm ² ), and the print density was measured with a Macbeth reflection densitometer (RD-918, manufactured by Macbeth).

(2) Evaluation of background fog The density of the background part (non-image part) after leaving each heat-sensitive recording material for 24 hours under the environmental condition of temperature 60 ° C. and relative humidity 20% was measured by Macbeth reflection densitometer. (RD-918, manufactured by Macbeth Co.). The lower the value, the better the background fog.

(3) Evaluation of image storability Each of the thermosensitive recording materials was printed with the same apparatus and conditions as in "(1) Measurement of sensitivity", and the density of the image immediately after printing,
The same image is placed in an atmosphere of 60 ° C and 20% relative humidity for 24 hours.
The density of the image after standing for a time was measured with a Macbeth reflection densitometer (RD-918, manufactured by Macbeth Co.). And
Based on the following formula, the ratio of the image density after leaving to the image density immediately after printing (%; density residual ratio) was calculated and used as an index for evaluating image storability. The higher the value, the better the image storability. Remaining density = [(image density after leaving) / (image density immediately after printing)] x 100

(4) Evaluation of light resistance Each of the above-mentioned heat-sensitive recording materials was printed with the same apparatus and conditions as in "(1) Measurement of sensitivity", and the density of the image immediately after printing,
The density after exposure of the printing section to a fluorescent lamp at 50 full Lux · h (measured with a digital illuminance meter T-1 (manufactured by Minolta Co., Ltd.)) and a Macbeth reflection densitometer (RD-918, manufactured by Macbeth Co.) ). Based on the following formula, the ratio of the image density after exposure to the image density immediately after printing (%; density residual ratio) was calculated and used as an index for evaluating light resistance. The higher the value, the better the light resistance. Remaining density = [(image density after exposure) / (image density immediately after printing)] x 100

(5) Evaluation of chemical resistance Each thermal recording material was printed with the same equipment and conditions as in "(1) Sensitivity measurement" above, and the surface of the background portion and the printing portion was printed with a fluorescent pen (zebra). Highlighter 2-Pink, Zebra Corporation
Written on each of the heat-sensitive recording materials after 1 day,
The degree of background fog on the background portion and the image density of the image portion were visually observed and evaluated according to the following criteria. [Criteria] ◯: No increase in fog density in the background area was observed, and no change in density in the image area was observed. Δ: A slight increase in the fog density in the background part was observed, and the image part was slightly lighter in density. X: The fog density in the background area was remarkably increased, and the image area almost disappeared.

(6) Evaluation of head loss Using a word processor (Lupo 95JV, manufactured by Toshiba Corp.), 1000 test charts with a print rate of 20% were printed in A4 sheet size, and the number of missing dots at that time was determined by the head. It was used as an index for evaluating breakage.

(7) Evaluation of Inkjet Suitability Ink Resistance In the same manner as in "(1) Sensitivity Measurement" above, printing was carried out on the thermosensitive recording layer of each thermosensitive recording material, and the image density (D ¹ ) immediately after printing. Was measured with a Macbeth reflection densitometer RD918 (manufactured by Macbeth). Next, the surface of the heat-sensitive recording layer of each of the printed heat-sensitive recording materials (printed printing portion) is brought into contact with the image printed with high quality by an inkjet printer (EPSON MJ930C, manufactured by Epson Corporation), and 2
The image density (D ² ) of each heat-sensitive recording layer after standing at 5 ° C. for 48 hours was measured by a Macbeth reflection densitometer RD918. Then, the density residual ratio (%; D ² / D ¹ × 100) of each thermal recording material was calculated from the obtained respective densities, and used as an index for evaluating the resistance to the inkjet ink. The higher the value, the better the ink resistance.

Inkjet recording suitability For each heat-sensitive recording material, a word processor (report JW-95J
U, manufactured by Toshiba Corp.) is used to print characters, and then each of the printed thermal recording layers is printed with an inkjet printer, and ink bleeding in the inkjet recording part and the character part printed with a word processor are performed. The degree of decolorization was visually evaluated according to the following criteria. [Criteria] ◯: There was little ink bleeding and decoloring of the character portion, and there was no problem in reading. Δ: A part of the character part was faint, but it was possible to read it somehow. X: The character portion completely disappeared, and the reading was impossible.

(8) Measurement of contact angle Distilled water was dropped on the surface (recording surface) of the thermosensitive recording layer of each thermosensitive recording material, and the contact angle after 0.1 second was measured by the FIBRO method.
It was measured using a system (DAT1100, manufactured by ab). The larger the value, the more useful it is in relation to the effect.

(9) Measurement of ion (Na ⁺ , K ⁺ ) concentration Each heat-sensitive recording material was extracted with hot water, and the extracted water was analyzed by ion quantitative analysis by atomic absorption spectrometry to obtain Na ⁺ and K ⁺ ions. Was measured. The ion concentration in Table 1 represents the total ion concentration of Na ⁺ and K ⁺ , and shows the total ppm value based on the total mass of the thermosensitive recording material.

[0174]

[Table 1]

From the results in Table 1 above, in the heat-sensitive recording materials (1) to (29) of the present invention, a high color density (high sensitivity) was obtained without impairing the background white color of the background (good printability). Moreover, the light resistance after printing and the image storability were also good. Moreover, with the improvement of the contact angle, it has an inkjet suitability, excellent chemical resistance, less head wear, and excellent thermal head matching. That is,
Light resistance, high sensitivity, background whiteness, image storability,
Inkjet suitability, chemical resistance, and thermal head matching (wear resistance) could be satisfied at the same time.

Further, in comparison with the heat-sensitive recording material (1), the heat-sensitive recording materials (2) and (3) containing an image stabilizer can further improve the image storability and the ink resistance, and thus have favorable adhesion. With the heat-sensitive recording material (6) using the agent (protective colloid), it was possible to further improve the sensitivity and reduce the background fog. Incidentally, the inclusion of the image stabilizer was particularly excellent in imprintability and handleability. The thermal recording materials (10) to (13) provided with the protective layer containing the specific inorganic pigment suitable for the present invention were able to further improve the image storability and the ink resistance (chemical resistance). Example 1
With the sensitizers used in Examples 4 to 20, as in the case of the heat-sensitive recording material (1) of Example 1, good performance was obtained.
Even with the electron-donating colorless dye used in Examples 25 to 25, good color developability and image storability were obtained while keeping the background fog low. As in Examples 1 and 26, the curtain coating method was more useful in terms of higher sensitivity. Even when the used paper pulp was contained in the support (Example 9), various performances were not affected.

On the other hand, in the heat-sensitive recording materials (30) to (31) for comparison, which did not use the compound represented by the general formula (1) as the electron-accepting compound, the sensitivity was not particularly high. However, it was inferior in light resistance, image storability, chemical resistance, and ink jet suitability, and it was not possible to simultaneously satisfy various properties that the thermal recording material should have.

[0178]

According to the present invention, it is possible to form a high-sensitivity and high-density image (printing suitability is good) while suppressing the fog density (background fog) in the background portion to be low, and the light resistance after printing, Image storability and chemical resistance are particularly excellent, and it has inkjet suitability that does not cause color fading or bleeding of inkjet images and image fading caused by inkjet inks.
Moreover, even when it is applied to a high-performance printer having high speed and a partial glaze structure, a thermal recording material having good thermal head matching property and less head wear and head stain (good head suitability) is provided. You can Further, in addition to these, a sharp and high-quality image can be obtained, the formed image has excellent light resistance, printing and imprinting can be performed on the heat-sensitive recording layer or the protective layer without bleeding, and a small coating amount ( It is possible to provide a heat-sensitive recording material which can be formed at a low cost with environmental suitability and which also has a plain paper-like feel if necessary.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] December 27, 2002 (2002.12.
27)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title of the invention Thermal recording material

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more specifically, it has excellent apparatus suitability without deterioration of apparatus durability such as head wear, and has printing suitability and stability as a recording medium. The present invention relates to a heat-sensitive recording material that is suitable as a plain paper-like recording medium and is suitable for printing suitability, printing suitability, environment suitability, and the like.

[0002]

2. Description of the Related Art Thermal recording technology has historically been used in 1960's.
In the 1980s, NCR developed a dye-based thermal paper using a colorless leuco dye and a phenolic acidic substance, and this system has become the mainstream of the current thermal recording system. After that, a thermal head was developed against the background of semiconductor technology,
Due to significant improvements in performance, downsizing of the device,
It has become possible to reduce the price, and along with this, the quality of the thermal paper (thermal recording material) itself has been improved (higher sensitivity, improved head matching, etc.), and
Thermal recording method is electrostatic recording, inkjet recording, PP
Thermal paper (hereinafter referred to as "thermosensitive recording material") was evaluated as being advantageous in terms of convenience, that is, convenience, low cost, maintenance-free, etc., as compared with each recording method such as C recording. ) Demand has grown dramatically.

However, as thermal recording materials have been used in fax machines and various printers due to their convenience and become familiar to daily life, the drawbacks of thermal recording materials have become well known. That is, for example: -Discoloration due to light-Discoloration when stored under high temperature (such as leaving in an automobile) -Chemicals (plasticizer in plastic film, oils and fats, organic solvent in marker pen, inkjet printer) The recorded image is discolored by ink for printing, etc. ・ Plain paper-like feeling (good stamping suitability such as dryness and no blurring, good readability with a matte recording surface, and writability with pencil etc.) Has been pointed out that there is no such thing as "good", that it is less likely to cause rubbing stains; and so on; hereinafter the same). Therefore, there has been a demand for the development and provision of a heat-sensitive recording material which eliminates the above-mentioned drawbacks of conventional heat-sensitive recording materials and enhances the added value.

In recent years, heat-sensitive recording materials have been used widely because they are generally relatively inexpensive and their recording equipment is compact and maintenance-free. Under such circumstances, sales competition of thermal recording materials has intensified recently, and further higher functionality that can be differentiated from conventional functions, especially color density, background whiteness, sharpness, stability during storage In addition, there is a high demand for a heat-sensitive recording material that has good hue and vividness for a full-color image recorded by an inkjet method, etc., and in order to meet these demands, the color-forming property and storability of the heat-sensitive recording material are high. Studies on various performances such as the above are being conducted earnestly.

The various performances that a thermal recording material should have are:
(1) High sensitivity (high density can be obtained), (2) High whiteness of the background area (non-image area) (low background fog), (3) Image storability after printing Excellent, (4) excellent light resistance, (5) excellent chemical resistance, (6) sharp and high image quality, (7) each hue even when recording a full-color image with an inkjet method. Good and vivid, (8) Good thermal head matching, and good head resistance with little thermal head wear.
(9) Having a plain paper-like feel, (10) having printability capable of being printed on a heat-sensitive recording layer and imprintability without bleeding,
(11) Applicability to high-performance printers such as high-speed printers, (12)
For example, it is required to have environmental suitability. Under the above-mentioned circumstances, it is required to satisfy all of these performances at the same time without impairing any performance.
However, at present, a thermal recording material capable of satisfying all of the above-mentioned various properties at the same time has not yet been provided.

In particular, in recent years, image stability capable of holding a formed image for a long period of time has been required, and it is also applicable to a field where image reliability is required for a long period of time due to the simplicity of the apparatus and recording. Is desired. On the other hand, 2,2-bis (4-hydroxyphenyl) propane (so-called "bisphenol A") has been widely used as an electron-accepting compound that reacts with an electron-donating colorless dye used in a heat-sensitive recording material to develop a color. Although it has been used, satisfactory results have not yet been obtained with this system in terms of sensitivity, background fog, and image storability.

Further, there is a problem in (13) suitability for ink jet as described below. That is, when full-color information is recorded on a heat-sensitive recording material, recording may be performed using an inkjet ink.
When ink-jet recording is performed on the recording surface of a normal thermosensitive recording material using, the hue of the ink cannot be faithfully reproduced and a vivid hue cannot be obtained, or the fading of a recorded image that has already been thermosensitively recorded. Could cause Further, when the above-mentioned ordinary heat-sensitive recording material is placed in contact with the medium recorded by the ink jet printer, the background fog may occur and the recorded image may be discolored.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the various problems in the prior art and achieve the following objects. That is, the present invention can form a high-sensitivity and high-density image while suppressing the fog density in the background part (background fog) (good printability), and light resistance after printing,
A high-performance printer with excellent image storability and chemical resistance, inkjet suitability that does not cause image color fading or bleeding of inkjet images, and image fading caused by inkjet inks, and has high speed and a partial glaze structure. Even when applied to, it is possible to provide a thermal recording material having good thermal head matching properties and less head wear and head stains (good head suitability), and in addition to these, a sharp and high-quality image can be obtained. The obtained image has excellent light resistance, printing and imprinting can be performed on the heat-sensitive recording layer or protective layer without bleeding, and it can be formed at a low cost with a small coating amount (environmental suitability). An object of the present invention is to provide a thermal recording material having a paper-like feeling.

[0009]

Means for Solving the Problems The inventors of the present invention have made the following findings as a result of extensive studies on a technique for simultaneously satisfying various performances that a thermal recording material should have at a high level. . <Higher sensitivity> The following points (1) to (3) are important for higher sensitivity. That is, firstly, (1) it is important to improve the heat transfer from the thermal head to the thermal recording layer. For this purpose, the surface smoothness of the recording surface of the thermal recording material is improved, and the cushion to the recording surface is improved. It is effective to impart sex. Secondly, (2) it is important to effectively utilize the heat transferred from the thermal head, and for this purpose, it is effective to make the support heat insulating and slim the heat-sensitive recording layer. Third, (3) It is important to improve the dissolution rate of the electron-donating colorless dye and the electron-accepting compound with respect to the sensitizer. For this purpose, the solubility is improved, the melt viscosity is reduced, and the material particle size is reduced. Is effective. The details will be described below.

(1) Improving heat transfer from the thermal head to the heat-sensitive recording layer A certain amount of heat is required to develop a color in the heat-sensitive recording layer to a certain density. How efficiently the heat from the head is transferred to the recording layer is important. Here, the thermal conductivity of a solid is significantly higher than that of a gas, and the conduction heat is much higher than the radiation heat. Therefore, it is effective to increase the contact rate between the surface of the thermal recording layer (hereinafter, also referred to as “recording surface”) and the thermal head during printing, and the heat from the thermal head is transferred to the thermal recording layer. It can be transmitted efficiently. In order to increase the contact rate between the recording surface and the thermal head, the physical properties required for the thermal recording material are:
It is particularly effective to enhance the smoothness of the recording surface in advance and enhance the cushioning property of the heat-sensitive recording material.

In order to improve the smoothness of the recording surface, it is effective to improve the flatness of the support. Specifically, it is desirable to use a base paper having a high flatness, and to provide an undercoat layer containing an oil-absorbing pigment as a main component to fill the irregularities of the pulp. In addition, it is also effective to apply a thermal recording layer or a supercalendering process after coating and drying the heat-sensitive recording layer to enhance smoothness. In addition, the cushioning property of the heat-sensitive recording material is enhanced (giving cushioning property).
Is effective based on the following findings. That is, when thermally printing on a thermal recording material using a thermal head, an appropriate pressure is applied using a platen roll, but in order to increase the contact rate between the thermal head and the recording surface under pressure, the thermal recording It is good if the material is easily deformed. Therefore,
As a specific means for imparting cushioning properties, it is effective to provide an undercoat layer containing an oil-absorbing pigment as a main component or to contain a pigment having a high oil absorption (for example, amorphous silica) in the heat-sensitive recording layer. . The concept of giving the cushioning property is particularly effective for high sensitivity when recording is performed using a thermal head having a partial glaze structure. here,
The partial glaze structure refers to a structure in which the cross-sectional shape of the glaze layer of the heating element portion is convex (mountain-shaped) on the substrate.

(2) Effective Utilization of Heat Transferred from Thermal Head In order to effectively utilize the heat transferred from the thermal head, it is effective to impart a heat insulating property to the support. It is effective to provide voids in the support as much as possible. In the case of a heat-sensitive recording material, for example, an undercoat layer containing a pigment having a high oil absorption is provided, the amount of binder used in the undercoat layer is reduced as much as possible, and hollow particles are contained in the undercoat layer. Further, in order to effectively use heat, it is also effective to slim the heat-sensitive recording layer. Considering that the heat capacity of the heat-sensitive recording layer contributes to the sensitivity, the heat-sensitive recording layer contains many components that do not contribute to color development, and the heat capacity is wasted. Examples of the component include release agents and waxes that suppress scratches between the thermal head and the recording layer, oil-absorbing pigments that absorb molten components, binders that impart dispersion of the material and coating strength, and the like. To do. The amount of heat consumed by these amounts to about 20 to 30%.
An improvement in sensitivity of 5% can be expected.

According to the results of studies by the present inventors, the sensitivity can be improved by reducing the content of the pigment and the binder in the recording layer. Since the sensitivity can be increased more than expected by reducing the amount of binder, contributions other than heat capacity are possible, but the cause is unknown. However, if the content of the binder is simply reduced, the head matching property of the thermal head and the coating strength will deteriorate, so the material should be distributed as efficiently as possible, that is, the necessary components should be used in the minimum amount in the required layers. Is important.

(3) Improvement of dissolution rate of electron-donating colorless dye and electron-accepting compound in sensitizer At the initial stage of technological development of a heat-sensitive recording material, the sensitizer is an electron-donating colorless dye and an electron-accepting compound. It has been selected as a melting point depressant for organic compounds for the purpose of developing color at lower temperatures. However, with this idea, there is a limit to increase the sensitivity while maintaining the color development start temperature, and it was difficult to achieve both background fog and sensitivity. Therefore, the present inventors regard the sensitizer as a material for dissolving an electron-donating colorless dye or an electron-accepting compound, and do not lower the eutectic point more than necessary, that is, keep the background fog low. As a result of investigating a sensitizer that realizes high sensitivity, it was found that the faster diffusion of an electron-donating colorless dye or an electron-accepting compound in a molten sensitizer is advantageous for higher sensitivity. I got the knowledge of. That is, it is preferable to select a sensitizer having not only high solubility but also low melt viscosity and to reduce the dispersed particle size of the electron-donating colorless dye or the electron-accepting compound, which are effective in increasing the sensitivity. If the dispersed particle size is too small, the background fog will worsen, so it is important to set it in an appropriate range.

<Providing Matching Property with Thermal Head and Head Durability> In the heat-sensitive recording material, the recording surface (the surface of the heat-sensitive recording layer) is brought into direct contact with the thermal head, which is a heating element, and the surface is rubbed to print ( Printed). Therefore, the melted component in the recording layer may adhere to the head and be deposited as dirt. Further, the life of the head itself may be shortened due to physical wear or corrosion of the surface of the thermal head. Therefore, it is desirable to apply the following means. That is, 1) From the viewpoint of preventing head contamination, it is important to absorb and retain substances such as dyes, developers and sensitizers, which are melted by heat, on the material side. It is effective to use a pigment having a high property or to provide an undercoat layer using a pigment having a high oil absorption property. 2) Further, it is important to suppress the content of ions (Na ⁺ , K ^+, etc.), which are likely to cause head corrosion, in the constituents of the recording material. 3) From the viewpoint of reducing physical wear as much as possible, it is important to consider the hardness, shape, particle size, etc. of the pigment.

<Compatibility of image storability (and chemical resistance) and background fog> In a color image, a chemical reaction caused by contact between a leuco dye and a color developer, which is a coloring principle of a heat-sensitive recording material, is melted by heat. Since it is a reaction, a reverse reaction easily occurs due to chemicals such as oils and fats and plasticizers. Therefore, hand creams and other cosmetics, or products with fats and oils on hands, plastic products containing plasticizers, products containing organic solvents, leather products (eraser, vinyl chloride desk mats and food packaging films, marker pens, etc. , Inkjet ink, wallet, commuter pass, etc.) Color images disappear in everyday life when placed in contact with
Problems tend to occur in terms of image storability and chemical resistance.

Various studies have been conducted in order to overcome the phenomenon (image disappearance, fading) resulting from the above coloring principle, for example, forming a protective layer on the recording layer for the purpose of physical shielding. The so-called overcoat type, the addition of a crosslinkable additive to the recording layer, and the like have been performed. However, even if a protective layer is provided, it is unavoidable that the oil and plasticizer will gradually permeate and the fading will progress over time, and as a result, it will not be possible to use the product for a short period of time, such as a measurement label attached to fresh food in supermarkets. There is a problem that it is limited to applications, it takes a considerable time from coloring to the effect even if a cross-linking substance is added, etc. Didn't.

Therefore, as a result of the investigations by the present inventors regarding the improvement of the storage stability, a specific electron-accepting compound is useful for improving the image storage stability, and the background fog can be compatible with it. Further, it was found that the background fog can be further improved by combining a specific sensitizer and an electron-donating colorless dye. Further, they have also found that by combining a specific image stabilizer, the image storability and the light resistance can be further improved without substantially deteriorating the background fog. According to these findings, it is possible to impart a high level of not only image storability but also stampability and handleability, which is difficult with the conventional storability imparting technology that relies on the overcoat. As described above, it is possible to achieve both printing suitability and image storability.

<Improvement of light resistance> Depending on the application, a heat-sensitive recording material having excellent light resistance may be required. However, since the leuco dye carrying an image is easily decomposed by ultraviolet rays or the like, long-time natural light is required. There was a problem in terms of light resistance, such as fading even when exposed to light. In order to improve the light resistance, it is important to provide a means for preventing the decomposition of the leuco dye by light. For this purpose, it is particularly effective to add an ultraviolet absorber (image stabilizer) for preventing ultraviolet rays, which is a high energy, to the thermosensitive recording layer or the protective layer, especially before ultraviolet rays reach the thermosensitive recording layer. From the viewpoint of efficiently blocking, it is more effective to wrap the liquid ultraviolet absorber in microcapsules and to contain it in the protective layer.

<Providing printability> Offset printing may be performed on the recording surface (surface of the thermosensitive recording layer) of the thermosensitive recording material depending on the application. For such an application, it is necessary to have a surface strength capable of withstanding a printing speed of 100 m / min of a rotary foam printing machine and a dampening water absorption property, and to prevent the formation of pigments or binders in the heat-sensitive recording layer. It is important to optimize the compounding ratio. For this purpose, an oil absorbing pigment such as calcium carbonate is preferred as the pigment, and polyvinyl alcohol (PVA) is preferred as the binder, and sulfo-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol are particularly preferred.

<Giving Plain Paper-Like Feeling> As a result of widespread use of heat-sensitive recording materials as recording paper for facsimiles in offices and homes, and for various printers,
I feel a sense of incongruity compared to the paper around me (PPC paper, notebook, report paper, etc.), that is, the surface is slippery, the writing is bad, and it does not rub when held by a thin hand. The point has come to be actively made. These are one of the reasons why office facsimiles have recently moved to the PPC type, which uses plain paper. From this point of view, the base paper as a support is made thicker to make it stronger, and by providing a protective layer, it gives a low gloss surface property, writability, and imprintability, etc. It is important to get closer to.

Here, the heat-sensitive recording material having a plain paper-like feeling eliminates the disadvantages of the conventional heat-sensitive paper as a processed paper, has a matte surface, has no slimy feel to the touch, and is less likely to be rubbed and smeared. It is considered that the recording image has a performance such as fading of the recorded image, and so far, it has been proposed that a protective layer is provided on the recording layer for the purpose of making it like plain paper. However, the conventional protective layer has not been given much attention to touchability, appearance (matte tone), writability, etc., so that the suitability for printing has not been taken into consideration. However, in view of the customs of Japan, it was considered that imprinting aptitude (no bleeding, good drying of stamps, etc.) is particularly important, and an improvement of the protective layer for a thermal recording material having plain paper-like properties was examined. .

As a result, it was found that the following pigments and binders are useful for the protective layer in order to obtain a plain-paper-like feel including imprintability. As the pigment, a pigment having an appropriate particle size and an oil absorption amount is preferable in order to give importance to imprintability, appearance (matte tone) and writability. If the particle size is too large, the image quality may deteriorate, and if it is too small, the writability and appearance may deteriorate. On the other hand, if the oil absorption is too large, the opacity of the protective layer increases and the recording density decreases, and if the oil absorption is too small, the imprintability (dryness) tends to deteriorate. As the binder,
A mixture of PVA and starch in an appropriate ratio is particularly preferable for the purpose of preventing imprinting suitability (bleeding). The PVA is a so-called fully saponified type (saponification degree of about 93% or more) from the viewpoint of imparting imprintability (dryness).
Are preferred.

<Higher Sensitivity and Head Matching Property in Combination with Device> In recent years, heat-sensitive recording materials have been adopted in many fields and applications, and heat-sensitive recording such as downsizing, low running cost and maintenance-free is a background. Not only was there an advantage of the system, but there have also been improvements in technology for both printers (hardware) and recording paper (media).
On the hardware side, for example, the recording speed is 10 inches (about 25 cm) per second, and the recording width is the maximum A0 size (about 90 cm).
0 mm), resolution is 600 dpi (24 dots / mm)
As such, high-performance printers that are not inferior to conventional dot printers and laser printers have emerged, and therefore,
It is important to combine each technology according to the application and to configure it so as to have an optimum design and control method.

That is, as the high-performance printer, a high-speed printer having a recording speed of 10 cm / sec or more, a printer having a thermal head having a partial glaze structure, and the like are preferable. In a high-speed printer with a speed of 10 cm / sec or more, the sensitivity of the conventional thermal recording material may be insufficient, and in a printer equipped with a thermal head having a partial glaze structure, head contamination tends to occur.

Therefore, as a result of studying design optimization on the side of the heat-sensitive recording material, when a specific developer (electron-accepting compound) is selected and used, a high-speed printer, a recording speed especially at a recording speed of 10 cm / sec or more, Even when combined with a printer equipped with a thermal head having a glaze structure, it has been found that high sensitivity and good head matching can be achieved while satisfying the performance required for the above-mentioned thermal recording material at a high level. Obtained.

<Improvement of image quality> In some hardware (apparatus) using the heat-sensitive recording material, the recording image quality may be important, such as in a facsimile when receiving a photograph. In order to improve the recording image quality, it is effective to improve the image quality by applying an undercoat layer mainly containing an oil-absorbing pigment, especially by applying the undercoat layer by curtain coating method or blade coating method (particularly blade coating method). We obtained the knowledge that

<Reduction of environmental load> In recent years, there has been a social demand for a system having a smaller environmental load, and the field of heat-sensitive recording materials is no exception. In order to reduce the environmental load, it is important to meet the required performance with less material usage and less energy usage. To this end, it is effective to apply a thermal recording layer or the like by the curtain coating method from the viewpoint of improving the color density, and to simultaneously coat a plurality of layers is an energy saving method for drying and handling. We have found that it is effective in reducing consumption. In other words, if the color density is the same, it is possible to obtain a material with a smaller amount of material than before and with low energy.

The present invention is based on the above findings,
The specific means for solving the above problems are as follows. <1> In a heat-sensitive recording material having a heat-sensitive recording layer containing, on a support, an electron-donating colorless dye and an electron-accepting compound that reacts with the electron-donating colorless dye to develop a color, the electron-accepting compound is 4-hydroxybenzenesulfone
A nilide and the support contains an oil-absorbing pigment.
A coating layer is provided, and the heat-sensitive recording layer is an image stabilizer.
And the image stabilizer is 1,1,3-tris (2-me
Cyl-4-hydroxy-5-tert-butylpheny
Ru) butane and 1,1,3-tris (2-methyl-4-)
Low content of hydroxy-5-cyclohexylphenyl) butane
It is a thermosensitive recording material characterized by being at least one.

According to the heat-sensitive recording material described in the above item <1>, 4-hydroxybenzene sulfone is used as one of the color-forming components.
Since honanilide is used, high sensitivity can be achieved while keeping the background fog low, and the long-term storability of the formed image (image storability; hereinafter the same), chemical resistance, and head matching of the thermal head. Can also be improved at the same time. Moreover, after thermal printing, the fluorescent lamp 5
00,000 Lux · h der density retention of the indicia image portion after irradiation is 80% or more in Runode, robust image is obtained, excellent light resistance.

<2> The thermosensitive recording layer is coated, and the dry coating amount after coating is less than 6 g / cm ² <1>
The heat-sensitive recording material described in 1. According to the heat-sensitive recording material as described in <2> above, the heat-sensitive recording layer is formed with a coating amount of the coating liquid for forming the layer of less than 6 g / cm ² .
Since a thin film is formed, the drying load is small, the whiteness of the background and the image storability are not impaired, and a plain paper-like feeling can be imparted.

Further, der electron-accepting compound according to the present invention
Since including that 4-hydroxybenzene sulfonanilide, effectively increasing sensitivity, image storage stability improving, enhancing head matching properties Hakare, causing an increase in background fogging of the background portion (fog density of background portion) Nor. Further above
As described above, since the heat-sensitive recording layer contains a specific image stabilizer, it is possible to suppress the shift of the color reaction (forward reaction) to the reverse reaction and further improve the image storability. At the same time, it contributes to the improvement of light resistance.

< 3 > The thermosensitive recording layer contains an inorganic pigment, and the inorganic pigment is at least one selected from calcite-based (light) calcium carbonate, amorphous silica, and aluminum hydroxide. Alternatively, the heat-sensitive recording material described in <2> . According to the heat-sensitive recording material described in < 3 > above, since the heat-sensitive recording layer contains a specific inorganic pigment, it is possible to further improve the head matching property with the thermal head in contact, and at the same time impart the printing suitability. can do.

< 4 > The thermosensitive recording layer contains an adhesive, and the adhesive is at least one selected from sulfo-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol. 3 > The heat-sensitive recording material according to any one of 3 >. According to the heat-sensitive recording material described in < 4 > above, since the heat-sensitive recording layer contains a specific water-soluble resin as an adhesive, both high sensitivity at a higher level and further reduction of background fog are achieved. be able to. Also, with this configuration, printability can be imparted at the same time. Furthermore,
Water resistance can also be imparted by combining with a crosslinking agent.

< 5 > The thermosensitive recording material according to any one of <1> to < 4 >, wherein the support contains waste paper pulp. According to the heat-sensitive recording material described in < 5 > above, since waste paper pulp is used as the support, it is possible to reuse resources and save resources.

< 6 > A protective layer is provided on the heat-sensitive recording layer, and the protective layer contains at least one inorganic pigment selected from aluminum hydroxide, kaolin and amorphous silica, and a water-soluble polymer. The heat-sensitive recording material according to any one of <1> to < 5 > above. According to the heat-sensitive recording material described in the above < 6 >, since the heat-sensitive recording layer is provided with the protective layer containing a specific inorganic pigment, the oil-absorbing property can improve the storability, and at the same time, the handleability and the stamping aptitude. Can also be realized (giving a feeling of plain paper).

< 7 > The above <1> to < 6, wherein the total ion concentration of Na ⁺ ions and K ⁺ ions is 1500 ppm or less.
> The heat-sensitive recording material according to any one of the above items. < 7 >
According to the heat-sensitive recording material described in (1), as a result of selectively using a material having a low ion content, the total ion concentration in the whole of the support, layers, etc. constituting the heat-sensitive recording material can be suppressed to be low, so that the ions attached to the head The amount can be suppressed, and the corrosion resistance (durability) of the thermal head can be improved.

< 8 > The thermosensitive recording material according to any one of <1> to < 7 >, wherein a contact angle is 20 ° or more after 0.1 second has passed after dropping distilled water on the surface of the thermosensitive recording layer. Is. According to the heat-sensitive recording material described in < 8 > above, since the contact angle of the surface of the heat-sensitive recording layer is 20 ° or more, ink bleeding at the time of inkjet recording or stamping is effectively suppressed, and imparting inkjet suitability. It is possible to improve the suitability for printing.

< 9 > The formed image after printing is printed at a temperature of 60 ° C.
After leaving for 24 hours under the environmental condition of relative humidity of 20%,
The heat-sensitive recording material according to any one of <1> to < 8 >, wherein the residual density in the formed image is 65% or more. According to the heat-sensitive recording material described in < 9 > above, since the formed image can be maintained at a high density for a long period of time, image reliability can be maintained for a long period of time such as storing important documents, advance tickets, receipts, cash vouchers, etc. It can be applied in the required fields.

< 10 > The heat-sensitive recording layer contains a sensitizer, and the sensitizer is 2-benzyloxynaphthalene, dimethylbenzyl oxalate, m-terphenyl, ethylene glycol tolyl ether, p-benzyl biphenyl, 1, Two
-The heat-sensitive recording material according to any one of <1> to < 9 >, which is at least one selected from diphenoxymethylbenzene, 1,2-diphenoxyethane, and diphenylsulfone. According to the heat-sensitive recording material as described in < 10 > above, since the heat-sensitive recording layer contains a specific sensitizer, the dissolution viscosity can be lowered to allow the color-forming component to be well diffused, without causing deterioration of the background fog. The sensitivity can be effectively increased.

< 11 > The content of the sensitizer is 4-hydro.
7 for 100 parts by weight of xylbenzenesulfonanilide
The heat-sensitive recording material according to < 10 >, which is 5 to 200 parts by mass. According to the heat-sensitive recording material as described in < 11 > above, since the sensitizer is contained in a range suitable for the amount of the electron-accepting compound, it does not hinder other various performances and is effectively high. It is possible to increase sensitivity.

< 12 > The electron-donating colorless dye is 2-anilino-3-methyl-6-diethylaminofluorane,
2-anilino-3-methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6- (N-ethyl-
N-isoamylamino) fluorane, 2-anilino-3
-Methyl-6- (N-ethyl-N-propylamino) fluorane, 2-anilino-3-methyl-6-di-n-amylaminofluorane, and 2-anilino-3-methyl-6- (N- <Ethyl-N-p-tolylamino) fluorane, which is at least one selected from the above <1> to <
11 > The heat-sensitive recording material as described in any one of < 11 >.

According to the heat-sensitive recording material described in the above < 12 >, since the heat-sensitive recording layer contains the specific electron-donating colorless dye, the sensitivity is improved at a higher level, the background fog is reduced, and the storage stability is improved. Can be satisfied at the same time.

< 13 > The above <1> to < 12, wherein at least one layer on the support is applied and formed by a curtain coating method.
> The heat-sensitive recording material according to any one of the above items. < 13
According to the heat-sensitive recording material described in <1>, at least one of the plurality of layers, particularly the heat-sensitive recording layer, is applied by the curtain coating method, so that the constituent components can be concentrated on the recording surface, and less material is used. The color density can be increased by the amount, and the image quality (image quality) can be improved. Further, when a plurality of layers are simultaneously coated by the curtain coating method, it is possible to reduce energy consumption during manufacturing.

[0045]

In the heat-sensitive recording material of the embodiment of the present invention, it has a heat-sensitive recording layer of the coloring system which is a combination of electron-donating colorless dye and an electron accepting compound, as the electron-accepting compound, 4- Fluorescent lamp 50 in a printing section containing hydroxybenzenesulfonanilide and thermally printed
The residual concentration ratio after irradiation of 10,000 Lux · h should be 80% or more .
Is desirable . Hereinafter, the heat-sensitive recording material of the present invention will be described in detail.

The heat-sensitive recording material of the present invention has one or two or more heat-sensitive recording layers on a support, and preferably has a protective layer. Moreover, you may have other layers, such as an intermediate | middle layer as needed. The <thermosensitive recording layer> The thermosensitive recording layer, and an electron-donating colorless dye, the color is developed by reaction with electron-donating colorless dye 4- arsenide
Droxybenzenesulfonanilide and image stabilizer (UV
Anti-ray agent) , preferably an inorganic pigment, an adhesive and a sensitizer, and optionally other components.

-Electron-donating colorless dye-The heat-sensitive recording layer according to the invention contains at least one electron-donating colorless dye as a color-forming component. The electron-donating colorless dye can be appropriately selected from conventionally known ones, for example, 2-anilino-3-methyl-6-diethylaminofluorane and 2-anilino-3-.
Methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6- (N-ethyl-N-isoamylamino) fluorane, 2-anilino-3-methyl-6- (N
-Ethyl-N-propylamino) fluorane, 2-anilino-3-methyl-6-di-n-amylaminofluorane, and 2-anilino-3-methyl-6- (N-ethyl-Np-tolylamino) ) Fluoran, 2-anilino-
3-Methyl-6-N-ethyl-N-sec-butylaminofluorane, 3-di (n-pentylamino) -6-methyl-7-anilinofluorane, 3- (N-isoamyl-N-ethyl) Amino) -6-methyl-7-anilinofluorane, 3- (Nn-hexyl-N-ethylamino)
-6-Methyl-7-anilinofluorane, 3- [N-
(3-Ethoxypropyl) -N-ethylamino] -6-
Methyl-7-anilinofluorane, 3-di (n-butylamino) -7- (2-chloroanilino) fluorane, 3
-Diethylamino-7- (2-chloroanilino) fluorane, 3- (N-cyclohexyl-N-methylamino)
-6-methyl-7-anilinofluorane and the like can be mentioned.

Among the above, 2-anilino-3-methyl-6-diethylaminofluorane, 2-anilino-3-
Methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6- (N-ethyl-N-isoamylamino) fluorane, 2-anilino-3-methyl-6- (N
-Ethyl-N-propylamino) fluorane, 2-anilino-3-methyl-6-di-n-amylaminofluorane, and 2-anilino-3-methyl-6- (N-ethyl-Np-tolylamino) ) It is particularly preferable to contain at least one selected from the group consisting of fluoran. Further, the electron-donating colorless dye may be used singly in a single heat-sensitive recording layer, or may be used in combination of two or more kinds.

By containing at least one selected from the above group as an electron-donating colorless dye, in particular, the color density is increased while the background fog is kept low, and the image storability of the image portion formed at the same time is also improved. It can be further improved.

In preparing a coating solution for forming a heat-sensitive recording layer (hereinafter, also referred to as "coating solution for heat-sensitive recording layer"), the particle diameter of the electron-donating colorless dye is a volume average particle diameter. 1.0 μm or less is preferable, and 0.4 to 0.7
μm is more preferable. If the volume average particle size exceeds 1.0 μm, the thermal sensitivity may decrease, and if it is less than 0.4 μm, background fog may worsen. The volume average particle diameter is a laser diffraction type particle size distribution measuring device (for example,
It can be easily measured by LA500 (manufactured by Horiba Ltd.) or the like.

[0051] The coating amount of the electron-donating colorless dye is preferably from 0.1 to 1.0 g / m ^2, in terms of color density and background fogging, and more preferably 0.2-0.5 g / m ² .

[0052] - an electron-accepting compound - the heat-sensitive recording layer according to the present invention, as the electron-accepting compound capable of coloring by reaction at the electron-donating colorless dye and heat, 4
-Contains hydroxybenzenesulfonanilide . By containing the compound as an electron-accepting compound,
Sensitivity can be increased while keeping the background fog low, and the formed image can be stored for a long time (image storability), chemical resistance,
The inkjet suitability and the head matching property of the thermal head can be improved at the same time. 4-hydroxybenzenesulfonanilide is most preferable from the viewpoint of the balance between image storability and background fog.

The content of the electron-accepting compound in a single heat-sensitive recording layer is preferably 50 to 400% by mass, and 100 to 30% by mass relative to the mass of the electron-donating colorless dye.
0 mass% is more preferable.

With 4-hydroxybenzenesulfonanilide , the effects of the present invention (in particular, reduction of background fog, high sensitivity, and improvement of image storability, chemical resistance, and head matching property) are not impaired. Other known electron-accepting compounds may be used in combination within the range. The known electron-accepting compound can be appropriately selected and used, and from the viewpoint of suppressing the background fog, a phenolic compound, a salicylic acid derivative or a polyvalent metal salt thereof is preferable.

Examples of the phenolic compound include 2,2'-bis (4-hydroxyphenol) propane (bisphenol A), 4-t-butylphenol, 4-phenylphenol, 4-hydroxydiphenoxide, 1,1. '-Bis (4-hydroxyphenyl) cyclohexane, 1,1'-bis (3-chloro-4-hydroxyphenyl) cyclohexane, 1,1'-bis (3
-Chloro-4-hydroxyphenyl) -2-ethylbutane, 4,4'-sec-isooctylidene diphenol, 4,4'-sec-butylylene diphenol, 4-
tert-octylphenol, 4-p-methylphenylphenol, 4,4'-methylcyclohexylidenephenol, 4,4'-isopentylidenephenol, 4
-Hydroxy-4-isopropyloxydiphenyl sulfone, benzyl p-hydroxybenzoate, and the like.

Examples of the salicylic acid derivative include:
4-pentadecylsalicylic acid, 3-5-di (α-methylbenzyl) salicylic acid, 3,5-di (tert-octyl) salicylic acid, 5-octadecylsalicylic acid, 5-α
-(P-α-methylbenzylphenyl) ethylsalicylic acid, 3-α-methylbenzyl-5-tert-octylsalicylic acid, 5-tetradecylsalicylic acid, 4-hexyloxysalicylic acid, 4-cyclohexyloxysalicylic acid, 4-decyloxysalicylic acid, 4-dodecyloxysalicylic acid, 4-pentadecyloxysalicylic acid, 4
-Octadecyloxysalicylic acid and the like, and zinc, aluminum, calcium, copper and lead salts thereof.

As the known electron-accepting compound, p-
N- (2-chlorophenyl) sulfamoylphenol, p-N-3-tolylsulfamoylphenol, p
-N-2-tolylsulfamoylphenol, p-N-
(3-methoxyphenyl) sulfamoylphenol,
p-N- (3-hydroxyphenyl) sulfamoylphenol, p-N- (4-hydroxyphenyl) sulfamoylphenol, 2-chloro-4-N-phenylsulfamoylphenol, 2-chloro-4- N- (3-
Hydroxyphenyl) sulfamoylphenol, 4 '
-Hydroxy-p-toluene sulfone anilide, 4,
4'-bis (p-toluenesulfonylaminocarbonylamino) diphenylmethane (= BTUM), 4-hydroxy-4'-isopropoxydiphenylsulfone, 2,
4-bis (phenylsulfonyl) phenol , etc. are also mentioned.
To be

When the known electron-accepting compound is used in combination, the content of the 4-hydroxybenzenesulfonanilide described above is based on the total mass of the electron-accepting compound.
50 mass% or more is preferable, and 70 mass% or more is particularly preferable.

When preparing a coating solution for forming a heat-sensitive recording layer,
The particle size of the electron-accepting compound is preferably 1.0 μm or less in volume average particle size, and more preferably 0.4 to 0.7 μm. When the volume average particle diameter exceeds 1.0 μm,
The thermal sensitivity may decrease. If it is less than 0.4 μm, the background fog may worsen. The volume average particle size is also measured by a laser diffraction type particle size distribution measuring device (for example, LA50
0 (manufactured by Horiba Ltd.) and the like can be easily measured.

—Sensitizer— The heat-sensitive recording layer according to the invention preferably contains a sensitizer. In particular, in that the sensitivity can be greatly improved, 2
-Benzyloxynaphthalene, dimethylbenzyl oxalate, m-terphenyl, ethylene glycol tolyl ether, p-benzyl biphenyl, 1,2-diphenoxymethylbenzene, 1,2-diphenoxyethane, and diphenyl sulfone (hereinafter , Sometimes referred to as "sensitizer according to the present invention").

The total content of the selected sensitizer in the heat-sensitive recording layer is 10% by weight of the electron-accepting compound (preferably 4-hydroxybenzenesulfonanilide).
75 to 200 parts by mass is preferable with respect to 0 parts by mass, and 1
More preferably, it is from 00 to 150 parts by mass. When the content is within the above range, the effect of improving the sensitivity is large and the image storability can be improved.

In addition to the sensitizer selected from the above group, other sensitizers appropriately selected from conventionally known ones may be used in combination as long as the effects of the present invention are not impaired. When the other sensitizer is used in combination, the amount of the sensitizer selected from the group is preferably 50% by mass or more, and more preferably 70% by mass or more of the total amount of the sensitizer contained in the layer. preferable.

Examples of the other sensitizers include aliphatic monoamide, aliphatic bisamide, stearyl urea,
Di (2-methylphenoxy) ethane, di (2-methoxyphenoxy) ethane, β-naphthol- (p-methylbenzyl) ether, α-naphthylbenzyl ether,
1,4-butanediol-p-methylphenyl ether, 1,4-butanediol-p-isopropylphenyl ether, 1,4-butanediol-p-tert-
Octyl phenyl ether, 1-phenoxy-2- (4
-Ethylphenoxy) ethane, 1-phenoxy-2-
(Chlorophenoxy) ethane, 1,4-butanediol phenyl ether, diethylene glycol bis (4-methoxyphenyl) ether, 1,4-bis (phenoxymethyl) benzene and the like can be mentioned.

-Image Stabilizer (UV Absorber) -The heat-sensitive recording layer according to the present invention contains an image stabilizer (including a UV absorber) . The UV absorber may be microencapsulated. By containing the image stabilizer, the storability of the formed color image (image storability) can be further improved.

As the image stabilizer, for example, a phenol compound, particularly a hindered phenol compound is effective, and, for example, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane. ,
1,1,3-tris (2-methyl-4-hydroxy-5)
-Cyclohexylphenyl) butane, 1,1,3-tris (2-ethyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1,3-tris (3,5-di-
tert-butyl-4-hydroxyphenyl) butane,
1,1,3-tris (2-methyl-4-hydroxy-5)
-Tert-butylphenyl) propane, 2,2'-methylene-bis (6-tert-butyl-4-methylphenol), 2,2'-methylene-bis (6-tert-
Butyl-4-ethylphenol), 4,4'-butylidene-bis (6-tert-butyl-3-methylphenol), 4,4'-thio-bis- (3-methyl-6-te).
(rt-butylphenol) and the like. The image stabilizers may be used alone or in combination of two or more.

Among others, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexyl) Phenyl) butane is preferred.

The total content of the image stabilizer in a single heat-sensitive recording layer is from the viewpoint of suppressing background fog and effectively improving image storability, and the electron-donating colorless dye 10 described above.
10 to 100 parts by mass is preferable with respect to 0 parts by mass, and 2
0 to 60 parts by mass is more preferable. Further, 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane and / or 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) When the above-mentioned image stabilizer other than these is used in combination with butane, in the single heat-sensitive recording layer,
1,3-tris (2-methyl-4-hydroxy-5-t
ert-butylphenyl) butane and / or 1,1,3
The content of -tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane is preferably 50% by mass or more, and more preferably 70% by mass or more, based on the total mass of the image stabilizer.

Examples of the ultraviolet absorber include the following ultraviolet absorbers.

[Chemical 1]

The content of the ultraviolet absorber in the single heat-sensitive recording layer is from the viewpoint of effectively improving the image storability, with respect to 100 parts by mass of the electron-donating colorless dye.
10 to 300 parts by mass is preferable, and 30 to 200 parts by mass is more preferable.

-Inorganic Pigment- In the heat-sensitive recording layer according to the present invention, as an inorganic pigment, at least one selected from calcite-based calcium carbonate, amorphous silica, and aluminum hydroxide (the inorganic pigment according to the present invention is used. ) Is preferably contained. By containing these, the head matching property with the thermal head in contact can be further improved, and at the same time, printability and plain paper-like property can be imparted.

(Light) calcium carbonate generally has crystal forms such as calcite, aragonite, vaterite, etc.,
Calcite-based (light) calcium carbonate is preferred from the viewpoints of color density when recording with a thermal head, prevention of head stains, absorption, hardness, etc. Among them, in particular, the particle shape is spindle-shaped or uneven. A triangular surface is preferable. Calcite-based (light) calcium carbonate can be produced by a known production method. The calcite-based (light) calcium carbonate preferably has a volume average particle diameter of 1 to 3 μm. The volume average particle size is
It can be measured in the same manner as the electron-donating colorless dye.

The content of the above-mentioned "inorganic pigment according to the present invention" in a single heat-sensitive recording layer is 100 parts by mass of the electron-accepting compound from the viewpoint of improving the color density and preventing the deposition of dust on the thermal head. 50 to 500 parts by mass, more preferably 70 to 350 parts by mass, 90 to 2 parts by mass
50 parts by mass are particularly preferred.

Further, other inorganic pigments may be used in combination with the above-mentioned inorganic pigment of the present invention within a range not impairing the effects of the present invention (in particular, improvement of head matching property, printability and plain paper-like property). . Examples of the other inorganic pigments include calcium carbonate excluding calcite (light) calcium carbonate, barium sulfate, lithopone, wax, kaolin, calcined kaolin, amorphous silica, kaolin, magnesium carbonate, magnesium oxide, and the like. To be The volume average particle size of the other inorganic pigment (by a laser diffraction particle size distribution measuring device (for example, LA500 (manufactured by Horiba Ltd.)) is preferably 0.3 to 1.5 μm, and 0.5 to 0.9
μm is more preferable.

When the inorganic pigment according to the present invention is used in combination with the other inorganic pigment, the ratio of the total mass (v) of the "inorganic pigment according to the present invention" to the total mass (w) of the other inorganic pigment. (V /
As w), 100/0 to 60/40 is preferable, and 1
00/0 to 80/20 are more preferable.

From the viewpoint of suppressing wear of the thermal head, an inorganic pigment having a Mohs hardness of 3 or less is preferable.
“Mohs hardness” means the Mohs hardness described in “English-Plastic Industry Dictionary, 5th Edition, p.616” (Shin Ogawa, published by Industrial Research Institute Co., Ltd.). Inorganic pigments having a Mohs hardness of 3 or less include calcium carbonate, aluminum hydroxide and the like.

When the inorganic pigment according to the present invention is used in a mixture with magnesium carbonate and magnesium oxide, it is preferable in that it is effective in reducing the background fog, and the content of magnesium carbonate and / or magnesium oxide in that case is preferable. , 3 to 50 mass% of the total mass of the inorganic pigment, especially 5 to 30
It is preferably set to mass%.

—Adhesive— At least one selected from sulfo-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol as an adhesive (or protective colloid during dispersion) in the heat-sensitive recording layer according to the present invention. It is preferable to contain one kind (that is, modified polyvinyl alcohol (hereinafter sometimes referred to as “specific modified PVA”)). By containing the specific modified PVA as an adhesive in the heat-sensitive recording layer, it is possible to give a plain paper-like feeling and to increase the adhesive force between the heat-sensitive recording layer and the support, which is generated during offset printing. Trouble such as peeling can be prevented, and printability can be improved. Further, it is possible to increase the color density when recording with the thermal head while suppressing the background fog to a lower level.

The specific modified PVA may be used alone or in combination, and may be used in combination with other modified PVA or polyvinyl alcohol (PVA). When the other modified PVA or PVA is used in combination, the specific modified PVA is used.
The ratio of 1 to the total mass of the adhesive component
0 mass% or more is preferable, and 20 mass% or more is more preferable.

The specific modified PVA preferably has a saponification degree of 85 to 99 mol%. When the saponification degree is less than 85 mol%, water resistance to the fountain solution used during offset printing may be insufficient, and so-called paper peeling may easily occur. To avoid this, the amount of modified PVA added If the color density is increased to prevent peeling of the paper, the color density may decrease. On the other hand, when the saponification degree exceeds 99 mol%, undissolved substances are likely to be produced during the preparation of the coating liquid, which may cause defective coating. In order not to impair the effects of the present invention, even when other modified PVA or PVA is used in combination, the saponification degree of the other modified PVA or PVA is preferably within the above range.

Further, the polymerization degree of the specific modified PVA is preferably 200 to 2000. The degree of polymerization is 200
If the amount is less than the above range, it may be easy to cause the paper peeling during offset printing, and if the addition amount is increased to avoid the paper peeling, the color density may decrease. Also,
When the degree of polymerization exceeds 2000, the modified PVA is difficult to dissolve in a solvent (water) and the viscosity of the liquid during preparation increases, so that it becomes difficult to prepare and apply a coating liquid for forming a heat-sensitive recording layer. is there. Further, in order not to impair the effects of the present invention, even when other modified PVA or PVA is used in combination, it is preferable that the degree of polymerization of the other modified PVA or PVA is within the above range. The degree of polymerization here means J
The average degree of polymerization determined by the method described in IS-K6726 (1994).

The content of the specific modified PVA in the heat-sensitive recording layer is an electron-donating colorless dye 10 from the viewpoint of improving the color density and imparting offset printing suitability (paper peeling prevention, etc.).
30 to 300 parts by mass is preferable with respect to 0 parts by mass, and 7
0 to 200 parts by mass is more preferable, and 100 to 170 parts by mass is particularly preferable. The specific modified PVA has a function as a dispersant, a binder, and the like, as well as a function as an adhesive that enhances interlayer adhesion.

Next, each of the specific modified PVA, that is, sulfo-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, and acetoacetyl-modified polyvinyl alcohol will be described in detail.

The sulfo-modified polyvinyl alcohol is
A polymer obtained by polymerizing an olefin sulfonic acid such as ethylene sulfonic acid, allyl sulfonic acid, or methallyl sulfonic acid or a salt thereof and a vinyl ester such as vinyl acetate in an alcohol or an alcohol / water mixed solvent is saponified. Method, a method of copolymerizing amide sodium salt and vinyl ester such as vinyl acetate, and saponifying the obtained copolymer, after treating PVA with bromine, iodine, etc., and then in an acidic sodium sulfite aqueous solution. It can be produced by a method of heating, a method of heating PVA in a concentrated aqueous solution of sulfuric acid, a method of acetalizing PVA with an aldehyde compound containing a sulfonic acid group, and the like.

The diacetone-modified polyvinyl alcohol is a partially or completely saponified product of a copolymer of a monomer having a diacetone group and a vinyl ester, wherein the monomer having a diacetone group and a vinyl ester are copolymerized. It can be produced by saponifying the resin thus obtained. In the diacetone-modified polyvinyl alcohol, the ratio of the diacetone group-containing monomer (repeating unit structure) is not particularly limited.

The acetoacetyl-modified polyvinyl alcohol is generally a solution of polyvinyl alcohol resin,
It can be produced by adding and reacting liquid or gaseous diketene to the dispersion or powder. The degree of acetylation of the acetoacetyl-modified polyvinyl alcohol can be appropriately selected depending on the quality of the intended heat-sensitive recording material.

-Other Components-In the heat-sensitive recording layer according to the invention, in addition to the above components, a crosslinking agent, other pigments, metal soaps, waxes, surfactants, binders, antistatic agents may be added depending on the purpose and need. Other components such as agents, defoamers and fluorescent dyes may be contained.

[Crosslinking Agent] The thermosensitive recording layer may contain a crosslinking agent which acts on the specific modified PVA used as the adhesive (or protective colloid) and other modified PVA. By containing the crosslinking agent, the water resistance of the heat-sensitive recording material can be improved. As the cross-linking agent,
It can be appropriately selected as long as it can crosslink the specific modified PVA (and preferably other modified PVA etc.), and among them, an aldehyde compound such as glyoxal and a dihydrazide compound such as adipic acid dihydrazide are particularly preferable. As the content of the crosslinking agent in the heat-sensitive recording layer, the specific modified PVA and other modified PVA to be crosslinked, etc. 10
1 to 50 parts by mass is preferable with respect to 0 parts by mass, and 3 to 2
0 mass part is more preferable. When the content of the crosslinking agent is within the above range, water resistance can be effectively improved.

[Mordant] The heat-sensitive recording layer may contain a mordant for the purpose of preventing bleeding during inkjet recording. The mordant is at least selected from an amide group, an imide group, a primary amino group, a secondary amino group, a tertiary amino group, a primary ammonium base, a secondary ammonium base, a tertiary ammonium base and a quaternary ammonium base. There may be mentioned a compound containing one kind of chaos group.

Specific examples thereof include polyamide epichlorohydrin, polyvinylbenzyltrimethylammonium chloride, polydiallyldimethylammonium chloride, polymethacryloyloxyethyl-β-hydroxyethyldimethylammonium chloride, polydimethylaminoethylmethacrylate hydrochloride, polyethyleneimine, polyallylamine, Examples thereof include polyallylamine hydrochloride, polyamide-polyamine resin, chaotic starch, dicyandiamide formalin condensate, dimethyl-2-hydroxypropylammonium salt polymer, and the like.

In addition to the above, cationic polymers are also suitable. Examples of the cationic polymer include polyethyleneimine, polydiallylamine, polyallylamine, polydiallyldimethylammonium chloride, polymethacryloyloxyethyl-β-hydroxyethyldimethylammonium chloride, polyallylamine hydrochloride, polyamide-polyamine resin, cationized starch. , Dicyandiamide formalin condensate, dimethyl-2
-Hydroxypropyl ammonium salt polymer, polyamidine, polyvinylamine and the like can be mentioned.

The molecular weight of the mordant is from 1000 to
About 200,000 is preferable. If the molecular weight is less than 1000, water resistance tends to be insufficient, and 200
If it exceeds 000, the viscosity may be high and the handling may be poor. The cationic polymer is
It may be added to either the heat-sensitive recording layer or the protective layer described later.

[Metal Soap, Wax, Surfactant] Examples of the metal soap include higher fatty acid metal salts such as zinc stearate, calcium stearate, and aluminum stearate. Examples of the wax include paraffin wax, microcrystalline wax, carnauba wax, methylol stearamide, polyethylene wax, polystyrene wax,
And fatty acid amide wax, etc. may be used alone or in a mixture of two or more. As the surfactant, for example, a sulfosuccinic acid-based alkali metal salt,
Fluorine-containing surfactants and the like can be mentioned.

[Binder] The electron-donating colorless dye described above,
Dispersion of the electron-accepting compound, the inorganic pigment, the adhesive and the sensitizer, and other components can be suitably carried out in a water-soluble binder. As the binder used here, a compound that is soluble in 5% by mass or more in water at 25 ° C. is preferable. Specifically, for example, polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose,
Examples thereof include starches (including modified starch), gelatin, gum arabic, casein, and saponified products of styrene-maleic anhydride copolymer.

The binder has a function of improving the film strength of the heat-sensitive recording layer as well as at the time of dispersion, and in order to exhibit this function, a styrene-butadiene copolymer, a vinyl acetate copolymer and an acrylonitrile- A synthetic polymer latex binder such as a butadiene copolymer, a methyl acrylate-butadiene copolymer, or polyvinylidene chloride can also be used in combination.

-Others- The above-mentioned electron-donating colorless dye, electron-accepting compound, inorganic pigment, adhesive and sensitizer are the ball mill, attritor,
It can be prepared as a coating solution by simultaneously or separately dispersing with a stirring / crushing machine such as a sand mill. In the coating liquid, if necessary, the above-mentioned other components, that is, a crosslinking agent,
A mordant, metal soap, wax, surfactant, binder, antistatic agent, defoaming agent, fluorescent dye and the like are added.

After being prepared as a coating solution as described above,
The coating liquid is applied on the surface of the support to form a heat-sensitive recording layer. The coating method for applying the coating liquid is not particularly limited, and may be appropriately selected from the coating methods using an air knife coater, roll coater, blade coater, curtain coater, etc., and is dried after coating. After drying, it is preferably subjected to a smoothing treatment by a calendar treatment before use. The dry coating amount of the coating liquids in the case of applying and forming a heat-sensitive recording layer, preferably less than ^{6g / m 2, 5g / m} 2 or less is particularly preferred.

In the present invention, high density (high sensitivity) can be obtained with a smaller amount of material used, and at the same time, image quality (image quality) can be obtained.
The curtain coating method using a curtain coater is particularly preferable in that it can also improve Further, as will be described later, when a protective layer and the like are laminated in addition to the heat-sensitive recording layer, the energy consumption during manufacturing can be further reduced by simultaneously coating a plurality of layers by the curtain coating method. Specifically, it is as follows.

The thermal recording material preferably comprises a single layer or a part or all of a plurality of layers provided on a support.
A single or a plurality of types of coating solutions are curtain coated on the surface of a support and then dried to produce the coating. The type of layer formed by curtain coating is not particularly limited, and examples thereof include an undercoat layer, a thermosensitive recording layer, and a protective layer.
A preferred mode is that these adjacent series of layers are simultaneously coated in multiple layers by curtain coating.

Specific examples of the combination of layers in the case of simultaneous multi-layer coating include a combination of an undercoat layer and a heat-sensitive recording layer, a combination of a heat-sensitive recording layer and a protective layer, a combination of an undercoat layer, a heat-sensitive recording layer and a protective layer, and a type thereof. Examples include, but are not limited to, a combination of two or more undercoat layers different from each other, a combination of two or more thermal recording layers different from each other, a combination of two or more protective layers different from each other, and the like.

The curtain coating device used for the curtain coating is not particularly limited, and examples thereof include an extrusion hopper type curtain coating device and a slide hopper type curtain coating device, among which a photographic photosensitive material is used. The slide hopper type curtain coating device described in JP-B-49-24133 is particularly preferable. By using this slide hopper type curtain coating device, it is possible to easily perform multi-layer simultaneous coating.

In the heat-sensitive recording material of the present invention, the heat-printed image area has a density residual ratio (light resistance) of 80% or more even when irradiated with a fluorescent lamp of 500,000 Lux · h. The density remaining ratio is the ratio of the density D ² of the printed area after irradiation to the density D ¹ of the printed area before irradiation (D ² / D ¹ × 1).
00). Each density is Macbeth reflection densitometer (RD-
918, manufactured by Macbeth) or the like. When the density residual ratio is less than 80%, the light resistance is insufficient, and the printing density decreases during storage after printing, resulting in a decrease in commercial value. Above all, 90% or more is desirable. In order to make the image residual ratio 80% or more, in particular, an image stabilizer (particularly an ultraviolet absorber) is contained in the heat-sensitive recording layer or the protective layer,
Electron-donating colorless dyes, types and formulations of electron-accepting compounds,
In addition, microencapsulation of the color-developing component can be performed by appropriately selecting it in a suitable mode.

<Protective Layer> At least one protective layer is preferably provided on the heat-sensitive recording layer. The protective layer contains organic or inorganic fine powder, a binder, a surfactant, a heat-fusible substance and the like. It can be comprised by containing. Examples of the fine powders include inorganic fine powders of calcium carbonate, silicas, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, kaolin, clay, talc, surface-treated calcium and silica, etc. Besides,
Examples thereof include urea-formalin resin, styrene / methacrylic acid copolymer, and organic fine powder such as polystyrene.

Examples of the binder contained in the protective layer include polyvinyl alcohol, carboxy-modified polyvinyl alcohol, vinyl acetate-acrylamide copolymer,
Silicon-modified polyvinyl alcohol, starch, modified starch, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, gelatins, arabic gum, casein, styrene-maleic acid copolymer hydrolyzate, polyacrylamide derivative, polyvinylpyrrolidone, and styrene-butadiene rubber latex, Examples thereof include acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, and latexes such as vinyl acetate emulsion.

A preferred mode is one in which a binder component in the protective layer is crosslinked to add a waterproofing agent for further improving the storage stability of the heat-sensitive recording material. Examples of the water-proofing agent include water-soluble initial condensation products such as N-methylol urea, N-methylol melamine, and urea-formalin, glyoxal, dialdehyde compounds such as glutaraldehyde, and inorganic materials such as boric acid, borax, and colloidal silica. Examples include a system cross-linking agent and polyamide epichlorohydrin.

Among the above, a particularly preferable protective layer is preferably an embodiment containing a water-soluble polymer and at least one inorganic pigment selected from aluminum hydroxide, kaolin and amorphous silica. By configuring in this mode, the storability can be improved, and at the same time, the handleability and the suitability for printing can be imparted. Further, a surfactant, a heat-fusible substance, etc. may be further contained.

The volume average particle diameter of the inorganic pigment contained in the protective layer is preferably 0.5 to 3 μm, and 0.7 to 2.5.
μm is more preferable. Among them, aluminum hydroxide having a thickness of 0.5 to 1.2 μm is preferable from the viewpoint of improving the suitability for printing, and amorphous silica is preferably used from the viewpoint of improving suitability for inkjet. The volume average particle size here can be measured in the same manner as that of the electron-donating colorless dye described above.

The total content of inorganic pigments selected from aluminum hydroxide, kaolin and amorphous silica is 10 based on the total solid content (mass) of the coating liquid for forming the protective layer.
-90 mass% is preferable, and 30-70 mass% is more preferable. Further, other pigments such as barium sulfate, zinc sulfate, talc, clay and colloidal silica may be used in combination within a range that does not impair the effects of the present invention (in particular, improvement of storage stability and imparting of handleability and imprintability). Good.

Examples of the water-soluble polymer include polyvinyl alcohol or modified polyvinyl alcohol (hereinafter collectively referred to as “polyvinyl alcohol”), starch or oxidized starch, urea phosphate esterified starch, etc. among the binders. Modified starch, styrene-maleic anhydride copolymer, styrene-maleic anhydride copolymer alkyl ester compound, carboxyl group-containing polymer such as styrene-acrylic acid copolymer, and the like. Among them, from the viewpoint of imprintability, polyvinyl alcohol, oxidized starch and urea phosphate esterified starch are preferable, and polyvinyl alcohol (x) and oxidized starch and / or urea phosphate esterified starch (y) are 90/10 to 10 Mass ratio of 10/90 (x /
It is particularly preferable to use a mixture of y). In particular, when all of the polyvinyl alcohol, the oxidized starch and the urea phosphate esterified starch are used in combination, the mass ratio (y ¹ / y) of the oxidized starch (y ¹ ) and the urea phosphate esterified starch (y ² ). ² ) is preferably 10/90 to 90/10.

As the modified polyvinyl alcohol,
Acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, and amide-modified polyvinyl alcohol are preferable,
In addition, sulfo-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol and the like are used. By combining these cross-linking agents that react with polyvinyl alcohol, it is possible to further improve the storability, handleability, and imprintability.

The content ratio of the water-soluble polymer is 10 to 10 based on the total solid content (mass) of the coating liquid for forming the protective layer.
90 mass% is preferable and 30-70 mass% is more preferable.

Examples of the cross-linking agent for cross-linking the water-soluble polymer include polyvalent amine compounds such as ethylenediamine, polyvalent aldehyde compounds such as glyoxal, glutaraldehyde and dialdehyde, dihydrazide such as adipic acid dihydrazide and phthalic acid dihydrazide. Compounds, water-soluble methylol compounds (urea, melamine, phenol), polyfunctional epoxy compounds, polyvalent metal salts (Al, T
(i, Zr, Mg, etc.) and the like are preferable. Of these, polyvalent aldehyde compounds and dihydrazide compounds are preferable.

The content ratio of the crosslinking agent is preferably about 2 to 30% by mass, more preferably 5 to 20% by mass, based on the mass of the water-soluble polymer. By containing the cross-linking agent, the film strength and water resistance can be further improved. The mixing ratio of the inorganic pigment selected from aluminum hydroxide, kaolin and amorphous silica and the water-soluble polymer in the protective layer may be the type of the inorganic pigment, its particle size, the type of the water-soluble polymer. Etc., but
The amount of water-soluble polymer is 50 to 4 with respect to the mass of the inorganic pigment.
The amount is preferably 00% by mass, more preferably 100 to 250% by mass. The total mass of the inorganic pigment and the water-soluble polymer in the protective layer is preferably 50% by mass or more of the total mass of the solid content of the protective layer.

In order to improve the suitability of the inkjet ink, a surfactant is added to the protective layer, that is, the coating liquid for forming the protective layer (hereinafter, may be referred to as "coating liquid for protective layer"). Aspects are also preferred. Examples of the surfactant include alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, sulfosuccinic acid alkyl ester salts such as dioctyl sodium sulfosuccinate, polyoxyethylene alkyl ether phosphates, sodium hexametaphosphate, perfluoroalkylcarboxylic acid. Acid salts and the like are preferable, and among them, sulfosuccinic acid alkyl ester salts are more preferable. The content ratio of the surfactant is preferably 0.1 to 5 mass% with respect to the total solid content (mass) of the coating liquid for forming the protective layer, and is 0.1.
5 to 3 mass% is more preferable.

The coating liquid for forming the protective layer contains the above-mentioned inorganic pigment selected from aluminum hydroxide, kaolin and amorphous silica, a water-soluble polymer, and, if necessary, a crosslinking agent, a surfactant and the like. It can be prepared by dissolving or dispersing in a desired aqueous solvent. Here, in the coating liquid, a lubricant, a defoaming agent, a fluorescent whitening agent, a colored organic pigment, or the like is impaired in the effects of the present invention (in particular, improvement of storage stability, and handling property and imprintability). It can be added in the range not present. Examples of the lubricant include metal soaps such as zinc stearate and calcium stearate, paraffin wax, microcrystalline wax, waxes such as carnauba wax and synthetic polymer wax, and the like.

-Support-As the support, a conventionally known support can be applied. Specific examples thereof include paper supports such as high-quality paper, coated paper obtained by coating paper with resin or pigment, resin-laminated paper, high-quality paper having an undercoat layer, synthetic paper, plastic film, and the like. It is also possible to use a support which contains mainly waste paper pulp, i.e. waste paper pulp accounts for 50% by weight of the support.

From the viewpoint of dot reproducibility, the support is preferably a smooth support having a smoothness defined by JIS-P8119 within the range of 300 seconds to 500 seconds. Furthermore, for the same reason as above, it is more preferable that the smoothness defined by JIS-P8119 is 100 seconds or more,
Those of 150 seconds or more are particularly preferable.

The used paper pulp is generally the following 1) to 3)
It is made from a combination of 3 steps. 1) Disaggregation: Waste paper is treated with mechanical force and chemicals using a pulper to disintegrate it into fibers, and the printing ink is separated from the fibers. 2) Dust removal ... Foreign matter contained in used paper (plastic, etc.)
And remove dust. 3) Deinking: The printing ink separated from the fibers is removed from the system by flotation or washing. If necessary, bleaching can be performed at the same time as deinking or in another step. A support for a thermal recording material is formed by a conventional method using 100% by mass of the waste paper pulp thus obtained or a mixture of the waste paper pulp and the virgin pulp having a content of less than 50% by mass.

[0118] If the undercoat layer on the support is al provided,
The undercoat layer is preferably provided on the surface of the support having a Steckigt size of 5 seconds or more, and preferably contains a pigment and a binder as main components. As the pigment for the undercoat layer, all common inorganic and organic pigments can be used, but especially J
Oil absorption specified by IS-K5101 is 40ml / 100
Oil absorbing pigments of g (cc / 100 g) or more are preferred. Specific examples of the oil absorbing pigment include calcined kaolin, aluminum oxide, magnesium carbonate, calcined diatomaceous earth, aluminum silicate, magnesium aluminosilicate, calcium carbonate, barium sulfate, aluminum hydroxide, kaolin, calcined kaolin, amorphous silica and urea. Formalin resin powder,
Etc. Above all, the oil absorption is 70 ml / 10.
Especially preferred is 0 g to 80 ml / 100 g of calcined kaolin.

When an undercoat layer is formed by coating on a support,
The coating amount of the pigment is preferably 2 g / m ² or more, 4g / m ² or more preferably, 7~12g / m ² is particularly preferred.

Examples of the binder for the undercoat layer include water-soluble polymers and aqueous binders. These may be used alone or in combination of two or more. Examples of the water-soluble polymer include starch, polyvinyl alcohol, polyacrylamide, carboxymethyl cellulose, methyl cellulose, and casein, and examples of the aqueous binder include synthetic rubber latex and synthetic resin emulsions. Examples thereof include styrene-butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex and vinyl acetate emulsion.

The amount of the binder used for the undercoat layer is determined in consideration of the film strength and the thermal sensitivity of the thermosensitive color developing layer, but is 3 to 10 relative to the mass of the pigment for the undercoat layer.
0 mass% is preferable, 5 to 50 mass% is more preferable,
8-15 mass% is especially preferable. Also, in the undercoat layer,
Wax, anti-fading agent, surfactant and the like may be added.

The coating liquid for forming the undercoat layer can be coated by a known coating method. Specific examples include a coating method using an air knife coater, a roll coater, a blade coater, a gravure coater, a curtain coater, etc. Among them, a coating method using a curtain coater or a blade coater is preferable, and a blade coater is used. The coating method is more preferable. After coating and drying, it may be further subjected to a smoothing treatment with a calender or the like before use.

The method using the blade coater is not limited to a coating method using a bevel type or a vent type blade, but includes a rod blade coating method, a bill blade coating method and the like, and is limited to an off-machine coater. The coating may be performed by an on-machine coater installed in the paper machine instead of the one. In order to obtain excellent smoothness and surface state by imparting fluidity during blade coating, the etherification degree of 0.6 to 0.8 is added to the coating liquid for forming the undercoat layer (coating liquid for the undercoat layer). , Weight average molecular weight 20000-200
1 to 5% by weight, preferably 1 to 3% by weight, may be added to the pigment amount.

The coating amount of the undercoat layer is not particularly limited, but is preferably ² g / m ² or more, more preferably 4 g / m ² or more, and more preferably 7 to 12 g depending on the characteristics of the heat-sensitive recording material.
/ M ² is particularly preferred.

In the present invention, an undercoat layer (particularly preferably an undercoat layer having high oil absorption, heat insulation effect and flatness) is provided from the viewpoint of improving the head matching property of the thermal head and improving the sensitivity and image quality. An undercoat base paper having a base coat having an oil-absorbing pigment using a blade coater is particularly preferable.

The total ion concentration of Na ⁺ ions and K ⁺ ions contained in the thermal recording material is preferably 1500 ppm or less, more preferably 1000 ppm or less from the viewpoint of preventing head corrosion of the thermal head in contact with the thermal recording material. It is preferably 800 ppm or less, and particularly preferably.
The measurement of the ion concentration of the Na ⁺ ion and K ⁺ ion is
It can be carried out by extracting the heat-sensitive recording material with hot water and measuring the ion mass of Na ⁺ ion and K ⁺ ion in the extracted water by an ion quantitative analysis method by an atomic absorption method. The total ion concentration is expressed in ppm with respect to the total mass of the thermosensitive recording material.

In the heat-sensitive recording material of the present invention, the wettability of the surface of the heat-sensitive recording layer, that is, the contact angle after lapse of 0.1 seconds after dropping distilled water on the surface of the heat-sensitive recording layer is 20 ° or more. It is preferably present, and more preferably 50 ° or more. By setting the contact angle in the above range, it is possible to prevent bleeding of the print when printing with an inkjet printer (giving inkjet printability and improving it). 4 already mentioned
-By containing hydroxybenzenesulfonanilide, the contact angle can be obtained, and in addition, the sensitizer and paraffin wax according to the present invention can be used as a material capable of maintaining a high contact angle of distilled water on the recording surface. It is also preferable to use a method such as inclusion in a layer.

The contact angle was measured by adding distilled water to the surface (recording surface) of the heat-sensitive recording layer of the heat-sensitive recording material, and then adding 0.1
It can be performed by measuring the contact angle after a lapse of seconds by a conventional method. For example, the FIBRO system (DA
It can be measured by a dynamic contact angle absorption tester such as T1100 (manufactured by ab) or the like.

The heat-sensitive recording material of the present invention is useful in that it is excellent in image storability, and preferably, the formed image after printing is left for 24 hours under an environmental condition of a temperature of 60 ° C. and a relative humidity of 20%. The density residual ratio in the formed image is set to 65% or more. As described above, by containing 4-hydroxybenzenesulfonanilide, preferably by containing an image stabilizer or the like, the concentration residual ratio can be set within the above range. As a result, the formed image can be maintained at a high density for a long period of time, and can be applied to fields requiring image reliability for a long period of time, such as storage of important documents, advance tickets, receipts, and cash vouchers.

The density remaining ratio of the image is calculated by the following formula, in an atmosphere of 60 ° C. and 20% relative humidity, printed under the same conditions as the image density measured by a Macbeth reflection densitometer (for example, RD-918) immediately after printing. It is represented by the ratio (%) of the image density after standing for 24 hours. Remaining density = [(image density after leaving) / (image density immediately after printing)] x 100

[0131]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Hereinafter, "parts" and "%" in the examples mean "parts by mass" and "mass%", respectively.

( Reference Example 1) <Preparation of coating liquid for thermosensitive recording layer> -Preparation of dispersion A (containing an electron-donating colorless dye) -The following components were dispersed and mixed in a ball mill to give a volume average particle diameter. To obtain a dispersion A having a particle size of 0.7 μm. The volume average particle size is
Laser diffraction particle size analyzer LA500 (HORIBA CORPORATION)
Manufactured). [Composition of Dispersion A] 2-anilino-3-methyl-6-diethylaminofluorane 10 parts (electron-donating colorless dye) Polyvinyl alcohol 2.5% solution 50 parts (PVA-105, Co., Ltd.) (Made by Kuraray)

-Preparation of Dispersion B (containing electron-accepting compound) -The following components were dispersed and mixed by a ball mill to obtain Dispersion B having a volume average particle size of 0.7 µm. The volume average particle size is
The measurement was performed in the same manner as in the case of Dispersion A. [Composition of dispersion B] 4-hydroxybenzenesulfonanilide 20 parts Polyvinyl alcohol 2.5% solution 100 parts (PVA-105, manufactured by Kuraray Co., Ltd.)

-Preparation of Dispersion C (with sensitizer) -The following components were dispersed and mixed in a ball mill to obtain Dispersion C having a volume average particle size of 0.7 µm. The volume average particle size is
The measurement was performed in the same manner as in the case of Dispersion A. [Composition of Dispersion C] 2-benzyloxynaphthalene (sensitizer) 20 parts Polyvinyl alcohol 2.5% solution 100 parts (PVA-105, manufactured by Kuraray Co., Ltd.)

-Preparation of Dispersion D (containing pigment) -The following components were dispersed and mixed in a sand mill to obtain Dispersion D having a volume average particle diameter of 2.0 µm. The volume average particle size is
The measurement was performed in the same manner as in the case of Dispersion A. [Composition of Dispersion D] Calcite light calcium carbonate ... 40 parts (Unibar 70, manufactured by Shiraishi Industry Co., Ltd.)-Sodium polyacrylate ... 1 part-Water ... 60 parts

-Preparation of coating liquid for thermosensitive recording layer- The following compositions were mixed to obtain a coating liquid for thermal recording layer. [Composition of coating liquid for thermal recording layer]   ・ Dispersion A ... 60 parts   ・ Dispersion B ... 120 parts   ・ Dispersion C ... 120 parts   Dispersion D ... 101 parts   ・ Zinc stearate 30% dispersion ... 15 parts   ・ Paraffin wax (30%): 20 parts   ・ Sodium dodecylbenzenesulfonate (25%)… 3 parts

<Preparation of coating liquid for support undercoat layer> The following components were stirred and mixed with a dissolver to obtain a dispersion liquid. -Calcined kaolin (oil absorption of 75 ml / 100 g) ... 100 parts-Sodium hexametaphosphate ... 1 part-Water ... 110 parts Subsequently, 20 parts of SBR (styrene-butadiene rubber latex) and oxidized starch (25 parts) were added to the resulting dispersion. %)
And 25 parts were added to obtain a coating solution for a support undercoat layer.

<Preparation of Thermosensitive Recording Material> As a support, J
A high-quality paper having a smoothness of 150 seconds according to IS-P8119 was prepared, and the coating liquid for a support undercoat layer obtained above was applied to the surface of the high-quality paper with a blade coater so that the coating amount was 8 g / m ^2. Was applied to form an undercoat layer. By applying the undercoat layer, the smoothness of the support according to JIS-P8119 was 350 seconds.

Then, the coating solution for thermal recording layer obtained above was coated on the undercoat layer by a curtain coater so that the coating amount after drying was 4 g / m ^2, and dried to obtain a thermal recording layer. Was formed. Then, the surface of the formed thermosensitive recording layer was subjected to a calendar treatment to obtain a thermosensitive recording material (1). Regarding the obtained thermal recording material (1),
The color density (according to Macbeth reflection densitometer RD-918) at an applied energy of the thermal head of 15.2 mJ / mm ² measured under the same conditions and methods as in the following (Evaluation) was 1.28.

Example 1- Preparation of Dispersion E-The following components were dispersed and mixed by a ball mill to obtain Dispersion E having a volume average particle size of 0.7 μm. The volume average particle size is
The measurement was performed in the same manner as in Reference Example 1. [Composition of Dispersion E] 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane (image stabilizer) 5 parts Polyvinyl alcohol 2.5% solution 25 parts (PVA-105, manufactured by Kuraray Co., Ltd .; adhesive)

-Preparation of coating liquid for heat-sensitive recording layer-Dispersion liquids A, B, C and D were prepared in the same manner as in Reference Example 1 and mixed with the dispersion liquid E obtained above in the following composition for heat-sensitive recording layer. A coating liquid was prepared, and in the same manner as in Reference Example 1, a thermal recording material (2) of the present invention was obtained. [Composition of coating liquid for thermosensitive color developing layer] Dispersion A ... 60 parts Dispersion B ... 120 parts Dispersion C ... 120 parts Dispersion E ... 30 parts Dispersion D ... 101 parts Zinc stearate 30% Dispersion: 15 parts Paraffin wax (30%): 20 parts Sodium dodecylbenzene sulfonate (25%): 3 parts

(Example 2 ) In Example 1 , the dispersion E
Used in the preparation of 1,1,3-tris (2-methyl-4-
Instead of hydroxy-5-tert-butylphenyl) butane (image stabilizer), 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl)
Dispersion E was prepared in the same manner as in Example 1 except that butane was used, and further in the same manner as in Example 1 to obtain a thermosensitive recording material (3) of the present invention.

Reference Examples 2 to 3 In place of 40 parts of the calcite-based light calcium carbonate (Unibar 70; inorganic pigment) used in the preparation of Dispersion D in Reference Example 1, amorphous silica (Mizukasil P832, Mizusawa Chemical Co., Ltd.) 2
0 parts or aluminum hydroxide (Hidilite H42,
Showa Denko Co., Ltd.) 40 parts, except for the use respectively, ginseng
In the same manner as considered Example 1 to obtain a heat-sensitive recording material (4) to (5).

Reference Example 4 Polyvinyl alcohol used in the preparation of dispersions A, B and C in Reference Example 1.
Reference Example 1 except that a 2.5% aqueous solution of sulfo-modified polyvinyl alcohol (Goselan L3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was used instead of the 5% aqueous solution (adhesive).
A heat-sensitive recording material (6) was obtained in the same manner as.

Reference Example 5 Polyvinyl alcohol used in the preparation of dispersions A, B and C in Reference Example 1.
The 5% aqueous solution (adhesive) was replaced with a 2.5% aqueous solution of diacetone-modified polyvinyl alcohol (D500, manufactured by Unitika Ltd.), and the resulting dispersions A, B and C were mixed in the same manner as in Reference Example 1. A thermosensitive recording material (7) was obtained in the same manner as in Reference Example 1 except that 13 parts of a 5% aqueous solution of adipic dihydrazide (crosslinking agent) was further added to the coating liquid for a thermosensitive recording layer.

Reference Example 6 Polyvinyl alcohol used in the preparation of dispersions A, B and C in Reference Example 1.
A 5% aqueous solution (adhesive) was replaced with a 2.5% aqueous solution of acetoacetyl-modified polyvinyl alcohol (Gosefimer Z210, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), and the resulting dispersions A, B and C were used as reference examples A thermosensitive recording material (8) was obtained in the same manner as in Reference Example 1 except that 13 parts of a 5% aqueous solution of glyoxal (crosslinking agent) was further added to the coating liquid for thermosensitive recording layer prepared by mixing in the same manner as in 1. It was

Reference Example 7 Instead of the high-quality paper used as the support in Reference Example 1, 70% recycled pulp and 30% LBKP were used.
The smoothness according to JIS-P8119 is 1
70 seconds recycled paper (50g / m ²⁾ except for using, ginseng
In the same manner as considered Example 1 to obtain a heat-sensitive recording material (9).

Reference Example 8 In place of <Preparation of Thermosensitive Recording Material> in Reference Example 1, instead of coating, drying and calendering the coating liquid for the thermal recording layer, which was performed after the undercoat layer was formed on the support. After forming the undercoat layer,
The thermosensitive recording layer coating solution obtained in Reference Example 1 and the protective layer coating solution consisting of the following were simultaneously multilayer coated using a curtain coater, dried, and the surface of the laminated protective layer was subjected to a calendering treatment. A thermal recording material (10) was obtained in the same manner as in Reference Example 1 except for the above. The dry coating amount of the protective layer is 2.0.
It was g / m ² .

—Preparation of Coating Liquid for Protective Layer— The following composition was dispersed by a sand mill to prepare a pigment dispersion having a volume average particle diameter of 2 μm. The volume average particle diameter was measured in the same manner as in Reference Example 1.・ Aluminum hydroxide (average particle size 1 μm) 40 parts (Hidilite H42, Showa Denko KK) ・ Sodium polyacrylate 1 part ・ Water 60 parts

Separately, 200 parts of urea phosphate esterified starch 15% aqueous solution (MS4600, manufactured by Nippon Shokuhin Kako Co., Ltd.) and polyvinyl alcohol 15% aqueous solution (PVA-10
5, manufactured by Kuraray Co., Ltd.), 60 parts of water was added to 200 parts of the mixture, the pigment dispersion obtained above was mixed, and the zinc stearate emulsion dispersion having a volume average particle diameter of 0.15 μm was further prepared. (Hydrin F115, manufactured by Chukyo Yushi Co., Ltd.) and 25 parts were mixed with 125 parts of a 2% sulfosuccinic acid 2-ethylhexyl ester sodium salt aqueous solution to obtain a coating liquid for a protective layer.

Reference Examples 9 to 11 Instead of 40 parts of aluminum hydroxide (Hydileite H42; inorganic pigment) used in the preparation of the coating liquid for the protective layer of Reference Example 8 , aluminum hydroxide (Hydileite H43, volume) was used. Average particle size 0.7 μm, Showa Denko KK 40 parts, Kaolin (Caobrite, volume average particle size 2.5 μm, Shiraishi Kogyo KK) 40 parts, or amorphous silica (Mizukasil P707, volume) A thermosensitive recording material (1) was prepared in the same manner as in Reference Example 8 except that 20 parts each having an average particle size of 2.2 μm and manufactured by Mizusawa Chemical Co., Ltd. were used.
1)-(13) were obtained.

( Reference Examples 12 to 18 ) Dispersion C of Reference Example 1
In place of 2-benzyloxynaphthalene (sensitizer) used in the preparation of dimethyl oxalate (HS352
0R-N, Dainippon Ink and Chemicals, Inc., m-terphenyl, ethylene glycol tolyl ether, p-benzyl biphenyl, 1,2-diphenoxymethylbenzene, diphenyl sulfone, or 1,2-diphenoxyethane. Thermal recording materials (14) to (20) were obtained in the same manner as in Reference Example 1 except that each was used.

Reference Examples 19 to 23 Dispersion A of Reference Example 1
In place of 2-anilino-3-methyl-6-diethylaminofluorane (electron donating colorless dye) used in the preparation of
2-anilino-3-methyl-6-dibutylaminofluorane, 2-anilino-3-methyl-6- (N-ethyl-
N-isoamylamino) fluorane, 2-anilino-3
-Methyl-6- (N-ethyl-N-propylamino) fluorane, 2-anilino-3-methyl-6-di-n-amylaminofluorane, or 2-anilino-3-methyl-6- (N- Thermal recording materials (21) to (25) were obtained in the same manner as in Reference Example 1 except that ethyl-Np-tolylamino) fluorane was used.

[0154] In (Reference Example 24) Reference Example 1, in place of the curtain coater used for coating of heat-sensitive recording layer coating solution, except for using an air knife coater, in the same manner as in Reference Example 1, the heat-sensitive recording material ( 26) was obtained.

( Reference Examples 25 to 27 ) Dispersion B of Reference Example 1
In place of 4-hydroxybenzenesulfonanilide (electron-accepting compound) used in the preparation of N-benzyl-4-
Hydroxybenzenesulfonamide (= p-N-benzylsulfamoylphenol), BTUM, or 4-hydroxy-4'-isopropoxydiphenylsulfone,
Thermal recording materials (27) to (29) were obtained in the same manner as in Reference Example 1 except that each of the above was used.

(Comparative Examples 1 and 2) Instead of 4-hydroxybenzenesulfonanilide (electron-accepting compound) used in the preparation of Dispersion B of Reference Example 1, 2,2'-bis (4-
Comparative thermal recording materials (30) to (31) were obtained in the same manner as in Reference Example 1 except that (hydroxyphenol) propane (bisphenol A) or 4,4′-dihydroxydiphenylsulfone was used.

[0157] (Comparative Example 3) except that 4-hydroxybenzene sulfonanilide (electron-accepting compound) 20 parts used to prepare the dispersion liquid B of Reference Example 1, was changed to 4 parts, ginseng
In the same manner as considered Example 1 to obtain a heat-sensitive recording material (32) of the comparison.

(Evaluation) Thermal recording material (1) obtained as described above
To (29) and comparative thermal recording materials (30) to (32)
The following measurements and evaluations were performed. The results of measurement and evaluation are shown in Table 1 below. (1) Sensitivity measurement part Thermal head having a glaze structure (KF200
Printing was performed using a thermal printing device equipped with 3-GD31A, manufactured by ROHM Co., Ltd. The printing is head voltage 24V,
Printing cycle 0.98ms / line (printing speed 12.8c
m / sec), the pulse width was 0.375 ms (applied energy 15.2 mJ / mm ² ), and the print density was measured with a Macbeth reflection densitometer (RD-918, manufactured by Macbeth).

(2) Evaluation of background fog The density of the background part (non-image part) after leaving each heat-sensitive recording material for 24 hours under the environmental condition of temperature 60 ° C. and relative humidity 20% was measured by Macbeth reflection densitometer. (RD-918, manufactured by Macbeth Co.). The lower the value, the better the background fog.

(3) Evaluation of image storability Each of the thermosensitive recording materials was printed with the same apparatus and conditions as in "(1) Measurement of sensitivity", and the density of the image immediately after printing, and
The same image is placed in an atmosphere of 60 ° C and 20% relative humidity for 24 hours.
The density of the image after standing for a time was measured with a Macbeth reflection densitometer (RD-918, manufactured by Macbeth Co.). And
Based on the following formula, the ratio of the image density after leaving to the image density immediately after printing (%; density residual ratio) was calculated and used as an index for evaluating image storability. The higher the value, the better the image storability. Remaining density = [(image density after leaving) / (image density immediately after printing)] x 100

(4) Evaluation of light resistance Each of the above-mentioned thermosensitive recording materials was printed with the same apparatus and conditions as in "(1) Measurement of sensitivity", and the density of the image immediately after printing,
The density after exposure of the printing section to a fluorescent lamp at 50 full Lux · h (measured with a digital illuminance meter T-1 (manufactured by Minolta Co., Ltd.)) and a Macbeth reflection densitometer (RD-918, manufactured by Macbeth Co.) ). Based on the following formula, the ratio of the image density after exposure to the image density immediately after printing (%; density residual ratio) was calculated and used as an index for evaluating light resistance. The higher the value, the better the light resistance. Remaining density = [(image density after exposure) / (image density immediately after printing)] x 100

(5) Evaluation of chemical resistance Each thermal recording material was printed with the same apparatus and conditions as in "(1) Measurement of sensitivity" above, and the surface of the background portion and the printing portion was printed with a fluorescent pen (zebra). Highlighter 2-Pink, Zebra Corporation
Written on each of the heat-sensitive recording materials after 1 day,
The degree of background fog on the background portion and the image density of the image portion were visually observed and evaluated according to the following criteria. [Criteria] ◯: No increase in fog density in the background area was observed, and no change in density in the image area was observed. Δ: A slight increase in the fog density in the background part was observed, and the image part was slightly lighter in density. X: The fog density in the background area was remarkably increased, and the image area almost disappeared.

(6) Evaluation of head loss Using a word processor (Lupo 95JV, manufactured by Toshiba Corp.), 1000 test charts with a print rate of 20% were printed on A4 sheet size, and the number of missing dots at that time was determined by the head. It was used as an index for evaluating breakage.

(7) Evaluation of Inkjet Suitability Ink Resistance In the same manner as in "(1) Sensitivity Measurement" above, printing was performed on the thermosensitive recording layer of each thermosensitive recording material, and the image density (D ¹ ) immediately after printing was printed. Was measured with a Macbeth reflection densitometer RD918 (manufactured by Macbeth). Next, the surface of the heat-sensitive recording layer of each of the printed heat-sensitive recording materials (printed printing portion) is brought into contact with the image printed with high quality by an inkjet printer (EPSON MJ930C, manufactured by Epson Corporation), and 2
The image density (D ² ) of each heat-sensitive recording layer after standing at 5 ° C. for 48 hours was measured by a Macbeth reflection densitometer RD918. Then, the density residual ratio (%; D ² / D ¹ × 100) of each thermal recording material was calculated from the obtained respective densities, and used as an index for evaluating the resistance to the inkjet ink. The higher the value, the better the ink resistance.

Inkjet recording suitability For each heat-sensitive recording material, a word processor (report JW-95J
U, manufactured by Toshiba Corp.) is used to print characters, and then each of the printed thermal recording layers is printed with an inkjet printer, and ink bleeding in the inkjet recording part and the character part printed with a word processor are performed. The degree of decolorization was visually evaluated according to the following criteria. [Criteria] ◯: There was little ink bleeding and decoloring of the character portion, and there was no problem in reading. Δ: A part of the character part was faint, but it was possible to read it somehow. X: The character portion completely disappeared, and the reading was impossible.

(8) Measurement of Contact Angle Distilled water was dropped on the surface (recording surface) of the thermosensitive recording layer of each thermosensitive recording material, and the contact angle after 0.1 second was measured by using FIBRO.
It was measured using a system (DAT1100, manufactured by ab). The larger the value, the more useful it is in relation to the effect.

(9) Measurement of Ion (Na ⁺ , K ⁺ ) Concentrations Each heat-sensitive recording material was extracted with hot water, and the extracted water was analyzed by an atomic absorption ion analysis method to determine Na ⁺ and K ⁺ ions. Was measured. The ion concentration in Table 1 represents the total ion concentration of Na ⁺ and K ⁺ , and shows the total ppm value based on the total mass of the thermosensitive recording material.

[0168]

[Table 1]

From the results in Table 1 above, with the heat-sensitive recording materials ( 2 ) to ( 3 ) of the present invention, a high color density (high sensitivity) was obtained without impairing the background white color of the background (good printability). Moreover, the light resistance after printing and the image storability were also good. Moreover, with the improvement of the contact angle, it has an inkjet suitability, excellent chemical resistance, less head wear, and excellent thermal head matching. That is,
Light resistance, high sensitivity, background whiteness, image storability,
Inkjet suitability, chemical resistance, and thermal head matching (wear resistance) could be satisfied at the same time.

Further, in comparison with the heat-sensitive recording material (1), the heat-sensitive recording materials (2) and (3) containing an image stabilizer can further improve the image storability and the ink resistance, and thus have favorable adhesion. With the heat-sensitive recording material (6) using the agent (protective colloid), it was possible to further improve the sensitivity and reduce the background fog. Incidentally, the inclusion of the image stabilizer was particularly excellent in imprintability and handleability. The thermal recording materials (10) to (13) provided with the protective layer containing the specific inorganic pigment suitable for the present invention were able to further improve the image storability and the ink resistance (chemical resistance). Reference example 1
By sensitizers used in 2 to 18, same good performance is obtained with the heat-sensitive recording material of Reference Example 1 (1), Reference Example 19
With the electron-donating colorless dyes used in Examples 23 to 23 , good color developability and image storability were obtained while keeping the background fog low. As in Reference Examples 1 and 24 , the curtain coating method was more useful in terms of higher sensitivity. Even if the support contained waste paper pulp ( Reference Example 7 ), various performances were not affected.

On the other hand, as an electron-accepting compound, 4-hydr
The comparative heat-sensitive recording materials (30) to (31) which did not use roxybenzenesulfonanilide not only failed to achieve high sensitivity, but also exhibited light resistance, image storability, chemical resistance, and inkjet suitability. It was inferior in terms of characteristics, and it was not possible to simultaneously satisfy various performances that the thermal recording material should have.

[0172]

According to the present invention, it is possible to form a high-sensitivity and high-density image (printing suitability is good) while suppressing the fog density (background fog) in the background portion to be low, and the light resistance after printing, Image storability and chemical resistance are particularly excellent, and it has inkjet suitability that does not cause color fading or bleeding of inkjet images and image fading caused by inkjet inks.
Moreover, even when it is applied to a high-performance printer having high speed and a partial glaze structure, a thermal recording material having good thermal head matching property and less head wear and head stain (good head suitability) is provided. You can Further, in addition to these, a sharp and high-quality image can be obtained, the formed image has excellent light resistance, printing and imprinting can be performed on the heat-sensitive recording layer or the protective layer without bleeding, and a small coating amount ( It is possible to provide a heat-sensitive recording material which can be formed at a low cost with environmental suitability and which also has a plain paper-like feel if necessary.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hirofumi Mitsuo             200, Onakazato, Fujinomiya City, Shizuoka Prefecture Fuji Photo             Within Film Co., Ltd. F term (reference) 2H026 AA07 BB14 BB25 DD01 DD02                       DD07 DD10 DD15 DD19 DD23                       DD32 DD45 DD53 DD55 EE03                       FF24

Claims (7)

[Claims] 1. A heat-sensitive recording material having a heat-sensitive recording layer comprising, on a support, an electron-donating colorless dye and an electron-accepting compound that reacts with the electron-donating colorless dye to develop a color. The compound is a compound represented by the following general formula (1) (excluding 2,4-bis (phenylsulfonyl) phenol), R ¹ -Ph-SO ₂ R ² ... General formula (1) Among them, R ¹ represents a hydroxyl group or an alkyl group. R ² is −
Ph, -NH-Ph, -Ph- OR 3, -NH-CO-
It represents NH-Ph, R ³ represents an alkyl group. Ph represents a phenyl group, may be substituted with a substituent containing a -SO ₂ R ^2. ] Further, the thermal recording material is characterized in that the density residual ratio of the printed portion after irradiation with a fluorescent lamp of 500,000 Lux · h is 80% or more. 2. The compound represented by the general formula (1) is 4-
The heat-sensitive recording material according to claim 1, which is hydroxybenzenesulfonanilide. 3. The thermal recording layer contains an image stabilizer, which comprises 1,1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane and 1,1,1. 3-tris (2-methyl-4-hydroxy-5)
The heat-sensitive recording material according to claim 1, which is at least one of -cyclohexylphenyl) butane. 4. The support contains waste paper pulp.
4. The heat-sensitive recording material according to any one of 3 to 3. 5. A thermosensitive recording layer having a protective layer, which comprises at least one inorganic pigment selected from aluminum hydroxide, kaolin and amorphous silica, and a water-soluble polymer. The thermal recording material according to any one of claims 1 to 4, which comprises: 6. The heat-sensitive recording layer contains a sensitizer, and the sensitizer is 2-benzyloxynaphthalene, dimethylbenzyl oxalate, m-terphenyl, ethylene glycol tolyl ether, p-benzyl biphenyl, 1,2. The heat-sensitive recording material according to any one of claims 1 to 5, which is at least one selected from diphenoxymethylbenzene, 1,2-diphenoxyethane, and diphenylsulfone. 7. An electron donating colorless dye is 2-anilino-
3-methyl-6-diethylaminofluorane, 2-anilino-3-methyl-6-dibutylaminofluorane, 2
-Anilino-3-methyl-6- (N-ethyl-N-isoamylamino) fluorane, 2-anilino-3-methyl-6- (N-ethyl-N-propylamino) fluorane, 2-anilino-3-methyl -6-di-n-amylaminofluorane, and 2-anilino-3-methyl-6-
7. The heat-sensitive recording material according to claim 1, which is at least one selected from (N-ethyl-Np-tolylamino) fluorane.