JP2005297306A - Multicolor thermosensitive recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high speed printable multicolor thermosensitive recording material in which neither problem of a color mixture among respective thermosensitive recording layers of Y, M and C nor ununiform density develops. <P>SOLUTION: In the multicolor thermosensitive recording material formed by stratifying the respective thermosensitive recording layers each developing colors of yellow (Y), magenta (M) and cyan (C), at least one thermosensitive recording layer among the respective thermosensitive recording layers develops a color having the same hue and the material is composed of at least two layers, coloring sensitivities to heat energy of which are different from one another. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording material, and more particularly to a multicolor heat-sensitive recording material that realizes a connection between highlight portions and a high color density and a method for producing the same.

Thermal recording has been developed recently because the recording apparatus is simple, reliable and does not require maintenance. Recently, multicolor thermal recording has been performed using thermal recording.
A multicolor thermosensitive recording material is provided with a plurality of thermosensitive recording layers on a support. In order to perform high-speed printing, it is necessary to reduce the maximum coloring energy. In the conventional method, the color development start energy is yellow (hereinafter also referred to as “Y”), magenta (hereinafter also referred to as “M”), and cyan (hereinafter also referred to as “C”). In other words, if the energy for starting magenta color development and the energy for starting cyan color development are made lower, the M color development will start before the Y color development is sufficiently developed, and the M color development will be sufficient. C coloring begins before the color develops.
That is, if the coloring energy of M and C is made low without reducing the coloring energy of Y, the next M coloring starts before reaching the first maximum Y coloring density (Dmax), and the maximum M coloring density is reached. Before reaching (Dmax), C color development started, and there was a problem of color mixing that it was difficult to obtain a high color density with good color purity.

  Therefore, conversely, by increasing the color development sensitivity with respect to the increase in thermal energy of each thermosensitive recording layer, that is, by setting the color development sensitivity to high gamma (γ), the problem of color mixing is solved at the high color density of the single color. .

However, there has been a problem that the color density change with respect to a slight energy fluctuation becomes large, and it becomes very difficult to control the printer in order to produce a uniform image. The actual situation is that there is no report on how to solve all of these problems.
The present invention has been made with respect to the problems as described above, and its object is to provide a multi-color capable of high-speed printing without any color mixing problem between the Y, M, and C thermal recording layers and without density unevenness. It is to provide a thermal recording material.

<1> In a multicolor thermosensitive recording material in which the thermosensitive recording layers that color each of yellow (Y), magenta (M), and cyan (C) are layered, at least one thermosensitive recording layer of each thermosensitive recording layer A multi-color heat-sensitive recording material comprising two or more layers that develop colors in the same hue and have different color development sensitivities to thermal energy.

<2> The multicolor thermosensitive recording material according to <1>, wherein the thermosensitive recording layer on the support side of each of the thermosensitive recording layers is a layer having the highest color development sensitivity to thermal energy.

<3> At least one of the two or more layers in which at least one heat-sensitive recording layer of each of the heat-sensitive recording layers develops the same hue and has different color-sensitivity to heat energy is a layer containing microcapsules. The multicolor thermosensitive recording material according to <1> or <2> above, wherein
<4> In the multicolor thermosensitive recording material according to any one of <1> to <3>, the thermosensitive recording layers are laminated in the order of cyan (C), magenta (M), and yellow (Y) from the support side. A multicolor heat-sensitive recording material characterized by the above.

<5> Any one of the above items <1> to <4>, wherein the thermal energy for maximally coloring the thermal recording layer closest to the support among the thermal recording layers is 95 mJ / mm ² or less. The multicolor thermosensitive recording material according to Item.
<6> At least one heat-sensitive recording layer of each of the heat-sensitive recording layers is colored with the same hue, and two or more layers having different color development sensitivities to heat energy are wall materials having different glass transition temperatures. The multicolor thermosensitive recording material according to any one of the above items <1> to <5>, comprising a configured microcapsule.
<7> At least one heat-sensitive recording layer of each heat-sensitive recording layer is colored in the same hue, and two or more layers having different color development sensitivities to thermal energy include microcapsules having different median diameters. The multicolor thermosensitive recording material according to any one of the above items <1> to <6>.

  According to the present invention, it is possible to provide a multicolor thermosensitive recording material which is free from the problem of color mixing between the Y, M and C thermosensitive recording layers and can perform high-speed printing without density unevenness.

The multicolor thermosensitive recording material of the present invention has each thermosensitive recording layer that develops color in each of Y, M, and C, and at least one thermosensitive recording layer of each thermosensitive recording layer develops color in the same hue. And two or more subdivided layers (hereinafter, also referred to as “subdivided layers”) having different color development sensitivities to thermal energy. Further, the layer on the support side of each heat-sensitive recording layer is preferably the layer having the highest color development sensitivity to thermal energy.
Furthermore, the multicolor thermosensitive recording material of the present invention can be provided with an intermediate layer, a backcoat layer, a protective layer and the like.

The term “colored in the same hue” does not mean exactly the same color, but may be in a general wavelength range of each of Y, M, and C hues. For example, Y is an absorption wavelength. The peak position may be in the range of 410 nm to 480 nm, M may be in the range of 510 nm to 580 nm, and C may be in the range of 600 nm to 700 nm.
Further, the “different color development sensitivity” means that the density change is different when heat energy is applied to the recording material. More specifically, when printing energy for color development with an OD value of 0.6 is applied, the difference in density change value when the energy change is changed by 1 mJ / mm ² indicates that Y is 0.03 or more, M Is 0.03 or more, and C is 0.02 or more.

  Next, the multicolor thermosensitive recording material of the present invention will be described with reference to the drawings. Here, a multicolor thermosensitive recording material in which each thermosensitive recording layer that develops colors in the order of C, M, and Y on the support is described as an example, but the present invention is not limited to this. .

FIG. 2A is a sensitivity curve of a conventional multicolor thermosensitive recording material, in which the thermal energy is plotted on the horizontal axis, and the color density when the thermal energy is applied is plotted on the vertical axis. Y, M, and C indicate sensitivity curves for each hue.
FIG. 2B shows sensitivity curves for Y, M, and C when the sensitivity curve of FIG. 2A can be developed by applying low energy.

As shown in FIG. 2 (A), in a print that can be used up to a high energy region without performing high-speed printing, overlapping of hues that cause color mixing is not seen as shown in FIG. 2 (A). In FIG. 2B, which corresponds to the case where the C maximum color development energy is lowered to perform the above, the coloration base point of each hue is located before reaching Dmax of the previous color development, which causes color mixing.
Specifically, when the Y coloring and the M coloring in FIGS. 2A and 2B are compared, in FIG. 2A, the Y coloring and the M coloring do not overlap (mixed colors), but FIG. In (B), M coloring occurs before Y coloring reaches Dmax, and an overlap that causes color mixing occurs between Y coloring and M coloring.
2A and 2B, each γ value in each hue shows a low γ value in the low energy and high energy regions and a high γ value in the medium energy region, respectively.

  FIG. 2C is an image of another conventional sensitivity curve, which is an example in which the density greatly fluctuates with a small amount of energy, making it difficult to design a printer or the like.

  On the other hand, FIG. 1 (A) shows a sensitivity curve of the multicolor thermosensitive recording material of the present invention, and is an image diagram in which the horizontal axis is the thermal energy and the vertical axis is the color density when the thermal energy is applied. Y, M, and C indicate sensitivity curves for each hue.

In FIG. 1A, in the Y color development composed of two or more layers, the density increase in the low density region is small with respect to the increase in energy, and the density increase in the high concentration region is large with respect to the increase in thermal energy. The same applies to M color development and C color development.
Here, the overlapping portion b of Y color development and M color development corresponds to a low density region where M color development starts in the M sensitivity curve, and corresponds to a high density region of Y color development or a region of Dmax in the Y sensitivity curve. Actually, the hue of M becomes an invisible part, and the Y hue becomes relatively remarkable.
As described above, by forming at least one heat-sensitive recording layer of each of the heat-sensitive recording layers into the same hue and having two or more subdivided layer structures having different color development sensitivities to heat energy, the color density is increased. It becomes possible to finely control the γ value of the region.
As shown in FIG. 1A, in each density region that develops colors in Y, M, and C, the low density region is set to a low γ value and the high density region is set to a high γ value. Color mixing can be prevented by becoming an invisible part.

Further, FIG. 1B is an image diagram showing a sensitivity curve of another embodiment of the multicolor thermosensitive recording material of the present invention.
It is a figure which shows that color mixing prevention is possible also by setting it as (gamma) value contrary to FIG. 1 (A). In other words, in the density regions that develop colors in Y, M, and C, respectively, by setting the low density region to a high γ value and the high density region to a low γ value, specifically, Y color development and M color development are observed. In the case of Y color development, the low density region is set to a high γ value, and the high density region is set to a low γ value. In the M color development, the Y color can be made invisible in the same manner as in the Y color development, and the M color development becomes a relatively visible part to prevent color mixing. However, in this case, as in FIG. 2C, the density greatly fluctuates with a small amount of energy, making it difficult to design a printer.
As a preferable range of the γ value in the present invention, Y is ΔO. D. = 0.3 / (mJ / mm ² ) or less, M is ΔO. D. = 0.2 / (mJ / mm ² ) or less, C is ΔO. D. = 0.1 / (mJ / mm ² ) or less, conversely, Y is ΔO. D. = 0.2 / (mJ / mm ² ) or more, M is ΔO. D. = 0.1 / (mJ / mm ² ) or more, C is ΔO. D. = 0.05 / (mJ / mm ² ) or more.
The printing speed in the present invention is preferably 6.0 mm / sec or more. At printing speeds of 6.0 mm / sec or less, it is difficult to achieve the effect of adjusting γ.

As described above, in the multicolor thermosensitive recording material in which the thermosensitive recording layers that color each of Y, M, and C are layered, at least one thermosensitive recording layer of each thermosensitive recording layer develops the same hue. In addition, by using two or more layered layers having different color development sensitivities to thermal energy, the color development sensitivity to thermal energy, that is, the γ value can be adjusted for each layer. By designing so that the increase in color density with respect to energy increase is small and the increase in color density density with respect to energy increase is large, it is possible to produce a high color density of clean single color with high color purity. Can be solved.
In addition, since an arbitrary sensitivity curve can be drawn easily by designing and overlaying heat-sensitive recording layers having different color developing sensitivities, various different heat-sensitive recording materials can be easily produced and provided according to purposes. Furthermore, by providing a suitable γ value and color density, printer design and picture creation can be made extremely easy.

Next, the layer configuration and components of the multicolor thermosensitive recording material will be described.
[Thermosensitive recording layer]
The heat-sensitive recording layer contains a color-forming component and, if necessary, other components such as a binder and a base. As the coloring component, a diazonium salt compound and a combination of a coupler that reacts with the diazonium salt compound to form a dye, an electron-donating dye precursor, and an electron-accepting compound that reacts with the electron-donating dye precursor to cause color development In addition to the combination, conventionally known coloring components can be used. The diazonium salt compound, the electron donating dye precursor and the like are preferably encapsulated in microcapsules.

Next, the coloring components used in the recording layer of the present invention will be described.
(Diazonium salt compound)
For details of the diazonium salt compound, JP-A-4-59287, JP-A-4-59288, JP-A-10-337961, JP-A-11-78233, JP-A-11-116553, JP-A-7-223368, JP-A-7-323660, JP-A-7-125446, JP-A-7-96671, JP-A-2001-162946, JP-A-2002-326981, JP-B-3-213120, JP-B-3-394613, JP-A-3-394613 No. 8-310133, Japanese Patent Application No. 2002-241646, and Japanese Patent Application No. 2002-261318.
In the multicolor thermosensitive recording material, as described above, one of the two diazo thermosensitive recording layers is a diazonium salt compound having a maximum absorption wavelength of 445 ± 50 nm, and the other is a diazonium salt compound having a maximum absorption wavelength of 365 ± 30 nm. It is desirable to contain. When a diazonium salt compound is used in a thermal recording layer (C layer) different from the diazo thermosensitive recording layer, it is desirable to contain a 305 ± 30 nm diazonium salt compound.

-Diazonium salt compound (DA compound) having a maximum absorption wavelength of 445 ± 50 nm-
When the maximum absorption wavelength exceeds the upper limit, the stability of the diazonium salt compound is deteriorated and the practicality is insufficient, and when the lower limit is exceeded, the maximum absorption wavelength range of the diazonium salt compound having a maximum absorption wavelength of 365 ± 30 nm is not preferable. The range of the maximum absorption wavelength of the diazonium salt compound (DA compound) is more preferably 395 to 475 nm.
The diazonium salt compound having a maximum absorption wavelength of 445 ± 50 nm is preferably a diazonium salt compound represented by the general formulas (1) to (5).

In general formulas (1) to (5), R ¹ , R ² , R ^{4 to} R ¹¹ , and R ^{13 to} R ¹⁵ may be the same or different and each represents a hydrogen atom, an alkyl group, or an aryl group, R ³ , R ¹² , and R ¹⁶ represent a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, a sulfonyl group, an acyl group, or an alkoxycarbonyl group, and D ¹ is an electron donor having a Hammett σp value of −0.05 or less. In particular, a substituted amino group, an alkylthio group, an arylthio group, an alkoxy group, or an aryloxy group is preferable. X ⁻ represents a counter anion. A represents an electron-withdrawing group having a Hammett σp value of 0.3 or more. Y ¹ and Y ² represent an oxygen atom or a sulfur atom. Each benzene ring in the general formulas (1) to (5) may further have a substituent.

R ¹ , R ² , R ^{4 to} R ¹¹ , and R ^{13 to} R ¹⁵ are preferably a hydrogen atom, an alkyl group having 1 to 15 carbon atoms, or an aryl group having 6 to 10 carbon atoms. In particular, a hydrogen atom, a C1-C10 alkyl group, and a phenyl group are preferable. The alkyl group may be branched and may be substituted with a halogen atom, an alkoxy group, an aryloxy group, a phenyl group, an alkoxycarbonyl group, an acyloxy group, or a carbamoyl group. The phenyl group may be substituted with a halogen atom, an alkyl group, an aryl group, an acyloxy group, an alkoxy group, an aryloxy group, an alkoxycarbonyl group, or an acyl group.
Specific examples of R ¹ , R ² , R ^{4 to} R ¹¹ , and R ^{13 to} R ¹⁵ include the following.

R ³ , R ¹² and R ¹⁶ are each a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, a chlorine atom, a fluorine atom, an alkoxy group having 1 to 15 carbon atoms, an alkylsulfonyl group having 1 to 12 carbon atoms, or a carbon number. A 6-18 arylsulfonyl group, a C1-C18 acyl group, or a C2-C18 alkoxycarbonyl group is preferable. The alkyl group and alkylsulfonyl group may be branched and may be substituted with a halogen atom, an alkoxy group, an aryloxy group, a phenyl group, an alkoxycarbonyl group, an acyloxy group, or a carbamoyl group.
The arylsulfonyl group may be substituted with a halogen atom, an alkyl group, or an alkoxy group.
Specific examples of R ³ , R ¹² , and R ¹⁶ include those shown below.

As A, a sulfonyl group, an acyl group, an alkoxycarbonyl group, or a cyano group is preferable. The sulfonyl group, acyl group and alkoxycarbonyl group have the same meanings as the sulfonyl group, acyl group and alkoxycarbonyl group represented by R ³ .
R ⁸ and R ⁹ , R ¹³ and R ¹⁴ may be bonded to each other to form a ring.

Examples of the counter anion X ⁻ include perfluoroalkyl carboxylic acids having 1 to 20 carbon atoms (for example, perfluorooctanoic acid, perfluorodecanoic acid, perfluorododecanoic acid), and perfluoroalkyl sulfonic acids having 1 to 20 carbon atoms. (For example, perfluorooctanesulfonic acid, perfluorodecanesulfonic acid, perfluorohexadecanesulfonic acid), aromatic carboxylic acid having 7 to 50 carbon atoms (for example, 4,4-di-t-butylsalicylic acid, 4-t- Octyloxybenzoic acid, 2-n-octyloxybenzoic acid, 4-t-hexadecylbenzoic acid, 2,4-bis-n-octadecyloxybenzoic acid, 4-n-decylnaphthoic acid), fragrance having 6 to 50 carbon atoms Group sulfonic acids (for example, 1,5-naphthalene disulfonic acid, 4-t-octyloxybenzene sulfone) Acid, 4-n-dodecylbenzenesulfonic acid), 4,5-di-t-butyl-2-naphthoic acid, tetrafluoroboric acid, tetraphenylboric acid, hexafluorophosphoric acid, bis (2-20 carbon atoms) Alkylsulfonyl) imine, bis (perfluoromethanesulfonyl) imine having 2 to 20 carbon atoms, and the like. Among them, perfluoroalkylcarboxylic acids having 6 to 16 carbon atoms, aromatic carboxylic acids having 10 to 40 carbon atoms, aromatic sulfonic acids having 10 to 40 carbon atoms, tetrafluoroboric acid, tetraphenylboric acid, hexafluorophosphoric acid Bis (perfluoromethanesulfonyl) imine having 2 to 20 carbon atoms is preferable.

When D ¹ represents a substituted amino group as an electron donating group having a Hammett's σp value of −0.05 or less, the substituted amino group includes an alkylamino group having 1 to 20 carbon atoms, and 2 to 20 carbon atoms. Dialkylamino groups, C6-C10 arylamino groups, C7-C20 N-alkyl-N-arylamino groups, and C2-C20 acylamino groups are preferred. You may have the above substituent. Moreover, substituents, such as the said alkyl group, may couple | bond together and a cyclic amino group may be formed.
When D ¹ represents an alkylthio group as an electron donating group having a Hammett's σp value of −0.05 or less, an alkylthio group having 1 to 18 carbon atoms is preferable, and when an arylthio group is represented, an arylthio group having 6 to 10 carbon atoms is preferable. Group is preferable, when an alkoxy group is represented, an alkoxy group having 1 to 18 carbon atoms is preferable, and when an aryloxy group is represented, an aryloxy group having 6 to 10 carbon atoms is preferable, and these groups further include 1 or 2 or more. It may have a substituent.
From the viewpoint of the stability of the diazonium salt compound, D ¹ is preferably a dialkylamino group, an N-alkyl-N-arylamino group, an acylamino group, an alkylthio group, an arylthio group, an alkoxy group, or an aryloxy group.

The alkyl group or aryl group in the substituted amino group, alkylthio group, arylthio group, alkoxy group, or aryloxy group, which is an electron donating group having a Hammett σp value of −0.05 or less represented by D ^1, is as follows: Such a thing is mentioned.

When D ¹ in the general formula (1) represents a substituted amino group, a cyclic amino group formed by bonding of substituents, and —N (R ⁸ ) R ⁹ in the general formula (2), and Examples of the cyclic group represented by —N (R ¹³ ) R ^{14 in} the general formula (5) include the following.

The benzene ring on the indolyl group of the general formula (3) may have a nuclear substituent, and an electron-withdrawing group is particularly preferable from the viewpoint of ring stability. The Hammett σp value of the electron withdrawing group is preferably 0.1 or more. Among these, an acyl group, a sulfonyl group, an alkoxycarbonyl group, a sulfonamide group, or a carbonamido group is preferable. An acyl group, a sulfonyl group, and an alkoxycarbonyl group have the same meanings as R ³ , and preferred embodiments are also the same. The sulfonamide group preferably has 1 to 12 carbon atoms, and specific examples thereof include the following.

  The carbonamido group preferably has 2 to 13 carbon atoms, and specific examples thereof include the following.

  Specific examples (exemplary compounds (DA1) to (DA16)) of the diazonium salt compounds (DA compounds) represented by the general formulas (1) to (5) are shown below, but the present invention is not limited to the following. Absent.

-Diazonium salt compound (DB compound) having a maximum absorption wavelength of 365 ± 30 nm-
When the maximum absorption wavelength exceeds the upper limit, the maximum absorption wavelength range of 445 ± 50 nm of the diazonium salt compound is not preferable. If the lower limit is exceeded, the stability and photodegradability of the diazonium salt compound are deteriorated. The range of the maximum absorption wavelength of the diazonium salt compound (DB compound) is more preferably 350 to 375 nm.
The diazonium salt compound having a maximum absorption wavelength of 365 ± 30 nm is preferably a diazonium salt compound represented by the following general formula (6).

In General Formula (6), R ¹⁷ and R ¹⁸ have the same meaning as R ¹ , and preferred examples are also the same.

D ² represents an alkoxy group or an aryloxy group. The alkyl part of the alkoxy group and the aryl part of the aryloxy group have the same meanings as the alkyl group and aryl group represented by R ¹ , and preferred examples are also the same.

  Although the specific example (exemplary compound (DB-1)-(DB-6)) of the diazonium salt compound represented by General formula (6) below is given, this invention is not limited to the following.

-Diazonium salt compound (DC compound) having a maximum absorption wavelength of 305 ± 30 nm-
When the maximum absorption wavelength exceeds the upper limit, the maximum absorption wavelength 365 ± 30 nm of the maximum absorption wavelength range of the diazonium salt compound is not preferable. When the lower limit is exceeded, the stability of the diazonium salt compound is deteriorated. The range of the maximum absorption wavelength of the diazonium salt compound (DC compound) is more preferably 280 to 325 nm.
As the diazonium salt compound having the maximum absorption wavelength of 305 ± 30 nm, diazonium salt compounds represented by the following general formulas (7) and (8) are preferable.

In the general formulas (7) and (8), D ³ and D ⁴ each represent a group having a Hammett σp value of −0.45 or more. R ¹⁹ represents a perfluoroalkyl group, an acyl group, or a sulfonyl group, and the acyl group and the sulfonyl group have the same meanings as R ³ described above.
As the perfluoroalkyl group, those having 1 to 8 carbon atoms are preferable, and —CF ₃ , —C ₃ F ₇ or —C ₈ F ₁₇ is particularly preferable.
X ⁻ in the general formula (7) represents a counter anion. Z in the general formula (8) represents —SO ₂ — or —CO—.

D ³ and D ⁴ representing a Hammett σp value of −0.45 or more include an alkoxy group, an aryloxy group, an alkyl group, an alkylthio group, an arylthio group, a halogen atom, a hydrogen atom, a nitro group, a cyano group, An alkylsulfonyl group and an alkoxycarbonyl group are preferred. More preferably, it is a group having a Hammett σp value of −0.30 or more.
The alkoxy group is preferably a substitutable alkoxy group having 1 to 20 carbon atoms such as methoxy (σp = −0.27), ethoxy, butyloxy (σp = −0.32), hexyloxy, octyloxy, 2 -Ethylhexyloxy, 3-methyl-5,5-dimethylhexyloxy, decyloxy, phenoxyethoxy, 2- (2,4-di-t-pentylphenyl) oxyethyloxy and the like.
The aryloxy group is preferably a substitutable aryloxy group having 6 to 20 carbon atoms, such as phenoxy (σp = −0.03), methylphenoxy, isopropylphenoxy, 2,4-di-t-pentylphenoxy, Examples include chlorophenoxy and methoxyphenoxy.
As an alkyl group, a C1-C8 alkyl group is preferable, for example, methyl ((sigma) p = -0.17), ethyl, isopropyl, t-butyl, hexyl, octyl etc. are mentioned.
The alkylthio group is preferably a substitutable alkylthio group having 1 to 8 carbon atoms, and examples thereof include methylthio, ethylthio (σp = 0.03), butylthio, octylthio, benzylthio and the like.
The arylthio group is preferably a substitutable arylthio group having 6 to 10 carbon atoms, and examples thereof include phenylthio (σp = 0.18), methylphenylthio, chlorophenylthio, methoxyphenylthio and the like.
As the halogen atom, a chlorine atom (σp = 0.23), a fluorine atom (σp = 0.06) and the like are preferable.
The alkylsulfonyl group is preferably an alkylsulfonyl group having 1 to 8 carbon atoms, and examples thereof include methylsulfonyl (σp = 0.72), ethylsulfonyl, butylsulfonyl, octylsulfonyl, benzylsulfonyl and the like.
The alkoxycarbonyl group is preferably an alkoxycarbonyl group having 2 to 10 carbon atoms, and examples thereof include methoxycarbonyl, ethoxycarbonyl (σp = 0.45), butyloxycarbonyl, octyloxycarbonyl and the like.

X ⁻ in the general formula (7) has the same meaning as in the general formula (1).
The benzene ring in the general formulas (7) and (8) may further have a substituent.
The substituent can be any substituent, but is preferably an alkyl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a halogen atom, a nitro group, a cyano group, an alkylsulfonyl group, an alkoxycarbonyl group, or the like. . The alkyl group, alkoxy group, alkylthio group, arylthio group, halogen atom, alkylsulfonyl group and alkoxycarbonyl group have the same meanings as the substituents corresponding to each of D ³ .
In General formula (7), it is preferable that it is substituted by the ortho position (o-position) of the diaionio group on the said benzene ring.
Specific examples (exemplary compounds (DC-1) to (DC-6)) of the diazonium salt compounds represented by the general formulas (7) and (8) are shown below, but the present invention is not limited to the following. Absent.

  The diazonium salt compound may be either oily or crystalline, but is preferably in a crystalline state at room temperature from the viewpoint of handleability. This diazonium salt compound may be used alone or in combination of two or more, or may be used in combination with an existing diazonium salt compound.

The content of the diazo heat-sensitive recording layer of the diazonium salt compound is preferably 0.02 to 5 g / m ^2, more preferably 0.1-4 g / m ² from the viewpoint of color density.

  In order to stabilize the diazonium salt compound, a complex compound can be formed using zinc chloride, cadmium chloride, tin chloride, or the like to stabilize the diazonium salt compound.

(coupler)
Next, couplers (coupling components) that can be used in the recording material of the present invention will be described.
As the coupler, any compound can be used as long as it forms a dye by coupling with a diazonium salt compound in a basic atmosphere and / or a neutral atmosphere. All so-called 4-equivalent coupler compounds for silver halide photographic light-sensitive materials can be used as couplers. A part of a 2-equivalent coupler can also be used. These can be selected according to the target hue.
For example, there are so-called active methylene compounds having a methylene group next to a carbonyl group, phenol derivatives, naphthol derivatives and the like, and they are used within a range meeting the purpose of the present invention.

  The details of the coupler are described in JP-A-4-201483, JP-A-7-223367, JP-A-7-223368, JP-A-7-323660, JP-A-7-125446, JP-A-7-96671, JP-A-7-167671. JP-A-7-223367, JP-A-7-223368, JP-A-9-156229, JP-A-9-216468, JP-A-9-216469, JP-A-9-203472, JP-A-9-319025, JP-A-10 -35113, JP-A-10-193801, JP-A-10-264532, and the like.

Among the above, in the present invention, a compound represented by the following general formula (9) or a tautomer thereof is particularly preferable.
Hereinafter, the coupler represented by the general formula (9) will be described in detail.

In the general formula (9), E ¹ and E ² each independently represent an electron-withdrawing group, and L represents a group that can be separated when azo coupling to form an azo dye. E ^{1 and} E ² may combine to form a ring.

The electron-withdrawing group represented by E ¹ and E ² means a substituent having a positive Hammett σp value, which may be the same or different. For example, acetyl group, propionyl Group, pivaloyl group, chloroacetyl group, trichloroacetyl group, trifluoroacetyl group, 1-methylcyclopropylcarbonyl group, 1-ethylcyclopropylcarbonyl group, 1-benzylcyclopropylcarbonyl group, benzoyl group, 4-methoxybenzoyl group An acyl group such as a thenoyl group; an oxycarbonyl group such as a methoxycarbonyl group, an ethoxycarbonyl group, a 2-methoxyethoxycarbonyl group, or a 4-methoxyphenoxycarbonyl group; a carbamoyl group, an N, N-dimethylcarbamoyl group, an N, N- Diethylcarbamoyl group, N-phenylcarbamoyl Carbamoyl groups such as N- [2,4-bis (pentyloxy) phenyl] carbamoyl group, N- [2,4-bis (octyloxy) phenyl] carbamoyl group, morpholinocarbonyl group; methanesulfonyl group, benzenesulfonyl group Alkylsulfonyl group such as toluenesulfonyl group or arylsulfonyl group; phosphono group such as diethylphosphono group; benzoxazol-2-yl group, benzothiazol-2-yl group, 3,4-dihydroquinazolin-4-one- Preferred examples include a heterocyclic group such as a 2-yl group and a 3,4-dihydroquinazolin-4-sulfon-2-yl group; a heterocyclic group; a nitro group; an imino group; and a cyano group.

Further, the electron-withdrawing groups represented by E ¹ and E ² may be bonded to form a ring. The ring formed by E ¹ and E ² is preferably a 5- to 6-membered carbocyclic or heterocyclic ring.

  L in the general formula (9) represents a group capable of leaving during azo coupling, and the leaving group L includes a halogen atom (fluorine, bromine, chlorine, iodine), a substituted alkyl group (hydroxymethyl group, dimethylaminomethyl group). ), Alkylthio group (for example, ethylthio group, 2-carboxyethylthio group, dodecylthio group, 1-carboxydodecylthio group), arylthio group (for example, phenylthio group, 2-butoxy-t-octylphenylthio group), alkoxyl group (For example, ethoxy group, dodecyloxy group, methoxyethylcarbamoylmethoxy group, carboxypropyloxy group, methylsulfonylethoxy group, ethoxycarbonylmethoxy group), aryloxy group (for example, 4-methylphenoxy group, 4-chlorophenoxy group, 4-methoxyphenoxy group, 4 Carboxyphenoxy group, 3-ethoxycarboxyphenoxy group, 3-acetylaminophenoxy group, 2-carboxyphenoxy group), acyloxy group (for example, acetoxy group, tetradecanoyloxy group, benzoyloxy group), arylsulfonyloxy group (for example, , Toluenesulfonyloxy group), dialkylaminocarbonyloxy group (for example, dimethylaminocarbonyloxy group, diethylaminocarbonyloxy group), diarylaminocarbonyloxy group (for example, diphenylaminocarbonyloxy group), alkoxycarbonyloxy group (for example, ethoxy Carbonyloxy group, benzyloxycarbonyloxy group), aryloxycarbonyloxy group (for example, phenoxycarbonyloxy group), or heterocyclic group (for example, , Imidazolyl group, pyrazolyl group, triazolyl group, tetrazolyl group).

  Specific examples of the coupler represented by the general formula (9) are shown below, but the present invention is not limited to these. The following tautomers of couplers can also be mentioned as suitable.

  The tautomer of the coupler is one that exists as an isomer of the coupler represented by the above, and has a relationship in which the structure easily changes between the two. The coupler used in the present invention As such, the tautomer is also preferable.

  The content of the coupler compound in the heat-sensitive recording layer is preferably 0.5 to 20 parts by mass and more preferably 1 to 10 parts by mass with respect to 1 part by mass of the diazonium salt compound. If the content is less than 0.5 parts by mass, sufficient color developability may not be obtained, and if it exceeds 20 parts by mass, the coating suitability may be deteriorated.

  The coupler compound (along with other components added as desired) can be used by adding a water-soluble polymer and solid-dispersing it with a sand mill or the like. It can also be used. Here, the method for solid dispersion or emulsification is not particularly limited, and a conventionally known method can be used. Details of these methods are described in JP-A-59-190886, JP-A-2-141279, and JP-A-7-17145.

(Other ingredients)
The heat-sensitive recording layer according to the present invention may contain a basic substance, a coloring aid, a binder, an antioxidant, and the like as the other components.
The basic substance is contained for the purpose of promoting the coupling reaction between the diazonium salt compound and the coupler compound. Specifically, one kind or two or more kinds of conventionally known substances can be used, and they can be appropriately selected from the basic substances described in the publications listed in the section of the coupler compound.
Examples of the basic substance include nitrogen-containing compounds such as tertiary amines, piperidines, piperazines, amidines, formamidines, pyridines, guanidines and morpholines.

  Among them, in particular, N, N′-bis (3-phenoxy-2-hydroxypropyl) piperazine, N, N′-bis (3- (p-methylphenoxy) -2-hydroxypropyl) piperazine, N, N′-bis (3- (p-methoxyphenoxy) -2-hydroxypropyl) piperazine, N, N′-bis (3-phenylthio-2-hydroxypropyl) piperazine, N, N′-bis (3- (β-naphthoxy)- 2-hydroxypropyl) piperazine, N-3- (β-naphthoxy) -2-hydroxypropyl-N′-methylpiperazine, 1,4-bis ((3- (N-methylpiperazino) -2-hydroxy) propyloxy) Piperazines such as benzene, N- (3- (β-naphthoxy) -2-hydroxy) propylmorpholine, 1,4-bis ((3-morpholino- Morpholines such as -hydroxy) propyloxy) benzene and 1,3-bis ((3-morpholino-2-hydroxy) propyloxy) benzene, N- (3-phenoxy-2-hydroxypropyl) piperidine, N-dodecylpiperidine And guanidines such as triphenylguanidine, tricyclohexylguanidine and dicyclohexylphenylguanidine are preferred.

The coloring aid is contained for the purpose of rapid and complete thermal printing with low energy. That is, the color assistant is a substance that increases the color density at the time of heat recording or controls the color development temperature, lowers the melting point of coupler compounds, basic substances, diazonium salt compounds, etc., and reduces the softening point of the capsule wall. Due to the lowering action, the diazonium salt compound, the basic substance, the coupler compound, etc. are made to react easily.
Examples of the coloring aid include phenol derivatives, naphthol derivatives, alkoxy-substituted benzenes, alkoxy-substituted naphthalenes, aromatic ethers, thioethers, esters, amides, ureidos, urethanes, sulfonamide compounds, hydroxy compounds, and the like.

  The binder can be selected from conventionally known binders, and examples thereof include water-soluble polymers such as polyvinyl alcohol and gelatin, and polymer latex.

  The antioxidant is contained for the purpose of improving fastness to light and heat of a thermochromic image or reducing yellowing due to light of an unprinted portion (non-image portion) after fixing. Examples of the antioxidant include European Patent No. 223739, Patent No. 309401, Patent No. 309402, Patent No. 310551, Patent No. 310552, Patent No. 457416, Patent Published German No. 3435443, JP-A-54-48535, JP-A-62-262047, JP-A-63-113536, JP-A-63-163351, JP-A-2-262654, JP-A-2-71262. And JP-A-3-121449, JP-A-5-61166, JP-A-5-119449, US Pat. No. 4,814,262, US Pat. No. 4,980,275, and the like.

(Method of microencapsulation)
As a microcapsule formation method, a conventionally known microcapsule formation method (specifications such as US Pat. Nos. 3,726,804 and 3,796,669) can be used. Specifically, Interfacial polymerization and internal polymerization are suitable. Specifically, a diazonium salt compound is dissolved in a water-insoluble or insoluble organic solvent together with a microcapsule wall precursor (wall material) to form an oil phase, and this is dissolved in an aqueous solution (water phase) of a water-soluble polymer. And then emulsified and dispersed with a homogenizer or the like, and heated to form a polymer film (wall film) that becomes a microcapsule wall at the oil / water interface.

  In the present invention, at least one of the two or more subdivided layers in which at least one heat-sensitive recording layer of each of the heat-sensitive recording layers develops the same hue and has different color development sensitivities to thermal energy is A layer containing capsules is preferred. By setting it as such an aspect, control of (gamma) can be made easier.

Furthermore, in the present invention, it is preferable that the two or more subdivided layers having the same hue each contain a microcapsule, and Tg of each microcapsule has a different glass transition temperature (Tg). It is preferable that it is the microcapsule comprised by these. When the glass transition temperature (Tg) is the tan δ peak value in the viscoelasticity measurement of the polymer, the difference in Tg (difference in peak) is preferably 10 ° C. or higher, more preferably 15 ° C. or higher.
By including microcapsules prepared with a certain difference in each Tg of the wall material of the microcapsules contained in the subdivided layer, fine adjustment of the γ value with respect to thermal energy tends to be facilitated. As a result, materials with different color densities can be easily manufactured according to the degree of demand in the field of use.

  Examples of the polymer material (wall material) used as the wall film of the microcapsule include polyurethane resin, polyurea resin, polyamide resin, polyester resin, polycarbonate resin, aminoaldehyde resin, melamine resin, polystyrene resin, and styrene-acrylate copolymer. Examples include coalesced resin, styrene-methacrylate copolymer resin, gelatin, polyvinyl alcohol and the like. Among these, microcapsules having a wall film made of polyurethane / polyurea resin are preferable.

In the present invention, at least one heat-sensitive recording layer of each of the heat-sensitive recording layers is colored in the same hue and has two or more subdivided layers (subdivided layers) having different color development sensitivities to thermal energy. As described above, each layer preferably contains microcapsules, and the microcapsules are preferably microcapsules having different median diameters.
When the particle size is measured using LA700 (manufactured by Horiba Seisakusho Co., Ltd.), the difference in the capsule particle size of the large particle size from that of the small particle size, that is, the difference in the median diameter has a significant difference in γ. It is preferable to include microcapsules that are preferably 10% or more, more preferably 15% or more, and particularly preferably 20% or more.

A method for producing a diazonium salt compound-encapsulating microcapsule (polyurea / polyurethane wall) will be described below as an example.
First, the diazonium salt compound is dissolved or dispersed in a hydrophobic organic solvent (including a low-boiling point solvent as necessary) serving as a capsule core to prepare an oil phase (organic solvent solution) serving as a microcapsule core. At this time, a polyvalent isocyanate as a wall material or a surfactant may be further added to the oil phase side for the purpose of uniformly emulsifying and dispersing. Further, additives such as an anti-fading agent and an anti-stain agent may be added.

The polyvalent isocyanate compound is preferably a compound having a trifunctional or higher functional isocyanate group, and may be a bifunctional isocyanate compound. Specifically, xylene diisocyanate and hydrogenated products thereof, hexamethylene diisocyanate, tolylene diisocyanate and hydrogenated products thereof, diisocyanates such as isophorone diisocyanate, and the like, and these dimers or trimers (burette or isocyanate). Nurate), other polyfunctional adducts of polyols such as trimethylolpropane and bifunctional isocyanates such as xylylene diisocyanate, adducts of polyols such as trimethylolpropane and bifunctional isocyanates such as xylylene diisocyanate Examples thereof include a compound in which a high molecular weight compound such as polyether having active hydrogen such as polyethylene oxide is introduced, and a formalin condensate of benzene isocyanate.
The compounds described in JP-A-62-212190, JP-A-4-26189, JP-A-5-317694, and Japanese Patent Application No. 8-268721 are also preferable.

  The amount of polyisocyanate used is determined so that the average particle diameter of the microcapsules is 0.3 to 12 μm and the wall thickness is 0.01 to 0.3 μm. The dispersed particle diameter is 0.2 About 10 μm is common.

  As the surfactant, a known surfactant for emulsification can be used, and the addition amount in the case of adding the surfactant is preferably 0.1 to 5% by mass relative to the mass of the oil phase, -2 mass% is more preferable.

In the preparation of the oil phase, the hydrophobic organic solvent that dissolves and disperses the diazonium salt compound is preferably an organic solvent having a boiling point of 100 to 300 ° C., for example, alkylnaphthalene, alkyldiphenylethane, alkyldiphenylmethane, alkylbiphenyl, Alkyl terphenyl, chlorinated paraffin, phosphate ester, maleate ester, adipate ester, phthalate ester, benzoate ester, carbonate ester, ether, sulfate ester, sulfonate ester, etc. Can be mentioned. You may use these in mixture of 2 or more types.
Further, when the solubility of the diazonium salt compound in the organic solvent is inferior, a low-boiling solvent having high solubility of the diazonium salt compound may be supplementarily used, and examples of the low-boiling solvent include ethyl acetate, Examples include propyl acetate, isopropyl acetate, butyl acetate, methylene chloride, tetrahydrofuran, acetonitrile, acetone and the like.

  That is, the diazonium salt compound preferably has an appropriate solubility in a hydrophobic organic solvent and a low-boiling solvent, and specifically, the solubility in a solvent in that the concentration of the following diazonium salt compound can be easily adjusted. Is preferably 5% or more. The solubility in water is preferably 1% or less.

  Subsequently, the prepared oil phase is emulsified and dispersed in the aqueous phase. At this time, an aqueous solution in which a water-soluble polymer is dissolved is used for the aqueous phase, and after the oil phase is added thereto, emulsification and dispersion are performed by means such as a homogenizer. The water-soluble polymer acts as a dispersion medium that makes the dispersion uniform and easy and stabilizes the emulsified and dispersed aqueous solution. Here again, the same surfactant as described above may be added for the purpose of further uniformly emulsifying and dispersing.

The water-soluble polymer used in the aqueous phase is preferably a water-soluble polymer having a water solubility of 5% or more at the temperature to be emulsified, such as polyvinyl alcohol and its modified products, polyacrylic acid amide and its derivatives. , Ethylene-vinyl acetate copolymer, styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, polyvinylpyrrolidone, ethylene-acrylic acid copolymer, vinyl acetate- Acrylic acid copolymers, carboxymethylcellulose, methylcellulose, casein, gelatin, starch derivatives, arabic gum, sodium alginate and the like can be mentioned.
The water-soluble polymer preferably has no or low reactivity with an isocyanate compound. For example, a polymer having a reactive amino group in a molecular chain such as gelatin may be modified beforehand. It is desirable to eliminate the reactivity.

In an emulsified dispersion in which an oil phase is added to an aqueous phase, a polyisocyanate polymerization reaction occurs at the interface between the oil phase and the aqueous phase to form a polyurea wall.
If a polyol and / or polyamine is further added to the hydrophobic solvent in the aqueous phase or oil phase, it can react with the polyvalent isocyanate and can be used as one of the components of the microcapsule wall. In the above reaction, it is preferable to keep the reaction temperature high or to add an appropriate polymerization catalyst from the viewpoint of increasing the reaction rate.

Specific examples of the polyol or polyamine include propylene glycol, glycerin, trimethylolpropane, triethanolamine, sorbitol, hexamethylenediamine and the like. When a polyol is added, a polyurethane wall is formed.
The polyvalent isocyanate, polyol, reaction catalyst, or polyamine for forming a part of the wall material is described in detail in Seisho (Polyurethane Handbook edited by Keiji Iwata, Nikkan Kogyo Shimbun (1987)). is there.

The emulsification can be carried out by appropriately selecting from known emulsifiers such as a homogenizer, a manton gorey, an ultrasonic disperser, a dissolver, and a teddy mill.
After emulsification, the emulsion is heated to 30 to 70 ° C. for the purpose of promoting the capsule wall formation reaction. Further, during the reaction, in order to prevent aggregation between the capsules, it is necessary to add water to reduce the collision probability between the capsules or to perform sufficient stirring. Further, a dispersion for preventing aggregation may be added during the reaction.
During the polymerization reaction, generation of carbon dioxide gas is observed as the polymerization progresses, and the end thereof can be regarded as an approximate end point of the capsule wall formation reaction. Usually, the target diazonium salt compound-containing microcapsules can be obtained by reacting for several hours.

  On the other hand, in the preparation of a coating liquid for forming a heat-sensitive recording layer (coating liquid for a heat-sensitive recording layer), a coupler that develops color of the diazonium salt compound is, for example, a sand mill However, it is particularly preferable to dissolve this in a high-boiling organic solvent that is hardly soluble or insoluble in water, and then contain a surfactant and / or a water-soluble polymer as a protective colloid. It is preferably used as an emulsified dispersion that is mixed with a polymer aqueous solution (aqueous phase) and emulsified with a homogenizer or the like. If necessary, a low boiling point solvent may be used as a dissolution aid.

Furthermore, couplers, organic bases, and the like can be emulsified and dispersed separately, or mixed and then dissolved in a high boiling point organic solvent to be emulsified and dispersed. A preferable emulsified dispersion particle size is 1 μm or less. The high-boiling organic solvent can be appropriately selected from, for example, high-boiling oils described in JP-A-2-141279, and esters are preferable and tricresyl phosphate is particularly preferable from the viewpoint of emulsion stability.
Examples of the low-boiling solvent include those similar to the low-boiling solvent in the oil phase.

  Further, as the surfactant contained in the aqueous phase, an anionic or nonionic surfactant that does not cause precipitation or aggregation with a water-soluble polymer can be appropriately selected. For example, sodium alkylbenzene sulfonate, Examples include sodium alkyl sulfate, dioctyl sulfosuccinate sodium salt, polyalkylene glycol (for example, polyoxyethylene nonyl phenyl ether), and the like.

(Protective layer)
The protective layer usually contains a binder, a pigment, a lubricant, a dispersant, a fluorescent brightening agent, a metal soap, a surfactant, a hardener, an ultraviolet absorber, a crosslinking agent and the like.
Examples of the binder include vinyl acetate-acrylamide copolymer, silicon-modified polyvinyl alcohol, starch, modified starch, methyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, gelatins, gum arabic, casein, and styrene-maleic acid copolymer hydrolysis. , Styrene-maleic acid copolymer half ester hydrolyzate, isobutylene-maleic anhydride copolymer hydrolyzate, polyacrylamide derivative, polyvinyl pyrrolidone, polystyrene sulfonate soda, sodium alginate, and styrene- Synthetic rubber latex such as butadiene rubber latex, acrylonitrile-butadiene rubber latex, methyl acrylate-butadiene rubber latex, vinyl acetate emulsion, synthetic resin emuls ® down, and the like.
Among the binders, gelatin is preferable, and as the gelatin, alkali-processed gelatin having a low isoelectric point, derivative gelatin obtained by reacting an amino group (for example, phthalated gelatin) and the like are preferable.

The pigment is not particularly limited. For example, kaolin, calcined kaolin, talc, wax, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, zinc oxide, lithopone, amorphous silica, colloidal silica, Examples include calcined stone, silica, magnesium carbonate, titanium oxide, alumina, barium carbonate, barium sulfate, mica, microballoons, urea-formalin filler, polyester particles, and cellulose filler.
As content of the said binder, 10-500 mass% is preferable with respect to the pigment in a protective layer, and 50-400 mass% is more preferable.

For the purpose of further improving the water resistance, it is effective to use a crosslinking agent and a catalyst for promoting the reaction in combination. Examples of the crosslinking agent include epoxy compounds, blocked isocyanates, vinyl sulfone compounds, and aldehyde compounds. , Methylol compounds, boric acid, carboxylic acid anhydrides, silane compounds, chelate compounds, halides, and the like, and those capable of adjusting the pH of the coating solution for forming the protective layer to 6.0 to 7.5 are preferable. Examples of the catalyst include known acids, metal salts, and the like, and those that can adjust the pH of the coating solution to 6.0 to 7.5 as described above are preferable.
Preferable examples of the lubricant include zinc stearate, calcium stearate, paraffin wax, polyethylene wax, and the like.

  Further, the protective layer may contain a surfactant, and as the surfactant, in addition to the acetylene glycol surfactant and silicone surfactant described above, sulfosuccinic acid alkali metal salt, fluorine-containing Surfactant etc. are mentioned suitably, Specifically, sodium salts, such as di- (2-ethylhexyl) sulfosuccinic acid and di- (n-hexyl) sulfosuccinic acid, ammonium salt, etc. are mentioned.

The coating solution for forming the protective layer (protective layer coating solution) is obtained by mixing the above-described components. Furthermore, you may add a mold release agent, a wax, a water repellent, etc. as needed.
The protective layer coating liquid containing these components has a dynamic surface tension of 35 mN / m or less when one bubble is generated in 200 ms by the bubble pressure differential pressure method, and one bubble in 1000 ms. When the dynamic surface tension when generated is 30 mN / m or less, it is applied as it is. When exceeding that, it is preferable to adjust the value of the dynamic surface tension of the coating liquid in the above range by adjusting the kind and amount of the surfactant to be added, from the viewpoint of ease of control.

The dry coating amount of the protective layer is preferably ^{0.2~7g / m 2, 1~4g / m} 2 is more preferable. If the dry coating amount is less than 0.2 g / m ² , the water resistance may not be maintained, and if it exceeds 7 g / m ² , the thermal sensitivity may be significantly lowered. You may perform a calendar process after application | coating formation of a protective layer as needed.

(Middle layer)
When a plurality of heat-sensitive recording layers are laminated, it is preferable to provide an intermediate layer between each heat-sensitive recording layer. In the intermediate layer, as in the protective layer, pigments, lubricants, surfactants, dispersants, fluorescent brighteners, metal soaps, ultraviolet absorbers and the like can be further added to various binders. As the binder, the same binder as the protective layer can be used.

(Support)
As the support, for example, plastic film, paper, plastic resin laminated paper, synthetic paper, and the like can be used.

[Multicolor thermal recording layer]
In the multicolor thermosensitive recording material of the present invention, the thermosensitive recording layer in which the hues that develop colors in Y, M, and C are layered, at least one of the thermosensitive recording layers develops the same hue, and It is composed of two or more subdivided layers (subdivided layers) having different color development sensitivities to thermal energy.

Each thermosensitive recording layer that develops one of the colors Y, M, and C may be laminated on the support in any order, but the layer closest to the support has a color development sensitivity to thermal energy. The lowest layer is preferred.
Specifically, when the layers are stacked in the order from the support, C layer / M layer / Y layer, C layer / Y layer / M layer, Y layer / C layer / M layer are preferable, and C layer / M layer / Y A layer is further preferable, and a C layer / M layer / Y layer is particularly preferable.

  The at least one thermosensitive recording layer may be a subdivided layer, and the number of subdivided layers is not particularly limited, but is preferably 2 or more and 5 or less from the viewpoint of ease of production. It is more preferably 4 layers or less, more preferably 2 layers or more and 3 layers or less, particularly preferably 2 layers.

The multicolor thermosensitive recording material of the present invention has, for example, three thermosensitive recording layers each having a subdivided layer, and a full color image can be obtained by selecting each of the colored hues to be the three primary colors, yellow, magenta and cyan in the subtractive color mixture. Recording is possible.
In this case, the coloring mechanism of the thermosensitive recording layer laminated on the support surface is not limited to 1) a diazo coloring system based on a combination of a diazonium salt compound and a coupler compound. For example, 2) an electron donating dye and the electron donating dye Coloring system combining electron-accepting dyes that develop color by reacting with reactive dyes, 3) Base coloring system that develops color upon contact with basic compounds, 4) Chelate coloring system, and 5) Reacting with nucleophiles Any color developing system may be used which causes a elimination reaction and develops color. Preferably, a color developing system in which the recording layer on the support side of each heat-sensitive recording layer is a layer having the highest color developing sensitivity to thermal energy is preferable. In this way, by making the color development sensitivity to the thermal energy of the subdivided thermosensitive recording layer closer to the support the highest, the low color density range is low gamma (γ) and the high color density range is high gamma. (Γ).
Further, at least one of the heat-sensitive recording layers needs to be two or more subdivided layers that have the same hue and have different color development sensitivities to thermal energy.

  Specifically, from the support side, it contains an electron-donating colorless dye and an electron-accepting compound, or a diazonium salt compound having a maximum absorption wavelength shorter than 350 nm and a coupler compound that reacts with the diazonium salt compound when heated to develop a color. Reaction of the first heat-sensitive recording layer with a subdivided layer (A-1 layer), an electron-donating colorless dye and an electron-accepting compound, or a diazonium salt compound having a maximum absorption wavelength shorter than 350 nm and the diazonium salt compound when heated. The first heat-sensitive recording layer containing a coupler compound that develops color (A-2 layer), a diazonium salt compound having a maximum absorption wavelength of 360 nm ± 20 nm, and the diazonium salt compound react with heat to develop color Subdivided layer (B-1 layer) of the second thermosensitive recording layer containing a coupler compound, diazonium chloride having a maximum absorption wavelength of 360 nm ± 20 nm A subdivided layer (B-2 layer) of a second thermosensitive recording layer containing a compound and a coupler compound that reacts with the diazonium salt compound when heated to produce a diazonium salt compound having a maximum absorption wavelength of 400 ± 20 nm; A subdivided layer (C-1 layer) of a third thermosensitive recording layer containing a coupler compound that reacts with the diazonium salt compound when heated, a diazonium salt compound having a maximum absorption wavelength of 400 ± 20 nm, and the diazonium salt Examples include those obtained by sequentially laminating a subdivided layer (C-2 layer) of a third thermosensitive recording layer containing a coupler compound that reacts with a compound when heated to develop a color.

The recording of the multicolor thermosensitive recording material will be described with reference to the above specific example. First, heating is performed so as to develop colors (C-1 layer) and (C-2 layer) which are the subdivided layers of the third thermosensitive recording layer ( For example, the thermal energy is 25 mJ / mm ² ), and the diazonium salt compound and the coupler compound contained in the layer are colored. Next, irradiation with light of 400 ± 20 nm is performed to decompose the unreacted diazonium salt compound contained in the C-1 and C-2 layers.

Next, heat (for example, thermal energy of 60 mJ / mm ² ) sufficient for color development of the subdivided layer (B-1 layer) and (B-2 layer) of the second heat-sensitive recording layer is applied and contained in the layer. The developed diazonium salt compound and coupler compound are colored. At this time, the C-1 and C-2 layers are also strongly heated at the same time, but the diazonium salt compound has already decomposed, and the color development ability is lost, so no color is produced. Thereafter, the diazonium salt compound contained in the B layer is decomposed by irradiation with light of 360 ± 20 nm.

Finally, heat is applied to the subdivision layers (A-1 layer) and (A-2 layer) of the first heat-sensitive recording layer to develop a color (for example, 90 mJ / mm ² ). At this time, the C layer and the B layer are also strongly heated at the same time, but the diazonium salt compound has already decomposed and the color developing ability is lost, so no color is developed.
Here, it is preferable in terms of high-speed printing that the thermal energy for maximizing the color of the thermal recording layer closest to the support among the thermal recording layers is 95 mJ / mm ² or less, and more preferably 92 mJ / mm ² or less. 90 mJ / mm ² or less is particularly preferable. In this specific example, the first subdivided layer (A-1 layer) and (A-2 layer) correspond.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples. Hereinafter, “parts” and “%” in the examples represent “parts by mass” and “% by mass”, respectively.

(Example 1)
<Preparation of aqueous solution of phthalated gelatin>
Phthalated gelatin (trade name: MGP gelatin, manufactured by Nippi Collagen Co., Ltd.) 32 parts, 1,2-benzothiazolin-3-one (3.5% methanol solution, manufactured by Daito Chemical Industry Co., Ltd.) 0.9143 Part and 367.1 parts of ion-exchanged water were mixed and dissolved at 40 ° C. to obtain a phthalated gelatin aqueous solution.

<Preparation of alkali-treated gelatin solution>
25.5 parts of alkali-treated low-ion gelatin (trade name: # 750 gelatin, manufactured by Nitta Gelatin Co., Ltd.), 1,2-benzthiazolin-3-one (3.5% methanol solution, Daito Chemical Industry Co., Ltd.) )) 0.7286 parts, calcium hydroxide 0.153 parts, and ion-exchanged water 143.6 parts were mixed and dissolved at 50 ° C. to obtain an aqueous gelatin solution for preparing an emulsion.

<Preparation of yellow thermosensitive recording layer coating solution a1>
-Preparation of diazonium salt compound-encapsulated microcapsule solution (a1)-
16.1 parts of ethyl acetate, 3.0 parts of the following compound A (diazonium salt compound, maximum absorption wavelength 420 nm), 1.4 parts of the following compound B (diazonium salt compound, maximum absorption wavelength 420 nm), monoisopropylbiphenyl 4.1 Parts, 5.5 parts of diphenyl phthalate, and 0.5 parts of diphenyl- (2,4,6-trimethylbenzoyl) phosphine oxide (trade name: Lucillin TPO, manufactured by BASF Japan Ltd.) are added at 40 ° C. And uniformly dissolved.
The resulting mixture was mixed with xylylene diisocyanate / trimethylolpropane adduct and xylylene diisocyanate / bisphenol A adduct (trade name: Takenate D119N (50 mass% ethyl acetate solution), Takeda Pharmaceutical Co., Ltd.) 8.6 parts) (mixed) was added and stirred uniformly to obtain a mixed liquid (I-1; oil phase).

  Separately, 16.3 parts of ion-exchanged water and 0.3 part of Scratch AG-8 (50% by mass; manufactured by Nippon Seika Co., Ltd.) were added to 58.6 parts of the phthalated gelatin aqueous solution, and the mixture (II -1; aqueous phase).

The mixed liquid (I-1) was added to the mixed liquid (II-1) obtained above, and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.). After adding 20 parts of water to the obtained emulsion and homogenizing it, the mixture was stirred at 40 ° C. to carry out an encapsulation reaction for 3 hours while removing ethyl acetate. Thereafter, 4.1 parts of ion exchange resin Amberlite IRA68 (manufactured by Organo Corp.) and 8.2 parts of Amberlite IRC50 (manufactured by Organo Corp.) were added and further stirred for 1 hour.
Subsequently, the ion exchange resin was removed by filtration, and the concentration was adjusted so that the solid content of the microcapsule solution was 20.0%, whereby a diazonium salt compound-encapsulating microcapsule solution (a) was obtained. As a result of measuring the particle size of the obtained microcapsule using LA-700 (manufactured by Horiba, Ltd.), the median diameter was 0.37 μm. Further, Tg of the resulting microcapsule polyurethane / urea shell was measured with a viscoelasticity measuring apparatus (DMS6100, manufactured by Seiko Instruments Inc.), and Tg was 95 ° C.

<Preparation of coating solution a2 for yellow thermosensitive recording layer>
-Preparation of diazonium salt compound-encapsulated microcapsule solution (a2)-
To 16.1 parts of ethyl acetate, 4.4 parts of the compound A (diazonium salt compound, maximum absorption wavelength 420 nm), 3.6 parts of monoisopropylbiphenyl, 5.0 parts of diphenyl phthalate, and diphenyl- (2,4,4) 0.5 part of 6-trimethylbenzoyl) phosphine oxide (trade name: Lucillin TPO, manufactured by BASF Japan Ltd.) was added and heated to 40 ° C. to dissolve uniformly.
The resulting mixture was mixed with xylylene diisocyanate / trimethylolpropane adduct and xylylene diisocyanate / bisphenol A adduct (trade name: Takenate D119N (50 mass% ethyl acetate solution), Takeda Pharmaceutical Co., Ltd.) 7.7 parts) was added and stirred uniformly to obtain a mixed liquid (I-2; oil phase).

  Separately, 14.7 parts of ion exchanged water and 0.5 part of Scraph AG-8 (50% by mass; manufactured by Nippon Seika Co., Ltd.) were added to 58.6 parts of the phthalated gelatin aqueous solution, and the mixture (II -2; aqueous phase).

The mixed solution (I-2) was added to the mixed solution (II-2) obtained above, and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.). After adding 20 parts of water to the obtained emulsion and homogenizing it, the mixture was stirred at 40 ° C. to carry out an encapsulation reaction for 3 hours while removing ethyl acetate. Thereafter, 4.1 parts of ion exchange resin Amberlite IRA68 (manufactured by Organo Corp.) and 8.2 parts of Amberlite IRC50 (manufactured by Organo Corp.) were added and further stirred for 1 hour.
Subsequently, the ion exchange resin was removed by filtration, and the concentration was adjusted so that the solid content of the microcapsule solution was 20.0%, whereby a diazonium salt compound-encapsulating microcapsule solution (a2) was obtained. As a result of measuring the particle size of the obtained microcapsule using LA-700 (manufactured by Horiba, Ltd.), the median diameter was 0.30 μm. The Tg of the resulting microcapsule polyurethane / urea shell was measured with a viscoelasticity measuring device (DMS6100, manufactured by Seiko Instruments Inc.). The Tg was 91 ° C.

-Preparation of coupler emulsion (a)-
To 33.2 parts of ethyl acetate, 9.9 parts of the following coupler compound (C), 9.9 parts of triphenylguanidine (manufactured by Hodogaya Chemical Co., Ltd.), and 4,4 ′-(m-phenylenediisopropylidene) di 18.8 parts of phenol (trade name: bisphenol M, manufactured by Mitsui Petrochemical Co., Ltd.) and 3,3,3 ′, 3′-tetramethyl-5,5 ′, 6,6′-tetra (1-propyloxy) ) -1,1'-spirobisindane, 5.3 parts, 4- (2-ethylhexyloxy) benzesisulfonic acid amide (manac Co., Ltd.) 13.6 parts, 4-n-pentyloxybenzenesulfone 6.8 parts of acid amide (manac Co., Ltd.) and 4.2 parts of calcium dodecylbenzenesulfonate (trade name: Pionein A-41-C (70% methanol solution), Takemoto Yushi Co., Ltd.) Dissolve and mix (III It was obtained.

Separately, 107.3 parts of ion-exchanged water was mixed with 206.3 parts of the alkali-treated gelatin aqueous solution obtained above to obtain a mixed liquid (IV).
Subsequently, the liquid mixture (III) was added to the liquid mixture (IV), and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.). The obtained coupler emulsion was heated under reduced pressure to remove ethyl acetate, and then the concentration was adjusted so that the solid content concentration was 26.5% by mass. As a result of measuring the particle size of the obtained coupler emulsion (a) with LA-700 (manufactured by Horiba, Ltd.), the median size was 0.23 μm.
Further, 100 parts of the coupler emulsion after concentration adjustment was prepared by adjusting the concentration of SBR latex (trade name: SN-307 (48%), manufactured by Sumika Aves Latex Co., Ltd.) to 26.5%. Nine parts were added and stirred uniformly to obtain a coupler emulsion (a).

-Preparation of coating solution for yellow thermosensitive recording layer-
The above-obtained diazonium salt compound-encapsulated microcapsule liquid (a1) and coupler emulsion liquid (a), and the microcapsule (a2) and coupler emulsion liquid (a) were combined into the mass of the coupler compound / diazonium salt compound, respectively. The mixture was mixed so that the ratio was 2.2 / 1 to obtain yellow thermosensitive recording layer coating liquids I and II.

<Preparation of coating solution for magenta thermosensitive recording layer>
-Preparation of diazonium salt compound-encapsulated microcapsule solution (b1)-
14.0 parts of ethyl acetate, 3.8 parts of the following compound D (diazonium salt compound, maximum absorption wavelength 365 nm), 3.2 parts of isopropyl biphenyl, 3.2 parts of tricresyl phosphate, 3.2 parts of diphenyl phthalate, sulfuric acid 1.1 parts of dibutyl, 0.38 parts of 2,4,6-trimethylbenzoylphenylphosphinic acid ethyl ester, and calcium dodecylbenzenesulfonate (surfactant; trade name: Pionine A-41-C (70% methanol solution) ); 0.15 part of Takemoto Yushi Co., Ltd.) was added and heated to dissolve uniformly.

10.9 parts of xylylene diisocyanate / trimethylolpropane adduct (trade name: Takenate D110N (75% ethyl acetate solution), manufactured by Takeda Pharmaceutical Co., Ltd.) as a capsule wall material is added to the resulting mixture. It stirred uniformly and the liquid mixture (V-1; oil phase) was obtained.
Separately, 26.3 parts of ion-exchanged water was mixed with 56.3 parts of the phthalated gelatin aqueous solution to obtain a mixed liquid (VI-1; aqueous phase).

The mixed solution (V-1) was added to the mixed solution (VI-1) obtained above, and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusyo Co., Ltd.). To the obtained emulsion, 27.3 parts of water was added for homogenization, and the mixture was stirred at 40 ° C. for 3 hours while removing ethyl acetate. Then, 1.16 parts of ion exchange resin Amberlite IRA67 (manufactured by Organo Corporation) and 2.33 parts of SWA100-HG (manufactured by Organo Corporation) were added and further stirred for 1.0 hour.
Subsequently, the ion exchange resin was removed by filtration, and the concentration was adjusted so that the solid content of the microcapsule solution was 18.5%, thereby obtaining a diazonium salt compound-encapsulating microcapsule solution (b1). As a result of measuring the particle size of the obtained microcapsule using LA-700 (manufactured by Horiba, Ltd.), the median diameter was 0.57 μm. Further, Tg of the resulting microcapsule polyurethane / urea shell was measured with a viscoelasticity measuring apparatus (DMS6100 manufactured by Seiko Instruments Inc.), and Tg was 120 ° C.

<Preparation of coating solution for magenta thermosensitive recording layer>
-Preparation of diazonium salt compound-encapsulated microcapsule solution (b2)-
12.8 parts of ethyl acetate, 3.8 parts of the compound D (diazonium salt compound, maximum absorption wavelength 365 nm), 3.2 parts of isopropyl biphenyl, 3.2 parts of tricresyl phosphate, 3.2 parts of diphenyl phthalate, sulfuric acid 1.1 parts of dibutyl, 0.38 parts of 2,4,6-trimethylbenzoylphenylphosphinic acid ethyl ester, and calcium dodecylbenzenesulfonate (surfactant; trade name: Pionine A-41-C (70% methanol solution) ); 0.30 part of Takemoto Yushi Co., Ltd.) was added, and then heated to dissolve uniformly.

A mixture of xylylene diisocyanate / trimethylolpropane adduct and xylylene diisocyanate / bisphenol A adduct as a capsule wall material (trade name: Takenate D119N (50% ethyl acetate solution), Takeda Pharmaceutical Co., Ltd. 16.35 parts) was added and stirred uniformly to obtain a liquid mixture (V-2; oil phase).
Separately, 26.3 parts of ion-exchanged water was mixed with 56.3 parts of the phthalated gelatin aqueous solution to obtain a mixed solution (VI-2; aqueous phase).

The mixed solution (V-2) was added to the mixed solution (VI-2) obtained above, and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusyo Co., Ltd.). To the obtained emulsion, 27.3 parts of water was added for homogenization, and the mixture was stirred at 40 ° C. for 3 hours while removing ethyl acetate. Thereafter, 1.16 parts of ion exchange resin Amberlite IRA67 (manufactured by Organo Corporation) and 2.33 parts of SWA100-HG (manufactured by Organo Corporation) were added, and the mixture was further stirred for 0.5 hours.
Subsequently, the ion exchange resin was removed by filtration, and the concentration was adjusted so that the solid content of the microcapsule solution was 18.5% to obtain a diazonium salt compound-encapsulated microcapsule solution (b2). As a result of measuring the particle size of the obtained microcapsule using LA-700 (manufactured by Horiba, Ltd.), the median diameter was 0.40 μm. The Tg of the resulting microcapsule polyurethane / urea shell was measured with a viscoelasticity measuring apparatus (DMS6100 manufactured by Seiko Instruments Inc.), and the Tg was 102 ° C.

-Preparation of coupler emulsion (b)-
33.0 parts of ethyl acetate, 6.3 parts of the following coupler compound (E), 14.0 parts of triphenylguanidine (manufactured by Hodogaya Chemical Co., Ltd.), and 4,4 ′-(m-phenylenediisopropylidene) 14.0 parts of diphenol (trade name: bisphenol M (manufactured by Mitsui Petrochemical Co., Ltd.)), 14 parts of 1,1 ′-(-p-hydroxyphenyl) -2-ethylhexane, 3,3,3 ', 3'-tetramethyl-5,5', 6,6'-tetra (1-propyloxy) -1,1'-spirobisindane, 3.5 parts of the following compound (G), 2.5 parts of tricresyl phosphate and 4.5 parts of calcium dodecylbenzenesulfonate (trade name: Pionein A-41-C (70% methanol solution), Takemoto Yushi Co., Ltd.) are dissolved and mixed ( VII).

Separately, 106.3 parts of ion-exchanged water was mixed with 206.3 parts of the alkali-treated gelatin aqueous solution obtained above to obtain a mixed liquid (VIII).
The mixed solution (VII) was added to the mixed solution (VIII), and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.). The resulting coupler emulsion was heated under reduced pressure to remove ethyl acetate, and then the concentration was adjusted so that the solid content concentration was 24.5% by mass to obtain a coupler emulsion (b). As a result of measuring the particle size of the obtained coupler emulsion (b) using LA-700 (manufactured by Horiba, Ltd.), the median diameter was 0.24 μm.

-Preparation of coating solution for magenta thermosensitive recording layer-
The diazonium salt compound-encapsulated microcapsule liquid (b1) and the coupler emulsion liquid (b) obtained from the above, and the microcapsule liquid (b2) and the coupler emulsion liquid (b), respectively, of the coupler compound / diazonium salt compound, It mixed so that mass ratio might be 1.9 / 1. Further, 10 parts by weight of 0.015 part (b2) with respect to 10 parts of the mixed diazonium salt compound-encapsulated microcapsule liquid (b1) with an aqueous polystyrenesulfonic acid (partially potassium hydroxide neutralized) aqueous solution (5% by mass). An amount of 0.15 parts was mixed to obtain magenta thermosensitive recording layer coating liquids I and II.

<Preparation of coating solution for cyan thermosensitive recording layer>
-Preparation of electron-donating dye precursor encapsulated microcapsule solution (c1)-
18.1 parts of ethyl acetate, 7.6 parts of the following electron donating dye precursor (H), and a mixture of 1-methylpropylphenyl-phenylmethane and 1- (1-methylpropylphenyl) -2-phenylethane ( 7.0 parts of trade name: Hysol SAS-310, manufactured by Nippon Petroleum Co., Ltd. and 9.0 parts of the following compound (I) (trade name: Irgaperm 2140, Ciba Geigy Co., Ltd.) are added and heated uniformly. Dissolved in.
To the obtained mixed liquid, 7.2 parts of xylylene diisocyanate / trimethylolpropane adduct (trade name: Takenate D110N (75% by mass ethyl acetate solution), Takeda Pharmaceutical Co., Ltd.) as a capsule wall material, Methylene polyphenyl polyisocyanate (trade name: Millionate MR-200, manufactured by Nippon Polyurethane Industry Co., Ltd.) (5.3 parts) was added and stirred uniformly to obtain a mixed liquid (IX-1).

Separately, 28.8 parts of the phthalated gelatin aqueous solution obtained above was added to 9.5 parts of ion-exchanged water, Scraph AG-8 (50% by mass), 0.17 part of Nippon Seika Co., Ltd., and dodecylbenzene. 4.3 parts of sodium sulfonate (10% aqueous solution) was added and mixed to obtain a mixed solution (X-1).
The mixed liquid (IX-1) was added to the mixed liquid (X-1) obtained above, and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.). To the obtained emulsion, 50 parts of water and 0.12 part of tetraethylenepentamine were homogenized, and the mixture was stirred at 65 ° C. for 3 hours while removing ethyl acetate. A microcapsule liquid whose concentration was adjusted so that the solid content concentration was 33% was obtained. As a result of measuring the particle size of the microcapsule at this time using LA-700 (manufactured by Horiba, Ltd.), the median diameter was 1.00 μm. The Tg of the resulting microcapsule polyurethane / urea shell was measured with a viscoelasticity measuring device (DMS6100, manufactured by Seiko Instruments Inc.). The Tg was 170 ° C.

  Furthermore, 3.7 parts of sodium dodecylbenzenesulfonate 25% aqueous solution (trade name: Neoperex F-25, manufactured by Kao Corporation) and 4,4′- An optical brightener (trade name: Kaycoll BXNL, manufactured by Nippon Soda Co., Ltd.) containing 4.3 parts of a bistriazinylaminostilbene-2,2′-disulfone derivative is added and stirred uniformly to provide an electron donating property. A dye precursor-encapsulated microcapsule solution (c1) was obtained.

<Preparation of coating solution for cyan thermosensitive recording layer>
-Preparation of electron-donating dye precursor-encapsulated microcapsule solution (c2)-
A mixture of 7.6 parts of the electron donating dye precursor (H), 1-methylpropylphenyl-phenylmethane and 1- (1-methylpropylphenyl) -2-phenylethane (18.1 parts of ethyl acetate) Product name: Hysol SAS-310, manufactured by Nippon Oil Co., Ltd. (9.0 parts) and Compound (I) (trade name: Irgaperm 2140, Ciba Geigy Co., Ltd.) (7.0 parts) were added and heated to homogeneity. Dissolved in.
To the resulting mixed liquid, 10.73 parts of xylylene diisocyanate / trimethylolpropane adduct (trade name: Takenate D110N (75% by mass ethyl acetate solution), Takeda Pharmaceutical Co., Ltd.) as a capsule wall material, 2.65 parts of methylene polyphenyl polyisocyanate (trade name: Millionate MR-200, manufactured by Nippon Polyurethane Industry Co., Ltd.) was added and stirred uniformly to obtain a mixed liquid (IX-2).

Separately, 28.8 parts of the phthalated gelatin aqueous solution obtained above were added to 9.5 parts of ion-exchanged water, 0.17 part of Scarph AG-8 (50% by mass), manufactured by Nippon Seika Co., Ltd., and dodecylbenzene. 4.3 parts of sodium sulfonate (10% aqueous solution) was added and mixed to obtain a mixed solution (X-2).
The mixed solution (IX-2) was added to the mixed solution (X-2) obtained above, and the mixture was emulsified and dispersed at 40 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho). To the obtained emulsion, 50 parts of water and 0.06 part of tetraethylenepentamine were homogenized, and the mixture was stirred at 60 ° C. for 3 hours while removing ethyl acetate. A microcapsule liquid whose concentration was adjusted so that the solid content concentration was 33% was obtained. As a result of measuring the particle size of the microcapsule at this time using LA-700 (manufactured by Horiba, Ltd.), the median diameter was 0.70 μm. The Tg of the resulting microcapsule polyurethane / urea shell was measured with a viscoelasticity measuring apparatus (DMS6100, manufactured by Seiko Instruments Inc.), and the Tg was 150 ° C.

  Furthermore, 3.7 parts of sodium dodecylbenzenesulfonate 25% aqueous solution (trade name: Neoperex F-25, manufactured by Kao Corporation) and 4,4′- An optical brightener (trade name: Kaycoll BXNL, manufactured by Nippon Soda Co., Ltd.) containing 4.3 parts of a bistriazinylaminostilbene-2,2′-disulfone derivative is added and stirred uniformly to provide an electron donating property. A dye precursor-encapsulated microcapsule solution (c2) was obtained.

-Preparation of electron-accepting compound dispersion liquid (c)-
To 11.3 parts of the phthalated gelatin aqueous solution obtained above, 30.1 parts of ion-exchanged water and 4,4 ′-(p-phenylenediisopropylidene) diphenol (trade names: bisphenol P, Mitsui Petrochemical Co., Ltd.) 15 parts) and 2% 2% sodium 2-ethylhexyl succinate aqueous solution were added and dispersed overnight using a ball mill to obtain a dispersion having a solid content concentration of 26.6%.
To 100 parts of this dispersion, 45.2 parts of the alkali-treated gelatin aqueous solution obtained above was added and stirred for 30 minutes, and then ion-exchanged water was added so that the solid content concentration of the dispersion was 23.5%. A receptive compound dispersion (c) was obtained.

-Preparation of coating solution for cyan thermosensitive recording layer-
The electron-donating dye precursor-encapsulated microcapsule liquid (c1) and the electron-accepting compound dispersion liquid (c) obtained above, and the electron-donating dye precursor-encapsulating microcapsule liquid (c2) and the electron-accepting compound dispersion are obtained. Liquid (c) Electron-accepting compound / electron-donating dye precursor was mixed so that the mass ratio was 10/1 to obtain cyan thermal recording layer coating liquids I and II.

<Preparation of coating solution for intermediate layer>
100.0 parts of alkali-treated low ion gelatin (trade name: # 750 gelatin, manufactured by Nitta Gelatin Co., Ltd.), 1,2-benzothiazolin-3-one (3.5% methanol solution, Daito Chemical Industry Co., Ltd.) )) 2.857 parts, 0.5 parts of calcium hydroxide and 521.643 parts of ion-exchanged water were mixed and dissolved at 50 ° C. to obtain an aqueous gelatin solution for preparing a coating solution for an intermediate layer.
10.0 parts of the obtained gelatin aqueous solution, 0.05 parts of sodium (4-nonylphenoxytrioxyethylene) butyl sulfonate (manufactured by Sankyo Chemical Co., Ltd .; 2.0 mass% aqueous solution), boric acid (4.0 mass) 1.5 part aqueous solution), 1.5 part polystyrene sulfonic acid (partially potassium hydroxide neutralized) aqueous solution (5 mass%) 0.19 part, 4% aqueous solution of the following compound (J) (manufactured by Wako Pure Chemical Industries, Ltd.) 1.32 parts, 0.44 part of a 4% aqueous solution of the following compound (J ′), and 0.67 part of ion-exchanged water were mixed to obtain an intermediate layer coating solution.

<Preparation of coating solution for light transmittance adjusting layer>
-Preparation of UV absorber precursor microcapsule solution-
In 71 parts of ethyl acetate, 14.5 parts of [2-allyl-6- (2H-benzotriazol-2-yl) -4-tert-octylphenyl] benzenesulfonate as a UV absorber precursor, 2,2′- 5.0 parts of t-octylhydroquinone, 1.8 parts of tricresyl phosphate, 5.8 parts of α-methylstyrene dimer (trade name: MSD-100, manufactured by Mitsui Chemicals), calcium dodecylbenzenesulfonate (trade name) : Pionein A-41-C (70% methanol solution), Takemoto Yushi Co., Ltd. 0.45 part was mixed and dissolved uniformly.

54.7 parts of xylylene diisocyanate / trimethylolpropane adduct (trade name: Takenate D110N (75% by mass ethyl acetate solution), Takeda Pharmaceutical Co., Ltd.) is added as a capsule wall material to the resulting mixture. And stirred uniformly to obtain a UV absorber precursor mixed solution.
Separately, 8.9 parts of a 30% phosphoric acid aqueous solution and 532.6 parts of ion-exchanged water are mixed with 52 parts of itaconic acid-modified polyvinyl alcohol (trade name: KL-318, manufactured by Kuraray Co., Ltd.) to obtain an ultraviolet absorber precursor. A body PVA aqueous solution was obtained.
The above-mentioned ultraviolet absorbent precursor mixed solution was added to 516.06 parts of the obtained ultraviolet absorbent precursor PVA aqueous solution, and the mixture was emulsified and dispersed at 20 ° C. using a homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.). After adding 254.1 parts of ion-exchanged water to the obtained emulsion and homogenizing it, an encapsulation reaction was performed for 3 hours with stirring at 40 ° C. Thereafter, 94.3 parts of ion exchange resin Amberlite MB-3 (manufactured by Organo Corporation) was added thereto, and the mixture was further stirred for 1 hour.

Subsequently, the ion exchange resin was removed by filtration, and the concentration was adjusted so that the solid content concentration of the microcapsule solution was 13.5%. As a result of measuring the particle size of the obtained microcapsule using LA-700 (manufactured by Horiba, Ltd.), the median diameter was 0.23 ± 0.05 μm.
To 859.1 parts of this microcapsule solution, 2.416 parts of carboxy-modified styrene-butadiene latex (trade name: SN-307 (48% aqueous solution), manufactured by Sumitomo Nougatac Co., Ltd.) and 39.5 parts of ion-exchanged water are added. By mixing, an ultraviolet absorbent precursor microcapsule solution was obtained.

-Preparation of coating solution for light transmittance adjusting layer-
1000 parts of the ultraviolet absorber precursor microcapsule solution obtained from the above, fluorinated surfactant (trade name: Megafac F-120 (5% aqueous solution), manufactured by Dainippon Ink & Chemicals, Inc.), 5.2 parts, 7.75 parts of a 4% aqueous sodium hydroxide solution and 73.39 parts of sodium (4-nonylphenoxytrioxyethylene) butyl sulfonate (manufactured by Sankyo Chemical Co., Ltd .; 2.0% aqueous solution) are mixed to transmit light. A coating solution for rate adjusting layer was obtained.

<Preparation of coating solution for protective layer>
-Preparation of PVA solution for protective layer-
160 parts of vinyl alcohol (PVA) -alkyl vinyl ether copolymer (trade name: EP-130, manufactured by Denki Kagaku Kogyo Co., Ltd.), a mixed liquid of sodium alkyl sulfonate and polyoxyethylene alkyl ether phosphate (trade name: Neoscore CM-57 (54% aqueous solution), Toho Chemical Industry Co., Ltd. (8.74 parts) and ion-exchanged water (3832 parts) were mixed and dissolved at 90 ° C. for 1 hour to homogenize the PVA solution for the protective layer. Obtained.

-Preparation of pigment dispersion for protective layer-
In 8 parts of barium sulfate (trade name: BF-21F (barium sulfate content 93% or more), manufactured by Sakai Chemical Industry Co., Ltd.), an anionic special polycarboxylic acid type polymer activator (trade name: Poise 532A ( 40% aqueous solution), manufactured by Kao Co., Ltd.) 0.3 parts and ion-exchanged water 11.7 parts were mixed and dispersed with a dynomill to obtain a barium sulfate dispersion. The particle size at this time was measured using LA-700 (manufactured by Horiba, Ltd.), and as a result, the median diameter was 0.17 μm or less.
Then, 8.1 parts of colloidal silica (trade name: Snowtex O (20% aqueous dispersion), manufactured by Nissan Chemical Co., Ltd.) is added to 45.6 parts of the obtained barium sulfate dispersion, and a protective layer is added. A pigment dispersion was obtained.

-Preparation of matting agent dispersion for protective layer-
An aqueous dispersion of 1,2-benzisothiazolin-3-one (trade name: PROXEL BD, IC) was added to 220 parts of wheat starch (trade name: wheat starch S, manufactured by Shinshin Food Industry Co., Ltd.). 3.81 parts manufactured by Co., Ltd. and 1976.19 parts ion-exchanged water were mixed and dispersed uniformly to obtain a matting agent dispersion for protective layer.

-Preparation of coating solution for protective layer-
To 1000 parts of the PVA solution for protective layer obtained above, 40 parts of the fluorosurfactant (trade name: Megafac F-120 (5% aqueous solution), manufactured by Dainippon Ink & Chemicals, Inc.), (4- Nonylphenoxytrioxyethylene) sodium butyl sulfonate (manufactured by Sankyo Chemical Co., Ltd .; 2.0% aqueous solution), 49.87 parts of pigment dispersion for protective layer obtained from above, for protective layer obtained from above 16.65 parts of matting agent dispersion, 48.7 parts of zinc stearate dispersion (trade name: Hydrin F115 (20.5% aqueous solution), manufactured by Chukyo Yushi Co., Ltd.) and 280 parts of ion-exchanged water are uniformly mixed. A protective layer coating solution was obtained.

<Preparation of support with undercoat layer>
-Preparation of coating solution for undercoat layer-
40 parts of enzyme-degraded gelatin (average molecular weight 10,000, PAGI viscosity = 15 mP, PAGI jelly strength = 20 g) is added to 60 parts of ion-exchanged water, and stirred and dissolved at 40 ° C. to prepare an undercoat layer coating solution. An aqueous gelatin solution was prepared.
Separately, 8 parts of water-swelling synthetic mica (aspect ratio 1000; trade name: Somasif ME100, manufactured by Coop Chemical Co., Ltd.) and 92 parts of water were mixed and then wet-dispersed with Viscomil, and the average particle size was 2.0 μm. A mica dispersion was obtained. Water was added to this mica dispersion so that the mica concentration was 5% and mixed uniformly to obtain a mica dispersion.

  120 parts of water and 556 parts of methanol were added to 100 parts of an aqueous gelatin solution for preparing a coating solution for an undercoat layer adjusted to 40% at 40 ° C. and sufficiently stirred and mixed, and then 208 parts of the mica dispersion adjusted to 5%. Then, the mixture was further sufficiently stirred and mixed, and 9.8 parts of a 1.66% polyethylene oxide surfactant was added. And the liquid temperature was hold | maintained at 35-40 degreeC, 7.3 parts of gelatin hardeners which are an epoxy compound were added, and the coating liquid (5.7%) for undercoat layers was obtained.

-Production of support with undercoat layer-
Next, the wood pulp comprising 50 parts of LBPS and 50 parts of LBPK was beaten to 300 cc Canadian freeness with a disc refiner, 0.5 parts of epoxidized behenamide, 1.0 part of anionic polyacrylamide, 1.0 part of aluminum sulfate, polyamide polyamine 0.1 parts of epichlorohydrin and 0.5 parts of cationic polyacrylamide were added in an absolutely dry mass ratio with respect to the pulp, and a base paper having a basis weight of 114 g / m ² was made with a long net paper machine, and then the thickness was determined by a calendering process. The thickness was adjusted to 100 μm.
Subsequently, after corona discharge treatment was performed on both surfaces of the obtained base paper, polyethylene was coated to a resin thickness of 36 μm using a melt extruder to form a resin layer consisting of a mat surface (this surface was designated as “ It's called the back side.) Next, on the surface opposite to the side on which the resin layer is formed, polyethylene containing 10% anatase-type titanium dioxide and a small amount of ultramarine blue is coated using a melt extruder so as to have a thickness of 50 μm. A resin layer composed of a surface was formed (this surface is referred to as “front side”).

After the corona discharge treatment is applied to the resin surface of the back surface, aluminum oxide (trade name: Alumina Sol 100, manufactured by Nissan Chemical Industries, Ltd.) and silicon dioxide (trade name: Snowtex O, Nissan Chemical Industries, Ltd.) are used as antistatic agents. (Made by Co., Ltd.) was dispersed in water at a ratio of 1/2 (= aluminum oxide / silicon dioxide; mass ratio), and this was applied so that the dry mass was 0.2 g / m ² .
Subsequently, after the corona discharge treatment was performed on the surface of the polyethylene resin layer on the front side, the coating solution for the undercoat layer obtained above was applied so that the mica coating amount was 0.26 g / m ² and dried. A support with an undercoat layer was obtained.

<Preparation of thermal recording material>
Cyan thermosensitive recording layer coating solution (c2), cyan thermosensitive recording layer coating solution (c1), intermediate layer coating solution, magenta thermosensitive recording layer on the surface of the undercoat layer of the undercoat support. Coating liquid (b2), magenta thermal recording layer coating liquid (b1), intermediate layer fabric liquid, yellow thermal recording layer coating liquid (a2), yellow thermal recording layer coating liquid (a1), light transmittance adjustment A coating solution for a layer and a coating solution for a protective layer are applied simultaneously and continuously (10 layers are simultaneously applied), and each is subjected to a drying treatment at 30 ° C., 30% RH drying conditions, and 40 ° C., 30% drying conditions, A multicolor thermal recording material was prepared.

At this time, the yellow thermal recording layer coating solution (a1) was subjected to yellow thermal recording so that the total coating amount of the diazonium salt compounds (A) and (B) was 0.078 g / m ^{2 in} terms of the solid coating amount. The coating solution for layer (a2) was prepared in such an amount that the coating amount of the diazonium salt compound (A) was 0.078 g / m ^{2 in} terms of the solid coating amount. The coating solution for magenta thermal recording layer (b1) was a diazonium salt compound ( The coating amount of D) is 0.1125 g / m ^{2 in} terms of the solid content coating amount, and the coating amount of the magenta thermosensitive recording layer (b2) is 0. The amount of 1125 g / m ² is applied to the cyan thermosensitive recording layer coating liquid (c1), and the amount of the electron donating dye precursor (H) applied is 0.1775 g / m ^{2 in} terms of solid content, The cyan thermosensitive recording layer coating solution (c2) is an electron donating dye precursor ( The coating amount of H) was applied so that the solid coating amount was 0.1775 g / m ² .
In addition, the intermediate layer coating solution is used in an amount such that the solid coating amount of gelatin is 2.064 g / m ² between the coating solution (a) and the coating solution (b). ) And the coating liquid (c), the amount of gelatin solid content coating amount is 2.885 g / m ^2, and the light transmittance adjusting layer coating liquid has a solid content coating amount of 2.35 g / m ^2. The amount of m ² was applied to the protective layer coating solution in such an amount that the solid content was 1.39 g / m ² .

(Comparative Example 1)
In the production of the thermosensitive recording material of Example 1, the cyan thermosensitive recording layer coating solution (c2), the magenta thermosensitive recording layer coating solution (b2), and the yellow thermosensitive recording layer coating solution (a2) were not used. Multicolor thermosensitive in the same manner as in Example 1, except that the recording layer coating solution (c1), the magenta thermosensitive recording layer coating solution (b1), and the yellow thermosensitive recording layer coating solution (a1) were each applied twice. A recording material was prepared.

(Comparative Example 2)
In the production of the thermosensitive recording material of Example 1, the cyan thermosensitive recording layer coating liquid (c1), the magenta thermosensitive recording layer coating liquid (b1), and the yellow thermosensitive recording layer coating liquid (a1) were not used. Multicolor thermosensitive in the same manner as in Example 1, except that the recording layer coating solution (c2), the magenta thermosensitive recording layer coating solution (b2), and the yellow thermosensitive recording layer coating solution (a2) were each applied twice. A recording material was prepared.

(Evaluation of single color maximum color density (Dmax) and density unevenness of thermal recording layer)
For the multicolor thermosensitive recording materials obtained in Example 1 and Comparative Examples 1 and 2, a thermal head (KST type, Kyocera Corporation) was used, and the recording energy per unit area was from 0 mJ / mm ² to 110 mJ / The applied voltage and pulse width are changed so as to continuously change to mm ^2, and after thermal printing is performed at a printing speed of 28 mm / s, ultraviolet rays are irradiated by an ultraviolet lamp having an emission center wavelength of 420 nm and an output of 40 W. The diazonium salt compounds of the yellow heat-sensitive recording layer and the magenta heat-sensitive recording layer that were not used for color development were deactivated.
Thereafter, the Y color density and the M color density were measured with a blue filter and a green filter using a Macbeth densitometer (reflection densitometer RD918, manufactured by Macbeth). Thereafter, the Y color density at which the M color development starts to mix in the Y color development portion was defined as the Y single color Dmax.

Next, the multicolor thermal recording material is irradiated with ultraviolet rays with an ultraviolet lamp having an emission center wavelength of 420 nm and an output of 40 W to deactivate the diazonium salt compound of the yellow thermal recording layer, and then a thermal head (KST type, Kyocera Corporation). The applied voltage and pulse width are changed so that the recording energy per unit area continuously changes from 0 mJ / mm ² to 100 mJ / mm ² , and thermal printing is performed at a printing speed of 21 mm / s. Then, the diazonium salt compound of the magenta thermosensitive recording layer that was not used for color development was deactivated by irradiating with an ultraviolet ray with an ultraviolet lamp having an emission center wavelength of 365 nm and an output of 40 W.
Thereafter, the M color density and the C color density were measured with a green filter and a red filter using a Macbeth densitometer (reflection densitometer RD918, manufactured by Macbeth).
Thereafter, the M color density at which the C color started to mix in the M color development portion was defined as Dmax of M single color.

  For a multicolor thermal recording material, first, the diazonium salt compound in the yellow thermal recording layer is deactivated by an ultraviolet lamp having an emission center wavelength of 420 nm and an output of 40 W, and then magenta thermal recording is performed by an ultraviolet lamp having an emission center wavelength of 365 nm and an output of 40 W. The layer diazonium salt compound was deactivated.

Then, the thermal head used (KST-type, Kyocera Co.), the voltage applied to the thermal head so as to change the recording energy per unit area continuously from 0 mJ / mm ² and 100 mJ / mm ^2, a pulse width The cyan thermal recording layer was subjected to thermal printing at a printing speed of 14 mm / s.

Thereafter, the maximum color density (Dmax) was measured with a red filter using a Macbeth densitometer (reflection densitometer RD918, manufactured by Macbeth). Further, the recording energy at which the maximum color density is obtained is defined as C maximum energy.
Further, the density unevenness at the time of each printing was evaluated by visual observation and used as a guideline for evaluating the graininess. The measurement results are shown in the following table.

<Evaluation criteria>
○: Level at which the unevenness is hardly noticed visually.
(Triangle | delta): The level which can recognize a nonuniformity visually.
X: Level so bad that a density difference can be clearly detected.

  As shown in Tables 1 and 2, according to the present invention, the yellow, magenta, and cyan layers are each composed of two or more subdivided layers that develop colors in the same hue and have different color development sensitivities to thermal energy. It can be seen that by using this multicolor thermal recording material, there is no problem of color mixing and high-speed printing without density unevenness becomes possible.

(A) It is an image figure which shows the Y, M, and C sensitivity curve in one Embodiment of the multicolor thermosensitive recording material of this invention. (B) It is an image figure which shows the Y, M, and C sensitivity curve in another one Embodiment of the multicolor thermosensitive recording material of this invention. (A) It is an image figure which shows the Y, M, and C sensitivity curve in the conventional multicolor thermosensitive recording material. (B) (A) It is an image figure which shows the Y, M, and C sensitivity curve at the time of making it colorable by applying low energy in the conventional multicolor thermosensitive recording material. (C) It is an image figure which shows the Y, M, and C sensitivity curve in another conventional multicolor thermosensitive recording material,

Explanation of symbols

Y yellow hue M magenta hue C cyan hue a Y visible part b M invisible part c C thermal energy level necessary for the highest color density d M color density e Y minute heat of the color density e Color density displacement relative to energy displacement

Claims (7)

In a multicolor thermosensitive recording material in which each thermosensitive recording layer that develops colors of yellow (Y), magenta (M), and cyan (C) is layered, at least one thermosensitive recording layer of each thermosensitive recording layer is identical. A multi-color heat-sensitive recording material comprising two or more layers which are colored in hue and have different color development sensitivities to heat energy. 2. The multicolor thermosensitive recording material according to claim 1, wherein the thermosensitive recording layer on the support side of each of the thermosensitive recording layers is a layer having the highest color development sensitivity to thermal energy. At least one of the two or more layers having different color development sensitivities with respect to thermal energy, wherein at least one of the thermal recording layers of each of the thermal recording layers is colored in the same hue, is a layer containing microcapsules. The multicolor thermosensitive recording material according to claim 1 or 2. The multicolor thermosensitive recording material according to any one of claims 1 to 3, wherein the thermosensitive recording layers are laminated in the order of cyan (C), magenta (M) and yellow (Y) from the support side. A multicolor thermal recording material. 5. The multicolor according to claim 1, wherein the thermal energy for maximally coloring the thermal recording layer closest to the support among the thermal recording layers is 95 mJ / mm ² or less. Thermal recording material. At least one heat-sensitive recording layer of each of the heat-sensitive recording layers is colored with the same hue, and two or more layers having different color development sensitivities to thermal energy are each made of a wall material having different glass transition temperatures. The multicolor thermosensitive recording material according to any one of claims 1 to 5, comprising a microcapsule. At least one heat-sensitive recording layer of each heat-sensitive recording layer is colored in the same hue, and two or more layers having different color development sensitivities to thermal energy include microcapsules each having a different median diameter. The multicolor thermosensitive recording material according to any one of claims 1 to 6.

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