JP2002362038A - Heat-sensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-sensitive recording medium with such advantages that the whiteness is high and the color development of a white paper part by an environment resistance test is inhibited and the color developing properties are high, and further, a reversible heat-sensitive recording medium which enables color development and decolorization to be performed only by a difference in heating conditions and shows a sharp color contrast and superb image retention properties. SOLUTION: This heat-sensitive recording medium has a sheet-like support, a colorless or pale-color dye precursor formed on the sheet-like support and a heat-sensitive recording layer including a developer which thermally develops a color through a chemical reaction with the dye precursor. In addition, the developer contains at least one kind of chemical compound having at least one boric acid group represented by formula -B(OH)2 ...(I).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosensitive recording medium containing a novel boric acid compound. More specifically, an object of the present invention is to provide a thermosensitive recording medium having a high whiteness, suppressing the color development of a white paper portion in an environmental resistance test, and having excellent color development characteristics.
Furthermore, a color-developed image is formed on a white background, color development and decoloration can be performed only by a difference in heating conditions, and a reversible thermosensitive recording medium having high contrast and excellent image storability is provided. Things.

[0002]

2. Description of the Related Art In general, a heat-sensitive recording material is formed on a support such as paper, synthetic paper, plastic film or the like by using a color-forming substance such as an electron-donating leuco dye and an organic acidic substance such as an electron-accepting phenolic compound. A heat-sensitive coloring layer mainly composed of a color-developing substance is provided, and these can be reacted by thermal energy to obtain a recorded image. Such a thermal recording medium is disclosed in JP-B-43-4160 and JP-B-45-14.
No. 039 and Japanese Patent Publication No. 48-27736, etc., and are widely used.

[0003] The thermal recording medium has a compact, inexpensive recording device and is easy to maintain. Therefore, the output of an electronic computer, a facsimile, an automatic ticket vending machine, a printer of a scientific measuring instrument, a printer of a CRT medical measurement, etc. Widely used in However, in the case of a thermosensitive recording medium in which a heat-sensitive coloring layer containing a color-forming dye substance, a color-developing substance, and a binder as active ingredients is coated on a support, a color image is white paper in a high-humidity, high-temperature atmosphere. There is a disadvantage that coloring of the part is observed. JP-A-6-115254 discloses that
Although a method using a hydroxyl group and a monovalent boric acid group as a color developer is disclosed, it has a drawback that fogging of a white paper portion occurs under high humidity.

On the other hand, the thermosensitive recording medium is also used as a magnetic recording card such as a prepaid card or a point card by combining with a magnetic recording. In these magnetic cards, the magnetic information is rewritten each time it is used, but the thermal recording image is not rewritten. Therefore, new information such as the residual number is added to the portion where no image is recorded. However, since the area of the recordable portion is limited, the actual situation is that the amount of information to be thermally recorded is unavoidably reduced, or the card is recreated when the recording area is exhausted. As a means for solving such a problem, development of a reversible thermosensitive recording medium which can be rewritten any number of times is strongly desired.

[0005] Against the background of garbage problems and deforestation problems, which have been actively discussed in recent years, there is a demand for the recycling of thermal recording paper. There are various methods for regenerating thermosensitive recording paper. Among them, as a versatile method that does not require a large device such as a deinking device, the development of a reversible thermosensitive recording material that can be rewritten many times has been developed. Is desired. Further, the reversible thermosensitive recording medium has attracted attention as a recording material for a simple display as disclosed in JP-A-3-233490 and JP-A-5-42762, and is suitable for these apparatuses. The development of a reversible thermosensitive recording medium is also strongly desired.

[0006] Against this background, various reversible thermosensitive recording media have been proposed. For example, JP-A-63-107
JP-A-584, JP-A-4-78573 and JP-A-4-35878 disclose a polymer type reversible thermosensitive recording medium utilizing a change in transparency due to heating conditions. However, this method has a disadvantage that visibility in a dark place is poor. Further, there is also a drawback that a white image is recorded on a colored background, and it is difficult to obtain a so-called paper-like recording body that records a colored image on a white background.

As a method for solving these problems, there has been proposed a dye-type reversible thermosensitive recording medium which enables reversible recording while using a dye used in a conventional thermosensitive recording medium. The dye-type reversible thermosensitive recording medium is easy to record a color image on a white background, and is a recording method using a change in absorption wavelength due to heating conditions.
A relatively high contrast is obtained. For example, the following system is known as a dye type reversible thermosensitive recording medium.

JP-A-63-173684 discloses a method using an ascorbic acid derivative as a color developer. However, there is a disadvantage that the color is not sufficiently erased during erasing. JP-A-5-124360 and JP-A-6-210954 disclose a method using an organic phosphoric acid compound having a long-chain alkyl group or a phenolic compound as a color developer. However, when erasing, there are drawbacks that the color may not be sufficiently erased, and the storability of the color image may be insufficient.

As described above, a number of techniques have been disclosed for the thermosensitive recording medium and the reversible thermosensitive recording medium, but each of them has various drawbacks, and none of them has satisfactory performance in practical use. Not obtained.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermosensitive recording medium having a high whiteness, suppressing the coloring of a blank portion in an environmental resistance test, and having excellent coloring characteristics. Further, the present invention provides a reversible thermosensitive recording medium which can form a color image on a white background and perform color development and decoloration only by a difference in heating conditions, has high contrast, and has excellent image storability.

[0011]

Means for Solving the Problems The present inventors have focused on a dye-type thermal recording system utilizing the reaction between a dye and a developer, and as a result of intensive studies, have used a boric acid compound as a developer. As a result, it has been found that a desired thermosensitive recording medium can be obtained, and the present invention has been completed.

The heat-sensitive recording material of the present invention has a sheet-like support, a colorless or light-colored dye precursor formed on the sheet-like support, and reacts with the dye precursor under heating to form a color. A heat-sensitive recording layer containing a color developing agent, wherein at least one of the following general formula (I):

Embedded image A thermosensitive recording medium comprising at least one compound having a boric acid group represented by the formula:

The reversible thermosensitive recording material of the present invention comprises a sheet-like support, a colorless or pale-colored dye precursor formed on the sheet-like support, and reversibly coloring and decoloring the same. And a heat-sensitive recording layer containing a color developing agent.
And at least one linear aliphatic group having 8 or more carbon atoms and the following general formula (I):

Embedded image And a compound having a boric acid group represented by the formula:

Further, in the reversible thermosensitive recording medium of the present invention, the color developer is represented by the following general formula (II):

Embedded image (Where X ¹ , X ² , and X ³ are independently of each other the following chemical formula:

Embedded image R ¹ represents a member selected from divalent groups represented by
And R ² independently represent a divalent hydrocarbon group having 1 to 20 carbon atoms, and R ³ is a linear aliphatic group having 8 to 30 carbon atoms. m represents an integer of 0 to 2, n, p and q each independently represent an integer of 0 or 1, and l represents 0 to 3
Represents an integer. It is preferred to be selected from the compounds represented by

The method for reversible thermal coloring and decoloring of a reversible thermosensitive recording medium according to one aspect of the present invention is to heat and color an image of the thermosensitive coloring layer of the recording medium, and to record the image in color. Thereafter, the thermosensitive coloring layer is heated at a temperature lower than the coloring heating temperature to erase the color image.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In a reversible thermosensitive recording medium according to one embodiment of the present invention, a thermosensitive recording layer containing a dye precursor and a color developer develops color rapidly by heating, and the color developing state is rapidly cooled. It is maintained at room temperature. On the other hand, the color image portion held at room temperature can be erased by heating to a color development temperature or lower, and the decolored state is maintained even when cooled to room temperature. Although the mechanism of the color development / decolorization is not clear, the boric acid group represented by the formula (I) in the color developer shows a strong color development ability with respect to the leuco dye to form a color. When is heated below the color development temperature, it is considered that the long-chain aliphatic group in the color developer is oriented to induce crystallization of the color developer, and the dye and the color developer are separated and decolorized. . Generally, the heating temperature for coloring is 120 to 240.
° C, and the temperature range in which decoloring occurs is 60 to 180 ° C, and lower than the color heating temperature. Generally, coloring is performed by a thermal head or the like, which is easy to rapidly cool after heating.However, decoloring is performed by maintaining the temperature in the decoloring temperature range equal to or lower than the coloring heating temperature. There is no need to control. The temperature holding time at the time of decoloring is 0.
Preferably, the time is 1 second or longer.

Specific examples of the aromatic compound used as a color developer in the reversible thermosensitive recording medium of the present invention are shown below, but are not limited thereto. These compounds may be used alone or in combination of two or more.

[0018]

Embedded image

[0019]

Embedded image

[0020]

Embedded image

In the heat-sensitive recording layer according to the present invention, the compounds used as dye precursors include triphenylmethane-based, fluoran-based and diphenylmethane-based compounds, which can be selected from conventionally known ones. For example,
3- (4-diethylamino-2-ethoxyphenyl)-
3- (1-ethyl-2-methylindol-3-yl)
-4-azaphthalide, crystal violet lactone, 3- (N-ethyl-N-isopentylamino) -6
-Methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluoran, 3- (N -Ethyl-N-p-toluidino) -6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofur Oran,
3- (N-cyclohexyl-N-methylamino) -6
Methyl-7-anilinofluoran, 3-diethylamino-7- (o-chloroanilino) fluoran, 3-diethylamino-7- (m-trifluoromethylanilino) fluoran, 3-diethylamino-6-methyl-7-chloro Fluoran, 3-diethylamino-6-methylfluoran, and 3-cyclohexylamino-6-chlorofluoran.

Further, 3- (N-ethyl-N-cyclohexyl) -6-methyl-7- (p-chloroanilino)
Fluoran, 3-di (n-pentyl) amino-6-methyl-7-anilinofluoran, 3- [N- (3-ethoxypropyl) -N-ethylamino] -6-methyl-7-
Anilinofluoran, 3- (Nn-hexyl-N-ethylamino) -7- (o-chloroanilino) fluoran, 3- (N-ethyl-N-2-tetrahydrofurfurylamino) -6-methyl- 7-anilinofluoran, 3
-(N-ethyl-N-isopentylamino) -6-methyl-7-anilinofluoran, 2,2-bis {4-
[6 ′-(N-cyclohexyl-N-methylamino)-
3'-methylspiro [phthalide-3,9'-xanthen] -2'-ylamino] phenyl} propane and 3
One or more selected from -dibutylamino-7- (o-chloroanilino) fluoran and the like can be used.

In the present invention, phenols or organic acids, sulfonyl (thio) urea-based aromatic compounds, and N-arylcarbonylarylsulfones having no long-chain alkyl group are used as long as the desired effects are not impaired. A conventionally known color developer composed of an amide aromatic compound,
The compound having a boric acid group represented by the general formula (I) according to the present invention can be used in combination.

These conventional developers are, for example, 2,2-
Bis (4-hydroxyphenyl) propane (bisphenol A), 1,1-bis (4-hydroxyphenyl)-
1-phenylethane, 1,4-bis (1-methyl-1-
(4′-hydroxyphenyl) ethyl) benzene, 1,
3-bis (1-methyl-1- (4′-hydroxyphenyl) ethyl) benzene, dihydroxydiphenyl ether (JP-A-1-180382), benzyl p-hydroxybenzoate (JP-A-5140483), Bisphenol S, 4-hydroxy-4'-isopropyloxydiphenyl sulfone (JP-A-60-13)
852), 1,1-di (4-hydroxyphenyl) cyclohexane, 1,7-di (4-hydroxyphenylthio) -3,5-dioxaheptane (Japanese Unexamined Patent Publication No.
52694), 3,3'-diallyl-4,4'-
Dihydroxydiphenyl sulfone (JP-A-60-208)
286).

A conventional developer which can be used in combination is N-
(P-toluenesulfonyl) -N′-phenylurea,
N- (p-toluenesulfonyl) -N '-(p-methoxyphenyl) urea, N- (p-toluenesulfonyl)
-N '-(o-tolyl) urea, N- (p-toluenesulfonyl) -N'-(m-tolyl) urea, N- (p-
Toluenesulfonyl) -N ′-(p-tolyl) urea,
N- (p-toluenesulfonyl) -N'-benzylurea (above, JP-A-5-32061), 4,4'-
Bis (p-toluenesulfonylaminocarbonylamino) -diphenylmethane, 4,4'-bis (o-toluenesulfonylaminocarbonylamino) -diphenylmethane, 4,4'-bis (benzenesulfonylaminocarbonylamino) -diphenylmethane, 1,2 -Bis [4 '-(p-toluenesulfonylaminocarbonylamino) phenyloxy] ethane, 4,4'-bis (p-toluenesulfonylaminocarbonylamino) diphenyl ether and 3,3'-bis (p-toluenesulfonylaminocarbonyl) Amino) diphenylsulfone (above, JP-A-5-147357), N- (o-toluoyl) -p-toluenesulfonamide, N-benzoyl-o-toluenesulfonamide (above, JP-A-4-4-275)
82291).

The heat-sensitive recording layer according to the present invention may contain a heat-fusible substance generally known as a sensitizer. Such sensitizers include, for example, oxalic acid diesters (Japanese Patent Application Laid-Open No. 64-1583), di (4-methylbenzyl) oxalate (Japanese Patent Publication No. 5-62597), 1,2-bis (m -Tolyloxy) ethane (JP-A-60-56588), diphenylsulfone (JP-A-60-15667), p-benzylbiphenyl (JP-A-60-82382), 1,4-bis [2 -(4-methylbenzyloxy) ethoxy] benzene (JP-A-11-20320), didodecylurea, N-stearylstearic acid amide, hexamethylenebisoleic acid amide, N, N'-didodecyloxadiamide, ( Japanese Patent Application No. 2000-139248). These compounds have the ability to promote high-density coloring of the thermosensitive recording material and the reversible thermosensitive recording material with relatively low applied energy, as well as to promote the decoloring reaction and improve the reversibility.

The heat-sensitive recording layer according to the present invention may further contain waxes and pigments as long as the effects of the present invention are not impaired, and usually contains a binder. As waxes, for example, known waxes such as paraffin, amide wax, and bisimide wax can be used.

Examples of the pigment include inorganic fine particles such as silica, clay, calcined clay, talc, calcium carbonate, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, and surface-treated calcium carbonate and silica. In addition to powder, organic fine powder such as urea-formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin can be used.

Examples of the binder include polyvinyl alcohol having various molecular weights and derivatives thereof (for example, acetoacetyl group-modified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, sulfonyl group-modified polyvinyl alcohol, etc.), starch and derivatives thereof (for example, oxidized starch, acetic acid, etc.). Vinyl graft starch, aldehyde-modified starch, etc.), cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylate copolymer, acrylamide / acrylate / Methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin And water-soluble polymer materials such as casein, and polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / Latexes such as vinyl acetate copolymers and styrene / butadiene / acrylic copolymers can be used. These binders may be used alone or in combination of two or more.

In the heat-sensitive recording layer according to the present invention, the content of the dye precursor is generally 5 to 4 times the dry weight of the heat-sensitive recording layer.
It is preferably 0% by weight, and the content of the developer is generally preferably 5 to 50% by weight of the dry weight of the heat-sensitive recording layer. When the content of the color developer is less than 5% by weight, the color developing ability becomes insufficient, and even when it is used in a large amount exceeding 50% by weight, the color developing ability is saturated, and the color forming density and the color erasing density are reduced. There is no particular improvement in the contrast of the image, which may be economically disadvantageous.

The heat-sensitive recording layer further comprises a phenol, an organic acid, a sulfonyl (thio) urea-based aromatic compound or an N-arylcarbonylarylsulfonamide-based aromatic compound having no long-chain alkyl group. When an agent is contained, its content is preferably 10% by weight or less of the weight of the heat-sensitive recording layer. Phenols,
When the content of a conventionally known color developer composed of an organic acid, a sulfonyl (thio) urea-based aromatic compound or an N-arylcarbonylarylsulfonamide-based aromatic compound having no long-chain alkyl group is more than 10% by weight. In some cases, the decoloring reaction is inhibited, and the contrast between the color-developed portion and the decolored portion is reduced.

When the wax and the pigment are contained in the heat-sensitive recording layer, the content thereof is 2 to 20% by weight,
Preferably, the content of the binder is 5 to 50% by weight.

The support used for the thermal recording medium of the present invention is made of paper (including acid paper and neutral paper), coated paper coated with pigment, latex, etc. on its surface, laminated paper, and polyolefin resin. In addition to synthetic paper, plastic films such as polyolefin, polyester, and polyimide, glass plates and conductive rubber sheets can be selected. On at least one surface of such a support, a coating solution containing a mixture of the above-mentioned required components is applied and dried to produce a thermosensitive recording medium. The coating amount is preferably 1 to 15 g / m ² in a state where the coating liquid layer is dried, and ² to 10 g / m ^2.
m ² is particularly preferred.

An undercoat layer may be provided below the thermosensitive coloring layer according to the present invention. In addition, the back side of the thermosensitive recording medium and the reversible thermosensitive recording body can be prevented from blocking when the front surface is in contact with the front surface, suppress the penetration of water or oil from the back surface, and have a back layer for curl control. it can. Furthermore, in order to improve the heat resistance, light resistance, printability, and coloring and decoloring durability, a protective layer, a coating layer such as a printing layer may be provided on the reversible thermosensitive recording layer. . The coating layer may be a single layer or two or more layers. Inorganic ultraviolet absorbers such as zinc oxide and titanium oxide, and organic ultraviolet absorbers such as benzotriazole-based compounds, salicylic acid-based compounds, and benzophenone-based compounds in the coating layer can improve light resistance, and By including pigments such as calcium carbonate, silica, aluminum hydroxide, barium sulfate, clay, calcined clay, and talc, the durability can be repeatedly improved. As the binder constituting the coating layer, various curable resins can be used, but using an unsaturated organic compound such as acrylates,
By curing this with an ultraviolet ray or an electron beam, a solid coating layer is obtained, and the repetition durability can be dramatically improved.

In the present invention, the thermal recording medium can be further processed in order to increase the added value of the thermal recording medium, and can be provided with a higher function. For example, adhesive paper, re-wet adhesive paper, delayed-tack paper by applying processing with adhesive, re-wet adhesive, delayed-tack adhesive on the back surface, or reversible heat-sensitive that can be magnetically recorded by magnetic processing It can be a recording medium. In addition, a recording paper capable of recording on both sides can be provided by using the back surface to have a function as thermal transfer paper, inkjet paper, carbonless paper, electrostatic recording paper, and xerographic paper. Of course, a double-sided thermosensitive recording medium can also be used.

An apparatus for recording (coloring) and erasing (erasing) an image can be selected from a thermal head, a constant temperature bath, a heating roller, a hot pen, a sheet heating element, a laser beam, an infrared ray, and the like according to the purpose of use. It is possible, but not limited to these.

Next, specific synthesis examples of the compound represented by the general formula (II) will be shown. <Synthesis Example 1> Synthesis of 4- (n-octadecanoylamino) phenylboronic acid (Compound No. 1): In a flask equipped with a reflux condenser, under a nitrogen atmosphere, 4-aminophenylboronic acid ( 6.8 g) is dissolved in tetrahydrofuran (150 ml) and pyridine (5 g) is added. While stirring in a water bath, stearoyl chloride (1
5.9 g) was slowly added dropwise, and after completion of the addition, the mixture was stirred at room temperature for 1 hour. This is poured into water (500 ml), and the crystals are collected by suction filtration to obtain the desired product (19.1 g).

<Synthesis Example 2> 4- [2- (n-docosanoylhydrazinocarbonyl)
Ethyl] phenylboronic acid (Compound No.
Synthesis method 9): In a flask equipped with a reflux condenser, under a nitrogen atmosphere, 4- (2-carboxyethyl) phenylboronic acid (5.80 g), docosanoyl hydrazide (11.2 g), and 1-hydroxy Benzotriazole monohydrate (5.05 g) was dissolved in tetrahydrofuran (180 ml) and N, N′-diisopropylcarbodiimide (4.16) was stirred in a water bath.
g) is added dropwise. After stirring at room temperature for 6 hours,
Heat for hours. After allowing to cool, the product is collected by suction filtration to obtain the desired product (13.6 g).

<Synthesis Example 3> Synthesis of 4- [5- (n-octadecanoylhydrazinocarbonyl) pentanoylamino] phenylboronic acid (Compound No. 12): In a flask equipped with a reflux condenser, Under a nitrogen atmosphere, 4-aminophenylboronic acid (6.8 g) is dissolved in tetrahydrofuran (50 ml), and pyridine (5 g) is added. Ethyl adipoyl chloride (10.
1 g) is slowly added dropwise, and after completion of the addition, the mixture is stirred at room temperature for 1 hour. A 5N aqueous solution of potassium hydroxide (50 m
l) is added dropwise and stirred at room temperature for 2 hours. Use this in water (25
0 ml), and 3N hydrochloric acid was added thereto until the pH reached 4 to 5 while stirring at room temperature. The precipitated crystals were collected by suction filtration to give 6-oxo-6- (4-boronophenylamino).
Hexanoic acid (10.2 g) is obtained. Subsequently, 6-oxo-6- (4-boronophenylamino)
Hexanoic acid (7.9 g), stearoyl hydrazide (9.85 g), and 1-hydroxybenzotriazole monohydrate (5.05 g) are dissolved in tetrahydrofuran (180 ml), and stirred in a water bath under N. , N'-diisopropylcarbodiimide (4.16
g) is added dropwise. After stirring at room temperature for 6 hours,
Heat for hours. After allowing to cool, the product is collected by suction filtration to obtain the desired product (14.2 g).

[0040]

The present invention will be specifically described below with reference to examples. Unless otherwise specified, “parts” and “%” represent “parts by weight” and “% by weight”, respectively. <Example 1> A thermosensitive recording paper was prepared by the following operation. (1) Preparation of pigment-coated paper calcined clay (trade names Ansilex, Engelhard &
Minerals) A dispersion obtained by dispersing 85 parts of water in 320 parts of water is mixed with 40 parts of a styrene-butadiene copolymer emulsion (50% solid content) and 5 parts of an aqueous 10% starch oxide solution.
The coating liquid obtained by mixing 0 parts was coated on a base paper of 48 g / m ² so that the coating amount after drying was 7.0 g / m ² to obtain a pigment-undercoated paper. (1) Preparation of Dispersion Liquid Ingredients Amount of A (parts) 3-dibutylamino-6-methyl-7-anilinofluoran 20 polyvinyl alcohol - using a sand grinder Le 10% solution 10 Water 70 The composition, average It was pulverized until the particle size became 1.1 μm.

[0041] (2) the dispersion prepared Ingredient Quantity of B (parts) 3-methylbenzene boronic acid 20 polyvinyl alcohol 10% solution 10 Water 70 The composition using a sand grinder, an average particle size of the 1.1μm Crushed until it became.

(3) Formation of heat-sensitive recording layer 100 parts of solution A, 250 parts of solution B, and 250 parts of a 10% aqueous solution of polyvinyl alcohol were mixed and stirred to obtain a coating solution. This coating solution was applied to one surface of a support so that the coating amount after drying was 5.0 g / m ^2, and dried to form a heat-sensitive recording layer, thereby preparing a heat-sensitive recording paper.

(6) Super calender treatment The heat-sensitive recording paper obtained as described above is treated with a super calender, and its surface is smoothed to 800 to 100.
0 seconds.

(7) Various tests (a) Whiteness The whiteness of the heat-sensitive recording paper sample was measured using a Hunter whiteness meter (manufactured by Toyo Seiki Seisaku-sho, Ltd.).

(B) Coloring Density The thermal recording medium thus obtained was subjected to a dynamic thermal coloring simulator THPMD (printing voltage: 21.7) manufactured by Okura Electric.
Using V), the sample was colored in a checkered pattern under a printing condition of an applied pulse width of 1.0 ms. The print color density was measured with a Macbeth reflection densitometer RD-914.

(C) White paper part wetland color development test The above heat-sensitive recording paper sample was placed in a thermo-hygrostat controlled at 40 ° C. and 90% for 24 hours, and the density of the white paper part was measured in the same manner as in (b) above. did. Table 1 shows the test results of (a), (b) and (c).

<Example 2> The same operation as in Example 1 was performed. However, in preparing Dispersion B, 1,4-phenylenebisboronic acid was used instead of 3-methylbenzeneboronic acid. Table 1 shows the test results.

<Comparative Example 1> The same operation as in Example 1 was performed. However, in preparing Dispersion B, 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) was used instead of 3-methylbenzeneboronic acid. Table 1 shows the test results.

<Comparative Example 2> The same operation as in Example 1 was performed. However, in preparing Dispersion B, bis (4-hydroxyphenyl) sulfone (bisphenol S) was used instead of 3-methylbenzeneboronic acid. Table 1 shows the test results.

Example 3 A reversible thermosensitive recording medium was prepared by the following operations (1) to (5). (1) Preparation of Dispersion Liquid Ingredients Amount of A (parts) 3-dibutylamino-6-methyl-7-anilinofluoran 20 polyvinyl alcohol - using a sand grinder Le 10% solution 10 Water 70 The composition, average It was pulverized until the particle size became 1.1 μm.

[0051] (2) Preparation of Dispersion Liquid Ingredients Amount of B (parts) 4-(n-octadecanoylamino) phenyl boronic acid (Compound No.1) 20 Polyvinyl alcohol 10% solution 10 Water 70 The composition Was ground using a sand grinder until the average particle size became 1.1 μm.

(3) Formation of reversible thermosensitive recording layer 100 parts of the above-mentioned liquid A, 250 parts of liquid B, and 250 parts of a 10% aqueous solution of polyvinyl alcohol were mixed and stirred to obtain a coating liquid. This coating solution was applied to one surface of the support so that the coating amount after drying was 5.0 g / m ^2, and dried to form a reversible thermosensitive recording layer.

(4) Formation of Intermediate Layer 60 parts of a 50% dispersion of kaolinite clay and 200 parts of a 10% aqueous polyvinyl alcohol solution were mixed and stirred to prepare a coating solution for the intermediate layer. The coating amount of the coating solution after drying was 1.5 g / m ² on the heat-sensitive recording layer described in the above item (3).
And dried to form an intermediate layer.

(5) Formation of Overcoat Layer 40 parts of polyester acrylate (Aronics M-830 manufactured by Toa Gosei Co., Ltd.), 40 parts of polyester acrylate (Aronix M-6200 manufactured by Toa Gosei Co., Ltd.)
20 parts of calcium carbonate (manufactured by Bihoku Powder Chemical Industry, Ryton A) were mixed and stirred, and the mixture was applied onto the intermediate layer described in the above (4) so that the application amount was 2.5 g / m ² . The obtained coating layer was irradiated with an electron beam under the conditions of an oxygen concentration of 300 ppm or less in an electron beam irradiation chamber, an acceleration voltage of 175 kV, and an absorbed dose of 3 Mrad to form an overcoat layer and obtain a reversible thermosensitive recording medium. .

(6) Color development and color erasure test The reversible thermosensitive recording medium thus obtained was subjected to printing with a printing voltage of 21.degree.
Printing was performed under the conditions of 7 v and a printing pulse of 1.0 ms. The print color density was measured with a Macbeth reflection densitometer RD-914. Further, the color-developed sample was heated using a thermal gradient tester manufactured by Toyo Seiki Co., Ltd. under the conditions of a heating temperature of 110 ° C., a pressure of 1 kg / cm ² and a heating time of 1.0 second. Measured at -914. Table 2 shows test results
Shown in

(7) Storage test After the print color density was measured in the same manner as in the color test in the above item (6), the obtained color sample was allowed to stand at 40 ° C. for 7 days, and the color density was similarly measured. Was measured. At this time, the storage stability of the image area was evaluated by the following formula: image storage ratio: (color density after standing at 40 ° C. for 7 days / color density immediately after printing) × 100 (%). Table 2 shows the test results.

(8) Repeated color development / color erasure test After the color development / color erasure test of the above item (6) was repeated 20 times, the print color density and the color erasure density were measured with a Macbeth reflection densitometer RD-914. did. Table 2 shows the test results.

<Example 4> A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 2. However, in preparing Dispersion B, 4- (n-octylaminocarbonylamino) phenylboronic acid (Compound No. 1) was used instead of 4- (n-octadecanoylamino) phenylboronic acid (Compound No. 1). 2) was used. Table 2 shows the test results.

Example 5 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing Dispersion B, 4- [2- (n-docosanoylhydrazinocarbonyl) was used instead of 4- (n-octadecanoylamino) phenylboronic acid (Compound No. 1).
Ethyl] phenylboronic acid (Compound No.
9) was used. Table 2 shows the test results.

<Example 6> A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing Dispersion B, 4- [5- (n-octadecanoylhydrazinocarbonyl) pentanoylamino was used instead of 4- (n-octadecanoylamino) phenylboronic acid (Compound No. 1). Phenylboronic acid was used. Table 2 shows the test results.

Example 7 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing dispersion B, 4- [6- (n-octadecylaminocarbonylamino) hexanoylamino] was used instead of 4- (n-octadecanoylamino) phenylboronic acid (Compound No. 1). Phenylboronic acid (Compound No. 19) was used. Table 2 shows the test results.

<Embodiment 8> Reversibility is performed in the same manner as in Embodiment 1.
A thermal recording medium was prepared and tested. However, formation of the protective layer
Was performed as follows. UV curable vehicle ビ Dainichi Seika
Made by Kogyo Co., Ltd., Trademark: Seikabeam PPC-D-9
(Revised) 2g / m by offset printing machine ²Drying
After applying the coating amount, a 1.2 KW mercury lacquer is applied to this coating layer.
Using an ultraviolet curing device with one lamp,
Irradiation with ultraviolet light at a distance of 10 cm and a transfer speed of 15 m / min
The protective layer was formed by irradiation. Table 2 shows test results
Shown in

<Example 9> A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing Dispersion A, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-) was used instead of 3-dibutylamino-6-methyl-7-anilinofluoran.
Methylindol-3-yl) -4-azaphthalide was used. Table 2 shows the test results.

Example 10 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing Dispersion B, 4- (n-heptylaminocarbonylamino) phenylboronic acid was used instead of 4- (n-octadecanoylamino) phenylboronic acid (Compound No. 1). Table 2 shows the test results.

<Comparative Example 3> A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing dispersion B, N- (4-hydroxyphenyl) -N ′-(n-octadecyl) urea was used instead of 4- (n-octadecanoylamino) phenylboronic acid (Compound No. 1). Was used. Table 2 shows the test results.

Comparative Example 4 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing Dispersion B, a salt of gallic acid and stearylamine was used instead of 4- (n-octadecanoylamino) phenylboronic acid (Compound No. 1). Table 2 shows the test results.

Comparative Example 5 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing Dispersion B, ascorbic acid was used instead of 4- (n-octadecanoylamino) phenylboronic acid (Compound No. 1). Table 2 shows the test results.

[0068]

[Table 1]

[0069]

[Table 2]

As is clear from comparison between Examples 1 and 2 and Comparative Examples 1 and 2, it is understood that the thermosensitive recording medium of the present invention has a high recording density and a high whiteness after a heat and humidity resistance test. As is clear from comparison of Examples 3 to 10 and Comparative Examples 3 to 5, the images formed on the reversible thermosensitive recording medium of the present invention were composed of a phenolic compound having a long alkyl chain, gallic acid and stearyl. It has higher contrast and higher preservability than color images obtained using a salt with an amine, ascorbic acid or the like as a color developer, and is excellent in repetition of color development and decoloration.

Further, as is apparent from a comparison between Example 4 and Example 10, the reversible thermosensitive recording material of the present invention is obtained by developing a boric acid compound having a linear aliphatic group having 8 or more carbon atoms. It can be seen that when used as an agent, extremely excellent coloring and decoloring effects are exhibited.

[0072]

The thermosensitive recording medium of the present invention has a high recording density and a high whiteness after a heat and humidity resistance test. Further, the reversible thermosensitive recording medium of the present invention forms a color image on a white background, has high contrast, and has excellent image storability. In particular, the color density after repeated coloring and decoloring does not decrease, and is stable in a place where the density after decoloring is low. Therefore, the thermosensitive recording medium of the present invention has extremely high practical value.

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Claims (3)

[Claims] 1. A heat-sensitive material comprising a sheet-like support, a colorless or light-colored dye precursor formed on the sheet-like support, and a developer which reacts with the dye precursor under heating to form a color. Having a recording layer, and further as the developer,
At least one of the following general formulas (I): A thermosensitive recording medium comprising at least one compound having a boric acid group represented by the formula: 2. A heat-sensitive recording layer comprising a sheet-like support, a colorless or light-colored dye precursor formed on the sheet-like support, and a developer for reversibly developing and decoloring the dye precursor. And as the developer, at least one straight-chain aliphatic group having 8 or more carbon atoms in one molecule and at least one of the following general formula (I): And at least one compound having a boric acid group represented by the formula: 3. The developer according to claim 1, wherein the developer is represented by the following general formula (II): (Where X ¹ , X ² , and X ³ are each independently the following chemical formula: R ¹ represents a member selected from divalent groups represented by
And R ² independently represent a divalent hydrocarbon group having 1 to 20 carbon atoms, and R ³ is a linear aliphatic group having 8 to 30 carbon atoms. m represents an integer of 0 to 2, n, p and q each independently represent an integer of 0 or 1, and l represents 0 to 3
Represents an integer. The reversible thermosensitive recording material according to claim 2, which is selected from the compounds represented by the following formula: