JPH11235870A - Reversible heat-sensitive recording body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a color-developed image having a high contrast and an excellent preservability and realize short-time erasion of the image by a method wherein a pigment, the pH according to JIS K 510 of which lies within a specified range, an aliphatic amide, the melting point of which lies within a specified range, and the like are compounded in a heat-sensitive recording layer. SOLUTION: On a sheet-like support, a reversible heat-sensitive recording body is formed by including one kind or more of a colorless or a light-colored dye precursor and a developer for reversibly developing and erasing color in the dye presursor. In addition, in the heat-sensitive recording layer, a pigment, the pH according to JIS K 510 of which is 5.0-8.0, an aliphatic amide, the melting point of which is 55-130 deg.C and one kind or more of a substance selected from a group consisting of an aliphatic amide derivative and waxes are included. The embodiment of the pigment is a zinc oxide, an aluminum oxide or the like. Its loading to the heat-sensitive recording layer is preferably 0.5-35 wt.% of the dry weight of the heat-sensitive recording layer. The loading of the aliphatic amide and the like is preferably 0.5-20 wt.% of the dry weight of the heat-sensitive recording layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the heating condition so that an image can be colored and erased, and the developed and erased states can be maintained at room temperature.
It relates to a reversible thermosensitive recording medium. More specifically, the present invention relates to a reversible thermosensitive recording medium which forms a color image on a white background and has high contrast and excellent image storability.

[0002]

2. Description of the Related Art Conventionally, heat-sensitive recording media have a compact recording device, are inexpensive, and are easy to maintain. Therefore, computers, measuring instruments, registers, CD / ATMs, facsimile machines, automatic ticket vending machines, handy terminals, etc. However, recently, it has been used as a magnetic heat-sensitive card such as a prepaid card or a point card due to its combination with 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 means for solving such a problem, development of a reversible thermosensitive recording medium which can be rewritten any number of times is strongly desired.

[0003] Against the background of garbage problems and deforestation problems that 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.

[0004] Against this background, various reversible thermosensitive recording media have been proposed. For example, JP-A-63-107
584, JP-A-4-78573 and 4-
Japanese Patent No. 358878 and the like disclose a polymer type reversible thermosensitive recording medium utilizing a change in transparency due to heating conditions. However, since the recording method uses transparency-white turbidity due to the phase change of the polymer, sufficient transparency or sufficient opacity cannot be easily obtained, and the contrast between the color-developed portion and the decolored portion becomes low, resulting in darkness. There is a problem that visibility in a place is poor. In addition, in general, a white image is recorded on a colored background, and it is difficult to obtain a so-called paper-like recording medium on which a colored image is recorded 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-58-191190 and JP-A-60-193691 disclose methods using gallic acid and phloroglucinol as a color developer. However, since water or water vapor is required for erasure,
There is a disadvantage that the decoloring device becomes large. JP-A-60-264285 and JP-A-62-1408.
No. 81 discloses a thermochromic material having hysteresis. However, the image holding temperature range is
Since it is limited at both the upper and lower limits, it has the drawback that the device becomes complicated and the temperature of the use environment is limited. 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-2-188293 and JP-A-2-188294 disclose a method using a salt of a specific organic acid such as gallic acid and a higher aliphatic amine as a color developer. . However, since the coloring reaction and the decoloring reaction are competing reactions, it is difficult to control so that either reaction proceeds selectively, and there is a disadvantage that it is difficult to obtain high contrast. JP-A-5-1243
No. 60 and JP-A-6-210954,
A method using an organic phosphoric acid compound having a long-chain alkyl group or a phenolic compound as a color developer is disclosed. 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 reversible thermosensitive recording media, but each of them has various drawbacks, and a practically satisfactory one has not yet been obtained.

As a reversible thermosensitive recording medium overcoming these problems, the present inventors have previously developed a reversible thermosensitive recording medium using a compound having a long-chain alkyl group and a sulfonyl (thio) urea group as a color developer. Proposed (Japanese Patent Laid-Open No. 9-272261)
No.). This reversible thermosensitive recording medium uses a small device to form a color image on a white background, and it is possible to color and decolor only by the difference in heating conditions, and the color image has high contrast and high storage stability. Are better. However, depending on the coloring and decoloring conditions, it may take some time to erase the image,
When erasing is performed in a short period of time within one second, the image is not sufficiently erased, and so-called erasure may occur. It is preferable that the erasing time is short in order to shorten the processing time of printing / erasing, and it is desirable that there is no remaining erasing in order to improve the visibility of new printing. Further, in the case of performing repeated use a plurality of times, if the coloring and decoloring are repeatedly performed in a state where the image is not sufficiently erased, the contrast may be reduced due to the gradual increase in the decoloring density,
It is desirable that there is no disappearance to improve visibility after repeated use.

[0009]

SUMMARY OF THE INVENTION According to the present invention, a color image can be formed on a white background using a small apparatus, and color development and decoloration can be performed only by a difference in heating conditions. It is an object of the present invention to provide a reversible thermosensitive recording medium capable of forming a colored image having a property and erasing the image in an extremely short time.

[0010]

Means for Solving the Problems In order to solve the above problems, the present inventors have further studied on a dye type reversible thermosensitive recording system, and have reached the present invention. That is, the present invention
"A heat-sensitive recording layer comprising at least one colorless or light-colored dye precursor on a sheet-like support, and a developer for reversibly developing and decoloring the dye precursor, wherein the heat-sensitive recording layer PH of 5.0 to 8.0 based on JIS K5101.
0, and at least one substance selected from fatty acid amides, fatty acid amide derivatives and waxes having a melting point of 55 ° C. or more and 130 ° C. or less ”.

Specific examples of the pigment used in the present invention include zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, barium sulfate, zinc sulfate, talc, and the like.
In addition to inorganic fine powders such as silica, kaolin, clay, calcined kaolin, and colloidal silica, and organic fine powders such as urea-formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin, and the like, One type or a mixture of two or more types can be used, and among them, those having a pH of 5.5 to 7.7 are preferable. When these pigments have a pH lower than 5.0, a problem such as background fogging occurs and a recording medium having a high whiteness cannot be obtained, and the pH is 8.0.
If it is higher, the effect of shortening the erasing time cannot be obtained. The amount of the pigment used in the present invention is preferably 0.5 to 35% by weight based on the dry weight of the heat-sensitive recording layer. If the amount is less than 0.5% by weight, the desired effect cannot be obtained. If the amount is more than 35% by weight, the color density is lowered.

In the present invention, the melting point of the fatty acid amide, its derivative or wax added to the heat-sensitive recording layer is 5
The temperature is from 5 ° C to 130 ° C, preferably from 60 ° C to 125 ° C. If the melting point is lower than 55 ° C., there is a problem in the storability of the image. If the melting point is higher than 130 ° C., the effect of shortening the erasing time cannot be obtained. Specific examples of fatty acid amides and derivatives thereof include the following compounds.

(1) Fatty acid monoamides Lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, hydroxystearic acid amide, oleic acid amide, erucic acid amide, ricinoleic acid amide and the like.

(2) Substituted amides N-stearylstearic acid amide, N-stearyloleic acid amide, N-oleylstearic acid amide,
-Stearyl erucamide, N-oleyl palmitamide, N-methylol palmitamide, N-methylol stearamide, N-methylol behenamide and the like.

(3) Fatty acid bisamide ethylene bis isostearamide, ethylene bis oleate amide, hexamethylene bis oleate amide, ethylene bis isostearamide, N, N'-
Dioleyl adipamide, N, N'-dioleyl sebacic amide and the like.

Examples of the wax include natural wax, petroleum wax, and synthetic wax. Among them, paraffin wax, polyethylene wax, and microcrystalline wax are preferable. These fatty acid amides, derivatives thereof or waxes may be used alone or as a mixture of two or more. The amount of the fatty acid amide, its derivative or wax used in the present invention is preferably 0.5 to 20% by weight of the dry weight of the heat-sensitive recording layer. If the addition amount is less than 0.5% by weight, the effect of shortening the erasing time cannot be obtained, and if it is more than 20% by weight, the color density and the storage stability decrease.

Further, the reversible thermosensitive recording material of the present invention comprises a sheet-like support, a colorless or light-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, wherein the color developing agent has the following general formula (I), (II),
It is characterized by containing at least one compound represented by (III).

[0018]

Embedded image (However, R ₁ represents a member selected from a naphthyl group or a phenyl group substituted by a hydrogen atom, a halogen atom, a lower alkyl group and a lower alkoxy group;
₁ is the following chemical formula:

Embedded image Represents one member selected from the divalent group represented by
Represents an integer of 10 to 29. )

The following general formula (II):

Embedded image (However, Y ₂ is the same as Y _1, m represents an integer of 11-30.)

The following general formula (III):

Embedded image (However, p represents an integer of 14 to 30.)

The reversible thermochromic recording and decoloring method of the reversible thermosensitive recording medium according to the present invention is characterized in that the thermosensitive coloring layer of the recording medium is heated to record an image in color, and after the recording is used,
The heat-sensitive coloring layer is heated at a temperature lower than the coloring heating temperature to erase the color-developed image.

R _{1 in the} general formula (I) represents a naphthyl group or a phenyl group substituted by a member selected from a hydrogen atom, a halogen atom, a lower alkyl group and a lower alkoxy group. Groups.

Embedded image

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the reversible thermosensitive recording medium of the present invention, a thermosensitive recording layer containing a dye precursor and a color developer develops color rapidly by heating, and the color development state is maintained at room temperature by rapid cooling. Is done. 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.

The mechanism of the color development / decolorization is not clear, but when the color former is heated below the color development temperature, the long-chain alkyl groups in the color developer are oriented to induce crystallization of the color developer. However, it is considered that the dye and the developer are separated and decolorized. Generally, the heating temperature for color development is 80 to 180 ° C., the temperature range in which decoloration occurs is 50 to 120 ° 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. Decoloring is performed by maintaining the temperature in a temperature range equal to or lower than the coloring heating temperature, and controls the heating / cooling speed. No need. The temperature holding time at the time of decoloring is preferably 0.1 second or more. The process of recording and erasing the color image will be described with reference to FIG.

In FIG. 1, when the unrecorded recording material in the state A is heated, the color density rapidly increases at the temperature T2 or higher via the state B, and further increases via the state C.
When the coloring reaction is completed, the state reaches the state D, which indicates the highest coloring density. When the state D is rapidly cooled to room temperature, the state F is reached via the state E. State F is a state in which coloring is maintained at room temperature, and the recording of the image is completed. When the recorded image is heated and held in the temperature range T1, the color density gradually decreases, and the state changes to the state A 'via the state G, and the color is completely erased. When this is cooled to room temperature, it reaches state A.
State A is a state where the decolored state is maintained at room temperature,
This completes the erasure of the image. The above color-decoloring reversible cycle can be repeatedly performed.

Specific examples of the aromatic compound of the formula (I) used as a developer in the reversible thermosensitive recording medium of the present invention are shown below.

Embedded image

[0027]

Embedded image

Specific examples of the aromatic compound of the formula (II) used as a developer in the reversible thermosensitive recording medium of the present invention are shown below.

Embedded image

Specific examples of the compound of the formula (III) used as a developer in the reversible thermosensitive recording medium of the present invention are shown below.

Embedded image These compounds may be used alone or
Mixtures of more than one species may be used.

In the thermosensitive recording layer of the reversible thermosensitive recording material of the present invention, the compound used as a dye precursor includes:
Examples thereof include triphenylmethane-based, fluoran-based, and diphenylmethane-based compounds, and can be selected from conventionally known compounds. For example, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, crystal violet lactone, 3,3-bis (4- Diethylamino-2-ethoxyphenyl) -4-azaphthalide, 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-anilinofluoran, 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-chlorofluoran, 3-diethylamino-6-methylfluoran,
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, a conventionally known color developer comprising a phenol or an organic acid and a sulfonyl (thio) urea aromatic compound having no long-chain alkyl group as long as the desired effect is not impaired. Can be used in combination with the sulfonylurea developer having a long-chain alkyl group according to the present invention.

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-52-140483), 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).

Further, N- (p-toluenesulfonyl) -N'-phenylurea, N- (p-toluenesulfonyl) -N '-(p-methoxyphenyl) urea,
-(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
No. 2061), 4,4′-bis (p-toluenesulfonylaminocarbonylamino) -diphenylmethane,
4,4'-bis (o-toluenesulfonylaminocarbonylamino) -diphenylmethane, 4,4'-bis (benzenesulfonylaminocarbonylamino) -diphenylmethane, 1,2-bis [4 '-(p-toluenesulfonylaminocarbonyl) Amino) phenyloxy] ethane, 4,4'-bis (p-toluenesulfonylaminocarbonylamino) diphenyl ether and 3,3'-
Bis (p-toluenesulfonylaminocarbonylamino) diphenylsulfone (as described in JP-A-5-14735)
No. 7).

The reversible thermosensitive recording medium of the present invention may contain a thermofusible substance generally known as a sensitizer in the thermosensitive recording layer. 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 and the like. These compounds have a relatively low applied energy to enable high-density color development of a reversible thermosensitive recording medium, It also has the ability to accelerate the decoloring reaction and improve reversibility.

The heat-sensitive recording layer of the present invention usually contains a binder, and specific examples thereof include polyvinyl alcohols having various molecular weights and derivatives thereof (for example, acetoacetyl group-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, sulfonyl group). Denatured polyvinyl alcohol, etc.), starch and its derivatives (eg, oxidized starch, vinyl acetate graft starch, aldehyde-modified starch, etc.), cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid Amide / acrylic ester copolymer, acrylamide / acrylic ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt Water-soluble polymer materials such as polyacrylamide, sodium alginate, gelatin, and casein; and polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate copolymer , Polybutyl methacrylate, ethylene / vinyl acetate copolymer,
Latex such as styrene / butadiene / acrylic copolymer can be used. These binders may be used alone or in combination of two or more, and the content is generally 5 to 20% by weight of the dry weight of the heat-sensitive recording layer.

In the heat-sensitive recording layer of the reversible thermosensitive recording material of the present invention, the content of the dye precursor is generally preferably from 5 to 40% by weight of the dry weight of the heat-sensitive recording layer, and the content of the developer Is preferably 5 to 50% by weight of the dry weight of the heat-sensitive recording layer. 5% by weight of developer
If the amount is less than 50%, the color developing ability becomes insufficient. Even if it is used in a large amount exceeding 50% by weight, the color developing ability is saturated, and there is no particular improvement in the contrast between the coloring density and the decoloring density. May be economically disadvantageous.

Further, the heat-sensitive recording layer is formed of a phenol, an organic acid, or a sulfonyl (thio) having no long-chain alkyl group.
When a conventionally known color developer comprising a urea-based aromatic compound is contained, its content is preferably 10% by weight or less of the weight of the heat-sensitive recording layer. Phenols, organic acids,
Alternatively, if the content of a conventionally known color developer comprising a sulfonyl (thio) urea-based aromatic compound having no long-chain alkyl group is more than 10% by weight, the decoloring reaction is inhibited, and the color-developing portion and the decoloring portion May decrease in contrast.

The support used in the reversible thermosensitive recording medium of the present invention.
The carrier is paper (acidic) that has been used for conventional thermal recording media.
Paper, neutral paper), and apply pigment, latex, etc.
Coated paper, laminated paper, polyolefin-based
Synthetic paper, polyolefin, polyester made from resin
Glass in addition to plastic films such as
You can choose from plates, conductive rubber sheets, etc.
You. On at least one surface of such a support, the required
Apply a coating solution containing a mixture of components and dry to
A thermal recording medium is manufactured. The amount of coating is the same as when the coating
1 to 15 g / m in the state ^TwoIs preferably 2 to 10 g / m^TwoBut special
Preferred.

In the present invention, an undercoat layer may be provided below the reversible thermosensitive coloring layer. Further, a back layer can be provided on the back surface of the reversible thermosensitive recording medium to prevent blocking at the time of contact between the surfaces, suppress permeation of water or oil from the back surface, and control curl. Furthermore, in order to improve heat resistance, light resistance, printability, and durability of repeated coloring and decoloring, a protective layer, a coating layer such as a printing layer may be formed on the reversible thermosensitive coloring layer. it can. The light resistance can be improved by including an ultraviolet absorber in the protective layer. Also, by using a surface resin coating cured layer containing, as a main component, an unsaturated organic compound that can be cured by electron beam irradiation or ultraviolet irradiation in the protective layer, the durability of repeated coloring and decoloring is dramatically improved. Can be.

In the present invention, the reversible thermosensitive recording medium can be further processed in order to enhance the added value of the thermoreversible thermosensitive recording medium to give 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 reversible thermosensitive recording medium can also be used. The device for recording (coloring) and erasing (erasing) images can be selected from thermal heads, thermostats, heating rollers, hot pens, sheet heating elements, laser light, infrared light, etc., depending on the purpose of use. It is not particularly limited to these.

[0042]

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 reversible thermosensitive recording medium was prepared by the following operation. (1) Preparation of Dispersion Liquid Ingredients Amount of A (parts) 3-dibutylamino-6-methyl-7-20 anilinofluoran polyvinyl alcohol - using a sand grinder Le 10% solution 10 Water 70 The composition, average Particle size is 1
Milled to a μm.

[0043] (2) Preparation Ingredients Amount of Dispersion B (parts) N-(2-naphthylsulfonyl)-N'-[4-(n-octadecanoylamino) phenyl] urea (Compound No.1) 20 Polyvinyl alcohol 10% solution 10 Water 70 The above composition was prepared using a sand grinder to obtain an average particle size of 1
Milled to a μm.

[0044] (3) Preparation of Dispersion Liquid Ingredients Amount of C (parts) [1,4-bis {2- (4-Mechirubenjiro) ethoxy}] benzene 20 Polyvinyl alcohol - le 10% solution 10 Water 70 The composition Using a sand grinder, the average particle size is 1
Milled to a μm.

[0045] (4) Preparation Ingredients Amount of Dispersion D (parts) behenic acid amide (melting point 104 ° C.) 20 Polyvinyl alcohol - using a sand grinder Le 10% solution 10 Water 70 The composition, average particle size of 1
Milled to a μm.

(5) Formation of reversible thermosensitive recording layer 75 parts of solution A, 150 parts of solution B, 150 parts of solution C and 2 parts of solution D
5 parts, 40 parts of a 50% dispersion of kaolin (pH 5.8),
And 100 parts of a 10% aqueous polyvinyl alcohol solution were mixed and stirred to obtain a coating solution. 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.

(6) Formation of Intermediate Layer Six parts of a 50% dispersion of calcined kaolin and 200 parts of a carboxylic acid-modified polyvinyl alcohol aqueous solution (solid content: 10%) were mixed and stirred to prepare an intermediate layer coating solution. This coating solution is
On the heat-sensitive recording layer described in the above item (5), coating was performed so that the coating amount after drying was 1.5 g / m ² , followed by drying to form an intermediate layer.

(7) Super calender treatment The heat-sensitive sheet obtained as described above is treated by a super calender to have a surface smoothness of 3000 to 500.
Adjusted to 0 seconds.

(8) Formation of Overcoat Layer Polyester acrylate (Aronix M-803, manufactured by Toa Gosei Co., Ltd.) was formed on the heat-sensitive sheet obtained in the above section (7).
0) 40 parts, 40 parts of a polyester acrylate (manufactured by Toagosei Co., Aronics M-6200) and 20 parts of calcium carbonate (manufactured by Bihoku Powder Chemical Industry, Ryton A) were mixed and stirred, and the intermediate layer described in (5) above was mixed. On top of the application amount 2.5
g / m ² . An oxygen concentration of 300 ppm or less in an electron beam irradiation chamber and an acceleration voltage of 175 were applied to the obtained coating layer.
An electron beam was irradiated under the conditions of kV and an absorbed dose of 3 Mrad to form an overcoat layer, and a reversible thermosensitive recording medium was obtained.

(9) 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 at a heating temperature of 100 ° C., a pressure of 1 kg / cm ² , and a heating time of 0.7 second using a thermal gradient tester manufactured by Toyo Seiki. Measured at -914. Table 1 shows test results
Shown in

(10) Storage test After measuring the print color density in the same manner as in the color test (9), the obtained color sample was allowed to stand at 40 ° C. for 14 days, and the color density was similarly measured. Was measured. At this time, the preservability of the image portion was evaluated by the image preservation ratio: (color density after standing at 40 ° C. for 14 days) / (color density immediately after printing). Table 1 shows the test results.

<Example 2> A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in forming the reversible thermosensitive recording layer, amorphous silica (pH 7.5) was used instead of kaolin (pH 5.8). Show test results
Shown in 1.

Example 3 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing Dispersion D, N-methylol stearamide (melting point 110 ° C.) was used instead of behenamide. Table 1 shows the test results.

<Example 4> A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, when the dispersion D is 2
Instead of 5 parts, 16.7 parts of a paraffin wax dispersion [manufactured by Chukyo Yushi Co., Ltd .: Hydrin D-336, melting point 63 ° C, solid content 30%] was used. Table 1 shows the test results.

<Example 5> A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, when the dispersion D is 2
Instead of 5 parts, 16.7 parts of a paraffin wax dispersion [manufactured by Chukyo Yushi Co., Ltd .: Hydrine E-139, melting point 75 ° C, solid content 30%] was used. Table 1 shows the test results.

<Example 6> A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, when preparing the dispersion B, N- (2-naphthylsulfonyl) -N′-
Instead of [4- (n-octadecanoylamino) phenyl] urea (Compound No. 1), N- (p-toluenesulfonyl) -N ′-[4- (n-octadecanoylamino) phenyl] urea ( Compound No. 11) was used.
Table 1 shows the test results.

<Example 7> A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, when preparing the dispersion B, N- (2-naphthylsulfonyl) -N′-
Using N- (4′-hydroxyphenyl) -N ′-(n-octadecyl) urea (Compound No. 23) instead of [4- (n-octadecanoylamino) phenyl] urea (Compound No. 1) Was. Table 1 shows the test results.

Example 8 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, when preparing the dispersion B, N- (2-naphthylsulfonyl) -N′-
Octadecylphosphonic acid (Compound No. 29) was used instead of [4- (n-octadecanoylamino) phenyl] urea (Compound No. 1). Table 1 shows the test results.

Example 9 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, the formation of the overcoat layer was performed as follows. Ultraviolet ray curable vehicle (manufactured by Dainichi Seika Kogyo Co., Ltd., trademark: Seikabeam PPC)
-D-9 (revised)｝ is 2g / m by offset printing machine
After applying with a dry coating amount of ² , a 1.2K
Using an ultraviolet curing device having one W mercury lamp, the overcoat layer was formed by irradiating ultraviolet rays at a distance of 10 cm from the lamp and a transport speed of 15 m / min. Table 1 shows the test results.

Comparative Example 1 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in forming the reversible thermosensitive recording layer, light calcium carbonate (pH 8.5) was used instead of kaolin (pH 5.8). Table 1 shows the test results. Comparative Example 2 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in forming the reversible thermosensitive recording layer, acid clay (p) was used instead of kaolin (pH 5.8).
H4.5) was used. Table 1 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 the dispersion D, N, N′-ethylenebisacetamide (melting point: 172 ° C.) was used instead of behenamide. Table 1 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, instead of the dispersion D, a paraffin wax dispersion [Chukyo Yushi Co., Ltd.
Manufacture: Hydrin P-7, melting point 54 ° C, solid content 30%] 1
6.7 parts were used. Table 1 shows the test results.

[0063]

[Table 1]

As is apparent from Table 1, according to the present invention,
The pH based on JIS K5101 is set to 5.
Only when it contains a pigment of 0 to 8.0 and one or more selected from fatty acid amides, derivatives thereof and waxes having a melting point of 55 ° C. or more and 130 ° C. or less, a color image has high contrast and high storage stability. In addition, it was confirmed that a reversible thermosensitive recording medium capable of erasing an image within an extremely short time was obtained.

[0065]

The reversible thermosensitive recording medium of the present invention forms a color image on a white background, has high contrast and high storage stability,
In addition, the image can be erased in a very short time. Therefore, the reversible thermosensitive recording medium of the present invention has extremely high practical value.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between temperature and color density in a color reversible thermosensitive recording medium of the present invention in a color development and color erasure cycle.

Claims (4)

[Claims] 1. A heat-sensitive recording layer comprising at least one colorless or light-colored dye precursor and a developer for reversibly developing and decoloring the dye precursor on a sheet-like support. PH based on JIS K5101 in thermosensitive recording layer
A reversible sensation comprising a pigment having a melting point of 5.0 to 8.0 and one or more substances selected from fatty acid amides, fatty acid amide derivatives and waxes having a melting point of 55 ° C. or more and 130 ° C. or less. Thermal recording medium. 2. The developer according to claim 1, wherein the developer is represented by the following general formula (I): (However, R ₁ represents a member selected from a naphthyl group or a phenyl group substituted by a hydrogen atom, a halogen atom, a lower alkyl group and a lower alkoxy group;
₁ is the following chemical formula: Represents one member selected from the divalent group represented by
Represents an integer of 10 to 29. 2. The method according to claim 1, further comprising at least one aromatic compound represented by the formula:
4. The reversible thermosensitive recording medium according to item 1. 3. The developer according to claim 1, wherein the developer is represented by the following general formula (II): (However, Y ₂ is the same as Y _1, m represents. An integer of 11 to 30) a reversible thermosensitive recording according to claim 1, characterized in that it comprises at least one aromatic compound represented by the body. 4. The developer represented by the following general formula (II)
I): The reversible thermosensitive recording material according to claim 1, comprising at least one compound represented by the following formula (where p represents an integer of 14 to 30).