JPH1095174A - Reversible thermal recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image from losing its qualitative stability even when the color development and decolorization are repeated by adding a sulfonyl urea developer with a varying carbon atom number of a long chain alkyl group as expressed by a specific structural formula to a thermal recording layer. SOLUTION: The thermal recording layer which contains a colorless or pale dye precursor and a color developer which reversibly develops the color of or decolorizes the precursor is formed on a sheet-like support. In this case, the color developer contains at least, one type of aromatic compound expressed by formula I (R1 is one member selected from a naphthyl group or a hydrogen atom, a halogen atom and a phenyl group substituted with a lower alkyl group and a lower alkoxy group) and at least, one type of aromatic compound expressed by formula II. Thus it is possible to obtain the reversible thermal recording medium which is capable of forming a color developed image on a blank, performing the color development and decolorization only by a difference in the heating conditions, showing a sharp contrast and further, is free from the deterioration of the qualitative stability of an image, if the color development and decolorization is repeatedly carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording medium capable of performing color development and decoloring by controlling heating conditions and maintaining the color developing state and the color decoloring state at room temperature. To elaborate further,
The present invention relates to a reversible thermosensitive recording medium that forms a color image on a white background, has a high contrast, and does not deteriorate the storability of the image even when color is repeatedly formed and erased.

[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
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, transparency due to polymer phase change-
Due to the recording method using turbidity, sufficient transparency or sufficient opacity cannot be easily obtained, resulting in low contrast between the color-developed part and the decolored part, and poor visibility in dark places. Have. 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 of solving the above-mentioned problem of the conventional reversible thermosensitive recording medium, a dye-type reversible thermosensitive recording medium which enables reversible recording while using the dye used in the conventional thermosensitive recording medium has been proposed. Proposed. The dye-type reversible thermosensitive recording medium can easily record a color image on a white background, and has a relatively high contrast because it is a recording method using a change in absorption wavelength due to heating conditions. 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 apparatus is complicated and the operating temperature 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 none of them has sufficiently practical performance yet. . The present inventors have previously proposed a reversible thermosensitive recording medium using a compound having a long-chain alkyl group and a sulfonyl (thio) urea group as a color developer (Japanese Patent Laid-Open No. Hei 8-
No. 132737). This reversible thermosensitive recording material uses a small device, forms a color image on a white background, can develop and decolor only by differences in heating conditions, has high contrast, and has excellent image storability. It is a recording medium. However, depending on the coloring and erasing conditions, the storability of the colored image may be reduced as the coloring and erasing are repeatedly performed.

[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. Another object of the present invention is to provide a reversible thermosensitive recording medium which does not deteriorate the storability of an image even after repeated coloring and decoloring.

[0010]

DISCLOSURE OF THE INVENTION The present inventors have conducted intensive studies on a sulfonylurea-based developer compound having a long-chain alkyl group in order to obtain a reversible thermosensitive recording medium which has solved the above-mentioned problems. It has been found that a desired reversible thermosensitive recording medium can be obtained by adding a sulfonylurea-based developer having a long-chain alkyl group having a different number of carbon atoms to the thermosensitive recording layer, thereby completing the present invention.

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 a developer for reversibly coloring and decoloring the dye precursor. And a heat-sensitive recording layer containing a colorant, and as the color developer, the following general formula (I):

Embedded image (Wherein R ₁ represents a naphthyl group or a member selected from a hydrogen atom, a halogen atom, a phenyl group substituted by a lower alkyl group and a lower alkoxy group.) And at least one aromatic compound represented by the following formula: General formula (II):

Embedded image And at least one aromatic compound represented by the formula:

The reversible thermochromic recording and decoloring method of the reversible thermosensitive recording medium according to the present invention is characterized in that the thermochromic layer of the recording medium is heated to color-record an image, and after the recording has been used,
The heat-sensitive coloring layer is heated at a temperature lower than the coloring heating temperature to erase the color-developed image. In the general formulas (I) and (II), R ₁ represents a naphthyl group or a phenyl group substituted by a hydrogen atom, a halogen atom, a lower alkyl group and a lower alkoxy group. Can be mentioned.

[0013]

Embedded image

[0014]

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 / decoloration is not clear, but the urea group in the sulfonylurea group in the color developer represented by the formula (I) or (II) is activated by the sulfonyl group adjacent thereto. Therefore, the color develops by showing a strong color developing ability with respect to the basic leuco dye, while, when the color forming body is heated to a color developing temperature or lower, the long chain alkyl group in the color developer is oriented and the color developer is developed. Is induced, and 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 is rapidly increased at the temperature T ₂ or higher via the state B, and further, 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. The recorded image, the temperature range T ₁ in the heating, holding, color density gradually decreases, completely decolorized state A 'next via state G. 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 color developer in the reversible thermosensitive recording medium of the present invention are represented by the following chemical formula:

[0017]

Embedded image

Compounds represented by the following formulas are preferred. 5 and Compound No. 5 Compound 6 is particularly preferred. Further, 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 represented by the following chemical formula:

[0019]

Embedded image

Compounds represented by the following formulas are preferred. 11 and Compound No. Twelve compounds are particularly preferred.

By containing a sulfonylurea-based developer having a different number of carbon atoms in the long-chain alkyl group in the heat-sensitive recording layer,
Although the mechanism for preventing the deterioration of image storability after repeated coloring and decoloring is not necessarily clear, the presence of long-chain alkyl groups having different numbers of carbon atoms causes a low-temperature region (40 ° C to 60 ° C). This is considered to suppress the crystallization of the color developer due to the orientation of the long-chain alkyl group in (2).

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- (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-
Np-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
1 selected from -chlorofluoran, 3- (N-ethyl-N-cyclohexyl) -6-methyl-7- (p-chloroanilino) fluoran, 3-dibutylamino-7- (o-chloroanilino) fluoran and the like. More than one species can be used.

Further, in the present invention, a conventionally known developer comprising a phenol or an organic acid and a sulfonyl (thio) urea-based aromatic compound having no long-chain alkyl group as long as the desired effect is not impaired. Can be used in combination with the sulfonyl (thio) urea-based developer having a long-chain alkyl group according to the present invention. These conventional developers include, 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-52-140)
No. 483), bisphenol S, 4-hydroxy-
4'-isopropyloxydiphenyl sulfone (JP-A-60-13852), 1,1-di (4-hydroxyphenyl) cyclohexane, 1,7-di (4-hydroxyphenylthio) -3,5-dioxa Heptane (JP-A-59-52694), 3,3'-diallyl-
4,4'-dihydroxydiphenyl sulfone (JP-A-6
0-208286).

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-toluenesulfonyl) Aminocarbonylamino) -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-Toluenesulfonylaminocarbonylamino) diphenylsulfone
47357).

The reversible thermosensitive recording medium of the present invention can contain a thermofusible substance generally known as a sensitizer in the thermosensitive recording layer. These include, for example, oxalic acid diesters (JP-A 64-1583), di (4-methylbenzyl) oxalate (JP-B 5-62597), 1,
2-bis (m-tolyloxy) ethane (JP-A-60-5)
6588), diphenyl sulfone (JP-A-60-1985)
No. 15667) and p-benzylbiphenyl (Japanese Patent Application Laid-Open No. 60-82382). These compounds have an ability to enable high-density color development of a reversible thermosensitive recording material with relatively low applied energy. In addition, it has the ability to accelerate the decoloring reaction and improve reversibility.

The heat-sensitive recording layer of the present invention can contain waxes and pigments, and usually contains a binder. Known waxes such as paraffin, amide-based wax, and bisimide-based wax can be used as the wax. However, the addition of a zinc salt typified by zinc stearate increases the density of the ground after erasing as the color is repeatedly developed and erased, which may cause incomplete erasing of the colored image. The content of the zinc salt is preferably 1% by weight or less of the dry weight of the heat-sensitive recording layer.

Examples of the pigment include inorganic fine powders such as calcium carbonate, silica, titanium oxide, aluminum hydroxide, barium sulfate, clay, calcined clay, talc, and surface-treated calcium carbonate and silica; Examples include organic fine powders such as formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin.

Examples of the binder include polyvinyl alcohols having various molecular weights, starch and derivatives thereof, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose and ethylcellulose;
Sodium polyacrylate, polyvinylpyrrolidone, acrylamide / acrylate copolymer, acrylamide / acrylate / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, polyacrylamide, alginic acid Water-soluble polymer materials such as soda, gelatin, and casein, and polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate copolymer, and polybutyl methacrylate , Ethylene / vinyl acetate copolymer, and styrene /
Latexes such as butadiene / acrylic copolymers can be used.

In the heat-sensitive recording layer of the reversible heat-sensitive recording material of the present invention, the content of the dye precursor is generally preferably from 5 to 40% by weight based on the total dry weight of the heat-sensitive recording layer. In general, the total content of the developer compound of I) and the developer compound of the formula (II) is preferably 5 to 50% by weight based on the total dry weight of the heat-sensitive recording layer. If the total content of the color developing compound is less than 5% by weight, the color developing ability becomes insufficient, and even if it is used in a large amount exceeding 50% by weight, the color developing ability is saturated, and the color density and the disappearance of the color develop. There is no particular improvement in color density contrast, which can be economically disadvantageous. The weight ratio of the developer compound of the formula (I) to the developer compound of the formula (II) is preferably in the range of 1/20 to 20/1. Outside this range, the degree of synergistic action caused by the combined use of two or more of the present invention is reduced.
In general, the content of the sensitizer is preferably 5 to 50% by weight based on the total dry weight of the heat-sensitive recording layer. When the content of the sensitizer is less than 5% by weight, the effect of promoting color erasure is insufficient, and when the content exceeds 50% by weight, the coloring density may be insufficient.

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 10% by weight of the weight of the heat-sensitive recording layer.
The following is preferred. The content of a conventionally known color developer composed of a phenol, an organic acid, or a sulfonyl (thio) urea-based aromatic compound having no long-chain alkyl group,
When the content is more than 10% by weight, the decoloring reaction is inhibited, and the contrast between the color-developed portion and the decolored portion may be reduced. When waxes and pigments are contained in the heat-sensitive recording layer, their contents are 5 to 20% by weight and 10 to 50% by weight, respectively.
Is preferable, and the content of the binder is generally 5 to 20% by weight.

To produce the reversible thermosensitive recording medium of the present invention
Disperses or dissolves the above-mentioned components in fine particles,
To prepare a coating solution for the thermosensitive coloring layer.
To form a thermosensitive coloring layer. The heat
Further heat resistance and repeated durability of color decoloring on the color forming layer
Coating layers such as protective layers, printing layers, etc. to improve
It can also be formed. For the reversible thermosensitive recording medium of the present invention
Support has been used for conventional thermal recording media
Paper (including acid paper and neutral paper), pigment and latex on the surface
Coated paper, laminated paper, poly ole
Synthetic paper, polyolefin, poly
Other than plastic films such as polyester and polyimide
To choose from glass plate, conductive rubber sheet, etc.
Can be. On at least one side of such a support
Apply a coating solution containing a mixture of the required components and dry it.
Produce an inverse thermosensitive recording medium. The coating amount is such that the coating liquid layer is dry
1 to 15 g / m ^TwoIs preferred, and 2 to 10 g /
m^TwoIs particularly preferred. In addition, support with a reversible thermosensitive coloring layer
A subbing layer may be provided between the bodies. Also reversible feeling
Blocking on the back side of the thermal recording medium when the surface comes into contact
To prevent water and oil penetration from the back side,
A back layer can be provided for
You.

In the present invention, the reversible thermosensitive recording medium can be further processed in order to enhance the added value of the reversible thermosensitive 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 material.
In addition, thermal transfer paper, inkjet paper,
A recording paper capable of recording on both sides may be provided by having functions as 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.

[0033]

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) using a sand grinder Dispersion Preparation Ingredients Amount of A (parts) 3-dibutylamino-6-methyl-7-20 anilinofluoran polyvinyl alcohol 10% solution 10 Water 70 The composition, average particle size Is 1
It was pulverized until it became not more than μm.

[0034] (2) Preparation Ingredients Amount of Dispersion B (parts) N-(p-toluenesulfonyl) -N '- [4- (n- octadecanoylamino) phenyl] urea (Compound No.2) 20 Polyvinyl alcohol 10% liquid 10 Water 70 The above composition was prepared using a sand grinder, and the average particle size was 1
It was pulverized until it became not more than μm. (3) Preparation Ingredients Amount of Dispersion C (parts) N-(p-toluenesulfonyl) -N '- [4- (n--hexadecanoylaminophenyl) phenyl] urea (Compound No.8) 20 Polyvinyl alcohol 10 % Liquid 10 water 70 Using a sand grinder, the above composition has an average particle size of 1
It was pulverized until it became not more than μm. (4) Preparation Ingredients Amount of Dispersion D (parts) of oxalic acid - using a sand grinder di -p- methylbenzyl ester 20 polyvinyl alcohol 10% solution 10 Water 70 The composition, average particle size of 1
It was pulverized until it became not more than μm.

(5) Formation of reversible thermosensitive recording layer 60 parts of solution A, 60 parts of solution B, 60 parts of solution C, and 120 parts of solution D
Parts, calcined clay 45 parts, 25% paraffin wax emulsion 2 parts and 10% polyvinyl alcohol aqueous solution 150 parts were mixed and stirred to obtain a coating liquid. This coating solution was applied to a 75 μm-thick polyester film 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 5 parts of a kaolinite clay dispersion (solid content: 60%, manufactured by Huber, HG clay), carboxy-modified polyvinyl alcohol aqueous solution (solid content: 10%, manufactured by Kuraray, KL)
-318) 200 parts were mixed and stirred to prepare an intermediate layer coating solution. This coating solution was applied onto the heat-sensitive recording layer described in the above item (5) so that the coating amount after drying was 1.5 g / m ^2, and dried to form an intermediate layer. (7) Super calender treatment The intermediate layer described in the above item (6) is treated with a super calender, and the smoothness of the surface Beck is 3000 to 5000.
Adjusted to seconds. (8) Formation of Overcoat Layer 40 parts of polyester acrylate (Aronix M-6030 manufactured by Toagosei Co., Ltd.), 40 parts of polyester acrylate (Aronix M-6200 manufactured by Toagosei Co., Ltd.)
Light calcium carbonate (Ryton A made by Bihoku Powder Chemical Industry) 2
0 parts were mixed and stirred, and coated on the intermediate layer calendered in the above item (7) so that the coating amount was 2.5 g / m ² . The obtained coating layer was coated with an oxygen concentration of 30 in the electron beam irradiation chamber.
0 ppm or less, acceleration voltage 175 kV, absorbed dose 3 Mra
Irradiation with an electron beam was performed under the conditions of d to form an overcoat layer, and a reversible thermosensitive recording medium was obtained.

(9) Test for Color Forming and Decoloring 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. Furthermore, after heating this color-developed sample under the conditions of a heating temperature of 100 ° C., a pressure of 1 kg / cm ² , and a heating time of 1 second using a thermal gradient tester manufactured by Toyo Seiki, the decolorization density was measured using a Macbeth reflection densitometer RD-914. Was measured. Table 1 shows the test results. (10) Storage test After measuring the print color density in the same manner as in the color test in section (9) above, the obtained color sample was allowed to stand at 40 ° C. for 7 days, and then the color density was measured in the same manner. did. At this time, the preservability of the image portion 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 1 shows the test results. (11) Storage test after repeated color development and color erasure test The print color density after repeating the color development and color erasure test of the above item (9) 50 times was measured, and the obtained color sample was evaluated as 40 samples. ° C
The color density after standing for 7 days under the conditions was measured in the same manner. Image preservation ratio at this time: (Coloring and decoloring tests were 5
The storage stability of the image area was evaluated by the color density / color developing property after leaving the color developing sample after repeating 0 times at 40 ° C. for 7 days and the color developing density immediately after repeating the color erasing test 50 times × 100 (%). did. 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 preparing the dispersion B, N- (2-naphthyl) was used instead of N- (p-toluenesulfonyl) -N ′-[4- (n-octadecanoylamino) phenyl] urea (Compound No. 2). Sulfonyl) -N '-[4-
(n-octadecanoylamino) phenyl] urea (compound No. 6), and in preparing dispersion C,
N- (p-toluenesulfonyl) -N '-[4- (n-hexadecanoylamino) phenyl] urea (compound N
o. 8) Instead of N- (2-naphthylsulfonyl)-
N '-[4- (n-hexadecanoylamino) phenyl] urea (Compound No. 12) was used. Table 1 shows the test results.

Example 3 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing the dispersion B, N- (benzenesulfonyl) was used instead of N- (p-toluenesulfonyl) -N ′-[4- (n-octadecanoylamino) phenyl] urea (compound No. 2). -N '-[4- (n-
Octadecanoylamino) phenyl] urea (compound N
o. Using 1) and preparing dispersion C, N-
(p-Toluenesulfonyl) -N '-[4- (n-hexadecanoylamino) phenyl] urea (Compound No.
8) Instead of N- (benzenesulfonyl) -N '-[4
-(N-hexadecanoylamino) phenyl] urea (Compound No. 7) was used. 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, in preparing Dispersion B, N- (p-methoxy) was used instead of N- (p-toluenesulfonyl) -N ′-[4- (n-octadecanoylamino) phenyl] urea (Compound No. 2). Benzenesulfonyl) -N'-
Using [4- (n-octadecanoylamino) phenyl] urea (Compound No. 5) and preparing dispersion C, N- (p-toluenesulfonyl) -N ′-[4-
Instead of (n-hexadecanoylamino) phenyl] urea (compound No. 8), N- (p-methoxybenzenesulfonyl) -N ′-[4- (n-hexadecanoylamino) phenyl] urea (compound No. 8) .11) was used. 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 the formation of the reversible thermosensitive coloring layer, solution B 1
20 parts, and the liquid C was not used. Table 1 shows test results
Shown in

Comparative Example 2 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, when forming the reversible thermosensitive coloring layer, C solution 1
The amount was 20 parts, and the liquid B was not used. Table 1 shows test results
Shown in

Comparative Example 3 A reversible thermosensitive recording medium was prepared and tested in the same manner as in Example 1. However, in preparing Dispersion C, n-octadecyl-N ′ was used instead of N- (p-toluenesulfonyl) -N ′-[4- (n-hexadecanoylamino) phenyl] urea (Compound No. 8). 4- (3-p-toluenesulfonyluylene) phenylurea was used. 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, in preparing Dispersion C, 10- (2-decayl) was used instead of N- (p-toluenesulfonyl) -N ′-[4- (n-hexadecanoylamino) phenyl] urea (Compound No. 8). Noylhydrazinocarbonyl)
Decyl = 4- (N'-p-toluenesulfonyluylene) benzoate was used. Table 1 shows the test results.

[0045]

[Table 1]

The reversible thermosensitive recording medium of the present invention has at least one aromatic compound represented by the general formula (I) and a general formula (II) as a color developer in the thermosensitive coloring layer. And at least one aromatic compound, the color image after repeated color development and decolorization is
It has high preservability. Further, as is clear from comparison of Examples 1 to 4 with Comparative Examples 3 and 4, when a sulfonylurea compound having a long-chain alkyl group and a different structure is mixed, the storage stability of a color image is reduced, No effect is exhibited.

[0047]

The reversible thermosensitive recording medium of the present invention forms a color image on a white background, has a high contrast, and has a reduced storage stability of the color image even when color is repeatedly formed and erased. Does not occur. Therefore, the reversible thermosensitive recording medium of the present invention,
It is of 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 (2)

[Claims] 1. 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 further, as the developer, the following general formula (I): (Wherein R ₁ represents a naphthyl group or a member selected from a hydrogen atom, a halogen atom, a phenyl group substituted by a lower alkyl group and a lower alkoxy group.) And at least one aromatic compound represented by the following formula: General formula (II): A reversible thermosensitive recording medium comprising at least one aromatic compound represented by the following formula: 2. The compound represented by the following general formula (I)
I), (IV): Wherein the general formula (II) is represented by the following chemical formula (V):
(VI): The reversible thermosensitive recording medium according to claim 1, which is selected from the group consisting of: