JP2754447B2 - Thermal recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a red-colored heat-sensitive recording material, and more particularly, to a color tone very similar to a red-colored color, less fogging of the background, and preservation of recorded images. The present invention relates to a vermilion-colored heat-sensitive recording material having excellent stability.

[0002]

2. Description of the Related Art Generally, a heat-sensitive recording material having a heat-sensitive recording layer mainly composed of a colorless or light-colored leuco dye and a color developer which reacts with the leuco dye when heated to form a color is disclosed in Japanese Patent Publication No. 45-1.
Published in No. 4035 and widely used. In order to perform recording on this thermosensitive recording medium, a thermal printer or the like having a built-in thermal head is used, but such a thermosensitive recording method is different from other recording methods that have been practically used conventionally.
There are no noise during recording, no need for development and fixing, maintenance-free, equipment is relatively inexpensive and compact, and the resulting color is very sharp, so computer output, facsimile,
It is widely used as a recorder for calculators and measuring machines, and as a ticket for automatic ticket vending machines. Since the thermal recording method has the above-described characteristics, there has recently been a demand for a thermal recording medium suitable for various uses as a recording medium particularly in the field of small printers. As one of the quality requirements, there is a demand for a heat-sensitive recording medium having a color tone close to the vermilion color of a seal and having excellent image stability and less background fog.

[0003] In spite of various proposals for leuco dyes that develop various colors, the leuco dyes that develop a red-to-orange or yellow color, which is close to vermilion, are developed. The color tone changes very much due to the difference in acidity, and there is almost no coloration required for the vermilion color.The main use of these leuco dyes themselves is toning of pressure-sensitive recording materials. When used, the color density is insufficient, the stability of the color image is difficult, or the background fog occurs, and a vermilion color heat-sensitive recording material that can withstand practical use has not been obtained. Is the current situation.

[0004]

SUMMARY OF THE INVENTION In view of the above problems, the present invention has a red color not only very similar in color tone to vermilion but also has less background fog and is excellent in storage stability of recorded images. Another object of the present invention is to provide a color-developing thermosensitive recording medium.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been found as a result of intensive studies to solve the above-mentioned problems, and provides a colorless or pale-colored leuco dye on a support and the color of the leuco dye when heated. In a thermosensitive recording medium provided with a thermosensitive recording layer containing a developer as a main component, 3-cyclohexylamino-6-chlorofluorane, 3-dibutylamino-6-methyl-7-bromofluoran , 3 −
Diethylamino-7-methylfluoran, 3-N-ethyl-N-isoamylamino-benzo [a] fluoran ,
A mixture of at least two compounds selected from 2- (4-dodecyloxy-3-methoxystyryl) quinoline and a compound represented by the following general formula (1) as a color developer. This is a heat-sensitive recording medium.

Embedded image (In the formula, R represents an alkyl group having 1 to 10 carbon atoms or a benzyl group which may have a substituent.)

Further, the present invention relates to a thermosensitive recording medium comprising a support having thereon a thermosensitive recording layer mainly composed of a colorless or light-colored leuco dye and a color developing agent capable of developing the leuco dye when heated. And a mixture of at least 3-cyclohexylamino-6-chlorofluorane and 3-dibutylamino-6-methyl-7-bromofluorane.

The leuco dye used in the present invention is selected from the above-mentioned specific compounds, and is used as a mixture of at least two or more kinds. One feature of the present invention is to use a mixture of two or more leuco dyes. Compared with the case where each of the leuco dyes is used alone, the storage stability of an image is improved by mixing and the background fog is reduced. This is because the effect of becoming In the present invention, it is preferable to use a mixture of 3-cyclohexylamino-6-chlorofluorane and 3-dibutylamino-6-methyl-7-bromofluorane as such a leuco dye. The coloring agent is not particularly limited. It is particularly preferable that the mixing ratio in this case is in the range of 5: 1 to 0.5: 1 by weight. With such a configuration, not only the color developability is good and the color tone is very similar to the vermilion color, but also the background fog is less than when the leuco dye is used alone, and the storage stability is that the recorded image has less fading. A heat-sensitive recording medium having particularly excellent heat resistance was obtained.

In the present invention, a compound represented by the following general formula (1) is used as a color developer.

Embedded image (In the formula, R represents an alkyl group having 1 to 10 carbon atoms or a benzyl group which may have a substituent.) Examples of the compound represented by the general formula (1) include 4-hydroxy -4'-methoxydiphenylsulfone, 4-hydroxy-4'-ethoxydiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 4-hydroxy-4'-n-propoxydiphenylsulfone, 4-hydroxy-4 ' -N-butoxydiphenyl sulfone, 4-hydroxy-4'-n-pentyloxydiphenyl sulfone, 4-hydroxy-4 '
-N-hexyldiphenylsulfone, 4-hydroxy-
4'-n-heptyloxydiphenyl sulfone, 4-hydroxy-4'-n-octyloxydiphenyl sulfone, 4-hydroxy-4'-n-nonyloxydiphenyl sulfone, 4-hydroxy-4'-n-decyloxydiphenyl Sulfone, 4-hydroxy-4'-benzyloxydiphenylsulfone, 4-hydroxy-4'-
(4-methylbenzyloxy) diphenyl sulfone, 4
-Hydroxy-4 '-(4-methoxybenzyloxy)
Diphenylsulfone, 4-hydroxy-4 '-(4-chlorobenzyloxy) diphenylsulfone, 4-hydroxy-4'-(2,6-dimethylbenzyloxy) diphenylsulfone, and the like, but are not limited thereto. is not. Among them, 4-hydroxy-4'-isopropoxydiphenyl sulfone, by being combined with the leuco dye, not only has excellent color vividness and color density, but also improves the stability of recorded images and has less background fog. The features are remarkably exhibited and are particularly preferable.

In the present invention, when a mixture of 3-cyclohexylamino-6-chlorofluorane and 3-dibutylamino-6-methyl-7-bromofluorane is used as a leuco dye as described above, As the color developer, the compound represented by the general formula (1) as described above is preferably used, and various organic acidic substances conventionally used as a color developer for leuco dyes can also be used.
For example, α-naphthol, β-naphthol, 4-t-butylphenol, 4-t-octylphenol, 4-phenylphenol, 2.2-bis (p-hydroxyphenyl) propane, 2.2-bis (p-hydroxyphenyl) 1.) butane, 4.4'-cyclohexylidenediphenol, 2.2-bis (2.5-dibromo-4-hydroxyphenyl) propane, 4.4'-isopropylidenebis (2-t-butylphenol), 2'-methylenebis (4-chlorophenol), 4.4'-sulfonyldiphenol, 4.4'-dihydroxydiphenylsulfone, 4.4'-thiobisphenol, benzoic acid, salicylic acid, gallic acid, and derivatives thereof No.
The ratio between the leuco dye and the developer used in the heat-sensitive recording layer is generally 0.5 to 1 part by weight of the leuco dye.
5 parts by weight, preferably 1 to 3 parts by weight.

In the heat-sensitive recording layer of the present invention, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, starch and derivatives thereof, casein, gelatin, alginic acid are used for binding the above-mentioned materials on a support. Soda, polyvinylpyrrolidone, polyacrylamide,
Water-soluble resins such as modified polyacrylamide, alkaline aqueous solution of isobutylene maleic anhydride resin, alkaline aqueous solution of diisobutylene maleic anhydride resin, alkaline aqueous solution of styrene maleic anhydride resin, aqueous polyester, aqueous polyurethane, styrene butadiene copolymer emulsion, Water-dispersible resins such as acrylate copolymers, styrene (meth) acrylate copolymers, polyvinyl acetate, polyvinylidene chloride and derivatives thereof are used alone or in combination.

In the present invention, various heat-fusible substances can be added as needed to improve the recording sensitivity. Examples of the heat-fusible substance include an organic compound having an appropriate melting point, for example, higher fatty acid amides such as stearamide, N-methylol stearamide, and the like.
Higher fatty acids, higher fatty acid esters, aromatic carboxylic acid esters such as dimethyl terephthalate and diphenyl phthalate, dibenzoyl oxalate, di (oxalate)
Diarylalkyl esters of aliphatic dibasic acids such as -methylbenzyl) ester, naphthalene derivatives such as β-naphthoic acid phenyl ether, β-naphthoic acid phenyl ester and 1-hydroxy-2-naphthoic acid phenyl ester, p-benzyl Biphenyl derivatives such as biphenyl, terphenyl derivatives and the like are used.

In the heat-sensitive recording layer of the present invention, inorganic and organic pigments as fillers such as heavy and light calcium carbonate, aluminum hydroxide, titanium oxide, zinc oxide, silica, barium sulfate, talc, clay, Addition of satin white, kaolinite, polyolefin particles, polystyrene particles, urea-formalin resin particles, etc. can improve the sharpness of a color image.

Further, in the heat-sensitive recording layer, waxes such as polyethylene wax, paraffin wax, microcrystalline wax, carnauba wax, montan wax, and sticking with a heat-sensitive head are provided. , Metal soaps,
For example, zinc stearate, calcium stearate, aluminum stearate and the like can be added. If necessary, conventional fluorescent dyes, ultraviolet absorbers, antioxidants and the like can be added.

In the thermosensitive recording medium of the present invention, providing a protective layer on the thermosensitive coloring layer is an effective means for further improving the storage stability. The protective layer provided on the heat-sensitive recording layer in the present invention is mainly provided with a water-soluble resin and a filler having good film-forming properties, and further, a water-proofing agent, a metal soap, a wax and the like are added as necessary. You. As the aqueous resin of the protective layer, a water-soluble resin or a water-dispersible resin can be used, for example, polyvinyl alcohol, modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch and its derivatives, casein, sodium alginate, polyvinyl pyrrolidone, poly Water-soluble resins such as acrylamide, modified polyacrylamide, aqueous polyester, aqueous polyurethane, (meth) acrylate copolymer, styrene- (meth) acrylate copolymer, polyvinyl acetate, polyvinylidene chloride and the like Water-dispersible resins such as derivatives can be used.

As the filler used in the protective layer, inorganic and organic pigments are used. For example, heavy and light calcium carbonate, aluminum hydroxide, titanium oxide, zinc oxide, silica, barium sulfate, talc, clay, satin White, kaolinite, polyolefin particles, polystyrene particles, urea-formalin resin particles, and the like.
These fillers not only improve the matching property with the thermal recording head, but also improve the adhesiveness of the printing ink when printing on a thermal recording medium. As the ratio of the aqueous resin and the filler in the protective layer, the aqueous resin 10
The filler is preferably 10 to 150 parts with respect to 0 part, and 15 to 15 parts.
When the filler is used in an amount of 0 part or more, the filler obscures the color-developed state of the heat-sensitive recording layer, and the color density becomes low. Conversely, when the amount is 10 parts or less, the effect of adding the filler does not appear.

Glyoxal, chromium ban, melamine resin, melamine formaldehyde resin, polyamide resin, polyamide-epichlorohydrin resin, zirconium compound and the like can be added as a water-resistant agent for the protective layer. Further, if necessary, metal soap, wax, or the like can be added for improving the matching property with the heat-sensitive recording head and preventing pressure coloring. Further, in the heat-sensitive recording medium of the present invention, an underlayer mainly composed of a filler and a binder can be provided between the support and the heat-sensitive recording layer, if necessary, to improve a recorded image.

Next, a method for manufacturing a typical thermosensitive recording layer of the present invention will be described. The leuco dye, the developer, and the heat-fusible substance to be added as necessary are pulverized in a water-soluble polymer aqueous solution such as polyvinyl alcohol by a media-type wet disperser to prepare a dispersion. The particle size of the dispersion is 5 μm or less, preferably 2 μm or less. These dispersions are mixed with a binder after dispersion, and if necessary, inorganic or organic pigments, surfactants, metal soaps, waxes,
An antioxidant, an ultraviolet absorber and the like are added to form a coating for the heat-sensitive recording layer. Above, the heat-sensitive recording layer coating is a support, for example, paper, synthetic paper, resin film, or a composite thereof, air knife coating, roll coating,
A heat-sensitive recording layer is formed by coating using a known coating method such as bar coating or blade coating and drying. In addition, if necessary, the thermal recording medium of the present invention can be obtained by performing a smoothing process by a calendering process or the like.

The coating amount of the heat-sensitive recording layer formed as described above is 1 to 15 g / m ² , preferably 2 to 1 g / m ² .
The range is 0 g / m ² . Further, the protective layer can be formed by a known coating method similarly to the heat-sensitive recording layer. The coating amount of the protective layer is about 1 to 15 g / m ² ,
Preferably it is about ² to 6 g / m ² . Incidentally, if the coating amount is too large, heat transfer to the heat-sensitive recording layer will be poor and the recording sensitivity will be reduced.
The function as a protective layer may not be sufficiently exhibited.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments. All parts in the examples are parts by weight. Example 1 In order to prepare a paint for a heat-sensitive recording layer, the following composition [A-
1] Liquid, [A-2] liquid and [B] liquid are subjected to dispersion treatment using a sand grinder as a dispersing machine, and dispersion liquid [A-
1], [A-2] and [B] were adjusted. [A-1] solution ・ 30 parts of 3-cyclohexylamino-6-chlorofluoran ・ 30 parts of 10% aqueous polyvinyl alcohol solution (manufactured by Kuraray Co., PVA203) ・ 40 parts of water [A-2] solution ・ 3-dibutylamino- 6-methyl-7-bromofluorane 30 parts ・ 10% aqueous polyvinyl alcohol solution (Kuraray Co., PVA203) 30 parts ・ Water 40 parts [B] solution ・ 4-hydroxy-4′-isopropoxydiphenyl sulfone 30 parts ・ Light Calcium carbonate 30 parts ・ 10% polyvinyl alcohol aqueous solution (Kuraray Co., PVA203) 40 parts ・ Water 100 parts

[A-1] solution 30 obtained as described above
Parts, [A-2] solution 20 parts and [B] solution 200 parts with 10% polyvinyl alcohol aqueous solution (Kuraray Co., Ltd., PVA11
7) was added and mixed with stirring to prepare a coating for a heat-sensitive recording layer, coated and dried on a support made of a high-quality paper of 60 g / m ² , and dried at a coating amount of 8 g / m ^2. Was formed. Next, a coating material having the following composition was prepared as a coating material for the protective layer, and was applied on the heat-sensitive recording layer so as to have a dry weight of 4 g / m ² , thereby producing a heat-sensitive recording material of the present invention.・ 100 parts of 10% polyvinyl alcohol aqueous solution (Kuraray Co., Ltd., PVA117) ・ 20 parts of 40% kaolin clay aqueous dispersion ・ 5 parts of 30% aqueous dispersion of zinc stearate ・ 15 parts of water

Example 2 30 parts of [A-1] solution and [A-
2] 20 parts of the liquid were mixed with 40 parts of the [A-1] liquid and the [A-2] liquid 1
A heat-sensitive recording material of Example 2 was produced in the same manner as in Example 1, except that 0 part was used. Example 3 30 parts of [A-1] solution and [A-
2] 20 parts of the liquid were mixed with 18 parts of the liquid [A-1] and the liquid 3
A heat-sensitive recording material of Example 3 was produced in the same manner as in Example 1 except that 2 parts were used.

Example 4 As the coating material for the heat-sensitive recording layer, 4-hydroxy-
A heat-sensitive recording material of Example 4 was prepared in the same manner as in Example 1, except that 4'-isopropoxydiphenylsulfone was replaced with 4-hydroxy-4'-benzyloxydiphenylsulfone.

Comparative Example 1 30 parts of [A-1] solution and [A-
2] A thermosensitive recording medium of Comparative Example 1 was prepared in the same manner as in Example 1 except that 20 parts of the liquid was changed to 50 parts of the liquid [A-1]. Comparative Example 2 30 parts of [A-1] solution and [A-
2] A thermosensitive recording medium of Comparative Example 2 was produced in the same manner as in Example 1 except that 20 parts of the liquid was changed to 50 parts of the liquid [A-2]. Comparative Example 3 4-Hydroxy-B of the liquid [B] as a coating for the heat-sensitive recording layer
A thermosensitive recording medium of Comparative Example 3 was produced in the same manner as in Example 5, except that 4'-isopropoxydiphenyl sulfone was replaced with 2.2-bis (4-hydroxyphenyl) propane.

Examples 1 to 5 and Comparative Example 1 obtained above
The thermal recording materials of Nos. 1 to 3 were applied to a thermal printing device manufactured by Matsushita Electronic Components Co., Ltd. with an applied power of 0.5 W / dot and a pulse width of 1.5.
Recording was performed at msec, and an image sample was prepared. With respect to the obtained image sample, the density of the image portion and the density of the background portion of the sample are measured with a Macbeth reflection densitometer (initial value).
Thereafter, the image area preservation characteristics and the background preservation characteristics were evaluated based on the density of the image area and the density of the background area after the test was performed by the test method described below.

1. Light fastness test The image sample was irradiated with a fluorescent lamp as a light source at 5000 Lux for 100 hours, and the density of the image portion and the background portion after the irradiation was evaluated. 2. Moisture resistance test The image sample was allowed to stand in a constant temperature room at 40 ° C. and 90% RH for one week, and the density of the image portion and the background after the standing was evaluated. 3. Water resistance test The image sample was immersed in tap water at 20 ° C. for 24 hours,
The density of the image area and the background area after drying at room temperature was evaluated. 4. Oil Resistance Test Castor oil was applied to the surface of the image sample in a 40 ° C. environment and allowed to stand for 24 hours, and the density of the image portion and the background portion after the standing was evaluated.

[0026]

[Table 1] From the evaluation results shown in Table 1, the thermosensitive recording medium of the present invention is excellent not only in that a recorded image with a vermilion color tone with a vivid color tone can be obtained, but also that there is little discoloration of the image upon storage and little discoloration of the background. Storage stability.

[0027]

The thermosensitive recording medium of the present invention can provide a brighter vermilion color image than ever before, and the color image has excellent storage stability. Are suitably used for applications in which is desired.

Claims (4)

(57) [Claims] 1. A thermosensitive recording medium comprising a support having thereon a thermosensitive recording layer mainly composed of a colorless or pale-colored leuco dye and a developer capable of causing the leuco dye to develop color when heated. Cyclohexylamino-6-chlorofluorane, 3-dibutylamino-6-methyl-7-bromofluorane , 3 -diethylamino-7-methylfluoran, 3-N-ethyl-N-isoamylamino-benzo [a] fluoran A mixture of at least two compounds selected from 2,2- (4-dodecyloxy-3-methoxystyryl) quinoline and a compound represented by the following general formula (1) as a color developer. Thermosensitive recording medium. Embedded image (In the formula, R represents an alkyl group having 1 to 10 carbon atoms or a benzyl group which may have a substituent.) 2. A thermosensitive recording medium comprising a support having thereon a thermosensitive recording layer mainly composed of a colorless or pale-colored leuco dye and a developer capable of causing the leuco dye to develop color when heated. -Cyclohexylamino-6-
Chlorofluorane and 3-dibutylamino-6-methyl-
A heat-sensitive recording material comprising a mixture of 7-bromofluorane and 7-bromofluorane. 3. The developer according to claim 1, wherein said developer is 4-hydroxy-4'-.
3. The thermosensitive recording medium according to claim 1, wherein isopropoxydiphenyl sulfone is used. 4. A thermosensitive recording medium according to claim 1, wherein a protective layer mainly comprising an aqueous resin and a filler is provided on said thermosensitive recording layer.