JPH08175028A - Thermal recording medium - Google Patents

Abstract

PURPOSE: To provide a red developing thermal recording medium good in recording aptitude such as color forming sensitivity or image density, high in background whiteness and having excellent environmental characteristics such as temp. and humidity resistance or light fastness especially required for ticket paper or a card. CONSTITUTION: In a thermal recording medium wherein a thermal recording layer based on a leuco dye and a coupler allowing the leuco dye to develop a color at the time of heating is provided on a support, a compd. represented by formula (R is a 1-8C lower alkyl group) is used as the leuco dye and the binder of the thermal recording layer contains a resin soluble in an aromatic hydrocarbon solvent as a main component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a red color thermosensitive recording medium which has not only excellent storage stability such as weather resistance, water resistance and chemical resistance but also good recording suitability and high background whiteness. In particular, the present invention relates to a thermal recording medium that can be applied to cards such as boarding tickets, commuter tickets, pass tickets, and prepaid cards.

[0002]

2. Description of the Related Art The heat-sensitive recording system is widely used in facsimiles and printers because it has the advantages that it can be made compact and lightweight, can record without noise, and that consumables such as developer and transfer paper are unnecessary. Not only is it used for output, etc., but it has also been actively applied in recent years to ticket papers, commuter tickets, pass tickets, and other cards, prepaid cards, and labels such as POS labels. . In particular, in the case of ticket papers and cards, there are many examples of combination with a magnetic recording system.
The recording medium used in the heat-sensitive recording system is Japanese Patent Publication No.
As described in Japanese Unexamined Patent Publication No. 14035, a so-called "NCR type" is widely used in which a colorless or light-colored leuco dye and a color developer, which is an acidic substance, are used as color-forming components. Such recording media include, for example, triarylmethanephthalides such as crystal violet lactone, fluoranes, fluorenephthalides,
Leuco dyes such as divinyl phthalides, phenothiazines, auramines, spiropyrans, rhodamine lactams, and phenols such as bisphenol A, thiobisphenols, naphthols, benzoic acid,
A thermosensitive recording layer obtained by dispersing a developer made of an acidic substance such as salicylic acid or gallic acid in an aqueous binder such as polyvinyl alcohol is provided on the substrate. This type of heat-sensitive recording medium has excellent features such as clear recording, high heat sensitivity, and white background.

However, this type of thermal recording medium is
In addition to problems such as decolorization of recorded areas and coloring of unrecorded areas due to contact with plasticizers such as DOP contained in vinyl chloride film and chemicals such as alcohols, basically paint is applied and dried using water as a medium. Since it is manufactured by the above method, there is a problem in water resistance that the thermosensitive recording layer is softened or eluted when it comes into contact with water and is lost. Especially when this type of thermal recording material is used for tickets and commuter tickets, etc., it is not only suitable for recording, but also strict quality characteristics, that is, temperature and humidity resistance, light resistance and other environmental conditions. Chemical resistance such as stability, plasticizer resistance, oil resistance, acid resistance, alkali resistance, sweat resistance, and water resistance are strongly required. Also, in the case of ticket papers and cards that are combined with a magnetic recording system, it is necessary to pass a ticket gate with a built-in magnetic head at a high speed in automatic ticket gates, etc.
Physical strength such as high wear resistance and strong adhesiveness to the coated surface is also required.

In order to solve these characteristics under such strict requirements, for example, in Japanese Patent Publication No. 3-26154, an aromatic hydrocarbon is used in order to form a heat-sensitive recording layer using an aromatic hydrocarbon solvent as a medium. Thermal recording using fluorane-based leuco dye and developer that are practically insoluble in solvent and polymethylmethacrylate resin, polyethylmethacrylate resin, and polybutylmethacrylate resin soluble in aromatic hydrocarbon solvent as binder Ink compositions for media have been proposed. However, such a conventional technique has been mainly studied mainly for a color-developing system that develops a black color, and as the application and development of the thermal recording medium progresses as described above, a color tone other than black is developed. Although the demand for a thermosensitive recording medium that develops red color is materialized, the thermosensitive recording medium of red color is excellent in environmental stability such as temperature and humidity resistance and light resistance, and is excellent in recording suitability and background whiteness. Has not been obtained yet.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is an excellent red color thermosensitive recording medium having good recording suitability such as color developing sensitivity and image density and high background whiteness. In particular, it is an object of the present invention to provide a red color thermosensitive recording medium having excellent environmental characteristics such as temperature and humidity resistance and light resistance which are particularly required for ticket papers and cards.

[0006]

DISCLOSURE OF THE INVENTION As a result of intensive investigations by the present inventors, a heat-sensitive recording medium provided with a heat-sensitive recording layer containing a leuco dye and a color developer which develops the color of the leuco dye under heat on a substrate as a main component. In the above, as the leuco dye, the following general formula (1)
It was found that the above object can be achieved by using the compound represented by the formula (1) and containing as a main component a resin soluble in an aromatic hydrocarbon solvent as a binder for the heat-sensitive recording layer, and completed the present invention.

Embedded image

The red-colored leuco dye, which is a compound represented by the above-mentioned general formula (1) in the present invention, was developed as a pressure-sensitive recording paper, but since it has high acid sensitivity, it is used as a heat-sensitive recording medium. When it is used, it causes a very strong background fog, which is not practically used at all. In the present invention, among a large number of red-colored leuco dyes, the compound represented by the general formula (1) is used as a binder by using a resin soluble in an aromatic hydrocarbon solvent without causing background fogging. It has been found that good background whiteness is achieved and that the recording medium has excellent recording characteristics.

Specific examples of the leuco dye represented by the above general formula (1) include bis (1-methyl-2-methylindol-3-yl) phthalide and bis (1-ethyl-).
2-methylindol-3-yl) phthalide, bis (1
-N-propyl-2-methylindol-3-yl) phthalide, bis (1-n-butyl-2-methylindol-3-yl) phthalide, bis (1-n-hexyl-2-)
Methylindol-3-yl) phthalide, bis (1-n
-Pentyl-2-methylindol-3-yl) phthalide, bis (1-n-hexyl-2-methylindole-
3-yl) phthalide, bis (1-n-heptyl-2-methylindol-3-yl) phthalide, bis (1-n-
Octyl-2-methylindol-3-yl) phthalide. Among them, it is difficult to dissolve in an aromatic hydrocarbon solvent, does not cause background fog, has a high color density, and is excellent in heat resistance and has good image stability.
Bis (1-ethyl-2-methylindol-3-yl)
Phthalide (melting point 228 ° C.) is preferred.

The red-coloring leuco dye used in the present invention is a compound of the general formula (1), but it should be used in combination with other red-coloring leuco dyes for the purpose of toning and the like within a range not deteriorating various properties. Is possible. Other red coloring dyes that can be used in combination include 3-cyclohexylamino-6-chlorofluorane, 3-dibutylamino-6-methyl-7-bromofluorane, 3-diethylamino-6,8-dimethylfluorane, 3-diethylamino-benzo [a] fluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-
Examples thereof include N-ethyl-N-isoamylamino-benzo [a] fluorane and 3-N-ethyl-N-p-methylphenylamino-7-methylfluorane. The combined use of these leuco dyes is 50% by weight or less, particularly preferably 20% by weight or less, based on the leuco dye of the general formula (1).

Examples of the color developer in the present invention include α
-Phenol compounds such as naphthol, β-naphthol, 4-t-butylphenol, 4-t-octylphenol, 4-phenylphenol, 4-acetylphenol, hydroquinone, 2,2-bis (4-hydroxyphenyl) propane, 2, 2-bis (4-hydroxyphenyl) butane, 1,1-bis (4-hydroxyphenyl)
Cyclohexane, 2,2-bis (2,5-dibromo-4)
-Hydroxyphenyl) propane, 2,2-bis (4-
Bisphenol compounds such as hydroxyphenyl) -4-methylpentane, 4,4′-dihydroxydiphenyl sulfide, 4,4′-thiobis (3-methyl-6-t-
Butylphenol) and other hydroxydiphenyl sulfide compounds, 4,4′-dihydroxydiphenyl sulfone, 2,4′-dihydroxydiphenyl sulfone, 4-
Hydroxy-4′-methyldiphenyl sulfone, 4-hydroxy-4′-methoxydiphenyl sulfone, 4-hydroxy-4′-isopropoxydiphenyl sulfone,
4-hydroxy-4′-benzyloxydiphenyl sulfone, 3,4-dihydroxy-4′-methyldiphenyl sulfone, hydroxydiphenyl sulfone compounds such as bis (3-allyl-4-hydroxydiphenyl) sulfone, 4,4′-dihydroxy Benzophenone, 4,4 '
-Hydroxybenzophenone such as dihydroxythiobenzophenone and 2,4'-dihydroxybenzophenone,
Hydroxythiobenzophenone compound, bis (4-hydroxyphenyl) acetic acid, 2,2-bis (4-hydroxyphenyl) ethanoic acid, 2,2-bis (4-hydroxyphenyl) propionic acid, 4,4-bis (4- Diphenyl acid compounds such as hydroxyphenyl) pentanoic acid, and their alkyl, aryl, aralkyl ester derivatives,
4-hydroxybenzoic acid, salicylic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2,
Aromatic hydroxycarboxylic acid compounds such as 6-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid and gallic acid, and alkyls thereof.
Examples thereof include aryl, aralkyl ester, and polyvalent metal salts thereof.

Among the above-mentioned color developers, in the present invention, it is difficult to dissolve in an aromatic hydrocarbon solvent, background fog does not occur, and a high color density can be obtained by reacting with a leuco dye when heated. From 4,4'-dihydroxydiphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 3,4-dihydroxy-4'-methyldiphenyl sulfone, bis (3-allyl-4-hydroxydiphenyl) sulfone, 4,4 ' -Dihydroxybenzophenone, bis (4-hydroxyphenyl) acetic acid, bis (4-
Hydroxyphenyl) acetic acid methyl ester, bis (4-
Hydroxyphenyl) acetic acid benzyl ester, gallic acid, and gallic acid methyl ester can be preferably used.

As the binder for the heat-sensitive recording layer used in the present invention, a resin soluble in an aromatic hydrocarbon solvent is used. The aromatic hydrocarbon solvent as used herein is specifically a hydrocarbon containing an aromatic compound such as benzene, toluene, xylene, etc. as a base, and a hydrocarbon containing a benzene ring. Examples of such a binder soluble in an aromatic hydrocarbon solvent include styrenes such as styrene, methylstyrene, ethylstyrene, n-butylstyrene, chlorostyrene, methyl acrylate, ethyl acrylate, and acrylic acid. n-Butyl, 2-ethylhexyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, acrylic acid esters such as phenyl methacrylate, acrylonitrile Examples thereof include homopolymers and copolymers containing acrylic acid derivatives such as methacrylnitrile and acrylamide as monomer components. In the present invention, by using such a hydrophobic resin as a binder, the leuco dye represented by the general formula (1) as described above causes an unnecessary reaction with the color developer during production or storage. It is possible to obtain a good background whiteness.

In the present invention, among the above binders,
Acrylic copolymer crosslinkable with an isocyanate-based or aziridine-based curing agent is preferable because it can achieve particularly excellent thermosensitive color development characteristics, temperature and humidity resistance and light resistance when used in combination with the leuco dye. When the thermosensitive recording layer is blended with a curing agent as described below, a crosslinked structure is formed and excellent water resistance, chemical resistance and the like are obtained. Further, the coating strength of the heat-sensitive recording layer and the adhesive strength of the protective layer described later are improved, and excellent physical strength is obtained. Such an acrylic copolymer is a copolymer containing at least the acrylic monomer as described above and an acrylic monomer having a functional group such as a carboxyl group, a hydroxyl group, an amino group, or the like as a copolymerization component. Examples of the acrylic monomer having such a specific functional group include organic acids such as acrylic acid, methacrylic acid, itaconic acid, and maleic acid,
(Meth) acrylic acid hydroxyalkyl esters such as hydroxyethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 2-hydroxybutyl (meth) acrylate; (Meth) acrylic acid aminoalkyl esters such as aminoethyl (meth) acrylate, 2-aminoethyl (meth) acrylate, 2-aminopropyl (meth) acrylate, and 2-aminobutyl (meth) acrylate, acrylic acid Examples thereof include amides, but are not limited to these. Among the above acrylic copolymers, acrylic copolymers having at least either an acid value of 10 or more or an OH value of 20 or more in terms of solid content are preferable. Further, considering the strength and adhesiveness of the coating film, it is preferable that the glass transition temperature is at least 50 ° C. or higher.

In the present invention, it is preferable to use an isocyanate type or aziridine type curing agent in order to cross-link the acrylic copolymer having the above functional group. As an isocyanate-based curing agent, at least 2 in the molecule
Those having three or more isocyanate groups are appropriately used, and examples thereof include tolylene diisocyanate, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, xylene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and modified products thereof. . Specifically, a coronate-based curing agent (Nippon Polyurethane Co., Ltd.) or a desmodur-based curing agent (Bayer Co.) can be used.
Examples of the aziridine-based curing agent include trimethylolpropane-tri-β-aziridinylpropionate,
Tetramethylolmethane-tri-β-aziridinylpropionate, N, N′-diphenylmethane-4,4-bis (1-aziridinecarboxamide), N, N′-hexamethylene-1,6-bis (1 -Aziridinecarboxamide) and the like.

The heat-sensitive recording medium of the present invention is prepared by dissolving the binder in the aromatic hydrocarbon solvent as described above, and using the solution as a dispersion medium, the leuco dye and the color developer, a ball mill, an aty lighter and a sand mill. The leuco dye and the color developer are each pulverized using a dispersing machine such as the above to prepare a dispersion liquid, and the heat-sensitive recording layer coating material prepared by mixing is applied and dried on a substrate. The coating amount of the thermal recording layer is
It is 0.5 to 10 g / m ² , preferably 1.5 to 6 g / m ² . The mixing ratio of leuco dye and developer is 10: 1.
To 1:10, preferably 1: 1 to 1: 3, and the proportion of the binder in the entire heat-sensitive recording layer is 5 to 95 in terms of solid content.
%, Preferably 15 to 50%.

If desired, various additives can be added to the heat-sensitive recording layer of the present invention. Examples of the additive include inorganic pigments such as aluminum hydroxide, calcium carbonate, silica, talc, and titanium oxide, organic pigments such as polyolefin resin fine particles, polystyrene fine particles, urea formalin resin fine particles, metal salts of higher fatty acids, waxes, and fluorocarbons. Examples thereof include lubricants and ultraviolet absorbers.
Further, various sensitizers can be added as long as the heat resistance is not impaired. Examples of the substrate used in the present invention include paper, polyethylene terephthalate film and other plastic films, coated paper, art paper, laminated paper, synthetic paper, etc. Films and synthetic papers are suitable.

In the present invention, it is preferable to provide a protective layer containing an ultraviolet ray or electron beam curable resin as a main component on the thermosensitive recording layer. This protective layer exhibits strong abrasion resistance, improves head matching with the thermal recording head, and also functions as a barrier layer against invasion of chemicals from the outside. If necessary, an intermediate layer may be provided between the heat sensitive recording layer and the protective layer. As the ultraviolet or electron beam curable resin used in the protective layer of the present invention, for example, a resin capable of radical polymerization such as a vinyl group-containing monomer or oligomer is used. Especially, many kinds such as oligo acrylate, urethane acrylate, and silicone acrylate can be applied. When curing with UV light, benzoyl alkyl ether,
It is necessary to include a photopolymerization initiator such as benzophenone or benzyl Michler's ketone. Further, an epoxy compound which undergoes ring-opening polymerization by a cationic reaction with a Lewis acid catalyst can also be used as an ultraviolet curable resin, and in this case, it is necessary to use an aromatic halonium salt of Lewis acid, an aromatic sulfonium salt of Lewis acid or the like as a photoinitiator. Is.

Since the protective layer is in direct contact with the thermal head,
When printing, it may be exposed to high temperatures of 300 ° C or higher.
A pigment, a higher fatty acid or a metal salt thereof, a heat-fusible lubricant, a lubricant and the like are added for the purpose of improving matching with the thermal head. As the pigment, for example, inorganic or organic pigments such as aluminum hydroxide, silica, talc and urea-formaldehyde resin are used. As the heat-fusible lubricant, polyethylene wax, paraffin wax, fluorocarbon or the like is used. Liquid lubricants such as paraffin and silicone oil, and solid lubricants such as reactive silicone resin are used as the lubricant. The protective layer may be formed by either a conventional coating method or printing method, and the protective layer has a thickness of 0.1 to 5 μm, preferably 0.5 to 3 μm.

[0019]

EXAMPLES The present invention will be described in detail below with reference to examples. All parts in the examples represent parts by weight. Example 1 A heat-sensitive recording layer coating having the composition shown below was applied on a substrate made of a milky white polyethylene terephthalate film having a thickness of 188 μm and dried at 70 ° C. to form a heat-sensitive recording layer. The dry coating amount was 5 g / m 2. [Preparation of coating material for heat-sensitive recording layer] [A] and [B] having the following composition
The average particle size of the liquid is 1.5 μm using a sand grinder.
Dispersion was carried out so as to obtain a dispersion liquid. Using the resulting dispersion, 100 parts of [A] liquid, 300 parts of [B] liquid, and 3 parts of an isocyanate-based curing agent (solid content 75% by weight, Coronate L manufactured by Nippon Polyurethane Co., Ltd.) as a curing agent were mixed to obtain heat sensitivity. A coating material for the recording layer was prepared. Liquid [A] -Bis (1-ethyl-2-methylindol-3-yl) phthalide 100 parts-Styrene / methyl methacrylate / hydroxyethyl acrylate copolymer resin toluene solution (solid content 20% by weight, OH value 65) ) 150 parts [B] liquid-Bis (4-hydroxyphenyl) acetic acid methyl ester 100 parts-Styrene / methyl methacrylate / hydroxyethyl acrylate copolymer resin toluene solution (solid content 20% by weight, OH value 65) 150 parts

Next, a mixture having the following composition was prepared as a protective layer on the heat-sensitive recording layer, printing was performed on the heat-sensitive recording layer by an offset method, and ultraviolet curing was performed to form a 1-μm protective layer. A heat-sensitive recording medium of the invention was obtained. -Polyester acrylate (manufactured by San Nopco, Photomer 5018) 100 parts-1- (4'-dodecylphenyl) -2-hydroxy-2-methylpropan-1-one 1 part-Polyethylene wax 5 parts-Reactive silicone resin (polyester Modified silicone resin) 2 parts-Aluminum hydroxide 5 parts

Example 2 Bis (1-ethyl-2-methylindol-3-yl) phthalide of the liquid [B] of Example 1 was replaced with bis (1-n-butyl-2-methylindol-3-yl) phthalide. A thermosensitive recording medium of the present invention was prepared in the same manner as in Example 1 except that Comparative Examples 1 to 6 Comparative Example 1 was repeated except that the bis (1-ethyl-2-methylindol-3-yl) phthalide of the liquid [B] of Example 1 was replaced with the leuco dye shown below. Examples 1-6
A heat-sensitive recording medium of was prepared. Comparative Example 1: 3-diethylamino-benzo [a] fluorane 2: 3-diethylamino-7-chlorofluorane 3: 3-diethylamino-6-methyl-7-chlorofluorane 4: 3-diethylamino-6,8-dimethyl Fluoran 5: 3-N-ethyl-N-isoamylamino-benzo [a] fluorane 6: 3-N-ethyl-Np-methylphenylamino-
7-methylfluorane

Comparative Example 7 The toluene solution of styrene / methyl methacrylate / hydroxyethyl acrylate copolymer resin used in the solutions [A] and [B] of Example 1 was replaced with a 20% polyvinyl alcohol aqueous solution, [A] using the obtained dispersion
A thermosensitive recording medium for comparison was prepared in the same manner as in Example 1 except that 100 parts of the liquid and 300 parts of the [B] liquid were mixed to prepare the coating material for the thermosensitive recording layer.

The following characteristics of the thermal recording media of Examples 1 and 2 and Comparative Examples 1 to 7 were evaluated. (1) Background density The background density of the obtained thermal recording medium was measured using a Macbeth reflection densitometer RD-914 to evaluate the background fog. (2) Color development characteristics A line type thin film thermal head was used to record at a printing energy of 1.0 mj / dot, and the recorded portion was measured for density using a Macbeth reflection densitometer to evaluate the color development characteristics. (3) Resistance to temperature and humidity The recorded thermal recording medium is placed in an environment of 55 ° C and 90% RH for 24 hours.
After left for a while, the recorded portion and the background portion were measured using a Macbeth reflection densitometer to evaluate the temperature and humidity resistance.

(4) Light resistance A thermal recording medium was exposed to light for 4 hours using a fade meter (FAL-AU manufactured by Suga Test Instruments Co., Ltd.) using an ultraviolet carbon arc as a light source, and the recorded portion and the background portion were Macbeth-reflected. It measured using the densitometer and evaluated the light resistance. (5) Water resistance The obtained thermosensitive recording medium was immersed in water for 24 hours, and the surface on the thermosensitive recording layer side was rubbed with a finger to evaluate whether or not the coated surface was missing.
The case where there was no problem was marked as ○, and the case where the lack was recognized was marked as ×. Table 1 shows the evaluation results.

[0025]

[Table 1]

As is clear from the results shown in Table 1, the heat-sensitive recording medium of the present invention has a high red color density and excellent recording characteristics, has little background fog, and has resistance to temperature and humidity, light resistance, and light resistance.
It was confirmed to have excellent water resistance. On the other hand, the thermal recording media of Comparative Examples were inferior in temperature and humidity resistance and light resistance, and the thermal recording medium of Comparative Example 7 was also inferior in water resistance, and it was confirmed that there was a problem in practical use.

[0027]

INDUSTRIAL APPLICABILITY As described above, the thermal recording medium of the present invention not only exhibits good red color-developing characteristics, but also has less background fog and is environmentally stable including temperature and humidity resistance and light resistance. It is excellent and can be sufficiently applied to applications such as passenger tickets, commuter tickets, pass tickets and prepaid cards.

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Claims (4)

[Claims] 1. A heat-sensitive recording medium comprising a substrate and a heat-sensitive recording layer containing a leuco dye and a color developing agent for coloring the leuco dye under heat as a main component, wherein the leuco dye is represented by the general formula (1). A heat-sensitive recording medium containing a compound soluble in an aromatic hydrocarbon solvent as a main component as a binder for the heat-sensitive recording layer. Embedded image 2. The leuco dye of the general formula (1) is bis (1
The thermosensitive recording medium according to claim 1, which is -ethyl-2-methylindol-3-yl) phthalide. 3. The thermal recording medium according to claim 1, wherein a protective layer containing an ultraviolet ray or electron beam curable resin as a main component is provided on the thermal recording layer. 4. A heat-sensitive recording layer containing an isocyanate or aziridine-based curing agent, and the resin of the heat-sensitive recording layer is an acrylic copolymer curable by the curing agent. Alternatively, the thermosensitive recording medium according to the item 3.