JPH04358880A - thermal recording medium - Google Patents

Abstract

PURPOSE:To provide the above thermal recording medium, which has higher light resistance and a manufacturing process of which can be simplified, regarding the thermal recording medium, particularly the thermal recording medium used as a pass, a prepaid card, etc. CONSTITUTION:A heat-sensitive color-developing layer 2 containing leuco dyes and a developer is formed onto one surface of a supporter 1, an intermediate layer 3 containing at least two kinds or more of ultraviolet absorbers having mutually different absorption bands while using a solvent resin employing a solvent having weak polarity as a binder is formed onto the heat-sensitive color-developing layer 2, and a protective layer 4 mainly comprising an ultraviolet curing resin is formed onto the intermediate layer 3, thus constituting a thermal recording medium.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a heat-sensitive recording medium,
In particular, it relates to thermal recording media used in commuter passes, prepaid cards, etc.

0002

[Prior Art] Heat-sensitive recording media having a heat-sensitive coloring layer containing a leuco dye and a color developer have been known, and are used in railway tickets, commuter passes, prepaid cards such as telephone cards, and various measuring instruments. Widely used for printer paper, etc. Conventional heat-sensitive recording media include a heat-sensitive coloring layer and a protective layer to prevent the heat-sensitive coloring layer from reducing density in the image area and discoloring the background area due to ultraviolet rays, etc. . However, conventional heat-sensitive recording media provided with a protective layer do not have sufficient light resistance, and higher light resistance has been required for heat-sensitive recording media, especially in applications where they are exposed to sunlight for a long time.

[0003] For this reason, a heat-sensitive recording medium having an intermediate layer containing an ultraviolet absorber between a heat-sensitive coloring layer and a protective layer has been proposed (Japanese Patent Application Laid-open No. 242878/1982). In such a heat-sensitive recording medium, an intermediate layer containing a water-soluble resin and a benzotriazole compound as an ultraviolet absorber is provided on the heat-sensitive coloring layer, and a protective layer using a water-soluble resin is further formed. Ta.

0004

[Problems to be Solved by the Invention] However, normal leuco dyes that produce dark colors such as black and do not have an absorption band in the infrared wavelength region have relatively high light resistance by themselves, but yellow, magenta, With color leuco dyes that produce colors such as cyan, and infrared-absorbing leuco dyes with absorption bands extending into the infrared wavelength region, sufficient light resistance cannot be obtained with conventional intermediate layers; Dyes have a problem in that the absorption band in the infrared absorption region disappears.

[0005] Furthermore, since the above-mentioned intermediate layer and protective layer use a water-soluble resin, there is a problem in that the coating and drying steps take time. On the other hand, leuco dyes tend to develop color with highly polar solvents, so there is a problem in that solvent-based resins cannot be used. Therefore, an object of the present invention is to provide a heat-sensitive recording medium that has higher light resistance and can simplify the manufacturing process.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a heat-sensitive recording medium comprising a support, a leuco dye and a color developer, and a heat-sensitive coloring medium provided on one side of the support. layer, an intermediate layer provided on the thermosensitive coloring layer and containing at least two or more types of ultraviolet absorbers having mutually different absorption bands using a solvent-based resin using a weakly polar solvent as a binder; and a protective layer mainly made of an ultraviolet curable resin.

[0007]

[Function] According to the present invention, since the intermediate layer contains two or more types of ultraviolet absorbers having different absorption bands, the ultraviolet rays received by the heat-sensitive recording medium are effectively absorbed by the intermediate layer, leading to deterioration of the heat-sensitive coloring layer. , discoloration, etc. are prevented. Furthermore, since the intermediate layer uses a solvent-based resin as a binder and the protective layer uses an ultraviolet curable resin, the time required for the coating and drying steps is extremely short. Furthermore, since the solvent-based resin used as the binder is a weakly polar solvent, the leuco dye does not develop color.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic cross-sectional view of a thermosensitive recording medium according to the present invention. The thermosensitive recording medium has a thermosensitive coloring layer 2 on a support 1 such as paper, synthetic paper, or plastic film, which contains a water-soluble normal leuco dye, a color leuco dye, an infrared absorbing leuco dye, etc.
is provided. An intermediate layer 3 containing a plurality of ultraviolet absorbers having different absorption bands is provided above the thermosensitive coloring layer 2 to improve the light resistance of the image area and the background area. Furthermore, a protective layer 4 made of an ultraviolet curing resin is provided on the intermediate layer 3 in order to protect the above-mentioned two layers and improve the smoothness of the surface of the photosensitive recording medium.

[0009] Hereinafter, the thermosensitive coloring layer 2, the intermediate layer 3, the protective layer 4
Each layer will be explained in more detail. The leuco dyes used in the thermosensitive coloring layer 2 of the above-mentioned thermosensitive recording medium include:
Very common ordinary leuco dyes, color leuco dyes, infrared absorbing leuco dyes, etc. are used.

Generally, as leuco dyes, triphenylmethane compounds, fluoran compounds, phenothiazine compounds, auramine compounds, spiropyran compounds, etc. are often used, and fluoran compounds are particularly used. More specifically, for example, 3-di-N-butylamino-7-o-chloroanilinofluorane, 3
-(N-methyl-N-cyclohexylamino)-6-
Examples include methyl-7-anilinofluorane and 1,2-benzo-6-diethylaminofluorane.

As the color leuco dye, triphenylmethane compounds, fluoran compounds, phenothiazine compounds, auramine compounds, spiropyran compounds, indosonophthalide compounds, etc. are used. More specifically, examples of compounds that develop a yellow color include 3,6-dimethoxyfluoran, 3-cyclohexylamino-6-chlorofluoran, and 3-(p-dimethylaminophenyl)-3-phenylphthalide. etc. In addition, examples of substances that develop magenta color include 3-diethylamino-7,8-benzfluoran, 3-diethylamino-6-methyl-7-chlorofluoran, and 3-di(1-ethyl-2methylindole). -3-yl-phthalide, 3-diethylamino-6
- Phenyl-7-azafluorane and the like. Furthermore, as a cyan coloring material, for example, 3,3
-bis(p-dimethylaminophenyl)phthalide, 3,
3-bis(p-dimethylaminophenyl)-6-dimethylamino-phthalide, 2-bis(p-dimethylaminophenyl)methyl-5-dimethylamino-benzoic acid, 3-(p-dimethylaminophenyl)-
Examples include 3-(p-dibenzylaminophenyl)phthalide. Furthermore, other color leuco dyes include rhodamine β-lactam, 3-diethylamino-5,7
- Dimethylfluoran, 3-diethylamino-7-methylfluoran, 3-dimethylamino-6-methoxyfluoran, 3,3-bis(p-dimethylaminophenyl)-6-chlorofluoran, 3,3-bis (p
-dimethylaminophenyl)-6-aminophthalide and the like.

Furthermore, examples of the infrared absorbing leuco dye include those represented by the following general formulas (I) and (II).

[0013]

[Chemical formula 1]

[0014]

embedded image In formula (I) and formula (II), R1, R2, R3
, R4, R5 and R6 are each a hydrogen atom,
Alkyl group having 1 to 18 carbon atoms, cycloalkyl group having 3 to 7 carbon atoms, lower alkoxy group, having 1 to 7 carbon atoms
18 represents a halogenated alkyl group, a phenyl group, an optionally substituted phenyl group, and a benzyl group. R7
, R8 and R9 each represent a hydrogen atom, a halogen atom, a lower alkyl group and a lower alkoxy group. Moreover, X represents a carbon atom, a nitrogen atom, and a sulfur atom. Further, R1 and R2 or R3 and R4 may form a heterocycle having 4 to 6 carbon atoms (which may contain an oxygen atom, a sulfur atom, or a second nitrogen atom) together with adjacent nitrogen atoms.

Among the fluorene leuco dyes represented by the general formulas (I) and (II), the following 5 are preferred.
These are compounds of the types (Formula (III) to Formula (VII)). However, R1, R2, R3, R4, R5
, R6, R7, R8 and R9 are as described above.

[0016]

[Chemical formula 3]

[0017]

[C4]

[0018]

[C5]

[0019]

[C6]

[0020]

[Image Omitted] Further, considering productivity, cost, and performance, the most preferable is 3,6, represented by the following structural formula (VIII),
6'-Tris(dimethylamino)spiro[fluorene-9,3'-phthalide] (mp.244-246°C
).

[0021]

embedded image embedded image Examples of the fluorene-based leuco dyes used in the present invention include, but are not limited to, the following. For example, leuco dyes represented by the following formulas (IX) to (XI) can be used.

[0022]

embedded image In the above formula (IX), J1 represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a nitro group, or an alicyclic amino group represented by the following formula (IXa).

[0023]

[Formula 10] However, Z represents an oxygen atom or a methylene group, and a, b
represents an integer of 1 to 3 satisfying a+b≧3. Also, J2
represents a hydrogen atom, a halogen atom, an alkoxy group, a nitro group, an amino group or a substituted amino group, J3 represents a hydrogen atom or an alkyl group, J4, J5, J6,
J7 represents a hydrogen atom, an alkyl group, an aralkyl group, a substituted aralkyl group, an allyl group, or a substituted allyl group, and J4
, J5 and J6, J7 may each form a heterocycle with an adjacent nitrogen atom. X and Y are hydrogen atoms,
Represents an alkyl group or an alkoxy group, m and n are 1 to 4
represents an integer.

[0024]

[Image Omitted] In the above formula (X), Q9 and Q10 are hydrogen atoms,
halogen atom, alkyl group, alkoxy group, nitro group,
Represents an amino group or a substituted amino group, Q1 , Q2 ,
Q3 , Q4 , Q5 , Q6 , Q7 , and Q8 each represent a hydrogen atom, an alkyl group, an aralkyl group, an alkoxy group, a substituted aralkyl group, an allyl group, or a substituted allyl group, and Q1 and Q2 , Q3 and Q4 , Q5 and Q
6 and Q7 and Q8 may each form a heterocycle with the adjacent nitrogen atom. X1, X2, Y1,
Y2 each represents a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, an alkylamino group, an amino group, or an acetylamino group, and m and n represent integers of 1 to 2.

[0025]

embedded image In the above formula (XI), T6 and T7 represent a hydrogen atom or a lower alkyl group, and T1, T2, T3 and T4 are each independently a hydrogen atom, a halogen atom, or a carbon atom which may have a side chain. Alkyl group having 1 to 8 atoms, lower alkoxy group, nitro group, amino group, substituted amino group,
Represents a cycloalkyl group or an optionally substituted allyl group, and benzene ring A is the 5th and 6th positions, the 6th and 7th positions, or the 7th position.
and the 8th position, the following formula (XIa) -CH=CH-CH=CH-...(X
Both ends of the group represented by Ia) may be bonded to form a naphthalene ring, and this naphthalene ring may have a halogen atom or a lower alkyl group as a substituent, Z represents a halogen atom, and l represents an integer from 0 to 4.

The color developer used in the heat-sensitive coloring layer 2 includes bisphenol A (BPA), benzyl p-hydroxybenzoate (POB), sulfur-containing phenol compounds, metal complex compounds, saccharin, thiodiphenylurea, Examples include quinones. Further, binders used in the thermosensitive coloring layer 2 include polyvinyl alcohol (PVA), modified PVA, starch, modified starch, methyl cellulose, hydroxyethyl cellulose, casein, alkylene maleic anhydride copolymer, polyvinyl pyrrolidone, and acrylamide water-soluble Examples include vinyl toluene butadiene resin, vinyl toluene acrylate resin, styrene acrylate resin, vinyl isobutyl ether resin, and aliphatic hydrocarbons.

Furthermore, other additives added to the heat-sensitive coloring layer 2 include sensitizers, anti-fading agents, pigments, lubricants, dispersants and the like. Note that the amounts of leuco dye, color developer, and binder contained in the thermosensitive coloring layer are 20% each.
-30% by weight, 20-30% by weight, and 40-60% by weight are suitable.

[0028] The thickness of such thermosensitive coloring layer 2 is 3 to 10
μm, preferably about 4 to 6 μm. The intermediate layer used in the heat-sensitive recording medium of the present invention contains a plurality of ultraviolet absorbers having different absorption bands. Examples of the ultraviolet absorber include benzotriazole compounds, benzophenone compounds, salicylate compounds, and the like.

More specifically, the following compounds can be mentioned as benzotriazole compounds. Chemical substance name
Absorption wavelength band: 2-(5-methyl-2-hydroxyphenyl) 270 to 370 nm
Benzotriazole 2-[2-hydroxy-3,5-bis(α,α
270-360nm
-dimethylbenzyl)phenyl] -2H-benzotriazole 2-(3-t-butyl-5-methyl-2-hydroxyphenyl) 270 to 380nm -5-
Chlorobenzotriazole
・2-(3,5-di-t-butyl-2-hydroxyphenyl) 270
~280 nm -5-chlorobenzotriazole, etc.

[0030] Examples of salicylate compounds include the following. Chemical substance name
Absorption wavelength band/pt-butylphenyl salicylate
290 ~ 330n
m ・2,4-di-t-butylphenyl-3',5'
- di-t-butyl-4'- hydroxybenzoate
240 to 280 nm, etc.

[0031] Examples of benzophenone compounds include the following. Chemical substance name
Absorption wavelength band/2,4-dihydroxybenzophenone
270 ~ 350n
m 2-hydroxy-4-methoxybenzophenone 270 to 350 nm, etc.

The above-mentioned ultraviolet absorber is contained in the intermediate layer in an amount of approximately 10 to 30 parts by weight based on 50 parts by weight of the binder. If the content is less than 10 parts by weight, the large energy of ultraviolet rays cannot be absorbed and the dissociative decomposition reaction cannot be inhibited, resulting in a problem of deterioration of light resistance. In addition, if the content is more than 30 parts by weight, the ink will contain too much pigment, resulting in a matte state, resulting in unevenness, deteriorating surface properties, deteriorating head suitability, and causing problems such as poor thermal recording sensitivity. .

In addition to ultraviolet absorbers such as benzotriazole, this intermediate layer also contains generated radicals (Ra
A UV stabilizer as an antioxidant having the property of scavenging dical) may also be included. Examples of such UV stabilizers include hindered amine compounds.

More specifically, the hindered amine compounds include the following. Dimethyl succinate-1-(2-hydroxyethyl)-
4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, poly[{6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4 -diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,
2,6,6-tetramethyl-4-piperidyl)imino], 2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-butylmalonic acid bis(1,
2,2,6,6-pentamethyl-4-piperidyl) and the like.

When using the above UV stabilizer,
The intermediate layer contains approximately 10 to 30 parts by weight of the above-mentioned ultraviolet absorber based on 50 parts by weight of the binder. Further, as the binder for the above-mentioned ultraviolet absorber and ultraviolet stabilizer, the same binder as the above-mentioned binder for the heat-sensitive coloring layer can be used. Furthermore, as the solvent for the coating solution for forming the intermediate layer, a low polarity solvent such as cyclohexane, a hydrocarbon solvent, or toluene is used.

[0036] Such an intermediate layer can be formed by gravure coating,
It can be formed by a known method such as a roll coating method, a comma coating method, a knife coating method, or a silk screen method, and the thickness of this intermediate layer is 1 to 4 μm, preferably 1 μm.
It is about 2 μm. The protective layer used in the present invention is mainly composed of an ultraviolet curable resin. As a result, compared to drying using a conventional water-soluble coating liquid,
It becomes possible to significantly shorten the drying process.

The UV-curable ink for the protective layer in the present invention includes organic pigments, extender pigments, colorants such as carbon black, titanium white, and metal powder, acrylic prepolymers, acrylates, methacrylates, vinyl ethers, itaconate esters, etc. monomer, an acrylic ketone type photopolymerization initiator, etc. Further, other additives include mist inhibitors, slip agents, antioxidants, desiccants, wetting agents, viscosity modifiers, waxes, polymerization inhibitors, and the like.

Next, the present invention will be explained in more detail by giving more specific examples. Examples Thermosensitive recording medium samples 1 to 4 and comparative samples 1 to 6 were prepared in the following manner. First, a polyethylene terephthalate film (PET: Toray E-22) was used as a support.
A leuco dye and a color developer having the following composition were stirred and mixed using a stirrer containing glass beads for 2 hours to prepare an ink for a heat-sensitive coloring layer, and the leuco dye and color developer having the following composition were mixed using a glass bead-containing stirrer to prepare an ink for the thermosensitive coloring layer. A heat-sensitive coloring layer was formed by coating one side of the support by roll coating.

Leuco dye composition 3-(N-ethyl-N-isoanyl)amino-6-methyl
−7− Anilinofluorane...
10 parts by weight ・Dianaru BR7
5 (acrylic resin) (manufactured by Mitsubishi Rayon)

...10 parts by weight
・Dianaru BR82 (acrylic resin) (manufactured by Mitsubishi Rayon)

...10 parts by weight ・Toluene
…
5 parts by weight Color developer composition ・Bisresorcinol ethylene ether... 5 parts by weight ・Gallic acid
…
5 parts by weight ・Dianaru BR
75 (acrylic resin) (manufactured by Mitsubishi Rayon)

...10 parts by weight
・Dianaru BR82 (acrylic resin)
(Made by Mitsubishi Rayon)

...10 parts by weight ・Toluene
... 5 parts by weight Further, the intermediate layer liquid having the composition shown in Table 1 below was stirred and mixed using a stirrer for 2 hours to obtain an intermediate layer ink, and the heat-sensitive coloring layer was mixed so that the dry coating amount was 2 g/m2. An intermediate layer was formed on top. However, in Comparative Sample 6, no intermediate layer was formed.

[0040]

[Table 1] Furthermore, ultraviolet curable resin (manufactured by Moroboshi Ink Co., Ltd.)
UVS-OP varnish) onto the middle layer using 3-4g/
UV-offset printing was performed on an area of about m2 and cured using a high-pressure mercury lamp to form a protective layer. However, comparative sample 7
No protective layer was formed.

Next, samples 1 to 1 obtained as described above were prepared.
6 and Comparative Samples 1 to 7, first, using a 130°C hot plate, color was developed for 5 seconds at a pressure of 200 g/cm2, and the light resistance and plasticizer resistance were evaluated in the colored and non-colored areas as follows. , alcohol resistance, and head matching were tested. a) Light resistance a-1) Exposure was performed under a fluorescent lamp (5000 lux) for 100 hours, and changes in concentration before and after exposure were measured using a Macbeth densitometer.

a-2) Apply ultraviolet rays using a fade meter.
Irradiation for 6 hours. a-3) Attach the sample to a glass plate and conduct an exposure test for one month. b) Place the sample in close contact with a plasticizer-resistant plastic eraser, and apply 100g/c.
Apply a pressure of m2 and leave at room temperature for 48 hours.

c) Alcohol Resistance Color Development Test The colored and uncolored parts of the sample were immersed in a 70% ethyl alcohol aqueous solution for 2 minutes, and the concentration was measured using a Macbeth densitometer. d) Head matching property Printing of 5 cm was repeated 30 times using a printer manufactured by Toshiba Corporation with a thermal energy of 1.0 mJ, and sticking and head residue adhesion were evaluated.

Table 2 shows the test results for each of the above items.

[0045]

[Table 2] As is clear from the above results, Samples 1 to 6 have good properties overall, but especially in light resistance, they have particularly good properties compared to Comparative Samples 1 to 7. . On the other hand, Comparative Samples 1 to 5 are inferior to Samples 1 to 6 in light resistance, Comparative Sample 6 is inferior in light resistance and alcohol resistance, and Comparative Sample 7 is inferior in plasticizer resistance, alcohol resistance, and head Matchability is poor.

[0046]

According to the present invention, since the intermediate layer contains a plurality of ultraviolet absorbers having different absorption bands, the ultraviolet absorption ability of the intermediate layer is improved, and even if the heat-sensitive coloring layer has low light resistance, the heat-sensitive This has the effect of improving the light resistance of the recording medium. In addition, a solvent-based resin is used for the intermediate layer,
Since the protective layer is formed using an ultraviolet curable resin, the process for forming the intermediate layer and the protective layer can be shortened.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a thermosensitive recording medium of the present invention.

[Explanation of symbols]

1...Support 2...Thermosensitive coloring layer 3...middle class 4...Protective layer

Claims (2)

[Claims] 1. A support, a heat-sensitive coloring layer containing a leuco dye and a color developer and provided on one side of the support, and a solvent provided on the heat-sensitive coloring layer using a weakly polar solvent. An intermediate layer containing at least two or more types of ultraviolet absorbers having different absorption bands using a binder based on a resin, and a protective layer mainly made of an ultraviolet curable resin provided on the intermediate layer. Features of heat-sensitive recording media. 2. The heat-sensitive recording medium according to claim 1, wherein the intermediate layer contains an ultraviolet stabilizer.