JPH04129794A - Thermal recording sheet - Google Patents

Abstract

PURPOSE:To ensure that duplication, forgery and alteration are prevented and confidentiality is maintained by adding an opaque concealing material which makes the visual reading of a visible recorded image difficult and is not absorbed by a near-infrared area of specific wavelength strength as one kind of basic colorless dye which is absorbed by a near-infrared area of specific wavelength and visualizes a visible recorded image. CONSTITUTION:Near-infrared light-absorbing leuco dye which has absorptive properties in the applicable near-infrared area of 700 to 1200nm is a compound which absorbs near-infrared beam for a thermally developed recorded image as shown by quality formula (I), (II) and (III). In these formula, R1-R17 are each a hydrogen atom, an alkyl group, etc.; T1-T3 are hydrogen atoms; X<1> and X<2> are 8C or lower alkyl groups; m and n are each 1, 2 or 3; and X<3> is a chlorine atom or a bromine atom. The concealing material contained in the thermally coloring layer is not absorbed in the near-infrared area as an essential condition and is, for example, represented by a color dye or a color pigment such as aniline black, cyanine black BX and permanent brown FG. In addition, organic developers are bisphenols A, 4-hydroxybenzoic acid esters and other types of developer.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a heat-sensitive recording sheet that is excellent in optical readability in the near-infrared region and that can be kept confidential by making it difficult to read visually. It is something.

(Prior art) In general, heat-sensitive recording sheets are produced by grinding and dispersing a colorless or light-colored basic colorless dye and an organic color developer such as a phenolic substance into fine particles, and then mixing them together, filling them with a binder, etc. A coating liquid obtained by adding agents, sensitivity improvers, lubricants, and other auxiliary agents is coated on a support such as paper, synthetic paper, film, or plastic. Color recording is obtained through an instantaneous chemical reaction caused by heating.

These impression recording sheets are used in a wide range of fields such as measurement recorders, computer terminal printers, facsimile machines, automatic ticket vending machines, and barcode labels.
Recently, as these recording devices have become more diversified and more sophisticated, the quality required for heat-sensitive recording sheets has also become more sophisticated. For example, as recording speeds increase, it is required to obtain clear colored images with high density even with minute thermal energy, and on the other hand, heat-sensitive recording sheets with excellent preservability such as light resistance, weather resistance, and oil resistance are required. requested.

On the other hand, in recent years, along with the rationalization of administrative processing, the near-infrared region (
Optical reading devices whose reading wavelength range is 700 to 1200 nm are becoming popular. For this reason, we are developing basic dyes suitable for reading using near-infrared light, that is, basic dyes whose colored images absorb in the near-infrared region, as well as various types of prepaid cards with barcodes for near-infrared reading. Applications are underway.

However, since these recorded images having absorption in the near-infrared region are near-infrared light read images or visible images at the same time, their presence can be easily recognized by visual inspection.

Therefore, there is a risk that the information on the recorded image may be intentionally damaged, copied, forged, or falsified.

(Problems to be Solved by the Invention) An object of the present invention is to provide a heat-sensitive recording sheet that can maintain the confidentiality of image information that cannot be forged or tampered with, even though it is a recorded image that has absorption in the near-infrared region. It is about providing.

(Means for Solving the Problems) The present inventors have discovered that among near-infrared light reading and visual reading of recorded images obtained by heating, near-infrared light reading causes any inconvenience in readability. As a result of consideration from the viewpoint that the confidentiality of image information can be maintained if only visual reading is made impossible, the following solution was found.

That is, the heat-sensitive recording sheet of the present invention has a heat-sensitive coloring layer containing a near-infrared light-absorbing basic colorless dye and an organic color developer as main components, or a layer above or below the heat-sensitive coloring layer. It is characterized by containing an opaque concealing material to make it difficult to visually read the visible recorded image.

These opaque hiding materials have a color tone that is similar to the visible image formed by near-infrared absorbing colorless dye or heating, or a color tone that can hide the visible image, and this hiding material has a range that includes the visible image. The presence of these colors makes it difficult to visually read the visible image by making it impossible to distinguish the visible image from the ground color, or by canceling out the color tone of the visible image.

In the present invention, opaqueness means colored including black and blackish colors, and white and whiteish colors.

On the other hand, regarding near-infrared reading, since the concealing material used in the present invention has substantially no absorption in the near-infrared region, it does not impede mechanical reading in any way.

In this way, by using the concealing material, it is possible to make only the latter impossible of near-infrared light reading and visual reading of a thermosensitive color image.

As mentioned above, the hiding material used in the present invention is required to have substantially no absorption in the near-infrared region, so specific examples include colored dyes or colored pigments such as those exemplified below. is suitable for use.

Aniline black, cyanine black BX, permanent brown FG, para brown, cobalt purple (dark),
Cobalt purple (light), manganese purple, fast violet B1 methyl violet lake, dioxazine violet, ultramarine, dark blue, cobalt blue, cerulean blue, alien, alkaline blue lake, peacock blue lake, Fanatone blue 6G, Victoria blue lake, Metal-free phthalocyanine blue, phthalocyanine blue, fast sky blue, indanthremble-R
8, Indan Stremburu-BC, Indigo, Chrome Green, Zinc Green, Chromium Oxide, Viridian, Emerald Green, Cobalt Green, Pigment Green B1 Naphthol Green B1 Green Gold, Acid Green Lake, Malachite Green Lake, Phthalocyanine Green, C, 1.Direct Viol
et l, C, l, Di [ecl Blue I
,C,1,Direct Green I ,C,1D
Direct Black 1? ,C,1,Ac1d
Blue 9, C, lAc1d Green 5゜The near-infrared light-absorbing leuco dye used in the present invention, which has absorption in the near-infrared region of 700 to 1200 nm, absorbs near-infrared light for the recorded image when heated and colored. Although not particularly limited, general formula (I),
The compounds represented by (n) and (I[) are particularly desirable.

Examples of the near-infrared light-absorbing leuco dye of general formula (I) used in the present invention include, but are not limited to, the following.

2-Methyl-6-p-(p-dimethylaminophenyl)
Aminoanilinofluoran 2-methoxy-6-p-(p-dimethylaminophenyl)Aminoanilinofluoran 2-chloro-6-p-(p-dimethylaminophenyl)
Aminoanilinofluorane 2-nitro-6-p-(p-diethylaminophenyl)
Aminoanilinofluorane 2-amino-6-p-(p-diethylaminophenyl)
Aminoanilinofluoran 2-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran 2-phenyl-6-
p-(p-phenylaminophenyl)aminoanilinofluorane 2-benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran 2-hydroxy-6-p-(p-phenylaminophenyl)amino Anilinofluorane 3-methyl-6-p-(
p-dimethylaminophenyl)aminoanilinofluoran 3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran 3-diethylamino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran 2-Methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluorane 2-chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran.

Examples of the near-infrared light-absorbing leuco dye of general formula (I[) used in the present invention include, but are not limited to, the following.

33-bis-[2-(p-dimethylaminophenyl)-
2-(p-methoxyphenyl)ethynyl]-4567-
Tetrabromophthalide 33-bis-[2-(p-dimethylaminophenyl)-
2-(p-methoxyphenyl)ethynyl]456.7-
Tetrachlorophthalide 33-bis-[1,1-bis(4-pyrrolidinophenyl)ethylene-2-yl] -4,5,6,7-titrabromophthalide 33-bis[1-(4-methoxy) phenyl)1-(4-
pyrrolidinophenyl)ethylene-2-yl]-4.5.
6.7-Titrachlorophthalide.

Examples of the near-infrared light-absorbing leuco dye of general formula (III) used in the present invention include, but are not limited to, the following.

3.6-bis(dimethylamino)fluorene-9spiro-3'-(6'-dimethylamino)phthalide 36-bis(diethylamino)fluorene-9spiro-
3'-(6'-dimethylamino)phthalide.

Moreover, in the present invention, general formulas (I), (n), (II
Of course, near-infrared absorbing leuco dyes other than I) can also be used. Specifically, the following can be mentioned.

1.1-bis-[2',2',2',2'-tetrakis-(p-dimethylaminophenyl)-ethynyl]
-2,2-dinitrile ethane 1.1-bis-[2',2',2',2'-tetrakis-(p-dimethylaminophenyl)-ethynyl]
-2-β-naphthoylethane 1.1-bis-[2',2',2',2'-tetrakis-(p-dimethylaminophenyl)-ethynyl]
-2,2-Diacetylethane bis-[2,2,2',2'-tetrakis(p-dimethylaminophenyl)-ethynyl]-methylmalonic acid dimethyl ester.

These near-infrared light absorbing leuco dyes can be used alone or in combination of two or more.

Further, as the organic color developer used in the present invention, bisphenol A, 4-hydroxybenzoic acid ester, 4-
Hydroxyphthalic acid diesters, phthalic acid monoesters, bis-(hydroxyphenyl) sulfides, 4
-Hydroxyphenylarylsulfones, 4-hydroxyphenylarylsulfonates, 1,3-di[2
-(Hydroxyphenyl)-2-propyl]-benzenes, 4-hydroxybenzoyloxybenzoate, bisphenol sulfones, and other color developers are preferred, and specific examples thereof are shown below.

Bisphenol A 4.4'-isopropylidene diphenol (also known as bisphenol A) 44'-cyclohexylidene diphenol p, p'-(
1-Methyl-n-hexylidene)diphenol 1,7-di(4-hydroxyphenylthio)-35-dioxahebutane.

4-hydroxybenzoic acid esters Benzyl 4-hydroxybenzoate Ethyl 4-hydroxybenzoate Propyl 4-hydroxybenzoate Isopropyl 4-hydroxybenzoate Butyl 4-hydroxybenzoate Isobutyl 4-hydroxybenzoate Methylbenzyl 4-hydroxybenzoate.

4-Hydroxyphthalic acid diesters Dimethyl 4-hydroxyphthalate Diisopropyl 4-hydroxyphthalate Dibenzyl 4-hydroxyphthalate Dihexyl 4-hydroxyphthalate.

Phthalic acid monoesters Phthalic acid monobenzyl ester Phthalic acid monocyclohexyl ester Phthalic acid monophenyl ester Phthalic acid monomethyl phenyl ester Phthalic acid monoethylphenyl ester Phthalic acid monopropyl benzyl ester Phthalic acid monohalogen benzyl ester Phthalic acid monoethoxybenzyl ester.

Bis-(hydroxyphenyl) sulfides bis-(4
-Hydroxy-3-1eN-butyl6-methylphenyl)sulfide bis-(4-hydroxy-2,5-dimethylphenyl)
Sulfide bis-(4-hydroxy-2-methyl-5-ethylphenyl) sulfide bis-(4-hydroxy-2-methyl-5-isopropylphenyl) sulfide bis-(4-hydroxy-2,3-dimethylphenyl)
Sulfide bis-(4-hydroxy-2,5-diethylphenyl)
Sulfide bis-(4-hydroxy-2,5-diisopropylphenyl) sulfide bis-(4-hydroxy-2,3,6-4-limethylphenyl) sulfide bis-(2,4,5-trihydroxyphenyl) sulfide bis-( 4-Hydroxy-2-cyclohexyl-5-methylphenyl)sulfidebis-(2,3,4-trihydroxyphenyl)sulfidebis-(4,5-dihydroxy-2-ter+-butylphenyl)sulfidebis-( 4-hydroxy-2,5-diphenylphenyl)sulfide bis-(4-hydroxy-2-tent-octyl-5
-methylphenyl) sulfide.

4-Hydroxyphenylarylsulfones 4-hydroxy-4'-isopropoxydiphenylsulfone 4-hydroxy-4'-propoxydiphenylsulfone 4-hydroxy-4'-n-butyloxydiphenylsulfone.

4-Hydroxyphenylarylsulfonates 4-hydroxyphenylbenzenesulfonate 4-hydroxyphenyl-p-tolylsulfonate 4-hydroxyphenylmethylenesulfonate 4-hydroxyphenyl-p-1eft-butylbenzenesulfonate 4-hydroxyphenyl- p-isopropoxybenzenesulfonate 4-hydroxyphenyl-17-naphthalenesulfonate 4-hydroxyphenyl-2'-naphthalenesulfonate.

13-di[2-(4-hydroxyphenyl)-2-propyl]benzene 13-di[2-(4-hydroxy-3-alkylphenyl)-2-propyl]benzene 1,3-di[2-(2 ，
4-dihydroxyphenyl)2-propyl] Hensen 1.3-di[2-(2-hydroxy-5-methylphenyl)-2-propyl]benzene.

Resorcinols 13-dihydroxy-6 (α,α-dimethylbenzyl)
-Benzene.

4-Hydroxybenzoyloxybenzoate ester Benzyl 4-hydroxybenzoyloxybenzoate Methyl 4-hydroxybenzoyloxybenzoate 4-Ethyl hydroxybenzoyloxybenzoate 4-Propyl hydroxybenzoyloxybenzoate 4-Butyl 4-hydroxybenzoyloxybenzoate Isopropyl hydroxybenzoyloxybenzoate 4-hydroxybenzoyloxybenzoate tell-butyl 4-hydroxybenzoyloxybenzoate hexyl 4-hydroxybenzoyloxybenzoate octyl 4-hydroxybenzoyloxybenzoate nonyl 4-hydroxybenzoyloxybenzoate cyclohexyl 4-hydroxy β-phenethyl benzoyloxybenzoate phenyl 4-hydroxybenzoyloxybenzoate α-naphthyl 4-hydroxybenzoyloxybenzoate β-naphthyl 4-hydroxybenzoyloxybenzoate sec butyl 4-hydroxybenzoyloxybenzoate.

Bisphenolsulfones (I) Bis-(3-1-butyl-4-hydroxy-6methylphenyl)sulfonebis-(3-ethyl-4-hydroxyphenyl)sulfonebis-(3-propyl-4-hydroxyphenyl)sulfonebis-(3 -Methyl-4-hydroxyphenyl)sulfonebis-(2-isopropyl-4-hydroxyphenyl)
Sulfonebis-(2-ethyl-4-hydroxyphenyl)sulfonebis-(3-chloro-4-hydroxyphenyl)sulfonebis(2,3-dimethyl-4-hydroxyphenyl)sulfonebis(2,5-dimethyl-4-hydroxyphenyl) Sulfone bis-(3-methoxy-4-hydroxyphenyl)sulfone 4-hydroxyphenyl-2'-ethyl-4' hydroxyphenyl sulfone 4-hydroxyphenyl-2' -isopropyl 4'
-Hydroxyphenylsulfone 4-hydroxyphenyl-3'-isopropyl-4'
-Hydroxyphenylsulfone 4-hydroxyphenyl-3'-5ecbutyl4' -Hydroxyphenylsulfone 3-chloro-4-hydroxyphenyl-3'isopropyl-4'-hydroxyphenylsulfone 2-hydroxy-5-t-butylphenyl- 4'-hydroxyphenylsulfone 2-hydroxy-5-t-aminophenyl-4'-hydroxyphenylsulfone 2-hydroxy-5-t-isopropylphenyl-4'
-hydroxyphenylsulfone 4'3' hydroxy-5-t-octylphenylhydroxyphenylsulfone hydroxy-5-t-butylphenylchlor-4'-hydroxyphenylsulfone 2-hydroxy-5-[-butylphenyl 3' -methyl- 4'-hydroxyphenylsulfone2-hydroxy-5-t-butylphenyl3'-isopropyl-4'-hydroxyphenylsulfone2-hydroxy-5-t-butylphenyl3'-chloro-4'-hydroxyphenylsulfone2- Hydroxy-5-t-butylphenyl 3'-methyl-4'-hydroxyphenylsulfone 2-hydroxy-5-t-butylphenyl-3'-isopropyl-4'-hydroxyphenylsulfone 2-hydroxy-5-t-butyl Phenyl 2'-methyl-4'-hydroxyphenylsulfone.

Bisphenol sulfones (■) 4.4'-sulfonyldiphenol 2.4'-sulfonyldiphenol 3.3'-dichloro-4,4'-sulfonyldiphenol 3.3'-dibromo-4,4 sulfonyldiphenol -3,3',5,5'-tetrabromo-44'-
Sulfonyldiphenol 3,3-diamino-4,4'-sulfonyldiphenol.

Other p-tell-butylphenol 2.4-dihydroxybenzophenone Novolac type phenolic resin 4-hydroxyacetophenone p-phenylphenol Benzyl-4-hydroxyphenylacetate p-benzylphenol These color developers can be used alone or in combination of two or more. can.

Furthermore, in the present invention, a polyvalent metal salt of an organic acid can be contained as a stabilizer in order to further improve storage stability such as light resistance, weather resistance, and oil resistance.

Among these stabilizers, the most preferred are those represented by the following general formula (I
V) is a halogen-substituted benzoic acid zinc salt derivative.

[wherein, represents an integer of 1 to 2, and m represents an integer of 0 to 5. In the explanation of general formula (IV), C
The 1-C12 alkyl group and the 01-CI2 alkoxy group may be linear or branched, and include a methyl group, ethyl group, n-propyl group, isopropyl group,
n-butyl group, isobutyl group, HC-butyl group, hexyl group, octyl group, nonyl group, dodecyl group, methoxy group,
Examples include ethoxy group and tent-butoxy group. 0
Examples of the 3-C1o cycloalkyl group include a cyclohexyl group, a 2-ethylcyclohexyl group, and a p-tent-butylcyclohexyl group.

The above stabilizer is a compound having a specific molecular structure selected from among many organic carboxylic acid metal salts. Benzoic acid zinc salts having one or two halogen atoms as substituents on the benzene nucleus have characteristics in light resistance, weather resistance, and oil resistance that are not found in similar organic carboxylic acids or their polyvalent metal salts.

Typical halogen-substituted benzoic acid zinc salt derivatives used in the present invention include, but are not limited to, the following.

I I l I Furthermore, as a sensitizer, fatty acid amides such as stearic acid amide and lumitic acid amide, ethylene bisamide, montan wax, polyethylene wax,
Dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, p-benzylbiphenyl, phenyl α-naphthyl carbonate, 1.
4-jethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, oxalic acid (p-methylbenzyl), β-benzyloxynaphthalene, 4-biphenyl p-tolyl ether, 1,2-di(3-methylphenoxy) ) Ethane etc. can also be added.

The binder for the thermosensitive coloring layer has a polymerization degree of 200 to 1.
900 fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, other modified polyvinyl alcohols, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, styrene - maleic anhydride copolymers, styrene-butadiene copolymers and cellulose derivatives such as ethylcellulose, acetylcellulose,
Examples include polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic ester, polyvinyl butyral, polystyrene and copolymers thereof, polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, and coumaron resin. can. These polymeric substances are used by dissolving them in solvents such as water, alcohols, ketones, esters, and hydrocarbons, or they are used by emulsifying or dispersing them in paste form in water or other media to meet the required quality. It can also be used in combination.

Examples of the filler used in the present invention include inorganic or organic fillers such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, and aluminum hydroxide.

In addition, release agents such as fatty acid metal salts, lubricants such as waxes, ultraviolet absorbers such as benzophenone and triazole, water resistance agents such as glyoxal, dispersants, and antifoaming agents can be used.

The amounts of the organic color developer and basic colorless dye, as well as the types and amounts of other various components constituting the heat-sensitive coloring layer of the present invention, are determined according to the required performance and recording suitability, and are not particularly limited. Normally, 1 to 8 parts of an organic color developer and 1 to 20 parts of a filler are used for the basic colorless dye IN, and the appropriate amount of binder is 10 to 25% of the total solid content. When it is contained in the layer, the above ratio is 0.41 to 10 parts.

In addition, if an opaque hiding material that makes it difficult to visually read a visible recorded image is placed above or below the heat-sensitive color forming layer, the binder of the heat-sensitive color forming layer may be one of the above-mentioned binders or an ultraviolet or electron beam curing type. The hiding layer can be formed by any means such as coating, printing, spraying, etc. using the resin.

In this case as well, the hiding material functions in the same way as when it is added to the heat-sensitive coloring layer, making it difficult only to visually read the visible recorded image and having a negative effect on near-infrared light reading. I won't give it. Depending on the use and performance of the thermosensitive recording material, a protective layer made of synthetic resin may be formed on the thermosensitive coloring layer to protect it from scratches and stains, or to improve the storage stability and sensitivity of recorded images. For this reason, it is sometimes provided under an undercoat layer containing oil-absorbing pigments or under a heat-sensitive coloring layer, but in such cases, even if a hiding material is added to these protective layers or undercoat layers, it will not be effective. It becomes a means of concealment.

The concealing material of the present invention does not need to be provided on the entire surface of the heat-sensitive recording sheet, but can be applied only to the recorded image that is to be partially kept confidential, thereby distinguishing between the hidden invisible part and the other visible part. can be used properly. Furthermore, a protective film made of an ultraviolet or electron beam curable resin having higher protective performance may be provided on the surface of the heat-sensitive coloring layer or the concealing layer or protective layer provided thereon.

Supports used in the present invention include paper, synthetic paper,
Examples include plastic films.

On the other hand, in the present invention, when it is desired to display non-confidential information as a visually readable recorded image in addition to a recorded image that is readable by near-infrared light and cannot be visually read, it is possible to display non-confidential information as a visually readable recorded image. Pressure-sensitive copying sheets, heat-sensitive recording sheets, current-carrying heat-sensitive recording sheets, ultrasonic recording sheets), electron beam recording sheets, electrostatic recording sheets, photosensitive recording sheets, inkjet recording sheets, which have been proposed for the back side of the body, A recording layer used in thermal transfer recording sheets, impact dot recording sheets, punch recording sheets, etc. can be provided and used for recording visible information.

The organic color developer, basic colorless dye, and materials to be added as necessary are pulverized to a particle size of several microns or less using a pulverizer such as a ball mill, attritor, or sand grinder, or an appropriate emulsifying device, and then the binder and Depending on the purpose, various additive materials are added to make a coating liquid.

(Function) The reason why the heat-sensitive recording sheet of the present invention is excellent in optical readability in the near-infrared region and confidentiality is as follows.

The heat-sensitive recording sheet of the present invention develops color upon contact with a heat-sensitive head, or the color tone of the developed color tone is the same as or hidden by the opaque hiding material contained within the heat-sensitive color layer, or in the upper or lower layer thereof. Because of the dark tone, the presence of the colored portion or the recorded content cannot be determined by visual inspection. However, the colored part hiding material is 700 to 120
Since it absorbs light in the near-infrared region of 0 nm, optical readability with near-infrared light is not impaired in any way.

(Examples) The present invention will be explained below using Examples and Comparative Examples. In the description, parts indicate parts by weight.

[Example 1] ■Liquid A 3.6 - Bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide 2.5 parts 10% polyvinyl alcohol aqueous solution 5.8 parts water
Mikawabe: This composition was pulverized with a sand mill to an average particle size of 1 μm.

■Solution B 4.4-Isobropylidenediphenol 6
0 parts p-chlorobenzoate zinc 45 parts 1
0% polyvinyl alcohol aqueous solution 188 parts water
112 parts of this composition was ground in a sand mill to an average particle size of 1 μm.

■Liquid C calcium carbonate (50% dispersion liquid) ■Liquid D Calcium carbonate (50% dispersion) ■Liquid D C, 1, Ac1d Green 5 50% aqueous solution (manufactured by Hodogaya Chemical Co., Ltd.) The mixture of the above compositions was mixed in the following ratio to form a thermosensitive coloring layer. It was used as a coating liquid.

Solution A: 11.4 parts Solution B: 405 parts Solution C: 120 parts Liquid: 10 parts
m1 manufactured by Toshisha Co., Ltd.), the coating liquid for the heat-sensitive coloring layer was applied and dried so that the coating amount after drying was 6 g/rIf, and the surface of the heat-sensitive coloring layer was supercalendered to a smoothness of 800 to 100.
(The heat-sensitive recording sheet for a prepaid card, whose entire surface was colored green, was obtained by processing it for 1 second.

[Example 2] In the preparation of Solution A, 2-chloro3-methyl-6-p was used instead of 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamine)phthalide. -(p-phenylaminophenyl)aminoanilinofluorane was used to prepare C,1,
A thermosensitive recording sheet colored black was prepared in the same manner as in Example 1, except that aniline black was used instead of Ac1d Green 5, and egg oil synthetic paper FPG250 was used instead of East Lumirror E62 as a support. Obtained.

[Example 3] In the preparation of Solution A, 3,3-bis[2-(p −
Dimethylaminophenyl)-2(p-methoxyphenyl)ethynyl]-4,5,6,7 tetrachlorophthalide was used to prepare C,1,Ac1d Gr
C, I instead of een 5, ^cidRed 4
A heat-sensitive recording sheet colored purple was obtained in the same manner as in Example 1, except that high-quality paper with a basis weight of 50 g/rrf was used as the support instead of East Lumir Mirror E62.

[Comparative Example 1] A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that no colored dye solution was used.

[Comparative Example 2] A thermosensitive recording sheet was obtained in the same manner as in Example 2 except that no colored dye was used.

[Comparative Example 3] A thermosensitive recording sheet was obtained in the same manner as in Example 3 except that no colored dye was used.

[Example 4 Part A Solution 3.6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide 2.5 parts 10% polyvinyl alcohol aqueous solution 58 parts water
31 parts of this composition was ground in a sand mill to an average particle size of 1 μm.

■Solution B 44'-isopropylidene diphenol 6.0 parts Zinc p-chlorobenzoate 45 parts IO% polyvinyl alcohol aqueous solution 188 parts Water
11.2 parts This composition was ground with a sand mill to an average particle size of 1 μm.

A liquid mixture of the above compositions was mixed in the following ratio to prepare a coating liquid for a heat-sensitive coloring layer.

Solution A 11.4 parts Solution B 40.5 parts ■Liquid E 50% aluminum hydroxide dispersion 800 parts 10%
Polyvinyl alcohol aqueous solution 32 parts water
10 parts ■F Solution C, 1, Ac1d Gteen 5 50% aqueous solution The mixture of the above compositions was mixed in the following proportions to prepare a coating solution for a protective layer.

50 parts of F solution 10 parts of F solution
1 (manufactured by Toshisha Co., Ltd.), the above coating liquid for the heat-sensitive coloring layer was first applied and dried so that the coating amount after drying was 6 g/rrf, and then the above coating liquid for the protective layer was coated in a coating amount of 6 g/rrf after drying. 3 g/rr
f, and the surface of the recording layer was treated with a supercalender to a smoothness of 800 to 1000 seconds.
A heat-sensitive recording sheet colored green for use in a prepaid card was obtained.

[Example 5] In the preparation of Solution A, 2-chloro-3-methyl-6 was used instead of 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylamino)phthalide.
-p-(p-phenylaminophenyl)aminoanilinofluorane was used to prepare C,1,^
A thermosensitive record colored black in the same manner as in Example 4, except that aniline black was used instead of cid G'een 5, and egg oil synthetic paper FPG250 was used instead of East Lumirror E62 as a support. Got a sheet.

[Example 6] 3.3-bis-[2-(p-dimethylaminophenyl) instead of 3.6-bis(dimethylamino)fluorene-9spiro-3'-(6'-dimethylamino)phthalide -2-(p-methoxyphenyl)ethynyl] -4
,5,6,7-titrachlorophthalide, and in the F solution preparation, C,1^cid Red 49 was used instead of C,1,Ac1dGreen 5, and East Lumirror E62 was replaced as a support. , basis weight 50g/i
A heat-sensitive recording sheet colored purple was obtained in the same manner as in Example 1, except that high-quality paper was used.

[Comparative Example 1] A thermosensitive recording sheet was obtained in the same manner as in Example 4 except that colored dye liquid F was not used.

[Comparative Example 2] A thermosensitive recording sheet was obtained in the same manner as in Example 5 except that colored dye solution F was not used.

[Comparative Example 3] A thermosensitive recording sheet was obtained in the same manner as in Example 6 except that colored dye solution F was not used.

The following quality performance tests were conducted on the heat-sensitive recording sheets obtained in the above Examples and Comparative Examples, and the results are shown in Table 1.

Note (1) PC3 value, using a 5WEDOT printer, applied voltage 30V, pulse width, 61
The recorded image recorded in milliseconds and the reflectance (%) of the background portion were measured with a spectrophotometer at a wavelength of 900 nm, and the PC3 value was calculated. Note that the PC8 value is a value at 900 nm. This PC
8 value is calculated by the following formula.

The closer the reflectance PO2 value before color development is to 1, the clearer the contrast and the higher the readability. Therefore, in order to increase the PO2 value, it is necessary to increase the reflectance (%) of the uncolored area and at the same time lower the reflectance (%) of the recorded area.

Note (2) Identification of colored images: Colored images printed by the method described in Note (1) were visually identified.

○: Unidentifiable ×: Identifiable (effects of the invention) (1) Excellent optical readability in the near-infrared region, so no misreading occurs during reading.

(2) Since the recorded image cannot be visually read, copying, forgery, alteration, etc. can be prevented, and confidentiality can be maintained.

Claims (2)

[Claims] (1) In a heat-sensitive recording sheet in which a heat-sensitive coloring layer containing a basic colorless dye and an organic color developer as main components is provided on a support, the basic colorless dye absorbs in the near-infrared region of 700 to 1200 nm. The heat-sensitive color forming material is at least one kind of dye that exhibits a visible recorded image with 1. A heat-sensitive recording sheet, characterized in that the heat-sensitive recording sheet contains a heat-sensitive material contained in a layer, an upper layer, or a lower layer thereof. (2) The dye having absorption in the near-infrared region of 700 to 1200 nm is at least one type of compound represented by the following general formula (I), (II) or (III). Heat sensitive recording sheet. ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(I) [In the formula, R_1, R_2, R_3, R_4, R_5, R_
6 and R_7 are each a hydrogen atom, an alkyl group, an alkoxy group, a cycloalkyl group, a halogen atom, a nitro group,
It represents a hydroxyl group, an amino group, a substituted amino group, an aralkyl group, a substituted aralkyl group, an aryl group, or a substituted aryl group. T_1, T_2 and T_3 are each a hydrogen atom, a C_1 to C_8 alkyl group, a C_3 to C_9 alkenyl group, or a C_3 to C_9 alkynyl group,
T_4 is a hydrogen atom, C_1 to C_8 alkyl group, C_
3 to C_9 alkenyl group, C_3 to C_9 alkynyl group, or phenyl group, and T_3 and T_4 are bonded to adjacent nitrogen atoms to form a monophorino group, pyrrolidino group, piperidino group, or hexamethyleneimino group. Also good. l represents an integer from 0 to 4. ] ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(II) [In the formula, R_1_0 is an alkyl group with 8 or less carbon atoms, R_
1_1 represents an alkyl group having 8 or less carbon atoms, a cycloalkyl group having 5 to 7 carbon atoms, a benzyl group or a phenyl group which may have a chlorine atom, bromine atom, or an alkyl group having 4 or less carbon atoms as a substituent. X^1 and X^2 have 8 carbon atoms
Indicates the following alkyl group, alkoxy group having 8 or less carbon atoms, fluorine atom, chlorine atom or bromine atom, where m and n are 0 and 1
, 2 or 3, X^1 comrade of (X^1)_m, (X
^2) _n's X^2 comrades may be the same or different. X^3 represents a chlorine atom or a bromine atom, and both of the four atoms may be present at the same time. ] ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(III) [In the formula, R_1_2, R_1_3, R_1_4, R_1
_5, R_1_6, R_1_7 are each hydrogen atoms; C_1
-C_8 alkyl group; C_5-C_8 cycloalkyl group; C_3-C_8 alkoxyalkyl group; C_3
~ C_9 unsaturated alkyl group; tetrahydrofurfuryl group; tetrahydropyran-2-methyl group; halogen atom, C_1 to C_4 alkyl group, C_1 to C_4 alkyl group optionally substituted; halogen atom, C_1 to C_4 alkyl group, C_1 to C_4
an aryl group optionally substituted with an alkoxyl group;
Halogen atom, alkyl group of C_1 to C_4; C_1 to
Indicates a C_2 to C_8 alkyl group having a phenoxy group which may be substituted with a C_4 alkoxyl group. Also, R_1_2 and R_1_3, R_1_4 and R_1_5,
R_1_6 and R_1_7 can also form a heterocycle with each other or with an adjacent benzene ring. ]