JP2533018B2 - 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 heat-sensitive recording medium having improved storage stability, and more particularly to cards such as tickets, commuter passes, and pass tickets, cards such as prepaid cards, and labels such as POS labels. The present invention relates to a heat-sensitive recording medium to which the above-mentioned is applicable.

[0002]

2. Description of the Related Art Thermosensitive recording systems have recently been used in facsimile machines and printers because of the advantages that the apparatus can be made smaller and lighter, recording can be performed without noise, and consumables such as toner and transfer paper are not required. Widely used, and also ticket,
It has come to be applied to ticket papers such as commuter passes and pass tickets, cards such as prepaid cards, and labels such as POS labels. In particular, there are many cases in which it is combined with a magnetic recording system for ticket papers and cards.

As a conventional heat-sensitive recording medium used in the heat-sensitive recording system, a so-called "NCR type" in which a colorless or light-colored leuco dye and a color developer are used as color-forming components is widely used. Such a heat-sensitive recording medium includes, for example, triphenylmethanephthalides such as crystal violet lactone, leuco dyes such as fluoranes, lactams and spiropyrans, and phenols such as bisphenol A, thiobisphenols and α- Naphthol,
A thermosensitive coloring layer formed by dispersing a color developing agent such as an acid derivative such as β-naphthol, benzoic acid, salicylic acid, tartaric acid, and gallic acid in an aqueous binder such as polyvinyl alcohol was provided on the substrate. It is a thing. This kind of heat-sensitive recording medium has excellent characteristics such as clear recording, high heat sensitivity, and white background.

However, the conventional thermal recording medium has a D
When it comes in contact with plasticizers such as OP, chemicals such as alcohol, and water, it may cause decoloration of recorded parts and coloration of unrecorded parts,
It has a problem of chemical resistance and water resistance that the heat-sensitive layer is significantly softened, and a problem of heat resistance.

Particularly when the thermal recording system is applied to ticket papers, cards such as tickets and commuter passes, and labels, severe quality characteristics, that is, plasticizer resistance, oil resistance, alcohol resistance,
Chemical resistance such as acid resistance, alkali resistance, sweat resistance, water resistance,
Heat resistance is strongly required. In addition, in the case of ticket papers and cards that are combined with the magnetic recording system, it is necessary to pass through a gate with a built-in magnetic head at a high speed in automatic ticket gates, so heat resistance against pressure coloring and high abrasion resistance are also required. Has been done.

In order to solve these various characteristics under such severe requirements, it has been proposed to provide a surface layer on the thermosensitive coloring layer as a thermosensitive recording material having both water resistance and plasticizer resistance at the same time. Has been done. Specifically, JP-A-56-
No. 126193, JP-A-57-139993, JP-A-57-29491, etc., using a modified surface treatment agent or JP-A-56-1467.
As disclosed in No. 94, a proposal has been made of a water-soluble polymer compound and a hydrophobic polymer compound emulsion or a combination of a water-resistant polymer compound and a waterproofing agent. However, even with these improved technologies, although water resistance and plasticizer resistance have each been improved, not only image characteristics but also chemical resistance, water resistance, heat resistance, wear resistance, etc. At present, a thermosensitive recording medium satisfying the above characteristics has not yet been obtained.

[0007]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to improve the chemical resistance, water resistance and heat resistance of a thermosensitive recording medium.

[0008]

Means for Solving the Problems The present inventors have studied many combinations of leuco dyes and color developers, and have further investigated the binder for the heat-sensitive layer in addition to water-based solvents and widely used as solvent-based results. The present invention has been achieved. That is, the present invention provides
A leuco dye represented by the following structural formula (1), and at least one type of color developing agent selected from compounds represented by the following structural formulas (2) to (4) that cause the leuco dye to develop color when heated. A heat-sensitive recording medium comprising a heat-sensitive color-developing layer containing a binder soluble in an aliphatic or aromatic hydrocarbon solvent as a main component.

[0009]

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In the present invention, as the leuco dye, it is desirable to use only the leuco dye represented by the above structural formula (1). A leuco dye can also be used in combination. Examples of specific compounds of other leuco dyes that can be used in combination include crystal violet lactone,
Diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-7-dibenzylaminofluoran, 3-pyrrolidino-6 -Methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-
Cyclohexylmethylamino-6-methyl-7-anilinofluoran, 3-ethylisoamylamino-6-methyl-7-anilinofluoran, 3-diethylamino-7
-(O-chloroanilino) fluoran, 3-ethylisoamylamino-7- (o-chloroanilino) anilinofluoran, 3-dibutylamino-7- (o-chloroanilino) fluoran and the like.

In the present invention, the developer has the structure
At least one kind of developer selected from the compounds represented by the formulas (2) to (4) is used, and two or more kinds may be mixed and used as necessary. Also,
As long as the chemical resistance, water resistance and heat resistance are not impaired, a conventionally used developer may be used in combination. Examples of such a developer include α-naphthol, β-naphthol, 4-t-butylphenol, 4-t-octylphenol, 4-phenylphenol, 2,2-bis (p-hydroxylphenyl) propane, 2, 2-bis (p-hydroxylphenyl) butane, 4,4'-cyclohexylidene diphenol, 2,2-bis (2,5-
Dibromo-4-hydroxylphenyl) propane, 4,
4'-isopropylidene bis (2-t-butylphenol), 2,2'-methylenebis (4-chlorophenol), 4,4'-sulfonyldiphenol, 4,4 '
-Thiobisphenol, bis- (4-hydroxy-3-
Examples include derivatives of allylphenyl) sulfone, benzoic acid, salicylic acid, tartaric acid, gallic acid and the like.

As the binder for the thermosensitive coloring layer in the present invention, a resin soluble in an aliphatic or aromatic hydrocarbon solvent is used. The aliphatic or aromatic hydrocarbon solvent as used herein does not substantially dissolve the specific leuco dye and the developer in the present invention but dissolves only the binder. In particular,
Examples include petroleum ether, petroleum benzine, rubber volatile oil, light oil, cyclohexane, methylcyclohexane, toluene, xylene, and naphtha. Examples of such a binder soluble in a hydrocarbon solvent include styrenes such as styrene, methyl styrene, ethyl styrene, n-butyl styrene and chlorostyrene, methyl acrylate, ethyl acrylate and n-acrylate. Butyl, 2-ethylhexyl acrylate, phenyl acrylate, methyl methacrylate,
Acrylic esters such as ethyl methacrylate, n-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, and acrylic acid derivatives such as acrylonitrile, methacrylonitrile, and acrylamide And homopolymers and copolymers composed of such monomers. Further, copolymers of olefin-based or other vinyl-based monomers copolymerizable with these monomers, rubbers such as cyclized rubbers, and the like can also be used.

The heat-sensitive recording medium of the present invention is a heat-sensitive recording medium obtained by dissolving a binder in the above-mentioned aliphatic or aromatic hydrocarbon solvent and further dispersing the leuco dye and the developer in the solution. It is prepared by applying a coating solution for a color forming layer onto a substrate and drying. Here, the compounding ratio of the leuco dye and the developer is 10: 1 to 1:10, preferably 1: 1 to 1
1: 3, and the ratio of the binder in the entire thermosensitive coloring layer is from 5 to 95%, preferably from 20 to 60%, in solid content.

In the thermosensitive coloring layer of the present invention, if necessary, for example, inorganic pigments such as aluminum hydroxide, calcium carbonate, silica, talc, etc., organic pigments such as polyolefin resins, polystyrene resins, urea-formalin resins, etc., Additives such as metal salts of higher fatty acids, waxes, lubricants such as fine particles of fluorocarbon, and ultraviolet absorbers can be added. It is also possible to use a curing agent for hardening the heat-sensitive coloring layer physically and chemically, and various sensitizers as long as the heat resistance is not impaired.

Examples of the substrate used in the present invention include polyethylene terephthalate film and other plastic films, coated paper, art paper, laminated paper, synthetic paper, glass, metal, etc. Synthetic paper is preferred.

In the present invention, a protective layer may be provided on the thermosensitive coloring layer in order to further improve the chemical resistance of the thermosensitive coloring layer and to improve the matching property with the thermosensitive head. This protective layer is made of a resin having a high softening temperature, a pigment or a lubricant, and an ultraviolet curable resin can be used as the resin. Further, in order to improve the adhesive strength between the thermosensitive coloring layer and the base, an under layer may be provided between the base and the thermosensitive coloring layer.

The thermal recording medium of the present invention can be combined with a magnetic recording layer in its implementation. That is, a magnetic recording layer is provided on the back surface of the substrate, or a magnetic recording layer, a layer for concealing coloring of the magnetic recording layer, and a thermosensitive coloring layer are sequentially laminated on the same surface of the substrate. Labeling can also be performed by providing an adhesive layer and a separator on the back surface of the substrate.

[0018]

EXAMPLES Examples of the present invention will be described below. Example 1 A thermosensitive coloring layer paint having the following composition was applied on a base made of a milky white polyethylene terephthalate film having a thickness of 188 μm, and dried at 70 ° C. to obtain a thermosensitive recording medium of the present invention. The dry coating amount was 7.2 g / m ² . Toluene dispersion of leuco dye of the structural formula (1) (solid content 20%) 10 g Toluene dispersion of developer of the structural formula (2) (solid content of 20%) 15 g Toluene dispersion of aluminum hydroxide (solid) 30%) 10 g Fluorocarbon toluene dispersion (solid content 10%) 10 g Polymethyl methacrylate (M _w = about 50,000) toluene solution 15 g (solid content 20%)

Example 2 A thermosensitive recording medium of the present invention was obtained in the same manner as in Example 1 except that the developer of Example 1 was replaced with the developer of the structural formula (3).

Example 3 A thermosensitive recording medium of the present invention was obtained by sequentially laminating the following layers on a white synthetic paper having a thickness of 250 μm (Yupo FPG250 manufactured by Oji Yuka Synthetic Paper Co., Ltd.). (1) Thermosensitive coloring layer A paint having the following composition was applied and dried at 70 ° C. The dry coating amount was 4.1 g / m ² . Toluene dispersion of leuco dye of the structural formula (1) (solid content 20%) 10 g Toluene dispersion of developer of the structural formula (4) (solid content of 20%) 15 g Polymethylmethacrylate (M _w = about 5) Ten thousand) toluene solution 22g (solid content 20%)

(2) Protective layer A coating material having the following composition was applied and dried at 70 ° C. The dry coating amount was 2.3 g / m ² . Fluorocarbon toluene dispersion (solid content 10%) 5 g Polymethyl methacrylate (M _w = about 50,000) toluene solution 14 g (solid content 20%)

Comparative Example 1 A thermosensitive recording medium for comparison was obtained in the same manner as in Example 1 except that the leuco dye in the thermosensitive coloring layer of Example 1 was replaced with a leuco dye having the following structural formula.

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Comparative Example 2 The developer in the thermosensitive color developing layer of Example 1 was 4'-methyl-3,
A comparative thermosensitive recording medium was obtained in the same manner as in Example 1 except that 4-dihydroxyphenyl sulfone was used instead.

Comparative Example 3 A thermosensitive color developing layer coating material having the composition shown below was coated on a milky white polyethylene terephthalate film substrate having a thickness of 188 μm and dried at 70 ° C. to obtain a thermosensitive recording medium for comparison. . The dry coating amount was 6.9 g / m ² . Aqueous dispersion of leuco dye of the structural formula (1) (solid content 20%) 10 g Aqueous dispersion of developer of the structural formula (2) (solid content 20%) 15 g Aqueous dispersion of calcium carbonate (solid content) 40%) 10 g Aqueous dispersion of zinc stearate (solid content 20%) 5 g Aqueous solution of polyvinyl alcohol (solid content 20%) 15 g Regarding the thermal recording media prepared in Examples 1 to 3 and Comparative Examples 1 to 3 below. The properties shown in Table 1 were evaluated.

(1) Recording characteristics 0.45 W using a line dot type thin film thermal head
An image was recorded at an energy of (1.0 mj / dot), and the solid black portion was measured with a visual filter of a Macbeth densitometer.

(2) Heat resistance The recorded thermosensitive recording medium was allowed to stand in a dryer at a temperature of 80 ° C. for 24 hours, and then the Macbeth densities of a solid black portion and a background portion were measured. Next, the above-described recording characteristics were evaluated again on the background portion of the heat-sensitive recording medium left for 24 hours in a dryer, and the image density of the re-recorded portion was measured.

(3) Plasticizer resistance After recording, a plasticizer-containing plastic eraser is added to the recording surface.
After pressing under a pressure of kg / cm ² and leaving for 24 hours, the eraser was removed and the state of the recording surface was observed. ○ No change at all △ Transfer of recording to eraser, peeling of recording surface, and slight stains. C: Transfer of the recording to the eraser, peeling of the recording surface, stains, etc. are considerably observed.

(4) Acid resistance After recording, the sample was dipped in an acetic acid aqueous solution having a pH of 3 for 2 minutes, and the state of the recording surface was observed. ○ Decoloring of the recording portion, coloring of the background portion, scratches, and peeling are hardly observed. Δ Decolorization of the recorded area, color development of the background area, scratches, and peeling are slightly observed. C: Decoloring of the recording portion, coloring of the background portion, scratches, and peeling are considerably observed.

(5) Alkali resistance After recording, the sample was dipped in an aqueous sodium hydroxide solution having a pH of 12 for 2 minutes and the state of the recording surface was observed. Evaluation criteria are based on the above-mentioned acid resistance.

(6) Alcohol resistance After recording, the sample was dipped in a 50% aqueous solution of ethanol for 2 minutes and the state of the recording surface was observed. Evaluation criteria are based on the above-mentioned acid resistance.

(7) Water resistance After recording, the sample is dipped in water at 20 ° C. for 5 days and then rubbed with a nail to check the water resistance. Evaluation criteria are based on the above-mentioned acid resistance.

The results are shown in Table 1. As is evident from the results in Table 1, the heat-sensitive recording medium of the present invention is excellent in chemical resistance, water resistance and heat resistance, and has excellent recording characteristics in practical use as compared with the prior art. all right.

[0033]

[Table 1]

[0034]

As described above, the heat-sensitive recording medium of the present invention is remarkably excellent in chemical resistance, water resistance and heat resistance by using a specific leuco dye, a color developer and a binder in the heat-sensitive color forming layer. It has become possible to improve. As a result, the present invention can be sufficiently applied not only to recording media for facsimiles and printers but also to paper sheets, cards, labels and the like.

Claims (1)

(57) [Claims] To 1. A substrate, a leuco dye represented by the following structural formula (1), the following structure for the leuco dye is hot color
Thermosensitive coloring containing at least one developer selected from the compounds represented by the formulas (2) to (4) and a binder soluble in an aliphatic or aromatic hydrocarbon solvent as main components A thermal recording medium comprising a layer. Embedded image