JPH0280293A - Thermal transfer recording medium - Google Patents

Abstract

PURPOSE:To obtain a thermal transfer recording medium from which information cannot be read from a transfer recording medium by providing an intermediate layer which is normally colorless or light-colored, develops a color during thermal printing, has about the same degree of color tone and density as an ink layer and, furthermore, does not transfer data to a paper receiving side during printing, between a support and the ink layer. CONSTITUTION:An intermediate layer consists mainly of leuco due, color developer and binder which fixes the former two to a support. The leuco dye used is preferably the leuco compound of triphenyl methane dye. The typical example of the leuco dye is 3,3-bis(p-dimothylaminophenyl)-phthalide. The ideal type of color developer is at a melting point or softening point of 200 deg.C or less. For instance, phenols belong to this type. The typical example of phenol is 4-tert-butylphenol. The binder used is for instance, polyvinyl alcohol. The intermediate layer consists of a liquid containing the appropriate quantity of each component applied on the support by ordinary methods such as gravure coating and subject to subsequent drying.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a thermal transfer recording medium, and more specifically, to improving the confidentiality of printed information in a thermal transfer recording method. Sometimes, only the heated area develops color, resulting in a color tone and density comparable to that of the ink layer.Furthermore, by providing an intermediate layer that is not transferred to the receiving paper side during printing, the image information remaining on the sheet I after printing is difficult to decipher. It is.

[Prior Art] The thermal transfer recording method is popular as a plain paper recording method with a simple device, but since the ink layer is colored and the support is colorless or nearly colorless in most cases, thermal transfer recording after printing is difficult. By looking at the recording medium, it is possible to know the printed content, which poses a major security problem if the printed information is confidential.

In order to solve these zero problems, there is a method of heating the used part of the thermal transfer recording medium, melting the remaining ink, and erasing the printed image (JP-A-56-53085, JP-A-60-109).
898), a method of containing or coating a material with the same color as the ink on a support (JP-A-57-120497, JP-A-58-2)
No. 4477, No. 59-98898@), etc. have been proposed. However, the method of heating the used portion of the thermal transfer recording medium requires the provision of a heater, which complicates the apparatus, and also generates a large amount of heat, which is thought to cause safety problems. In the latter method, in which the support contains or coats a material with the same color as the ink, the image information remaining on the sheet may be difficult to copy with a copying machine or visually read, but it is transparent in the ink transfer marks and non-transfer areas. Because of the difference in density, it can be read by shining strong transmitted light or projected on an OHP, creating a problem in which confidentiality cannot be maintained.

[Problems to be Solved by the Invention] An object of the present invention is to provide a thermal transfer recording medium in which information cannot be read from the transfer recording medium after transfer.

[Means for Solving the Problems] According to the present invention, an ink layer is provided on an opaque support,
A feature is that an intermediate layer is provided between the support and the ink layer, which is usually colorless or light in color, develops color during heating printing, has the same color tone and density as the ink layer, and is not transferred to the receiving paper side during printing. A thermal transfer recording medium is provided.

As the support, relatively heat-resistant plastic films such as polyester, polycarbonate, triacetyl cellulose, nylon, polyind, etc., cellophane, parchment paper, condenser paper, etc. can be used. If necessary, the opposite side of the support from the ink layer, Alternatively, a heat-resistant protective layer made of silicone resin, fluororesin, polyimide resin, epoxy resin, phenol resin, melamine resin, nitrocellulose, etc. or a stick prevention layer such as wax may be provided on the metal thin film layer provided thereon. .

The thickness of the support is preferably 1 to 6 μm, but it may be 1 to 20 μm if it is treated to improve the usage conditions and heat transfer efficiency.
It can be used up to a range of thickness.

The main components of the ink seed are a heat-fusible substance and a colorant, and the heat-fusible substance can be any material used in ordinary thermal transfer inks. For example, whale wax, beeswax, carnauba wax, candelilla wax, lanolin, montan wax,
Natural wax such as montan wax, paraffin wax,
Petroleum wax such as microcrystalline wax, ester wax, synthetic wax such as low molecular weight polyethylene, various modified waxes, hydrogenated wax, long chain fatty acids, etc.
Also polyethylene, polyethylene oxide, polypropylene, terpene resin, ketone resin, ethylene/vinyl acetate copolymer, ethylene/acrylic copolymer, acrylic resin,
Polyester resin, Coumaron resin, rosin and its derivatives, polyamide resin, epoxy resin, polyvinyl chloride, polyurethane resin, polystyrene resin, phenolic resin,
Examples include cellulose resin.

As the coloring agent, various inorganic and organic dyes, colored dyes, sublimation dyes, etc. can be used, but carbon black is particularly effective for creating high-density images.

In addition, the ink layer contains animal and vegetable oils, mineral oils, liquid paraffin, carbonate esters, phthalate esters, higher fatty acids,
Oils such as higher alcohols, plasticizers, surfactants, etc., or additives such as dispersants, penetrants, adhesion modifiers, fluidity control agents, etc. may be added as necessary.

The proportion of each material is based on the multilayer basis: waxes 20-90%, binder resin O-50%, additives O-30z1, colorants 5-5
0% is appropriate. The thickness of the ink layer is 2 to 20 μm,
More preferably, it is 3 to 10 μm. If it is thinner than 2 μm, image density cannot be ensured, and if it exceeds 20 μm, transferability deteriorates.

This ink layer may be formed by applying a solution prepared by dissolving or dispersing the above materials in water or an organic solvent, or by a hot melt method. However, when coating the ink layer, it is necessary to adjust the drying conditions, coating temperature, etc. so that the intermediate layer described below does not develop color. Water-based coating is optimal in this respect. The intermediate layer, which is a feature of the present invention, mainly consists of a leuco dye, a color developer, and a binder that fixes them to a support.

As a leuco dye, 1. All the materials traditionally used for pressure-sensitive paper and thermal paper can be used, and leuco compounds of dyes such as triphenylmethane, fluoran, phenothiazine, auramine, spiropyran, and indolinophthalide can be used. Favorably operated. Specific examples of these leuco dyes are shown below.

3.3-bis(p-dimethylaminophenyl)-phthalide, 3.3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (also known as crystal violet lactone), 3.3-bis(p- dimethylaminophenyl)-6-diethylaminophenyl, 3.3-bis(p-dimethylaminophenyl)-6-chlorophthalide, 3.3-bis(p-dibutylaminophenyl)phthalide, 3-cyclohexylamino-6-chlor Fluorane, 3
-dimethylamino-5,7-dimethylfluorane, 3-
Diethylamino-7-chlorofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-
1,8-benzfluorane, 3-diethylamino-6-
Methyl-7-chlorofluorane, 3-(N-1)-tolyl-N-ethylamino)-6-
Methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 2-[N-(3°-trifluoromethylphenyl)amino 1-6-dinithylaminofluorane, 2 -(3,6-
Bis(diethylamino)-9-(0-chloroanilino)
xantylbenzoic acid lactam), 3-diethylamino-
6-Methyl-7-(m-trichloromethylanilino)fluoran, 3-diethylamino-7-(O-chloroanilino)fluoran, 3-dibutylamino-7-(O-taruroanilino)fluoran, 3-N-methy, fluorane N-amylamino-6-methyl-7
-anilinofluorane, 3-tomethyl-N-cyclohexylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-(N,N-diethylamino )-5-methyl-7-(
N.

N-dibenzylamino) fluorane, benzoylleucomethylene blue 6°-chloro-8°-methoxy-benzoindolinobilillospirane, 6°-bromo-3°-methoxy-benzoindolinobilillosvirane, 3-(2°-hydroxy -4-dimethylaminophenyl)-3-(2-methoxy-5'-chlorophenyl)phthalide, 3-(2°-hydroxy-4-dimethylaminophenyl)-3-(2°-methoxy-5°-nitro phenyl)phthalide, 3-(2°-hydroxy-4°-diethylaminophenyl)-3-(2°-methoxy-5′-methylphenyl)
Phthalide, 3-(2°-methoxy-4°-dimethylaminophenyl)-3-(2°-hydroxy-4°-chloro-5°-methylphenyl)phthalide.

As the color developer, one having a melting point or softening point of 200°C or less, preferably about 50 to 150°C is used. Examples include phenols, naphthols, organic acids or their salts or esters. A specific example is shown below.

[Color developer] (The number in parentheses indicates the melting point.) 4-t
ert-butylphenol (98), 4-hydroxydiphenyl ether (84), 1-naphthol (98),
2-naphthol (121), methyl-4-hydroxybenzoate (131), 4-human Oxyacetophenone (109), 2,2°-dihydroxydiphenyl ether (79), 4-phenylphenol (166)
, 4-tert-octylcatechol (109),
2,2°-dihydroxydiphenyl (103), 4.
4'-methylenebisphenol (160), 2,2°
-methylenebis(4-chlorophenol (164) 1
．． 2.2-methylenebis(4-methyl-6-tert-
Butylphenol (125), 4.4-isopropylidene diphenol (156), 4.4'-isopropylidene bis(2-chlorophenol) (90), 4,
4°-isopropylidene bis(2,5-dibromophenol (172), 4,4°-isopropylidene bis(
2-tert-butylphenol) (110), 4
, 4°-isopropylidene bis(2-methylphenol> (136), 4,4°-isopropylidene bis(
2,5-dimethylphenol) (168), 4,4°
-5ec-butylidene diphenol (119), 4.
4'-5eC-butylidene bis(2-methy/L/phenol) (142), 4.4'-cyclohexylidene diphenol (180), 4.4-cyclohexylidene bis(2-methylphenol) (184), Salicylic acid (163), salicylic acid methalyl ester (7
4), salicylic acid phenacyl ester (110), 4
-Hydroxybenzoic acid methyl ester (131), 4
-Hydroxybenzoic acid ethyl ester (116), 4
-Hydroxybenzoic acid propyl ester (98), 4-
Hydroxybenzoic acid inpropyl ester (86), 4
-Hydroxybenzoic acid butyl ester (71), 4-hydroxybenzoic acid isoamyl ester (50), 4-hydroxybenzoic acid phenyl ester (178), 4-
Hydroxybenzoic acid benzyl ester (111), 4
-Hydroxybenzoic acid cyclohexyl ester (119
), 5-hydroxysalicylic acid (200), 5-chlorsalicylic acid II (172), 3-chlorsalicylic acid (178), thiosalicylic acid (164), 2-chloro-5-nitrobenzoic acid 1 (165), 4-methoxy Phenol (53), 2-hydroxybenzyl alcohol (87), 2.5-dimethylphenol (75), benzoic acid (122), orthotolyl Wi (107),
metatolyl 1 (111), paratolylic acid (181)
), orthochlorobenzoic acid (142), metaoxybenzoic acid (200), 2゜4-dioxyacetophenone (97), resorcinol monobenzonate (
135), 4-hydroxybenzophenone (133)
, 2. a-dihydroxybenzophenone (144)
, 2-naphthoic acid (184), 1-hydroxy-2-naphthoic acid (195),
3.4-dihydroxybenzoic acid ethyl ester (128
), 3,4-dihydroxybenzoic acid phenyl ester (189), 4-hydroxypropiophenone (1
50), salicyl salicylate (14B), phthalic acid monobenzyl ester (107).

The color developer used in the present invention is generally 1 to 10 parts by weight, preferably 2 to 6 parts by weight, per 1 part by weight of the leuco dye.
Used in parts by weight.

In the present invention, in order to bind and support the leuco dye and color developer on the support, various conventional binders can be used as appropriate, and water-soluble or water-dispersible binders are preferred. Specific examples of this binder include the following.

Polyvinyl alcohol, starch and its derivatives, cellulose derivatives such as methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, sodium polyacrylate,
Polyvinylpyrrolidone, acrylic amide/acrylic ester copolymer, acrylic amide/acrylic ester/methacrylic acid ternary copolymer, styrene/maleic anhydride copolymer alkali salt, isobutylene/maleic anhydride copolymer alkali In addition to water-soluble polymers such as salt, polyacrylamide, sodium alginate, gelatin, and casein, polyvinyl acetate, polyurethane, styrene/butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride/vinyl acetate copolymer , polybutyl methacrylate, ethylene/vinyl acetate copolymer, styrene/
Butadiene/acrylic copolymer, etc.

The intermediate layer is produced by applying a liquid containing appropriate amounts of the above-mentioned components onto a support by conventional means such as gravure coating or wire bar coating, and drying. At this time, additives such as surfactants may be added to improve coatability on the support. Further, a primer layer may be provided in advance to improve adhesion to the support.

It is also possible to add an inorganic pigment having an appropriate particle size to this intermediate layer to form irregularities on the surface of the intermediate layer, thereby giving it the effect of a matte layer. This makes the surface of the image printed on the transfer paper uneven, making it possible to form an image that is less glossy and easier to read.

Inorganic pigments that can be used include silica, talc, calcium carbonate, magnesium carbonate, barium sulfate, alumina,
Examples include tin oxide and titanium white.

The thickness of the intermediate layer is 0.2 to 10 μm, more preferably 0.2 μm to 10 μm.
．． It is 5 to 6 μm. If it is thinner than 0.2 μm, it will not be possible to obtain the density necessary to make it difficult to read the print marks, and if it exceeds 10 μm, it will adversely affect the transferability of the ink layer.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples. Note that the amounts (parts) of each component described in the Examples are parts by weight.

Example 1 A heat-resistant anti-stick layer was provided on one side of a polyester film having a thickness of 4.5 μm, and an intermediate layer was provided on the opposite side by the following method.

[Liquid A] 3-(N-methyl-N-cyclohexyl)amino-6-
Methyl-7-anilite fluorane 200 parts Hydroxyethylcellulose wt% aqueous solution 50 parts Water
30
Part [Liquid B] Benzyl p-hydroxybenzoate 30 parts Silica 20 parts Polyvinyl alcohol 10 wt% aqueous solution 50 parts Liquid A, B
After each liquid was dispersed in a ball mill for 48 hours, they were mixed uniformly at a ratio of [Liquid A]: [Liquid B] = 1:3, stirred uniformly, and coated so that the dry coating weight was 4 CI/m, and dried to form an intermediate layer. did.

[Liquid C] Carbon black 2 parts Acrylic resin 2 parts Carnauba wax 14.5 parts Polyvinyl alcohol 1 part Nonionic surfactant
0.5 part water
After dispersing 80 parts of liquid C in a ball mill for 72 hours, it was coated on the intermediate layer to a coating weight of 3.5 a/m and dried to provide an ink plate. A thermal transfer recording medium was thus obtained.

Example 2 A thermal transfer recording medium was obtained in the same manner as in Example 1 except that benzyl p-hydroxybenzoate in Solution B 1 was replaced with bisphenol A.

Example 3 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilite fluorane in [Liquid A] of Example 2 was replaced with 3,3-bis(dimethylaminophenyl)-phthalide. A thermal transfer recording medium was obtained in the same manner as in Example 2 except for the above.

Comparative Example 1 A thermal transfer recording medium was produced in the same manner as in Example 1 except that 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilite fluorane in [Liquid A] of Example 1 was removed. (qta.

Comparative Example 2 Thermal transfer was carried out in the same manner as in Example 1 except that 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilite fluorane in [Liquid A] of Example 1 was replaced with carbon black. Obtained a recording medium.

Comparative Example 3 A thermal transfer recording medium was obtained in the same manner as in Example 1 except that the intermediate layer in Example 1 was removed.

A commercially available thermal transfer line printer (applied energy: 1.0IIIJ) was used to print plain paper (Beck smoothness: 20) using the thermal transfer recording media prepared in the above examples and comparative examples.
0sec). The used portion of the thermal transfer recording medium used at that time was evaluated as follows.

Copy 2: Copied from the ink side using a commercially available plain paper copying machine.

O: Image information remaining on the thermal transfer recording medium after printing is not copied.

X: The image information remaining on the thermal transfer recording medium after printing is copied and is legible.

Projection: Projected onto a white wall using a commercially available OHP.

0... Image information remaining on the thermal transfer recording medium after printing is 011
Due to P, it is not projected onto the wall and is unreadable.

Δ... Image information is vaguely projected onto the wall by OHP and is legible.

X: Image information is clearly projected on the wall by OHP and can be easily read.

The results are shown in Cloth 1 below.

¥R1 Next, the cross sections of the thermal transfer recording media before and after printing in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Figure 1 (a), (b) (Examples 1 to 3), and Figure 2 ( a), (b) (Comparative Example 1.3) and FIG. 3(a), (b) (Comparative Example 2).

[Effects of the Invention] As explained above, when the thermal transfer recording medium of the present invention is used in the thermal transfer recording method, the confidentiality of printed information is improved.

[Brief explanation of the drawing]

Figures 1(a) and (b) are cross-sectional views of the thermal transfer recording medium before and after printing in Example 1.2.3, with Figure 1(a) being before printing and Figure 1(b) being after printing. Indicates the status of FIGS. 2(a) and 2(b) are cross-sectional views of the thermal transfer recording medium before and after printing in Comparative Example 1.3, with FIG. 2(a) showing the state before printing and FIG. 2(b) showing the state after printing. shows. FIGS. 3(a) and 3(b) are cross-sectional views of the thermal transfer recording medium before and after printing in Comparative Example 2, with FIG. 3(a) showing the state before printing and FIG. 3(b) showing the state after printing. . In addition, in FIGS. 1 to 3, the hatched portions are shown as black, and the other portions are shown as white or transparent. DESCRIPTION OF SYMBOLS 1... Ink layer, 2... Intermediate layer, 3... Support, 4... Transfer part, 5... Coloring part, 11...
- Ink layer, 21... Intermediate layer, 31... Support, 41... Transfer portion.

Claims (1)

[Claims] It has an ink layer on an opaque support, and the space between the support and the ink layer is usually colorless or light-colored, and it develops color during heating printing to have the same color tone and density as the ink layer. A thermal transfer recording medium characterized by having a non-transferable intermediate layer provided on the side.