JPH0122158B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a thermal recording medium, and more particularly to a thermal recording medium that has excellent printing stability and is suitable for high-speed recording. Conventionally, heat-sensitive recording materials that utilize a coloring reaction between a coloring agent and a coloring agent that develops color upon contact with the coloring agent, and obtain a colored image by bringing the two coloring materials into contact with each other using heat, are often used. Are known. Such thermosensitive recording media are relatively inexpensive, the recording equipment is compact, and maintenance is relatively easy, so they are used not only as recording media for facsimile machines and various computers, but also in a wide range of fields. However, such heat-sensitive recording materials generally have poor water resistance, oil resistance, organic solvent resistance, and plasticizer resistance. There is a drawback that the print density will drop significantly if these objects come into contact with the printer. Further, there are drawbacks in that if the heat-sensitive recording layer is touched with a hand during handling, fingerprint-like fogging may occur, and even a slight touch may cause unnecessary color development. Furthermore, there is also a drawback that the printed colored area becomes white and powdery due to crystallization of the coloring agent or the coloring agent. As a method to overcome these drawbacks, a method is proposed in which an aqueous emulsion of a resin having film-forming ability and chemical resistance is coated on the heat-sensitive recording layer (Japanese Patent Laid-Open Publication No.
54-128347), a method of applying a water-soluble polymer compound such as polyvinyl alcohol (Utility Model 56-
125354) etc. have been proposed. However, new drawbacks accompany the improvements, and at present, satisfactory results are not necessarily obtained. That is, in a heat-sensitive recording material provided with such a protective layer, the protective layer acts as a heat transfer inhibiting layer during recording, so the dynamic sensitivity of the heat-sensitive recording layer is reduced, and a clear recorded image can be obtained in the case of low-speed recording. Of course,
This method is not suitable for high-speed recording and results in unclear recorded images. In view of the current situation, the present inventors aimed to obtain a heat-sensitive recording material that has sufficient high-speed recording suitability even if a protective layer is provided on the heat-sensitive recording layer, and has excellent printing stability. As a result of extensive research into the composition of the protective layer provided in The present inventors have discovered that a thermosensitive recording material having the following properties can be obtained, and have achieved the present invention. The present invention provides a color forming agent and/or a 2,2'-methylene bis(4
-ethyl-6-tert-butylphenol), 2,
2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-butylidenebis(6-
tert-butyl-3-methylphenol), 1,1,
3-tris(2-methyl-4-hydroxy-5-
tert-butylphenyl)butane, terphenyl,
At least one sensitizer selected from isophthalic acid dibenzyl ester, p-benzyloxybenzoic acid benzyl ester, α-naphthyl benzyl ether, β-naphthyl benzyl ether, and 1-hydroxy-2-naphthoic acid phenyl ester.
This is a heat-sensitive recording material characterized by being provided with a protective layer containing 0.1 to 25% by weight. In the present invention, there are no particular limitations on the combination of the coloring agent and the coloring agent contained in the recording layer, and any combination that causes a coloring reaction when the two come into contact with each other due to heat can be used. Examples include combinations of colorless or light-colored basic dyes and inorganic or organic acidic substances, and combinations of higher fatty acid metal salts such as ferric stearate and phenols such as gallic acid. Furthermore, it is also possible to apply the present invention to various heat-sensitive recording materials that obtain a developed color image (recorded image) by heat, such as a heat-sensitive recording material that combines a diazonium compound, a coupler, and a basic substance. These recording bodies are also included. However, the specific protective layer of the present invention provided on the recording layer is particularly effective in improving print storage stability when applied to a combination of a basic dye and an acidic substance, and is therefore particularly preferably used for such a combination. Various types of colorless to light-colored basic dyes are known, and examples include the following. 3,3-bis(p-dimethylaminophenyl)
-6-dimethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)phthalide, 3-
(p-dimethylaminophenyl)-3-(1,2-
dimethylindol-3-yl)phthalide, 3-
(p-dimethylaminophenyl)-3-(2-methylindol-3-yl)phthalide, 3,3-bis(1,2-dimethylindol-3-yl)-
5-dimethylaminophthalide, 3,3-bis(1,2-dimethylindol-3-yl)-6-
Dimethylaminophthalide, 3,3-bis(9-ethylcarbazol-3-yl)-6-dimethylaminophthalide, 3,3-bis(2-phenylindol-3-yl)-6-dimethylaminophthalide 3-p-dimethylaminophenyl-3-(1
triallylmethane dyes such as -methylpyrrol-3-yl)-6-dimethylaminophthalide, 4,
Diphenylmethane dyes such as 4'-bis-dimethylaminobenzhydryl benzyl ether, N-halophenyl-leucoauramine, N-2,4,5-trichlorophenylleucoauramine, benzoylleucomethylene blue, p-nitrobenzoylleuco Thiazine dyes such as methylene blue, 3
-Methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methyl-naphtho(6'-methoxybenzo)spiropyran, 3-propyl-spiro - Spiro dyes such as dibenzopyran, lactam dyes such as rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o-chloroanilino) lactam, 3-dimethylamino-7-methoxyfluoran, 3 -diethylamino-6-methoxyfluorane, 3-diethylamino-7-methoxyfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,7 -dimethylfluorane, 3-(N-ethyl-p-toluidino)-7
-Methylfluorane, 3-diethylamino-7-
N-acetyl-N-methylaminofluorane, 3
-diethylamino-7-N-methylaminofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-N-methyl-N-benzylaminofluorane, 3-diethylamino-7-N-chloroethyl -N-methylaminofluorane, 3-diethylamino-7-N
-diethylaminofluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-phenylaminofluorane, 3-(N-ethyl-p-toluidino)-6-methyl-7-(p- toluidino)fluoran, 3-diethylamino-6-methyl-7
-phenylaminofluorane, 3-diethylamino-7-(2-carbomethoxy-phenylamino)
Fluoran, 3-(N-ethyl-N-iso-amylamino)-6-methyl-7-phenylaminofluoran, 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylamino Fluoran, 3-pyrrolidino-6-methyl-7-phenylaminofluoran, 3-piperidino-6-methyl-7-phenylaminofluoran, 3-diethylamino-6-methyl-7-xylidinofluoran, 3-diethylamino-7-(o-chlorophenylamino)fluoran, 3-dibutylamino-7-(o-chlorophenylamino)fluoran,
Fluoran dyes such as 3-pyrrolidino-6-methyl-7-p-butylphenylaminofluoran. Various types of acidic substances are also known that change color when they come into contact with basic colorless dyes, such as the following. 4-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4-hydroxyacetophenol, 4-tert
-Octylcatechol, 2,2'-dihydroxydiphenol, 2,2'-methylenebis(4-methyl-6-tert-isobutylphenol), 4,4'-isopropylidenebis(2-tert-butylphenol), 4 , 4'-sec-butylidene diphenol, 4
-Phenylphenol, 4,4'-isopropylidenediphenol (bisphenol A), 2,2'-
Methylenebis(4-chlorophenol), hydroquinone, 4,4'-cyclohexylidene diphenol, 4,4'-thiobis(6-tert-butyl-3
-methylphenol), 4,4'-dihydroxydiphenylsulfone, 4-hydroxybenzoic acid benzyl ester, 4-hydroxyphthalic acid dimethyl ester, hydroquinone monobenzyl ether, novolak type phenolic resin, phenolic polymer, etc. , benzoic acid, p-
tert-butylbenzoic acid, trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid, salicylic acid, 3 -isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3-chloro-5-(α-methylbenzyl)
Aromatic carboxylic acids such as salicylic acid, 3,5-di-tert-butylsalicylic acid, 3-phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3,5-di-α-methylbenzylsalicylic acid, and polyesters thereof. valence metal salts, etc. In the heat-sensitive recording material of the present invention, the ratio of the color former and color former in the recording layer is appropriately selected depending on the type of color former and color former used, and is not particularly limited. For example, when using a basic colorless dye and an acidic substance, generally 1 to 50 parts by weight, preferably 2 parts by weight, per 1 part by weight of the basic colorless dye.
~10 parts by weight of acidic substance are used. To prepare a coating solution containing these substances, generally water is used as a dispersion medium and a ball mill, attritor,
A coating liquid is prepared by dispersing the coloring agent and the coloring agent together or separately using a stirring or pulverizing machine such as a sand grinder. Such coating liquids usually contain starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene/maleic anhydride copolymer salt, styrene/maleic anhydride copolymer as binders. Salt, ethylene/acrylic acid copolymer salt, styrene/acrylic acid copolymer salt, styrene/butadiene copolymer emulsion, etc. have a total solid content of 10
It is used in an amount of from 70% by weight, preferably from 15 to 50% by weight. Furthermore, various auxiliary agents can be added to the coating liquid. For example, sodium dioctylsulfosuccinate, sodium dotesylbenzenesulfonate,
Examples include dispersants such as lauryl alcohol sulfate/sodium salt and fatty acid metal salts, ultraviolet absorbers such as benzophenone and triazole, antifoaming agents, fluorescent dyes, and coloring dyes. In addition, waxes such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, kaolin, clay, talc,
Inorganic pigments such as calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, particulate anhydrous silica, activated clay, stearic acid amide, stearic acid methylene bisamide, oleic acid amide, palmitic acid amide, matcha oleic acid amide, coconut fatty acid amide, Sensitizers such as hindered phenols can also be added. In the heat-sensitive recording material of the present invention, there are no particular limitations on the method of forming the recording layer, and the recording layer can be formed according to conventionally well-known techniques, such as air knife coating, blade coating, etc. It is formed by applying and drying. The amount of coating liquid to be applied is also not particularly limited, but it is usually 2 to 12 g/m ² in terms of dry weight, preferably 3 to 10 g/m ²
is within the range of As described above, the heat-sensitive recording material of the present invention has an important feature in that a protective layer containing a specific amount of at least one selected from a coloring agent and a specific sensitizer is provided on the thus formed recording layer. However, as the coloring agent contained in the protective layer, various known coloring agents contained in the recording layer as described above can be used, and organic acidic substances are most preferably used. Various substances are known as sensitizers, such as 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), -butylphenol), 4,4'-butylidenebis(6-tert-butyl-3-methylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, etc. Dophenol compound, terphenyl, isophthalic acid dibenzyl ester, p-benzyloxybenzoic acid benzyl ester, α-naphthylbenzyl ether, β-naphthylbenzyl ether, 1-hydroxy-2-
Naphthoic acid phenyl ester and the like are particularly excellent in achieving the desired effects of the present invention, and are therefore used. However, stearic acid amide, stearic acid methylene bisamide, oleic acid amide, palmitic acid amide, matcha oleic acid amide, coconut fatty acid amide, which are generally known as sensitizers,
Amides such as methylolamide can be added to the protective layer to improve the dynamic sensitivity of the recording medium, but since they are accompanied by defects that cause uneven gloss in recorded images during recording, they are not protected by the present invention. It is excluded from the sensitizers added into the layer. In the present invention, the effect of improving dynamic sensitivity can be obtained when the amount of at least one substance selected from color formers and sensitizers contained in the protective layer is less than 0.1% by weight of the protective layer. On the contrary,
If it exceeds 25% by weight, fingerprint resistance and alcohol resistance will decrease. Accordingly, such substances should be contained in the protective layer in an amount of 0.1 to 25% by weight, more preferably 0.5 to 15%, and most preferably 2.5 to 10% by weight. Thus, the protective layer of the present invention containing at least one substance selected from a coloring agent and a sensitizer in a specific proportion is mainly composed of water-soluble polymers such as polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, and acetoacetyl group. It is formed from modified polyvinyl alcohol, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, starch and its derivatives, casein, sodium alginate, polyvinylpyrrolidone, polyacrylamide, styrene-maleic acid copolymer salt, and the like. Incidentally, a pigment may be added to the above-mentioned specific protective layer in the present invention, if necessary, in order to improve the printability and staking of the protective layer. Specific examples of such pigments include inorganic pigments such as calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, zinc sulfate, talc, kaolin, clay, calcined clay, colloidal silica, and styrene. Micro balls, nylon powder, polyethylene powder urea/formalin resin filler,
Examples include organic pigments such as raw starch granules. The amount used is generally desirably in the range of 5 to 500 parts by weight per 100 parts by weight of the resin component. Furthermore, in the coating liquid, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, and surfactants (dispersants, wetting agents, etc.) such as sodium dioctyl sulfosuccinate are added as necessary. ), various auxiliary agents such as antifoaming agents can also be added as appropriate. In the present invention, the coating liquid forming the protective layer is generally prepared as an aqueous coating liquid, and if necessary, after being thoroughly mixed and dispersed using a mixing/stirring machine such as a mixer, attritor, ball mill, or roll mill, It is applied onto the heat-sensitive recording layer using a known coating device. The coating amount of the protective layer coating liquid is not particularly limited, but if it is less than 0.1 g/m ² , the desired effect of the present invention cannot be sufficiently obtained, and if it is less than 20 g/m ²
In general, the dry weight is 0.1 to 20.
g/m ² , preferably within the range of 0.5 to 10 g/m ² . Thus, in the present invention, by providing a specific protective layer containing at least one kind of substance selected from a coloring agent and a sensitizer on the heat-sensitive recording layer, excellent print storage stability and high-speed recording suitability can be achieved. A thermosensitive recording material having the following properties can be obtained. In addition, it is also possible to further improve the storage stability by providing a protective layer on the back side of the heat-sensitive recording material, if necessary. Furthermore, various known techniques in the field of heat-sensitive recording material production may be added as necessary, such as providing an undercoat layer on the support, applying an adhesive treatment to the back surface of the recording material, and processing it into an adhesive label. The present invention will be described in more detail with reference to Examples below, but it is of course not limited thereto. Note that parts and % in the examples indicate parts by weight and % by weight, respectively, unless otherwise specified. Example 1 Preparation of liquid A 3-(N-cyclohexyl-N-methylamino)
-6-methyl-7-phenylaminofluorane
10 parts Methyl cellulose 5% aqueous solution 5 parts Water 40 parts This composition was ground with a sand grinder to an average particle size of 3 μm. Preparation of Solution B 20 parts of 4-hydroxybenzoic acid benzyl ester 5% methylcellulose aqueous solution 5 parts Water 55 parts This composition was ground with a sand grinder to an average particle size of 3 μm. Formation of recording layer: 55 parts of liquid A, 80 parts of liquid B, silicon oxide pigment (oil absorption
180ml/100g) 15 parts, 20% oxidized starch aqueous solution 50
1 part and 20 parts of water were mixed and stirred to prepare a coating liquid. The obtained coating liquid was applied to base paper of 50 g/m ² with a coating weight of 7 after drying.
A heat-sensitive recording paper was obtained by coating and drying to give a coating weight of g/m ² . Preparation of Solution C: 1-Hydroxy-2-naphthoic acid phenyl ester 20 parts Methyl cellulose 5% aqueous solution 5 parts Water 55 parts This composition was ground with a sand grinder to an average particle size of 3 μm. Formation of Protective Layer 12 parts of Liquid C, 400 parts of 15% oxidized starch aqueous solution, 37 parts of kaolin, and 222 parts of water were mixed and stirred to prepare a coating solution.
The obtained coating liquid was applied onto the recording layer of the heat-sensitive recording paper,
A protective layer was formed by coating and drying so that the coating amount after drying was 3 g/m ² . Example 2 A thermosensitive recording paper having a protective layer was obtained in the same manner as in Example 1 except that a coating liquid having the following composition was used for forming the protective layer. Preparation of Solution D 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane 10 parts 4,4'-cyclohexylidene diphenol 10 parts Methylcellulose 5% aqueous solution 5 parts Water 55 parts The composition was ground to an average particle size of 3 μm using a sand grinder. Preparation of protective layer forming coating liquid 20 parts of Solution D, 400 parts of 15% oxidized starch aqueous solution, 35 parts of kaolin, and 216 parts of water were mixed and stirred to prepare a protective layer forming coating liquid. Example 3 A thermosensitive recording paper having a protective layer was obtained in the same manner as in Example 1 except that a coating liquid having the following composition was used for forming the protective layer. Preparation of Liquid E 4-hydroxyphthalic acid dimethyl ester 10 parts 4,4'-cyclohexylidene diphenol 10 parts Methyl cellulose 5% aqueous solution 5 parts Water 55 parts This composition was ground with a sand grinder to an average particle size of 3 μm. Preparation of protective layer forming coating liquid 40 parts of Liquid E, 400 parts of 15% oxidized starch aqueous solution, 30 parts of kaolin, and 202 parts of water were mixed and stirred to prepare a protective layer forming coating liquid. Example 4 A thermosensitive recording paper having a protective layer was obtained in the same manner as in Example 1 except that a coating liquid having the following composition was used for forming the protective layer. Preparation of Solution F 4,4'-thiobis(6-tert-butyl-3-methylphenol) 20 parts Methylcellulose 5% aqueous solution 5 parts Water 55 parts This composition was ground to an average particle size of 3 μm using a sand grinder. Preparation of protective layer forming coating liquid 40 parts of Solution F, 400 parts of 15% oxidized starch aqueous solution, 30 parts of kaolin, and 202 parts of water were mixed and stirred to prepare a protective layer forming coating liquid. Example 5 A thermosensitive recording paper having a protective layer was obtained in the same manner as in Example 1 except that a coating liquid having the following composition was used for forming the protective layer. Preparation of protective layer forming coating liquid 80 parts of the above liquid F, 40 parts of 15% oxidized starch aqueous solution, 20 parts of kaolin, and 172 parts of water were mixed and stirred to prepare a protective layer forming coating liquid. Comparative Example 1 In Example 1, no protective layer was provided. Comparative Example 2 A thermosensitive recording paper having a protective layer was obtained in the same manner as in Example 1 except that a coating liquid having the following composition was used for forming the protective layer. Preparation of protective layer forming coating solution 120 parts of the above solution F, 400 parts of 15% oxidized starch aqueous solution,
10 parts of kaolin and 142 parts of water were mixed and stirred to obtain a protective layer forming coating liquid. Comparative Example 3 A thermosensitive recording paper having a protective layer was obtained in the same manner as in Example 1 except that a coating liquid having the following composition was used for forming the protective layer. Preparation of protective layer forming coating solution: 400 parts of 15% oxidized starch aqueous solution, 40 parts of kaolin,
281 parts of water was mixed and stirred to obtain a protective layer forming coating solution. The eight types of thermosensitive recording paper thus obtained were evaluated for dynamic color development, fingerprint resistance, diazo resistance, and ethanol resistance, and the results are shown in Table 1.
The evaluation method is as follows. [Dynamic color development] High-speed thermal facsimile (manufactured by Hitachi, Hitachi
HIFAX-700), and the printed color density was measured using a Macbeth densitometer (manufactured by Macbeth, Model RD-100R). [Fingerprint resistance] Thermal gradient tester (manufactured by Toyo Seiki Co., Ltd., conditions: 120℃,
2 Kg/cm ² for 10 seconds), a fingerprint was pressed onto the printed area, and the degree of decolorization of the print was evaluated after 2 days. [Diazo resistance] Using a diazo copying machine (Ricoh Co., Ltd., Ricopy Super Dry 100), photosensitive paper (Ricopy SDF)
A developing solution was applied to the paper, and the coated surface was placed on the recording surface of a heat-sensitive recording paper (pressing pressure: 5 g/cm ² ), and the degree of color development of the white background portion after 1 hour was evaluated. [Ethanol resistance] Several drops of ethanol were placed on the white area of the recording surface of the thermosensitive recording paper, and after 30 minutes, the degree of color development in that area was evaluated.

【table】

【table】

[Table] As is clear from the results in Table 1, the heat-sensitive recording material according to the present invention has excellent dynamic color development, is suitable for high-speed recording, and has extremely excellent print storage properties. It was hot.

Claims (1)

[Claims] 1. A color former and/or 2,2'-methylenebis(4-ethyl-
6-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-butylidenebis(6-tert-butyl-3-methylphenol), 1,1, 3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, terphenyl, isophthalic acid dibenzyl ester, p-benzyloxybenzoic acid benzyl ester, α-naphthylbenzyl ether, β-naphthylbenzyl ether, 1 A heat-sensitive recording material comprising a protective layer containing 0.1 to 25% by weight of at least one sensitizer selected from -hydroxy-2-naphthoic acid phenyl ester.