JP3409449B2 - Thermal recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording medium, and more particularly, to a colorless or slightly pale leuco dye and a developer for causing the leuco occupation to develop color when heated. The present invention relates to an improved heat-sensitive recording medium provided with a heat-sensitive color developing layer, and particularly to an excellent heat-sensitive recording medium having high coloring sensitivity (thermal response) and little background fogging during storage under high temperature or high temperature and high humidity. 2. Description of the Related Art A thermosensitive recording system using a colorless or slightly pale leuco dye and a developer which causes the leuco dye to develop color when heated is generally unnecessary in a developing step, and maintenance of hardware is easy. Since it has certain features, it is widely used for facsimile, scientific measuring instruments, CD / ATM, POS label recording, and the like. Recently, with the remarkable progress of the thermal recording system,
High-speed printing is possible for thermal facsimile and printer,
In a thermal facsimile, an A4 standard document is recorded in 10 seconds or less, and a high-speed printer of 100 mm / sec is also manufactured in the printer field. As described above, with the increase in speed in the hardware field, there is a demand for a heat-sensitive recording medium to be used which is excellent in high-speed recording suitability. Conventionally, as a means for improving the color sensitivity of a thermosensitive recording medium, a thermofusible substance having a melting point lower than that of a leuco dye or a developer has been added as a sensitizer to a thermosensitive recording layer.
It is widely known that a sensitizer is melted by heat from a thermal head to lower a color development start temperature by melting a leuco dye or a developer (JP-A-57-8957).
994, JP-A-58-98285, JP-A-58-8
No. 7094, JP-A-60-56588, JP-A-2-7
No. 23, JP-A-2-239975, etc.). [0005] As disclosed above, the aim of improving the sensitivity of a thermosensitive recording medium is to develop a sensitizer having excellent thermal response. Yes, as the melting point of the sensitizer decreases, the thermal responsiveness improves, but it may cause background fogging during high-temperature storage and high-temperature and high-humidity storage. In the development of such a sensitizer, no satisfactory sensitizer has been obtained yet in terms of characteristics such as color sensitivity and color density. Further, as a method of improving thermal responsiveness and dispersibility by dispersion, carboxy-modified PVA is used in JP-A-59-159394, and JP-A-4-182.
No. 189, oxyalkylene group-containing PVA was used as a dispersant, and JP-A-1-225588 disclosed a sulfonate-containing P having an average degree of polymerization of 500 or less.
A method in which VA and a solid surfactant at room temperature are used in combination is disclosed. However, the desired sensitivity cannot be obtained in any case, and in the latter case, by using a surfactant,
There is an adverse effect that the discoloration of the printed portion of the obtained thermosensitive recording medium becomes large, and the background fog becomes further large. JP-A-4-105989 discloses a method in which dibenzyl oxalate, which is a specific sensitizer, is finely pulverized with a styrene maleic acid copolymer salt. The purpose is to suppress hydrolysis during dispersion of the ester. Further, Japanese Patent Application Laid-Open No. 3-128280 discloses that at least two or more of styrene maleic acid monoester copolymer salt, sulfosuccinate salt and methylcellulose are used in combination, but that sulfosuccinate salt is used in combination. Then, background fogging occurs due to high-temperature storage and high-temperature, high-humidity storage. Further, by using methylcellulose in combination, the thermal responsiveness is reduced, and the original performance is not exhibited. SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-sensitive recording medium having high sensitivity and low background fog even under high temperature storage and high temperature and high humidity storage. Means for Solving the Problems A colorless or slightly pale leuco dye, a color developer which comes into contact with the leuco dye when heated and melted, and, if necessary, a sensitizer which improves color sensitivity. In a thermosensitive recording medium provided with a thermosensitive coloring layer,
At least one of the above substances has a weight average molecular weight of 5,000 to 30,000 and a degree of esterification of 50% to 90%, and is represented by the following general formula (1). This can be achieved by using only the ester as a dispersant. Embedded image Here, R is an alkyl group having 1 to 10 carbon atoms, and M is any of an alkali metal, ammonium and amine. X and Y represent integers that have a relationship of Y = 0.2 to 1 when X = 1. [0011] Here, R is an alkyl group having 1 to 10 carbon atoms, and M is any of an alkali metal, ammonium and amine. X and Y each represent an integer having a relationship of Y = 0.2 to 1 when X = 1. The amount of styrene maleic acid half ester used as a dispersant is in the range of 1.5 to 10 parts by weight, preferably 2 to 5 parts by weight, based on 100 parts by weight of the dispersion. Is good. This is because the more the dispersing agent, the more stable the protective colloid effect is obtained, but the lowering of the coloring component is necessary, so the amount of the binder component must be reduced, and the coating strength of the thermosensitive coloring layer is relatively high. This is because a problem of becoming weak occurs. The weight average molecular weight of styrene maleic acid is 3
When it is more than 000, the dispersion efficiency is deteriorated. Conversely, if the weight average molecular weight is 5,000 or less, the stability of the coating is poor. If the weight average molecular weight is remarkable, the dispersed slurry is immediately aggregated immediately after dispersion. The weight average molecular weight referred to here is GPC
(Gel permeation chromatogram) is the average molecular weight measured by the method. On the other hand, when the degree of esterification is 50% or less, the dispersion efficiency is lowered and the viscosity of the dispersion slurry is also increased. When the degree of esterification is 90% or more, the wettability with the object to be dispersed is remarkably reduced, and bubbles are easily held during dispersion,
The liquid specific gravity of the dispersed slurry decreases. When a dispersion slurry having a reduced liquid specific gravity is used in this manner, when a heat-sensitive paint is prepared and applied, depending on the coating method, bubbles held in the coating may appear on the coating surface. The leuco dye used for forming the thermosensitive coloring layer may be used alone or as a mixture of two or more. Examples thereof include triphenylmethane, fluoran, spiropyran, phenothiazine, and auramine dyes. And indolinophthalide compounds. Specifically, 3,3-bis (p-dimethylaminophenyl) phthalide, 3,3-bis (p-dimethylphenyl) -6-dimethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3,3-bis (p-dimethylaminophenyl) -6-chlorophthalide, 3,3-bis (p-dibutylaminophenyl) phthalide, 3-cyclohexylamino-6-chlorofluoran, 3-dimethyl Amino-5,7-dimethylfluoran, 3-N-methyl-N
-Isobutyl-6-methyl-7-anilinofluoran; 3-N-ethyl-N-isoamyl-6-methyl-7-anilinofluoran; 3-dimethylamino-7-chlorofluoran; 3-diethylamino-7-methylfluorin Oran, 3-diethylamino-7, 8-benzfluoran, 3-diethylamino-6-methyl-7
-Chlorofluorane, 3- (N-ethyl-Np-tolyl) -6-methyl-7-anilinofluoran, 3- (Np-tolyl-N-ethylamino) -6-methyl-7-anilinofluoran, 3-pyrrolidinol 6-methyl-7-anilinofluoran, 2- {N- (3'-trifluoromethylphenyl) amino} -6-diethylaminofluoran,
2- {3,6-bis (diethylamino) -9- (o-chloroanilino) xanthyl benzoate lactam}, 3-diethylamino-6-methyl-7- (m-trichloroanilino) fluoran, 3-diethylamino-7- (o
-Chloroanilino) fluoran, 3-dibutylamino-7- (o-chloroarinino) fluoran, 3-N-methyl-N-amylamino-6-methyl-7-anilinofluoran, 3-N-methyl-N-cyclohexylamino-6-methyl-7- Anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran,
3-diethylamino-6-methyl-7- (2 ′, 4′-dimethylamino) fluoran, 3- (N, N-diethylamino) -5-methyl-7- (N, N-dibenzylamino) fluoran, benzoylleucomethylene blue, 6′-chloro- 8'-methoxy-benzoindolinopyrrolospiran, 6'-bromo-3'-methoxy-benzoindolinopyrrolospiran, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2'-methoxy- 5'-chlorophenyl) phthalide, 3- (2'-hydroxy-4'-dimethylaminophenyl) -3- (2'-methoxy-5'-nitrophenyl) 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; 3-morpholino 7- (N-propyl-trifluoromethylanilino) fluoran; -Diethylamino-5-chloro-7- (N-benzyl-trifluoromethylanilino) fluoran, 3-pyrrolidinol 7- (di-p-chlorophenyl) methylaminofluoran, 3-diethylamino-5-chloro-7- (α-phenylethylamino) ) Fluorane, 3- (N-ethyl-p-toluidino) -7- (α-phenylethylamino) fluoran, 3-diethylamino-7- (o-methoxycarbonylphenylamino) fluoran, 3-diethylamino-5-methyl-7ー (α-phenyle Tylamino) fluoran, 3-diethylamino-7-piperidinofluoran, 2-chloro-3- (N-methyltoluidino) -7- (pn-butylanilino) fluoran, 3-dibutylamino-6-methyl-7-ani Rinofluoran, 3,6-bis (dimethylamino) fluorenespiro (9,3 ')-6'-dimethylaminophthalide, 3- (N-benzyl-N-
Cyclohexylamino) -5,6-benzo-7-αnaphthylamino-4'-bromofluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-N-ethyl-N- (2-ethoxypropyl) Amino-6-methyl-7-anilinofluoran, 3-N-ethyl-N-tetrahydrofurfurylamino-6-methyl-7-anilinofluoran, 3
-Diethylamino-6-methyl-7-mesitidino 4 ', 5'-benzofluoran, 3-N-propyl-N-methylamino-6-methyl-7-anilinofluoran and the like are used. A developer used in the thermosensitive coloring layer is also an electron-accepting compound which is brought into contact with the above-mentioned leuco dye and the like when heated and melted to form a color, such as a phenolic compound and a thiophenolic compound. Thiourea derivatives, organic acids and metal salts thereof, and specific examples thereof include: 4,4'-isopropylidenebisphenol, 4,4'-isopropylidenebis (o-methylphenol), 4,4 ' -Secondarybutylidene bisphenol, 4,4'-isopropylidenebis (2-tert-butylphenol), 4,4'-cyclohexylidenediphenol, 4,4'-isopropylidenebis (2-chlorophenol), 2,2 '-Methylenebis (4-methyl-6-tert-butylphenol), 2,2'-methylenebis (4- Chiru 6
-Tert-butylphenol), 4,4'butylidenebis (6-tert-butyl-2-methylphenol), 1,1,3 tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,
1,3 tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 4,4′-thiobis (6-tert-butyl-2-methylphenol),
4,4'-diphenolsulfone, 4-isopropoxy-4'-hydroxyphenylsulfone, 4-benzyloxy-4'-hydroxydiphenylsulfone, 4,
4 'diphenol sulfoxide, isopropyl p-hydroxybenzoate,
Benzyl p-hydroxybenzoate, Benzyl protocaquitenate, Stearyl gallate, Lauryl gallate, Octyl gallate, 1,7-Bis (4-hydroxyphenylthio) -3,5-dioxaheptane,
1,5-bis (4-hydroxyphenylthio) -3-oxapentane, 1,3-bis (4-hydroxyphenylthio) -propane, 1,3-bis (4-hydroxyphenylthio) -2-hydroxypropane, N, N '
Diphenylthiourea, N, N'-di (m-chlorophenyl) thiourea, salicylanilide, 5-chloro-salicylanilide, 2-hydroxy-3naphthoic acid, 2-hydroxy-1naphthoic acid, 1-hydroxy-2naphthoic acid, hydroxynaphthoic acid Metal salts of acids such as zinc, aluminum and calcium; methyl bis (4-hydroxyphenyl) acetate; benzyl bis (4-hydroxyphenyl) acetate; butyl bis (4-hydroxyphenyl) acetate; 3-bis (4-hydroxycumyl) benzene, 1,4-bis (4-hydroxycumyl) benzene, 2,4′diphenolsulfone, 3,3 ′
Diallyl-4,4'diphenol sulfone, α,
α-bis (4-hydroxyphenyl) α-methyltoluene, an antipyrine complex of zinc thiocyanate, tetrabromobisphenol A, tetrabromobisphenol S and the like are used. In the paint for forming the thermosensitive coloring layer,
Polymers used as binders include starch and derivatives thereof, hydroxymethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, cellulose derivatives such as ethyl cellulose,
Polyvinyl alcohol, sodium polyacrylate, polyvinyl pyrrolidone, acrylamide / acrylate copolymer, acrylamide / acrylate / methacrylic acid copolymer, styrene / maleic anhydride copolymer alkali salt, isobutyl / maleic anhydride copolymer Water-soluble polymers such as coalesced alkali salts, polyacrylamide, sodium alginate, gelatin, casein, etc., and polyvinyl acetate, polyurethane, polyacrylate, polymethacrylate,
Aqueous emulsions such as vinyl chloride, vinyl acetate copolymer, ethylene-vinyl acetate copolymer, etc., and water-dispersible polymers such as latex such as styrene-butadiene copolymer, styrene-butadiene-acrylic copolymer are used. You. The paint for forming the thermosensitive coloring layer may further contain usual auxiliary components such as pigments, heat-fusible substances, lubricants, surfactants, fluorescent dyes, storage stabilizers, coloring dyes and the like. However, as a matter of course, pigments such as calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, and talc can be used in combination, if necessary. And pigments such as organic fine powders such as surface-treated inorganic fine particles such as calcium and silica, urea-formalin resin, styrene / methacrylic copolymer, polystyrene resin, etc. Fatty acids such as stearic acid and behenic acid, stearic acid amide, p-benzylbiphenyl, terphenyl, triphenylmethane, p-benzyloxy ammonium Kosan benzyl, beta chromatography benzyloxynaphthalene, beta Nafutoe acid phenyl ester, 1-hydroxy-2 Nafutoe acid phenyl ester, 1-hydroxy-2 Nafutoe acid methyl ester, diphenyl carbonate, terephthalic acid dibenzyl ester, 1,4-dimethoxynaphthalene,
1,4-diethoxynaphthalene, 1,4-dibenzyloxoinaphthalene, 1,2-bis (phenoxy) ethane, 1,2- (3-methylphenoxy) ethane,
1,2-bis (4-methylphenoxy) ethane, 1,
4-bis (phenoxy) butane, 1,4-bis (phenoxy) -2-butene, dibenzoylmethane, 1,4
-Bis (phenylthio) butane, 1,4-bis (phenylthio) -2-butene, 1,3-bis (2-vinyloxyethoxy) benzene, 1,4-bis (2-vinyloxyethoxy) benzene, p- (2 -Vinyloxyethoxy)
Biphenyl, p-aryloxybiphenyl, p-
Propargyloxybiphenyl, dibenzoyloxymethane, 1,3 dibenzoyloxypropane, dibenzyl disulfide, 1,1 diphenylethane,
1,1 diphenylpropanol, p- (benzyloxy) benzyl alcohol, 1,3 diphenoxy-2-propanol, N-octadecylcarbonyl-p
Thermally fusible substances such as -methoxycarbonylbenzene and N-octadecylcarbamoylbenzene are used. The support used in the present invention is not particularly limited, and examples thereof include high quality paper, recycled paper, matte paper, oil resistant paper, coated paper, art paper, cast coated paper, finely coated paper, and resin laminated paper. And polyolefin-based synthetic paper, synthetic fiber paper, synthetic resin film and the like can be used as appropriate. Further, the heat-sensitive recording material of the present invention may be provided with an intermediate layer mainly composed of an inorganic pigment and a binder between the support and the heat-sensitive coloring layer, if necessary. An overcoat layer may be provided, and a backcoat layer for curl adjustment or the like may be provided. [Test Method I] Uses a TH-PMD simulator (Okura Electric Co., Ltd.)
Was measured under the following conditions. Thermal head: KJT-256-8MGF1-TS
(Manufactured by Kyocera) Dot density: 8 dot / mm Dot size: 0.11 × 0.15 mm ² Resistance value: 2807Ω Power: 0.205 w / dot Pulse width: 5 msec Applied pulse width can be changed from 0.5 msec to 1.5 msec. The concentration was measured using a Macbeth densitometer (RD-914, manufactured by Macbeth). The value (msec) of the applied pulse width when the Macbeth concentration reached 1.0 was used as an index of the sensitivity (thermal response). [Test Method II] Storage test The obtained thermosensitive recording medium was recorded under the above printing conditions at an applied pulse width of 1.5 ms, and was stored together with the background under the following conditions. After storage, the density of the recording portion and the background were measured with a Macbeth densitometer. did. High temperature test: The obtained heat-sensitive recording medium is stored for 24 hours in an environment of 60 ° C.-dry. High-temperature high-humidity test: The obtained heat-sensitive recording medium was subjected to 40 ° C.-90% R
Store under H environment for 24 hours. EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples. Unless otherwise specified, “parts” and “%” represent “parts by weight” and “% by weight”, respectively. Example 1 Preparation of heat-sensitive paint Liquid A: 9 parts of 3-dibutylamino-6-methyl-7-anilinofluoran Polyvinyl alcohol: 12% aqueous solution 15 parts Water 31 parts Liquid B: bisphenol A 20 parts Phenyl 20 parts Ammonium salt of styrene maleic acid half ester [Degree of esterification 70%: weight average molecular weight 10,000-20,000] (trade name KS-1333: manufactured by Arakawa Chemical): 20% aqueous solution 5 parts Water 105 parts or more composition Were separately dispersed by a sand grinder until the average particle diameter became 1 μm or less. Liquid C: Synthetic silica (Mizukasil P-527: manufactured by Mizusawa Chemical) 20 parts Water 80 parts Liquid C was dispersed for 15 minutes using a homomixer. Solution A prepared above: 55 parts, Solution B: 15
0 parts and 100 parts of liquid C are mixed, and 20 parts of zinc stearate (30% dispersion), 66.7 parts of polyvinyl alcohol (12% aqueous solution) and 80 parts of water are added to the mixture, and heat is added. Paint. [0043] The heat-sensitive coating onto a woodfree paper having a basis weight 50 g / m ² was applied as a coating amount after air drying is 5 g / m ^2, further OKen smoothness of surface by gloss calendering process Finishing treatment was performed for about 500 seconds to obtain a thermosensitive recording medium. Example 2 In Example 1, a styrene maleic acid half ester having a weight average molecular weight of 20,000 to 30,000 and a degree of esterification of 90% was used.
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the above-mentioned material was used. Example 3 Example 1 was repeated except that 1.5 parts of the styrene maleic acid half ester used in Example 1 was used as the aqueous solution of polyvinyl alcohol as the liquid A, and 44.5 parts of water was used. In the same manner as in Example 1, a thermosensitive recording medium was obtained. Comparative Example 1 In Example 1, 20 parts of polyvinyl alcohol aqueous solution was used instead of the styrene maleic acid half ester of Solution B.
In the same manner as in Example 1, except that 90 parts of water were used. The heat-sensitive recording medium obtained above was subjected to the above-described color development characteristics test and storage test. Table 1 shows the test results of each thermosensitive recording medium. [Table 1] * 1: The smaller the value of sensitivity (msec), the higher the sensitivity. * 2: Storage characteristics: The upper part shows the Macbeth density of the background / the lower part shows the Macbeth density of the recording part. * 3: Comprehensive evaluation was performed based on the above results. [Judgment Criteria] ：: Excellent, ○: Good, Δ: Slightly poor, ×: Poor. As is clear from the table, the heat-sensitive recording material of the present invention has high sensitivity, and has excellent storage stability even at high temperature and high temperature and high humidity. This was a heat-sensitive recording medium having a low density.

Continuation of the front page (56) References JP-A-54-84745 (JP, A) JP-A-59-41295 (JP, A) JP-A-59-448186 (JP, A) JP-A-3-128280 (JP) , A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B41M 5/28-5/34

Claims (1)

(57) Claims 1. A colorless or slightly light-colored leuco dye, a color developer which comes into contact with the leuco dye when heated and melted, and, if necessary, a color sensitivity on a support. In a thermosensitive recording medium provided with a thermosensitive coloring layer containing a sensitizer to be improved, as a dispersant for at least one of the above substances,
The following general formula (1) having a weight average molecular weight of 5,000 to 30,000 and a degree of esterification of 50% to 90%.
A heat-sensitive recording material characterized by using only a styrene maleic acid half ester represented by the formula: Embedded image Here, R is an alkyl group having 1 to 10 carbon atoms, and M is any of an alkali metal, ammonium and amine. X and Y are integers that have a relation of Y = 0.2 to 1 when X = 1.