JP2017177514A - Thermosensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermosensitive recording medium excellent in image quality of a recording image and color development sensitivity.SOLUTION: In the thermosensitive recording medium having a support, an undercoat layer formed on the support and containing a pigment and a binder as main components and further containing a dispersant and a thermosensitive recording layer formed on the undercoat layer and containing a colorless or pale color electron donative leuco dye and an electron receptive developer as main components, the pigment which the undercoat layer contains is a rosette type light calcium carbonate produced by forming second particles by radially aggregating spindle-shaped primary particles; the bulk density of the rosette type light calcium carbonate is 240 g/L or less; and the dispersant which the undercoat layer contains is sodium polyacrylate.SELECTED DRAWING: None

Description

  The present invention utilizes a coloring reaction between a colorless or light-colored electron-donating leuco dye (hereinafter also referred to as “leuco dye”) and an electron-accepting developer (hereinafter also referred to as “developer”). The present invention relates to a heat-sensitive recording material which is excellent in image quality and color development sensitivity of a recorded image.

In general, a heat-sensitive recording material is usually a colorless or light-colored electron-donating leuco dye and an electron-accepting developer such as a phenolic compound, which are ground and dispersed into fine particles, and then mixed together to form a binder, a filling A coating solution obtained by adding an agent, a sensitivity improver, a lubricant and other auxiliaries to a support such as paper, synthetic paper, film, plastic, etc., thermal head, hot stamp, heat Color is developed by an instantaneous chemical reaction by heating with a pen, laser light or the like, and a recorded image is obtained. Currently, thermal recording media are used for facsimiles, computer terminal printers, automatic ticket vending machines, measurement recorders, receipts for supermarkets and convenience stores, labels, tickets, bank ATMs, gas and electric meter readings. It is widely used as a recording medium for money tickets such as car tickets and car betting tickets.
In recent years, recording devices such as handy terminals have been miniaturized, and there has been an increasing demand for a thermal recording material that develops color with lower applied energy, that is, has good color development sensitivity. In addition, since barcode readability is required for labels, tickets, etc., high-quality printed images can be obtained in any region from low density to high density, that is, the quality of the recorded image is good. Is required.
In response to such a requirement, it has been proposed to provide a primer layer containing an inorganic pigment or plastic particles between the support and the heat-sensitive recording layer to improve the color development sensitivity and printing runnability (Patent Document 1). 2).

JP 05-162446 A JP2012-076228

The inventors of the present invention have studied to improve the image quality and color development sensitivity of the recorded image of the thermal recording medium by providing an undercoat layer between the support and the thermal recording layer.
Accordingly, an object of the present invention is to provide a heat-sensitive recording material excellent in image quality and color development sensitivity of a recorded image.

As a result of intensive studies, the present inventors have provided an undercoat layer between the support of the heat-sensitive recording medium and the heat-sensitive recording layer, and spindle-shaped primary particles as a pigment aggregated radially into the undercoat layer as secondary particles. In addition to containing light calcium carbonate having a characteristic rosetta shape, limiting the bulk density to a specific bulk density, and containing a dispersant of a specific structure, the image quality and color development sensitivity of the recorded image The present invention has been completed.
Rosetta-type light calcium carbonate used in the present invention has a specific shape and bulk density, and the undercoat layer containing such a pigment has high heat insulation properties, and heat transfer from the heat-sensitive recording layer to the support side. It is considered that the color development sensitivity is excellent.
Furthermore, since the dispersion of calcium carbonate generally has low stability and tends to aggregate and settle, the use of calcium carbonate as a pigment for the undercoat layer results in poor uniformity of the undercoat layer. If the undercoat layer is inferior in uniformity, the heat insulation property of the undercoat layer also becomes non-uniform. Therefore, even if a thermal recording layer is applied to the thermal recording layer with a uniform thermal energy, the portion with high heat insulation has high print density and heat insulation properties. The print density is low in the low part. Since the difference in the print density appears as uneven coloring, it is considered that the image quality of the recorded image is inferior.
However, when sodium polyacrylate is included as a dispersant, the aggregation and sedimentation of the calcium carbonate dispersion are effectively suppressed, the uniformity of the undercoat layer is improved, and the image quality of the recorded image is improved. In order to uniformly inhibit the heat transfer from the recording layer to the support side, it is considered that the color development sensitivity is also improved.

  That is, the present invention provides a support, an undercoat layer comprising a pigment and a binder as main components provided on the support, and further containing a dispersant, and a colorless or light-colored electron provided on the undercoat layer. In a heat-sensitive recording material having a heat-sensitive recording layer containing a donor leuco dye and an electron-accepting developer as main components, the pigment contained in the undercoat layer has a spindle-shaped primary particle aggregated radially. The heat-sensitive recording material is a rosetta-type light calcium carbonate formed with secondary particles, the bulk density of which is 240 g / L or less, and the dispersant contained in the undercoat layer is sodium polyacrylate.

The heat-sensitive recording material of the present invention comprises a support, an undercoat layer provided on the support, and a heat-sensitive recording layer provided on the undercoat layer.
This undercoat layer mainly comprises a pigment and a binder, and further contains a dispersant. This pigment is a rosetta-type light calcium carbonate formed by agglomerating spindle-shaped primary particles radially to form secondary particles. is there.
The bulk density of the rosetta type light calcium carbonate is 240 g / L or less, preferably 150 to 220 g / L. This bulk density is measured in accordance with JIS-K-5101-12-1 (pigment test method-part 12: apparent density or apparent specific volume-section 1: stationary method).
The dispersant is sodium polyacrylate.

Rosetta-type light calcium carbonate used in the present invention is formed by agglomerating primary particles of spindle-shaped light calcium carbonate in a radial manner to form secondary particles. From the vicinity of the center, the primary particles are radially extended in the longitudinal direction.
Rosetta-type light calcium carbonate used in the present invention is, for example, Specialty Minerals Inc. It is available as Albuquer LO (bulk density: 210 g / L) manufactured by KK or TP221BM (bulk density 230 g / L) manufactured by Okutama Kogyo Co., Ltd.
Rosetta-type light calcium carbonate may be used after being pulverized by a known pulverizer such as a ball mill, an attritor, or a sand glider.

In the undercoat layer of the present invention, a pigment other than the rosetta-type light calcium carbonate of the present invention may be used. Examples of pigments other than rosetta-type light calcium carbonate include light calcium carbonate formed by forming irregularly shaped secondary particles, and light brown chestnut light formed by agglomerating needle-like primary particles radially to form secondary particles Calcium carbonate, light calcium carbonate, heavy calcium carbonate, primary calcium, spindle, columnar, square, spherical, etc., without forming secondary particles, (calcined) kaolin, clay, talc, silica , Aluminum oxide, zinc oxide, titanium oxide, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, aluminum silicate, magnesium silicate, calcium silicate and the like. These pigments can be used alone or in admixture of two or more.
When the undercoat layer contains a pigment other than the rosetta type light calcium carbonate of the present invention, the content of the rosetta type light calcium carbonate of the present invention is the same as the total pigment contained in the undercoat layer (the rosetta type light calcium carbonate of the present invention). Inclusive) is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more.

When the undercoat layer of the present invention further contains organic hollow particles, the thermal insulation of the undercoat layer is improved and a heat-sensitive recording material excellent in color development sensitivity is obtained, which is preferable.
The organic hollow particles used in the present invention are fine hollow particles that have a thermoplastic resin as a shell and contain air or other gas inside, and are already in a foamed state.
Examples of the thermoplastic resin include polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyacrylic acid ester, polyacrylonitrile, polybutadiene, and copolymers thereof. In particular, styrene resins such as polystyrene, acrylic resins such as polyacrylic acid esters and polyacrylonitrile, copolymers thereof, or copolymer resins mainly composed of polyvinylidene chloride and polyacrylonitrile are preferable. Specifically, such organic hollow particles are available under the trade name SX8782 manufactured by JSR Corporation, trade names MH5055 and MH8103K manufactured by Nippon Zeon Co., Ltd., and trade name Ropeke HP-91 manufactured by Rohm & Haas Japan.

The hollow ratio of the organic hollow particles is preferably 40 to 90%, more preferably 45 to 90%. When the hollow ratio is less than 40%, the heat insulation becomes insufficient, and heat energy from the thermal head or the like is easily released out of the heat-sensitive recording medium through the support. A sufficient effect may not be obtained.
Here, the hollow ratio is calculated from the outer diameter and inner diameter of the hollow particles, and is represented by the hollow ratio = (the inner diameter of the hollow particles / the outer diameter of the hollow particles) ³ × 100 (%).

The average particle diameter of the organic hollow particles is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. When the average particle size is larger than 10 μm, the smoothness of the surface of the heat-sensitive recording layer formed on the undercoat layer is lowered, and the adhesion between the heat-sensitive recording material and the thermal head is lowered, so that a sufficient effect cannot be obtained. There is. On the other hand, when the average particle size is smaller than 0.5 μm, the amount of the gas contained in the hollow particles is small, and thus a sufficient effect may not be obtained.
Here, the average particle diameter is indicated by a median diameter d _{50 in} which the particles on the large side and the small side are equivalent (volume basis) when the particles are divided into two according to the diameter. It can be measured by the device.

As a binder used in the undercoat layer, polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, cation-modified polyvinyl alcohol, and terminal alkyl-modified polyvinyl alcohol, hydroxyethyl cellulose, Cellulose ethers and derivatives thereof such as methylcellulose, ethylcellulose, carboxymethylcellulose, acetylcellulose, starch, enzyme-modified starch, thermochemically modified starch, oxidized starch, esterified starch, etherified starch (for example, hydroxyethylated starch, etc.), cationization Starch and other starches, polyacrylamide, cationic polyacrylamide, anionic polyacrylamide, amphoteric polyacryl Water-soluble resins such as polyacrylamides such as amides; Urethane resins such as polyester polyurethane resins, polyether polyurethane resins, polyurethane ionomer resins, styrene-butadiene copolymers, styrene-butadiene-acrylonitrile copolymers, styrene -Styrene-butadiene resin such as butadiene-acrylic copolymer, acrylic resin composed of monomer components copolymerizable with (meth) acrylic acid and (meth) acrylic acid such as (meth) acrylonitrile, ethylene, Polyolefin resin, polyvinyl acetate, consisting of monomer components that can be copolymerized with olefins such as propylene and butylene, and olefins such as unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, itaconic acid, and fumaric acid , Vinyl chloride-acetic acid Illustrative non-water-soluble resins such as nyl copolymers, polyvinyl chloride, polyvinylidene chloride, polyacrylates, polystyrose and their copolymers, silicone resins, petroleum resins, terpene resins, ketone resins, coumarone resins be able to.
Among these, as the water-soluble resin, polyvinyl alcohols, cellulose ethers and derivatives thereof, and starches are preferable, and polyvinyl alcohols are more preferable. The water-soluble resin can be used by dissolving in a solvent such as water.
Further, as the water-insoluble resin, styrene-butadiene resin, acrylic resin, and polyolefin resin are preferable, and styrene-butadiene resin is more preferable. The water-insoluble resin can be used as an emulsion dispersed in water or another medium in the form of an emulsification or paste.
Two or more kinds of these binders may be used in combination according to the required quality.

As the binder used in the undercoat layer of the present invention, it is preferable to use a water-soluble resin and a water-insoluble resin in combination at a certain ratio.
The weight ratio (solid content) of the water-soluble resin / water-insoluble resin is preferably 35/100 or less, more preferably 3/100 to 30/100, still more preferably 3/100 to 20/100.
When the weight ratio of the water-soluble resin / water-insoluble resin exceeds 35/100, the heat discoloration resistance, print image quality, and head residue resistance tend to be lowered (see Examples below).
Further, if the water-soluble resin is less than 3/100, the effect of suppressing migration described later cannot be sufficiently obtained, and the strength of the coating layer may be lowered.

Water-soluble resins such as polyvinyl alcohols generally have high viscosity and water retention and are easy to penetrate and fix in the voids of the undercoat layer containing the pigment having the specific shape and bulk density of the present invention. Therefore, it is considered that the gap of the undercoat layer is filled and the heat insulation is lowered.
On the other hand, water-insoluble resins such as styrene-butadiene resins generally have low viscosity and water retention, and pass through the undercoat layer containing a pigment having a specific shape and bulk density according to the present invention to the support. So-called migration that penetrates easily occurs.
By properly adjusting the mixing ratio of water-soluble resin and water-insoluble resin and using them together, the undercoat layer can be made bulky (low density) while suppressing migration. It is thought that sensitivity can be obtained.

The dispersant used in the undercoat layer is sodium polyacrylate.
In the present invention, sodium polyacrylate is used as a dispersant, but a dispersant other than sodium polyacrylate may be used in combination.
Examples of such a dispersant include sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate, sodium polycarboxylate, and fatty acid metal salts.
In the present invention, the total amount of the dispersant is preferably sodium polyacrylate, but when a dispersant other than sodium polyacrylate is used in combination, the weight ratio of sodium polyacrylate in the dispersant is 60% by weight or more. Preferably, 70 weight% or more is more preferable, and 85 weight% or more is still more preferable.

  In the present invention, a plasticizer, a thickener, a surfactant, an active agent, a pH adjuster, a defoaming agent, a water retention agent, an antiseptic, and a coloring dye are applied to the undercoat layer as long as the desired effects on the above-described problems are not inhibited. Various auxiliary agents such as ultraviolet absorbers, antioxidants, and water / oil repellents can be used.

The amount of the pigment, organic hollow particles, and binder used in the undercoat layer is determined according to the required performance and recordability and is not particularly limited, but is usually 100 parts by weight of the total solid content of the undercoat layer. The pigment (the total of pigments other than Rosetta-type light calcium carbonate and Rosetta-type light calcium carbonate) is 50 to 95 parts by weight, preferably 70 to 90 parts by weight in terms of solid content. Further, the content of the organic hollow particles with respect to 100 parts by weight of the total solid content of the undercoat layer is preferably 1 to 18 parts by weight, more preferably 3 to 15 parts by weight in terms of solids. Increasing the content of organic hollow particles tends to improve the color development sensitivity, but if the content exceeds 18 parts by weight, the residue adheres to the thermal head and the like, and the print running property (head residue resistance) decreases. There are things to do. The content of the binder is preferably 7 to 30 parts by weight, more preferably 10 to 25 parts by weight in terms of solid content.
Further, the amount of the dispersant used in the undercoat layer is determined according to the required performance and recordability, and is not particularly limited, but the dispersant (dispersant other than sodium polyacrylate and sodium polyacrylate) The total content is preferably 0.10 to 0.24 parts by weight, more preferably 0.15 to 0.20 parts by weight with respect to 100 parts by weight of the pigment contained in the undercoat layer. is there. When the content of the dispersant exceeds 0.24 parts by weight, the viscosity of the pigment dispersion becomes too low, and it becomes difficult to obtain a desired coating amount when applying the undercoat layer coating solution, and an excessive amount of the dispersant is used. On the other hand, the stability of the pigment dispersion may be lowered, and reaggregation and sedimentation of the pigment may easily occur.

In the present invention, the support and the means for applying an undercoat layer on the support are not particularly limited, and are well known and commonly used on a support made of an appropriate material such as paper, recycled paper, plastic film, and synthetic paper. Can be applied according to technique. For example, an air machine, a rod blade coater, a vent blade coater, a bevel blade coater, a roll coater, a curtain coater, etc. When using a blade coater such as a blade coater, vent blade coater, or bevel blade coater, high-concentration coating is possible, so that the undercoat layer coating solution does not easily penetrate into the support and forms a uniform undercoat layer. Therefore, it is preferable.
The coating amount of the undercoat layer is determined according to the required performance and recording suitability, and is not particularly limited, but the general coating amount is about 1 to 15 g / m ² in terms of solid content.

  Next, various materials used in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention are exemplified. However, binders, cross-linking agents, pigments, dispersants, and the like are within a range that does not impair the desired effect on the above-described problems, as necessary. It can also be used for each coating layer provided.

  As the developer, any known developer in the field of conventional pressure-sensitive or thermal recording paper can be used, and is not particularly limited. For example, activated clay, attapulgite, colloidal silica, aluminum silicate, etc. Inorganic acidic substance, 4,4′-isopropylidene diphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4′-dihydroxy Diphenyl sulfide, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 4,4′-dihydroxydiphenyl sulfone, 2,4′-dihydroxydiphenyl sulfone, 4-hydroxy-4′-isopropoxydiphenyl sulfone, 4-hydroxy-4 '-N-propoxydiphenyl sulfone, (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4′-methyldiphenylsulfone, 4-hydroxyphenyl-4′-benzyloxyphenylsulfone, 3,4-dihydroxyphenyl-4′-methylphenylsulfone 1- [4- (4-hydroxyphenylsulfonyl) phenoxy] -4- [4- (4-isopropoxyphenylsulfonyl) phenoxy] butane, a phenol condensation composition described in JP-A-2003-154760, JP-A-8 Aminobenzenesulfonamide derivatives described in Japanese Patent No. -59603, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, butyl bis (p-hydroxyphenyl) acetate Bis (p-hydroxyphenyl) vinegar Methyl, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 1,3-bis [α- Methyl-α- (4′-hydroxyphenyl) ethyl] benzene, di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), 2,2′-thiobis (4 -Tert-octylphenol), phenolic compounds such as diphenylsulfone cross-linking compounds described in WO 97/16420, compounds described in WO 02/081229 or JP-A No. 2002-301873, and N, N′-di-m- Thiourea compounds such as chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate, bis [4- (n-octylo) Cicarbonylamino) zinc salicylate] dihydrate, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- (p-tolylsulfonyl) propyloxy] salicylic acid, 5- [p- (2 -P-methoxyphenoxyethoxy) cumyl] aromatic carboxylic acids of salicylic acid and salts of these aromatic carboxylic acids with polyvalent metal salts such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, Examples thereof include an antipyrine complex of zinc thiocyanate, and a composite zinc salt of terephthalaldehyde acid and other aromatic carboxylic acid. These developers can be used alone or in combination of two or more. 1- [4- (4-Hydroxyphenylsulfonyl) phenoxy] -4- [4- (4-isopropoxyphenylsulfonyl) phenoxy] butane is available, for example, under the trade name JKY-214 manufactured by API Corporation. Yes, the phenol condensation composition described in JP-A No. 2003-154760 is available, for example, under the trade name JKY-224 manufactured by API Corporation, and is a diphenylsulfone cross-linking compound described in International Publication No. WO 97/16420 Is available under the trade name D-90 manufactured by Nippon Soda Co., Ltd. Moreover, the compound as described in WO02 / 081229 etc. is available as Nippon Soda Co., Ltd. brand name NKK-395 and D-100. In addition, a metal chelate color-developing component such as a higher fatty acid metal double salt and a polyvalent hydroxyaromatic compound described in JP-A-10-258577 can also be contained.

  As the leuco dye, those known in the conventional pressure-sensitive or thermal recording paper field can be used, and are not particularly limited. However, triphenylmethane compounds, fluorane compounds, fluorene compounds, divinyl compounds are not limited. Compounds and the like are preferred. Specific examples of typical colorless or light-colored dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination of two or more.

<Triphenylmethane leuco dye>
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide (also known as malachite green lactone)

<Fluoran leuco dye>
3-diethylamino-6-methylfluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-diethylamino- 6-methyl-7-chlorofluorane, 3-diethylamino-6-methyl-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7- (o-chloroanilino) fluorane, 3- Diethylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-diethylamino-6-methyl-7- (o-fluoroanilino) fluorane, 3-diethylamino-6-methyl-7- (m-methylanilino) fluorane 3-diethylamino-6-methyl-7-n-octylanilinofluorane, 3-di Tilamino-6-methyl-7-n-octylaminofluorane, 3-diethylamino-6-methyl-7-benzylaminofluorane, 3-diethylamino-6-methyl-7-dibenzylaminofluorane, 3-diethylamino- 6-chloro-7-methylfluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3-diethylamino-6-chloro-7-p-methylanilinofluorane, 3-diethylamino-6-ethoxy Ethyl-7-anilinofluorane, 3-diethylamino-7-methylfluorane, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino- 7- (o-chloroanilino) fluorane, 3-diethylamino-7- (p Chloroanilino) fluorane, 3-diethylamino-7- (o-fluoroanilino) fluorane, 3-diethylamino-benzo [a] fluorane, 3-diethylamino-benzo [c] fluorane, 3-dibutylamino-6-methyl-fluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3-dibutylamino-6-methyl-7- ( o-chloroanilino) fluorane, 3-dibutylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-dibutylamino-6-methyl-7- (o-fluoroanilino) fluorane, 3-dibutylamino-6 -Methyl-7- (m-trifluoromethylanilino) fluorane, 3-dibutylamino- 6-methyl-7-chlorofluorane, 3-dibutylamino-6-ethoxyethyl-7-anilinofluorane, 3-dibutylamino-6-chloro-7-anilinofluorane, 3-dibutylamino-6- Methyl-7-p-methylanilinofluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-dibutylamino-7- (o-fluoroanilino) fluorane, 3-di-n-pentylamino -6-methyl-7-anilinofluorane, 3-di-n-pentylamino-6-methyl-7- (p-chloroanilino) fluorane, 3-di-n-pentylamino-7- (m-trifluoro Methylanilino) fluorane, 3-di-n-pentylamino-6-chloro-7-anilinofluorane, 3-di-n-pentylamino-7- (p-chloro) Nilino) fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3- (N-methyl-N-propylamino) -6-methyl -7-anilinofluorane, 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-cyclohexylamino) -6-methyl-7 -Anilinofluorane, 3- (N-ethyl-N-xylamino) -6-methyl-7- (p-chloroanilino) fluorane, 3- (N-ethyl-p-toludino) -6-methyl-7-ani Linofluorane, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isoamylamino) -6-chloro-7-a Linofluorane, 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isobutylamino) -6-methyl-7-anilinofur Oran, 3- (N-ethyl-N-ethoxypropylamino) -6-methyl-7-anilinofluorane, 3-cyclohexylamino-6-chlorofluorane, 2- (4-oxahexyl) -3-dimethyl Amino-6-methyl-7-anilinofluorane, 2- (4-oxahexyl) -3-diethylamino-6-methyl-7-anilinofluorane, 2- (4-oxahexyl) -3-dipropyl Amino-6-methyl-7-anilinofluorane, 2-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane, 2-methoxy-6-p -(P-dimethylaminophenyl) aminoanilinofluorane, 2-chloro-3-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane, 2-chloro-6-p- (p- Dimethylaminophenyl) aminoanilinofluorane, 2-nitro-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-amino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 2-phenyl-6-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane, 2-benzyl-6 -P- (p-phenylaminophenyl) aminoanilinofluorane, 2-hydroxy-6-p- (p-phenylamino) Nophenyl) aminoanilinofluorane, 3-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane, 3-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane, 3 -Diethylamino-6-p- (p-dibutylaminophenyl) aminoanilinofluorane, 2,4-dimethyl-6-[(4-dimethylamino) anilino] -fluorane

<Fluorene leuco dye>
3,6,6′-tris (dimethylamino) spiro [fluorene-9,3′-phthalide], 3,6,6′-tris (diethylamino) spiro [fluorene-9,3′-phthalide]

<Divinyl leuco dye>
3,3-bis- [2- (p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [2- (P-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalide, 3,3-bis- [1,1-bis (4-pyrrolidinophenyl) ) Ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3,3-bis- [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2- Yl] -4,5,6,7-tetrachlorophthalide

<Others>
3- (4-Diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- ( 1-octyl-2-methylindol-3-yl) -4-azaphthalide, 3- (4-cyclohexylethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl)- 4-azaphthalide, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, 3,6-bis (diethylamino) fluorane-γ- (3′-nitro) anilinolactam, 3,6 -Bis (diethylamino) fluorane-γ- (4′-nitro) anilinolactam, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylamino) Enyl) -ethenyl] -2,2-dinitrileethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2- β-naphthoylethane, 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2,2-diacetylethane, bis- [2, 2,2 ′, 2′-Tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

  A conventionally well-known sensitizer can be used as a sensitizer. Examples of the sensitizer include fatty acid amides such as stearamide and palmitic acid amide, ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-bis- (3-methylphenoxy) ethane, p-benzylbiphenyl, β- Benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 1,2-diphenoxyethane, dibenzyl oxalate, di (p-chlorobenzyl) oxalate, di (p-methylbenzyl) oxalate, Dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, o-xylene-bis -(Phenyl ether), 4- (m-me Tilphenoxymethyl) biphenyl, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di (3-methylphenoxy) ethylene, bis [2- (4-methoxy- Phenoxy) ethyl] ether, methyl p-nitrobenzoate, phenyl p-toluenesulfonate, o-toluenesulfonamide, p-toluenesulfonamide and the like. These sensitizers may be used alone or in combination of two or more.

  Examples of the pigment include kaolin, calcined kaolin, calcium carbonate, aluminum oxide, titanium oxide, magnesium carbonate, aluminum silicate, magnesium silicate, calcium silicate, aluminum hydroxide, silica and the like, and can be used in combination according to the required quality. .

  As the binder, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetyl modified polyvinyl alcohol, carboxy modified polyvinyl alcohol, amide modified polyvinyl alcohol, sulfonic acid modified polyvinyl alcohol, butyral modified polyvinyl alcohol, olefin modified polyvinyl alcohol, Nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer and ethyl cellulose, acetyl Cellulose derivatives such as cellulose Casein, arabic gum, oxidized starch, etherified starch, dialdehyde starch, esterified starch, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic ester, polyvinyl butyral, polystyrose and copolymers thereof, polyamide resin, Silicone resin, petroleum resin, terpene resin, ketone resin, coumarone resin and the like can be exemplified. These polymer substances are used by dissolving them in solvents such as water, alcohol, ketones, esters, hydrocarbons, etc., and are used in the state of being emulsified or pasted in water or other media to achieve the required quality. It can also be used in combination.

  Examples of the crosslinking agent include epichlorohydrin resins such as polyamine epichlorohydrin resins and polyamide epichlorohydrin resins, polyamide urea resins, polyalkylene polyamine resins, polyalkylene polyamide resins, polyamine polyurea resins, and modified polyamines. Polyamine / polyamide resins such as resins, modified polyamide resins, polyalkylene polyamine urea formalin resins, or polyalkylene polyamine polyamide polyurea resins, glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, potassium persulfate, ammonium persulfate, persulfate Examples thereof include sodium sulfate, ferric chloride, magnesium chloride, borax, boric acid, alum, and ammonium chloride.

  As the dispersant, a dispersant used in an undercoat layer such as sodium polyacrylate can be appropriately used.

  Examples of the lubricant include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, and silicone resins.

  In the present invention, 4,4′-butylidene (6-tert-butyl-3-methylphenol), 2 as a stabilizer for improving the oil resistance and the like of the image area as long as the desired effect on the above problems is not impaired. 2,2'-di-t-butyl-5,5'-dimethyl-4,4'-sulfonyldiphenol, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane and the like can also be added. In addition, benzophenone and triazole ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, and the like can be used.

  The types and amounts of the leuco dye, developer, sensitizer, and other various components used in the heat-sensitive recording layer of the present invention are determined according to the required performance and recording suitability, and are not particularly limited. Usually, 0.5 to 10 parts by weight of developer, 0.1 to 10 parts by weight of sensitizer, 0.5 to 20 parts by weight of pigment, and 0.01 to 10 parts by weight of stabilizer for 1 part by weight of leuco dye. Parts and other components of about 0.01 to 10 parts by weight. The binder is suitably about 5 to 25% by weight based on the solid content of the heat-sensitive recording layer.

  In the present invention, the leuco dye, the developer, and the material to be added as necessary are finely divided to a particle size of several μm or less by a pulverizer such as a ball mill, an attritor, or a sand glider, or an appropriate emulsifying device. Depending on the purpose, various additive materials are added to obtain a coating solution. As a solvent used for this coating liquid, water or alcohol can be used, and its solid content is about 20 to 40% by weight.

  The heat-sensitive recording material of the present invention has an undercoat layer on the support and a heat-sensitive recording layer provided on the undercoat layer, but a layer other than the undercoat layer and the heat-sensitive recording layer may be provided as appropriate. For example, a protective layer can be provided on the heat-sensitive recording layer, and a backcoat layer can be provided on the opposite side of the support from the heat-sensitive recording layer.

In the present invention, means for applying a coating layer other than the undercoat layer, that is, a heat-sensitive recording layer, a protective layer, a backcoat layer, and the like are not particularly limited, and can be applied according to a well-known common technique. For example, an off-machine coating machine or an on-machine coating machine equipped with various coaters such as an air knife coater, a rod blade coater, a vent blade coater, a bevel blade coater, a roll coater, and a curtain coater is appropriately selected and used.
The coating amount of the coating layer other than the undercoat layer is determined according to the required performance and recording suitability, and is not particularly limited, but the general coating amount of the heat-sensitive recording layer is 2 to 12 g in solid content. / ^m is about ^2, the coating amount of the protective layer is 0.5 to 5.0 g / ^{m 2} is preferred solids.
Further, various known techniques in the heat-sensitive recording material field can be added as appropriate, such as applying a smoothing process such as supercalendering after coating each coating layer.

  The following examples illustrate the invention but are not intended to limit the invention. In Examples and Comparative Examples, “parts” represents “parts by weight” and “%” represents “% by weight” unless otherwise specified. Various dispersions or coating solutions were prepared as follows.

[Example 1]
A pigment dispersion was prepared by stirring and dispersing a formulation comprising the following formulation.
<Pigment dispersion 1>
Rosetta type light calcium carbonate (Specialty Minerals Inc.
Product name: Albuquer LO, bulk density: 210 g / L) 100.0 parts Dispersant (manufactured by Toagosei Co., Ltd., trade name: Aron T-50, sodium polyacrylate,
(Solid content 40%) 0.45 parts water 170.0 parts

Next, an undercoat layer coating solution was prepared by mixing the pigment dispersion and the blend at the following ratio.
<Undercoat layer coating solution 1>
Pigment dispersion 1 270.5 parts Styrene / butadiene copolymer latex (manufactured by Nippon Zeon Co., Ltd.,
Product name: ST5526, solid content 48%) 40.0 parts Completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., product name: PVA117)
(Solid content 10%) 30.0 parts

Next, the undercoat layer coating solution 1 was applied to one side of a support (high-quality paper having a basis weight of 60 g / m ² ) with a vent blade coater so that the coating amount was 10.0 g / m ² in terms of solid content. Thereafter, drying was performed to obtain an undercoat layer-coated paper.

The developer dispersion (liquid A) and the leuco dye dispersion (liquid B) having the following composition were separately wet-ground with a sand grinder until the average particle size became 0.5 μm.
Developer dispersion (liquid A)
4-hydroxy-4′-isopropoxydiphenylsulfone (manufactured by API Corporation, trade name: NYDS) 6.0 parts completely saponified polyvinyl alcohol aqueous solution (trade name: PVA117, manufactured by Kuraray Co., Ltd.)
(Solid content 10%) 18.8 parts water 11.2 parts
Leuco dye dispersion (liquid B)
3-dibutylamino-6-methyl-7-anilinofluorane (manufactured by Yamamoto Kasei Co., Ltd.,
Product name: ODB-2) 6.0 parts Completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., product name: PVA117)
(Solid content 10%) 4.6 parts water 2.6 parts

Subsequently, each dispersion liquid was mixed in the following ratio to prepare a thermosensitive recording layer coating liquid.
<Thermosensitive recording layer coating solution 1>
Developer dispersion (liquid A) 36.0 parts Leuco dye dispersion (liquid B) 13.2 parts Completely saponified polyvinyl alcohol aqueous solution (trade name: PVA117, manufactured by Kuraray Co., Ltd.)
Solid content 10%) 25.0 parts Aluminum hydroxide (made by Showa Denko KK, trade name: Heidilite H-32,
50% dispersion) 12.0 parts

Next, on the undercoat layer of the undercoat layer-coated paper, the thermal recording layer coating solution 1 is applied with a rod blade coater so that the coating amount is 2.5 g / m ^{2 in} solid content, and then dried. And a heat-sensitive recording material was obtained by processing with a super calendar so that the smoothness was 500 to 1000 seconds.

[Example 2]
The amount of pigment dispersion 1 dispersant (product of Toagosei Co., Ltd., trade name: Aron T-50, sodium polyacrylate, solid content 40%) is 0.25 part, and the amount of water is 170.2 parts. A thermosensitive recording material was produced in the same manner as in Example 1 except that.
[Example 3]
The amount of pigment dispersion 1 dispersant (product of Toagosei Co., Ltd., trade name: Aron T-50, sodium polyacrylate, solid content 40%) is 0.38 parts, and the amount of water is 170.1 parts. A thermosensitive recording material was produced in the same manner as in Example 1 except that.
[Example 4]
Except that the blending amount of the dispersant for pigment dispersion 1 (manufactured by Toagosei Co., Ltd., trade name: Aron T-50, sodium polyacrylate, solid content 40%) was changed to 0.50 part, it was the same as in Example 1. Thus, a heat-sensitive recording material was produced.
[Example 5]
The amount of pigment dispersion 1 dispersant (product of Toagosei Co., Ltd., trade name: Aron T-50, sodium polyacrylate, solid content 40%) is 0.63 parts, and the amount of water is 168.8 parts. A thermosensitive recording material was produced in the same manner as in Example 1 except that.

[Example 6]
Except that 100.0 parts of Rosetta-type light calcium carbonate (Albuquer LO) in Pigment Dispersion 1 were changed to 100.0 parts of Rosetta-type light calcium carbonate (Okutama Kogyo Co., Ltd., trade name: TP221BM, bulk density 230 g / L), A thermosensitive recording material was produced in the same manner as in Example 1.

[Example 7]
A thermosensitive recording material was produced in the same manner as in Example 1 except that the undercoat layer coating solution 2 was used instead of the undercoat layer coating solution 1.
<Undercoat layer coating solution 2>
Pigment dispersion 1 216.4 parts Organic hollow particles (Rohm and Haas, product name: HP1055,
Average particle diameter (d ₅₀ ) 1.0 μm, hollow ratio 50%) 20.0 parts Styrene-butadiene copolymer latex (manufactured by Nippon Zeon Co., Ltd.,
Product name: ST5526, solid content 48%) 40.0 parts Completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd., product name: PVA117)
(Solid content 10%) 30.0 parts

[Comparative Example 1]
100.0 parts of Rosetta-type light calcium carbonate (Albuquer LO) in Pigment Dispersion Liquid 1 were made into 100.0 parts of Rosetta-type light calcium carbonate (Specialty Minerals Inc., trade name: Albuquer 5970, bulk density: 250 g / L). A thermosensitive recording material was produced in the same manner as in Example 1 except that.
[Comparative Example 2]
A thermosensitive recording material was produced in the same manner as in Example 7 except that 100.0 parts of Rosetta type light calcium carbonate (Albuquer LO) in Pigment Dispersion Liquid 1 were changed to 100.0 parts of Rosetta type light calcium carbonate (Albuquer 5970). .

[Comparative Example 3]
Heat sensitive as in Example 1, except that 100.0 parts of Rosetta-type light calcium carbonate (Albuquer LO) in Pigment Dispersion 1 was replaced with 100.0 parts of calcined clay (trade name: Ansilex 93, manufactured by BASF). A recording body was produced.

[Comparative Example 4]
A heat-sensitive recording material was produced in the same manner as in Example 1 except that the pigment dispersion 3 was used instead of the pigment dispersion 1.
<Pigment dispersion 3>
Rosetta type light calcium carbonate (Specialty Minerals Inc.
Product name: Albuquer LO, bulk density: 210 g / L) 100.0 parts Water 170.5 parts

[Comparative Example 5]
A heat-sensitive recording material was produced in the same manner as in Example 1 except that the pigment dispersion 4 was used in place of the pigment dispersion 1.
<Pigment dispersion 4>
Rosetta type light calcium carbonate (Specialty Minerals Inc.
Product name: Albuquer LO, bulk density: 210 g / L) 100.0 parts Dispersant (manufactured by San Nopco, trade name: SN Dispersant 5041,
Sodium polycarboxylate, solid content 40%) 0.45 parts water 170.0 parts [Comparative Example 6]
A heat-sensitive recording material was produced in the same manner as in Example 1 except that the pigment dispersion 5 was used instead of the pigment dispersion 1.
<Pigment dispersion 5>
Rosetta type light calcium carbonate (Specialty Minerals Inc.
Product name: Albuquer LO, bulk density: 210 g / L) 100.0 parts Dispersant (manufactured by San Nopco Co., Ltd., product name: Rome D,
Highly condensed sodium naphthalene sulfonate, solid content 100%) 0.18 parts water 170.3 parts

The following evaluation was performed about the produced thermosensitive recording material.
<Color development sensitivity (print density)>
Using the TH-PMD manufactured by Okura Electric Co., Ltd. (with a thermal recording paper printing tester and a Kyocera thermal head installed), the printed thermal recording medium was solid printed at an applied energy of 0.21 mJ / dot and a printing speed of 50 mm / sec. did. The printing density of the solid printing part was measured with a Macbeth densitometer (RD-914, using an amber filter) to evaluate the color development sensitivity.

<Image quality of recorded images>
Using the TH-PMD manufactured by Okura Electric Co., Ltd. (with a thermal recording paper printing tester and a Kyocera thermal head installed), the printed thermal recording medium was solid printed at an applied energy of 0.15 mJ / dot and a printing speed of 50 mm / sec. did. The solid print portion was visually observed and the image quality of the recorded image was evaluated according to the following criteria. If the evaluation is ◎ or ○, there is no practical problem.
(Double-circle): The white-out part is hardly observed.
○: Some white spots are observed, but the whole is solid.
Δ: White spots are observed.
X: There are many white spots.

  The evaluation results are shown in Table 1.

＊表中、ＰＶＡ／ＳＢＲ（％）は、ＳＢＲ（スチレン・ブタジエン共重合体ラテックス）に対するＰＶＡ（完全ケン化型ポリビニルアルコール）の重量割合（固形分％）を表す。

* In the table, PVA / SBR (%) represents a weight ratio (solid content%) of PVA (fully saponified polyvinyl alcohol) to SBR (styrene-butadiene copolymer latex).

Claims (7)

A support, an undercoat layer comprising a pigment and a binder as main components provided on the support, further containing a dispersant, and a colorless to light-colored electron-donating leuco dye and an electron provided on the undercoat layer In a heat-sensitive recording material having a heat-sensitive recording layer containing a receptive color developer as a main component, the pigment contained in the undercoat layer forms secondary particles by agglomerating spindle-shaped primary particles radially. A heat-sensitive recording medium comprising Rosetta-type light calcium carbonate, having a bulk density of 240 g / L or less, and the dispersant contained in the undercoat layer is sodium polyacrylate. The heat-sensitive recording material according to claim 1, wherein the bulk density is 150 to 220 g / L. The heat-sensitive recording material according to claim 1 or 2, wherein the binder contained in the undercoat layer comprises a water-soluble resin and a water-insoluble resin, and the weight ratio of water-soluble resin / water-insoluble resin is 35/100 or less. The heat-sensitive recording material according to claim 1 or 2, wherein the binder contained in the undercoat layer comprises a water-soluble resin and a water-insoluble resin, and the weight ratio of water-soluble resin / water-insoluble resin is 3 to 30/100. . The heat-sensitive recording material according to any one of claims 1 to 4, wherein the water-soluble resin is a polyvinyl alcohol. The heat-sensitive recording material according to any one of claims 1 to 5, wherein the water-insoluble resin is a styrene-butadiene resin. The heat-sensitive recording material according to claim 1, wherein the rosetta-type light calcium carbonate is 70% by weight or more of the total pigment contained in the undercoat layer.