JP2017030301A - Thermosensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermosensitive recording medium which is high in recording density, suppresses the generation of head scum sticking to a thermal head during recording and has excellent sticking resistance, chemical barrier properties and suitability for sealing.SOLUTION: There is provided a thermosensitive recording medium which comprises a thermosensitive recording layer containing an electron-donating compound and an electron-accepting compound and a protective layer containing a pigment and an aqueous adhesive as main components in this order on a substrate, wherein the pigment contained in the protective layer is fine silica secondary particles having an average particle diameter of 30 to 900 nm formed by aggregation of amorphous silica primary particles having a particle diameter of 3 to 70 nm, the protective layer further contains an anionic polyethylene wax in a ratio of 0.5 to 20 mass% in the total solid content of the protective layer and the anionic polyethylene wax has a melting point of 90 to 110°C and an average particle diameter of 0.01 to 0.1 μm.SELECTED DRAWING: None

Description

  The present invention relates to a heat-sensitive recording material that utilizes a color-forming reaction between an electron-donating compound and an electron-accepting compound and that can obtain a recorded image by a color-forming reaction by thermal energy.

  A heat-sensitive recording material in which a recorded image is obtained by bringing an electron-donating compound and an electron-accepting compound into contact with each other by thermal energy is well known. Such a heat-sensitive recording material is relatively inexpensive, has a compact recording device, and is easy to maintain. Therefore, it is used for recording media such as facsimiles and various computers.

  In recent years, in particular, receipts for gas, water, electricity bills, ATM usage statements for financial institutions, various receipts, etc., financial record sheets (for so-called handy terminals), thermal recording labels for POS systems, and thermal recording labels. Thermal recording materials are also used for recording tags and the like.

  In particular, thermal recording paper for handy terminals may be used in a low-temperature environment. In winter, the components of the thermal recording material melted by heat are fused to the recording head and are forcibly conveyed by a feed roll to be melted. The so-called sticking that peels off the attachment portion easily occurs. In addition, it may be used outdoors when it rains, or it may be used indoors in contact with water, so the thermal recording material is excellent in water resistance, and it may not tear or become delaminated even when wet. Desired.

In order to solve the problem of sticking, a method of adding an oil-absorbing filler such as calcium carbonate, clay, talc, urea-formalin resin, amorphous silica or the like to the heat-sensitive recording layer is well known (Non-Patent Document 1). reference).
Among them, amorphous silica is particularly preferably used because it has a large oil absorption and a heat-sensitive recording material having high whiteness can be obtained. The primary particle diameter is 30 nm or more and the secondary particle diameter is 200 to 1000 nm, but the primary particle diameter is quite large, but the recording layer uses amorphous silica with a remarkably fine secondary particle diameter (see Patent Document 1). A recording layer using finely divided silica (see Patent Document 2), a recording layer using spherically treated silica fine particles (see Patent Document 3), and a recording layer using amorphous silica having a specific oil absorption (Patent Document 3) Reference 4), a recording layer using amorphous silica whose secondary particles have an average particle diameter of 3 to 10 μm and further defining oil absorption (see Patent Document 5), and a recording layer using amorphous silica (Patent Document) 6) has been proposed, but further improvement is required in terms of suppression of unnecessary color development due to sticking and scratching, recording density, barrier properties, and the like.

  For the purpose of improving the water resistance, it is common to use a combination of a modified polyvinyl alcohol having a reactive group and a curing agent as a binder for the protective layer of the thermal recording material. Examples thereof include a method using acetoacetyl-modified polyvinyl alcohol and a water-soluble polyamide resin (see Patent Document 7), a method using diacetone-modified polyvinyl alcohol and a polyamidoamine / epichlorohydrin resin (see Patent Document 8), and the like. Further, a method using a water-resistant resin (see Patent Document 9) has also been proposed.

  Furthermore, a method of adding an oxidized wax having an average particle size of 0.1 μm or less (see Patent Document 10) has been proposed, and an effect of improving the barrier property against plasticizers and oils is recognized, but higher barrier property and Since it may be used for payment handling slips for fees, etc., the suitability for stamping is also required.

JP 59-22794 A JP 59-26292 A JP 62-176878 A JP-A-7-76172 JP-A-8-310132 JP 2003-11519 A JP 2002-301868 A JP 2002-127601 A JP 2004-74531 A JP 2013-188955 A

Satoshi Shiga, Pulp and Paper Technology Times, 27 (8), 34 (1984)

  The main object of the present invention is to provide a heat-sensitive recording material having a high recording density, suppressing generation of head wrinkles that adhere to the thermal head during recording, and having excellent anti-sticking properties, barrier properties, and imprintability.

  As a result of various studies on the above problems, the present inventors have found, on the support, a heat-sensitive recording layer containing a leuco dye and a colorant, and a protective layer containing a pigment and a water-based adhesive as main components in this order. The pigment contained in the protective layer is a secondary particle having an average particle diameter of 30 to 900 nm formed by agglomerating amorphous silica primary particles having a particle diameter of 3 to 70 nm. 0.5-20 mass% of anionic polyethylene wax which is fine silica, has a melting point of 90-110 ° C. and an average particle size of 0.01-0.1 μm, based on the total solid content of the protective layer As a result, the inventors have found that the above-mentioned problems can be solved and have completed the present invention. That is, the present invention relates to the following thermal recording material.

  Item 1: A heat-sensitive recording material comprising, on a support, a heat-sensitive recording layer containing an electron-donating compound and an electron-accepting compound, and a protective layer containing a pigment and a water-based adhesive as main components in this order, The pigment contained in the protective layer is fine silica which is a secondary particle having an average particle diameter of 30 to 900 nm formed by agglomerating amorphous silica primary particles having a particle diameter of 3 to 70 nm, and the protective layer is further anionic polyethylene The wax is contained at a ratio of 0.5 to 20% by mass in the total solid content of the protective layer, the melting point of the anionic polyethylene wax is 90 to 110 ° C., and the average particle size is 0.01 to 0.1 μm. A heat-sensitive recording material.

  Item 2: The heat-sensitive adhesive according to Item 1, wherein the aqueous adhesive contained in the protective layer is at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol. Recorded body.

  Item 3: The heat-sensitive recording material according to Item 1 or 2, wherein the protective layer further contains a basic pigment as a pigment.

  Item 4: The heat-sensitive recording material according to any one of Items 1 to 3, wherein the aqueous adhesive in the protective layer is contained in a range of 20 to 100 parts by mass with respect to 100 parts by mass of the pigment.

  Item 5: The heat-sensitive recording material according to any one of Items 1 to 4, wherein the fine silica in the protective layer is contained at a ratio of 1 to 40% by mass in the total solid content of the protective layer.

  The heat-sensitive recording material of the present invention has a high recording density, suppresses generation of head wrinkles that adhere to the thermal head during recording, and is excellent in sticking resistance, barrier properties, and printing suitability.

  In this specification, the expression “comprising” includes the concepts of “comprising”, “consisting essentially of”, and “consisting solely”.

  The thermal recording material according to the present invention will be described in detail below. In the present invention, the support has a thermal recording layer and a protective layer in this order, the thermal recording layer contains a leuco dye and a colorant, and the protective layer contains fine silica and fine anionic polyethylene wax. It is characterized by including.

  First, the anionic polyethylene wax contained in the protective layer of the present invention will be described.

Currently, the production methods for polyethylene wax are roughly divided into the following four methods.
(1) A method of polymerizing at a high temperature and a high pressure with an ethylene radical catalyst, or a method of polymerizing at a low pressure with a Ziegler catalyst.
(2) A method of reducing molecular weight of general molding polyethylene by thermal decomposition.
(3) A method of separating and refining low molecular weight polyethylene produced as a by-product when producing general molding polyethylene.
(4) A method for oxidizing polyethylene for general molding.

  In general, emulsion waxes are obtained by oxidizing a polyethylene wax produced by the methods (1), (2), and (3) among these methods by an oxidation method such as air oxidation to add a carboxyl group or a hydroxyl group. These waxes are those produced by the method of (4) above, and these waxes are stable in a small amount of surfactant or in a soap-free state because of the carboxyl groups and hydroxyl groups present in the molecule. An aqueous suspension or an aqueous emulsion can be obtained.

  Various physical properties such as melting point, density, compatibility with other resins, etc. of the manufactured polyethylene wax are very large due to differences in molecular structure such as the length of their side chains, the amount of branched chains, and the difference in molecular weight. to cause. In general, polyethylene with many side chains and long polyethylene is of high density type (density 0.96 or more), polyethylene with short side chains and short is low density type (density of 0.93 or less), and density is 0.94 to 0.95. Are classified as medium density type.

  In the present invention, low density polyethylene having a melting point of 90 to 110 ° C. and a density of 0.93 or less is preferably used.

  Moreover, when making polyethylene wax into an emulsion, anionic, nonionic, and cationic polyethylene waxes can be obtained depending on the type of emulsifier. In the present invention, anionic polyethylene wax is obtained using an anionic emulsifier. In general, the thermal recording layer coating liquid is anionic, so when nonionic or cationic polyethylene wax emulsions are used, aggregates are formed in the thermal recording layer coating liquid, or color development of the thermal recording layer is inhibited. To do.

  In the case where an emulsifier is not used and the average particle size is reduced to 0.1 μm or less, an anionic polyethylene wax obtained using an anionic dispersant is preferred.

  The melting point of the anionic polyethylene wax in the present invention is 90 to 110 ° C. By setting the melting point to 110 ° C. or less, the gap between the pigment and the aqueous adhesive can be entered. On the other hand, by setting it as 90 degreeC or more, melt viscosity does not become low and a polyethylene film can be formed in a protective layer and on a protective layer. Further, if the average particle size is in the range of 0.01 to 0.1 μm, it is considered that the barrier property against the plasticizer and the like is improved by more uniformly dispersing in the protective layer.

Next, the fine silica contained in the protective layer of the present invention will be described.
In the protective layer of the present invention, by using the secondary particles having the specific average particle diameter formed by agglomerating the amorphous silica primary particles, the adhesion with the printing ink (fixing property of the printing ink) is excellent. In addition, when printing with the thermal head of the printing unit, the protective layer absorbs the melted printing ink component, thereby preventing ink adhesion to the thermal head and suppressing sticking. Further, since the transparency is high, there is an advantage that the recording sensitivity is improved.

  The method for producing secondary particles having an average particle diameter of 30 to 900 nm obtained by agglomerating amorphous silica primary particles having a particle diameter of 3 to 70 nm used in the present invention is not particularly limited. Bulk raw materials such as regular silica, precipitates obtained by chemical reaction in the liquid phase, etc., sol-gel method by hydrolysis of metal alkoxide, high temperature hydrolysis in the gas phase, etc. It can be obtained by the method. Examples of the mechanical means include an ultrasonic wave, a high-speed rotary mill, a roller mill, a container drive medium mill, a medium agitation mill, a jet mill, a sand grinder, and a wet medialess atomizer. When mechanically pulverizing, it is preferable to pulverize in water to obtain an aqueous silica dispersion.

  Here, the particle diameter Dp of the primary particles can be calculated from the following formula.

Asp (m ² / g) = SA × n (1)
In the above formula (1), Asp represents the specific surface area, SA represents the surface area of one primary particle, and n represents the number of primary particles per gram.

Dp (nm) = 3000 / Asp (2)
In the above formula (2), Dp represents the particle size of the primary particles, and Asp represents the specific surface area.

The above formula (2) is derived on the assumption that the shape of the silica primary particles is a true sphere and the density of the silica is d = 2 (g / cm ³ ).

  The specific surface area is a surface area per unit mass of amorphous silica (that is, per 1 g). As can be seen from the above formula (2), the larger the specific surface area, the smaller the primary particle diameter. When the primary particle size is reduced, the pores formed from the primary particles (that is, the pores formed in the secondary particles obtained by agglomerating the primary particles) are reduced, and the capillary pressure is increased. Therefore, it is considered that the melted ink component is quickly absorbed and sticking is suppressed. Further, the secondary particles formed from the primary particles are also complicated, and it is assumed that a capacity capable of sufficiently absorbing the melted ink component can be secured. About the particle diameter of a primary particle, it is 3-70 nm, Preferably it is 5-50 nm, More preferably, it is 7-40 nm, More preferably, it is 7-20 nm. As for the upper limit of the primary particle size, the smaller the value, the better the head wrinkle suppression and the sticking resistance.

  Here, the specific surface area of the amorphous silica was measured by measuring the nitrogen adsorption and desorption isotherm of the powder sample obtained by drying the fine pigment (that is, the amorphous silica used in the present invention) at 105 ° C. Measured after vacuum degassing at 200 ° C. for 2 hours using an apparatus (SA3100 type manufactured by Coulter). E. The T specific surface area is calculated.

  From the above, the particle size of the primary particles of the amorphous silica used in the present invention was calculated by the above formula (2) by actually measuring the specific surface area using the above specific surface area measuring device (SA3100 type manufactured by Coulter). Is.

  Moreover, the average particle diameter of a secondary particle is 30-900 nm, Preferably it is 40-700 nm, More preferably, it is 50-500 nm. Secondary particles having an average particle diameter of less than 30 nm are difficult to produce, and if the average particle diameter is less than 30 nm, the volume of pores formed is too small to permeate the melted ink component and sticking occurs. May occur. On the other hand, if it exceeds 900 nm, the transparency may be lowered, and the recording sensitivity may be lowered, or the barrier property against a plasticizer or the like may be lowered.

Here, the average particle diameter of the secondary particles means that the silica aqueous dispersion obtained by the above-mentioned method is adjusted to a solid content concentration of 5%, and immediately after stirring and dispersing with a homomixer at 5000 rpm for 30 minutes. After coating so that the coating amount after drying is about 3 g / m ² on the polyester film subjected to hydrophilic treatment, it is dried to obtain a sample, which is observed with an electron microscope (SEM and TEM) and 10,000 to 40 This is the result of taking a magnifying electron micrograph and measuring the martin diameter of secondary particles in a 5 cm square of the electron micrograph, and averaging (see “Fine Particle Handbook”, Asakura Shoten, p52, 1991).

  In addition, the stirring and dispersion in the homomixer is merely performed for uniform dispersion in order to improve the measurement accuracy, and the size of the secondary particles changes substantially before and after the stirring and dispersion in the homomixer. It is not considered.

  The content ratio of the fine silica as secondary particles in the protective layer is preferably about 1 to 40% by mass, more preferably about 2.5 to 30% by mass in the total solid content of the protective layer. If it is the said 1-40 mass% range, the said desired effect will be easy to be acquired, and it will be excellent in especially oil resistance and plasticizer resistance.

  The protective layer preferably further contains a basic pigment as a pigment. As a result, the background density can be kept low, and the background fog resistance can be improved. The basic pigment is preferably at least one selected from magnesium carbonate, magnesium silicate, light calcium carbonate, heavy calcium carbonate, and aluminum hydroxide. These are preferable from the viewpoint of head wrinkle suppression and anti-sticking. The light calcium carbonate is preferably highly oil-absorbing. If necessary, other known pigments can be added as long as the desired effects of the present invention are not lost. Examples of such other pigments include plastic pigments such as kaolin, calcined kaolin, titanium oxide, colloidal silica, synthetic layered mica, and urea-formalin resin filler. Here, the basic pigment is a pigment that brings the pH of the dissolved aqueous solution to the alkali side.

  In addition, colloidal silica is substantially composed of primary particles, and secondary particles that are aggregates of the primary particles are substantially absent.

  The total use ratio of these other pigments is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 45% by mass or less, and particularly preferably 35% by mass or less in the total solid content of the protective layer.

  In the present invention, as the water-based adhesive used in the protective layer, at least one selected from the group consisting of conventionally known water-soluble adhesives and water-dispersible adhesives can be appropriately used.

  Specific examples of the water-soluble adhesive include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, and itaconic acid-modified polyvinyl alcohol. Modified polyvinyl alcohol; starch such as starch and oxidized starch or derivatives thereof; cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose; in addition, sodium polyacrylate, polyvinylpyrrolidone, acrylamide-acrylate Polymer, acrylamide-acrylic acid ester-methacrylic acid terpolymer, styrene-maleic anhydride Phosphate copolymer alkali salt, isobutylene - maleic anhydride copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, gum arabic, casein and the like.

  Examples of water-dispersible adhesives include polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic ester, vinyl chloride-vinyl acetate copolymer, polybutyl methacrylate, ethylene-vinyl acetate copolymer emulsion, and styrene-butadiene. Copolymers, styrene-butadiene-acrylic copolymers and the like can be mentioned, and these can also be used as dispersions (latex).

  These water-soluble adhesives and water-dispersible adhesives may be used alone or in combination of two or more.

  The aqueous adhesive in the protective layer is preferably contained in the range of 20 to 100 parts by mass, more preferably in the range of 30 to 60 parts by mass with respect to 100 parts by mass of the pigment. By setting it as said range, an anionic polyethylene wax will enter into the clearance gap between a pigment and a water-based adhesive, and the effect of this invention can be exhibited regretfully.

  In the protective layer in the present invention, among these water-soluble adhesives and water-dispersible adhesives, particularly for sticking suppression and water resistance, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol and At least one modified polyvinyl alcohol selected from carboxy-modified polyvinyl alcohol (hereinafter also referred to as “specific modified polyvinyl alcohol”) is preferably used.

  The acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol contained in the protective layer are a monomer and vinyl ester having an acetoacetyl group, a diacetone group, a silyl group, and a carboxy group, respectively. It is produced by saponifying a resin obtained by copolymerization.

  The degree of saponification is preferably from about 85 mol% to about 100 mol% of complete saponification, more preferably from about 90 to 100 mol%. The average degree of polymerization is preferably about 300 to 3000, and more preferably about 400 to 2000. The degree of modification is preferably about 0.5 to 10 mol%, more preferably about 1 to 9 mol%. The higher the degree of polymerization and the degree of saponification, the better the water resistance, but it can be selected according to the situation from the paint concentration, viscosity, coating property or drying property.

  If the degree of modification is in the range of about 0.5 to 10 mol%, sufficient water resistance is obtained, and the solubility in water does not decrease, so that the solution concentration can be prevented from being lowered.

  The use ratio of the specific modified polyvinyl alcohol used in the protective layer is preferably about 10 to 90% by mass, more preferably about 15 to 50% by mass, and more preferably about 20 to 40% by mass in the total solid content of the protective layer. Is more preferable.

  Other adhesives can be used in combination as long as the effects of the present invention are not impaired. Examples of the adhesive include diisobutylene-maleic anhydride copolymer salt, ethylene-acrylic acid copolymer salt, styrene-acrylic acid copolymer salt, urea resin, melamine resin, amide resin, and the like. In addition, acrylic resin or urethane resin latex may be used.

  Furthermore, the stability of the coating liquid for the protective layer is further improved by incorporating a water-soluble acidic compound in the protective layer. The water-soluble acidic compound added to the protective layer coating solution is not particularly limited, but boric acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, Water-soluble organic acids having a carboxyl group such as adipic acid, pimelic acid, fumaric acid, maleic acid, tartaric acid, citric acid, lactic acid, benzoic acid, phthalic acid, benzenetricarboxylic acid and the like are preferable.

  The addition amount of the water-soluble acidic compound is not particularly limited, but is preferably added so that the pH of the protective layer coating solution is 3.0 to 7.0, and is in the range of 4.0 to 6.0. Is more preferable. If pH is the range of 3.0-7.0, it can suppress that the viscosity of a coating liquid becomes high with time.

  Other auxiliary agents that can be added to the protective layer coating solution include, for example, lubricants such as zinc stearate, calcium stearate, carnauba wax, paraffin wax, ester wax, sodium alkylbenzene sulfonate, sodium dioctyl sulfosuccinate, sulfone-modified polyvinyl alcohol. , Surfactants such as sodium polyacrylate, dialdehyde starch, methylol urea, glyoxylate, epoxy compound, hydrazine compound and other water-resistant agents, ultraviolet absorbers, fluorescent dyes, coloring dyes, mold release agents, Auxiliaries such as antioxidants can also be added.

The protective layer in the present invention is a mixture of specific fine silica and anionic polyethylene wax, water-based adhesive, other pigments, water-soluble acidic compounds, various auxiliaries, if necessary, using water as a medium, for example. The coating solution for protective layer prepared by the above is applied and dried on a heat-sensitive recording layer described later so that the coating amount after drying is 1 to 6 g / m ² .

The heat-sensitive recording material of the present invention advantageously has a printing part formed by printing on the protective layer. As the ink used for printing, ultraviolet curable ink is preferable, and printing may be performed by a commonly used method.

  Various types of ultraviolet curable inks are known, and are generally composed of a color material, a prepolymer, a monomer, a photoinitiator, and an additive. Examples of the color material include organic color pigments, inorganic color pigments, dyes, and fluorescent dyes.

  Examples of the prepolymer include polyol acrylate, epoxy acrylate, urethane acrylate, polyester acrylate, alkyd acrylate, and polyether acrylate.

  Examples of the monomer include monoacrylate, diacrylate, and triacrylate.

  What is necessary is just to select a photoinitiator suitably from a well-known photoinitiator according to the prepolymer and monomer to be used.

  Examples of the additive include a lubricant, an antifoaming agent, and a surfactant.

  As the ultraviolet curable ink containing these components, various commercially available products are available on the market, such as Flash Dry Series (Toyo Ink Co., Ltd.), for example, FDS TK Series, FDS New Series, etc .; BESTCURE (T & K TOKA Co., Ltd.) ), For example, “UV RNC”, “UV NVR”, “UV STP”, etc .; DAI Cure (manufactured by Dainippon Ink, Inc.), for example, “Aviglio”, “Scepter”, “MU seal”, etc. .

Next, the thermal recording layer will be described.
Examples of the thermal recording system having an electron donating compound and an electron accepting compound include a combination of a leuco dye and a colorant, a combination of a diazonium salt and a coupler, a transition element such as iron, cobalt, copper, and a chelate compound. Examples thereof include combinations and combinations of aromatic isocyanate compounds and imino compounds. Among these, a combination of a leuco dye and a colorant is preferably used because of excellent color density. Hereinafter, the thermosensitive recording layer comprising a combination of a leuco dye and a colorant will be described in detail.

  Various known leuco dyes and colorants can be used. Specific examples of the leuco dye include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide and 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl). ) -6-dimethylaminophthalide, 3- (N-ethyl-Np-tolyl) amino-7-N-methylanilinofluorane, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-6 -Methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3-di (n-butyl) ) Amino-6-methyl-7-anilinofluorane, 3-di (n-pentyl) amino-6-methyl-7-anilinofluorane, 3- (N-ethyl-p) Toluidino) -6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-chloro-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl) ethylene-2-yl] -4,5 6,7-tetrachlorophthalide, 3-p- (p-dimethylaminoanilino) anilino-6-methyl-7-chlorofluorane, 3-p- (p-chloroanilino) anilino-6-methyl-7- Examples include chlorofluorane, 3,6-bis (dimethylamino) fluorene-9-spiro-3 ′-(6′-dimethylamino) phthalide, and the like.

  Of course, it is not limited to these, Moreover, 2 or more types can also be used together. The ratio of the leuco dye used is not particularly limited because it varies depending on the colorant to be used. For example, the total solid content of the heat-sensitive recording layer is preferably about 3 to 50% by mass, and about 5 to 40% by mass. More preferred.

  Examples of the colorant include 4,4′-isopropylidenediphenol, 4,4′-cyclohexylidenediphenyl, 1,1-bis (4-hydroxyphenyl) -ethane, 1,1-bis (4-hydroxy). Phenyl) -1-phenylethane, 4,4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-allyloxydiphenylsulfone, 3,3′-diallyl-4,4′-dihydroxydiphenylsulfone, 2,2′-bis [4- (4-hydroxyphenyl) phenoxy] diethyl ether, Np-toluenesulfonyl-N′-3- (p -Toluenesulfonyloxy) phenylurea, 4,4′-bis [(4-methyl-3-phen Xoxycarbonylaminophenyl) ureido] diphenylsulfone, 4-hydroxybenzoic acid benzyl ester, N, N′-di-m-chlorophenylthiourea, Np-tolylsulfonyl-N′-phenylurea, 4,4′-bis (P-tolylsulfonylaminocarbonylamino) diphenylmethane, N- [2- (3-phenylureido) phenyl] benzenesulfonamide, 4- [2- (p-methoxyphenoxy) ethyloxy] zalicylic acid zinc, 4- {3- ( Examples include zinc p-tolylsulfonyl) propyloxy] salicylate, zinc 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylate, and a diphenylsulfone crosslinked compound represented by the following general formula (1).

（式（１）中、ｎは１〜７の整数を表す。）

(In formula (1), n represents an integer of 1 to 7)

  The ratio of the colorant used is not particularly limited because it varies depending on the leuco dye used, but is preferably about 10 to 70% by mass and more preferably about 12 to 50% by mass in the total solid content of the heat-sensitive recording layer. .

  The heat-sensitive recording layer can contain a storability improving agent. Thereby, the storage stability of a recording part can be improved. Specific examples of the storage stability improver include, for example, 2,2′-ethylidenebis (4,6-di-tert-butylphenol), 4,4′-thiobis (2-methyl-6-tert-butylphenol), 1, 1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 2,2- Hindered phenol compounds such as bis (4-hydroxy-3,5-dimethylphenyl) propane, 4,4′-diglycidyloxydiphenylsulfone, 4-benzyloxy-4 ′-(2-methylglycidyloxy) diphenylsulfone, Diglycidyl terephthalate, cresol novolac epoxy resin, phenol novolac epoxy resin, bisphenol Epoxy compounds such Lumpur A type epoxy resin, N, N'-di-2-naphthyl -p- phenylenediamine, bis (4-ethylene iminocarbonyl aminophenyl) include methane and the like.

  When a preservability improver is used, its use ratio may be an effective amount for improving the preservability, but usually about 1 to 30% by mass is preferable in the total solid content of the heat-sensitive recording layer, A range of about 5 to 20% by mass is more preferable.

  The heat-sensitive recording layer can contain a sensitizer. Thereby, the recording sensitivity can be increased. Specific examples of the sensitizer include, for example, stearamide, methylenebisstearate, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, 2-naphthylbenzyl ether, m-terphenyl, p-benzylbiphenyl, p- Tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy) ethane, 1,2-di (4-methylphenoxy) ethane, 1,2-di (4-methoxyphenoxy) ) Ethane, 1,2-di (4-chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (3-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p-acetoluidide, p-acetophene Examples include zido, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, oxalic acid di-p-chlorobenzyl ester, oxalic acid di-p-methylbenzyl ester, and oxalic acid dibenzyl ester. .

  When a sensitizer is used, the proportion used may be an effective amount for sensitization, but usually it is preferably about 2 to 40% by mass in the total solid content of the thermal recording layer, A range of about 25% by mass is more preferable.

  The heat-sensitive recording layer can contain an aqueous adhesive. What is necessary is just to select what can be contained in the said protective layer suitably as a water-based adhesive. Among these, it is preferable to contain at least one modified polyvinyl alcohol selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol.

  Furthermore, various auxiliary agents can be added to the thermal recording layer coating liquid as necessary. For example, kaolin, light (heavy) calcium carbonate, calcined kaolin, titanium oxide, magnesium carbonate, aluminum hydroxide, Amorphous silica, pigments such as urea / formalin resin filler, dispersants such as sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate, fatty acid metal salt, zinc stearate, calcium stearate, polyethylene wax, carnauba wax, Waxes such as paraffin wax and ester wax, hydrazine compounds, glyoxal, boric acid, dialdehyde starch, methylolurea, glyoxylate, epoxy compounds and other water resistance agents, antifoaming agents, colored dyes and fluorescent dyes Is .

The heat-sensitive recording layer is, for example, water as a dispersion medium, an electron-donating compound such as a leuco dye, an electron-accepting compound such as a colorant, and a sensitizer and a storage stability improver, if necessary, separately or separately. The coating amount for the heat-sensitive recording layer prepared by adding a water-based adhesive after finely dispersing with an agitator / sand mill such as an attritor or sand mill is finely dispersed so that the average particle size is 2 μm or less. It is formed by applying and drying on one surface of the support so as to be ² to 20 g / m ² .

  The support used in the heat-sensitive recording material of the present invention is not particularly limited, and examples thereof include neutral or acidic high-quality paper, synthetic paper, transparent or translucent plastic film, and white plastic film. In addition, although the thickness of a support body is not specifically limited, Usually, it is about 20-200 micrometers.

  In the present invention, if necessary, an undercoat layer can be provided between the support and the thermosensitive recording layer in order to further improve the recording sensitivity and the recording runnability. The undercoat layer has an oil absorption amount of 70 ml / 100 g or more, in particular, about 80 to 150 ml / 100 g of an oil-absorbing pigment and / or organic hollow particles and / or thermally expandable particles, and an undercoat layer coating solution containing an adhesive as a main component. Is coated on a support and dried. Here, the oil absorption is a value determined according to the method of JIS K 5101.

  Various types of oil-absorbing pigments can be used. Specific examples include inorganic pigments such as calcined kaolin, amorphous silica, light calcium carbonate, and talc. The average particle diameter of the primary particles of these oil-absorbing pigments is preferably about 0.01 to 5 μm, more preferably about 0.02 to 3 μm. The use ratio of the oil-absorbing pigment can be selected from a wide range, but generally it is preferably about 2 to 95% by mass, more preferably about 5 to 90% by mass in the total solid content of the undercoat layer.

For the undercoat layer, for example, the coating amount for the undercoat layer containing an oil-absorbing pigment, organic hollow particles, adhesive, etc., with water as the dispersion medium, is preferably about 3 to ²⁰ g / m ² , more preferably after drying. Is formed by coating and drying on a support so as to be about 4 to 8 g / m ² .

  The method for forming the undercoat layer, the heat-sensitive recording layer and the protective layer is not particularly limited. For example, an appropriate application such as air knife coating, varibar blade coating, pure blade coating, rod blade coating, short dwell coating, curtain coating, die coating, etc. Depending on the method, the undercoat layer coating solution is applied and dried on the support, and then the thermal recording layer coating solution and the protective layer coating solution are applied and dried on the undercoat layer.

  If necessary, a protective layer, a printing layer, a magnetic recording layer, or an ink jet recording layer can be provided on the surface of the support opposite to the surface having the thermosensitive recording layer (hereinafter also referred to as the back surface). . Further, it is possible to perform a smoothing process using a super calendar or the like in an arbitrary process after the formation of each layer or after the formation of all the layers. Further, various known techniques in the heat-sensitive recording body production field, such as providing an adhesive layer on the back side of the support of the heat-sensitive recording body, can be added as necessary.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” and “%” respectively represent “parts by mass” and “% by mass” unless otherwise specified.

  In addition, the average particle diameter of the secondary particles of silica and the particle diameter of the primary particles used in Examples and Comparative Examples were measured by the following methods.

<Average particle diameter of secondary particles>
The silica dispersion obtained by the following preparation method was diluted with water to adjust the concentration to 5% by mass, and the obtained diluted silica dispersion was stirred and dispersed with a homomixer at 5000 rpm for 30 minutes. Immediately after that, the dispersion was applied onto a hydrophilically treated polyester film so that the coating amount after drying was about 3 g / m ² , and then dried to obtain a sample, and an electron microscope (SEM and TEM). Observed, taken an electron micrograph of 10,000 to 400,000 times, and measured and averaged the martin diameter of secondary particles in a 5 cm square of the obtained electron micrograph (“Particle Handbook”, Asakura Shoten , P52, 1991).

  In addition, the "average secondary particle diameter" of the commercially available silica used for the production of the silica dispersions A to F describes the manufacturer's catalog value unless otherwise specified.

  Moreover, regarding the commercially available silica used for the production of silica dispersions A to F and the silica dispersion after pulverization and dispersion, the “particle diameter of primary particles” is a value calculated according to the above formula (2) using the value of specific surface area. It is. In addition, regarding the silica dispersion after pulverization and dispersion, the “average particle diameter of secondary particles” is a value measured according to the method described in the above section <Average particle diameter of secondary particles>.

  The silica dispersion used in Examples and Comparative Examples was prepared as follows.

<Preparation of silica dispersion A>
Commercially available silica (trade name: Leolosil QS-30, average secondary particle diameter 1500 nm determined by laser light scattering method, primary particle diameter 10 nm, specific surface area 300 m ² / g, manufactured by Tokuyama Corporation) is dispersed in water using a sand grinder. Then, using a wet medialess atomizer (trade name: Nanomizer, manufactured by Yoshida Kikai Kogyo Co., Ltd.), pulverization and dispersion were repeated, and 10% silica having a primary particle diameter of 10 nm and a secondary particle average particle diameter of 80 nm. A dispersion was obtained.

<Preparation of silica dispersion B>
Commercially available silica (trade name: Fineseal X-45, average secondary particle size 4500 nm, primary particle size 12 nm, specific surface area 260 m ² / g, manufactured by Tokuyama Corporation) is dispersed in water with a sand grinder and then wet medialess. Using a atomizer (trade name: Nanomizer, manufactured by Yoshida Kikai Kogyo Co., Ltd.), pulverization and dispersion were repeated to obtain a 10% silica dispersion having a primary particle diameter of 12 nm and a secondary particle average particle diameter of 300 nm.

<Preparation of silica dispersion C>
Commercially available silica (trade name: Fineseal X-45, average secondary particle size 4500 nm, primary particle size 12 nm, specific surface area 260 m ² / g, manufactured by Tokuyama Corporation) is dispersed in water with a sand grinder and then wet medialess. Using a atomizer (trade name: Nanomizer, manufactured by Yoshida Kikai Kogyo Co., Ltd.), pulverization and dispersion were repeated to obtain a 10% silica dispersion having a primary particle diameter of 12 nm and a secondary particle average particle diameter of 500 nm.

<Preparation of silica dispersion D>
Commercially available silica (trade name: Fineseal X-45, average secondary particle size 4500 nm, primary particle size 12 nm, specific surface area 260 m ² / g, manufactured by Tokuyama Corporation) is dispersed in water with a sand grinder and then wet medialess. Using a atomizer (trade name: Nanomizer, manufactured by Yoshida Kikai Kogyo Co., Ltd.), pulverization and dispersion were repeated to obtain a 10% silica dispersion having a primary particle diameter of 12 nm and a secondary particle average particle diameter of 700 nm.

<Preparation of silica dispersion E>
Commercially available silica (trade name: Mizukasil P-527, average secondary particle size 4500 nm, primary particle size 54 nm, specific surface area 56 m ² / g, manufactured by Mizusawa Chemical Co., Ltd.) is water-dispersed and pulverized with a sand grinder. Using a atomizer (trade name: Nanomizer, manufactured by Yoshida Kikai Kogyo Co., Ltd.), pulverization and dispersion were repeated to obtain a 10% silica dispersion having a primary particle diameter of 54 nm and a secondary particle average particle diameter of 900 nm.

<Preparation of silica dispersion F>
Commercially available silica (trade name: Fine Seal X-45, average secondary particle size 4500 nm, primary particle size 12 nm, specific surface area 260 m ² / g, manufactured by Tokuyama Corporation) is dispersed in water with a stirrer, and the primary particle size 12 nm. A 10% silica dispersion having an average secondary particle diameter of 4500 nm was obtained.

<Preparation of silica dispersion G>
Commercially available silica (trade name: Fineseal X-45, average secondary particle size 4500 nm, primary particle size 12 nm, specific surface area 260 m ² / g, manufactured by Tokuyama Corporation) is dispersed in water with a sand grinder and then wet medialess. Using a atomizer (trade name: Nanomizer, manufactured by Yoshida Kikai Kogyo Co., Ltd.), pulverization and dispersion were repeated to obtain a 10% silica dispersion having a primary particle diameter of 12 nm and a secondary particle average particle diameter of 1000 nm.

<Preparation of silica dispersion H>
Commercially available silica (trade name: Mizukasil P-527, average secondary particle size 4500 nm, primary particle size 54 nm, specific surface area 56 m ² / g, manufactured by Mizusawa Chemical Co., Ltd.) is water-dispersed and pulverized with a sand grinder. Using a atomizer (trade name: Nanomizer, manufactured by Yoshida Kikai Kogyo Co., Ltd.), pulverization and dispersion were repeated to obtain a 10% silica dispersion having a primary particle diameter of 54 nm and a secondary particle average particle diameter of 1200 nm.

Example 1
-Preparation of coating solution for undercoat layer Fine hollow particles (trade name: Ropaque SN-1055) were dispersed in a dispersion obtained by dispersing 60 parts of calcined kaolin (trade name: Ansilex 93, manufactured by BASF) in 80 parts of water. , 75 parts by Rohm & Haas, solid content concentration 26.5%), 31 parts styrene-butadiene latex (trade name: L-1571, solid content concentration 48% by Asahi Kasei Chemicals) and carboxymethyl cellulose (product) Name: Serogen 7A, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 2.5 parts, similarly, a composition comprising 1 part of carboxymethyl cellulose (trade name: Serogen AG gum, Daiichi Kogyo Seiyaku Co., Ltd.) and 15.5 parts of water are mixed. By stirring, a coating solution for undercoat layer was obtained.

Preparation of leuco dye dispersion (liquid A) A composition comprising 10 parts of 3-di- (n-butyl) amino-6-methyl-7-anilinofluorane, 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water. A leuco dye dispersion was obtained by pulverizing with a sand mill using a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) until the median diameter became 0.5 μm.

-Colorant dispersion (liquid B) preparation A composition comprising 10 parts of bis (3-allyl-4-hydroxyphenyl) sulfone, 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water was subjected to laser diffraction particle size using a sand mill. The colorant dispersion was obtained by pulverizing until a median diameter of 1.5 μm was obtained using a measuring instrument SALD2200 (manufactured by Shimadzu Corporation).

-Colorant dispersion (liquid C) preparation A composition comprising 10 parts of a diphenylsulfone cross-linking compound (trade name: D-90, manufactured by Nippon Soda Co., Ltd.), 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water was added to a sand mill. Were pulverized with a laser diffraction particle size analyzer SALD2200 (manufactured by Shimadzu Corporation) until the median diameter became 1.0 μm to obtain a colorant dispersion.

-Preparation of sensitizer dispersion (liquid D) A composition comprising 10 parts of di-p-methylbenzyl oxalate, 5 parts of a 5% aqueous solution of methylcellulose and 15 parts of water was subjected to a laser diffraction particle size analyzer SALD2200 using a sand mill. A sensitizer dispersion was obtained by pulverizing until the median diameter by Shimadzu Corporation was 1.0 μm.

-Preparation of coating solution for heat-sensitive recording layer 41 parts of liquid A, 70 parts of liquid B, 32 parts of liquid C, 29 parts of liquid D, acetoacetyl-modified polyvinyl alcohol (trade name: Gohsenx Z-200, degree of saponification: 99.4 mol) %, Average polymerization degree: 1000, modification degree: 5 mol%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., 90 parts of 10% aqueous solution, butadiene copolymer latex (trade name: L-1571, manufactured by Asahi Kasei Co., Ltd., solid content concentration 48%) 2.1 parts, silica (trade name: Nipseal E-743, manufactured by Tosoh Silica) 18 parts, light calcium carbonate (trade name: Brilliant-15, manufactured by Shiroishi Kogyo Co., Ltd.), 3 parts, zinc stearate A composition comprising 19 parts of an aqueous dispersion (trade name: Hydrin Z-8-36, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 36%) and 70 parts of water was mixed and stirred to obtain a thermal recording layer coating solution. .

-Preparation of coating solution for protective layer Acetacetyl-modified polyvinyl alcohol (trade name: Gohsenx Z-200, degree of saponification: 99.4 mol%, average degree of polymerization: 1000, degree of modification: 5 mol%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd. ) 10% aqueous solution 253 parts, silica dispersion A 10% dispersion 140 parts, aluminum hydroxide (trade name: Hygielite H-42M, Showa Denko KK) 40 parts, highly oil-absorbing light calcium carbonate (product) Name: Callite KT, manufactured by Shiraishi Kogyo Co., Ltd.) 5 parts, aqueous zinc stearate dispersion (trade name: Hydrin Z-8-36, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 36%), 10 parts, anionic polyethylene wax emulsion (Product name: Meikatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid concentration 25%, melting point 100 ° C., particle size 0.04 μm) 6 parts, sodium glyoxylate A composition comprising 5 parts of a 10% aqueous solution (trade name: SPM-01, manufactured by Nippon Synthetic Chemical Industry) was mixed and stirred, and adjusted to pH 5 with an aqueous 10% acetic acid solution to obtain a coating solution for a protective layer. .

- a heat-sensitive recording material prepared basis weight of 60 g / m ² on one surface of woodfree paper, undercoat layer coating liquid, heat-sensitive recording layer coating solution, and respectively the protective layer coating liquid application amount after drying 6.0g / ^m 2, was coated to a 4.5 g / ^{m 2,} and 2.5 g / ^{m 2,} dried, subbing layer, the heat-sensitive recording layer, and after sequentially forming a protective layer, the surface supercalendered Was subjected to a smoothing treatment to obtain a heat-sensitive recording material.

Example 2
A thermosensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for protective layer of Example 1, 140 parts of silica dispersion B was used instead of 140 parts of silica dispersion A.

Example 3
A thermosensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for protective layer of Example 1, 140 parts of silica dispersion C was used instead of 140 parts of silica dispersion A.

Example 4
A thermosensitive recording material was obtained in the same manner as in Example 1 except that, in the preparation of the coating liquid for protective layer of Example 1, 140 parts of silica dispersion D was used instead of 140 parts of silica dispersion A.

Example 5
A thermosensitive recording material was obtained in the same manner as in Example 1 except that, in the preparation of the protective layer coating liquid of Example 1, 140 parts of silica dispersion E140 was used instead of 140 parts of silica dispersion A.

Example 6
In the preparation of the coating liquid for protective layer of Example 1, instead of silica dispersion A140 parts, commercially available silica dispersion (trade name: silo jet 703A, concentration 20%, average secondary particle diameter 300 nm, average of secondary particles A thermosensitive recording material was obtained in the same manner as in Example 1 except that 70 parts of a particle diameter of 300 nm, a primary particle diameter of 11 nm, a specific surface area of 280 m ² / g, manufactured by Grace Devison Co., Ltd. were used.

  The “average secondary particle size” is a value described in the catalog of the manufacturer. The “particle size of primary particles” is a value calculated according to the above formula (2) using the value of the specific surface area. The “average particle diameter of secondary particles” is a value measured according to the method described in the section <Average particle diameter of secondary particles>.

Example 7
A thermosensitive recording material was obtained in the same manner as in Example 2 except that in the preparation of the coating solution for the protective layer of Example 2, 30 parts of silica dispersion B was used instead of 140 parts of silica dispersion B.

Example 8
A thermosensitive recording material was obtained in the same manner as in Example 2 except that in the preparation of the coating liquid for protective layer of Example 2, 300 parts of silica dispersion B was used instead of 140 parts of silica dispersion B.

Example 9
In the preparation of the coating solution for the protective layer of Example 1, an anionic polyethylene wax emulsion (trade name: Maycatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 100 ° C., particle size 0.04 μm) 6 Example 1 except that 6 parts of an anionic polyethylene wax emulsion (trade name: Meikatex KSP, manufactured by Meisei Chemical Co., Ltd., solid content concentration 24%, melting point 95 ° C., particle size 0.03 μm) were used instead of parts. In the same manner, a heat-sensitive recording material was obtained.

Example 10
In the preparation of the coating solution for the protective layer of Example 1, an anionic polyethylene wax emulsion (trade name: Maycatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 100 ° C., particle size 0.04 μm) 6 Example 1 except that 10 parts of an anionic polyethylene wax emulsion (trade name: Nopcoat PEM-17, manufactured by San Nopco, solid concentration 40%, melting point 105 ° C., particle size 0.04 μm) were used instead of parts. In the same manner, a heat-sensitive recording material was obtained.

Example 11
In the preparation of the protective layer coating liquid of Example 1, acetoacetyl-modified polyvinyl alcohol (trade name: Gohsenx Z-200, degree of saponification: 99.4 mol%, average degree of polymerization: 1000, degree of modification: 5 mol%, Japan 260 parts of 10% aqueous solution of diacetone-modified polyvinyl alcohol (trade name: DF-24, degree of polymerization: 2400, manufactured by Nippon Acetate / Poval) was used instead of 250 parts of 10% aqueous solution of Synthetic Chemical Industry). Except for the above, a heat-sensitive recording material was obtained in the same manner as in Example 1.

Example 12
In the preparation of the protective layer coating liquid of Example 1, acetoacetyl-modified polyvinyl alcohol (trade name: Gohsenx Z-200, degree of saponification: 99.4 mol%, average degree of polymerization: 1000, degree of modification: 5 mol%, Japan Instead of 250 parts of 10% aqueous solution of Synthetic Chemical Industry Co., Ltd., 250 parts of 10% aqueous solution of silicon-modified polyvinyl alcohol (trade name: R-1130, polymerization degree: 1700, manufactured by Kuraray Co., Ltd.) was used, and sodium glyoxylate ( A thermosensitive recording material was obtained in the same manner as in Example 1 except that a 10% aqueous solution (trade name: SPM-01, manufactured by Nippon Synthetic Chemical Industry) was not used.

Comparative Example 1
In the preparation of the coating liquid for protective layer of Example 1, instead of using 140 parts of silica dispersion A, the amount of aluminum hydroxide (trade name: Hygielite H-42M, Showa Denko KK) was changed to 40 parts and 54 parts. A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the above-mentioned parts were used.

Comparative Example 2
In the preparation of the protective layer coating solution of Example 1, 70 parts of colloidal silica (trade name: Snowtex 20, solid content concentration 20%, manufactured by Nissan Chemical Co., Ltd.) was used instead of 140 parts of silica dispersion A. In the same manner as in Example 1, a heat-sensitive recording material was obtained.

Comparative Example 3
In the preparation of the protective layer coating liquid of Example 1, Example 1 was used except that 35 parts of 40% dispersion of kaolin (trade name: UW90, manufactured by Engelhard) was used instead of 140 parts of silica dispersion A. In the same manner, a heat-sensitive recording material was obtained.

Comparative Example 4
A thermosensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for protective layer of Example 1, 140 parts of silica dispersion F140 was used instead of 140 parts of silica dispersion A.

Comparative Example 5
A thermosensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for the protective layer of Example 1, 140 parts of silica dispersion G140 was used instead of 140 parts of silica dispersion A.

Comparative Example 6
A thermosensitive recording material was obtained in the same manner as in Example 1 except that in the preparation of the coating liquid for protective layer of Example 1, 140 parts of silica dispersion H140 was used instead of 140 parts of silica dispersion A.

Comparative Example 7
In the preparation of the coating solution for the protective layer of Example 1, an anionic polyethylene wax emulsion (trade name: Maycatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 100 ° C., particle size 0.04 μm) 6 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that no part was used.

Comparative Example 8
In the preparation of the coating solution for the protective layer of Example 1, an anionic polyethylene wax emulsion (trade name: Meikatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 100 ° C., particle size 0.04 μm) A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the amount was changed to 100 parts instead of 6 parts.

Comparative Example 9
In the preparation of the coating solution for the protective layer of Example 1, an anionic polyethylene wax emulsion (trade name: Maycatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 100 ° C., particle size 0.04 μm) 6 Example, except that 12.5 parts of an anionic polyethylene wax emulsion (trade name: SN coat 87, manufactured by San Nopco, solid concentration 40%, melting point 80 ° C., particle size 0.05 μm) was used instead of parts. In the same manner as in No. 1, a heat-sensitive recording material was obtained.

Comparative Example 10
In the preparation of the coating solution for the protective layer of Example 1, an anionic polyethylene wax emulsion (trade name: Maycatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 100 ° C., particle size 0.04 μm) 6 Except for using 20 parts of anionic polyethylene wax emulsion (trade name: Meikatex HP-602A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 130 ° C., particle size 0.05 μm) instead of parts. A heat-sensitive recording material was obtained in the same manner as in Example 1.

Comparative Example 11
In the preparation of the coating solution for the protective layer of Example 1, an anionic polyethylene wax emulsion (trade name: Maycatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 100 ° C., particle size 0.04 μm) 6 Instead of using 12.5 parts of soap-free polyolefin wax dispersion (trade name: Chemipearl W4005, manufactured by Mitsui Chemicals, solid content concentration 40%, melting point 110 ° C., particle size 0.6 μm), A heat-sensitive recording material was obtained in the same manner as in Example 1.

Comparative Example 12
In the preparation of the coating solution for the protective layer of Example 1, an anionic polyethylene wax emulsion (trade name: Maycatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 100 ° C., particle size 0.04 μm) 6 Except that 16.7 parts of an anionic paraffin wax emulsion (trade name: Hydrin P-7, manufactured by Chukyo Yushi Co., Ltd., solid content concentration 30%, melting point 54 ° C., particle diameter 1.1 μm) was used instead of A heat-sensitive recording material was obtained in the same manner as in Example 1.

Comparative Example 13
In the preparation of the coating solution for the protective layer of Example 1, an anionic polyethylene wax emulsion (trade name: Maycatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 100 ° C., particle size 0.04 μm) 6 Except that 22.7 parts of a cationic polyethylene wax emulsion (trade name: Meikax PEC-17, manufactured by Meisei Chemical Co., Ltd., solid content concentration: 22%, melting point: 90 ° C., particle size: 0.04 μm) was used instead of the parts. In the same manner as in Example 1, a heat-sensitive recording material was obtained.

Comparative Example 14
In the preparation of the coating solution for the protective layer of Example 1, an anionic polyethylene wax emulsion (trade name: Maycatex HP-598A, manufactured by Meisei Chemical Co., Ltd., solid content concentration 25%, melting point 100 ° C., particle size 0.04 μm) 6 Nonionic polyethylene wax emulsion (trade name: Meikax HP-65, manufactured by Meisei Chemical Co., Ltd., solid content concentration 40%, melting point 100 ° C., particle size 0.06 μm) was used in place of 12.5 parts. In the same manner as in Example 1, a heat-sensitive recording material was obtained.

  The heat-sensitive recording material thus obtained was allowed to stand at 40 ° C. and 50% RH for 24 hours, and then evaluated for the following items. The results were as shown in Table 1.

(Background density and recording density)
Using a thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording body was recorded at an applied energy of 0.24 mJ / dot, and the resulting printed portion and unrecorded portion (background portion) ) In the visual mode of a reflection densitometer (RD-914, manufactured by Macbeth). The printing portion shows that the larger the numerical value, the higher the recording density, and it is preferably 1.20 or more practically. The background density of the unrecorded portion is preferably 0.15 or less.

(Head wrinkle suppression)
Using a thermal recording evaluation machine (trade name: TH-PMD, manufactured by Okura Electric Co., Ltd.), each thermal recording medium was recorded at an applied energy of 0.40 mJ / dot, and the fouling state of the thermal head was visually observed. Evaluation based on the criteria.
A: There is no adhesion and no problem.
B: There is almost no adhesion and there is no problem in practical use.
C: There is adhesion, which may cause a problem of printing trouble.
D: There is a problem that adhesion is remarkable and printing trouble occurs.

(Anti-sticking)
The heat-sensitive recording material of the present invention advantageously has a printing part formed by printing on the protective layer. On the protective layer, T & K TOKA's UV peel OP varnish UP-2 ink was printed, and the print portion of each obtained thermal recording medium was used with a handy terminal high-speed thermal printer SP650V (manufactured by Osaki Datatech Co., Ltd.) Printing was performed in an environment of −10 ° C., and the sticking property of the printed portion was visually observed and evaluated according to the following criteria.
A: There is no sticking at all and there is no problem.
B: There is almost no sticking and there is no problem in practical use.
C: Sticking is observed, which may cause a problem of printing failure.
D: There is a problem that sticking is remarkably caused to cause a printing failure.

(Barrier properties)
A wrap film (trade name: High Wrap KMA-W, manufactured by Mitsui Chemicals Co., Ltd.) is wrapped on a polycarbonate pipe (diameter 40 mm) in a triple layer, and a heat-sensitive recording medium colored under the recording density evaluation condition is placed on the wrap film. A wrap film was wound on the lap film three times, and the remaining condition of the recording part after being allowed to stand at 40 ° C. for 24 hours was visually observed, and the barrier property against the plasticizer was evaluated according to the following criteria.
A: There is no decoloring and there is no problem.
B: There is almost no decoloring and there is no problem in practical use.
C: There is decoloration, which may cause a problem in practical use.
D: Discoloration is remarkable and there is a problem.

(Sealability)
The heat-sensitive recording surface (the surface of the protective layer) was imprinted with rust bellflower color meat ink, “Shachihata name” manufactured by Shiachihata Co., Ltd., and the following criteria (1) to (3) were confirmed and evaluated according to the following criteria.
(1) Immediately after that, wipe with a tissue and check whether the characters can be read.
(2) Seal and confirm the drying property of the ink after 5 days.
(3) After stamping and leaving for 10 minutes, and then immersing in water for 10 minutes, take it out from the water and rub it 10 times with your finger to check whether the stamped characters can be read.
A: There is no problem.
B: Almost no color erasure and no problem in practical use. Also, the ink drying property is almost untouchable and has no practical problem.
C: Discoloration is observed and may cause a problem. In addition, there is a practical problem with respect to the drying property of the ink.
D: Discolored remarkably and there is a problem. In addition, the drying property of the ink is not dried, and the surroundings are significantly stained.

Claims (5)

  A heat-sensitive recording layer comprising, on a support, a heat-sensitive recording layer containing an electron-donating compound and an electron-accepting compound, and a protective layer containing a pigment and a water-based adhesive as main components in this order. The pigment contained is fine silica which is a secondary particle having an average particle diameter of 30 to 900 nm formed by agglomerating amorphous silica primary particles having a particle diameter of 3 to 70 nm, and the protective layer further protects the anionic polyethylene wax. It is contained at a ratio of 0.5 to 20% by mass in the total solid content of the layer, the melting point of the anionic polyethylene wax is 90 to 110 ° C., and the average particle size is 0.01 to 0.1 μm. A thermal recording medium.   The heat-sensitive recording material according to claim 1, wherein the aqueous adhesive contained in the protective layer is at least one selected from acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, and carboxy-modified polyvinyl alcohol. .   The heat-sensitive recording material according to claim 1, wherein the protective layer further contains a basic pigment as a pigment.   The heat-sensitive recording material according to any one of claims 1 to 3, wherein the aqueous adhesive in the protective layer is contained in a range of 20 to 100 parts by mass with respect to 100 parts by mass of the pigment.   The heat-sensitive recording material according to any one of claims 1 to 4, wherein the fine silica in the protective layer is contained in a proportion of 1 to 40% by mass in the total solid content of the protective layer.