JP2012116158A - Heat-sensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-sensitive recording medium that has superior image quality printed to a thermal recording surface, and especially bar code reading performance when printed at a backside (opposite surface of a heat-sensitive recording layer) of a heat-sensitive recording medium, and in which print density, color developing sensitivity, and reprinting performance are favorable.SOLUTION: In the heat-sensitive recording medium which prepares a heat-sensitive recording layer containing an electron donative leuco dye of colorlessness or light color, and an electron accepting developer on a support, the support comprises a pulp containing 5 wt.% of a mechanical pulp, a drip infusion water absorbency (based on a drip infusion water absorbency specified by Japan Technical Association of the Pulp and Paper Industry J.TAPPI No.32-2:2000 except for setting an amount of dropping water to 0.001 ml) of a surface of the support in which a heat-sensitive recording layer is prepared is at least 50 seconds, and the heat-sensitive recording layer contains at least one kind of a diphenylsulfone compound shown by the following general formula (1) as an electron accepting developer. In the formula, Rdenotes a n-propoxy group, an isopropoxy group, or a n-butoxy group.

Description

  The present invention is excellent in print back-through when the back surface of the heat-sensitive recording material is printed, and has excellent print quality on the heat-sensitive recording surface, in particular, barcode readability, and good print density, color sensitivity, and reprintability. About the body.

  The heat-sensitive recording medium usually contains 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”) such as a phenolic compound, After grinding and dispersing into fine particles, mixing the two, adding a binder, filler, sensitivity improver, lubricant and other auxiliaries, the resulting coating solution is paper, synthetic paper, film, plastic The color is developed by an instantaneous chemical reaction by heating with a thermal head, hot stamp, thermal pen, laser beam or the like, and a recorded image is obtained. The thermal recording medium is widely used as a recording medium for facsimiles, computer terminal printers, automatic ticket machines, measurement recorders, receipts such as supermarkets and convenience stores, and when used as a recording medium for receipts, Opportunities to print advertisements on the reverse side are increasing, and in addition to the traditionally required color sensitivity and image quality for thermal recording media, general printing suitability (prevention of print back-through prevention, fleshing property, printing workability) Etc.) is required.

When general printing is performed on the back side of the thermal recording medium, if the opacity of the support of the thermal recording medium is insufficient, the ink penetrates into the opposite side (the side with the thermal recording layer) when printing, and the thermal recording There arises a problem that characters printed on the recording layer are difficult to read (that is, print back-through). For this reason, it is important to improve the opacity of the support of the thermal recording medium.
In general, as a method for improving the opacity of paper, it is known to make the paper bulky. In the field of thermal recording media, thermal recording media having improved color development sensitivity (printing density under low applied energy conditions) using a support to which a bulking agent such as polyhydric alcohol is added are disclosed (Patent Documents). 1).
In addition, mechanical pulp is used as a raw material for newspapers and magazines, but it is generally known that the use of mechanical pulp makes the paper bulky (Patent Document 2, etc.).
In addition, in a thermal recording material having ink jet recording suitability on the back surface, by providing two undercoat layers between the support and the thermal recording layer, the ink jet ink is applied to the thermal recording surface when ink jet recording is performed. A method for suppressing the influence is disclosed (Patent Document 3).

JP 2002-293023 A JP-A-6-286308 JP2008-105222

However, when a bulking agent is used for the support in order to improve the opacity, the rigidity of the support is lowered, so that the printing workability is lowered. In addition, since the surface strength of the support also decreases, troubles such as paper peeling and picking occur during general printing.
When mechanical pulp is used for the support, when the thermal recording layer is applied on the support, the coating liquid is easily impregnated in the support, and the coating property and smoothness of the coating layer are reduced ( Sinking), print density, color sensitivity (print density under low applied energy conditions) and reprintability (print density after storage) are reduced.
Therefore, the present invention is excellent in image quality printed on the heat-sensitive recording surface, particularly barcode readability, even when printed on the back surface (opposite surface of the heat-sensitive recording layer) of the heat-sensitive recording material, and with print density, color sensitivity, It is an object of the present invention to provide a heat-sensitive recording material having good reprintability.

（１）
（式中、Ｒ１はｎ−プロポキシ基、イソプロポキシ基、ｎ−ブトキシ基を表す。）
即ち、本発明は、支持体上に、無色ないし淡色の電子供与性ロイコ染料及び電子受容性顕色剤を含有する感熱記録層を設けた感熱記録体であって、該支持体が機械パルプを５重量％以上含有するパルプから成り、該支持体の感熱記録層を設ける面の点滴吸水度（滴下水の量を０．００１ｍｌとする以外は、紙パルプ技術協会 Ｊ．ＴＡＰＰＩ Ｎｏ．３２−２：２０００に規定される点滴吸水度に準じる。）が５０秒以上でであり、該感熱記録層が電子受容性顕色剤として下記一般式（１）で表されるジフェニルスルホン化合物を少なくとも１種類含有することを特徴とする感熱記録体である。

（１）
（式中、Ｒ１はｎ−プロポキシ基、イソプロポキシ基、ｎ−ブトキシ基を表す。） As a result of diligent study of the above problems, the inventors of the present invention provided a thermosensitive recording medium provided with a thermosensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on the support. A mechanical pulp is contained in the support, the sizing degree of the support (degree of treatment with the sizing agent) is adjusted, and the drip water absorption on the surface on which the heat-sensitive recording layer of the support is provided is 50 seconds or more. It has been found that the above problem can be solved when the recording layer contains at least one diphenylsulfone compound represented by the following general formula (1) as an electron-accepting developer, and the present invention has been completed.

(1)
(In the formula, R1 represents an n-propoxy group, an isopropoxy group, or an n-butoxy group.)
That is, the present invention is a heat-sensitive recording material provided with a heat-sensitive recording layer comprising a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on a support, and the support is made of mechanical pulp. Drip water absorption on the surface of the support on which the heat-sensitive recording layer is provided comprising 5% by weight or more (except that the amount of water dropped is 0.001 ml, J. TAPPI No. 32-2 : According to the drip water absorption specified in 2000) for 50 seconds or more, and the heat-sensitive recording layer has at least one diphenylsulfone compound represented by the following general formula (1) as an electron-accepting developer. It is a heat-sensitive recording material characterized by containing.

(1)
(In the formula, R1 represents an n-propoxy group, an isopropoxy group, or an n-butoxy group.)

  According to the present invention, even when printing is performed on the back surface of the heat-sensitive recording material (that is, the surface opposite to the heat-sensitive recording layer), the quality of the image printed on the heat-sensitive recording surface, in particular, the barcode readability is excellent (that is, print back-through is not caused). A heat-sensitive recording material having good print density, color development sensitivity (print density under low applied energy conditions), and reprintability (print density after storage) can be obtained.

When mechanical pulp is contained in the support, the following effects are exhibited.
Compared with chemical pulp, which has almost the same form of wood fiber and is made into a single fiber, mechanical pulp is mostly broken fibers and fiber bundles. Therefore, the sheet | seat containing mechanical pulp has high opacity by becoming bulky. Furthermore, since mechanical pulp is hardened with hydrophobic lignin, it has high adsorptivity to ink and mechanical pulp itself has voids. Therefore, the sheet containing mechanical pulp is excellent in the ink setting property which is hydrophobic.
On the other hand, the sheet containing the bulking agent that is hydrophilic has high opacity due to the increase in bulk, but the inking property to the ink that is hydrophobic is insufficient, There is a problem that ink easily penetrates into the opposite surface when printing (that is, print back-through) occurs.

In the present invention, the mechanical pulp constituting the support refers to pulp obtained by physically crushing wood, and includes pulp that has been treated with chemicals or heat before crushing. Examples of the mechanical pulp include ground pulp (GP), refiner ground pulp (RGP), semi-chemical pulp (SCP), chemi-ground pulp (CGP), and thermomechanical pulp (TMP). If it is based on, it will not be limited to these, It can use individually or in combination of 2 or more types.
In particular, thermomechanical pulp (TMP) has a higher specific scattering coefficient than other mechanical pulps and can provide high opacity, so that it is preferably used as a support for the heat-sensitive recording material of the present invention.

  In the present invention, this mechanical pulp and chemical pulp (softwood bleached kraft pulp (NBKP), unbleached kraft pulp (NUKP), hardwood bleached kraft pulp (LBKP), unbleached kraft pulp (LUKP)), non-wood pulp Or the like can be appropriately blended depending on the required quality of the support.

Waste paper pulp may be used for the support of the present invention.
Waste paper pulp refers to pulp obtained by using waste paper as a raw material and removing ink contained in the waste paper in a deinking process. As inks contained in waste paper, printing inks (edited by the Japan Printing Society, “Printing Engineering Handbook”, Gihodo, p.606, 1983), non-impact printing inks (“latest and special function inks”, CMC, p1, 1990) ) And non-heated osmotic drying offset inks used mainly in newspapers and paper-based magazines (Akiyuki Goto, Journal of Japan Printing Society, 38 (5), 7, (2001), etc.).
Used paper includes used paper containing newspaper, flyers, magazines, cardboard and other mechanical pulp as the main raw material pulp, coated paper magazines, heat / pressure sensitive paper, imitation / color-quality paper, copy paper, computer output paper It is largely divided into used paper containing chemical pulp as the main raw material pulp.
Mechanical pulp and chemical pulp contained in waste paper retain their properties. As described above, the mechanical pulp contained in the waste paper is bulky, and the sheet containing the waste paper containing the mechanical pulp has high opacity.
Non-wood pulp includes bagasse pulp and straw pulp.

In the present invention, the blending ratio of the mechanical pulp to the total pulp of the support is 5% by weight or more, preferably in the range of 5 to 95% by weight, more preferably 10 to 50% by weight, still more preferably 10 to 25% by weight. is there.
If the blending ratio of the mechanical pulp is less than 5% by weight with respect to the whole pulp of the support, it becomes difficult to obtain sufficient opacity, and the effect of preventing the ink see-through cannot be expected. On the other hand, when the blending ratio of the mechanical pulp is more than 25% by weight, the effect of preventing ink back-through is improved, but the smoothness of the support surface tends to decrease. As a result, the uniformity of the coated surface when the thermosensitive recording layer is coated on the support is lowered, and the fineness of the printed image is lowered, so that the improvement effect of the barcode readability tends to be saturated. . In particular, when the blending ratio of mechanical pulp is more than 50% by weight, the fineness of the printed image is greatly reduced and the print density and reprintability are lowered, and the support is accompanied by a decrease in entanglement (bonding between fibers) of pulp fibers. Since the strength of the ink is reduced, problems such as paper peeling that causes the support surface layer to peel off may occur due to tackiness (adhesiveness) of the ink during printing.
When used paper pulp is used, this mechanical pulp includes mechanical pulp contained in the used paper pulp, and the blending ratio of the mechanical pulp in the used paper pulp is measured according to JIS P8120. The mixing ratio of the waste paper pulp to the whole pulp of the support is preferably in the range of 5 to 95% by weight, more preferably 5 to 80% by weight for the purpose of optimizing the balance between the effect of preventing the ink see-through and the fineness of the printed image. %, More preferably 5 to 60% by weight.

  In order to improve whiteness and opacity, a filler may be added to the support. As fillers, known fillers generally used in the past, specific examples include inorganic fillers such as calcium carbonate, kaolin, clay, white carbon, titanium oxide, styrene-methacrylic copolymer resins, urea-formalin resins. And organic fillers such as polystyrene resin. The addition amount of the filler is not particularly limited, but is preferably adjusted to be added so that the ash content of the support is 2 to 20%. If the ash content of the support exceeds 20%, the entanglement of the pulp fibers is hindered, so that sufficient strength may not be obtained. The ash content of the support is measured according to JIS P8251.

In the support of the heat-sensitive recording material of the present invention, the drip water absorption on the surface on which the heat-sensitive recording layer is provided is 50 seconds or more.
This drip water absorbency is the same as that of J. Pulp and Paper Technology, except that the amount of dripped water is 1 μl (0.001 ml). TAPPI No. It is measured according to 32-2: 2000 (paper—water absorption test method—part 2: dropping method). That is, when a test specimen (paper) is stretched horizontally and 1 μl (0.001 ml) of distilled water is dropped on the measurement surface (ie, the surface on which the heat-sensitive recording layer is provided), the water droplets are absorbed by visual observation. Measure the time to complete. The size of the test specimen (paper) may be any size as long as this measurement is possible. For example, a circular test piece having a diameter of at least about 40 mm may be used. The drip water absorption is expressed in time (seconds). The higher the drip water absorption, the lower the water absorption, and the lower the drip water absorption, the higher the water absorption.
The drip water absorption on the surface of the support on which the heat-sensitive recording layer is provided is 50 seconds or more, thereby suppressing the sinking of the coating liquid when the heat-sensitive recording layer is coated on the support, and the effectiveness of the coating layer Since the layer thickness is increased and a uniform coated surface is obtained, the fineness of the printed image is improved, and the barcode readability, print density, and reprintability are improved. The drip water absorption is preferably 80 seconds or more, and more preferably 100 seconds or more. When the drip water absorption is high, the barcode reading property, printing density, and reprinting property are good. When the drip water absorption on the surface of the support on which the heat-sensitive recording layer is provided is less than 50 seconds, the coating liquid sinks greatly when the heat-sensitive recording layer is applied onto the support, and sufficient barcode readability is obtained. Printing density and reprintability cannot be obtained. On the other hand, if the drip water absorption is too high, in general printing, printing unevenness due to ink repellency (especially density unevenness at halftone dots) may occur, or retransfer due to a decrease in ink fixability (after printing, the ink may In other words, the drip water absorption is preferably 300 seconds or less, more preferably 200 seconds or less.

  In the present invention, the drip water absorption on the surface of the support on which the thermosensitive recording layer is provided is adjusted by treating the support with a sizing agent. The sizing agent may be internally added in the paper making process of the support, or may be applied after paper making (external addition), but is preferably applied after paper making (external addition). The desired drip water absorption can be obtained by appropriately selecting and adjusting the type, amount of use, and addition method of such a sizing agent according to the pulp constituting the support.

  The internal addition is a method in which a sizing agent is added to the pulp slurry at a so-called wet end, and the sizing agent is incorporated into the support at the same time as the paper making, and the external addition is a blade coater after paper making of the support. In this method, a sizing agent is coated on the surface of a support using a coating machine represented by a gate roll coater, a size press coater, a rod metering size press and the like.

As the sizing agent for internal addition (internal sizing agent), in the case of acidic papermaking, reinforced rosin sizing agent, emulsion sizing agent, synthetic sizing agent, etc., in the case of neutral papermaking, alkyl ketene dimer (AKD), Alkenyl succinic anhydride (ASA) and the like are used.
In addition, as a sizing agent for external addition (external sizing agent), cationic polymers such as styrene-maleic acid copolymer resins and styrene-acrylic acid copolymer resins, anionic polymers, and styrene polymers are used. , Cationic polymers such as isocyanate polymers, saponified alkyd resins such as rosin, tall oil and phthalic acid, anionic low molecular compounds such as saponified products of petroleum resin and rosin, α-olefin-maleic acid copolymer resins Acrylate-acrylic acid copolymer resin, alkyl ketene dimer (AKD), etc., but styrene-acrylic acid copolymer resin that easily interacts with carboxyl groups in cellulose under neutral papermaking. Cationic polymers and alkyl ketene dimers (AKD) are preferred, especially styrene-actene. Cationic polymer Le acid copolymer resin is more preferable.

In general, when the above-mentioned mechanical pulp is contained in the support, the support becomes bulky and voids in the support increase, so that the drip water absorption tends to decrease.
In addition, when the support contains waste paper pulp, the drip water absorption of the support tends to decrease due to the influence of a surfactant contained in the waste paper pulp.
Even in such a case, a desired drip water absorption can be obtained by appropriately selecting and adjusting the type, amount of use, and addition method of the sizing agent.

  When the sizing agent is simply added in the papermaking process, or when the same sizing agent is applied to the surface opposite to the surface on which the heat-sensitive recording layer is provided (that is, the printing surface), the heat-sensitive recording layer is removed. The drip water absorption of the surface to be provided is the same as that measured on the opposite surface of the thermal recording medium.

The paper making method of the support is not particularly limited, and a long net machine including a top wire, a circular net machine, a combination machine of both, a Yankee dryer machine, and the like can be used. The papermaking method can be appropriately selected from acidic papermaking, neutral papermaking, and alkaline papermaking, and is not particularly limited.
Furthermore, if necessary, the support may be appropriately mixed with chemicals usually used in the paper making process, for example, various auxiliary agents such as a paper strength enhancer, an antifoaming agent and a colorant.
When the sizing agent is added internally, the addition amount may be set so as to give a desired drip water absorbency, but it is preferably 0.05 to 1% by weight with respect to the weight of the pulp in terms of solid content, more preferably 0.8%. 05 to 0.5% by weight.

In order to externally add the sizing agent to the support, for example, using a known coating apparatus such as a blade coater, a gate roll coater, a size press coater, or a rod metering size press, the sizing agent used for the external addition described above is used. In addition, the support is impregnated or coated with a coating liquid that may further contain a water-soluble polymer substance, a pigment, and the like that increase the surface strength.
Examples of water-soluble polymer substances that increase the surface strength include starch, enzyme-modified starch, thermochemically-modified starch, oxidized starch, esterified starch, etherified starch (for example, hydroxyethylated starch), cationized starch and the like. Starch, polyvinyl alcohol, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxyl modified polyvinyl alcohol, silanol modified polyvinyl alcohol, cation modified polyvinyl alcohol, polyvinyl alcohol such as terminal alkyl modified polyvinyl alcohol, polyacrylamide, cationic poly Polyacrylamides such as acrylamide, anionic polyacrylamide, amphoteric polyacrylamide, styrene-butadiene copolymer, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, poly Fluoride, polyvinylidene chloride, polyacrylic acid esters. These are used individually or in mixture of 2 or more types.
Various auxiliary agents such as a dispersant, a plasticizer, a pH adjuster, an antifoaming agent, a water retention agent, an antiseptic, an adhesive, a coloring dye, and an ultraviolet ray inhibitor may be appropriately blended in the coating liquid as necessary. Good.
The solid content concentration of the coating liquid is appropriately adjusted depending on the composition, the coating apparatus, and the like, but is usually about 5 to 15% by weight.

The coating amount in the case of externally adding a sizing agent may be an amount that gives a desired drip water absorbency, but is preferably used when a coating apparatus capable of one-side coating such as a blade coater is used. Has a dry coating amount of 0.005 to 0.25 g / m ² on the surface of the support on which the heat-sensitive recording layer is provided, and more preferably has a dry coating amount of 0.025 on the surface of the support on which the heat-sensitive recording layer is provided. it is a ~0.125g / ^{m 2.}
In addition, when using a coating device that performs simultaneous double-side coating, such as a gate roll coater or a size press coater, the coating is evenly applied on both sides of the support, so that the surface of the support on which the thermosensitive recording layer is provided is coated. The amount of work is half of the amount of coating that combines both sides.

  Further, the surface opposite to the surface on which the heat-sensitive recording layer of the support of the present invention is provided may be the same surface treatment as the surface on which the heat-sensitive recording layer is provided, but appropriate surface treatment or the like is performed so as to be suitable for general printing. Also good.

In the present invention, the basis weight of the support of the thermosensitive recording medium is preferably 30 to 100 g / ^{m 2,} more preferably 40 and 80 g / ^{m 2,} more preferably from 40 to 50 g / ^{m 2.} In this case, even when printing is performed on the back surface of the heat-sensitive recording material, the effects of the present invention, such as excellent bar code reading performance, are exhibited to the maximum. If the basis weight of the support is less than 30 g / m ² , there is a possibility that sufficient strength as a support for the heat-sensitive recording material cannot be obtained. On the other hand, when the basis weight of the support exceeds 100 g / m ² , it becomes difficult to obtain smoothness when the surface of the coating layer is treated with a calendar or the like, and there is a tendency that printing density and reprintability are lowered. The basis weight of the support is measured according to JIS P8124.

  The heat-sensitive recording layer of the present invention contains an electron-donating leuco dye and an electron-accepting developer, and at least one of the electron-accepting developers is a diphenylsulfone compound represented by the general formula (1). It is. If necessary, an electron-accepting developer other than the diphenylsulfone compound represented by the general formula (1), a sensitizer, a binder, a crosslinking agent, a pigment, a lubricant, a stabilizer, and the like may be included.

The reason why the heat-sensitive recording material of the present invention has excellent quality is presumed as follows.
As described above, the support of the present invention is prepared by adjusting the degree of sizing of the support (degree of treatment with the sizing agent) and setting the drip water absorption of the surface on which the thermosensitive recording layer of the support is provided to 50 seconds or more. As a result, the fineness of the printed image is improved, and the barcode readability, print density, and reprintability are improved. Further, when the heat-sensitive recording layer contains at least one diphenylsulfone compound represented by the general formula (1) as an electron-accepting developer, the print density is further improved and the color sensitivity (printing under low applied energy conditions) is achieved. Density) is excellent, and it is possible to obtain an extremely excellent thermal recording material.

  When the heat-sensitive recording layer of the present invention contains a developer other than the diphenylsulfone compound represented by the general formula (1), the content of the diphenylsulfone compound represented by the general formula (1) depends on the heat-sensitive recording. It is preferably 50% by weight or more, more preferably 90% by weight or more of the total developer (including the diphenylsulfone compound represented by the general formula (1)) to be contained in the layer.

  Hereinafter, various materials used for the heat-sensitive recording layer of the present invention will be exemplified, but these materials can also be used for each coating layer provided as necessary including the heat-sensitive recording layer.

  In the present invention, the organic developer contains at least one diphenylsulfone compound represented by the general formula (1). Specific examples of the diphenylsulfone compound represented by the general formula (1) include 4-hydroxy-4′-n-propoxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4 ′. -N-butoxydiphenyl sulfone. 4-Hydroxy-4'-n-propoxydiphenyl sulfone or 4-hydroxy-4'-isopropoxydiphenyl sulfone is more preferred because the printing density and color development sensitivity are particularly good. These developers may be used alone or in combination of two or more.

  As the color developer other than the diphenylsulfone compound represented by the general formula (1) used in the present invention, those known in the field of conventional pressure-sensitive or thermal recording paper as long as the desired effect in the present invention is not impaired. Are all usable and are not particularly limited. Examples of color developers other than the diphenylsulfone compound represented by the general formula (1) include inorganic acidic substances such as activated clay, attapulgite, colloidal silica, aluminum silicate, 4,4′-isopropylidenediphenol, 1, 1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4′-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, benzyl 4-hydroxybenzoate, 4 , 4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4′-methyldiphenylsulfone, 4-hydroxyphenyl-4′-benzyl Oxyphenyl sulfone, 3,4-di Droxyphenyl-4'-methylphenylsulfone, aminobenzenesulfonamide derivatives described in JP-A-8-59603, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio)- 3-oxapentane, butyl bis (p-hydroxyphenyl) acetate, methyl bis (p-hydroxyphenyl) acetate, 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 crosslinking type compounds described in WO97 / 16420, compounds described in WO02 / 081229 or JP2002-301873, and thios such as N, N′-di-m-chlorophenylthiourea Urea compound, p-chlorobenzoic acid, stearyl gallate, zinc bis [4- (n-octyloxycarbonylamino) salicylate] dihydrate, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- (p-Tolylsulfonyl) propyloxy] salicylic acid, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] aromatic carboxylic acid of salicylic acid, and zinc, magnesium, aluminum of these aromatic carboxylic acids , Calcium, titanium, manganese, tin, nickel, etc. Salts with valency metal salts, more like antipyrine complex of zinc thiocyanate, etc. composite zinc salt of terephthalaldehyde acid with other aromatic carboxylic acids. These developers can be used alone or in combination of two or more. The diphenylsulfone cross-linking compound described in WO 97/16420 is available as a 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 used in the present invention, any known leuco dyes in the field of conventional pressure-sensitive or thermal recording paper can be used, and are not particularly limited, but include triphenylmethane compounds, fluoran compounds, fluorenes. And divinyl compounds 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-di-n-butylamino-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-dibutyla Mino-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- Trifluoromethylanilino) fluorane, 3-di-n-pentylamino-6-chloro-7-anilinofluorane, 3-di-n-pentylamino-7- (p- Loloanilino) 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- -Anilinofluorane, 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-N-isobutylamino) -6-methyl-7 -Anilinofluorane, 3- (N-ethyl-N-ethoxypropylamino) -6-methyl-7-anilinofluorane, 3-cyclohexylamino-6-chlorofluorane, 2- (4-oxahexyl) -3-dimethylamino-6-methyl-7-anilinofluorane, 2- (4-oxahexyl) -3-diethylamino-6-methyl-7-anilinofluorane, 2- (4-oxahexyl)- 3-dipropylamino-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) aminoanilino Fluorane, 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-phen Ruaminophenyl) 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

  In the present invention, the leuco dye is at least selected from 3-di-n-pentylamino-6-methyl-7-anilinofluorane or 3-di-n-butylamino-6-methyl-7-anilinofluorane. One type is preferable because the print density, color development sensitivity, and ground color (whiteness) of the white paper portion are good. Further, when 3-di-n-pentylamino-6-methyl-7-anilinofluorane and 3-di-n-butylamino-6-methyl-7-anilinofluorane are used in combination, a plasticizer It is particularly preferable because of its good properties.

As the sensitizer used in the heat-sensitive recording material of the present invention, a conventionally known sensitizer can be used.
Examples of such sensitizers include fatty acid amides such as stearamide and palmitic acid amide, ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-di- (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-methyl) Ruphenoxymethyl) biphenyl, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di (3-methylphenoxy) ethylene, bis [2- (4-methoxy- Examples thereof include, but are not limited to, phenoxy) ethyl] ether, methyl p-nitrobenzoate, phenyl p-toluenesulfonate, and the like. These sensitizers may be used alone or in combination of two or more.

（２）
（Ｒ３〜Ｒ８は、水素原子、アルキル基、ハロゲン原子、ニトロ基、アルコキシ基、シアノ基、アリルオキシ基を表す。）

（３）
（式中、Ｒ９は炭素数１５または１７のアルキル基を表す。） In the present invention, when the sensitizer is at least one selected from a diphenylsulfone derivative represented by the following general formula (2) or a saturated fatty acid monoamide represented by the following general formula (3), the print density and the color sensitivity. Is preferable. In addition, when a diphenylsulfone derivative represented by the following general formula (2) and a saturated fatty acid monoamide represented by the following general formula (3) are used in combination, the color development sensitivity is good and powder blowing (printing with sublimation of the color development material) This is particularly preferable because the phenomenon that the portion is white and powder is less likely to occur.

(2)
(R3 to R8 represent a hydrogen atom, an alkyl group, a halogen atom, a nitro group, an alkoxy group, a cyano group, or an allyloxy group.)

(3)
(In the formula, R9 represents an alkyl group having 15 or 17 carbon atoms.)

  The binder used in the present invention includes fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, and 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 Cellulose like ethyl cellulose, acetyl cellulose Derivatives, casein, gum arabic, oxidized starch, etherified starch, dialdehyde starch, esterified starch, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylate, polyvinyl butyral, polystyrose and copolymers thereof, Examples thereof include polyamide resin, silicone resin, petroleum resin, terpene resin, ketone resin, coumarone resin, and the like. 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 used in the present invention include glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, potassium persulfate, ammonium persulfate, sodium persulfate, chloride chloride Examples include ferric iron, magnesium chloride, borax, boric acid, alum, ammonium chloride and the like.

  Examples of the pigment used in the present invention include inorganic pigments such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, and aluminum hydroxide.

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

Further, in the present invention, 4,4′-butylidene (6-tert-butyl-3-methylphenol) is used as an image stabilizer exhibiting an oil resistance effect of a recorded image and the like within a range that does not hinder a desired effect on the above problems. ), 2,2′-di-t-butyl-5,5′-dimethyl-4,4′-sulfonyldiphenol, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) Butane, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 4-benzyloxy-4 ′-(2,3-epoxy-2-methylpropoxy) diphenyl sulfone, etc. Can also be added.
In addition, benzophenone and triazole ultraviolet absorbers, dispersants, surfactants, antifoaming agents, antioxidants, fluorescent dyes, and the like can be used.

The types and amounts of leuco dyes, color developers, sensitizers and other various components used in the heat-sensitive recording material of the present invention are determined according to the required performance and recording suitability, and are not particularly limited. The developer is about 0.5 to 10 parts by weight and the sensitizer is about 0.5 to 10 parts by weight with respect to 1 part by weight of the leuco dye.
The leuco dye, color developer, and materials to be added as necessary are finely pulverized to a particle size of several microns or less with a pulverizer such as a ball mill, attritor or sand glider, or an appropriate emulsifier, and depending on the binder and purpose. Add various additive materials to make a coating solution.

The coating amount of the thermosensitive recording layer is not particularly limited, but the dry coating amount is preferably in the range of 2.0 to 12.0 g / m ² . In particular, when the dry coating amount is in the range of 4.0 to 8.0 g / m ² , good bar code readability, print density, and reprintability can be obtained. When the dry coating amount of the heat-sensitive recording layer is less than 2.0 g / m ² , the support is not sufficiently covered with the heat-sensitive recording layer, and there is a possibility that the barcode reading property and the print density are insufficient. When the dry coating amount of the heat-sensitive recording layer exceeds 12.0 g / m ² , the surface strength may be lowered.

In the heat-sensitive recording material of the present invention, an undercoat layer may be provided between the support and the heat-sensitive recording layer. This undercoat layer mainly comprises a binder and a pigment.
As the binder for the undercoat layer of the present invention, a generally used water-soluble polymer or hydrophobic polymer emulsion can be used as appropriate. Specific examples include cellulose derivatives such as polyvinyl alcohol, polyvinyl acetal, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch and its derivatives, polyacrylic acid soda, polyvinyl pyrrolidone, acrylic acid amide / acrylic acid ester copolymer, acrylic acid Water-soluble polymers such as amide / acrylic acid ester / methacrylic acid copolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, casein, Polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylate ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / acetic acid Cycloalkenyl copolymer, can be used styrene / butadiene / emulsion of a hydrophobic polymer such as an acrylic copolymer. These binders may be used alone or in combination of two or more.

As the pigment of the undercoat layer of the present invention, known pigments generally used conventionally, specific examples include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, magnesium hydroxide, calcined kaolin, clay, Inorganic pigments such as talc can be used. These pigments may be used alone or in combination of two or more. The pigment in the undercoat layer is usually 50 to 95% by weight, preferably 70 to 90% by weight, based on the total solid content of the undercoat layer.
Various additives such as a dispersant, a plasticizer, a pH adjuster, an antifoaming agent, a water retention agent, an antiseptic, a coloring dye, and an ultraviolet ray inhibitor may be appropriately blended in the undercoat layer coating liquid as necessary. Good.

The support of the heat-sensitive recording material of the present invention is designed so that the drip water absorption on the surface on which the heat-sensitive recording layer is provided is 50 seconds or more. Even in the coating solution for the undercoat layer, Similarly, there is an effect of suppressing sinking of the coating liquid into the support. Therefore, even if the coating amount of the undercoat layer after drying is small, the effective thickness of the undercoat layer is thick and a uniform coated surface can be obtained. By applying the coating solution for the heat-sensitive recording layer on this coated surface, sinking of the coating solution for the heat-sensitive recording layer is suppressed compared to the case where no undercoat layer is provided, and the effective layer thickness of the heat-sensitive recording layer is reduced. A thick and highly uniform coated surface can be obtained. As a result, the quality of the image printed on the heat-sensitive recording surface, that is, barcode readability, print density, and reprintability are particularly good.
Further, when printing is performed on the back surface of the heat-sensitive recording material (that is, the surface opposite to the heat-sensitive recording layer), the undercoat layer has an effect of suppressing the penetration of ink into the heat-sensitive recording surface. In the present invention, as described above, since the effective thickness of the undercoat layer is large and a uniform coating surface is obtained, the undercoat layer is thickened or has a barrier property that prevents the ink from permeating. There is no need to let it. Therefore, in the heat-sensitive recording material of the present invention, the coating amount after drying of the undercoat layer is relatively small.
Dry coating amount of the undercoat layer is preferably 15 g / ^{m 2} or less, more preferably 1 to 15 g / ^{m 2,} more preferably from 3 to 10 g / ^{m 2.}

In the heat-sensitive recording material of the present invention, a protective layer and other coating layers commonly used for heat-sensitive recording materials may be provided on the heat-sensitive recording layer, if necessary.
General-purpose coating machines such as curtain coater, air knife coater, blade coater, gravure coater, roll coater, lip coater and bar coater are used for coating each coating layer other than the thermal recording layer such as undercoat layer and protective layer. Can be used.

The following examples illustrate the invention but are not intended to limit the invention.
In each example, “parts” represents “parts by weight” and “%” represents “% by weight” unless otherwise specified. The freeness (Canadian standard freeness, hereinafter referred to as “CSF”) of each pulp was measured according to JIS P8121.
In the following examples and comparative examples, the support was adjusted to a density of about 0.7 g / cm ³ by machine calendering so that the density would be about the same for the purpose of clarifying the effects of the invention. did.
The drip water absorbency refers to the drip water absorbency of the surface of the paper support on which the undercoat layer is not provided, on which the heat-sensitive recording layer is provided.

A support was prepared as follows.
(Support 1)
A raw material obtained by adding and mixing 0.7 parts of aluminum sulfate and 10 parts of calcium carbonate to 100 parts of pulp consisting of 20 parts of TMP of 90 ml of CSF and 80 parts of LBKP of 300 ml of CSF was made with a long net paper machine. A clear-size coating solution comprising hydroxyethylated starch (ETHYLEX 2035 manufactured by STALEY) and a cationic sizing agent (cationic polymer of styrene-acrylic acid copolymer resin, LC-5 manufactured by Harima Kasei Co., Ltd.) on both sides. The dry coating amount on both surfaces of the hydroxyethylated starch support is 0.67 g / m ² (the dry coating amount on the surface on which the thermosensitive recording layer is provided is 0.335 g / m ² ), and the support of the cationic sizing agent. Coating was performed with a gate roll coater so that the dry coating amount on both sides was 0.15 g / m ² (the dry coating amount on the surface on which the heat-sensitive recording layer was provided was 0.075 g / m ² ). A paper support having a basis weight of 48 g / m ² and an ash content of 5% was obtained by processing so as to have a density of 0.7 g / cm ³ with a calendar. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 170 seconds.

Next, on one side of the paper support obtained above, an undercoat layer coating solution having the following composition was applied and dried by the rod blade method, so that the dry coating amount of the undercoat layer was 8.0 g / m ^2. It was. Hereinafter, the support provided with the undercoat layer is referred to as support 1.
<Coating liquid for undercoat layer>
Baked kaolin (manufactured by Engelhard: Ansilex 90) 100 parts Styrene / butadiene copolymer latex (manufactured by Nippon Zeon: ST5526)
40% solid content) 40 parts Completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., Ltd .: PVA117,
Solid content 10%) 30 parts Water 146 parts

[Example 1]
(Thermosensitive recording layer)
The developer dispersion liquid (A liquid), leuco dye dispersion liquid (B liquid) and sensitizer dispersion liquid (C liquid) having the following composition are separately wetted with a sand grinder until the average particle size becomes 0.5 μm. Grinding was performed.
Developer dispersion (liquid A)
4-hydroxy-4′-n-propoxydiphenyl sulfone (JKY146)
6.0 parts Completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., Ltd .: PVA117,
18.8 parts water 11.2 parts leuco dye dispersion (liquid B)
3-di-n-butylamino-6-methyl-7-anilinofluorane (ODB-2) 1.0 part 3-di-n-pentylamino-6-methyl-7-anilinofluorane (BLACK305) 1.0 part Completely saponified polyvinyl alcohol aqueous solution (Kuraray Co., Ltd .: PVA117,
(Solid content 10%) 4.6 parts water 2.6 parts sensitizer dispersion (liquid C)
Diphenylsulfone 3.0 parts Stearic acid monoamide 3.0 parts Completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd .: PVA117,
(Solid content 10%) 18.8 parts water 11.2 parts

Next, the dispersion liquid is mixed at the following ratio to prepare a heat-sensitive recording layer coating liquid, and this heat-sensitive recording layer coating liquid is dried onto the undercoat layer of the support 1 obtained above. Coating and drying were carried out by a rod blade method so as to be 6.0 g / m ² . This sheet was processed with a super calendar so that the smoothness of the heat-sensitive recording surface was 500 to 1000 seconds to obtain a heat-sensitive recording material.
<Coating liquid for thermosensitive recording layer>
Developer dispersion (liquid A) 36.0 parts Leuco dye dispersion (liquid B) 9.2 parts Sensitizer dispersion (liquid C) 36.0 parts Light calcium carbonate dispersion (manufactured by Shiraishi Calcium Co., Ltd .: Brilliant) 15,
20.0 parts of a completely saponified polyvinyl alcohol aqueous solution (manufactured by Kuraray Co., Ltd .: PVA117)
(Solid content 10%) 10.0 parts

[Example 2]
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the pulp composition was changed to 70 parts of TMP and 30 parts of LBKP. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 100 seconds.
[Example 3]
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the pulp composition was 10 parts of TMP, 10 parts of RGP (CSF 70 ml), 5 parts of NBKP (CSF 470 ml), and 75 parts of LBKP. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 155 seconds.
[Example 4]
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the pulp was mixed with 95 parts of TMP 5 parts and CSF 300 ml of waste paper pulp (mixing ratio of mechanical pulp 10%, hereinafter the same). The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 155 seconds.
[Example 5]
A heat-sensitive recording material was obtained in the same manner as in Example 4 except that the pulp content was 40 parts TMP and 60 parts waste paper pulp. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 130 seconds.
[Example 6]
Example 4 except that the dry coating amount of the both sides of the support of the cationic sizing agent was 0.06 g / m ² (the dry coating amount on the surface on which the thermosensitive recording layer was provided was 0.03 g / m ² ). In the same manner, a heat-sensitive recording material was obtained. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 90 seconds.
[Example 7]
Example 4 except that the dry coating amount of the both sides of the support of the cationic sizing agent was 0.04 g / m ² (the dry coating amount on the surface on which the thermosensitive recording layer was provided was 0.02 g / m ² ). In the same manner, a heat-sensitive recording material was obtained. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 60 seconds.
[Example 8]
Example 4 except that the dry coating amount of both surfaces of the support of the cationic sizing agent was 0.6 g / m ² (the dry coating amount on the surface on which the thermosensitive recording layer was provided was 0.3 g / m ² ). In the same manner, a heat-sensitive recording material was obtained. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 320 seconds.
[Example 9]
In the support material, an alkyl ketene dimer (AD 1604 manufactured by Seiko PMC Co., Ltd., 30% solid content) is added as an internal sizing agent so that the solid content is 0.15% per pulp weight with respect to the pulp slurry, Example 4 except that the dry coating amount of the both sides of the support of the cationic sizing agent was 0.06 g / m ² (the dry coating amount on the surface on which the thermosensitive recording layer was provided was 0.03 g / m ² ). In the same manner, a heat-sensitive recording material was obtained. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 110 seconds.
[Example 10]
A thermosensitive recording material was obtained in the same manner as in Example 4 except that the cationic sizing agent of the clear size coating solution was alkyl ketene dimer (SK Resin S-20 manufactured by Nippon PMC Co., Ltd.). The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 150 seconds.
[Example 11]
The same procedure as in Example 1 was conducted except that 4-hydroxy-4′-n-propoxydiphenylsulfone in the developer dispersion (liquid A) was replaced with 4-hydroxy-4′-isopropoxydiphenylsulfone (NYDS). A heat-sensitive recording material was obtained.
[Example 12]
1.0 part of 3-di-n-butylamino-6-methyl-7-anilinofluorane (ODB-2) and 3-di-n-pentylamino-6-methyl in a leuco dye dispersion (liquid B) Replacing 1.0 part of -7-anilinofluorane (BLACK305) with 2.0 parts of 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane (S-205) Except for the above, a heat-sensitive recording material was obtained in the same manner as in Example 1.
[Example 13]
A thermal recording layer was obtained by applying the thermal recording layer coating solution in the same manner as in Example 1 except that the undercoat layer was not provided on the support.

[Comparative Example 1]
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the pulp composition was changed to 100 parts of LBKP. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 190 seconds.
[Comparative Example 2]
Except for adding 100 parts of LBKP to the pulp slurry and adding a bulking agent (KB115 manufactured by Kao Corporation, ester of polyhydric alcohol and saturated fatty acid) to 0.5% per weight of pulp. In the same manner as in Example 1, a heat-sensitive recording material was obtained. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 160 seconds.
[Comparative Example 3]
In order to improve the bulk, a heat-sensitive recording material was obtained in the same manner as in Example 1 except that the refiner strength during the production of LBKP was changed and LBKP having a freeness (CSF) of 570 ml was used. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 140 seconds.

（４） [Comparative Example 4]
Example 4 except that the dry coating amount of the both sides of the support of the cationic sizing agent was 0.02 g / m ² (the dry coating amount on the surface on which the thermosensitive recording layer was provided was 0.01 g / m ² ). In the same manner, a heat-sensitive recording material was obtained. The drip water absorption on the surface of the paper support on which the heat-sensitive recording layer was provided was 10 seconds.
[Comparative Example 5]
A thermosensitive recording medium was prepared in the same manner as in Example 1 except that 4-hydroxy-4′-n-propoxydiphenyl sulfone in the developer dispersion (liquid A) was replaced with a compound represented by the following chemical formula (4). Obtained.

(4)

The following evaluation was performed on the heat-sensitive recording material obtained as described above.
[Print density]
Using TH-PMD manufactured by Okura Electric Co., Ltd. as the thermal recording material, printing was performed at an applied energy of 0.35 mJ / dot, and the print density after printing was measured with a Macbeth densitometer (RD-914, using an amber filter). did.
[Color sensitivity (print density under low applied energy conditions)]
Using TH-PMD manufactured by Okura Electric Co., Ltd. on the thermal recording medium, printing was performed at an applied energy of 0.25 mJ / dot, and the print density after printing was measured with a Macbeth densitometer (RD-914, using an amber filter). did.
[Reprintability] (Print density after storage)
The heat-sensitive recording material was stored for 24 hours in an environment of 40 ° C. and 90% RH. Using TH-PMD manufactured by Okura Electric Co., Ltd. as the thermal recording medium after storage, printing was performed with an applied energy of 0.35 mJ / dot, and the print density was measured with a Macbeth densitometer (RD-914, using an amber filter). did.
[Whiteness]
The produced thermal recording material was measured for whiteness (%) with a spectral color / whiteness meter PF-10 manufactured by Nippon Denshoku Industries Co., Ltd. The higher the value, the better the whiteness.

[Barcode readability (printing through)]
On the surface opposite to the heat-sensitive recording surface of the produced heat-sensitive recording material, an offset rotary printing ink (black) is printed using an RI printing machine and dried, and then a bar is printed on the heat-sensitive recording surface with a Zebra label printer 140XiIII. After code printing (CODE39), the printed barcode was evaluated with a barcode reader (Quick Check PC600, manufactured by Nihon Systechs). Evaluation was performed by ANSI grade (CEN method, average of 10 times of measurement).
If the evaluation value is 1.5 or more, it is at a level where there is no practical problem in barcode readability. On the other hand, if the evaluation value is less than 1.5, a practical problem occurs in barcode readability.

[Surface strength]
After printing on the surface opposite to the thermal recording surface of the produced thermal recording medium using an offset sheet-fed printing machine (two colors) manufactured by Roland, using offset sheet-fed ink (High Unity M manufactured by Toyo Ink Co.), The indigo single-color solid portion picking (the surface of the support was peeled off by ink tack (adhesiveness)) was visually evaluated.
Excellent: No picking is observed. Good: Little picking is observed. Yes: Picking is slightly observed, but there is no practical problem. No: There is much picking or the inside of the support is destroyed.

  The evaluation results are shown in the table below. The drip water absorption in the table refers to the drip water absorption on the surface of the support on which the heat-sensitive recording layer is provided.

Claims (5)

A heat-sensitive recording material provided with a heat-sensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on a support, wherein the support contains 5% by weight or more of mechanical pulp. Drip water absorption on the surface of the support, on which the thermal recording layer of the support is provided (unless the amount of water dropped is 0.001 ml, specified in J.TAPPI No. 32-2: 2000 The heat-sensitive recording layer contains at least one diphenylsulfone compound represented by the following general formula (1) as an electron-accepting developer. Thermal recording material.

(1)
(In the formula, R1 represents an n-propoxy group, an isopropoxy group, or an n-butoxy group.) 2. The heat-sensitive recording material according to claim 1, wherein the support comprises a pulp containing 10 to 50% by weight of mechanical pulp. The thermosensitive recording material according to claim 1 or 2, wherein the compound represented by the general formula (1) is 4-hydroxy-4'-n-propoxydiphenyl sulfone. The thermosensitive recording material according to claim 1 or 2, wherein the compound represented by the general formula (1) is 4-hydroxy-4'-isopropoxydiphenyl sulfone. The thermal recording according to any one of claims 1 to 4, wherein an undercoat layer comprising a binder and a pigment is provided between the support and the thermal recording layer, and the coating amount is 15 g / m ² or less. body.