JP2010240860A - Thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording medium combining excellent color developing sensitivity, heat resistance and wet heat resistance. <P>SOLUTION: The thermal recording medium is provided with a thermal recording layer containing a colorless or light-colored electron-donative leuco dye and an electron-acceptive color developer on a support body. The thermal recording layer uses, as the electron-acceptive color developer, particles of a 4,4'-dihydroxydiphenylsulfone substitution product whose particle size distribution (volume reference) measured by a laser diffraction type particle size distribution measuring device is 0.5 μm or less at 50% diameter and 1.2 μm or less at 90% diameter. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a heat-sensitive recording material that obtains a recorded image by utilizing a color development reaction by heat between a colorless or light-colored basic leuco dye and an electron-accepting developer.

A recorded image can be obtained by utilizing a coloring reaction caused by heat between a colorless or light-colored basic leuco dye (hereinafter also referred to as “dye”) and an electron-accepting developer (hereinafter also referred to as “developer”). The heat-sensitive recording material that can be obtained is widely used in the facsimile and computer fields, various measuring instruments, etc. due to the advantages such as very clear color development, no noise during recording, relatively inexpensive equipment, compactness, and easy maintenance. It has become. Furthermore, recently, in addition to labels and tickets, applications are rapidly expanding as output media for various printers and plotters such as small portable terminals (handy terminals) for outdoor measurement and delivery slips. In particular, the use of portable printers (handy terminals) for meter reading applications such as electricity, gas, water, etc., in-house sales of trains (Shinkansen, etc.), inventory management in warehouses, etc. has increased significantly. The handy terminal is reduced in size so that it is convenient to carry, and printing energy and driving energy tend to save power. For this reason, the color development sensitivity of the thermal recording medium is required to be higher than before. In addition, this application is often used outdoors, and it can withstand use in harsher environments than conventional ones, such as moisture and moisture such as rain, and high temperatures in the car in midsummer, especially water resistance and heat resistance. Is becoming necessary.
In order to improve the color development sensitivity, a sensitizer having a low melting point is generally used. In addition, the color development sensitivity is improved by using a dye, a developer or a sensitizer atomized by the method of Patent Documents 1 to 3.

4-61635 Japanese Patent No. 3703148 JP 2003-144950 A

However, when a sensitizer having a low melting point is used, there arises a problem (heat resistance) that the background portion of the thermal recording paper is colored under a high temperature environment. In addition, when using atomized dyes, color developers or sensitizers, sufficient heat resistance is not exhibited, and at the same time, the problem of image fading (humid heat resistance) occurs in a high humidity environment. To do.
Therefore, an object of the present invention is to provide a heat-sensitive recording material having excellent color development sensitivity, heat resistance, and heat and humidity resistance.

（式中、Ｒは炭素数１〜４の直鎖または分岐の飽和または不飽和炭化水素を示す。Ｒ'はアルケニル基を示し、ｎは０〜２の整数を示す）で表される４，４’−ジヒドロキシジフェニルスルホン置換体を顕色剤として含有させることにより、優れた発色高感、耐熱性、耐湿熱性を有する感熱記録体が得られることを見出し、本発明を完成させるに至った。 The inventors of the present invention provided that the particle size distribution (volume basis) of the fine particles measured by a laser diffraction type particle size distribution measuring device was 50% in diameter and 0.5 μm or less, and 90% in diameter on the thermosensitive recording layer provided on the support. The following general formula (Chemical Formula 1):

(Wherein R represents a linear or branched saturated or unsaturated hydrocarbon having 1 to 4 carbon atoms, R ′ represents an alkenyl group, and n represents an integer of 0 to 2) 4, It has been found that by containing a 4′-dihydroxydiphenylsulfone substituted product as a developer, a heat-sensitive recording material having excellent color development sensitivity, heat resistance, and heat and humidity resistance can be obtained, and the present invention has been completed.

  The heat-sensitive recording material of the present invention has a heat-sensitive recording material that has excellent color development sensitivity, heat resistance, and heat-and-moisture resistance, and is therefore suitable for use in handy terminals that are often used outdoors. Can do.

ここで、Ｒはハロゲン原子、水酸基、炭素数１〜４の直鎖または分岐の飽和または不飽和炭化水素を表すが、飽和炭化水素基の炭素数は好ましく１〜５、より好ましくは１〜４であり、飽和炭化水素基としては、例えば、メチル、エチル、ｎ−プロピル、イソプロピル、ｎ−ブチル、ｔ−ブチル、ｔ−アミル等が挙げられる。また、不飽和炭化水素基の炭素数は好ましくは２〜５であり、不飽和炭化水素基として、例えば、エチレン、1−ｎ−プロベニル、２−ｎ−プロベニル、イソプロベニル、１−ｎ−ブテン、２−ｎ−ブテン、３−ｎ−ブテン等が挙げられる。
Ｒ'は炭素数1〜４のアルケニル基を表すが、炭素数３が好ましい。アルケニル基としては、例えば、ビニル基、アリル基、ブテニル基が挙げられ、アリル基が好ましい。ｎは０〜２の整数を表すが、ｎ＝０または１が好ましい。
一般式（化１）で表される化合物の具体例としては、４−ヒドロキシ−４'−イソプロポキシジフェニルスルホン、４−ヒドロキシ−４’−ｎ−プロポキシジフェニルスルホン、４−ヒドロキシ−４’−２−プロピレキシジフェニルスルホン、４−ヒドロキシ−４’−１−プロベニルジフェニルスルホン、４−ヒドロキシ−４’−エトキシジフェニルスルホン、４−ヒドロキシ−４’−ｎ−ブトキシジフェニルスルホン、４−ヒドロキシ−４’−ベンゾキシジフェニルスルホン、２,２’−ジアリル−４，４’−ジヒドロキシジフェニルスルホン等が挙げられる。特に、発色感度の点から、４−ヒドロキシ−４’−イソプロポキシジフェニルスルホン、４−ヒドロキシ−４’−ｎ−プロポキシジフェニルスルホン、４−ヒドロキシ−４’−アリルオキシジフェニルスルホン、２,２’−ジアリル−４，４’−ジヒドロキシジフェニルスルホンが好ましい。 The 4,4′-dihydroxydiphenylsulfone substituted product used as a developer in the present invention is represented by the following formula.

Here, R represents a halogen atom, a hydroxyl group, a linear or branched saturated or unsaturated hydrocarbon having 1 to 4 carbon atoms, and the saturated hydrocarbon group preferably has 1 to 5 carbon atoms, more preferably 1 to 4 carbon atoms. Examples of the saturated hydrocarbon group include methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, t-amyl and the like. The unsaturated hydrocarbon group preferably has 2 to 5 carbon atoms, and examples of the unsaturated hydrocarbon group include ethylene, 1-n-probenyl, 2-n-probenyl, isoprobenyl, 1-n-butene, Examples include 2-n-butene and 3-n-butene.
R ′ represents an alkenyl group having 1 to 4 carbon atoms, preferably 3 carbon atoms. As an alkenyl group, a vinyl group, an allyl group, and a butenyl group are mentioned, for example, An allyl group is preferable. n represents an integer of 0 to 2, and n = 0 or 1 is preferable.
Specific examples of the compound represented by the general formula (Formula 1) include 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-n-propoxydiphenylsulfone, and 4-hydroxy-4′-2. -Propylexidiphenylsulfone, 4-hydroxy-4'-1-probenyldiphenylsulfone, 4-hydroxy-4'-ethoxydiphenylsulfone, 4-hydroxy-4'-n-butoxydiphenylsulfone, 4-hydroxy-4 Examples include '-benzoxydiphenyl sulfone, 2,2'-diallyl-4,4'-dihydroxydiphenyl sulfone. In particular, from the viewpoint of color development sensitivity, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-n-propoxydiphenylsulfone, 4-hydroxy-4′-allyloxydiphenylsulfone, 2,2′- Diallyl-4,4′-dihydroxydiphenyl sulfone is preferred.

  In the present invention, in addition to the 4,4′-dihydroxydiphenylsulfone substituted product represented by the general formula (Formula 1), a conventionally known developer is used as a developer as long as the desired effect is not inhibited. You may use together. The particle size of such a developer is not particularly limited and is generally about 0.3 to 1 μm in average particle size, and is atomized in the same manner as the condensation composition represented by the general formula (Formula 1). May be. Further, when such a developer is used in combination, the ratio of the other developer to the whole developer to be used is particularly limited as long as it is appropriately adjusted within a range not inhibiting the desired effect. However, when the total amount of the developer is 100% by weight, the 4,4′-dihydroxydiphenylsulfone substituted product represented by the general formula (Formula 1) is 50% by weight or more, preferably 70% by weight or more. It is desirable to use as follows.

  Examples of such developers 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-hydroxybenzenesulfonanilide, JP-A-8-59603 Aminobenzenesulfonamide derivatives, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, butyl bis (p-hydroxyphenyl) acetate, bis ( p-hydroxyphenyl) Acid methyl, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 1,3-bis [α -Methyl-α- (4′-hydroxyphenyl) ethyl] benzene, di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), 2,2′-thiobis ( 4-tert-octylphenol), phenolic compounds such as diphenylsulfone cross-linked compounds described in International Publication No. WO 97/16420, 4,4′-bis (3- (phenoxycarbonylamino) methylphenylureido) diphenylsulfone (Asahi Kasei Corporation) Product name: UU), compounds described in International Publication WO02 / 081229 or JP2002-301873 (Japan) Soda Co., Ltd. trade names D-102 and D-100), compounds described in Japanese Patent Nos. 34566792 and 36127746, thiourea compounds such as N, N′-di-m-chlorophenylthiourea, p-chlorobenzoic acid, gallic acid Stearyl acid, zinc bis [4- (n-octyloxycarbonylamino) salicylate] dihydrate, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- (p-tolylsulfonyl) propyl Oxy] salicylic acid, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] salicylic acid aromatic carboxylic acid, and zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel of these aromatic carboxylic acids Salts with polyvalent metal salts such as zinc thiocyanate antipyrine complex, terephthalate Examples include complex zinc salts of aldehyde and other aromatic carboxylic acids. These may use 1 type or may use several types together.

  In the present invention, a 4,4′-dihydroxydiphenylsulfone substituted product having a specific particle size distribution is used as a developer, and the particle size distribution of the developer is the laser diffraction particle size distribution. When measured by a measuring apparatus, the particle size at 50% from the small particle size side (hereinafter also referred to as “50% diameter” or simply “average particle diameter”) in the volume-based cumulative particle size distribution frequency is 0.5 μm. Similarly, the particle diameter at 90% (hereinafter referred to as “90% diameter”) is 1.2 μm or less.

In the present invention, the 4,4′-dihydroxydiphenylsulfone substituted product represented by the general formula (Chemical Formula 1) can greatly improve the sensitivity by having the particle size distribution. The reason for this is not clear, but by making this 4,4′-dihydroxydiphenylsulfone substituted product into the above particle size distribution, the contact frequency with the dye as the color forming component increases, and the color sensitivity is greatly improved. When the particle size distribution of the '-dihydroxydiphenylsulfone substituted product is outside the above range, the contact frequency with the dye is decreased and sufficient color development sensitivity cannot be obtained.
The color development mechanism when a dye, developer, and sensitizer are included in the heat-sensitive recording layer is that the sensitizer with the lowest melting point of the dye, developer, and sensitizer melts first. When the dye and the developer are dissolved in the melted sensitizer, the dye and the developer develop a color reaction at the molecular level. In the present invention, by atomizing the developer, the solubility in the melted sensitizer is improved and the color development sensitivity is improved. For this reason, it is not necessary to use a low-melting point sensitizer that has a large effect of improving the color sensitivity, which tends to deteriorate the heat resistance, in order to obtain the required color sensitivity. It is possible to obtain a heat-sensitive recording material.

The electron-accepting developer of the present invention has a tendency to thicken or aggregate during the atomization process, and it is difficult to obtain a sharp particle size distribution. It is preferable that the medium is separated into a dispersion and discharged from the bead mill by the above action because a desired particle size distribution can be obtained.
For atomizing the developer, it is desirable to use a wet pulverizer, and it is preferable to use microbeads having a bead diameter of 0.3 mm or less. When the bead diameter exceeds 0.3 mm, the impact force per bead used for pulverization (proportional to the weight of the bead, and the bead weight is proportional to the cube of the bead diameter) becomes excessive, and the developer particles Since the surface is damaged and the particle surface is activated unnecessarily, thickening and agglomeration occur due to interaction between particles, resulting in generation of coarse particles and difficulty in atomization.

  Further, the pulverizer to be used is not limited as long as the above-mentioned bead diameter can be used, but preferably a pulverizer using a centrifugal separation system is used for the separation mechanism of the treatment liquid and the beads. desirable. The bead separation mechanism by the centrifugal separation method is a wet type pulverizer having a separation mechanism using centrifugal force, which is largely different from the screen or gap method used in the conventional pulverizer. As the separation mechanism, the moment when both the atomized dispersion and the beads enter the centrifugal rotor, the centrifugal force due to the rotation of the rotor causes the beads to move at the outer periphery of the rotor at the Stokes settling velocity Vt due to the specific gravity difference between the dispersion and the beads. While being discharged in the direction, the dispersion flows from the outer periphery of the rotor toward the shaft center at a velocity v. At this time, in principle, separation is possible if Vt is greater than v, and scale-up is easy. In addition, since no screen or gap that blocks the flow of the dispersion liquid is used, clogging does not occur and industrially stable production is possible. In addition, since the flow rate can be set high, a high flow rate / high pass number of times can be processed, and a very sharp and finely dispersed dispersion can be obtained by mild and uniform atomization treatment for each particle.

  If a crusher that centrifuges the dispersion and beads is used, microbeads with a particle size of 0.3 mm or less, which are difficult to separate due to clogging or biting in screen type or gap type crushers, are used. Atomization is possible. This technique has been known in other fields such as a method for producing a wet silica dispersion (JP 2005-2319545), but quality problems such as coating defects are caused by mixing beads in the treatment liquid as in the present invention. Until now, it has not been known to apply this type of pulverizer to the atomization of the resulting thermal recording material component. The inventors of the present invention can obtain a developer by using a bead having a particle size of 0.3 mm or less and atomizing the dispersion and the bead using a pulverizer for centrifuging the dispersion and the bead. It was found that a thermal recording material containing a developer having a particle size distribution measured by a laser diffraction method of 0.5 μm or less at a 50% diameter and 1.2 μm or less at a 90% diameter can be obtained stably. .

  Of course, the atomization method is not particularly limited in the present invention, and a screen-type or gap-type pulverizer can also be used as long as atomization within the particle size distribution range is possible. For example, a pulverizer described in JP-A-10-15411 can be cited as a pulverizer capable of processing at a high flow rate / high pass number with a gap type. This crusher is provided with a cylindrical crushing container closed at both ends, and the crushing container and the axis aligned with the axis, and the crushing container has two chambers, an inner chamber and an outer chamber in the radial direction. And a cylindrical separator in which a plurality of slits communicating between the two chambers are formed over the entire circumference, and a stirring member that is rotatably provided in the inner chamber with the axis of the pulverization container aligned. A processing product supply port that communicates between the inside and outside of the interior and a discharge port for processing product that communicates between the outside and the inside of the chamber. , The processed material is stirred and pulverized together with the beads by the stirring member, and flows radially outward by the action of centrifugal force to reach the position of the separator. Then, the processed material and the beads are separated by the separator, the pulverization medium is left in the inner chamber, the processed material flows into the outer chamber through the slit, and is discharged from the outer chamber to the outside of the pulverization container through the discharge port. The In this case, the separator is provided with a plurality of slits over its entire circumference, and a sufficient effective area for processing a large amount of processed material can be secured. And the flow of the large flow volume processed material is not restrict | limited by the part of a separator, and a large flow volume processed material can be processed efficiently. Moreover, since the opening part which penetrates the inside and outside is provided in the cylindrical part of the stirring member, a strong centrifugal force can be made to act on a processed material and a bead by the opening part. Therefore, the processed material and the beads flow from the opening to the outer peripheral side of the stirring member by the centrifugal force, flow on the outer peripheral side of the stirring member in the axial direction of the stirring member, and flow to the inner portion of the stirring member. The processed material and beads circulate in the inner chamber along a series of flows, and both are in a completely mixed state. Therefore, it is possible to obtain good operation characteristics in the long term without the beads and the processed product being shifted to a part in the pulverization container and affecting the operation or making the operation difficult. Furthermore, although the pulverization container is formed to be short in the axial direction (L / D ratio is small), D (diameter of the pulverization container) is formed to be larger by a smaller amount of L (length in the axial direction of the pulverization container). As a result, the pulverization efficiency of the processed product does not decrease, and an excellent pulverization efficiency can be obtained. The ratio (L / D ratio) between the length (L) in the axial direction and the diameter (D) is preferably 1.0 or less.

  Further, a disperser having a dispersion liquid supply port, a dispersion liquid discharge port, a cylindrical rotor, and a cylindrical casing described in JP-A-2005-153205, wherein the outer diameter of the cylindrical rotor, the inner surface of the cylindrical casing, It is also useful to increase the dispersion efficiency and shear efficiency by widening the interval. In this method, when the outer diameter of the cylindrical rotor that is a stirring member is d and the inner diameter of the cylindrical casing is D, the range is 0.7 ≦ d / D ≦ 0.9, and further, the cylindrical rotor Where h is the height of the inner surface of the cylindrical casing and H is the height of the inner surface of the cylindrical casing, by making the range 0.6 ≦ h / H ≦ 0.9, beads can be efficiently contributed to dispersion. This makes it possible to obtain a sharper and more finely divided dispersion, which enables processing with high dispersion efficiency.

  In the case of a wet pulverizer using beads, the viscosity after the atomization treatment of the dispersion is important. This is because, when the viscosity of the dispersion subjected to the atomization treatment is extremely high, the beads are difficult to move and the atomization efficiency is reduced. This is because it becomes difficult to be transmitted to the beads, and the beads are discharged while mixed in the dispersion. In particular, the latter phenomenon tends to occur when the flow rate of the dispersion liquid is set high. Therefore, the flow rate within the range in which the media can be separated may be appropriately selected. It is preferable that the temperature is 30 ° C., the rotation speed is 60 rpm, and the rotor No. 2) is 2000 mPa · s or less.

  Moreover, the peripheral speed (speed of an outermost peripheral part) of a rotor is 5-30 m / s, More preferably, it is the range of 5-20 m / s. When the peripheral speed of the rotor is less than 5 m / s, it takes time for atomization and is inefficient. Further, in the case of 30 m / s or more, there is a concern that the particles to be atomized will have an excessive share and thus cause aggregation.

  In the present invention, the particle diameter of the medium to be used may be appropriately selected depending on the desired particle diameter to be obtained, but in order to promote a sharp particle size distribution and atomization, a range of 0.03 to 0.5 mm diameter. The material is preferably selected from glass, zirconia, and alumina. In the present invention, the apparent filling rate of the bead particles in the grinding chamber is preferably 30 to 95% by volume, more preferably 40 to 90% by volume. By setting the filling rate of the bead particles within the above range, the developer can be atomized efficiently and a short pass can be prevented.

  In the present invention, it is desirable that the processing temperature when the developer is pulverized be 50 ° C. or less. When processed at 50 ° C. or higher, re-aggregation or denaturation is caused by heat, so there is a concern that the color development sensitivity is lowered. This reduction in color development sensitivity due to aggregation or the like can be evaluated with a 90% diameter, and is preferably about twice or less than the target average particle diameter (50% diameter). In addition, when the dispersion is mixed at 50 ° C. or higher, the mixed paint is colored. Therefore, it is necessary to use the solution after cooling it to 50 ° C. or lower, which reduces the production efficiency.

The method for cooling the dispersion is not particularly limited, but a method of cooling by circulating a cooling medium in the jacket portion of the grinding chamber is simple. The temperature control method is not particularly limited, but when the cooling medium is circulated, the flow rate and temperature may be controlled. The method automatically measures the temperature of the dispersion using a sensor and controls the value. Alternatively, simply determine the conditions for measuring the temperature of the dispersion at the highest dispersion outlet while changing the cooling medium, flow rate, and temperature to bring the desired dispersion temperature. Also good.
A normal cooling medium such as water or ethylene glycol can be used as the cooling medium.
In addition, before the atomization operation, a coarse dispersion operation is performed as a pretreatment, for example, a ball mill, an attritor, a sand mill, a sand grinder, a grain mill, a pearl mill, a matter mill, an aniler mill, a coball mill, a tower mill, a dynamic mill, an OB mill, an apex mill, an SC. There are various deformation types and designations such as a mill and a three-roll mill, and among these, there are many more types of deformation, but a necessary coarse dispersion treatment may be appropriately performed. Further, the atomization operation may be a continuous system by connecting pulverizers in series, or a system in which the pulverizer is circulated and passed multiple times.

  Specific examples of a pulverizer for centrifuging a dispersion liquid and beads as a preferable pulverizer to be used include Super Apex Mill (SAM-05 type, SAM-1 type, SAM-2 type, manufactured by Kotobuki Kogyo Co., Ltd.). , SAM-5 type, SAM-10 type, SAM-30 type), Ultra Apex mill (UAM-015 type, UAM-05 type, UAM-1 type, UAM-2 type, UAM-5 type, UAM-10 type) , UAM-30 type) and MSC mills (MSC100, MSC150, MSC220) manufactured by Mitsui Mining Co., Ltd. These pulverizers are screenless, so the rough dispersion treatment for the purpose of preventing clogging and biting is omitted. You can also In addition, Star Mill LMZ (LMZ06, LMZ2, LMZ4, LMZ10, LMZ25, LMZ60), Starmill ZRS (ZRS2, ZRS4, ZRS10) manufactured by Ashizawa Finetech Co., Ltd., which uses both a centrifugal separation and a screen mechanism for bead separation. However, it is not limited to these as long as atomization within the particle size distribution range is possible. Specific examples of the gap type include bead mills (SC100, SC220, etc.) manufactured by Mitsui Mining Co., Ltd., but are not limited thereto.

  As a dispersion medium used when the developer is dispersed, an aqueous solution of a water-soluble polymer compound is generally used. For example, polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, ethylcellulose, sodium acrylate, polyvinylpyrrolidone, acrylamide / acrylate ester copolymer, acrylamide / acrylate ester / In addition to water-soluble polymers such as methacrylic acid terpolymers, styrene / maleic anhydride copolymer alkali salts, isobutylene / maleic anhydride copolymer alkali salts, polyacrylamide, sodium alginate, gelatin and casein, polyacetic acid Vinyl, polyurethane, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate Emulsion and styrene / butadiene copolymers such as polymers, such as latex, such as styrene / butadiene / acrylic copolymer may also be mentioned.

When these dispersants (solid content) are used in an amount of 0.01 to 1.0 part with respect to 1 part by weight of the object to be dispersed, they are advantageous for finer particles, improved dispersibility and stability of the dispersion. Therefore, it is preferable. If the amount is too small, aggregation is caused and the stability of the dispersion is poor. On the other hand, when the amount is too large, quality is adversely affected, such as sensitivity reduction due to desensitization, which is not preferable.
The density | concentration of the dispersion target object in a dispersion liquid is about 20 to 70 weight% normally.
Using such a material, a developer dispersion is prepared and atomized under the above conditions. Ball mill, Attritor, Sand mill, Sand grinder, Grain mill, Pearl mill, Matter mill, Aniler mill, Coball mill, Tower mill, Dynamic mill, OB mill, Apex mill, SC What was disperse | distributed with the conventional grinders, such as a mill and a three roll mill, can be used.

  As the basic leuco dye used in the present invention, those known in the conventional pressure-sensitive or heat-sensitive recording paper field can be used, and are not particularly limited, but triphenylmethane compounds, fluoran compounds, Fluorene-based and divinyl-based 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; 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-diethylamino-6-methyl-7-n-octylaminofluorane; 3-diethylamino-6-methyl-7-benzylaminofluorane; 3-diethylamino-6-methyl-7-dibenzylaminofluorane; 3-diethylamino-6-chloro-7-anilinofluorane; 3-diethylamino-6-chloro-7-p-methylanilinofluorane; 3-diethylamino-6 3-Ethoxyethyl-7-anilinofluorane; 3-diethylamino-7-methylfluorane; 3-diethylamino-7-chlorofluorane; 3-diethylamino-7- (m-trifluoromethylanilino) fluorane; Diethylamino-7- (o-chloroanilino) fluorane; 3-diethyla 3-diethylamino-7- (o-fluoroanilino) fluorane; 3-diethylamino-benzo [a] fluorane; 3-diethylamino-benzo [c] fluorane; 3-dibutylamino 3-dibutylamino-6-methyl-7-anilinofluorane; 3-dibutylamino-6-methyl-7- (o, p-dimethylanilino) fluorane; 3-dibutylamino- 6-methyl-7- (o-chloroanilino) fluorane; 3-dibutylamino-6-methyl-7- (p-chloroanilino) fluorane; 3-dibutylamino-6-methyl-7- (o-fluoroanilino) fluorane 3-dibutylamino-6-methyl-7- (m-trifluoromethylanilino) fluorane 3-dibutylamino-6-methyl-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-pentyl Mino-7- (p-chloroanilino) 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-anilinofluorane; 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane; 3- (N-ethyl-N-isoamido) Amino) -6-chloro-7-anilinofluorane; 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane; 3- (N-ethyl-N-isobutyl) Amino) -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) aminoani 2-methoxy-6-p- (p-dimethylaminophenyl) aminoanilinofluorane; 2-chloro-3-methyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane; Chloro-6-p- (p-dimethylaminophenyl) aminoanilinofluorane; 2-nitro-6-p- (p-diethylaminophenyl) aminoanilinofluorane; 2-amino-6-p- (p- 2-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane; 2-phenyl-6-methyl-6-p- (p-phenylaminophenyl) aminoani Linofluorane; 2-benzyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane; 2-hydroxy-6-p- (p-phenylaminophenyl) 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] -Fluoran

<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)- 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-dimethyla Nophenyl) -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 Especially 3- (N-ethyl-Np-toluidinoamino) -6-methyl-7-anilinofur Oran and 3-diethylamino-7- (m-trifluoromethylanilino) fluorane are dyes having good light resistance, and are therefore preferably used for applications used in hot weather.

As the sensitizer used in the present invention, conventionally known sensitizers can be used as long as the desired effects on the above-described problems are not inhibited.
Such sensitizers include stearamide, methylolamide, ethylenebisamide, montanic acid wax, polyethylene wax, p-benzylbiphenyl, β-benzyloxynaphthalene, 4-biphenyl-p-tolyl ether, m-terphenyl, 4 , 4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, bis [2- (4-methoxy-phenoxy) ethyl] ether, methyl p-nitrobenzoate, dibenzyl oxalate, dioxalate (P-chlorobenzyl), di (p-methylbenzyl) oxalate, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-tolyl carbonate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene 1-hydroxy-2-naphtho Acid phenyl ester, 4- (m-methylphenoxymethyl) biphenyl, orthotoluenesulfonamide, paratoluenesulfonamide, 1,2-diphenoxyethane, 1,2-di (3-methylphenoxy) ethane, methylbiphenylketone Although it can illustrate, it is not restrict | limited in particular to these. These sensitizers may be used alone or in combination of two or more.

As other components that can be used in the present invention, a pigment, an adhesive, or a so-called binder may be used as necessary.
Examples of the pigment used in the present invention include inorganic or organic fillers such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide, and aluminum hydroxide. When emphasizing the prevention of head residue and sticking, it is preferable to use highly oil-absorbing fine silica. As such amorphous silica, the average particle diameter is 5 μm or more, preferably 5 to 10 μm, the oil absorption is 150 ml / 100 g or more, preferably 150 to 400 ml / 100 g, and the non-surface area is 150 m 2 / g or less, preferably 50 to 150 m2 / g. The average particle diameter is measured according to a master sizer (D50% diameter). The oil absorption is measured according to JIS K5101. This non-surface area is measured according to the BET method.
If the average particle diameter of the amorphous silica is smaller than 5 μm, the sticking resistance of the heat-sensitive recording layer is deteriorated. If it is larger than 10 μm, the life of the thermal head is shortened or the coating layer strength of the paper is weakened. The image quality may deteriorate. Further, if the oil absorption is less than 150 ml / 100 g, the head residue and sticking are not good, and if the specific surface area is more than 150 m 2 / g, the whiteness of the paint may be lowered. Examples of such amorphous silica include Carplex 101 (manufactured by Degussa Japan), Fine Seal P-8 (manufactured by Tokuyama), and the like.
Further, it is preferable to use calcium carbonate having an average particle size of 3 μm or more (hereinafter also referred to as “charcoal cal”) in order to prevent head scum and sticking. In addition, the measurement of an average particle diameter is performed according to a master sizer (D50% diameter).
Examples of such calcium carbonate include, for example, white sinter flower PZ (cubic calcium carbonate aggregate), PC / PCX (spindle type calcium carbonate), callite SA (aragonite type calcium carbonate), and tunex E (spindle type) made of Shiroishi calcium. Calcium carbonate aggregates).

  As the binder, those generally known as adhesives for heat-sensitive recording layers can be used as long as the desired effects of the present invention are not impaired in order to improve the fluidity of the paint. Specifically, fully saponified polyvinyl alcohol having a degree of polymerization of 200 to 1900, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, and other modified polyvinyl alcohols , Hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, ethylcellulose, cellulose derivatives such as acetylcellulose, styrene-maleic anhydride copolymer, styrene-butadiene copolymer, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic Acid ester, polyvinyl butyllar, polystyrene and copolymers thereof, polyamide resin, silicone resin, petroleum resin, terpene resin, Ton resin, can be exemplified Khumalo resin. These polymer substances are used by dissolving in water, alcohol, ketone, ester, hydrocarbon, or other solvents, and are used in the form of emulsification or paste dispersion in water or other media to achieve the required quality. It is also possible to use it together.

  In addition, 4,4′-butylidene (6-tert-butyl-3-methylphenol), 2,2 ′ is used as a stabilizer that imparts oil resistance and the like of recorded images within a range that does not impair the desired effect on the above-described problems. -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-butylphenylbutane, 4-benzyloxy-4 '-(2,3-epoxy-2-methylpropoxy) diphenylsulfone epoxy resin, etc. can also be added. .

  In addition to the above materials, lubricants such as waxes, benzophenone and triazole UV absorbers, water-resistant agents such as glyoxal, dispersants, antifoaming agents, phenolic antioxidants, fluorescent dyes, etc. are used. can do.

  The types and amounts of the basic leuco dye, developer, and other various components used in the heat-sensitive recording material of the present invention are determined according to required performance and recording suitability, and are not particularly limited. About 0.5 to 10 parts of the developer and 0.5 to 10 parts of the pigment are used with respect to 1 part of the conductive leuco dye. The sensitizer is preferably used in an amount of about 0.5 to 10 parts by weight with respect to 1 part by weight of the dye. About another component, a suitable quantity can be used in the range which does not impair the effect of this invention.

In order to obtain the heat-sensitive recording material of the present invention, for example, a dispersion in which a basic leuco dye and a developer are dispersed together with a binder, and other necessary additives such as pigments are added and mixed, and a heat-sensitive recording layer coating liquid is prepared. It can be manufactured by preparing and applying and drying on a substrate (support) to form a thermosensitive recording layer.
As a solvent used for this coating liquid, water, alcohol, etc. can be used, The solid content is about 10 to 50 weight%.
As the support, paper, recycled paper, synthetic paper, film, plastic film, foamed plastic film, non-woven fabric and the like can be used. Moreover, you may use the composite sheet which combined these as a support body.
Basic 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 emulsifying device. Add various additive materials to make a coating solution. The application means is not particularly limited, and can be applied according to well-known conventional techniques. For example, an off-machine coating having various coaters such as an air knife coater, a rod blade coater, a bill blade coater, a roll coater, and a curtain coater. A machine or an on-machine coating machine is appropriately selected and used.
The coating amount of the thermosensitive recording layer is not particularly limited, and is usually ² to 12 g / m ² by dry weight.

  In addition, an overcoat layer is provided on the heat-sensitive recording layer for the purpose of enhancing the storage stability, and an undercoat layer such as a polymer substance containing a pigment or an organic filler is provided under the heat-sensitive recording layer for the purpose of enhancing the color development sensitivity. Or may be provided. It is also possible to provide a backcoat layer on the opposite side of the support from the thermosensitive recording layer to correct the back barrier and curl. Also, various known techniques in the heat-sensitive recording material field can be added as appropriate, such as applying a smoothing process such as supercalendering after coating each layer. Furthermore, it can be processed into various forms such as providing a pressure-sensitive adhesive layer and release paper on the opposite surface of the support to the thermosensitive recording layer to form a label.

The following examples illustrate the invention but are not intended to limit the invention.
In each example, “parts” means “parts by weight” unless otherwise specified.
Example 1
For each material of the dye and the sensitizer, a dispersion having the following composition was prepared in advance, and wet grinding was performed with a sand grinder until the average particle size became 0.5 μm.
<Dye dispersion>
3-di-n-butylamino-6-methyl-7-anilinofluorane (trade name: ODB-2 manufactured by Yamamoto Kasei Co., Ltd.) 3.0 parts 10% aqueous polyvinyl alcohol solution 6.9 parts water 3.9 parts
<Sensitizer dispersion>
Diphenylsulfone (DPS) 6.0 parts 10% aqueous polyvinyl alcohol solution 18.8 parts Water 11.2 parts

The developer is a zirconia having a diameter of 0.3 mm by using a bead mill (Ultra Apex Mill UAM-015 model manufactured by Kotobuki Industries Co., Ltd.) that makes a dispersion having the following composition in advance and centrifuges the medium and the dispersion. Filling rate of beads 65% (grinding chamber volume 0.17 L), rotor peripheral speed 12 m / sec, flow rate 10 L / Hr (flow rate / grinding chamber volume = 59: the larger this value, the larger the flow rate with respect to the grinder scale) Then, the wet pulverization was performed until the residence time (the time during which the dispersion per unit volume was ground in the pulverization chamber) was 5 minutes.
The normal operation was performed by changing the cooling medium, the temperature and the flow rate, and the conditions under which the dispersion temperature measured at the dispersion outlet, which becomes the highest during the dispersion treatment, were around 40 ° C. were determined as follows.
Cooling medium: ethylene glycol Cooling medium temperature: -2 ° C
Flow rate (circulation method): 15 L / min
<Developer dispersion>
4-Hydroxy-4′-isopropoxydiphenylsulfone (manufactured by Nippon Soda Co., Ltd., trade name D-8) 6.0 parts 10% aqueous polyvinyl alcohol solution 18.8 parts water 11.2 parts

As a result, a developer dispersion having the particle size shown below was obtained.
The particle size was measured using a laser diffraction type particle size distribution analyzer (manufactured by Malvern, Mastersizer S). The dispersed particles of the obtained developer dispersion had a 50% size of 0.42 μm and a 90% size of 0.99 μm.

Next, the following compositions were mixed to obtain a thermal recording layer coating solution. This coating solution is applied and dried on a high-quality paper having a basis weight of 50 g / m ^{2 so} that the coating amount after drying becomes 6 g / m ^2, and processed so that the Beck smoothness becomes 200 to 600 seconds with a super calendar, A heat-sensitive recording material was obtained.
Developer dispersion 36.0 parts Dye dispersion 13.8 parts Sensitizer dispersion 36.0 parts Silica (manufactured by Mizusawa Chemical Co., Ltd., trade name: Mizukasil P537) 25% dispersion
13.0 parts Calcium carbonate (trade name: Tunex E, manufactured by Shiraishi Calcium Co.) 50% dispersion
13.0 parts Zinc stearate 30% dispersion 6.7 parts

Example 2
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the developer of Example 1 was changed to 4-hydroxy-4′-n-propoxydiphenylsulfone. The dispersed particles of the obtained developer dispersion had a 50% diameter of 0.45 μm and a 90% diameter of 1.02 μm.

Example 3
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the developer of Example 1 was changed to bis (3-allyl-4-hydroxyphenyl) sulfone (manufactured by Nippon Kayaku Co., Ltd., trade name TGSH). The dispersed particles of the obtained developer dispersion had a 50% diameter of 0.46 μm and a 90% diameter of 1.08 μm.

Example 4
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the diameter of the zirconia beads used in Example 1 was changed to 0.1 μm. The dispersed particles of the obtained developer dispersion had a 50% diameter of 0.34 μm and a 90% diameter of 0.71 μm.

Comparative Example 1
A bead mill (Dynomill TYPE KDL, manufactured by Shinmaru Enterprises Co., Ltd.) that screens the media and the dispersion using a pulverizer under the atomization conditions of the developer in Example 1.
The zirconia beads with a diameter of 0.5 mm were filled at 80% (grinding chamber volume: 1.4 L), the rotor peripheral speed was 12 m / sec, the flow rate was 18 L / Hr (flow rate / grinding chamber volume = 13: the larger this value, Example 1 except that wet pulverization was performed until the residence time (the time during which the dispersion per unit volume was ground in the pulverization chamber) was 5 minutes under the conditions of a large flow rate with respect to the pulverizer scale). A heat-sensitive recording material was obtained. The 50% diameter of the dispersed particles of the obtained developer dispersion is 0.61 μm, 9
The 0% diameter was 1.45 μm.

Comparative Example 2
A heat-sensitive recording material was obtained in the same manner as in Comparative Example 1 except that the developer of Comparative Example 1 was changed to 4-hydroxy-4′-n-propoxydiphenylsulfone. The dispersed particles of the obtained developer dispersion had a 50% diameter of 0.59 μm and a 90% diameter of 1.48 μm.

Comparative Example 3
A thermal recording material was obtained in the same manner as in Comparative Example 1 except that bis (3-allyl-4-hydroxyphenyl) sulfone (trade name TGSA, manufactured by Nippon Kayaku Co., Ltd.) was used as the developer of Comparative Example 1. The dispersed particles of the obtained developer dispersion had a 50% diameter of 0.52 μm and a 90% diameter of 1.51 μm.

The following evaluation tests were performed on the heat-sensitive recording materials obtained in the above examples and comparative examples.
[Color development sensitivity]
Using TH-PMD manufactured by Okura Electric Co., Ltd., applied energy 0.25
And 0.34 mJ / dot. The image density after printing and after the quality test was measured with a Macbeth densitometer (RD-914, using an amber filter).
[Moisture and heat resistance] (Image remaining rate)
A thermal recording medium printed using TH-PMD manufactured by Okura Electric Co., Ltd. with an applied energy of 0.34 mJ / dot was allowed to stand in an environment of 50 ° C. and 90% for 24 hours. It measured with the densitometer, and calculated the image residual ratio with the following formula.
Image residual ratio (%) = density after test / density before test × 100
[Heat resistance] (background density)
After pressing on a hot plate at 70 ° C. for 5 seconds, the color density of the background portion was measured with a Macbeth densitometer.

  The evaluation results are shown in the table below.

  As is clear by comparing Examples 1 to 4 and Comparative Examples 1 to 3, the heat-sensitive recording material of the present invention in which the developer is atomized is excellent in color development sensitivity, heat resistance, and heat and humidity resistance.

Claims (2)

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 heat-sensitive recording layer is used as an electron-accepting developer. The following general formula (Formula 1) in which the particle size distribution (volume basis) of the fine particles measured with a laser diffraction particle size distribution analyzer is 0.5 μm or less at 50% diameter and 1.2 μm or less at 90% diameter:

(Wherein R represents a linear or branched saturated or unsaturated hydrocarbon having 1 to 4 carbon atoms, R ′ represents an alkenyl group, and n represents an integer of 0 to 2) 4, A heat-sensitive recording material, which is a 4′-dihydroxydiphenylsulfone substituted product.   The electron-accepting developer is wet pulverized by a bead mill together with a pulverizing medium, separated into a medium and a dispersion by the action of centrifugal force, and discharged from the bead mill. Thermal recording material.