JP2543596B2 - Method for manufacturing thermal recording material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a heat-sensitive recording material, and more specifically to a method for producing a heat-sensitive recording material having excellent continuous recording suitability. .

[Conventional technology]

The heat-sensitive recording method is highly evaluated for its advantages, such as the ability to obtain a color image simply by heating, and the relatively simple and compact recording device, and is widely used as various information recording methods. ing.

Particularly, in recent years, thermal facsimiles and thermal printers using such a thermal recording system have been improved in their apparatuses, and high-speed recording, which has been difficult in the past, is now possible. With the speeding up of such equipment and hardware fields, the thermal recording materials used are also required to have improved recording sensitivity, and many proposals have been made regarding this. As such a heat-sensitive recording material, a heat-sensitive recording layer mainly composed of a binder and a thermochromic substance is formed as a single layer or a multilayer on a support made of paper, a plastic film, a synthetic paper, or the like. What is used is generally used.

In order to improve the recording sensitivity of the heat-sensitive recording material having such a constitution, conventionally, 1) addition of a low-melting heat-fusible substance, 2) improvement of surface smoothness, and 3) increase of color-forming component have been devised. However, all of these means have the drawbacks that the adhesion of the melted component in the heat-sensitive recording layer to the thermal head is increased, which causes printing trouble.

Therefore, in order to solve such a defect, it has been proposed to make the average particle diameter of the basic dye particles 2.0 μm or less as a means for improving the recording sensitivity without increasing the amount of the color-forming component (Japanese Patent Laid-Open No. 2003-242242). 57-47693).

However, if the average particle size of the basic dye is merely 2.0 μm or less, the effect of improving the recording sensitivity is insufficient. Therefore, as a method for uniformly dispersing the dye particles in the heat-sensitive recording layer-forming coating liquid. It has been proposed to use a horizontal sand mill (Japanese Patent Laid-Open No. 58-69089).

The horizontal sand mill can disperse the dispersoid material with a high shearing force, so that it is easy to make the dye and the developer into fine particles, and the flow of the dispersion medium is horizontal.
Therefore, regardless of the specific gravity of the dispersion, there is an advantage that the residence time in the vessel becomes almost constant, and a stable dispersion having a sharp distribution can be obtained. In particular, it is extremely effective when a dye or a color developer and an additive such as a heat-fusible substance are mixed and dispersed at the same time, and separation of different kinds of materials and composition change are hardly caused. Has been done.

However, it is said that the average particle size of the components must be 0.7 μm or less in order to increase the sensitivity of the heat-sensitive recording layer. To achieve such ultrafine particles, it seems to be conventionally used. When dispersing using solid particulate dispersion media (glass, alumina spheres, etc.) with a diameter of 0.5 to 1 mm, the number of dispersion operations must be 10 or more. It was not the target. Also, in order to make the dispersion operation more efficient, the diameter of the dispersion medium should be 0.1-
If you use 0.3 mm, the horizontal sand mill's stirring shaft and separation plate are rotating at high speeds (1000 to 6000 rpm), so the dispersion media are severely destroyed and continuous dispersion operation cannot be continued. Met.

[Problems to be Solved by the Invention]

As described above, in the conventional method for producing a heat-sensitive recording material, when adjusting the dye dispersion liquid and the developer dispersion liquid using a horizontal sand mill, without destroying the dispersion medium,
It has been difficult to disperse the dye particles and the developer particles in a particle size of 0.7 μm or less, and to carry out the dispersing operation continuously.

The present invention solves the above problems and provides a method for producing a high-quality heat-sensitive recording material excellent in continuous recording property with high efficiency.

[Means for solving the problem]

The method for producing a heat-sensitive recording material of the present invention comprises a dye dispersion containing a substantially colorless electron-donating color-forming dye, and an electron-accepting color-developing agent which causes a color reaction by contact reaction with the color-forming dye under heating. A method of preparing a thermosensitive recording coating liquid by mixing a compound-containing developer dispersion, coating the coating liquid on one surface of a sheet-like support, and solidifying to form a thermosensitive recording layer. A dispersion liquid of at least one of the dye dispersion liquid and the developer dispersion liquid, a horizontal vessel, a raw material supply port formed in the vessel, and a dispersion liquid discharge port, and a plurality of sheets arranged in the vessel. A stirring blade and a horizontal rotary shaft for driving the stirring blade,
And a horizontal plate which is disposed adjacent to the discharge port, has a separation plate for guiding the mixed dispersion liquid to the discharge port, and contains a solid particulate dispersion medium, wherein The separation plate is rotated independently from the rotation shaft for the stirring blade, and the rotation speed ratio of the rotation shaft for the stirring blade to the rotation shaft for the separation plate is controlled to 20: 1 to 5: 1. It is a thing.

As a result of earnest research on a method for continuously preparing a uniform dispersion having a particle size of less than 0.7 μm, the present inventors have found that in a horizontal sand mill, the separation plate at the outlet is not directly connected to the stirring shaft, It was found that a sufficient dispersion effect can be achieved by one dispersion operation by rotating the shaft at a lower rotation speed and controlling the stirring shaft / separation plate shaft rotation speed ratio to 20: 1 to 5: 1. The present invention has been completed. In the horizontal sand mill used in the present invention, the separation plate at the discharge port and the space between the vessels (slits) rotate at a speed lower than the stirring shaft, so that the dispersion media (beads) are less worn between the slits. In addition, the slit width is 0.1 m in the conventional horizontal sand mill that rotates at high speed in terms of machining accuracy.
Although it was difficult to reduce the width to m or less, it is easy to form a slit width of less than 0.1 mm in the horizontal sand mill used in the method of the present invention. As a result, it became possible to use beads having a particle diameter of 0.1 to 0.3 mm, which has been conventionally unusable for continuous dispersion, as a dispersion medium. That is, even if beads with a particle size of 0.1 to 0.3 mm are used, the slit width is less than 0.1 mm and smaller than the particle size of the beads, so that the beads do not penetrate into the slit and the dispersed particles are dispersed here. Objects are separated and collected from the beads.
When beads with a particle size of 0.5 to 1 mm are replaced with a dispersion medium with a particle size of 0.1 to 0.3 mm, the number of dispersion media per unit volume increases dramatically, which makes it possible for the substance to be dispersed to become more stable within a certain processing time. It came into contact with many media and passed between them, thus resulting in a uniform, small particle size dispersion.

Conventional horizontal sand mill, the dispersion vessel is mounted horizontally, in which the dispersion medium having a particle diameter of 0.2 ~ 5 mm, for example, glass beads, or alumina particles are filled, around the rotation axis horizontally mounted in the dispersion vessel. It is equipped with dispersion wings.

In the conventional horizontal sand mill shown in FIG. 2, the horizontal vessel 5 has the raw material supply port 1 and the dispersion liquid discharge port 2, and the horizontal rotation shaft 3 extends horizontally in the vessel 5.
A plurality of stirring blades 4 extend from the horizontal rotary shaft 3. Further, a separation plate 6 is attached to the horizontal rotary shaft 3 adjacent to the dispersion liquid discharge port 2, whereby the dispersion liquid can be guided to the discharge port 2.

In the horizontal sand mill used in the method of the present invention,
As shown in FIG. 1, the separation plate 6 is independent of the horizontal rotary shaft 3 for stirring blades, is connected to a separate rotary shaft 7, and is independent of the rotation of the horizontal rotary shaft 3. Rotating at a lower rotation speed (rotation speed ratio of the horizontal rotation shaft 3 to the separation plate rotation shaft = 20: 1 to 5: 1), the horizontal vessel 5 is rotated.
The dispersion liquid prepared in the inside can be guided to the dispersion liquid chamber 9 through the slit 8 and further guided to the discharge port 2 to be discharged therefrom. In the method of the present invention, one surface of the sheet-like support is coated with a thermal recording coating liquid, and the coating liquid is solidified,
A thermosensitive recording layer is formed.

Paper, a plastic sheet or a film is used as the sheet-shaped support, and natural pulp paper, synthetic pulp paper, synthetic paper or the like can be used as the paper. Generally, those having a weight of 30 to 200 g / m ² are preferred.

The coating liquid for heat-sensitive recording comprises a dispersion liquid containing a substantially colorless electron-donating color-forming dye, and a color-developing dye containing a compound containing an electron-accepting color-developing compound that reacts by contact under heating. A colorant dispersant is included.

Generally, the dye and the color developer are dispersed using an aqueous solution of a water-soluble polymer compound as a dispersion medium. As the dispersion medium,
Generally, polyacrylamide, polyvinylpyrrolidone,
Water-soluble synthetic polymer compounds such as polyvinyl alcohol and styrene-maleic anhydride copolymer, and water-soluble natural polymer compounds or derivatives thereof such as hydroxyethyl cellulose, starch derivatives, gelatin, and casein are used. To be

The polymer compound is used in the dye dispersion liquid and the developer dispersion liquid in an amount of preferably 1 to 20% by weight, more preferably 3 to 10% by weight.

The color forming dye used in the method of the present invention is not particularly limited as long as it is used for general pressure sensitive recording paper, heat sensitive recording paper and the like. Specific examples are (1) triarylmethane compounds such as 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3- (p-
Dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis -(9-Ethylcarbazol-3-yl) -5-dimethylaminophthalide, 3,3-bis- (2-phenylindol-3-yl) -5-dimethylaminophthalide, etc .: (2) Diphenylmethane system A compound such as 4,4'-bis-dimethylaminobenzhydrin benzyl ether,
N-halophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, etc .: (3) Xanthene compounds such as rhodamine B-anilinofuctam, 3-diethylamino-7-cibenzylaminofluorane, 3 -Diethylamino-7-butylaminofluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-piperidino-6-
Methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-anilinofluorane, 3-cyclohexyl-methylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6- Chloro-7-
(Β-Ethoxyethyl) aminofluorane, 3-diethylamino-6-chloro-7- (γ-chloropropyl) aminofluorane, etc .: (4) Thiazine-based compounds, for example, benzoylleuco methylene blue, p-nitrobenzoylleuco methylene blue Etc .: (5) Spiro compounds, for example, 3-methyl-spiro-
There are dinaphthopyran, 3-ethyl-spiro dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3-methylnaphtho- (3-methoxy-benzo) -spiropyran, and the like, and these are used alone or as a mixture of two or more kinds. To be The dye is selected and used depending on the application and desired properties.

As the color developer used in the method of the present invention, phenol derivatives and aromatic carboxylic acid derivatives are preferable, and bisphenols are particularly preferable. Specifically, as phenols, p-octylphenol, p-tert-butylphenol, p-phenylphenol, 1,1-bis (p-
Hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxyphenyl) hexane, 2,2-bis ( p-Hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl)
Examples include 2-ethyl-hexane and 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane.

As the aromatic carboxylic acid derivative, p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, butyl p-hydroxybenzoate, 3,5-di-tert-butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid and Examples of the carboxylic acid include these polyvalent metal salts.

These color developing agents are added as a eutectic with a low melting point fusible substance in order to cause a color reaction by melting at a desired temperature, or a low melting point compound is used as a color developing agent. It is preferable to add it in a state of being fused to the surface of the particles.

In the method of the present invention, at least one member of the dye dispersion and the developer dispersion is adjusted using a horizontal sand mill,
At that time, for example, by using a horizontal sand mill having the configuration shown in FIG. 1, the separation plate is rotated independently of the rotating shaft for the stirring blades, and its rotation speed is higher than that of the rotating shaft for the stirring blades. Try to keep it low.

In this dispersion operation, it is preferable to use glass or alumina beads having a diameter of 0.1 to 1 mm as the solid particulate dispersion medium.

The dispersed particles in the dispersion liquid have a particle size in the range of 0.05 to 2 μm, and preferably have an average particle size of 0.1 to 0.7 μm.

In the method of the present invention, the rotating shaft for the stirring blade is 600 to 240.
It is preferable that the separation plate is rotated at a rotation speed of 0 rotations / minute, and the separation plate is rotated at a constant rotation speed of 50 to 600 rotations / minute. Further, the rotation speed ratio between the rotating shaft for the stirring blade and the separation plate is controlled to 20: 1 to 5: 1.

When the rotation speed ratio is greater than 20: 1, the rotation of the separation plate becomes significantly slower than the rotation of the stirring blade, and dispersion medium accumulates at the entrance of the slit and blocks it, making it difficult to discharge the dispersion. become. By setting the rotation speed of the separation plate at a certain number or more, the dispersion medium is stirred and dispersed, and the dispersion is easily discharged. On the other hand, if the rotation speed ratio is less than 5: 1, the rotation of the separation plate becomes faster, and the vibration of the separation plate reduces the accuracy of the slit width, and the dispersion medium is caught in the slit and destroyed. Therefore, it becomes impossible to continue the dispersion operation.

Further, generally, the filling rate of the dispersion medium in the horizontal vessel for dispersion is 50 to 85%.

The obtained dye and developer dispersions are mixed with each other, and if desired, inorganic pigments, waxes, higher fatty acid amides, metal soaps, and further ultraviolet absorbers if necessary,
A coating solution is prepared by adding an antioxidant or a latex binder.

The above additives may be added during the dispersing operation.

The coating liquid is coated on one surface of the sheet-shaped support so as to have a concentration of 3 to 8 g / m ² (dry) and dried by a conventional method, whereby a thermosensitive recording layer is formed.

Examples of waxes contained in the heat-sensitive recording layer include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, and higher fatty acid amides such as stearic acid amide, ethylene bisstearamide, and higher fatty acid ester.

Examples of the metal soap include higher fatty acid polyvalent metal salts, that is, zinc stearate, aluminum stearate, calcium stearate, zinc oleate and the like.

As inorganic pigments, kaolin, calcined kaolin talc,
Examples include wax, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium, titanium oxide and barium carbonate.

These are generally water-soluble binders (binders) dispersed and applied in a binder, such as polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymer, and styrene-anhydrous. Examples thereof include maleic acid copolymer, isobutylene-maleic anhydride copolymer, polyacrylic acid, starch derivative, casein, gelatin and the like. In addition, a water resistance imparting agent (gelling agent, crosslinking agent) is added to these binders for the purpose of imparting water resistance, or a hydrophobic emulsion such as styrene-butadiene rubber latex or acrylic resin emulsion is added. You can also

In the method of the present invention, prior to the dispersion operation by the horizontal sand mill, the dye dispersion liquid and the developer dispersion liquid are subjected to a pre-dispersion treatment by a conventional dispersion operation, for example, a ball mill, an attritor, a sand mill, or a three-roll mill. You may perform dispersion operation.

〔Example〕

 The invention is further described by the examples.

Unless otherwise specified, "parts" and "%" in the examples mean "parts by weight" and "% by weight".

Example 1 2 kg of 3- (N-isopentyl-N-ethylamino)
-6-Methyl-7-anilinofluorane (basic dye)
2.5% polyvinyl alcohol (polymerization degree 500 saponification degree
99%) Aqueous solution 4kg was charged into an improved horizontal sand mill (Ultra Visco Mill manufactured by Igarashi Kikai Seisakusho), and glass beads with a diameter of 0.3 mm were used as the dispersion medium, and the filling rate was 85.
%, The dispersion operation was performed at a processing rate of 0.3 l / min. The rotation speed of the rotating shaft for the stirring blade was 945 rpm, the rotation speed of the separation plate was 100 rpm, and the rotation speed ratio was 9.45: 1.

The dispersion average particle diameter of the obtained dye was 0.6 μm, and 75% of all the dispersed particles were 1.0 μm or less. The particle size was measured using LPA-3000 / 3100 manufactured by Otsuka Electronics Co., Ltd.

The above dye dispersion is mixed with a developer dispersion (containing bisphenol A and polyvinyl alcohol) produced by a conventional method to prepare a heat-sensitive recording coating solution by a conventional method,
This was applied and solidified on one surface of a high quality paper (basis weight: 50 g / m ² ) to form a 7 g / m ² thermosensitive recording layer. When this heat-sensitive recording paper was used in a normal heat-sensitive recording operation, heat-sensitive color development was extremely fast and an image of good quality was obtained.

Example 2 8 kg of benzyl p-hydroxybenzoate (developing agent)
2.5% polyvinyl alcohol (polymerization degree 500, saponification degree 99
%) Solution 16 kg with conventional horizontal sand mill (WILLY A.BA
CHOFEN's Dyno Mill KD-PILOT type), using 0.8 mm diameter glass beads as the dispersion medium, and filling rate 85
% After roughly dispersing at a processing speed of 0.3 l / min, and then charged into an improved horizontal sand mill (Ultra Visco Mill manufactured by Igarashi Kikai Co., Ltd.) with glass beads of 0.3 mm diameter as a dispersion medium at a filling rate of 85%. Filled and dispersed at a processing rate of 1 per minute. The resulting developer has a dispersed particle size of 0.4 μm, and 75% of all dispersed particles have a particle size of 0.8 μm or less. The stirring shaft / separating plate shaft rotation speed ratio at this time was 9.45: 1.

A dye dispersion liquid (3- (N-isobenthyl-N-ethylamino) -6-
Methyl-7-anilinofluorane and polyvinyl alcohol were mixed) to prepare a heat-sensitive recording coating solution by a conventional method. This coating solution was applied onto one surface of a high-quality paper (basis weight: 50 g / m ² ) and solidified to form a 7 g / m ² thermosensitive recording layer. When the obtained thermal recording paper was subjected to a normal thermal recording operation,
The heat-sensitive color development was extremely fast, and an image of good quality was obtained.

Comparative Example 1 The same operation as in Example 1 was performed. However, instead of the improved horizontal sand mill, the conventional horizontal sand mill (Dyno Mill KD
-PILOT type), glass beads having a diameter of 0.8 mm were filled at a filling rate of 85% as a dispersion medium, and a dispersion operation was performed at a processing rate of 0.3 l / min. The average particle size of the obtained dye particles is 1.2 μm, and 75% of all dispersed particles have an average particle size of 3 μm.
It was below. The stirring shaft / separation plate shaft rotation speed ratio at this time is
It was 1: 1.

The heat-sensitive color development speed of the obtained heat-sensitive recording paper was lower than that of Example 1.

Comparative Example 2 The same operation as in Example 2 was performed. However, instead of the improved horizontal sand mill, a vertical sand mill (1 / 2G type sand mill,
Glass beads having a diameter of 1.0 mm were filled as a dispersing medium at a filling rate of 65% by using Igarashi Machinery Co., Ltd., and the dispersing operation was performed at a processing speed of 1 minute. The stirring shaft / separating plate shaft rotation speed ratio at this time was 1: 1. The average particle size of the obtained developer particles is 1.0 μm, and the average particle size of 75% of all dispersed particles is 2.5 μm.
It was m or less. The heat-sensitive color development speed of the obtained heat-sensitive recording paper was lower than that of Example 2.

〔The invention's effect〕

According to the method of the present invention, a heat-sensitive recording coating liquid containing fine particle dispersions having a uniform particle size distribution can be efficiently obtained, which makes it possible to produce a heat-sensitive recording material having a high heat-sensitive color development rate and good quality. It was

[Brief description of drawings]

FIG. 1 is a sectional explanatory view of an embodiment of an improved horizontal sand mill used in the method of the present invention, and FIG. 2 is a sectional explanatory view of an embodiment of a conventional horizontal sand mill. 1 ... Raw material supply port, 2 ... Dispersion discharge port, 3 ... Horizontal rotation shaft, 4 ... Stirring blade, 5 ... Horizontal vessel, 6 ... Separation plate, 7 ... Separation plate rotation shaft, 8 …… Slit, 9 ……
Dispersion chamber.

Claims (1)

(57) [Claims] 1. A color development containing a dye dispersion containing a substantially colorless electron-donating color-forming dye and an electron-accepting color-developing compound that reacts with the color-forming dye under heating to develop the color. A method for preparing a heat-sensitive recording coating liquid by mixing with an agent dispersion liquid, applying the coating liquid on one surface of a sheet-like support, and solidifying to form a heat-sensitive recording layer. And at least one dispersion of the developer dispersion, a horizontal vessel, a raw material supply port formed in this vessel, and a dispersion discharge port, a plurality of stirring blades arranged in this vessel, A horizontal axis of rotation that drives
And a horizontal plate which is disposed adjacent to the discharge port, has a separation plate for guiding the mixed dispersion liquid to the discharge port, and contains a solid particulate dispersion medium, wherein The separation plate is rotated independently from the rotation shaft for the stirring blade, and the rotation speed ratio of the rotation shaft for the stirring blade to the rotation shaft for the separation plate is controlled to 20: 1 to 5: 1. , A method for manufacturing a thermal recording material.