JPH03121885A - Production of thermal recording material - Google Patents

Abstract

PURPOSE:To produce a thermal recording material having a high thermal color forming speed and good quality by preparing a coating solution for a thermal recording layer by mixing a dye dispersion and a coupler dispersion at least one of which is prepared using a specific horizontal sand mill and applying the coating solution to the surface of a sheetlike support and solidifying the same to form the thermal recording layer. CONSTITUTION:A dye dispersion containing a substantially colorless electron donating color forming dye and a coupler dispersion containing an electron acceptive coupling compound generating the contact reaction with the color forming dye under heating to form a color are prepared so that at least one of them is prepared using a horizontal sand mill and both of the dye dispersion and the coupler dispersion are mixed to prepare a coating solution for thermal recording. This coating solution is applied to one surface of a sheetlike support and solidified to form a thermal recording layer. At this time, the horizontal sand mill is inclined downwardly from the dispersion supply port 1 thereof to the discharge port 2 thereof pref. at an angle of 10-30 deg.. When the dispersion of a thermal color forming material is performed using the horizontal sand mill thus arranged, the color forming material can be dispersed by utilizing high shearing force and, therefore, the color former and the coupler are easily pulverized.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a heat-sensitive recording material,
More specifically, the present invention relates to a method for producing a heat-sensitive recording material with excellent continuous recording suitability.

[Conventional technology]

Thermal recording method allows you to obtain a colored image by simply exposing it to heat.
Furthermore, the advantages of this recording device, such as its ability to be relatively simple and compact, have been highly evaluated, and it has been widely used as a variety of information recording methods.

Particularly in recent years, thermal facsimiles and thermal printers using such thermal recording methods have been improved in terms of equipment, and high-speed recording, which was previously considered difficult, has become possible. As the speed of such devices and devices increases, the heat-sensitive recording materials used are required to have improved recording sensitivity, and many proposals have been made regarding this. (1) (2) Formation of a heat-sensitive recording layer containing a binder and a thermochromic substance as main components on a support made of paper, plastic film, synthetic paper, etc., either as a single layer or as a multilayer. are commonly used.

In order to improve the recording sensitivity of a heat-sensitive recording material having such a structure, conventional techniques have been taken such as 1) adding a low-melting thermofusible substance, 2) improving surface smoothness, and 3) increasing the amount of color-forming components. However, all of these methods have drawbacks such as increased adhesion of molten components in the heat-sensitive recording layer to the thermal head, causing printing problems.

Therefore, in order to eliminate these drawbacks, we have developed a color-forming ingredient ■
As a means of improving recording sensitivity without increasing the amount of basic dye particles, the average particle size of basic dye particles is increased by 2. It has been proposed to make it CD- or lower (Japanese Patent Application Laid-Open No. 57-47693).

However, simply reducing the average particle size of the basic dye to 2.0p or less is insufficient to improve recording sensitivity, and for this reason, there is a method for uniformly dispersing dye particles in the heat-sensitive recording layer forming coating solution. The use of a horizontal sand mill has been proposed as a method (Japanese Patent Application Laid-Open No. 5869089).

Horizontal sand mills can disperse dispersoid materials with high shear force, making it easy to make dyes and color developers into fine particles, and the flow of the dispersion medium is horizontal, so the specific gravity of the dispersion can be reduced. Regardless of the type of dispersion, it has the advantage that the residence time in the vessel is approximately constant and a stable dispersion with a sharp distribution can be obtained. It is particularly effective when mixing dyes or color developers with additives such as thermofusible substances and dispersing them at the same time, and there is almost no separation of different materials or compositional changes. has been done.

However, it is said that in order to increase the sensitivity of the heat-sensitive recording layer, it is necessary to reduce the average particle size of the components to 0.7p or less, and in order to achieve such ultra-fine particle size, conventionally used When performing dispersion using dispersion media (glass, alumina spheres, etc.) with a diameter of 0.5 to 1 mm, it is necessary to perform the dispersion operation 10 times or more. It wasn't practical. In addition, in order to make the dispersion operation more efficient, the diameter of the dispersion media is set to 0.1~
When using a 0.3 mm diameter sand mill, the stirring shaft (3) (4) of the horizontal sand mill and the separation plate rotate together at high speed (1000 to 6000 rpm), resulting in severe destruction of the dispersion media and continuous dispersion. It was not possible to continue the distributed operation.

Therefore, the present inventors developed a horizontal sand mill used for preparing a dispersion by rotating the separation plate independently from the rotating shaft for the stirring blade to maintain the rotational speed of the separation plate closer to the rotational speed of the stirring blade. proposed, and thereby succeeded in eliminating or reducing the above problems. However, further improvement in dispersion efficiency is strongly desired.

[Problem to be solved by the invention]

As mentioned above, in the conventional method for producing heat-sensitive recording materials, when preparing a dye dispersion liquid and a color developer dispersion liquid using a horizontal sand mill, dye particles and color developer particles can be prepared without destroying the dispersion medium. It has been considered difficult to disperse the particles to a particle size of 0.7 square feet or less and to carry out this dispersion operation continuously, and further improvement of the dispersion efficiency has been desired.

The present invention aims to solve the above-mentioned problems and provide a method for manufacturing high-quality heat-sensitive recording materials with excellent continuous recording properties with high efficiency.

[Indispensable means to solve problems]

The method for producing a heat-sensitive recording material of the present invention includes a dye dispersion containing a substantially colorless electron-donating color-forming dye, and an electron-accepting color developer that develops color by contacting and reacting with the color-forming dye under heating. At least one of them is prepared using a horizontal sand mill, and a coating liquid for thermal recording is prepared by mixing the dye dispersion and the color developer dispersion. In the method of applying a coating liquid to one surface of a meat-like support and solidifying it to form a heat-sensitive recording layer, the horizontal sand mill is tilted downward from its dispersion supply port to its discharge port. , is characterized in that the dispersion is prepared.

The present inventors have discovered that when a thermosensitive coloring material is dispersed using a horizontal sand mill installed at an angle, it can be dispersed with extremely good dispersion efficiency, and the present invention has been completed (5) and (6). The inclined horizontal sand mill is a conventionally commercially available horizontal sand mill such as WiLLY A, Dyno Mill manufactured by BACHOFEN, and Ultra Visco Mill manufactured by Igarashi Kikai Seisaku.
When installed, it is characterized in that it is inclined downward from the dispersion supply port toward the discharge port, preferably at an angle of 5 to 45 degrees with respect to the horizontal, more preferably at an angle of 10 degrees to 30 degrees. It is something.

Dispersing the heat-sensitive coloring material using the horizontal sand mill set up in this manner provides the following three advantages.

(1) Since dispersion can be performed by utilizing the high shear force that is characteristic of the conventional horizontal sand mill, it is easy to make the color former and color developer into fine particles.

(Since the two-vessel cell is tilted downward at 5 to 45 degrees from the dispersion liquid supply port to the discharge port, there are many dispersion media (glass bead sand, alumina beads, etc.) with acid groups in the vessel on the discharge port side. As a result, dispersions with large particle sizes near the supply port are dispersed by a smaller amount of dispersion media (beads) than on the discharge port side, and as a result, dispersions with larger particle sizes near the supply port are dispersed by a smaller amount of dispersion media (beads) than on the discharge port side. A dispersion with a small particle size is dispersed by a larger amount of dispersion media (beads), which significantly improves the efficiency of dispersion into fine particles.

Generally, particles can be divided and dispersed relatively easily when the particle size is large, but as the particle size becomes smaller, division and dispersion becomes more difficult.

In the method of the present invention, for particles exhibiting such splitting and dispersion behavior, by tilting the horizontal sand mill downward, the distribution of the dispersion medium is made appropriate, thereby efficiently preparing dispersed particles with a sharp particle size distribution. can do.

In the method of the present invention, the inclination angle of the horizontal sand mill is 10
If the angle is less than 45 degrees, the improvement in dispersion efficiency may not be sufficient compared to the conventional method, and if it is greater than 45 degrees, the distribution of the dispersion media in the vessel will be inappropriate and the motor will not be affected during startup. This results in the inconvenience of an increased load.

There are no particular restrictions on the types (7) and (8) of the model sand mill used in the method of the present invention. For example, a model sand mill such as that shown in FIGS. 1 and 2 can be used.

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

In the horizontal sand mill shown in FIG. 2, a dispersion vessel is filled with dispersion media such as glass beads or alumina particles having a particle size of 0.2 to 5 ml11.

In the horizontal sand mill shown in FIG. The dispersion liquid prepared in the horizontal vessel 5 is guided to the dispersion liquid chamber 9 through the slit 8, and further guided to the discharge port 2, where it is discharged. can.

In the method of the present invention, a heat-sensitive recording coating liquid is applied to one surface of a sheet-like support and solidified to form a heat-sensitive recording layer.

In the horizontal sand mill shown in Fig. 1, the separation plate at the discharge port can be rotated at a slower speed than the stirring shaft between the vessels (slits). ) has less wear. Furthermore, in terms of machining accuracy, it was difficult to reduce the slit width to 0.1 W or less with the horizontal sand mill shown in Fig. 1, which rotates at high speed, but with the horizontal sand mill used in the method of the present invention, it was difficult to reduce the slit width to 0.1Φ1 or less. It is easy to form the slit width.

This makes it possible to use beads with a particle diameter of 0.1 to 0.3 mm as a dispersion medium, which was conventionally considered impossible to use for continuous dispersion. Particle size 0,
5-1 m+n beads, particle size 0.1-0.3 m
If the number of dispersion media is replaced by m, the number of dispersion media per unit capacity increases dramatically, and as a result, the material to be dispersed comes into contact with more media within a given processing time. As a result, a uniform dispersion with a small particle size can be obtained.

The sheet-like support used in the method of the present invention includes paper,
A plastic sheet or film is used, and as the paper, natural pulp paper, synthetic pulp paper, synthetic paper, etc. can be used. In general, those having a weight of 30 to 200 g/m' are preferred.

The coating liquid for heat-sensitive recording consists of a dispersion containing a substantially colorless electron-donating color-forming dye and a developer containing an electron-accepting color-developing compound that reacts with the color-forming dye under heating to develop color. It contains a colorant dispersant.

The color-forming dye used in the method of the present invention is not particularly limited as long as it is generally used in pressure-sensitive recording paper, heat-sensitive recording paper, etc. To give a concrete example, (1))'J
Arylmethane 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-phenylindole-3
-yl)phthalide, 3,3-bis-(9ethylcarbazol-3-yl)-5-dimethylaminophthalide, 3,
3-bis-(2-phenylindol-3-yl)-5
-dimethylaminophthalide, etc. (2) Diphenylmethane compounds, e.g. 44' -
Bis-dimethylaminobenzhythrin benzyl ether, N-herophenyl leukoolami 7, N-1,4,5
-) dichlorophenyl leukoolamine, etc.: (3) Xanthine compounds, such as rhodamine B-anilinofukucum, 3-diethylamino-7-sibenzylaminofluoran, 3-diethylamine-7-butylaminofluorane, 3-diethylamino-7- (2-Chloroanilino)fluorane, 3-diethylamine-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl (11) (12) Nianiritflurane, 3-ethyl-tolylamino-6-methyl -7-anilinofluorane, 3-cyclohexyl-methylamino-6-methyltoanilinofluorane, 3-diethylamino 6-chloro-7-(β-ethoxyethyl)aminofluorane, 3-diethylamino-
6-chloro7-<r-chloropropyl)aminofluorane, etc.: (4) Thiazine compounds, such as benzoylleucomethylene blue, p-nitrobenzoylleucomethylene blue, etc.: (5) Spiro compounds, such as 3-methylspiro- dinaphthopyran, 3-ethyl-spirodinaphthopyran, 3
-benzylspiro-dinaphthopyran, 3-methylnaphtho-(3-methoxy-benzo)-spiropyran, etc., and these may be used alone or as a mixture of two or more.

The dye used is selected 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 preferred, and bisphenols are particularly preferred.

Specifically, the phenols include p-octylphenonope, p-tert-butylphenonope, p-phenylphenol, 1.1-bis(p-hydroxyphenyl)propane, and 2.2-bis(p-hydroxyphenyl)propane. , 1.1-bis(p-hydroxyphenyl)pentane, 1.1-bis(p-hydroxyphenyl)hexane,
2.2bis(p-hydroxyphenyl)hexane, 11
-bis(p-hydroxyphenyl)-2-ethylhexane, 2,2-bis(4-hydroxy3,5-dichlorophenyl)propane, etc. are used.

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

(13) (14) These color developers can be added as a eutectic with a thermofusible substance with a low melting point, or can be added as a eutectic with a thermofusible substance with a low melting point, in order to melt at a desired temperature and cause a color reaction. It is preferable that the compound is added in a state of being fused to the surface of the color developer particles.

In the method of the invention, at least one of the dye dispersion and the developer dispersion is prepared using a horizontal sand mill installed at an angle, for example a horizontal sand mill having the configuration shown in FIG. It is preferable to use a sand mill to rotate the dispersion plate independently of the stirring blade rotation shaft, and maintain the rotation speed lower than the rotation speed of the stirring blade rotation shaft.

In this dispersion operation, the dispersion media is 0.1~
It is preferred to use glass or alumina beads with a diameter of 1 mm.

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

Generally, it is preferable that the rotating shaft for the stirring blade rotates at a rotation speed of 600 to 2400 times/minute, and the separation plate rotates at a constant rotation speed of 50 to 600 times/minute. Moreover, it is preferable that the rotational speed ratio of the rotation shaft for the stirring blade and the separation plate is 20: to 5:1.

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

Generally, dyes and color developers are dispersed by mixing an aqueous solution of a water-soluble polymer compound with a dispersion medium. Dispersion media generally include water-soluble synthetic polymer compounds such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, and styrene-maleic anhydride copolymers, as well as hydroxyethyl cellulose, starch derivatives, gelatin, and casein. Such water-soluble natural polymer compounds or derivatives thereof are used.

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

The obtained dispersion of dye and color developer is mixed with each other, and if desired, inorganic pigments, waxes, higher fatty acid amides, metal soaps, and (15) (16) if necessary, ultraviolet absorbers, A coating solution is prepared by adding an antioxidant or a latex binder.

There is no problem in adding the above additives during the dispersion operation.

The coating solution is applied onto one surface of the belt-like support at a rate of 3 to 8 g/m' (
The heat-sensitive recording layer is formed by coating the film so as to dry it and drying it by a conventional method.

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 esters.

Examples of the metal soap include polyvalent metal salts of higher fatty acids, such as zinc stearate, aluminum stearate, calcium stearate, and zinc oleate.

Inorganic pigments include kaolin, calcined kaolin talc, waxite, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium, titanium oxide,
Examples include barium carbonate.

These are binders (
Binders) are generally water-soluble, such as polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, imbutylene-maleic anhydride copolymer, Examples include polyacrylic acid, starch derivatives, casein, and gelatin. In addition, in order to impart water resistance to these binders, water resistance imparting agents (gelling agents, crosslinking agents) are added, or hydrophobic emulsions, specifically styrene-butadiene rubber latex, acrylic resin emulsions, etc. You can also add

In the method of the present invention, before the dispersion operation using a horizontal sand mill, the dye dispersion liquid and the color developer dispersion liquid are subjected to a pre-dispersion treatment using a conventional dispersion operation such as a ball mill, an attritor, a sand mill, and a three-roll mill. You can perform a dispersion operation (17) (18).

〔Example〕

The invention will be further illustrated by examples.

In the examples, "parts" and "%" represent "parts by weight" and "% by weight" unless otherwise specified.

Example 1 2 kg of 3-(N-isopentyl-N-ethylamino)
-6-Methyl-7-anirite fluorane (basic dye)
and 4 kg of an aqueous solution of 2.5% polyvinyl alcohol (polymerization degree 500, saponification degree 99%) were charged into an improved horizontal sand mill (Ultra Visco Mill manufactured by Igarashi Kikai Seizo Co., Ltd.) installed at an angle, and 0.0% was added as a dispersion media. Using glass beads with a diameter of 3 mm, at a filling rate of 85%, the speed was 0.3 per minute.
The dispersion operation was performed at a processing speed of β. At this time, the inclination angle of the horizontal sand mill is 10 degrees, the rotation speed of the rotating shaft for stirring blades is 945 rpm, and the rotation speed of the separation plate is lQQrp.
It was m.

The dispersed average particle size of the obtained dye was 0.4 μm, and 75% of all dispersed particles were 0.7 μm or less. The particle diameter was measured using LPA-3000/3100 manufactured by Tenri Denshi.

The above dye fraction liquid was mixed with a color developer dispersion (containing bisferrule A and polyvinyl alcohol) prepared by a conventional method to prepare a heat-sensitive recording coating liquid by a conventional method. 50 g/m') was coated on one side and solidified to form a heat-sensitive recording layer of 7 g/m'. When this heat-sensitive recording paper was used for normal heat-sensitive recording operations, heat-sensitive color development was extremely rapid and images of good quality were obtained.

Example 2 8 kg of benzyl p-hydroxybenzoate (color developer) was installed along with 16 kg of 2.5% polyvinyl alcohol (polymerization degree 500, saponification degree 99%) solution in the first type of incline. Horizontal sand mill (IIILYA, BA
The mixture was charged into a Dyno Mill KD-PILOT type (manufactured by CHOFEN). At this time, the inclination angle of the model sand mill was 10 degrees, glass beads with a diameter of 0.8 mm were used as the dispersion media, and the processing rate was 0.3 A per minute (1
9) Dispersed at (20) speed.

The dispersed particle size of the obtained color developer was 1.0 mm, and the particle size of 75% of all dispersed particles was 2βm or less.

A dye component H' prepared by a conventional method was added to the above color developer dispersion as a solution (3-(N-isobenthyl-N-ethylamino)-6
-Methyl-7-anilite fluorane and polyvinyl alcohol) were mixed to prepare a heat-sensitive recording coating liquid by a conventional method. Apply this coating liquid to high-quality paper (basis weight 50g/rn').
was coated on one side of the film and solidified to form a heat-sensitive recording layer of 7 g/m'. When the resulting thermal recording paper was subjected to normal thermal recording operations, it was found that the thermal color development was extremely fast.
Images of good quality were obtained.

Comparative Example 1 The same operation as in Example 1 was performed. However, the improved horizontal sand mill was installed horizontally without being tilted.

The average particle size of the obtained dye particles was 0.6 tones, and the average particle size of 75% of all dispersed particles was 1.0 Jrm or less.

The thermal coloring speed of the obtained thermal recording paper was lower than that of Example 1.

Comparative Example 2 The same operation as in Example 2 was performed. However, the horizontal sand mill was installed horizontally without being tilted.

The average particle size of the obtained color developer particles was 1.2J1m,
The average particle size of 75% of all dispersed particles is 3. OJ! m or less. The thermal coloring speed of the obtained thermal recording paper was lower than that of Example 2.

〔Effect of the invention〕

By the method of the present invention, a heat-sensitive recording coating liquid containing fine particle dispersion with a uniform particle size distribution can be efficiently obtained, thereby making it possible to produce a heat-sensitive recording material with a high heat-sensitive color development rate and good quality. Ta.

[Brief explanation of drawings]

1 and 2 are cross-sectional explanatory views of one embodiment of a horizontal sand mill used in the method of the present invention, respectively. 1... Raw material supply port, 2... Dispersion liquid discharge port, (
21) (22) 3...Horizontal rotating shaft, 5...Horizontal vessel, 7... Rotating shaft for separation plate, 9... Dispersion liquid chamber. 4... Stirring blade, 6... Separation plate, Slit...

Claims (1)

[Scope of Claims] 1. A dye dispersion containing a substantially colorless electron-donating color-forming dye, and an electron-accepting color-developing compound that develops color by contacting with the color-forming dye under heating. At least one of them is prepared using a horizontal sand mill, and a coating liquid for thermal recording is prepared by mixing the dye dispersion liquid and the color developer dispersion liquid. , in a method of coating one surface of a sheet-like support and solidifying it to form a heat-sensitive recording layer, the horizontal sand mill is tilted downward from its dispersion supply port toward its discharge port, and the dispersion is A method for producing a heat-sensitive recording material, which comprises preparing a liquid.