JP2621662B2 - Manufacturing method of high brightness thermal recording material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermosensitive recording material having high whiteness. More specifically, the present invention relates to a method for producing a thermosensitive recording material having high whiteness and excellent recording sensitivity.

[0002]

2. Description of the Related Art A thermal recording system has the advantages that a color image can be obtained simply by heating, and that the recording apparatus can be made relatively simple and compact. It is widely used as various information recording methods.

In particular, in recent years, improvements have been made in thermal facsimile machines and thermal printers using a thermal recording system, and high-speed recording, which has conventionally been considered difficult, has become possible. As the speed of such devices has been increased, the thermal recording materials used therein have also been required to further improve the recording sensitivity, and many proposals have been made regarding this.

As such a thermosensitive recording material, a thermosensitive recording layer mainly composed of a binder and a thermochromic substance is formed as a single layer on a support made of paper, plastic film, synthetic paper or the like. Or those formed as a plurality of layers are generally used.

[0005] In order to improve the recording sensitivity of the heat-sensitive recording material having such a structure, conventionally, 1) addition of a low melting point heat-fusible substance, 2) improvement of surface smoothness, and 3) increase of color-forming components. However, all of these means have disadvantages such as increased adhesion of the molten component in the heat-sensitive recording layer to the thermal head and causing trouble in printing.

Therefore, in order to solve such a defect, it has been proposed to reduce the average particle size of the basic dye particles to 2.0 μm or less as a means for improving the recording sensitivity without increasing the amount of the coloring component. . (For example, JP-A-57-47693).

In general, the recording sensitivity is dramatically improved by making the thermochromic component finer (particularly an average particle size of 0.7 μm or less). However, the color of the dispersion becomes black, and the whiteness of the recording paper using the same is reduced. It extremely decreases, which causes problems such as loss of practical value as recording paper.

As a method for preventing the decrease in whiteness of recording paper due to the formation of fine particles of the color forming component, it has been proposed to increase the dispersion temperature (Japanese Patent Laid-Open No. 54-98253).
However, this method is not practical because it has a disadvantage that aggregation of the dispersion is easily induced.

[0009] As a method other than the above, a method of adding amines to a coating solution (Japanese Patent Application Laid-Open No. 48-101943) and a method of maintaining the pH of a coating solution in an alkaline region (Japanese Patent Application Laid-Open No. 49-11141) Publication), a method of adding a basic inorganic pigment (JP-A-49-90142)
JP-A-58-34307), and a method of adding acetylene alcohol or acetylene glycol (JP-B-58-34307)
And so on. However, none of these methods is very effective in preventing the whiteness of the recording paper from decreasing when the average particle diameter of the dispersion is 0.7 μm or less. In addition, in the method described above, even if the whiteness of the recording paper can be improved to a certain extent, when the fine particles of the coloring component are advanced, pressure coloring occurs in the calendering process after the application of the heat-sensitive recording layer. And the whiteness is reduced.

[0010] As described above, the reasons why the whiteness is reduced due to the generation of fine particles of the color-forming component and the pressure-coloring occurs in the calendar process are considered as follows. That is, when preparing a dispersion of a chromogenic dye precursor or an electron-accepting color-developing compound, first coarse particles having a particle size of several hundred μm are sand grinders,
The powder is pulverized to a particle size of 1 μm or less by various wet dispersers such as an attritor, a ball mill and a cobo mill. Because the new interface of the material to be dispersed formed by this pulverization process has high reactivity, when preparing a heat-sensitive paint, mixing the color-forming dye precursor with the electron-accepting developer dispersion liquid , Both react with each other to form a color, especially when the average particle size of the dispersion is 0.7 μm.
If it is less than m, the color development becomes intense and the whiteness is extremely reduced.

When a calendering treatment is applied to the heat-sensitive recording layer after the heat-sensitive recording layer is applied, the heat-sensitive recording layer undergoes pressure deformation. At this time, contact between the dye and the developer occurs. The number of contact points increases, which results in pressure development.

In order to solve such a problem, a method has been proposed in which a water-soluble polymer substance is added to a dispersion liquid to block an active interface formed on the material to be dispersed at the time of grinding. JP-A-54-70056, JP-B-45-14039,
And JP-A-48-17344).

However, the effect of the addition of such a water-soluble resin alone is weak. In particular, a sufficient reaction-suppressing effect is not recognized on the color-forming component particles having an average particle diameter of 0.7 μm or less.

Conventionally, polyvinyl alcohol is generally used as such a water-soluble resin, but the polyvinyl alcohol used is limited to those having an average degree of polymerization of 500 or less.

That is, in the above-mentioned method, when the average degree of polymerization of polyvinyl alcohol is more than 500, the viscosity of the dispersion increases, and the efficiency of forming fine particles in the dispersion step is remarkably reduced. However, when using a polyvinyl alcohol having a polymerization degree of 500 or less, as described above,
The effect of blocking the active interface formed on the material to be dispersed at the time of pulverization is not sufficient, and particularly, the color forming component particles have an average particle size of 0.7 μm.
When the particles are formed into fine particles as described below, pressure coloring due to calendering of the obtained heat-sensitive recording layer is inevitable.

[0016]

As described above, in the conventional method for producing a coating solution for a heat-sensitive recording material, if the dispersion operation is strengthened to make the color-forming component particles finer, the average particle size of the color-forming component particles is particularly reduced. When the thickness is 0.7 μm or less, there is a problem that the whiteness of the obtained recording paper is reduced and pressure coloring occurs in calendar processing. An object of the present invention is to solve the above-mentioned problems and to provide a method capable of stably producing a high-quality heat-sensitive recording material having high recording sensitivity and excellent continuous recording properties.

[0017]

The present invention provides a dye dispersion,
And / or the use of a dispersion medium containing a particular acetylenically unsaturated compound together with polyvinyl alcohol having a degree of polymerization of 800 to 2000 and a degree of saponification of 75 to 95% in the preparation of the developer dispersion. , Which successfully solved the above-mentioned problems.

That is, the method for producing a high whiteness thermosensitive recording material of the present invention comprises contacting a substantially colorless dye dispersion containing an electron-donating color-forming dye precursor with the color-forming dye precursor under heating. A coating solution for a heat-sensitive recording layer containing a developer dispersion liquid containing an electron-accepting color-developing compound that reacts and develops a color is prepared, and this coating liquid is applied to one surface of a sheet-like support and dried. In the method for producing a heat-sensitive recording material, which comprises forming a heat-sensitive recording layer, in at least one of the dispersion operation of the dye dispersion and the developer dispersion, a polymerization degree of 800 to 2,000 and a saponification degree of 75 to 95%. And a polyvinyl alcohol having the following general formula (1):

[0019]

Embedded image

[However, in the above formula (1), R ₁ and R ₂ each independently represent -CH ₃ , -C ₂ H ₅ ,-
Represents a C ₃ H ₇ or —C ₄ H ₉ group, and R ₃ represents — (OC ₂ H ₄ ) _n OH,
— (OC ₃ H ₆ ) _n OH or —OH group, and R ₄ represents — (OC ₃ H ₆ ) _n OH or —OH group.
₂ H ₄ ) _m OH, — (OC ₃ H ₆ ) _m OH, —OH group or CH ₃ group, n represents an integer of 1 to 10, and m represents an integer of 1 to 10 And the average particle size of solid particles contained in the dispersion is adjusted to 0.7 μm or less using an aqueous dispersion medium containing the compound represented by the formula (1).

The present inventors use a dye and a developer in order to increase the sensitivity of a heat-sensitive recording material.
In order to solve the problems such as the decrease in whiteness that occurs in the recording paper obtained by using the particles when the particles are reduced to μm or less and the color development by calendering, the water-soluble We conducted intensive research on what kind of polymer materials would be effective.

As a result, a degree of polymerization of 800 to 2000 and a degree of saponification of 75 to
Even if the average particle size of the solid particles contained in the dispersion liquid is reduced to 0.7 μm or less, the whiteness of the recording paper is reduced and the calendering treatment is carried out by including 95% of a high polymerization degree polyvinyl alcohol in the dispersion medium. Has been found to be able to very effectively prevent pressure-induced color development. Conventionally, when polyvinyl alcohol having such a high degree of polymerization is used, there have been problems such as thickening of the dispersion and a decrease in the dispersion efficiency, but the compound represented by the general formula (1) is simultaneously added. As a result, they have found that these problems can be solved.

[0023]

As the polyvinyl alcohol used in the method of the present invention, a non-modified polyvinyl alcohol can be expected to have a sufficient effect. The same effect can be obtained for the prevention of color development by calendering.

The degree of polymerization of polyvinyl alcohol used in the method of the present invention is 800 to 2,000, and the degree of saponification is 75 to 95%.
When the degree of polymerization is less than 800, the effect of blocking the interface of the finely divided dye or developer fine particles becomes insufficient, and when the average particle size of the solid particles is 0.7 μm, prevention of reduction in whiteness and prevention of pressure coloring. Is not effective enough. On the other hand, if the degree of polymerization is higher than 2,000, the viscosity of the dispersion becomes too high, the efficiency of micronization decreases, and furthermore, the solid content of the dispersion cannot be increased.

If the degree of saponification is out of the range of 75 to 95%, the dispersion liquid is agglomerated and the efficiency of fine particle formation is undesirably reduced.

In the method of the present invention, the amount of polyvinyl alcohol contained in the aqueous dispersion medium is preferably 1 to 50% by weight, more preferably 1 to 50% by weight, based on the weight of the material to be dispersed, that is, the dye or the color developer. Is 2 to 30% by weight. The amount of the acetylenically unsaturated compound represented by the general formula (1) is preferably 0.01 to 5% by weight, more preferably 0.1 to 1% by weight.

The acetylenically unsaturated compound represented by the general formula (1) is, for example, 2,4,7,9-tetramethyl-5
Ethylene oxide adduct of decyne-4,7-diol and 2,5-dimethyl-3-hexyne-2,5-
It can be selected from ethylene oxide adducts of diols and the like.

The color-forming dye precursor 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 include (1) a triarylmethane compound, for example, 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, and 3,3-bis- (2-phenylindol-3-yl) -5-dimethylaminophthalide, and the like:

(2) Diphenylmethane compounds, such as 4,4'-bis-dimethylaminobenzhydrin benzyl ether, N-halophenylleucouramine, and N-2,4,5-trichlorophenylleucouramine;

(3) Xanthene compounds such as rhodamine B-anilinolactam and 3-diethylamino-7
-Dibenzylaminofluoran, 3-diethylamino-
7-butylaminofluoran, 3-diethylamino-7
-(2-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-ethyl-tolylamino-6-methyl-7- Anilinofluoran, 3-cyclohexyl-methylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6
Chloro-7- (β-ethoxyethyl) aminofluoran, 3-diethylamino-6-chloro-7- (γ-chloropropyl) aminofluoran, 3- (N-ethyl-N
-Isoamyl) -6-methyl-7-phenylaminofluoran and 3-dibutylamino-6-methyl-7-
Anilino fluoran and others:

(4) Thiazine compounds such as benzoyl leucomethylene blue and p-nitrobenzoyl leucomethylene blue:

(5) Spiro compounds, for example, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran,
And 3-methylnaphtho (3-methoxy-benzo)-
Spiropyran, etc., which are used alone or
Used as a mixture of more than one species. These paint precursors are appropriately selected and used depending on the use of the recording material and desired properties.

The developer used in the method of the present invention includes:
Phenol derivatives and aromatic carboxylic acid derivatives are preferred, and bisphenols are particularly preferred. In particular,
As phenols, p-octylphenol, p-te
rt-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) -2-ethyl -Hexane,
2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane and dihydroxydiphenyl ether.

The 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 polyvalent metal salts of the above carboxylic acids.

In dispersing the dye and the developer particles, a pulverizer such as a ball mill, an attritor, and a sand grinder is used.

The resulting dispersions of the dye and the developer are mixed with each other, and if necessary, inorganic pigments, waxes, higher fatty acid amides, metal soaps, sensitizers, and if necessary, an ultraviolet absorber, An antioxidant or a latex binder is added to prepare a coating solution for the heat-sensitive recording layer.

The above additives can be added at any time in the dispersing apparatus. The coating solution is applied on one surface of the sheet-like support so as to have a coating weight of ³ to 8 g / m ² (dry weight), and dried by a conventional method to form a heat-sensitive recording layer.

The waxes contained in the heat-sensitive recording layer include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, higher fatty acid amide (for example, stearic acid amide), ethylenebisstearamide, and higher fatty acid. Esters and the like.

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

As the inorganic pigments, kaolin, calcined kaolin talc, pyroxene, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesium,
Titanium oxide, and barium carbonate.

As sensitizers, p-benzylbiphenyl, dibenzyl terephthalate, 1-hydroxy-2-
Examples include phenyl naphthoate, dibenzyl oxalate, di-o-chlorobenzyl adipate, 1,2-di (3-methylphenoxy) ethane, and di-p-chlorobenzyl oxalate.

As a method for forming the heat-sensitive recording layer, any of known coating methods such as an air knife method, a blade method, a gravure method, a roll coater method, a spray method, a dip method, a bar method, and an extrusion method can be used. is there.

In the method of the present invention, the support material of the heat-sensitive recording material is not particularly limited. For example, paper, synthetic fiber paper,
A synthetic resin film or the like can be appropriately used. Generally, it is preferable to use paper.

[0044]

The present invention will be further described by way of examples.

Example 1 (a) A coating solution for forming a thermosensitive recording layer was prepared by the following steps. Preparation Ingredients Amount of dye precursor dispersion (parts by weight) 3- (N-ethyl--N- isoamylamino - 20 6-methyl-7-anilinofluoran polyvinyl alcohol 10% solution 10 (polymerization degree 1000, saponification degree 90%) Olphin Y (trademark, a compound of 0.05 R ₁ , R ₂ CHCH ₃ , R ₃ , R ₄ OHOH in the general formula (1), water 70 manufactured by Nissin Chemical Industry Co., Ltd. A sand mill (sand grinder manufactured by Igarashi Kikai Co., Ltd.) was charged, and the dispersion and refining operation was performed using 1.2 mm diameter glass beads as a dispersion medium.
Minutes, followed by charging the above composition into a horizontal sand mill (Igarashi Machine Manufacturing Co., Ltd. Ultra Visco Mill)
Using a glass bead having a diameter of 0.6 mm as a dispersing medium, a dispersion refinement operation was performed for 30 minutes to adjust the average particle diameter of the dye precursor to a value shown in Table 1.

[0046] Preparation Ingredient amount of Developer Dispersion (parts by weight) of 2,2-bis (p- hydroxyphenyl) 10 propane p- benzylbiphenyl 10 polyvinyl alcohol 10% solution 10 (polymerization degree 1000, saponification degree 90% Orfin Y (trademark) 0.05 Water 70 The above composition was dispersed by the same method as that for preparing the dye precursor dispersion, and the average particle size of the developer was adjusted to the value shown in Table 1.

Preparation of Coating Solution for Thermosensitive Recording Layer To 40 parts of the dye precursor dispersion and 160 parts of the developer dispersion, 40 parts of calcium carbonate and 30% paraffin dispersion 20 were added.
Parts, and 180 parts of a 10% aqueous solution of polyvinyl alcohol.
The mixture was stirred to prepare a coating solution.

(B) Formation of heat-sensitive recording layer The above-mentioned coating solution was applied onto one side of 50 g / m ² base paper so that the coating amount after drying was 7.5 g / m ^2, and dried to form a heat-sensitive coloring layer. Was formed, and then calendered to produce a thermal recording paper. The change in whiteness before and after calendering was measured with a Hunter whiteness meter using a blue filter.

To measure the particle size of the dispersed particles in the dye precursor dispersion and the developer dispersion, LPA-3000 / 31 manufactured by Otsuka Electronics Co., Ltd.
00 was used. The recording sensitivity is a standard chart of the Institute of Image Electronics Engineers of Japan with a high-speed facsimile manufactured by NEC Corporation: Nefax 6.
Printing was performed using No. 2, and the color density at that time was measured with a Macbeth densitometer RD-914, and the value was taken as a value representative of the recording sensitivity of the thermosensitive recording paper. Table 1 shows the results of these tests.

Example 2 The same operation as in Example 1 was performed. However, in preparing the dye precursor dispersion and the developer dispersion, acetylenol EL was used instead of adding Olfin Y.

Acetyleneol EL (trademark) is a compound represented by the general formula (1) wherein R ₁ , R 6 = CH ₃ , R ₂ , R 5
_{= C 4 H 9, R 3} = (OC 2 H 4) n OH, R 4 = (OC 2 H 4) m OH, n
= 1 to 3 and m = 1 to 3 where n + m = 4 (manufactured by Kawaken Fine Chemical Co., Ltd.).

Table 1 shows the average particle size of the particles and the test results.

Example 3 The same operation as in Example 1 was performed. However, acetylenol EH was used instead of the olefin Y used in the dispersion operation.
Acetyleneol EH (trademark) is represented by the general formula (1) where R ₁ , R 6 = CH ₃ , R ₂ , R 5
_{= C 4 H 9, R 3} = (OC 2 H 4) n OH, R 4 = (OC 2 H 4) m OH, n
= 1 to 9 and m = 1 to 9, where n + m = 10 (manufactured by Kawaken Fine Chemical Co., Ltd.).

Table 1 shows the average particle size of the particles and the test results.

Comparative Example 1 The same operation as in Example 1 was performed. However, Olfin Y was not added in preparing the dye precursor dispersion and the developer dispersion. Table 1 shows the average particle size of the particles and the test results.

Comparative Example 2 The same operation as in Example 1 was performed. However, the degree of polymerization of polyvinyl alcohol used in preparing the dye precursor dispersion and the developer dispersion was 300.

Table 1 shows the average particle size of the particles and the test results.

Comparative Example 3 The same operation as in Example 1 was performed. However, in preparing the dye precursor dispersion and the developer dispersion, polyvinyl alcohol having a polymerization degree of 1000 was not used.

Table 1 shows the average particle size of the particles and the test results.

[0060]

[Table 1]

[0061]

According to the method of the present invention, fine particles of the dye precursor and the color developer having an average particle size of 0.7 μm or less can be achieved without lowering the whiteness. As a result, a high-quality thermosensitive recording material having excellent recording sensitivity and high whiteness can be efficiently manufactured.

Claims (1)

(57) [Claims] 1. A dye dispersion containing a substantially colorless electron-donating color-forming dye precursor, and an electron-accepting color-developing compound which reacts with said color-forming dye precursor under heating to form a color therefrom. A heat-sensitive recording layer is prepared by preparing a coating solution for a heat-sensitive recording layer containing a developer dispersion liquid containing: and applying and drying this coating solution on one surface of a sheet-like support to form a heat-sensitive recording layer. In the method, the dispersion operation of at least one of the dye dispersion and the developer dispersion is performed in a degree of polymerization of 800 to 2,000, and a degree of polymerization of 75 to 95.
% Of a polyvinyl alcohol having a degree of saponification and the following general formula (1): [However, in the above formula (1), R ₁ and R ₂ each independently represent -CH ₃ , -C ₂ H ₅ , -C ₃ H ₇ , or-
Represents a C ₄ H ₉ group, and R ₃ represents — (OC ₂ H ₄ ) _n OH, — (OC ₃ H ₆ ) _n
OH, or an -OH group, R _{4 is, - (OC 2 H 4)} m OH, - (O
_{C 3 H 6) m OH,} -OH group or; represents CH ₃ group, n is 1 to 10
And m represents an integer of 1 to 10), using an aqueous dispersion medium containing a compound represented by the following formula: and the average particle diameter of solid particles contained in the dispersion liquid is 0.7 μm or less A method for producing a high whiteness thermosensitive recording material, characterized in that: