JPH0497892A - Preparation of thermal recording material - Google Patents

Abstract

PURPOSE:To stably prepare a thermal recording material having high sensitivity, excellent in preservability and having high whiteness by preparing a dye precursor dispersion by dispersing a specific dye precursor, a specific compound and at least one kind of wax. CONSTITUTION:A dye precursor dispersion is prepared by dispersing a dye precursor based on 2-anilino-3-methyl-6-(N-ethyl-ethoxypropylamino) fluorane, compounds represented by general formulae (I), (II) and at least one kind of wax until a mean particle size becomes 1.2mum or less. This dye precursor dispersion is mixed with a developer dispersion containing an electron acceptive developing compound subjected to the contact reaction with a color forming dye precursor under heating to develop a color to prepare a coating solution for thermal recording and this coating solution is applied to the surface of a sheet-like support and solidified to form a thermal color forming layer. By this method, a thermal recording material having high sensitivity, excellent in preservability and having high whiteness can be stably prepared.

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 that has high whiteness, high sensitivity, and excellent storage stability.

[Prior Art] A heat-sensitive recording material that forms a colored image by utilizing a heated color-developing reaction between a small amount of colorless or light-colored basic dye precursor and a color developer such as a phenol or an organic acid is Various types of heat-sensitive recording materials have been announced so far (Japanese Patent Publication No. 45-14039, etc.) and have been widely put into practical use. It is applied to a wide range of fields such as ticket vending machines and CD/ATMs.These recording devices are equipped with a heating element such as a thermal head or a thermal pen, and by bringing this heating element into contact with a thermosensitive coloring layer, a colored recorded image is created. Recently, applications have become more diversified and equipment has become more sophisticated, and along with this, the quality required for thermal recording paper has also become more sophisticated.For example, facsimile machines require A4-size recording. There is a need for recording materials that can record in less than a minute, whereas conventionally it took several minutes.

Under these circumstances, adding a sensitizer has been proposed as a method to improve the sensitivity of thermal recording paper, but this method has problems with color development sensitivity, color image stability, recording suitability,
A material that satisfies all of the various performances required of a heat-sensitive recording material in a well-balanced manner has not yet been obtained.

In thermosensitive recording paper, a color-forming substance and a color developer such as a phenolic compound are dispersed in the form of fine particles in the heat-sensitive coloring layer, and when heated, one or both of them dissolve and come into close contact with each other. It is thought that the color develops when

As a suitable phenol compound to be used for this purpose, 2,2-bis(
4'-hydroxyphenyl)propane (bisphenol A, melting point 156°C) is widely used (eg, US Pat. No. 1,509,375). However, this bisphenol A has poor thermal responsiveness and cannot necessarily satisfy the market demand for higher sensitivity of thermal recording paper as thermal recording apparatuses become faster and more compact. Many sensitizers have been proposed to compensate for this drawback, including waxes (Japanese Patent Application Laid-Open No. 19231-1982) and phthalate esters (Japanese Patent Application Laid-open Nos. 116690-1982 and 58-1982). -98285), benzyl phenyl ether derivatives (JP-A No. 59-155096), benzylbiphenyl (JP-A No. 60-82382), naphthol derivatives (JP-A No. 58-87094), carbonic acid diesters (JP-A No. 58-87094), No. 58-136489) has been proposed, but when combined with the above-mentioned bisphenol A, sufficient quality has not been obtained in terms of whiteness, color development sensitivity, fog, etc. 144193
In the issue, benzyl p-hydroxybenzoate or methylbenzyl p-hydroxybenzoate is proposed as a color developer to increase the sensitivity of heat-sensitive recording sheets, but the colored parts turn white (flourishing) during record storage. Because of this phenomenon, there is a problem with its storage stability.

The type of dye precursor has the most influence on the storage stability of heat-sensitive recording materials, but dye precursors with good storage stability generally tend to reduce the whiteness of the heat-sensitive coloring layer, and the difference between storage stability and whiteness is No dye precursor has been found that satisfactorily satisfies both of these requirements. In order to overcome these drawbacks, it has been proposed to increase the temperature during dispersion to prevent a decrease in whiteness (Japanese Patent Laid-Open No. 54-98253). However, this method has the drawback of easily inducing aggregation of the dispersion, and is not very practical.

Methods other than the above include adding amines to the coating liquid (Japanese Patent Application Laid-Open No. 48-101943), keeping the pH of the coating liquid alkaline (Japanese Patent Application Laid-Open No. 19-11141), and basic inorganic Method of adding pigment (JP-A-49-90
142), or a method of adding acetylene alcohol or acetylene glycol, which is a compound similar to the compound of formula (II) (Japanese Patent Publication No. 58-3430
Publication No. 7) etc. have been proposed. However, a heat-sensitive recording material that can fully meet the high quality demands of the market in terms of whiteness, storage stability, color development sensitivity, etc. has not yet been completed.

[Problem to be solved by the invention]

When heat-sensitive recording materials with high sensitivity and excellent storage stability are produced using conventional production methods, a decrease in whiteness cannot be avoided. The present invention aims to solve this problem and provide a method for stably producing a heat-sensitive recording material that has high sensitivity, excellent storage stability, and high whiteness.

[Means to solve the problem]

The method for producing a heat-sensitive recording material of the present invention involves contacting and reacting a dye precursor dispersion containing a substantially colorless electron-donating color-forming dye precursor with the color-forming dye precursor under heating to form a color. A step of preparing a heat-sensitive recording coating solution by mixing a color developer dispersion containing an electron-accepting color developer compound, and applying the coating solution to one surface of a sheet-like substrate and solidifying it to form a heat-sensitive coloring layer. forming the dye precursor dispersion into 2-anilino-3-methyl-
A dye precursor containing 6-(N-ethyl-N-ethoxypropylamino)fluoran as a main component and the following formulas (I) and (II): % formula % [However, in the above formulas (I) and (II) , R9 and R
2 each independently represents a hydrogen atom, a chlorine atom, or a methyl group, R3 and R6 each independently represent a methyl, ethyl, propyl, or butyl group, and R4 is -(OC2H4) -OR,-(OCjH&)
Represents IIIOwl or -OH group, R3 is -(OCJ4)#OH, -(OCFIJi)
# represents OH or -Go, n represents 0 or an integer from 1 to 2, m and ! each independently represents an integer from 1 to 10. ] A compound represented by the formula and at least one selected from waxes are dispersed until the average particle size becomes 1.2- or less, and the surface of the heat-sensitive coloring layer is heated for 200 seconds or more. It is characterized by smoothing so as to show the smoothness (according to JIS P8119).

The particular chromogenic dye precursors used in the present invention are highly sensitive, but impart poor shelf life to the resulting heat-sensitive recording material. These characteristics of the specific dye precursor used in the present invention are that the functional group substituted at the 6-position is a special -(N -ethyl-N-ethoxypropylamino) group.

Generally, the above-mentioned specific dye precursor is contained in the thermosensitive coloring layer at a concentration of 0.2%.
Contained in an amount of ~1.0 g/rrf. Further, when dispersing the dye precursor, the compound of the formula (■) or (II),
Alternatively, wax is used. Such waxes include animal waxes such as beeswax and Serratus wax, vegetable waxes such as carnauba wax, petroleum waxes such as paraffin wax and microcrystalline wax, polyethylene wax, polyhydric alcohol esters of higher fatty acids, and higher amines. , higher amides, condensates of higher fatty acids and amines, synthetic paraffins, and synthetic waxes such as chlorinated paraffins.

However, if the melting point of the wax is below 60°C, the storage stability of the resulting recording material tends to be somewhat poor.
It is preferable to use a wax having a melting point of .degree. C. or higher.

Furthermore, when the compounds represented by formulas (I) and (II) are used, the storage stability of the resulting recording material is not adversely affected.

However, it is necessary for these compounds to be present in the dye precursor dispersion during the dispersion process, and if this is not done, their effects will not be sufficiently expressed.

In the present invention, the above (I
) The compound represented by the formula is preferably used in an amount of 0.5 to 5 parts by weight, more preferably 0.5 to 3 parts by weight.

The compound represented by formula (II) is preferably used in an amount of 0.0001 to 0.1 part by weight, more preferably 0.000 part by weight, per 1 part by weight of the dye precursor.
It is 5 to 0.01 parts by weight.

Further, the wax is o-oo to 1 part by weight of the dye precursor.
It is preferably used in a proportion of i~0°5 parts by weight,
More preferably, it is 0.01 to 0.1 part by weight.

Further, the average particle size of solid particles in the dye precursor dispersion is 1.2
- It is necessary to make it less than 1.2, and if it is greater than 1.2, sufficient coloring properties cannot be obtained. Even if the solid particles have an average particle size of 1.2 nm or less, it is necessary to perform a dispersion operation in the presence of the above-mentioned additives, and if such additives are not used, recording materials with high whiteness may not be produced. can't get it. In the present invention, other dye precursors different from the specific dye precursor may be blended to the extent that the effects of the present invention are not impaired. In the method of the present invention, the surface of the formed thermosensitive photolayer is smoothed so that its Bekk smoothness (according to JIS-P8119) is 200 seconds or more.

In this way, the adhesion between the thermal head and the surface of the thermosensitive coloring layer becomes good, and sufficient color density can be obtained. When the Bekk smoothness is less than 200 seconds, it becomes difficult to obtain sufficient color density.

The color developer used to form the thermosensitive coloring layer in the present invention is a substance that has the property of liquefying or dissolving when the temperature rises, and has the property of causing color development when it comes into contact with the dye precursor. That's fine. Typical specific examples include 4-tert-butylphenol, 4-acetylphenol, 4tert-octylphenol, 4tert-butylphenol, 4tert-butylphenol, 4tert-octylphenol,
, 4'-5ec-butylidenediphenol, 4-phenylphenol, 4.4'-dihydroxy-diphenylmethane, 4゜4'-isopropylidenediphenol, hydroquinone, 4,4'-cyclohexylidenediphenol, 4.4' -dihydroxydiphenyl sulfide, 4.4'-thiobis(6-tert-butyl-3-methylphenol), 4.4'-dihydroxydiphenylsulfone, 4-hydroxy-4'-isoproboxydiphenylsulfone, 4-hydroxy benzophenone,
Dimethyl 4-hydroxyphthalate, methyl 4-hydroxybenzoate, ethyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate, 4-hydroxybenzoic acid-5
ec butyl, phenyl 4-hydroxybenzoate, benzyl 4-hydroxybenzoate, tolyl 4-hydroxybenzoate, chlorophenyl 4-hydroxybenzoate, 4.4'
-phenolic compounds such as dihydroxydiphenyl ether, benzoic acid, p-tert-butylbenzoic acid,
Trichlorobenzoic acid, terephthalic acid, salicylic acid, 3-
Aromatic carboxylic acids such as isopropylsalicylic acid, 3-tert-butylsalicylic acid, 3-benzylsalicylic acid, 3-(α-methylbenzyl)salicylic acid, 3.5-di-tert-butylsalicylic acid, and these phenolic compounds, aromatic Examples include organic acidic substances such as salts of carboxylic acids and polyvalent metals such as zinc, magnesium, aluminum, and calcium.

Generally, the color developer is contained in the heat-sensitive coloring layer in a range of 0.2 to 2. It is preferably contained in an amount of Og/bo.

During the dye precursor dispersion operation in the method of the present invention, in addition to the specific dye precursor, and a small number of additives selected from the compounds of formulas (I) and (If) and waxes, , surfactants and water-soluble synthetic polymer compounds such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, and styrene-maleic anhydride copolymers within the range that does not impair the effects of the present invention;
and hydroxyethyl cellulose, starch derivatives,
Various additive auxiliaries such as gelatin, a water-soluble natural polymer compound such as casein or a derivative thereof, or an antifoaming agent may be used in combination.

The preparation operation of the dye precursor dispersion liquid can be carried out using various wet crushers such as a sand grinder, attritor, ball mill, copor mill, etc., whereby the solid particles in the dispersion liquid are divided into particles having an average particle diameter of 1.2. tm or less,
Preferably 1. OI! It is atomized until it becomes less than m. When preparing a paint for a heat-sensitive recording layer, in addition to the dye precursor dispersion and the color developer dispersion, inorganic pigments, waxes, metal soap ultraviolet absorbers, antioxidants, or latex binders may be added as desired. etc. may be added.

Furthermore, a preservability improver may be added to the coating solution to further prevent fading of the colored image formed on the recording material.
Phenolic compounds are effective as such storage improvers, such as 1°1.3-)lis(2-methyl-4-hydroxy-5-t-butylphenyl)butane,
1,1.3 Tris(2-methyl-4-hydroxy-5-
cyclohexyl) titanium, 1,1-bis(2-methyl 4
-hydroxy-5-t-butylphenyl)butane, 4.
4'-(I-phenylethylidene)bisphenol, 4
．． Use one consisting of at least one of 4'-(I,4-phenylenebis(I-methylethylidene))bisphenol, 4.4'-(I,3-phenylenebis(I-methylethylidene))bisphenol, etc. Can be done.

Such a preservability improver is generally used in the heat-sensitive coloring layer at a concentration of 0.
It is preferably contained in an amount of 0.02 to 0.1 g/rrf.

Waxes that can be added to the coating solution 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 metal soaps include polyvalent metal salts of higher fatty acids, ie, zinc stearate, aluminum stearate, calcium stearate, zinc oleate, and the like.

Examples of inorganic pigments include kaolin, calcined kaolin, talc, waxite, diatomaceous earth, calcium carbonate, aluminum hydroxide, magnesium hydroxide, magnesia, titanium oxide, barium carbonate, and the like.

Sensitizers include p-benzylbiphenyl, dibenzyl terephthalate, phenyl 1-hydroxy-2-naphthoate, dibenzyl oxalate, di(p-methylbenzyl oxalate) di-0chlorobenzyl adipate, and 1,2-dibenzyl dibenzyl adipate. (
Examples include 3-methylphenoxy)ethane and di-p-chlorobenzyl oxalate.

In addition, water-soluble binders are generally used, such as polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, etc. Polyacrylic acid, polyacrylic acid, starch, casein, gelatin, etc. Further, for the purpose of imparting water resistance to these binders, a water resistance imparting agent may be added, or a hydrophobic emulsion, specifically a styrene-butadiene rubber lux, an acrylic resin emulsion, etc. may be added. Generally, the binder is preferably contained in the thermosensitive coloring layer in an amount of 0.05 to 1.0 g/m.

The coating liquid is 3 to 8 g/nf (dry) on one surface of the sheet-like substrate.
A heat-sensitive coloring layer is formed by applying the coloring layer in a coating amount of . The thermosensitive coloring layer can be formed using any of the known coating methods such as air knife method, blade method, gravure method, roll coater method, spray method, dip method, bar method, and extrusion method. Good too.

The sheet-like base material used in the present invention is not particularly limited, and for example, paper, synthetic fiber paper, synthetic resin film, etc. can be used as appropriate.

Note that, if necessary, a sheet-like substrate having various known coating layers such as an undercoat layer and an overcoat layer may be used.

Generally, it is preferable that the sheet-like substrate has a basis weight of 40 to 60 g/po.

〔Example〕

The present invention will be further explained below with reference to examples, but the present invention is not particularly limited by these examples.

"Parts" and "%" in Examples and Comparative Examples refer to "parts by weight" and "% by weight" unless otherwise specified.

Part A (Dye Precursor Dispersion) Preparation Ingredients Quantity Polyvinyl alcohol 10% solution 30 parts Di(P-methylbenzyl oxalate) 20 parts Water
40 parts of this composition was micronized using a sand grinder until the average particle size of the solid particles was 1.0 mm.

The following margin ■ Preparation of B solution (developer dispersion) 10% polyvinyl alcohol solution 20 parts water
20 parts of this composition was micronized using a sand grinder until the average particle size of the solid particles was 160 mm.

■ Preparation of coating solution 30 parts of solution A, 20 parts of solution B, 30 parts of 50% calcium carbonate dispersion, 8 parts of 30% zinc stearate dispersion and 10%
75 parts of polyvinyl alcohol aqueous solution was added and stirred to prepare a coating solution.

(2) Formation of thermosensitive coloring layer This coating solution was coated and dried on a base paper of 50 g/m so that the coating weight after drying was 7g/rrf to form a thermosensitive coloring layer, thereby preparing thermosensitive recording paper.

The heat-sensitive recording paper thus obtained was subjected to supercalender finishing so that the Bekk smoothness (according to JIS-P8119) was 200 seconds or more.

After printing on the above thermal recording paper using UF-60 manufactured by Matsushita Electric Transmission Co., Ltd., the recording density of this colored image was recorded using RD manufactured by Macbeth Co., Ltd.
-Measured using a 100R type concentration needle.

Furthermore, using the prints obtained in the above recording density test,
The storage stability test described below was conducted, and the residual rate of recorded density was calculated using the following formula.

A coating solution was prepared.

(2) Amount of ingredients for preparing liquid A 10% polyvinyl alcohol solution 10 parts (I) Heat resistance test Niblint was left in an atmosphere of 60°C12O%RH for 24 hours.

(2) Moisture resistance test Niblint at 40°C 190% RFI
It was left for 24 hours in an atmosphere of

In addition, for measuring the average particle size of solid particles in the dispersion,
LPA-3000/3100 manufactured by Otsuka Electronics Co., Ltd. was used.

Further, the white layer of the heat-sensitive coloring layer was measured using a Hunter whiteness meter.

These results are shown in Table 1.

The same operation as in Example 1 was performed. However, prepare the following solutions A and C, and add water as described below.
80 parts of this composition was ground using a sand grinder until the average particle size of the solid particles was 0.9 tones.

■ Solution B was prepared in the same manner as in Example 1.
P-methylbenzyl) 40 parts polyvinyl alcohol 10 parts
% solution 20 parts water
20 parts of this composition was ground using a sand grinder until the solid particles had an average particle size of 1.0 tile.

■ Preparation of coating solution and formation of thermosensitive coloring layer 10 parts of solution A;
20 parts of solution B, 20 parts of solution C, 30 parts of 50% calcium carbonate dispersion, 8 parts of 30% zinc stearate dispersion and 10%
Add 75 parts of polyvinyl alcohol aqueous solution and stir,
It was used as a coating liquid. This coating liquid was coated and dried on a base paper of 50 g/rd so that the coating weight after drying was 7 g/board to form a heat-sensitive color, thereby obtaining a heat-sensitive recording paper.

The test results are shown in Table 1.

The same operations as in the actual ship-based Example 2 were performed. However, Solution A was prepared as follows.

(2) Preparation of Solution A Polyvinyl alcohol 10% fi 10 parts Water 80 parts This composition was ground using a sand grinder until the average particle size of the solid particles was 1.0 pm.

The test results are shown in Table 1.

The same operation as in Example 3 was performed. However, when preparing Liquid A, the same amount of methylolstearamide dispersion (manufactured by Chukyo Yushi Co., Ltd., melting point 110 °C) was used instead of paraffin wax, and the average particle size of the solid particles was adjusted to 0.95-0. I crushed it until it became solid.

The test results are shown in Table 1.

In addition, the same operations as in Example 1 were performed. However, in preparing Solution A, the same amount of 3-dibutylamino-6methyl-7-phenylaminofluoran was used instead of 2-anilino-3-methyl-6-(N-ethyl-N-ethoxypropylamino)fluoran. The solid particles were ground with a sand grinder until the average particle size of the solid particles was 0.9-.

The test results are shown in Table 1.

The same operations as in Example 2 were performed for this U shadow. However, when preparing Liquid A, Surfynol SE was not used, and the solid particles were ground with a sand grinder until the average particle size was 1.0 mm.

The test results are shown in Table 1.

Comparison group The same operation as in Comparative Example 2 was performed. However, after preparing the coating liquid, the same amount of Surfynol SE as in Example 2 was added.

The test results are shown in Table 1.

Comparative spots ↓ The same operation as in Comparative Example 2 was performed. However, after preparing the coating solution, the same amount of paraffin wax as in Example 3 was added to the coating solution.

The test results are shown in Table 1.

The same operation as in Comparative Example 4 was performed. However, the same amount of methylolstearamide was used instead of paraffin wax.

The test results are shown in Table 1.

Kitakai Opening■ The same operation as in Example 1 was performed. However, when preparing Ai, use a sand grinder to reduce the average particle size of the solid particles to 1
．． I made it 3-.

The test results are shown in Table 1.

Comparison (1) The same operation as in Example 1 was performed. However, the Bekk smoothness of the surface of the heat-sensitive coloring layer was made 150 seconds by calendering.

The test results are shown in Table 1.

Margins below [Effects of the Invention] The present invention has made it possible to stably produce a heat-sensitive recording material with high sensitivity, excellent storage stability, and high whiteness.

Claims (1)

[Scope of Claims] 1. A dye precursor dispersion containing a substantially colorless electron-donating color-forming dye precursor, and a dye precursor dispersion containing electrons that react with the color-forming dye precursor under heating to develop color. A step of preparing a coating liquid for heat-sensitive recording by mixing a color developer dispersion containing a receptive color-developing compound, and applying the coating liquid to one surface of a sheet-like substrate and solidifying it to form a heat-sensitive coloring layer. and converting the dye precursor dispersion into 2-anilino-3-methyl-
A dye precursor whose main component is 6-(N-ethyl-N-ethoxypropylamino)fluoran and the following formulas (I) and (II): ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) and ▲mathematical formulas , chemical formulas, tables, etc. ▼ (II) [However, in the above formulas (I) and (II), R_1 and R_2 each independently represent a hydrogen atom, a chlorine atom, or a methyl group, and R_3 and R_6 each independently represents a methyl, ethyl, propyl or butyl group, R_4 is -(OC_2H_4)_mOH, -(OC_
3H_6)_mOH or -OH group, R_5 is -(OC_2H_4)_lOH, -(OCH
_3H_6)_lOH or -OH group, n is 0,
or represents an integer of 1 to 2, and m and l each independently represent an integer of 1 to 10. ] and at least one selected from waxes
The heat-sensitive coloring layer is prepared by dispersing the seeds until the average particle size is 1.2 μm or less, and the surface of the heat-sensitive coloring layer is smoothed so as to exhibit a Bekk smoothness of 200 seconds or more (according to JIS P8119). A method for producing a heat-sensitive recording material, characterized by: