JPH03169676A - Thermal recording material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat-sensitive recording medium, and more specifically, it relates to a heat-sensitive recording medium that has high whiteness and excellent suitability for high-speed recording. [Prior Art] Heat-sensitive recording materials that utilize a heating coloring reaction between normally colorless or light-colored leuco dyes and phenols or organic acids are disclosed, for example, in Japanese Patent Publication No. 43-4160 and Japanese Patent Publication No. 45-14039.
It is disclosed in Japanese Patent Publication No. 48-27736, etc., and has been widely put into practical use. In recent years, such heat-sensitive recording materials have been known to form colored images simply by heating;
It is widely used as a variety of information recording materials due to its advantages such as the fact that the recording device can be made relatively compact. In particular, the devices of thermal facsimiles, thermal printers, etc. that use such thermal recording materials have been improved, and it has become possible to perform high-speed printing and high-speed image formation, which was previously considered difficult.

As the speed of such equipment and hardware increases, the heat-sensitive recording media used are required to have significantly improved recording sensitivity than before. Many proposals have been made to meet this requirement, but most of these proposals are characterized by the combination of dye precursor and color developer contained in the heat-sensitive coloring layer.
Or, it is characterized by the combined use of a thermofusible substance in addition to these. The above-mentioned thermofusible substance is also called a sensitizer, and examples include J-hydroxy-2-naphthoic acid phenyl ester (Japanese Patent Application Laid-open No. 57-191089), p-pendylbiphenyl (Japanese Patent Application Laid-Open No. 60-82382). , penzyl naphthyl ether (JP 58-87094), dibenzyl terephthalate (JP 58-98285), p.
-Benzyl penzyloxybenzoate (JP-A-57-20
No. 1691), diphenyl carbonate, ditolyl carbonate (JP-A-58-136489),
7-89994), 1,2-bis(m-tolyloxy)ethane (Japanese Unexamined Patent Publication No. 60-56588), and the like.

[Problem to be solved by the invention]

When the thermosensitive coloring layer containing the above-mentioned thermofusible substance is heated, the thermofusible substance first melts, which dissolves the dye precursor and the color developer, so that both of them are dissolved at the molecular level. They mix together and a color reaction is induced. Therefore, these thermofusible substances have a suitable melting point (preferably 60-1
40° C.) and must have excellent compatibility with the dye precursor and color developer. It is also important that the thermofusible substance does not reduce the whiteness of the thermosensitive recording medium, and for this purpose, it is desirable that the thermofusible substance be extremely poorly soluble in water. Furthermore, it is desirable that the material has properties such as low sublimability. The sublimation property of thermofusible substances is thought to be closely related to the so-called whitening phenomenon, in which the heated colored portion of a thermosensitive recording material becomes powdery over time. In practical terms, an extremely important property is that no white phenomenon occurs. Although many materials have been proposed as the above-mentioned thermofusible materials, there are few that satisfy all of the above conditions, and therefore there has been a demand for new materials.

The present invention has a heat-sensitive coloring layer formed using a novel thermofusible substance together with the dye precursor and color developer described above, and the recording sensitivity is significantly improved without deteriorating recording performance. It is an object of the present invention to provide a heat-sensitive recording material having the following properties.

[Means and actions to solve the problem]

The heat-sensitive recording material of the present invention includes a sheet-like substrate, a colorless to light-colored dye precursor formed on at least one surface of the sheet-like substrate, and a colorless dye precursor that reacts with the dye precursor under heating to develop color. The thermosensitive coloring layer has the following general formula (■): (However, in the above formula, Rl represents a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom. It is characterized in that it further contains at least one ether compound represented by:

The present inventors discovered that the use of the thermofusible substance of the above formula (I) as a sensitizer has been proposed as a typical thermofusible substance (Japanese Patent Publication No. 14531/1983), and Compared to the use of higher fatty acid amides such as stearic acid amide and palmitic acid amide, which have been put into practical use, there is no decrease in the whiteness of the heat-sensitive coloring layer, and the quality of the colored image is improved over time. The present inventors have discovered that extremely high recording sensitivity can be obtained without causing phenomena such as worsening whitening, and have completed the present invention.

The heat-sensitive recording material of the present invention is a colorless or monochromatic basic leuco dye (dye precursor) and a heat-sensitive coloring material that utilizes the coloring reaction of a color developer that can develop a color when it comes into contact with this dye precursor. It is characterized in that it has a layer, and the compound of formula (I) is contained in this heat-sensitive coloring layer. The reason why the specific thermofusible substances (hereinafter referred to as sensitizers) improve the coloring sensitivity of the heat-sensitive coloring layer is not yet fully clear, but it is important that the viscosity of this compound is low in the molten state. It is assumed that part of the reason for this is that it has appropriate compatibility with the dye precursor, which tends to occur, and the color developer, thereby promoting the reaction between the two. The reason why this sensitizer does not reduce the whiteness of the heat-sensitive coloring layer is considered to be because it is poorly soluble in water. Furthermore, the reason why this sensitizer hardly causes the whitening phenomenon that deteriorates the quality of recorded images is considered to be due to its low sublimation property. but,
The inventor does not adhere to this interpretation. Specific examples of the sensitizer of formula (1) used in the present invention include the following compounds (1) to (21).

113 CH, L:H 30 QC}l , C, H, C, H, these compounds can be synthesized by various known synthesis methods, but the simplest method is to use the Ullmann reaction shown below. It can be easily synthesized with high yield. In the reaction formula below, R1 has the same definition as above. The sensitizer of formula (1) is contained in the thermosensitive coloring layer together with the dye precursor and the color developer. Further, other sensitizers can also be used in combination within a range that does not inhibit the desired effects of the present invention. The amount of the sensitizer used in the present invention is preferably from 10 to 1000% by weight, and from 50 to 1000% by weight, based on the weight of the developer.
More preferably, it is 300% by weight. If the amount of the sensitizer added is less than 10% by weight, the sensitizing effect on the resulting heat-sensitive coloring layer will be unsatisfactory, and it will be less than 100% by weight.
If it is used in a large amount exceeding % by weight, the effect will be saturated and the content of the dye precursor and color developer will decrease,
This causes inconveniences such as insufficient color density.

The thermosensitive coloring layer containing the sensitizer of the present invention mainly consists of a dye precursor, a color developer made of phenols or an organic acid, and is used to bind these and bond the thermosensitive coloring waste to the sheet-like substrate. It preferably contains a binder, and further contains an inorganic pigment, and may further contain a wax, if necessary.

The leuco dye used as a dye precursor can be selected from conventionally known ones, such as crystal violet lactone, 3-(N-ethyl-N-isopentylamino)-6-methyl-7-anilinofluoran. , 3-diethylamino-6methyl-7-anilinofluorane, 3
-diethylamino-6methyl-7-(o,ρ-dimethylanilino)fluorane, 3-(N-ethyl-p-}luidino>-6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl -7-anilinofluorane, 3-
Dibutylamino-6-methyl-7-anilinofluorane, 3-(N-cyclohexine-N-methylamino)-6
-Methyl-7-anilinofluorane, 3-diethylamino-7-(0chloroanilino)fluoran, 3-diethylamino-7-(m-trifluoromethylanilino)fluoran 3-diethylamino-6-methyl-7-chlorofluoran One or more selected from orane, 3-diethylamino-6-methylfluorane, 3-cyclohexylamino-6-chlorofluorane, etc. can be used.

As the color developer made of phenols or organic acids, conventionally known ones can be used, such as bisphenol A, benzyl ρ-hydroxybenzoate (JP-A-52
-140483), bisphenol S, 4-hydroxy-4'-isobrobyloxydiphenylsulfone (JP-A-60-13852), 1,■-di(4-hydroxyphenyl>cyclohexane, 1,7-di(4 -Hydroxyphenylthio)-3,5-dioxaheptane (JP-A-59-52694) and the like can be used.

Other sensitizers that can be used in combination with the sensitizer of the present invention include thermofusible organic compounds with a melting point of 50 to 150°C, but these have already been described in the prior art.
This is as explained using typical examples in the section.

In addition, organic or inorganic pigments used in the heat-sensitive coloring layer include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, dumbbell hydroxide, barium 1a acid, clay, calcined clay, talc, and surface Examples include inorganic fine powders such as treated calcium carbonate and silicate, and organic fine powders such as urea-formalin resin, styrene/methacrylic acid copolymer, and polystyrene resin.

Furthermore, the heat-sensitive coloring layer of the present invention may contain various waxes as required. As such waxes, known waxes such as paraffin, amide wax, bisimide wax, and metal salts of highly absorbent fatty acids can be used.

In addition, the adhesive contained in the heat-sensitive coloring layer includes polyvinyl alcohol of various molecular weights, starch, and its derivatives, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, and sodium polyacrylate.
Polyvinylpyrrolidone, acrylic amide/acrylic ester copolymer, acrylic amide/acrylic ester/methacrylic acid ternary copolymer, styrene/maleic anhydride copolymer alkali salt, polyacrylamide, sodium anoregic acid, Water-soluble polymer materials such as gelatin and casein, polyvinyl acetate, polyurethane, styrene/butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate A latex containing at least one of 1., ethylene/vinyl acetate copolymer, and styrene/butadiene/acrylic copolymer can be used.

The sheet-like substrate used in the thermal recording medium of the present invention is paper,
Coated paper whose surface is coated with clay plastic, etc.
You can choose from synthetic paper, which is mainly made from plastic, or plastic film. A coating liquid containing a mixture of the above-mentioned necessary components is applied onto at least one surface of such a sheet-like substrate and dried to produce a heat-sensitive recording material.

The coating amount at this time is 1 to 1 when the coating liquid layer is dry.
It is preferable to be 5g/t*2, and 2 to 10g/Il
2 is particularly preferred. The heat-sensitive recording material of the present invention thus obtained has excellent high-speed recording suitability, high whiteness, and does not cause undesirable phenomena such as whitening in the recorded image area. [Example] The present invention will be explained in more detail with reference to the following example.

Note that unless otherwise specified, "part J" and "%" represent "part J" and "% by weight", respectively.

21.6Hcr) o-cresol (guaiacol) and 1
1.2 g of potassium hydroxide was added to 200 cc of toluene, and the mixture was heated to 130° C. to reflux the toluene to prepare a potassium salt of O-cresol. After that, toluene was distilled off. At that time, the produced water was also removed by azeotropic distillation. To this, 31.2 g of 4,4'-dibromodiphenyl
, and further 50 cc of pyridine and 2.0 ml of anhydrous cupric chloride as a catalyst. Og was added, and the resulting reaction mixture was heated to 15
It was heated at 0°C under reflux for 8 hours. The resulting reaction mixture was extracted with ether, and the Koichitel extract was washed with an alkali and acid, and the Koichitel was distilled off to obtain a pale brown solid.

This was recrystallized from ethyl alcohol to obtain 14.5 g of white solid. Its melting point was 120°C. This white solid was confirmed to be 4,4'-bis(2-methylphenoxy)biphenyl by mass spectrometry and nuclear magnetic resonance spectroscopy.

The same operation as in example 1 was performed. However, 21.6 g of m-cresol was used instead of 21.6 g of O-cresol. 16.2g of white solid was obtained. Its melting point is 73℃
Met. This white solid was confirmed to be 4,4'-bis(3methylphenoxy)biphenyl by mass spectrometry and nuclear magnetic resonance spectroscopy.

The same operation as in Synthesis Example 1 was performed. However, 18.8 g of phenol was used instead of 21.6 g of 0-cresol. 17.2g of white solid was obtained. Its melting point was 149°C. Through mass spectrometry and nuclear magnetic resonance spectrometry,
This white solid was confirmed to be 4,4' diphenoxybiphenyl.

Real - Kneeling example - 1 A thermosensitive recording paper was prepared by the following procedure.

Fluoran 20% vorivinyl alcohol 10% water
70 The above composition was subjected to a sand grinder and ground until the average particle size was 1 μm.

Side - 140Uu 10% polyvinyl alcohol 10% water 10
70 The above composition was subjected to a sand grinder, and the average particle size was 1μ.
It was ground to m.

40 parts of liquid A, 160 parts of liquid B, 4 parts of calcium carbonate pigment
0 parts, 20 parts of a 30% paraffin dispersion, and 180 parts of a 10% polyvinyl alcohol aqueous solution were mixed and stirred to prepare a coating liquid. This coating liquid was applied to one side of base paper with a basis weight of 50 g/m2 so that the coating amount after drying was 7.0 g/m2, and it was dried to form a heat-sensitive coloring layer, thereby creating a heat-sensitive recording paper. .

The heat-sensitive recording paper obtained as described above is treated with a supercalender, and its surface smoothness is adjusted to 600 to 100.
It was set to 0 seconds. The samples thus obtained were subjected to the following tests to measure recording sensitivity, measure color density of uncolored areas on the recording layer surface, and compare whitening.

(a) Record 1 (using Toyo Seiki thermal gradient tester, temperature 120℃, pressure 2
．． The sample was heated for 100 milliseconds under the condition of 5 kHz/cm2, and the color density at that time was measured using a Macbeth densitometer RD-914. This measured value represents the recording sensitivity of the thermal paper. The density of the uncolored area (blank area) on the surface of the recording layer was measured using the above densitometer, and the measured value was expressed as the degree of whiteness.

(b) After developing the sample at a temperature of 150°C in the above tester, the printed area was left in an environment of 40'C and 90% for 24 hours, and changes in the surface were sensually evaluated. . In Table 1, "Good j" indicates that no change in the colored printed area is observed;
``Defective'' indicates that the printed surface becomes powdery, so-called whitening. The test results are shown in Table I.

Shoumaru Sacred L4 A thermosensitive recording paper was prepared by the following procedure.

l Face = 4 coats = 1 85 parts of fired clay (trade name: Ansilex) to 320 parts of water
40 parts of styrene-butadiene copolymer emulsion (solid content 50%) and 10%
Mix with 50 parts of oxidized starch aqueous solution, apply the resulting coating liquid on one side of base paper with a basis weight of 48 g/m' so that the coating amount after drying is 7.0 g/m2, and dry. A pigment-primed paper was created.

Heat sensitive layer door 150 parts of A dispersion, 200 parts of B dispersion, 2 parts of calcium carbonate
5 parts, 20 parts of a 30% paraffin dispersion, and 180 parts of a 10% polyvinyl alcohol aqueous solution were mixed and stirred to prepare a coating liquid. The obtained coating liquid was applied and dried on the pigment-coated surface of the pigment undercoated paper so that the coating amount after drying was 5.0 g/m 2 to form a thermosensitive coloring layer, thereby producing thermosensitive recording paper. .

The same test as in Example 1 was conducted using this thermosensitive recording paper. The results are shown in Table 1. Implementation - Bonito work The same operations as in Example 2 were carried out. However, in preparing Solution B used for forming the heat-sensitive coloring layer, 4,4'-bis(3-methylphenoxy)biphenyl was used instead of 4,4'bis(2-methylphenoxy)biphenyl.

The results are shown in Table 1.

Comparison: The same operation as in Example 1 was performed. However, in preparing Solution B, stearic acid amide was used instead of 4,4'-bis(2-methylphenoxy)biphenyl.

The test results are shown in Table 1.

Comparison by Tsuji - Placement 3 - The same operation as in Example 2 was performed. However, in preparing Solution B, stearic acid amide was used instead of 4,4'-bis(2-methylphenokidi)biphenyl.

The test results are shown in Table 1.

Tsujiminato tΣ The same operation as in Example 2 was performed. However, in preparing Solution B, 1-hydroxy-2-naphthoic acid phenyl ester was used instead of 4,4'-bis(2-methylphenoxy)biphenyl.

The test results are shown in Table 1.

〔Effect of the invention〕

Since the heat-sensitive recording material of the present invention has a heat-sensitive coloring layer containing a sensitizer made of a new thermofusible material, it has excellent high-speed recording suitability, high whiteness, and undesirable problems such as whitening. It does not induce any phenomena, has extremely well-balanced properties in terms of quality, and has extremely high practical value.

Claims (1)

[Claims] 1. A sheet-like substrate, a colorless or light-colored dye precursor formed on at least one surface of the sheet-like substrate, and reacting with the dye precursor under heating to develop color. a heat-sensitive coloring layer containing a color developer, and the heat-sensitive coloring layer has the following general formula (I): ▲There are mathematical formulas, chemical formulas, tables, etc.▼...(I) (However, the formula R_1 represents a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom.