JPH03114881A - Thermal recording body - Google Patents

Abstract

PURPOSE:To obtain a thermal recording paper material, which has excellent recording and coloring properties, suppressed static coloring property in which a whitening phenomenon is not induced, by forming a thermal coloring layer containing a specific thermally fusible material. CONSTITUTION:A thermal coloring layer including a sheet-shaped base body, a colorless or light-colored dye prescursor, and a developer reacting with the dye precursor under heating and color-developing the precursor is provided. The thermal coloring layer is colorless or light-colored, and contains at least one kind of an organic liquid crystalline compound having the melting point of 70-120 deg.C and the degree of solubility of 50mg/l or less to water. Accordingly, extremely high recording sensitivity and heat resistance are acquired without lowering whiteness and without generating the phenomenon of whitening, by which the quality of a colored picture is deteriorated with time.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a heat-sensitive recording material, and more specifically, it relates to a heat-sensitive recording material having a heat-sensitive coloring layer with high whiteness and excellent suitability for high-speed recording. It is something.

[Conventional technology]

Thermosensitive recording materials that utilize a heated coloring reaction between normally colorless or light-colored leuco dyes and phenols or organic acids have been published in Japanese Patent Publication No. 43-4160, Japanese Patent Publication No. 14039-1983, Japanese Patent Publication No. 4B-27736, etc. , has been widely put into practical use. In recent years, such heat-sensitive recording materials have been widely used as various information recording materials because they have the advantage of forming colored images simply by heating and allowing recording devices to be made relatively compact. ing. 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 difficult.

As the speed of equipment and hardware increases, the thermal recording media used are required to have significantly higher recording sensitivity than before. Many proposals have been made to meet this requirement, but most of them involve combinations of leuco dyes and coloring agents.
It also relates to the combined use of thermofusible substances. These thermofusible substances are called sensitizers, such as 1-hydroxy-2-naphthoic acid phenyl ester (Japanese Patent Application Laid-open No. 57-19
1089), p-benzylbiphenyl (Unexamined Japanese Patent Publication No. 1089-
No. 82382), benzyl naphthyl ether (JP-A No. 5
8-87094), dibenzyl terephthalate (JP 58-98285), benzyl p-benzyloxybenzoate (JP 57-201691), diphenyl carbonate, ditolyl carbonate (JP 58-136489) ,
m-terphenyl (JP 57-89994), 1,
2-bis(m-tolyloxy)ethane (JP-A-60-5
6588), 1,5-bis(p-methoxyphenoxy)-3-oxapencune (Japanese Patent Application Laid-open No. 181183/1983), and the like.

[Problem to be solved by the invention]

When a heat-sensitive recording material containing a thermofusible substance as described above is heated, the thermofusible substance melts, and the dye precursor,
By dissolving the color developer and the color developer, the two are mixed at the molecular level and a color reaction is induced. Therefore, these thermofusible substances have a suitable melting point (preferably 80 to 120
℃) and must have excellent compatibility with dyes and coloring agents. In addition, in order not to reduce the whiteness of the heat-sensitive recording material, it is desirable that these thermofusible substances are extremely poorly soluble in water and do not color the heat-sensitive coloring layer. It is desirable to have characteristics such as having little sex. In particular, the sublimation property of thermofusible substances is thought to be closely related to the so-called whitening phenomenon, in which the heat-colored portion of a thermosensitive recording material becomes powdery over time. In practical terms, low sublimability is an extremely important property. Furthermore, the heat-sensitive recording material temporarily temperature ranges from 60'C to 70'' during use.
It is often placed under a relatively high temperature of C, and it is desired that the coloring of the thermosensitive coloring layer is suppressed even at such high temperatures. Among the many thermofusible materials that have been proposed in the past, there are almost none that satisfy all of the above conditions, and therefore there has been a demand for the development of new materials that meet these requirements.

The present invention provides a novel thermofusible material for use with the aforementioned dye precursor and developer to overcome the problems of conventional sensitizers, thereby providing high recording sensitivity and high quality recording. The object of the present invention is to provide a heat-sensitive recording medium that can form images at high speed.

[Means to solve the problem]

The heat-sensitive recording material of the present invention includes a sheet-like substrate, a colorless or light-colored dye precursor formed on at least one surface of the sheet-like substrate, and a dye precursor that reacts with the dye precursor under heating to develop color. It has a heat-sensitive coloring layer containing a color developer, the heat-sensitive coloring layer is colorless or light-colored, and has a temperature of 70″C.
-120℃ melting point and 50■/! for water! It is characterized by containing at least one organic liquid crystal compound having the following solubility. When the organic liquid crystalline compound used in the present invention is particularly selected from the following group of compounds, it has been proposed as a typical thermofusible substance (Japanese Patent Publication No. 14531/1983), In addition, compared to higher fatty acid amides such as stearic acid amide and valmitic acid amide, which have been put into practical use, it does not cause a decrease in whiteness and does not cause the phenomenon of whitening that deteriorates the quality of colored images over time. It has been found that extremely high recording sensitivity and heat resistance can be obtained without this occurrence.

That is, the organic liquid crystal compound useful in the present invention is preferably selected from the following compounds.

(1) p-substituted oxycinnamic acid p-1 substituted phenyl ester compound represented by the following structural formula (1): C. However, in the above formula, R2 and R2 each independently represent an alkyl group. ] (2) (Poly) p-substituted oxybenzoic acid p-1f substituted phenyl ester compound represented by the following structural formula [II]: [However, in the above formula, R1 represents an alkyloxycarbonyl group, and R4 represents an alkyl group. represent. ] (3) The following structural formula (
Biphenyl monocarboxylic acid ester compound represented by 1[I): [However, in the above formula, R6 and R& each independently represent an alkyl group, and n represents 0 or 1.

] (4) Alkyl-substituted cyclohexyl biphenyl compound represented by the following structural formula (IV) or (V): [However, in the above formula, Rt , Rs , R9 and R1 each independently represent an alkyl group,] (1
)~(V)2, R,,R,,R4°Rs,
The alkyl group represented by R&, Rt, Rs, R9 and R1°, and the alkyl group in the alkyloxycarbonyl group represented by R1 each independently have 1 to 6 carbon atoms. is preferred.

The reason why the above-mentioned liquid crystalline thermofusible substance (hereinafter referred to as sensitizer) improves the coloring sensitivity of the thermosensitive coloring layer containing it is not yet fully clear, but the inventors have It is hypothesized that such liquid crystalline thermofusible substances have high crystallinity, which particularly stabilizes the colored dye. As is well known, liquid crystals contain cholesteric,
Nematic, smectic, and discotic
Although the types are known, similar effects were observed for all of these compounds having liquid crystallinity. Further, in order not to reduce the whiteness, the liquid crystalline compound of the present invention is required to have a low solubility in water of 50 [I1 g/l or less]. Furthermore, it is thought that the reason why phenomena such as whitening that deteriorate the recorded image quality are extremely low is due to the low sublimation properties of these compounds, and the reason why they have heat resistance is because they have an appropriate melting point. Specific representative examples of these compounds include the following liquid crystalline organic compounds.

p-Methoxycinnamic acid-p-methylphenyl ester (
Melting point: 105°C 1 Isotropic liquid transition point (when cooled: 98°C)
0°C, isotropic liquid transition point: 114°C), p-n-hexyloxy-p-biphenylcarboxylic acid ethyl ester (melting point: 100°C, nematic to isotropic liquid transition point: 120”
C), 2-acetyl-? -n-heptyloxyfluorene (melting point 106°C, smectic → nematic transition point 10
8℃), 4-(4"-pentylcyclohexyl)-4'(4"-
methylcyclohexyl)-biphenyl (melting point 96°C, isotropic liquid transition point 284°c), and 4-(4''-pentylcyclohexyl)-4'ethoxybiphenyl (melting point 89°C, isotropic liquid transition point 148°C). ℃).

In addition to the above, aromatic carboxylic acids and their derivatives, azomethine compounds, and azo compounds are known as organic compound groups that exhibit liquid crystallinity; however, the first group of compounds is highly soluble in water. , the second group of compounds is unsuitable for use in thermosensitive recording materials due to their instability in water, and the last group of compounds is due to their coloring properties.

The liquid crystalline organic compounds used in the present invention can be synthesized by various synthetic methods, and typical synthetic reactions for each series are shown below. However, Rl
""" R1G is a substituent as defined above.

(a) (b) (■J (c) (d) (3) Chromatogram separation Liquid crystalline compounds useful in the present invention include: dye precursor, It is included in the heat-sensitive coloring layer together with 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 liquid crystal compound of the present invention used is 10 to 1000% by weight, preferably 50 to 300% by weight, based on the color developer.

The thermosensitive coloring layer containing the liquid crystal compound of the present invention mainly contains a dye precursor such as a leuco dye, a color developer made of phenols or an organic acid, and an organic liquid crystal compound.

Further, the heat-sensitive coloring layer preferably contains an inorganic pigment in addition to the above-mentioned components, and may further contain waxes if necessary.

In addition, a binder for fixing these components to the support is included as an essential component.

The content of the dye precursor in the thermosensitive coloring layer is generally 5 to 20% by weight, and the content of the color developer is generally 10 to 40% by weight.
It is. The content of the binder is generally 5 to 20% by weight, and when white pigments and waxes are included, the content of each is generally 10 to 50% by weight.
, and about 5 to 30% of heavy visibility.

Conventionally known leuco dyes are used as dye precursors,
Examples include:

Crystal violet lactone, 3-(N-ethyl-
N-isopentylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-
7(o,p-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-cyclohexyl-N
-Methylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-7-(o-chloroanilino)fluorane, 3-diethylamino-7-(m-trifluoromethylanilino)fluorane, 3-diethylamino-
6-methyl-7-chlorofluoran, 3-diethylamino-6-methylfluoran, 3-cyclohexylamino-6-chlorofluoran, and two or more of these may be used as a mixture.

As the color developer made of phenols or organic acids, conventionally known ones may be used, and examples thereof include the following.

Bisphenol A, benzyl p-hydroxybenzoate (
JP-A-52-140483), bisphenol S, 4
-Hydroxy-41-isopropyloxydiphenyl sulfone (JP-A-60-13852), l.

1-di(4-hydroxyphenyl)cyclohexane, 1
．． 7-di(hydroxyphenylthio)-35-dioxahebutane (JP 59-52694).

Here, as other sensitizers that can be used in combination with the organic liquid crystal compound of the present invention, thermofusible organic compounds with a melting point of 80 to 120°C are used, and representative examples of these are already mentioned. I explained.

Organic or inorganic pigments used in the heat-sensitive coloring layer include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, fired clay, talc, and surface-treated carbonate. Examples include inorganic fine powders such as calcium and silica, as well as 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. These adhesives may be known ones such as paraffin, amide wax, bisimide wax, metal salts of superabsorbent fatty acids, etc. The adhesives used include polyvinyl alcohol of various molecular weights, starch and its derivatives, methoxy cellulose, carboxy cellulose, etc. Cellulose derivatives such as methylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic amide/acrylic ester copolymer, acrylic amide/acrylic ester/methacrylic acid ternary copolymer, styrene/maleic anhydride In addition to water-soluble polymers such as copolymer alkali salts, polyacrylamide, sodium alginate, gelatin, and casein, polyvinyl acetate, polyurethane, styrene/butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride/acetic acid Latexes such as vinyl copolymers, polybutyl methacrylate, ethylene/vinyl acetate copolymers, styrene/butadiene/acrylic copolymers, etc. can be used.

The heat-coloring mixture obtained by appropriately mixing these materials can be used on a sheet-like support, such as paper, coated paper whose surface is coated with clay plastic, synthetic paper made mainly from plastic, or even plastic film. It is coated on one side of the film to form a heat-sensitive coloring layer. The coating amount of the heat-sensitive coloring layer is 1-10g/rrf in dry state.
It is preferable that it is, and it is even more preferable that it is 2-7 g/rrf.

The heat-sensitive recording material of the present invention having the above structure has excellent high-speed recording suitability, high whiteness, and does not exhibit undesirable properties such as whitening in recorded image areas.

EXAMPLES The present invention will be specifically explained below with reference to Examples.

Note that unless otherwise specified, "1 part" and "1%" represent parts by weight and % by weight, respectively.

〔Example〕

17.8 g (0,
10 mol) of p-methoxycinnamic acid (altri.vti) and 11.9 g of thionyl chloride were charged. When this mixture was slowly heated in a hot water bath, generation of hydrogen chloride gas was observed. After the generation of hydrogen chloride gas was completed, the mixture was cooled to room temperature and 10.8 g
of p-cresol was added. When this mixture was heated again in a hot water bath, generation of hydrogen chloride gas was observed. Continue heating for 2 hours, then remove the hot water bath when gas generation stops.
The mixture was heated to 200° C. using oil/gas. The mixture was again cooled to room temperature and extracted with ether. The ether extract layer was washed several times with water, and the ether was distilled off to obtain pale yellow crude crystals. The crude crystals were recrystallized from ethyl alcohol to obtain 20.0 g of slightly yellow crystals. The melting point of this crystal was 105°C. The above white crystals were confirmed to be P-methoxycinnamate p-methylphenyl ester by measurements of nuclear magnetic resonance spectra and mass spectrometry spectra.

Example 1 ■ Preparation of dispersion A Dye dispersion having the following composition: 3-(N-isopentyl-N-ethyl 20 amino)-6-methyl-7-anilite fluoran 10% polyvinyl alcohol solution 10 water
70 was prepared and ground to an average particle size of 1 kon with a sand grinder.

■ Preparation of dispersion B Color developer and sensitizer dispersion with the following composition: 4.4'-isopropylidene biphene 10Nol p-methyl p-methoxycinnamate 10Phenyl ester polyvinyl alcohol 10% solution 10Water
70
was prepared and ground with a sand grinder to an average particle size of 1-.

(2) Preparation of coloring layer To 40 parts of liquid A and 160 parts of liquid B, 40 parts of calcium carbonate pigment, 20 parts of 30% paraffin dispersion, and 180 parts of lO% polyvinyl alcohol aqueous solution were mixed and stirred to form a coating liquid. And so. 50g/rtf of this coating liquid
The mixture was coated on base paper so that the coating amount after drying was 7.0 g/rrf and dried to form a heat-sensitive coloring layer, thereby obtaining heat-sensitive recording paper.

The heat-sensitive recording paper obtained as described above was subjected to a supercalender treatment so that the surface smoothness measured with a smoothness meter was 600 to 1000 seconds.

The samples thus obtained were subjected to recording sensitivity measurements, color density measurements of uncolored areas on the recording layer surface, and whitening comparison tests.

The results of these tests are shown in Table 1.

To measure the recording sensitivity of and , a Toyo Seiki equipment tilt tester was used to measure the recording sensitivity of 100 m5 at a temperature of 120°C and a pressure of 2.5 kg/cj.
The ec sample was heated, and the color density at that time was measured using a Macbeth densitometer RD-914, and this value was taken as a value representative of the recording sensitivity of the thermal paper. The density of the uncolored area (blank area) on the surface of the recording layer was also measured with the above densitometer, and the obtained value was taken as a representative value of whiteness.

・ゝ゛Also, using the above tester, test the sample at a temperature of 70°C and a pressure of 2.5°C.
kg/cffl for 5 seconds, and the color density at that time was measured using the above densitometer. The color development at this time is called static color development (70'C), and the obtained measured value was taken as a representative value of how well the sample maintains its white background density at a relatively high temperature. When the sample is actually used as recording paper for facsimile communication, the ambient temperature is 60~60℃ due to continuous printing.
It is known that the temperature can rise up to 70℃, and the above value is
It is a measure of how white the non-printing area can maintain even in such a high temperature environment, and the static color density is 0.
．． It is preferably 2 or less.

The JIL value whitening is determined by heating the sample to 150°C using the above testing machine to develop color in the heat-sensitive coloring layer, leaving the printed area in an environment of 190% at 40°C for 24 hours, and observing the changes in the surface. evaluated. In Table 1, O indicates that no change was observed in the colored printed area, and × indicates that so-called whitening, in which the printed surface became powdery, occurred.

Example 2 ■ Preparation of pigmented undercoated paper 85 parts of baked Ray (trade name: Ansilex) were mixed with 32 parts of water.
40 parts of styrene-butadiene copolymer emulsion (solid content 50%) and 10 parts of styrene-butadiene copolymer emulsion (solid content 50%)
% oxidized starch aqueous solution, and the resulting coating liquid was applied onto a base paper of 48 g/I to a coating weight of 7.0 g after drying.
Pigment undercoated paper was prepared by applying the pigment to 0 g/n.

(2) Formation of coloring layer 25 parts of calcium carbonate, 20 parts of a 30% paraffin dispersion, and 180 parts of a 10% polyvinyl alcohol aqueous solution are mixed with 50 parts of the above dispersion A and 200 parts of the dispersion B.
The mixture was stirred to obtain a coating liquid. The obtained coating liquid was applied onto the pigment coated surface of the pigment undercoated paper so that the coating amount after drying was 5.0 g/
rd, and dry to form a heat-sensitive coloring layer.
A thermosensitive recording paper was obtained.

The test results are shown in Table 1.

Example 3 The same operation as in Example 2 was carried out, except that p-n-hexyloxy-p-biphenylcarboxylic acid ethyl ester was used instead of p-methoxycinnamic acid p-methylphenyl ester in the BwL preparation. A thermosensitive recording paper was obtained.

The test results are shown in Table 1.

Example 4 The same operation as in Example 2 was performed, except that B? & In the preparation, 4-(4”-pentylcyclohexyl)-4 instead of p-methoxycinnamate p-methylphenyl ester
A thermosensitive recording paper was obtained using '-ethoxybiphenyl.

The test results are shown in Table 1.

Comparative Example 1 The same operation as in Example 1 was performed, except that in the preparation of B solution,
A thermosensitive recording paper was obtained using 1-hydroxynaphthoic acid phenyl ester instead of p-methoxycinnamic acid p-methylphenyl ester.

The test results are shown in Table 1.

Comparative Example 2 A heat-sensitive recording paper was obtained by carrying out the same operation as in Example 2, except that stearic acid amide was used instead of p-methoxycinnamic acid p-methylphenyl ester in the BW1 preparation.

The test results are shown in Table 1.

Table [Effects of the Invention] The heat-sensitive recording paper material of the present invention has a heat-sensitive color forming layer containing a new thermofusible material, and therefore has excellent high-speed recording permeability, high whiteness, and static It produces little color, does not induce undesirable phenomena such as whitening, and is extremely well-balanced in terms of quality.

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;
The thermosensitive coloring layer includes a color developer that reacts with this dye precursor and develops color under heating, and the thermosensitive coloring layer comprises:
colorless or light-colored, with a melting point of 70°C to 120°C;
A heat-sensitive recording material comprising at least one organic liquid crystal compound having a solubility in water of 50 mg/l or less. 2. The organic liquid crystal compound is the following compound group: (1) p-substituted oxycinnamic acid represented by the following structural formula [I]
p-Substituted phenyl ester compound: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [I] [However, in the above formula, R_1 and R_2 each independently represent an alkyl group. ] (2) (Poly)p-substituted oxybenzoic acid-p-substituted phenyl ester compound represented by the following structural formula [II]: ▲There are numerical formulas, chemical formulas, tables, etc.▼ [II] [However, in the above formula, R_3 represents an alkyloxycarbonyl group, and R_4 represents an alkyl group. ] (3) Biphenyl monocarboxylic acid ester compound represented by the following structural formula [III]: ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [III] ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [However, in the above formula, R_5 and R_6 each independently represents an alkyl group, and n represents 0 or 1. ] and (4) Alkyl-substituted cyclohexyl biphenyl compounds represented by the following structural formulas [IV] and [V]: ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [IV] ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [V ] [However, in the above formula, R_7, R_8, R_9 and R_10
each independently represents an alkyl group, and
indicates the configuration of hydrogen atoms. ] The heat-sensitive recording material according to claim 1, which is selected from the following.