JP2760587B2 - Thermal recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thermosensitive recording medium, and more specifically, to a thermosensitive recording medium having a high whiteness and excellent high-speed recording suitability.

[Conventional technology]

A heat-sensitive recording material that forms a recorded image on a heat-sensitive coloring layer by utilizing a heat-coloring reaction of a colorless or light-colored Roy dye (dye precursor) with a phenol or an organic acid is disclosed in, for example, JP-B-43-4160. JP-B-45-14039 and JP-B-48-2
It is disclosed in, for example, No. 7736, and has been widely used. recent years,
Such a heat-sensitive recording medium has been widely used as various information recording materials because of its advantages such as the formation of a color image by simply heating and the fact that the recording apparatus can be made relatively compact. I have. In particular, thermal facsimile machines, thermal printers, and the like using such a thermal recording medium have been improved in their devices, and high-speed printing and high-speed image formation, which have been considered difficult in the past, are now possible. With the increase in the speed of such devices and hardware, there has been a demand for a thermosensitive recording medium to be used which has a greatly improved recording sensitivity as compared with the related art. Many proposals have been made to satisfy this demand, but many of them are characterized by the combination of the dye precursor and the developer, or by the combination of a heat-fusible substance. Things. The heat-fusible substance contained in the thermosensitive coloring layer is called a sensitizer, for example, 1-
Hydroxy-2-naphthoic acid phenyl ester (JP-A
No. 57-191089), p-benzylbiphenyl (JP-A-60-1985)
No. 82382), benzyl naphthyl ether (JP-A-58-870)
No. 94), dibenzyl terephthalate (JP-A-58-98285)
No.), benzyl p-bedyloxybenzoate (Japanese Unexamined Patent Publication No.
201691), diphenyl carbonate, ditolyl carbonate (JP-A-58
-136489), m-terphenyl (JP-A-57-89994)
No.), 1,2-bis (m-tolyloxy) ethane (Japanese Unexamined Patent Publication No.
No. 0-56588) is known.

[Problems to be solved by the invention]

When the heat-sensitive coloring layer containing the heat-fusible substance is heated, the heat-fusible substance first melts, and this dissolves the dye precursor and the developer. Is induced. Therefore, the thermoplastic must have an appropriate melting point (preferably 60-140 ° C.) and have excellent compatibility with the dye precursor and the developer. Further, in order not to reduce the whiteness of the thermosensitive coloring layer, it is desirable that the heat-fusible substance is extremely poorly soluble in water, and further has a property of low sublimability. desirable. The sublimability of the heat-fusible substance is considered to be deeply related to the phenomenon of so-called whitening, in which the heated coloring portion of the thermosensitive coloring layer becomes dusty with time. , A very important property. As described above, many heat-fusible substances for the heat-sensitive coloring layer have been proposed, but few satisfy all of the above-mentioned conditions. Therefore, development of a new material has been demanded.

The present invention provides a novel heat fusible material for use with a dye precursor and a developer, thereby having significantly improved recording sensitivity without adversely affecting the performance required for recording, Another object of the present invention is to provide a thermosensitive recording medium having high whiteness.

[Means and actions to solve the problem]

In order to achieve the above object, the present inventors have conducted repeated studies and found that a colorless or pale-colored dye precursor and a thermosensitive recording medium having a thermosensitive coloring layer using a color reaction with a color developer were set. It has been found that the above problem can be solved by using a heat-fusible substance having the chemical structure of the above, and the present invention has been completed.

The heat-sensitive recording material of the present invention comprises a sheet-like substrate, a colorless or pale-colored dye precursor formed on at least one surface thereof, and a developer which reacts with the dye precursor under heating to develop a color. And a heat-sensitive color-forming layer comprising the following formula (I): (In the above formula (I), R ¹ , R ² and R ³ each independently represent a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a nitro group, or a halogen. Wherein R ¹ , R ² and R ³ are not all hydrogen atoms at the same time, and X and Y each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, a nitro group Represents an aryl group, a halogen atom, or an aralkyl group, or forms a cyclic structure linked to an adjacent benzene ring, and m and n are each independently of the other
Represents an integer of 0 or 3 or less. ), Further comprising a sensitizer containing at least one diether compound represented by the following formula:

When the compound of the above formula (I) is used as a sensitizer in a heat-sensitive coloring layer, it has been conventionally proposed as a typical sensitizer (heat-fusible substance) (Japanese Patent Publication No. 50-14531), and Experience a phenomenon such as whitening that does not cause a decrease in whiteness and deteriorates the quality of a color image over time, as compared with higher fatty acid amides such as stearic acid amide and palmitic acid amide that are in practical use. Therefore, extremely high recording sensitivity can be obtained. Although the reason why the sensitizer comprising the heat-fusible compound of the above formula (I) improves the generation sensitivity of the heat-sensitive layer containing no sensitizer is not sufficiently clear yet,
It is supposed that part of the reason is that this compound has a low viscosity in a molten state and has appropriate compatibility with dyes and color developers. The reason that the sensitizer does not lower the whiteness is that it is hardly soluble in water, and the phenomenon of deteriorating the recorded image quality such as whitening is extremely small.
It is thought that it has low sublimability. However, the inventor does not adhere to the above interpretation. Specific examples of the compound of the formula (I) contained in the sensitizer of the present invention include the following.

These compounds can be synthesized by various synthesis methods, but most easily can be synthesized easily and in high yield by utilizing the so-called Williamson reaction shown below.

(In the above reaction formula, R ^{1 to} R ³ , X and m are as defined above.) The sensitizer of the present invention is used together with a dye precursor and a color developer. The use amount of this sensitizer is 10 to
Preferably it is 1000% by weight, more preferably 50-300% by weight. The sensitizer of the present invention may be used in combination with other sensitizers within a range that does not impair the desired effects of the present invention.

The thermosensitive coloring layer containing the sensitizer of the present invention contains a dye precursor mainly composed of a leuco dye and a developer composed of a phenol or an organic acid, and preferably further contains an inorganic or organic pigment. Further, if necessary, waxes may be contained. Further, the thermosensitive coloring layer contains, as an essential component, a pressure-sensitive adhesive for binding the above components and fixing the components to a support.

As a colorless or pale color dye precursor, a conventionally known leuco basic dye, for example, crystal violet lactone, 3- (N-ethyl-N-isopentylamino) -6
-Methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluoran, 3- (N -Ethyl-p-toluidino)
-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-
(N-cyclohexyne-N-methylamino) -6-methyl-7-anilinofluoran, 3-diethylamino-7
-(O-chloroanilino) fluoran, 3-diethylamino-7- (m-trifluoromethylanilino) fluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-6-methylfluoran, and What consists of at least one kind, such as 3-cyclohexylamino-6-chlorofluorane, can be used.

Phenols, or as a developer consisting of organic acids,
Conventionally known organic acidic substances, for example, bisphenol A,
Benzyl p-hydroxybenzoate (JP-A-52-140483)
No.), bisphenol S, 4-hydroxy-4'-isopropyloxydiphenyl sulfone (JP-A-60-13852)
No.), 1,1-di (4-hydroxyphenyl) cyclohexane and 1,7-di (hydroxyphenylthio)-
It is possible to use at least 11 compounds such as 3,5-dioxaheptane (JP-A-59-52694).

Here, as the other sensitizer that can be used in combination with the sensitizer of the present invention, a heat-fusible organic compound having a melting point of 50 to 150 ° C. is used, and these are already represented in the section of the “prior art”. I explained it with a typical example.

Examples of the organic or inorganic pigment used in the thermosensitive coloring layer include, for example, calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, calcined clay, talc, and surface-treated pigments. And inorganic fine powders such as calcium carbonate and silica, and organic fine powders such as urea-formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin.

Further, in the present invention, the heat-sensitive coloring layer may contain various waxes as required. These waxes are paraffin, amide wax, bisimide wax,
It can be selected from known ones such as metal salts of higher fatty acids. The binder is, for example, polyvinyl alcohol of various molecular weight, starch and derivatives thereof, methoxycellulose, carboxymethylcellulose, methylcellulose,
Cellulose derivatives such as ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylamide /
Water-soluble polymers such as acrylate copolymer, acrylamide / acrylate / methacrylic acid terpolymer, alkali salt of styrene / maleic anhydride copolymer, polyacrylamide, sodium alginate, gelatin, and casein Binder, polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene /
It may contain at least one latex such as a vinyl acetate copolymer and a styrene / butadiene / acrylic copolymer.

Generally, in the thermosensitive coloring layer of the present invention, the dye precursor is 2 to 20% by weight, the developer is 2 to 60% by weight, and the binder is 2 to 40% by weight.
% By weight, 0 to 80% by weight of pigments and 0 to 20% by weight of waxes.

The sheet-like substrate used in the present invention can be selected from paper, coated paper coated on its surface with clay, plastic, or the like, synthetic paper mainly made of plastic, and plastic film.

To prepare the thermosensitive recording medium of the present invention, a coating solution is prepared by mixing the above components, and the coating solution is applied on at least one surface of a sheet-like substrate by an appropriate coating method, and dried and solidified. What is necessary is just to form a thermosensitive coloring layer. The coating amount at this time is preferably from 1 to 10 g / m ² , particularly preferably from ² to 7 g / m ² , in a state where the coating liquid layer is dried.

The heat-sensitive recording material of the present invention thus obtained is excellent in high-speed recording suitability, high in whiteness, and does not cause undesired phenomena such as whitening in a recorded image portion.

〔Example〕

Hereinafter, the present invention will be described specifically with reference to Examples.
Unless otherwise specified, “parts” and “%” represent “parts by weight” and “% by weight”, respectively.

Synthesis Example 1 (1,4-bis (benzyloxy) -2,3-dimethylbenzene) 55.2 g of 2,3-dimethylhydroquinone was dissolved in 300 cc of dimethyl sulfoxide, and 53.8 g of potassium hydroxide was added to this solution. The mixture was stirred for 2 to 3 hours while heating to 90 ° C to prepare a potassium salt of 2,3-dimethylhydroquinone. 121.4 g of benzyl chloride was added to the reaction product,
The solution was added dropwise with care so that the temperature of the solution did not exceed 100 ° C., and reacted for 2 hours. After cooling the resulting reaction solution, it was poured into cold water and filtered to remove water-soluble substances. Ether was added to the obtained filtration residue and extracted with ether, and ether was distilled off from the ether phase to obtain a brown solid. This crude product was recrystallized from ethyl alcohol to obtain 89 g of a white solid. Its melting point was 108 ° C. According to mass spectrometry and measurement of the magnetic resonance spectrum, this solid was 1,4
-Bis (benzyloxy) -2,3-dimethylbenzene.

Synthesis Example 2 (1,4-bis (benzyloxy) -2,3,5-trimethylbenzene) The same operation as in Synthesis Example 1 was performed. However, instead of 55.2 g of 2,3-dimethylhydroquinone, 60.8 g of 2,3,5-trimethylhydroquinone was used. 81 g of a white solid was obtained. Its melting point was 73 ° C.

By mass spectrometry and nuclear magnetic resonance spectrum measurement,
This solid was confirmed to be 1,4-bis (benzyloxy) -2,3,5-trimethylbenzene.

Example 1 Thermal recording paper was prepared by the following operation.

Subjecting the dispersion prepared Ingredient Quantity of A (parts) 3- (N-isopentyl -N- ethylamino) -6-methyl-7-anilino fluoran 20 polyvinyl alcohol 10% solution 10 Water 70 The composition sand grinder, Average particle size 1μ
m.

Preparation Ingredients Amount of Dispersion B (parts) 4,4'-isopropylidene-biphenol 10 1,4-bis (benzyloxy) -2, 3-dimethyl-benzene 10 polyvinyl alcohol 10% solution 10 Water 10 sand grinder of this composition 1 μm average particle size
Until ground.

Preparation of thermosensitive hue 40 parts of the above solution A, 160 parts of solution B, calcium carbonate pigment 40
Parts, 20 parts of a 30% paraffin dispersion and 180 parts of a 10% aqueous solution of polyvinyl alcohol were stirred and mixed to prepare a coating liquid. This coating solution was coated and dried on one side of a base paper having a basis weight of 50 g / m ² so that the coating amount after drying was 7.0 g / m ² to form a thermosensitive coloring layer, thereby preparing a thermosensitive recording paper. .

The recording surface of the heat-sensitive recording paper obtained as above is smoothed by a super calender, and the smoothness is 600 to 100.
Adjusted to 0 seconds. For the sample of the heat-sensitive recording paper whose surface was smoothed, the measurement of the recording sensitivity, the measurement of the color density of the uncolored portion of the recording layer surface, and the comparison test of the whitening resistance were performed as follows, and the results are shown in Table 1. Was.

(1) Recording sensitivity Using a thermal gradient tester manufactured by Toyo Seiki, temperature 120 ℃, pressure 2.5kg
The sample was heated for 100 msec under the condition of / cm ² , and the coloring density at that time was measured by Macbeth densitometer RD-914, and the measured value was used to express the recording sensitivity of the thermosensitive recording paper. The density of the uncolored portion (white paper portion) of the recording layer surface was measured by the above densitometer, and the measured value was used to represent whiteness.

(2) Whitening resistance Using the tester described above, the sample was colored at a temperature of 150 ° C.
The printed part was left in an environment of 40 ° C. and 90% for 24 hours, and the change in the surface was sensory evaluated. In Table 1, "good" indicates that no change was observed in the color-printed portion, and "poor" indicates that so-called whitening occurred, in which the printed surface became dusty.

Example 2 A thermosensitive recording paper was prepared as described below and tested in the same manner as in Example 1.

Preparation of pigment-undercoated paper A dispersion obtained by dispersing 85 parts of calcined clay (trade name Ansilex) in 320 parts of water is mixed with 40 parts of a styrene-butadiene copolymer emulsion (solid content 50%) and 10% oxidized starch. 50 parts of an aqueous solution are mixed, and the obtained coating solution is
On one side of the base paper 48g / m ^2, coating weight after drying it is applied to Yo become 7.0g / m ^2, and dried to create a pigment undercoat paper.

Formation of thermosensitive coloring layer A dispersion 50 parts, B dispersion 200 parts, calcium carbonate 25
Parts, a 30% paraffin dispersion, 20 parts, and a 10% aqueous polyvinyl alcohol solution, 180 parts, were mixed and stirred to prepare a coating solution. The obtained coating solution was applied onto the pigment-coated surface of the pigment-undercoated paper and dried so that the coating amount after drying was 5.0 g / m ² to form a thermosensitive coloring layer, thereby obtaining a thermosensitive recording paper. .

 Table 1 shows the test results.

Example 3 The same operation as in Example 2 was performed. However, in preparing the solution B used for forming the thermosensitive coloring layer, instead of 1,4-bis (benzyloxy) -2,3-dimethylbenzene, 1,4-bis (benzyloxy) -2,3,5- Trimethylbenzene was used.

 Table 1 shows the test results.

Comparative Example 1 The same operation as in Example 1 was performed. However, in the preparation of the solution B, stearic acid amide was used instead of 1,4-bis (benzyloxy) -2,3-dimethylbenzene.

 Table 1 shows the test results.

Comparative Example 2 The same operation as in Example 2 was performed. However, in the preparation of the solution B, stearic acid amide was used instead of 1,4-bis (benzyloxy) -2,3-dimethylbenzene.

 Table 1 shows the test results.

Comparative Example 3 The same operation as in Example 2 was performed. However, in the preparation of solution B, phenyl 1-hydroxy-2-naphthoate was used in place of 1,4-bis (benzyloxy) -2,3-dimethylbenzene.

 Table 1 shows the test results.

[Effects of the Invention] The heat-sensitive recording material of the present invention uses a sensitizer composed of a novel heat-fusible compound, so that it is excellent in high-speed recording suitability, has high whiteness, and is not preferable such as whitening. It has extremely well-balanced properties in terms of quality, such as not inducing phenomena, and is of high practical value.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41M 5/30-5/34

Claims (1)

(57) [Claims] 1. A sheet-like substrate, comprising a colorless or pale-colored dye precursor formed on at least one surface thereof, and a developer which reacts with the dye precursor under heating to develop a color. A thermosensitive coloring layer, wherein the thermosensitive coloring layer has the following general formula (1): (In the above formula (1), R ¹ , R ² and R ³ each independently represent a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a nitro group, or a halogen. Wherein R ¹ , R ² , and R ³ are not all hydrogen atoms at the same time, and X and Y each independently represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, Group, an aryl group, a halogen atom, or an aralkyl group, or forms a cyclic structure linked to an adjacent benzene ring, m and n are each independently of the other
Represents an integer of 0 or 3 or less. A heat-sensitive recording material further comprising a sensitizer containing at least one diether compound represented by the following formula: