JP2530723B2 - Thermal recording - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-sensitive recording medium, and more particularly to a heat-sensitive recording medium having high whiteness and excellent suitability for high-speed recording.

[Conventional technology]

Normally colorless or pale leuco dye (dye precursor),
The heat-sensitive recording materials utilizing the heat color reaction with phenols or organic acids are disclosed in, for example, JP-B-43-4160 and JP-B-45-14.
It is disclosed in Japanese Patent No. 039 and Japanese Patent Publication No. 48-27736, and is widely put into practical use. In recent years, such a thermal recording material is capable of forming a color image by simply heating,
It is widely used as various information recording materials because of the advantages that the recording apparatus can be made relatively compact. In particular, thermal facsimiles and thermal printers using such thermal recording media are
As the apparatus is improved, 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 fields of equipment and hardware, the thermal recording medium used is required to have a significantly higher recording sensitivity than ever before. Many proposals have been made to meet this requirement, but many of them are characterized by a combination of a dye precursor and a color former, or by using a heat-fusible substance together. There is something. The heat-fusible substance is also called a sensitizer, and for example, 1-hydroxy-2-naphthoic acid phenyl ester (JP 57-191089 A), p.
-Benzylbiphenyl (JP-A-60-82382), benzylnaphthyl ether (JP-A-58-87094), dibenzyl terephthalate (JP-A-58-98285), benzyl p-benzyloxybenzoate (JP-A-SHO) 57-201691), diphenyl carbonate, ditolyl carbonate (JP-A-58-136489),
Known are m-ta-phenyl (JP-A-57-89994), 1,2-bis (m-tolyloxy) ethane (JP-A-60-56588) and the like.

[Problems to be Solved by the Invention] When a thermosensitive recording medium containing a heat-fusible substance as described above is heated, the heat-fusible substance is first melted, which melts the dye precursor and the developer. As a result, the two are mixed at the molecular level and a color-developing reaction is induced. Therefore, the heat-fusible substance must have an appropriate melting point (preferably 60 to 140 ° C.) and excellent compatibility with the dye precursor and the developer. It is also important not to reduce the whiteness of the thermal recording material.
It is desirable that the heat-fusible substance be extremely sparingly soluble in water, and it is desirable that the heat-fusible substance has properties such as low sublimability. The sublimability of the heat-fusible substance is particularly due to the fact that the heat-developed coloring portion of the heat-sensitive recording material becomes dusty with time.
It is considered to be closely related to the phenomenon of so-called whitening, which is an extremely important property for practical use of the thermal recording material. As described above, a large number of heat-fusible substances have been proposed in the past, but few of them satisfy all the above conditions, and therefore new materials have been required to appear.

The present invention has a thermosensitive color forming layer formed by using a novel heat-fusible substance together with the above-mentioned dye precursor and a color developer, and has a significantly improved recording sensitivity without degrading various recording performances. It is intended to provide a thermosensitive recording medium.

[Means and actions for solving the problem]

The heat-sensitive recording material of the present invention is a sheet-like substrate, a colorless or light-colored dye precursor formed on at least one surface of the sheet-like substrate, and reacts with the dye precursor under heating to develop a color. A thermosensitive coloring layer containing a color developing agent,
The thermosensitive coloring layer has the following general formula (I): (In the formula, R ¹ and R ² each independently represent a lower alkyl group, a lower alkoxy group, a nitro group, an aryl group, a halogen atom or an aralkyl group, or R ¹
And R ² each form a ring structure in which adjacent benzene rings are linked, and m and n each independently represent 0 or an integer of 3 or less. ) Further, at least one diether compound represented by The present inventors have heretofore proposed using a heat-fusible substance represented by the above formula (I) as a sensitizer (Japanese Patent Publication No. 50-14531), and Phenomenon such as whitening that does not deteriorate the whiteness and deteriorates the quality of the color image over time, as compared with the case of using higher fatty acid amides such as stearic acid amide and palmitic acid amide that are in practical use. It has been found that an extremely high recording sensitivity can be obtained without experiencing the above-mentioned problems, and the present invention has been completed.

The present invention provides a colorless or light-colored basic leuco dye (dye precursor) and a thermosensitive recording medium utilizing a color reaction of a color developer capable of developing a color by contacting the dye precursor,
It is characterized in that the thermosensitive coloring layer contains the compound of the above formula (I). The reason why the specific heat-fusible substance (hereinafter referred to as a sensitizer) improves the color development sensitivity of the heat-sensitive color developing layer is not fully clear, but this compound has a low viscosity in a molten state and a dye precursor. It is presumed that the compatibility with the body and the developer is part of the reason. Further, the reason why the whiteness of the thermosensitive coloring layer is not lowered is that it is hardly soluble in water, and it is its low sublimation property that the phenomenon that deteriorates the recorded image quality such as whitening is extremely small. it is conceivable that. However, the inventor does not stick to this interpretation. The following can be mentioned as specific examples of the sensitizer of the formula (I) used in the present invention.

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

The sensitizers of formula (I) are used with dye precursors and developers. Further, it may be used in combination with other sensitizers within a range that does not impair the desired effects of the present invention. The amount of the sensitizer used in the present invention is 10 to 10 relative to the weight of the color developer.
It is preferably 00% by weight, more preferably 50 to 300% by weight.

The heat-sensitive color forming layer containing the sensitizer of the present invention mainly comprises a dye precursor, a color developer consisting of a phenol or an organic acid, and a binder for bonding these to bond the heat-sensitive color developing layer to a sheet-like substrate. It preferably contains a binder and further contains an inorganic pigment, and may further contain waxes if necessary.

The leuco dye used as the dye precursor can be selected from conventionally known ones, for example, 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-toluidino) -6-methyl-7-anilinofluorane, 3-
Pyrrolidino-6-methyl-7-anilinofluorane, 3
-Dibutylamino-6-methyl-7-anilinofluorane, 3- (N-cyclohexyne-N-methylamino)-
6-methyl-7-anilinofluorane, 3-diethylamino-7- (o-chloroanilino) fluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7
One or more selected from -chlorofluorane, 3-diethylamino-6-methylfluorane, and 3-cyclohexylamino-6-chlorofluorane can be used.

As a color developer consisting of phenols or organic acids,
Conventionally known compounds can be used. For example, bisphenol A and benzyl p-hydroxybenzoate (JP-A-52)
-140483), bisphenol S, 4-hydroxy-
4'-isopropyloxydiphenyl sulfone
60-13852), 1,1-di (4-hydroxyphenyl) cyclohexane, and 1,7-di (hydroxyphenylthio) -3,5-dioxaheptane (JP-A-59-52694). One or more of them can be used.

Here, as other sensitizers 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. This is as explained with a specific example.

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

Further, the thermosensitive coloring layer of the present invention may contain various waxes as required. Known waxes such as paraffin, amide wax, bisimide wax, and metal salt of higher fatty acid can be used as these waxes. Further, regarding the adhesive, polyvinyl alcohol, starch and derivatives thereof having various molecular weights, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester Polymers, acrylic acid amides / acrylic acid esters / methacrylic acid terpolymers, styrene / maleic anhydride copolymers alkaline salts, polyacrylamides, sodium alginates, gelatin, and water-soluble polymeric materials such as casein, and
Polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylic ester,
For example, latexes of vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, and styrene / butadiene / acrylic copolymer can be used.

The sheet-like substrate used in the thermosensitive recording medium of the present invention includes:
It can be selected from paper, coated paper coated with clay plastic or the like, synthetic paper mainly made of plastic, or plastic film. At least one surface of such a sheet-like substrate is coated with a coating solution containing a mixture of the above-mentioned required components and dried to produce a thermosensitive recording medium. The coating amount is 1 to 10 when the coating liquid layer is dried.
The amount is preferably made in ^{g / m 2, 2~7g / m} 2 is particularly preferred.

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

〔Example〕

The present invention will be specifically described below with reference to examples. still,
Unless otherwise specified, "part" and "%" represent "part by weight" and "% by weight", respectively.

Synthesis Example 1 (α, α′-di (4-methylbenzyloxy))
-Synthesis of p-xylene) 55.2 g of α, α'-dihydro-p-xylene was dissolved in 300 cc of dimethylsulfoxide, 53.8 g of potassium hydroxide was added thereto, and the reaction mixture was heated to 90 ° C. ,
The potassium salt of α, α'-dihydro-p-xylene was prepared by stirring for 2-3 hours. To this salt, 134.9 g of p-methylbenzyl chloride was added dropwise while being careful not to let the temperature of the solution exceed 100 ° C., and the reaction was carried out for 2 hours. After cooling, the reaction solution was poured into cold water to remove water-soluble substances. Ether was added thereto, the reaction product was extracted with ether, and the ether was distilled off to obtain a brown solid. This was recrystallized from ethyl alcohol to obtain 120 g of a white solid. Its melting point is
It was 98 ° C. It was confirmed by mass spectrometry and nuclear magnetic resonance spectroscopy that the solid product was α, α′-di (4-methylbenzyloxy) -p-xylene.

Example 1 A thermosensitive recording paper was prepared by the following operation.

Subjecting the dispersion A prepared INGREDIENT AMOUNT (parts) 3- (N-isopentyl -N- ethylamino) -6-methyl-7-anilinofluoran 20 polyvinyl alcohol 10% solution 10 Water 70 The composition in a sand grinder The powder was pulverized until the average particle size became 1 μm.

Sand dispersion B prepared INGREDIENT AMOUNT (parts) 4,4'-isopropylidene-biphenol 10 alpha,. Alpha .'- di (4-methyl-benzyloxycarbonyl)-p-xylene 10 polyvinyl alcohol 10% solution 10 Water 70 The composition It was subjected to a grinder and pulverized until the average particle size became 1 μm.

Preparation of color forming layer 40 parts of solution A, 160 parts of solution B, calcium carbonate pigment 40
, 20 parts of a 30% paraffin dispersion and 180 parts of a 10% aqueous solution of polyvinyl alcohol were mixed and stirred to obtain a coating liquid. This coating solution was applied 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 back surface of the thermal recording paper obtained as described above was treated with a super calender and the surface smoothness was adjusted to 600-1.
000 seconds. The samples thus obtained were subjected to the following tests to measure the recording sensitivity, the color density of the uncolored portion of the recording layer surface, and the whitening comparison test. The results are shown in Table 1.

(A) Recording sensitivity Using a thermal gradient tester manufactured by Toyo Seiki, temperature 120 ° C, pressure 2.5 kg
The sample was heated for 100 milliseconds under the condition of / cm ² , and the color density at that time was measured by a Macbeth densitometer RD-914. The recording sensitivity of the thermal paper was represented by the measured value. Further, the density of the uncolored part (white paper part) of the recording layer surface was measured by the above densitometer, and the whiteness was expressed by the measured value.

(B) Whitening resistance After the color of the sample was developed at the temperature of 150 ° C by the above tester, the printed portion was left in an environment of 40 ° C and 90% for 24 hours, and the change of the surface was sensory evaluated. In Table 1, "good" means that no change was observed in the color printed portion, and "bad" means that the printed surface became dusty, that is, so-called whitening occurred.

 The test results are shown in Table 1.

Example 2 A thermosensitive recording paper was prepared by the following operation.

Preparation of Pigmented Undercoat Paper 40 parts of styrene-butadiene copolymer emulsion (solid content 50%) and 10% oxidized starch were added to a dispersion obtained by dispersing 85 parts of calcined clay (trade name: Ansilex) in 320 parts of water. 50 parts of the aqueous solution is mixed and the resulting coating solution is weighed.
A pigment-undercoated paper was prepared by coating one surface of a base paper of 48 g / m ² so that the coating amount after drying was 7.0 g / m ² .

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

Using this thermal recording paper, the same test as in Example 1 was conducted.

 The results are shown in Table 1.

Comparative Example 1 The same operation as in Example 1 was performed. However, in the preparation of solution B, stearic acid amide was used instead of α, α′-di (4-methylbenzyloxy) -p-xylene.

 The test results are shown in Table 1.

Comparative Example 2 The same operation as in Example 2 was performed. However, in the preparation of solution B, stearic acid amide was used instead of α, α′-di (4-methylbenzyloxy) -p-xylene.

 The test results are shown in Table 1.

Comparative Example 3 The same operation as in Example 2 was performed. However, in the preparation of solution B, 1-hydroxy-2-naphthoic acid phenyl ester was used instead of α, α′-di (4-methylbenzyloxy) -p-xylene.

 The test results are shown in Table 1.

[Advantages of the Invention] The thermosensitive recording medium of the present invention has a thermosensitive coloring property containing a sensitizer made of a novel heat-fusible material, and thus has excellent high-speed recording suitability, high whiteness, and whitening. It does not induce such an unfavorable phenomenon as described above, has an extremely well balanced property in terms of quality, and has an extremely high practical value.

Claims (1)

(57) [Claims] 1. A sheet-like substrate, a colorless or light-colored dye precursor which is formed on at least one surface of the sheet-like substrate, and a developer which reacts with the dye precursor under heating to develop a color. And a thermosensitive coloring layer containing the thermosensitive coloring layer, wherein the thermosensitive coloring layer has the following general formula (I): (However, in the formula, R ¹ and R ² each independently represent a lower alkyl group, a lower alkoxy group, a nitro group, an aryl group, a halogen atom, or an aralkyl group, or
R ¹ and R ² form a cyclic structure linked to adjacent benzene rings, and m and n each independently represent 0 or an integer of 3 or less. ) A thermosensitive recording medium further containing at least one diether compound represented by