JPH0911629A - Thermal recording medium - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a thermal recording material having excellent color development sensitivity, no background fog, and excellent image storage stability and chemical resistance. A thermosensitive recording medium comprising a support and a thermosensitive recording layer containing an electron-donating colorless or light-colored leuco compound, a fatty acid ferric iron salt and 4-hydroxysalicylanilide, wherein the fatty acid ferric iron salt is emulsified. It is refined by the dispersion method and its average particle size is 0.05 μm to 1.5 μm.
-Diffraction angle in X-ray diffraction analysis curve with Kα ray (2
θ) The ratio (H / H) of the height (H) of the main peak and the half width at half maximum (W) within the range of 21.8 ± 0.5 degrees.
W) is 10 or more, and has a main endothermic peak in a differential thermal analysis curve at 100 ° C. or more, and a thermosensitive recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having excellent color development sensitivity, no background fogging, and excellent image storage stability and chemical resistance.

[0002]

2. Description of the Related Art A thermosensitive recording medium has a support and a thermosensitive coloring layer formed on the support. Various types of thermosensitive coloring layers are used, and a typical one is a leuco dye type.

The leuco dye-type thermosensitive coloring layer contains, as main components, an electron-donating colorless or pale-colored leuco compound and an electron-accepting color developing agent for coloring the leuco compound. Thermal recording is performed by heating with a thermal head, a thermal pen, laser light, etc., and a method of forming a recorded image by instantly reacting the leuco compound in the thermosensitive coloring layer with the developer (For example, Japanese Patent Publication No. 43-4160, Japanese Patent Publication No. 45-14039, etc.). Hereinafter, this coloring system is referred to as a leuco dye type.

The heat-sensitive recording material used for heat-sensitive recording is not limited to the case of the above-mentioned leuco dye-type heat-sensitive color developing layer, but generally, a recorded image can be obtained by a relatively simple apparatus and maintenance is easy. Also, it has an advantage that no noise is generated during operation. For example, a recorder for measurement,
It is used in a wide range of fields such as facsimiles, printers, computer terminals, labels, and automatic ticket vending machines such as tickets for transportation.

However, the leuco dye type thermosensitive coloring layer has a drawback that its coloring mechanism is essentially reversible, so that the image is discolored when exposed to various environments or when it is exposed to a specific chemical. There is.

On the other hand, as a thermosensitive recording medium utilizing a mechanism in which one or both of the components in the thermosensitive coloring layer are melted and reacted to form a chelate compound, a long-chain fatty acid ferric salt and a polyvalent salt are used as a thermosensitive recording medium. A color-developing system in combination with phenol has been disclosed (JP-A-48-27738). Polyhydric phenol is a typical chelating agent that reacts with a fatty acid metal salt to form a chelate compound and develops a color. The image obtained by color development of the ferric salt of long-chain fatty acid and the chelating agent has good storage stability and chemical resistance. Hereinafter, this coloring system is referred to as a chelate compound type.

However, in the thermosensitive recording medium which utilizes the coloring mechanism associated with the formation of this kind of chelate compound, the long-chain fatty acid ferric salt used is colored so that the background is flesh-colored and the coloring sensitivity is poor. There is.

[0008] Proposals have been made for compensating for the drawbacks of the leuco dye type and the chelate compound type to obtain a more excellent recording material, but none is satisfactory.

For example, there is a proposal that both are mixed in the same layer (JP-A-57-176196).
Although the drawbacks of both can be compensated for, the phenolic substance used for the leuco dye type and the polyhydric phenol used for the chelate compound type have a melting point drop, and the leuco dye is likely to develop color, so that background fogging is likely to occur, which is extremely important. There are drawbacks.

In order to improve this drawback, there is also a proposal that the same phenolic substance as the chelate compound type is used for the phenolic substance used for the leuco dye type (Japanese Patent Laid-Open No. 62-105688). Although there are certainly polyhydric phenols that have a coloring effect on both leuco dyes and fatty acid metal salts, no polyhydric phenol has been found that can develop both in a well-balanced color and does not cause background fog.

4-Hydroxysalicylanilide has been proposed as a compound having both the properties of an electron-accepting color developer that develops a leuco compound and a chelating agent that develops a fatty acid metal salt (Japanese Patent Laid-Open No. 4-42). 1646
No. 87). Certainly, with this method, it is possible to color both the leuco dye and the fatty acid metal salt without causing background fog, but the disadvantage is that the chelate coloring of the fatty acid metal salt is inferior to that of the leuco dye. There was a desire to find a more effective method.

[0012]

On the other hand, the present invention takes advantage of the characteristics of these leuco dye type and chelate compound type, and has excellent color development sensitivity, no background fog, and image storage stability and chemical resistance. Another object of the present invention is to provide a heat-sensitive recording material having excellent properties.

[0013]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a leuco compound on a support is finely divided by an emulsion dispersion method and the average particle size thereof is 0.
05 μm to 1.5 μm, and the diffraction angle (2θ) in the X-ray diffraction analysis curve with Cu-Kα rays was 21.8 ± 0.
The ratio (H / W) of the height (H) of the main peak and the peak half width (W) existing within the range of 5 degrees is 10 or more, and the main endothermic peak in the differential thermal analysis curve is 100 ° C. By using each of the fatty acid ferric iron salt and 4-hydroxysalicylanilide, which have the above, it has excellent color development sensitivity, no background fog, and excellent storage stability and chemical resistance of images. A thermosensitive recording medium could be obtained.

4-Hydroxysalicylanilide has a coloring effect with both the leuco compound and the ferric iron salt of fatty acid, and by producing a coloring effect with the leuco compound, highly sensitive coloring can be obtained. By causing the action, color development excellent in storage stability and chemical resistance of the image can be obtained, so that a thermosensitive recording medium can be obtained in which the characteristics of the leuco dye type and the chelate compound type are utilized.

The height (H) and the peak half width (W) of the main peak existing within the range of the diffraction angle (2θ) of 21.8 ± 0.5 degrees in the X-ray diffraction analysis curve with Cu-Kα ray. The fatty acid ferric iron salt having a ratio (H / W) of 10 or more and having a main endothermic peak in the differential thermal analysis curve at 100 ° C. or higher has high crystallinity, and thus a chelate with less background fogging. Coloring is obtained, but the crystallinity decreases when a method such as a sand grinder, an attritor, or a ball mill is used to make it finer by mechanical impact. However, if the emulsification dispersion method is used for micronization, the micronization can be performed without lowering the crystallinity, the background fog is less, and the chelate coloration excellent in color development sensitivity can be obtained.

For the X-ray diffraction analysis of the ferric fatty acid ferric salt with Cu-Kα radiation, an applied voltage of 35 KV, an applied current of 25 mA FULL RANGE 8000 cps TIME CONST 1 sec was used by using a 2027 type X-ray diffractometer manufactured by Rigaku Corporation. 2θ 1 ° / min. The chart speed was 1 cm / min.

Further, the differential thermal analysis of the ferric acid fatty acid salt was carried out using a DSC 210 type differential scanning calorimeter manufactured by Seiko Denshi Kogyo Co., Ltd. at a heating rate of 10 ° C./min. The temperature range was from 30 to 160 ° C.

Unless otherwise specified, "average particle diameter" in the text means "median diameter" obtained by a laser diffraction / scattering particle size distribution analyzer [LA910] manufactured by Horiba Ltd. The fatty acid ferric acid salt can obtain chelate coloration excellent in color development sensitivity by reducing the average particle size to 1.5 μm or less. At this time, if the emulsification dispersion method is used, fineness can be achieved without lowering the crystallinity. Fatty acid second
It is difficult to set the average particle size of the iron salt to 0.05 μm or less even if the emulsification dispersion method is used, and the average particle size is set to 0.
Even if it is less than 05 μm, the color development sensitivity is not improved so much, and the background fog is rather deteriorated, which is not preferable.

The emulsification and dispersion method referred to here is that water and ferric fatty acid ferric salt are heated under pressure, the ferric fatty acid ferric salt is once melted, and this mixture is stirred with high speed stirring such as with a homomixer. Suspension in which the ferric fatty acid ferric salt is solidified with water as the dispersion medium and the disperse phase is the ferric acid ferric salt as a dispersion medium. Make (solid / liquid dispersion system). The particle size and crystallinity of the ferric acid fatty acid salt are determined by the dispersant used at this time, the stirring method, the quenching method, the heating conditions, and the pressurizing conditions.

In the thermosensitive recording medium of the present invention, the fatty acid ferric iron salt used in the thermosensitive coloring layer has a diffraction angle (2θ) of 21.8 ± 0.
The ratio (H / W) of the height (H) of the main peak and the peak half width (W) existing within the range of 5 degrees is 10 or more, and the main endothermic peak in the differential thermal analysis curve is 100 ° C. It is necessary to have the above, and as the fatty acid ferric iron salt falling within the range of these values, the carbon number is 6 to 2
5, preferably 9 to 22 linear or branched saturated or unsaturated ferric salts of fatty acids, more specifically, ferric stearate, ferric myristate. , Ferric behenic acid, ferric lauric acid, ferric pelargonic acid, and the like. A fatty acid ferric salt having less than 6 carbon atoms has a too low melting point, so that when they are used in the thermosensitive color developing layer, background fogging occurs. On the contrary, a fatty acid ferric salt having more than 25 carbon atoms has a too high melting point, so that the color developing sensitivity is lowered.

As the leuco compound contained in the heat-sensitive recording layer in the heat-sensitive recording material of the present invention, those used in conventional heat-sensitive recording materials are used. Specifically, (1) triarylmethane compounds such as 3 , 3-bis (p-dimethylaminophenyl)
-6-Dimethylaminophthalide (Crystal Violet Lactone), 3- (p-Dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl)
Phthalide, 3- (p-dimethylaminophenyl) -3-
(2-Phenylindol-3-yl) phthalide, 3,
3-bis (p-ethylcarbazol-3-yl) -3-
Dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -5-dimethylaminophthalide, etc .;

(2) Diphenylmethane compound For example, 4,4-bis-dimethylaminobenzhydrin benzyl ether, N-halophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine and the like;

(3) Xanthene compound For example, rhodamine B-anilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-butylaminofluorane, 3-diethylamino-7- (2- Chloroanilino) fluoran, 3
-Diethylamino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-anilinofluorane, 3-cyclohexyl- Methylamino-6-methyl-7-anilinofluorane,

3-diethylamino-6-chloro-7-
(Β-Ethoxyethyl) aminofluorane, 3-diethylamino-6-chloro-7- (γ-chloropropyl) aminofluorane, 3-diethylamino-6-chloro-7
-Anilinofluorane, 3-N-cyclohexyl-N-
Methylamino-6-methyl-7-anilinofluorane,
3-diethylamino-7-phenylfluorane, 3-
(N-isoamyl-N-ethylamino) -6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane and the like;

(4) Thiazine-based compounds For example, benzoyl leuco methylene blue, p-nitrobenzoyl leuco methylene blue and the like;

(5) Spiro compounds For example, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-benzyl-spiro-dinaphthopyran, 3-methylnaphtho- (3-methoxy-benzo) -spiropyran and the like; Furthermore, a mixture of these is used and is selected based on the properties desired depending on the application of the thermosensitive recording medium.

The mixing ratio of the leuco dye and the ferric acid fatty acid salt is generally 1: 9 to 9: 1 by weight, preferably 2: 8.
~ 8: 2.

In the present invention, the addition amount of 4-hydroxysalicylanilide used as a color developer and a chelating agent is such that the total weight of the leuco dye and the fatty acid ferric salt is 10
It is generally 50 to 500 parts by weight, preferably 70 to 400 parts by weight, and most preferably 1 to 0 parts by weight.
It is from 00 to 300 parts by weight.

The water-soluble or water-dispersible binder used for forming the thermosensitive coloring layer is various starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, styrene-anhydrous. Water-soluble binders such as maleic acid copolymers and ethylene-maleic anhydride copolymers, and styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic ester-butadiene copolymers, etc. A binder can be used.

The amount of the binder to be added is the solid component 1 other than that.
It is sufficient to use 5 to 50 parts by weight with respect to 00 parts by weight.

It is necessary to add a pigment to the coating solution for forming the thermosensitive coloring layer in order to prevent sticking and to prevent the melt from adhering to the thermal head. As the pigment, diatomaceous earth, clay, calcined clay, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, alumina, aluminum hydroxide, inorganic pigments such as synthetic aluminum silicate, Organic pigments such as polystyrene, polymethacrylic acid ester, urea resin and urea-formalin resin are used.

Further, for the purpose of preventing head wear and stacking, higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, oxidized paraffin, polyethylene, oxidized polyethylene, stearic acid amide and castor wax are used. ,Also,
Various oxalate esters such as metaterphenyl, parabenzylbisphenyl, esters of hydroxynaphthoic acid, stearic acid amide, tribenzylamine, naphthalene derivative, dibenzyl terephthalate, dibenzyl oxalate, bis (paramethylbenzyl oxalate), etc. Etc. can be used.

Further, a dispersant such as sodium dioctylsulfosuccinate, a surfactant, a fluorescent dye and the like are used as desired.

As the support in the heat-sensitive recording material of the present invention, high quality paper, recycled paper, single-glossy paper, oil resistant paper, coated paper, art paper, cast coated paper, lightly coated paper, resin laminated paper, polyolefin-based synthetic Paper, synthetic fiber paper, synthetic resin film, various non-woven fabrics, plastic films, metal foils, etc., or composite sheets combining these can be used as appropriate.

A conventionally known undercoating layer containing an inorganic or organic pigment may be provided between the support and the thermosensitive recording layer, and a conventionally known protective layer may be provided on the thermosensitive recording layer.

As a method for preparing a coating solution for forming a heat-sensitive recording layer, a fatty acid ferric salt is dispersed by an emulsion dispersion method, and other substances are wet-dispersed by a side grinder, an atlanter, a ball mill or the like. It is adjusted by dispersing the substances to be used with a machine and mixing them.

The method for forming the thermosensitive recording layer on the support is as follows:
Known coating machines such as an air knife coater, various blade coaters, roll coaters, curtain coaters and bar coaters can be used, and the coating amount of the heat-sensitive recording layer is not particularly limited, but generally ² to 12 g / m ^{2 in} dry weight. It is preferably coated in the range of about 3 to 10 g / m ² . Smoothing with a super calendar after coating is also effective in improving image quality.

[0038]

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples. In the examples, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively, unless otherwise specified.

Example 1 Preparation of Liquid A Ferric acid fatty acid 10 parts by weight Surfactant 0.5 parts Water 40 parts A dispersion having an average particle diameter of 0.2 μm was prepared from this composition by an emulsion dispersion method. Liquid B Preparation 3-dibutylamino-6-methyl-7-anilinofluorane 10 parts 20% polyvinyl alcohol (Kuraray Poval 105, Kuraray Co., Ltd.) 10 parts water 20 parts This composition has a mean particle size of 0.8 μm in a sand mill. It was crushed until it became. Liquid C Preparation 4-Hydroxysalicylanilide 10 parts 20% Polyvinyl alcohol (Kuraray Poval 105, manufactured by Kuraray) 10 parts Water 20 parts This composition was ground with a sand mill until the average particle size became 1.0 μm. Liquid D Preparation Metaterphenyl 10 parts 20% Polyvinyl alcohol (Kuraray Poval 105, manufactured by Kuraray) 10 parts Water 20 parts This composition was ground with a sand mill until the average particle size became 1.0 μm. Formation of thermosensitive recording layer In preparation of solution A, fatty acid ferric salt was added with X by Cu-Kα ray
The diffraction angle of the main peak in the line diffraction analysis curve (2
θ) The ratio (H / H) of the height (H) of the main peak and the half width at half maximum (W) within the range of 21.8 ± 0.5 degrees.
W) and the temperature of the main endothermic peak in the differential thermal analysis curve are 21.6 and 118.6 ° C., respectively, and ferric stearate is used.
Parts, C liquid 60 parts, D liquid 60 parts, 20% polyvinyl alcohol (Kuraray Poval 105, manufactured by Kuraray) 60 parts, calcium carbonate 35 parts, 30% zinc stearate dispersion liquid (D
(-523, manufactured by Chukyo Yushi Co., Ltd.) and 100 parts of water were mixed and stirred to obtain a heat-sensitive recording layer coating liquid. 50 g / m of the obtained coating liquid
Coated on ² high-quality paper so that the dry weight is 4 g / m ² ,
Dried.

Example 2 In the preparation of solution A of Example 1, H / W was used instead of ferric stearate having H / W and endothermic peak temperatures of 21.6 and 118.6 ° C., respectively. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that ferric behenic acid having an endothermic peak temperature of 66.3 and 119.7 ° C. was used.

Example 3 In the preparation of solution B of Example 1, 3-dibutylamino-6 was used.
Instead of methyl-7-anilinofluorane, 3-
(N-isoamyl-N-ethylamino) -6-methyl-
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 7-anilinofluorane was used.

Example 4 In the formation of the thermosensitive recording layer of Example 1, 12.5 parts of solution A was used.
Parts and 25 parts of solution B, respectively, were used to obtain a thermosensitive recording medium in the same manner as in Example 1.

Example 5 In the formation of the thermosensitive recording layer of Example 1, the solution A was added to 37.5.
Part, and 8.3 parts of solution B were used, respectively, but in Example 1
In the same manner as in the above, a thermosensitive recording medium was obtained.

Comparative Example 1 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the composition A was prepared by pulverizing the composition by a sand mill until the average particle size became 1.0 μm in the preparation of solution A. Got

Comparative Example 2 A thermosensitive recording medium was prepared in the same manner as in Example 1 except that the composition was pulverized by a sand mill until the average particle size became 0.2 μm in the preparation of the liquid A of Example 1 instead of the emulsion dispersion method. Got

Comparative Example 3 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the solution A was not used and the solution B was used in the amount of 33.3 parts in the formation of the thermosensitive recording layer of the example 1.

Comparative Example 4 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the solution B was not used and the solution A was used in an amount of 50 parts in the formation of the thermosensitive recording layer of the example 1.

Comparative Example 5 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that stearyl gallate was used in place of 4-hydroxysalicylanilide in the preparation of the liquid C of Example 1.

Comparative Example 6 A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 4,4′-isopropylidene bisphenol was used instead of 4-hydroxysalicylanilide in the preparation of the liquid C of Example 1. .

The following 11 evaluations were made on the 11 kinds of thermal recording materials obtained as described above. Coloring Density Using the Nisshinbo Printer XP-6250, the applied pulse was kept constant to develop the color of the thermosensitive recording material, and the color density and background density of the obtained recorded image were measured by a Macbeth densitometer (RD9
14 type, Macbeth Co.). High temperature storage test 60 ° C, 15% R
After being stored in a H atmosphere for 24 hours, the density of the recorded image and the background density of each thermosensitive recording medium were measured by a Macbeth densitometer (RD91
4 type, Macbeth Company). High humidity test 40 ° C, 90% R for thermosensitive recording material with printed color
After being stored in a H atmosphere for 24 hours, the density of the recorded image and the background density of each thermosensitive recording medium were measured by a Macbeth densitometer (RD91
4 type, Macbeth Company). Chemical resistance test (1) Plasticizer test A vinyl chloride wrap film (manufactured by Mitsui Toatsu Kagaku Co., Ltd.) was wound around a paper tube (40 mmφ) in three layers, and the thermosensitive recording material was printed on it and the printed surface was outside. The vinyl chloride wrap film was wrapped in three layers, and the film was stored in a constant temperature bath at 40 ° C. for 24 hours to evaluate the storability of the printed color portion. ○ The printed part is not decolorized and legible. × The printed part is decolorized and unreadable (2) Solvent resistance test Hair liquid (Shiseido, Brabus) is applied to the color-developed part of the thermosensitive recording material that has been color-developed. After coating, the storability of the printed color portion was evaluated. ○ The printed part is not erased and legible. × The printed part is erased and legible.

[0051]

[Table 1]

[0052]

As is clear from the results of Table 1, the thermosensitive recording medium obtained in the present invention has excellent color development sensitivity, no background fog, and excellent storage stability and chemical resistance of images. It was a thermosensitive recording medium.

Claims (1)

[Claims] 1. A thermosensitive recording medium comprising a support and a thermosensitive recording layer containing an electron-donating colorless or pale-colored leuco compound and a fatty acid ferric iron salt and 4-hydroxysalicylanilide. Was finely divided by an emulsion dispersion method, and the average particle diameter thereof was 0.05 μm to 1.5 μm, and the diffraction angle (2θ) in the X-ray diffraction analysis curve by Cu-Kα ray was 21.8 ± 0.5 degrees. The ratio (H / W) of the height (H) of the main peak existing in the range to the peak half width (W) is 10 or more, and the main endothermic peak in the differential thermal analysis curve is 100 ° C or more. A thermal recording material characterized by being