JPH0664331A - Heat-sensitive recording medium - Google Patents

Abstract

PURPOSE:To provide absorption wavelength at a near infrared part and obtain a developed black-color image excellent in sharpness and storage capability by permitting a fatty acid ferric salt and a plurality of phenolic compounds having a hydroxyl group at their respectively specified positions to be contained in a heat-sensitive color forming layer formed on a base material. CONSTITUTION:A heat-sensitive recording medium has a heat-sensitive color forming layer formed on the upper face of a base material. In this case, the heat-sensitive color forming layer contains a fatty acid ferric salt, a phenolic compound (A) having hydroxyl groups in at least 3- and 4-positions, and a phenolic compound (B) having hydroxyl groups in 2- and 4-positions only. The phenolic compound (A) is composed of a gallic acid ester, a 3,4-dihydroxybenzoic acid ester or a 3,4-dihydroxy-4-methyldiphenyl sulfone, or a mixture thereof. Further, the phenolic compound (B) is composed of a 2,4-dihyroxybenzophenone or a 2,4-dihydroxybenzoic acid ester, or a mixture thereof.

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 to be subjected to heat recording, and has a black colored image which has an absorption region in the near infrared region and is clear and has excellent storage stability. Provided is a thermosensitive recording medium to be recorded.

[0002]

2. Description of the Related Art A thermosensitive recording medium generally comprises a substrate and a thermosensitive coloring layer formed on the substrate, and is an electron-donating, usually colorless or light-colored leuco compound and an electron-accepting layer which develops the leuco compound. The thermosensitive coloring layer mainly composed of the above-mentioned color developing agent (generally called a dye-based thermosensitive coloring layer) is used, and the leuco compound in the thermosensitive coloring layer can be obtained by heating with a thermal head, a heating pen, a laser beam or the like. And the developer react instantaneously to form a color image (for example, Japanese Patent Publication No. 43-4).
No. 160, Japanese Patent Publication No. 45-14039, etc.).

In such a thermosensitive recording medium, a color-developed image can be obtained by a relatively simple device, and the maintenance is easy.
Further, since it has an advantage that it does not generate noise, it is used in a wide range of fields such as measuring recorders, facsimiles, printers, computer terminals, labels, and automatic ticket vending machines such as tickets.

In particular, heat-sensitive recording labels are used in applications requiring a sticking process after printing, such as bar code labels for POS (point-of-sale information management) systems, price display labels, and shipping / shipping labels. It is widely used in large-scale mass retailers such as supermarkets and department stores, as well as specialty stores and restaurants that are developing chains. This POS system is for collecting and analyzing the sales information of products in order to clearly understand the needs of consumers and establish a rational management strategy, and one of them is the products sold in stores. A method of optically reading a bar code or an OCR character displayed on the screen with a scanner is rapidly spreading.

At present, various printing methods have been tried for labels for POS systems. Among them, the heat-sensitive recording method using a heat-sensitive recording material, in particular, the printing method is chemical or physical of a substance by heating. An image is formed by utilizing changes, does not require fixing of development, and
It has various merits such as no need to replenish printing ink. Further, the heat-sensitive recording system has advantages that the machine can be downsized, simplified, and the recording speed can be increased, and that there is no stain on the hands or products due to ink, or ink is not scratched.

On the other hand, for reading a bar code or the like of a color-developed image obtained by the thermal recording system, a wavelength of 633n has been conventionally used.
He.Ne laser light having m red light has been used, and recently, semiconductor lasers have come to be used. It can be directly modulated by current, can be miniaturized, is easy to use, low cost, and has an oscillation wavelength of 700 ~ 15.
Since it is located in the near-infrared region of 00 nm, it has the advantage that there are few malfunctions due to dirt, and it is beginning to be widely used. Therefore, also in the field of heat-sensitive recording labels, there is a demand for a heat-sensitive recording material of the type capable of obtaining a color image readable by a semiconductor laser.

However, a heat-sensitive recording material having a two-component heat-sensitive color developing layer containing a leuco compound and a color developer, which have been conventionally used, has a long wavelength absorption wavelength of a color image even in a black color developing system. That is, since the absorption wavelength is in the range of 550 to 620 nm, it is possible to read with a He / Ne laser beam, but it is not possible to read with a semiconductor laser having a near infrared wavelength.

On the other hand, one or both of the components in the thermosensitive color developing layer utilizes a mechanism in which one or both of the components melts and reacts to form a chelate compound to develop a color, and one of an organic acid heavy metal salt or an organic acid noble metal salt is used. A color-developing system is known in which a component is combined with the other component consisting of one of an organic reducing agent, a sulfur compound and an amino compound. In most of such color-developing systems, a color-developed image having an absorption wavelength in the near infrared region can be obtained. For example, there is a thermosensitive color-developing layer of a color-developing system composed of a combination of long-chain fatty acid iron salt and polyhydric phenol.

However, in the conventional thermosensitive recording medium which utilizes the coloring mechanism associated with the formation of this type of chelate compound,
The combination of a long-chain fatty acid iron salt and a polyhydric phenol has the drawbacks that the hue of the resulting color image is red to purple and that background fog is likely to occur. It should be noted that the fact that the hue of the color-developed image of the thermosensitive color-developing layer is red to purple has a difficulty in visual reading compared to the black color-developed image.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides a thermosensitive recording medium which has a white background and has an absorption wavelength in the near infrared region, and which can obtain a clear black colored image having good storage performance. To do.

[0011]

According to the present invention, a thermosensitive coloring layer on a substrate is composed of a ferric acid fatty acid salt, a phenolic compound having a hydroxyl group at at least the 3rd and 4th positions, and 2nd and 4th positions only. By forming a coating material containing a phenolic compound having a hydroxyl group, a heat-sensitive recording material that achieves the above-mentioned object is obtained.

The present inventors have examined a color-developing system by combining a ferric acid fatty acid salt and a polyhydric phenol, and found that a ferric fatty acid salt and a phenolic compound having a hydroxyl group at least at the 3- and 4-positions are used. In the case of the color-developing system by the combination, a color-developed image having a high density and an absorption wavelength in the near-ultraviolet region was obtained, and it was confirmed that the hue of this color-developed image was purple and the background fogging was likely to occur.

Further, in the case of a color-developing system in which a fatty acid ferric iron salt is combined with a phenolic compound having a hydroxyl group only at the 2- and 4-positions, although the background fog is unlikely to occur, a concentration of a red to brown hue is obtained. It was confirmed that a light colored image was obtained.

On the basis of these facts, a color image in the thermosensitive coloring layer is obtained by combining a fatty acid ferric iron salt and a phenolic compound having a hydroxyl group at at least the 3rd and 4th positions, and a fatty acid ferric iron salt. By synergizing with a combination of a phenolic compound having a hydroxyl group only at the 2- and 4-positions, the object of the present invention is to obtain a heat-sensitive recording material, that is, there is no background fog and the absorption wavelength in the near infrared region. In addition, it is possible to obtain a clear black colored image which has good storage performance.

The fatty acid ferric iron salt used in the thermosensitive coloring layer of the thermosensitive recording medium of the present invention is a straight chain or branched chain saturated or unsaturated fatty acid having 6 to 25 carbon atoms, preferably 9 to 22 carbon atoms. A ferric salt, for example, stearic acid second
Consists of iron, ferric myristate, ferric behenate, ferric laurate, ferric pelargonate, etc., and ferric salts of saturated fatty acids are particularly preferable.

Phenolic compounds having a hydroxyl group at least at the 3- and 4-positions include, for example, gallic acid esters,
Examples thereof include 3,4-dihydroxybenzoic acid ester and 3,4-dihydroxy-4-methyldiphenyl sulfone, and those listed below or a mixture of two or more thereof can be used.

In the general formula C ₆ H ₂ (OH) ₃ (COOR), a gallic acid ester in which R is an alkyl group having 1 to 28 carbon atoms, a phenyl group or a benzyl group and derivatives thereof, for example, methyl gallate, Propyl gallate, octyl gallate, lauryl gallate, cetyl gallate, stearyl gallate, behenyl gallate, etc., 3,
4-dihydroxybenzoic acid butyl ester, 3,4-dihydroxybenzoic acid benzyl ester, 3,4-dihydroxybenzoic acid-β-phenylethyl ester, 3,4
-Dihydroxy-5-chlorobenzoic acid benzyl ester, 3,4-dihydroxybenzoic acid-α-phenylethyl ester, 3,4-dihydroxy-4-methyldiphenyl sulfone,

The phenolic compound having a hydroxyl group only at the 2- and 4-positions is, for example, 2,4-dihydroxybenzophenone, 2,4-dihydroxybenzoic acid ester, etc., and those listed below or those 2 Mixtures of more than one species can be utilized. 2,4-dihydroxybenzoic acid propyl ester, 2,4-dihydroxybenzoic acid butyl ester, 2,4-dihydroxybenzoic acid cyclohexyl ester, 2,4-dihydroxybenzoic acid benzyl ester 2,4-dihydroxybenzoic acid-p-methyl ester Benzyl ester 2,4-dihydroxybenzoic acid-p
-Chlorobenzyl ester 2,4-dihydroxybenzoic acid-α-phenylethyl ester, 2,4-dihydroxybenzoic acid-β-phenylethyl ester, 2,4-dihydroxy-6-methylbenzoic acid ethyl ester, 2,
4-Dihydroxy-6-methylbenzoic acid propyl ester, 2,4-dihydroxy-6-isopropylbenzoic acid ethyl ester, 2,4-dihydroxy-6-pentylbenzoic acid ethyl ester, 2,4-dihydroxy-6-
Methoxybenzoic acid butyl ester, 2,4-dihydroxy-6-methylbenzoic acid cyclohexyl ester, 2,
4-Dihydroxy-6-methylbenzoic acid benzyl ester, 2,4-dihydroxy-6-propylbenzoic acid p-
Chlorobenzyl ester, 2,4-dihydroxy-6-
Methoxybenzoic acid p-methylbenzyl ester, 2,4
-Dihydroxy-6-methylbenzoic acid p-isopropylbenzyl ester, 2,4-dihydroxy-6-methylbenzoic acid p-methylphenoxyethyl ester, 2,4
-Dihydroxy-5-chlorobenzoic acid-p-chlorobenzyl ester, 2,4-dihydroxybenzophenone,

Ferric acid fatty acid salt and at least the 3rd and 4th positions
A phenolic compound having a hydroxyl group at the 2-position and 2- and 4-positions
In the thermosensitive coloring layer containing a phenolic compound having a hydroxyl group only at the position, when the amount of the fatty acid ferric salt is small, the storage property of the color image and the absorption property in the near infrared region are deteriorated, and conversely, the fatty acid If the amount of diiron salt is too large, the background density becomes high and the color image lacks sharpness. For this reason,
Usually, the total amount of the phenolic compound having hydroxyl groups at at least the 3rd and 4th positions and the phenolic compound having hydroxyl groups at only the 2nd and 4th positions is 50 with respect to 100 parts by weight of the ferric acid fatty acid salt. It is preferable to mix them in a mixing ratio of about 500 parts by weight.

Further, between the phenolic compound having a hydroxyl group at least at the 3rd and 4th positions and the phenolic compound having a hydroxyl group at only the 2nd and 4th positions, at least 3
If the amount of the phenolic compound having hydroxyl groups at the 4th and 4th positions is too small, the density of the color image obtained may decrease, and if too large, background fog tends to occur. Therefore, the phenolic compound having a hydroxyl group at least at the 3rd and 4th positions and the phenolic compound having a hydroxyl group at only the 2nd and 4th positions are 80 to 20% by weight: 20 to 80% by weight.
It is preferable to mix them in a mixing ratio of wt%.

Next, the main components of the optional components other than the above components used in the thermosensitive coloring layer of the thermosensitive recording medium of the present invention will be specifically described below.

As the water-soluble binder, starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer. Water-soluble binders such as styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, and latex-based water-soluble binders such as methyl acrylate-butadiene copolymers are used.

As the pigment, diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, urea-formalin resin and the like are used.

Further, for the purpose of preventing head wear and sticking, higher fatty acid metal salts such as zinc stearate and calcium stearate, waxes such as paraffin, oxidized paraffin, polyethylene, polyethylene oxide, stearic acid amide and castor wax are used. ,Also,
Various oxalic acids such as metatarphenyl, parabenzylbisphenyl, esters of hydroxynaphthoic acid, stearic acid amide, tribenzylamine, naphthalene derivative, dibenzyl terephthalate, dibenzyl oxalate, bis (paramethylbenzyl oxalate), etc. Esters and the like are used.

Furthermore, a dispersant such as sodium dioctylsulfosuccinate, a UV absorber such as a benzophenone type or a benzotriazole type, a surfactant, a fluorescent dye and the like are used as desired.

Further, a conventionally known dye-based heat-sensitive color former may be added for the purpose of further increasing the density of the color image.

Paper is mainly used as the substrate in the thermosensitive recording medium of the present invention, but various non-woven fabrics, plastic films, synthetic papers, metal foils, etc., or composite sheets combining these are optionally used. .

The thermal recording material of the present invention having the above-mentioned constitution is generally used for ordinary facsimiles, printers and other special applications for detecting near-infrared light, and particularly has high storability of color images. If desired, it is preferable to protect the uncolored portion and the colored image portion from the external environment by forming a protective layer covering the thermosensitive coloring layer. In addition,
As the main component of the protective layer, various water-soluble resins, latex, ionizing radiation curable resin by ultraviolet rays or electron beams, etc. are used, and further, if necessary, pigments, water resistant agents, water repellents, defoamers. Agents, ultraviolet absorbers and the like can be added.

The heat-sensitive recording material of the present invention is manufactured by substantially the same manufacturing method as that of the conventional dye-based heat-sensitive recording material. In particular,
A method of using a water-based coating agent obtained by separately pulverizing and dispersing each of the ferric fatty acid ferric salt and the phenolic compound separately in a water system using a sand grinder, attritor, or ball mill, or A method using a water-based coating agent obtained by microcapsulating either a ferric acid fatty acid salt or a phenolic compound.

[0030]

The heat-sensitive recording material of the present invention can obtain a black image whose color image can be read by a semiconductor laser beam containing near-infrared light and which has an excellent function in color development and storability. To be

[0031]

EXAMPLES The specific constitution of the thermosensitive recording medium of the present invention will be explained based on examples.

Example 1 Solution A and solution B having the following compositions were separately dispersed by a sand grinder.

Liquid A Ferric stearate (ferric fatty acid ferric salt): 10 parts by weight Light calcium carbonate: 20 parts by weight Polyvinyl alcohol 12% by weight aqueous solution ... 40 parts by weight Water ... ........................................ 50 parts by weight

Liquid B Stearyl gallate (a phenolic compound having a hydroxyl group at least at the 3- and 4-positions) ... 20 parts by weight 2,4-dihydroxybenzoic acid benzyl ester (phenolic compound having a hydroxyl group only at the 2- and 4-positions) 20 parts by weight light calcium carbonate 20 parts by weight 12% by weight aqueous solution of polyvinyl alcohol ... 70 parts by weight water ... 70 parts by weight

Next, 120 parts by weight of solution A, 200 parts by weight of solution B and 50 parts by weight of a 12% by weight aqueous solution of polyvinyl alcohol were mixed and stirred to prepare an aqueous coating solution for the thermosensitive color developing layer.

Then, the coating solution for the thermosensitive coloring layer was added to 5
0 g / m ² of the substrate on the coating weight 7g made of woodfree paper (dr
A thermosensitive recording material having a thermosensitive color developing layer having a Beck smoothness of 500 seconds was obtained by applying the composition at a ratio of y) / m ² , followed by drying and calendering.

Examples 2 to 5 A fatty acid ferric iron salt in solution A of the aqueous coating solution for the thermosensitive color developing layer used in Example 1 and a phenolic compound having a hydroxyl group at at least the 3rd and 4th positions in solution B were used. As a phenolic compound having a hydroxyl group only at the 2- and 4-positions,
Each of the liquids listed in the predetermined column of [Table 1] was used, and for the other components, liquids having the same compositional components as those of the liquids A and B used in Example 1 were prepared. A coating solution formulated in the same manner as in the corresponding step of Example 1 was applied in the same manner as in the corresponding step of Example 1 to obtain each thermosensitive recording material having a thermosensitive color developing layer having a Bekk smoothness of 500 seconds. Obtained. () In each column of [Table 1]
The numbers inside are parts by weight.

[0038]

[Table 1]

Comparative Examples 1 to 2 As the fatty acid ferric iron salt in the solution A and the phenolic compound in the solution B of the coating solution for the thermosensitive color developing layer used in Example 1, the compounds are displayed in the predetermined columns of [Table 2]. The ingredients used in Example 1 were used for the other ingredients.
Using each liquid having the same composition components as the liquid and the liquid B, a coating liquid formulated in the same manner as in the corresponding step of Example 1 was applied in the same manner as in the corresponding step of Example 1. A thermosensitive recording material having a thermosensitive coloring layer having a Bekk smoothness of 500 seconds was obtained. The numbers in each column of [Table 2] indicate parts by weight.

[0040]

[Table 2]

Evaluation The thermal recording materials obtained in Examples 1 to 5 and Comparative Examples 1 to 2 were evaluated in the following (1) to (5). The results are shown in [Table 3]. (1) Background density The optical density of the background was measured using Macbeth RD918. (2) Color density Print with label printer XP6250 (manufactured by Nisshinbo),
The optical density of the color image was measured using Macbeth RD918. (3) Image storability A color image was stored for 1 week in an environment of 50 ° C. and 90%, and the optical density was measured using Macbeth RD918. (4) Near-infrared light reading When the reflectance spectrum value at 780 nm is 30% or less, it is possible to read with a GaAs semiconductor laser (780 nm), so the reflectance spectrum value at 780 nm in the color development part When is less than 30% ...
◯, when more than 30% was indicated by ... ×.
The reflection spectrum of the color-developing part was measured by a measuring method using an integrating sphere using a self-recording spectrophotometer U-3400 manufactured by Hitachi, Ltd. (5) Hue The hue of the developed image was visually determined.

[0042]

[Table 3]

[0043]

[Effect] The thermosensitive recording medium of the present invention has an absorption region in the near infrared region and is capable of recording a black colored image which is clear and has excellent storage stability. It is readable and has extremely high practical value as a thermal recording material in the field of thermal recording labels and the like, and has a high utility value.

Claims (3)

[Claims] 1. A thermosensitive color forming layer formed on a substrate, a ferric acid salt of fatty acid, a phenolic compound having a hydroxyl group at least at the 3rd and 4th positions, and a phenol having a hydroxyl group at only the 2nd and 4th positions. A heat-sensitive recording material containing a thermosensitive compound. 2. A phenolic compound having a hydroxyl group at at least the 3- and 4-positions is a gallic acid ester, 3,4.
A thermosensitive recording medium according to claim 1, which comprises a dihydroxybenzoic acid ester, 3,4-dihydroxy-4-methyldiphenyl sulfone, or a mixture thereof. 3. The phenolic compound having a hydroxyl group only at the 2- and 4-positions comprises 2,4-dihydroxybenzophenone, 2,4-dihydroxybenzoic acid ester or a mixture thereof. Thermal recording material.