JPH06206377A - Heat sensitive recording body - Google Patents

Abstract

PURPOSE:To provide a heat sensitive recording body which can obtain a clear and color development image having an absorption sphere at a near infrared part and possess properties superior in storage-stability of texture. CONSTITUTION:A color development layer formed on a substrate contains fatty acid ferric salt and a chelate reagent and in the foregoing fatty acid ferric salt, an average particle diameter pulverized by an emulsification scattering method is 0.05 to 1.5mum and a ratio (H/W between a height (H) of a main peak which is in existence within a range of diffraction angle of (2theta) 21.8 + or -0.5 degrees in an X-ray diffraction analysis curve by Cu-Kalpha rays and a half- width (W) of the peak is at least 10. Moreover, this is a heat sensitive recording body comprised of stearic acid ferric salt or behenic acid ferric salt or a mixture of those having a min heat absorption peak in a differential thermal analysis curve at 10 deg.C or higher.

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 in particular, a clear color image having an absorption region in the near infrared region can be obtained, and there is no background fog and the background. To provide a heat-sensitive recording material having excellent storage stability.

[0002]

2. Description of the Related Art A heat-sensitive recording material has a substrate and a heat-sensitive recording layer formed on the substrate. Generally, an electron-donating, usually colorless or pale-colored leuco compound and the leuco compound are used. A heat-sensitive recording layer (generally referred to as a dye-based heat-sensitive recording layer) containing an electron-accepting color developer that develops a color is used.

Thermal recording on this thermal recording medium is performed by a thermal head,
A leuco compound in the heat-sensitive recording layer is caused to react instantaneously with a developer by heating with a hot pen, a laser beam or the like to form a recorded image (for example, Japanese Patent Publication No. S43-43).
-4160, Japanese Patent Publication No. 45-14039, etc.).

The heat-sensitive recording body used for heat-sensitive recording by such a mechanism can obtain a recorded image by a relatively simple device, is easy to maintain, and does not generate noise during operation. Because of its advantages, 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 application fields that require sticking 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 necessary for collecting and analyzing sales information of products in order to clearly grasp the needs of consumers and establish a rational management strategy.
As one of them, a method of optically reading a bar code, an OCR character or the like attached to a product sold at a store with a scanner has been rapidly spread.

At present, various printing methods have been attempted for labels for POS systems. Among them, the thermal recording method utilizing a thermal recording medium is a printing method in which the printing method chemically or physically Since the image is formed by utilizing the change, it has various merits such as no need for steps such as development and fixing, and no need for supplementation of printing ink.

Further, in the heat-sensitive recording system, the size and simplification of the machine and the speed of recording can be achieved, and there is no fear that the fingertips or the products will be stained with ink. It also has the merit of not passing.

By the way, in reading a bar code or the like by a color image obtained by the thermal recording system, a wavelength of 63 is conventionally used.
He / Ne laser light having a red light of 3 nm has been used, but recently, semiconductor laser light has come to be used. This semiconductor laser light can be directly modulated by an electric current, the size of the device can be reduced, it is easy to use and supplied at a low price, and the oscillation wavelength is 700 to 15
Since it is located in the near infrared region of 00 nm, it has started to be widely used because it has advantages such as less malfunction due to dirt.
Therefore, in recent years, there has been an increasing demand for a thermosensitive recording medium from which a color image readable by a semiconductor laser beam can be obtained.

However, a heat-sensitive recording material having a two-component type heat-sensitive recording layer containing a leuco compound and a color developer which has been conventionally used has a wavelength of absorption of a color image even in a black color system. 550 to 620 even on the long wavelength side
Since the wavelength is nm, reading with He / Ne laser light is possible, but reading with semiconductor laser light in the near infrared region having an oscillation wavelength of 700 to 1500 nm is impossible.

On the other hand, one or both of the components in the heat-sensitive recording layer are melted and reacted to form a chelate compound, and a heat-sensitive recording material utilizing a mechanism of developing a color is formed from an organic acid heavy metal salt or an organic acid noble metal salt. With one component,
A coloring system is known which is combined with a chelating reagent which is the other component composed of one of an organic reducing agent, a sulfur compound and an amino compound.
A thermosensitive coloring layer utilizing a coloring system composed of a combination of a fatty acid iron salt and a polyhydric phenol, a combination of a fatty acid iron salt and a dithiocarbamate salt, etc. is known.

However, in the conventional thermosensitive recording medium which utilizes the coloring mechanism associated with the formation of this kind of chelate compound, background fogging is apt to occur in the thermosensitive coloring layer containing the chelating agent, particularly at high temperature or high temperature. When stored in a humid atmosphere, the degree of background fog is severe, which makes it difficult to read a color image.

[0013]

DISCLOSURE OF THE INVENTION The inventors of the present invention have found that the problem of background fogging occurring in the thermosensitive coloring layer depends on the properties of the fatty acid ferric iron salt in the thermosensitive coloring layer. In a coloring mechanism in combination with a chelating agent utilizing one or more ferric fatty acid ferric salt selected from ferric stearate and ferric behenate as a salt, the fatty acid ferric salt may be Cu The ratio (H / W) between the height (H) of the main peak and the peak half width (W) existing within the range of (2θ) 21.8 ± 0.5 degrees in the X-ray diffraction analysis curve at −Kα line. ) “The following ratio (H / W) may be expressed as crystallinity” is 10 or more, and
The main endothermic peak in the differential thermal analysis curve is 100
It has been found that the problem of background fogging occurring in the thermosensitive color developing layer can be improved by using a material having a temperature of at least ° C.

However, it was confirmed by subsequent investigations that the background fogging still occurred in some cases even when such a fatty acid ferric iron salt was used.

[0015]

Means for Solving the Problems The present inventors have found that, as the fatty acid ferric iron salt in the thermosensitive coloring layer, the range of (2θ) 21.8 ± 0.5 degrees in the X-ray diffraction analysis curve with Cu-Kα line. The ratio (H / W) between the height (H) of the main peak and the half-value width (W) of the peak is 10 or more, and the main endothermic peak in the differential thermal analysis curve is 100 ° C.
When the reason for the background fogging of the thermal recording medium which is still generated when the above-mentioned ones are used was examined, the following findings were obtained.

(1) The fatty acid ferric iron salt used in the heat-sensitive recording layer is used by making it fine, and at this time, a method of giving a mechanical impact by a sand grinder, an attritor, a ball mill or the like to make it fine If this is taken, the degree of crystallinity of the ferric acid fatty acid salt will decrease, which will cause background fog. It was completely unexpected that the crystallinity of the ferric fatty acid salt could be easily changed by mechanical impact.

(2) In order to increase the sensitivity of the thermosensitive coloring layer, it is necessary to make the fatty acid ferric iron salt finer. The finer the finely divided fatty acid ferric iron salt, the smaller the sensitivity of the thermosensitive coloring layer. Becomes higher. However, if the fatty acid ferric iron salt is finely divided by a mechanical method, the degree of crystallinity is reduced to some extent.

(3) By solving the contradictory properties in the mechanical dispersion method of further refining the fatty acid ferric salt and maintaining the crystallinity, the thermosensitive color developing layer has high sensitivity and less background fogging. A thermosensitive recording medium can be obtained.

(4) To further refine the fatty acid ferric iron salt and maintain the crystallinity, the fatty acid ferric iron salt is miniaturized by utilizing an emulsion dispersion method without mechanically refining the ferric fatty acid salt. By doing so, the purpose can be achieved.

In the thermosensitive recording medium of the present invention, the thermosensitive coloring layer containing the ferric acid fatty acid salt and the chelating agent is formed on the substrate, and the ferric acid fatty acid salt is prepared by the emulsion dispersion method. The refined volume average particle diameter is 0.05 to 1.5μ
Moreover, the height (H) of the main peak and the peak half-value width (H) that are present 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 ( W) and the ratio (H / W) is 10 or more, and the main endothermic peak in the differential thermal analysis curve is 100 ° C.
It is composed of ferric stearate, ferric behenate, or a mixture thereof.

The X-ray diffraction analysis of ferric stearate and ferric behenate with Cu-Kα radiation was carried out using a 2027 type X-ray diffractometer manufactured by Rigaku Co., Ltd.
・ ・ ・ 35KV, Applied current ・ ・ ・ ・ ・ ・ 25mA, FULL
RANGE ・ ・ ・ ・ ・ ・ 8000 cps, TIME CO
NST ... ・ ・ ・ 1sec, 2θ ・ ・ ・ ・ ・ ・ 1 ° / mi
n. , Chart speed ... 1 cm / min. It was performed under the conditions of.

For the differential thermal analysis of ferric stearate or ferric behenate, a DSC 210 type differential scanning calorimeter manufactured by Seiko Denshi Kogyo Co., Ltd. is used, and the temperature rising rate is ...
.... 10 ° C / min. , Temperature range ... 30-160
It was carried out under the condition of ° C.

Further, the particle size of ferric stearate or ferric behenate is measured by a method such as a microscope method, a Coulter counter method, a precipitation method, a precipitation classification method, a centrifugal sedimentation method or an electromagnetic wave scattering method. obtain.

The emulsified dispersion of ferric stearate or ferric behenate is carried out by heating water and ferric fatty acid under pressure to melt the ferric fatty acid salt, and then mixing this mixture. After stirring with a stirrer capable of high-speed stirring such as a homomixer to once make an emulsion (liquid / liquid dispersion system), this liquid is rapidly cooled to solidify the ferric fatty acid ferric salt and the dispersion medium is water. It is carried out by making a suspension (solid / liquid dispersion system) in which the dispersed phase is a ferric acid fatty acid salt.

The particle size and crystallinity of the ferric acid fatty acid salt are determined by the dispersant, stirring method, quenching method, heating condition and pressurizing condition used at this time.

The ferric stearate or ferric behenate used in the thermosensitive coloring layer of the thermosensitive recording medium of the present invention is
Even before the dispersion step, the height (H) 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 line and the peak half value width ( The ratio (H / W) to W) is preferably 10 or more, and the main endothermic peak in the differential thermal analysis curve is 100 ° C. or more, preferably 110 ° C. or more.

As the chelating agent, for example, gallic acid ester, dihydroxybenzoic acid ester, diphenylcarbazide, diphenylcarbazone, hexamethylenetetramine, spirobenzopyran, 1-formyl-4-phenylsemicarbazide and the like are preferable.

Among these chelating agents, as gallic acid ester and dihydroxybenzoic acid ester, those exemplified below are used.

Gallic acid ester; general formula C ₆ H ₂ (O
H) 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, gallic acid Lauryl, cetyl gallate, stearyl gallate, behenyl gallate, etc.

Dihydroxybenzoic acid ester; (1) 2,4-dihydroxybenzoic acid propyl ester (2) 2,4-dihydroxybenzoic acid butyl ester (3) 2,4-dihydroxybenzoic acid cyclohexyl ester (4) 2,4 -Dihydroxybenzoic acid benzyl ester (5) 2,4-dihydroxybenzoic acid-p-methylbenzyl ester (6) 2,4-dihydroxybenzoic acid-p-chlorobenzyl ester (7) 2,4-dihydroxybenzoic acid-α -Phenylethyl ester (8) 2,4-dihydroxybenzoic acid-β-phenylethyl ester (9) 2,4-dihydroxy-6-methylbenzoic acid ethyl ester (10) 2,4-dihydroxy-6-methylbenzoic acid Propyl ester (11) 2,4-dihydroxy-6-isopropylbenzoic acid ethyl ester (12) 2,4-di Hydroxy-6-pentylbenzoic acid ethyl ester (13) 2,4-dihydroxy-6-methoxybenzoic acid butyl ester (14) 2,4-dihydroxy-6-methylbenzoic acid cyclohexyl ester (15) 2,4-dihydroxy- 6-Methylbenzoic acid benzyl ester (16) 2,4-dihydroxy-6-propylbenzoic acid p
-Chlorobenzyl ester (17) 2,4-dihydroxy-6-methoxybenzoic acid p
-Methylbenzyl ester (18) 2,4-dihydroxy-6-methylbenzoic acid p-
Isopropylbenzyl ester (19) 2,4-dihydroxy-6-methylbenzoic acid p-
Methylphenoxyethyl ester (20) 2,4-dihydroxy-5-chlorobenzoic acid-p
-Chlorobenzyl ester (21) 3,4-dihydroxybenzoic acid butyl ester (22) 3,4-dihydroxybenzoic acid benzyl ester (23) 3,4-dihydroxybenzoic acid-β-phenylethyl ester (24) 3,4 -Dihydroxy-5-chlorobenzoic acid benzyl ester (25) 3,4-dihydroxybenzoic acid-α-phenylethyl ester

Further, as dithiocarbamate,
For example, (1) sodium dibutyldithiocarbamate (2) copper dimethyldithiocarbamate (3) ferric dimethyldithiocarbamate (4) tellurium diethyldithiocarbamate (5) zinc butylxanthogenate (6) zinc dibutyldithiocarbamate (7) N Zinc-ethyl-N-phenyldithiocarbamate (8) Zinc dibenzyldithiocarbamate (9) Zinc N-pentamethylenedithiocarbamate (10) Sodium dimethyldithiocarbamate (11) Sodium diethyldithiocarbamate (12) Pentamethylenedithiocarbamate piperidine salt (13) Pipecolyl dithiocarbamate pipecoline salt (14) Zinc dimethyldithiocarbamate (15) Zinc diethyldithiocarbamate

Next, the main components of the optional components other than the above-mentioned components used in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention will be specifically described.

The water-soluble binder includes 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.

Further, a dispersant such as sodium dioctylsulfosuccinate, an ultraviolet absorber such as a benzophenone type or a benzotriazole type, a surfactant, a fluorescent dye and the like are added as desired.

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 may also be used.

The heat-sensitive recording material of the present invention having the above constitution is
It is also used for ordinary applications such as facsimiles and printers, as well as special applications that detect near-infrared light. Particularly when high storability of the color image is desired, it is preferable to protect the uncolored portion and the color image portion from the external environment by forming a protective layer that covers the thermosensitive recording layer.

As the main component of the protective layer, various water-soluble resins, latexes, ionizing radiation curable resins by ultraviolet rays or electron beams, etc. are used, and further, if necessary, pigments, water-proofing agents, repellants, etc. A water solution, a defoaming agent, an ultraviolet absorber, etc. can be added.

The heat-sensitive recording material of the present invention is manufactured by almost the same manufacturing method as that of the conventional dye-based heat-sensitive recording material except that the method of emulsifying and dispersing the ferric fatty acid salt is adopted. Specifically, the fatty acid ferric iron salt and the phenolic compound are separately dispersed and used, and the fatty acid ferric iron needs to be emulsified and dispersed. The phenolic compound is pulverized and dispersed in a water system using a sand grinder, an attritor, a ball mill or the like.

Thereafter, a water-based coating agent obtained by mixing the two is applied to the substrate, or a microcapsule of a ferric fatty acid salt and a phenolic compound is used. The thermosensitive coloring layer may be formed by applying the obtained water-based coating agent or the like.

[0042]

EXAMPLES The specific constitution of the heat-sensitive recording material of the present invention will be described below based on manufacturing examples, and various characteristics of the heat-sensitive recording material will be described in comparison with the heat-sensitive recording material of the comparative example.

Examples 1 to 4 and Comparative Examples 1 to 7 A liquid having the following composition in which ferric stearate or ferric behenate was used as a fatty acid ferric salt was emulsified and dispersed in Examples. In the comparative example, a sand grinder was used for mechanical dispersion.

The diffraction angle (2θ) of the main peak in the X-ray diffraction analysis curve of Cu-Kα line of the ferric stearate used in solution A was 21.8 degrees, and the height of the main peak ( H) and peak half width (W) (H /
W) is 21.6, the temperature of the main endothermic peak in the differential thermal analysis curve is 118.6 ° C., and the diffraction angle of the main peak in the X-ray diffraction analysis curve by the Cu-Kα line of ferric behenic acid salt. (2θ) is 21.8 degrees, the ratio (H / W) between the height (H) of the main peak and the peak half width (W) at the diffraction angle is 66.3, and the main endotherm in the differential thermal analysis curve The peak temperature is 119.7 ° C.

Similarly, the dispersion of the liquid B having the following composition was carried out by a sand grinder in both the examples and the comparative examples.

Liquid A Ferric acid fatty acid ferric salt ... 0 parts by weight Surfactant ... 5 parts by weight Water ... ..... 40.0 parts by weight

Solution B Stearyl gallate: 40.0 parts by weight Light calcium carbonate・ ・ ・ ・ ・ ・ ・ ・ ・ 40.0 parts by weight Polyvinyl alcohol 12% by weight solution ・ ・ ・··························································・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 100.0 parts by weight

The type of fatty acid ferric iron salt used in the examples and comparative examples, and the diffraction angle (2) of the fatty acid ferric iron salt after liquid A was emulsified or dispersed by a sand grinder.
θ), main peak height (H) and peak half width (W)
The ratio (H / W), the temperature of the main endothermic peak, and the particle size are shown in [Table 1].

[0049]

[Table 1]

Next, 50.5 parts by weight of solution A and solution 270.
0 parts by weight and 12% by weight polyvinyl alcohol solution 50.
0 parts by weight were mixed and stirred to prepare an aqueous coating liquid for the heat-sensitive recording layer.

Then, the coating solution for the heat-sensitive recording layer was added to 5
The substrate on consisting of woodfree paper of 0 g / m ^2, the coating amount 6 g (d
ry) / m ² and then calendered to obtain a thermosensitive recording layer having a thermosensitive recording layer having a Bekk smoothness of 500 seconds. Got the body

[Evaluation] The background density of each of the thermal recording media obtained in Examples 1 to 4 and Comparative Examples 1 to 5 and the preservability of the background density were evaluated by comparing the background density of each thermal recording material before storage with the background density before storage. The thermosensitive recording medium is kept at 40 ° C. and 90% RH for 24 hours at 60 ° C., d
The evaluation was performed by comparing the background density after storage for 24 hours in a ry environment and for 100 hours under irradiation with a 5000 lux fluorescent lamp, respectively.

The background density is represented by a numerical value obtained by measuring the optical density of the background of the thermosensitive recording medium using a Macbeth RD918. The results are shown in [Table 2].

[0054]

[Table 2]

In the thermosensitive recording medium of Comparative Example 5, the background density storage property was good, but the sensitivity of the thermosensitive coloring layer was remarkably low.

[0056]

The heat-sensitive recording material of the present invention has an absorption region in the near-infrared region and records a clear color image, and
It has an excellent effect on storage stability of the background, can be read by a semiconductor laser, and is highly practical as a thermal recording material in the field of thermal recording labels, for example.
It has a high utility value.

Claims (1)

[Claims] 1. A thermosensitive recording medium comprising a substrate and a thermosensitive coloring layer containing a fatty acid ferric salt and a chelating agent, wherein the fatty acid ferric salt is finely divided by an emulsion dispersion method. With an average particle size of 0.05 to 1.5μ,
Moreover, the height (H) of the main peak existing within the range of the diffraction angle (2θ) 21.8 ± 0.5 degrees in the X-ray diffraction analysis curve with Cu-Kα line and the peak half width (W). Ferric stearate, ferric behenate having a ratio (H / W) of 10 or more and having a main endothermic peak in a differential thermal analysis curve at 100 ° C. or more, or a ferric behenate of these. A heat-sensitive recording material comprising a mixture.