JPH0560433B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a heat-sensitive recording material, and particularly to a heat-sensitive recording material that absorbs in the near-infrared region and provides a colored image with excellent storage stability. (Prior Art) A heat-sensitive recording material generally has a heat-sensitive recording layer on a support, the main components of which are an electron-donating, usually colorless or light-colored dye precursor, and an electron-accepting developer. When heated with a thermal head, thermal pen, laser beam, etc., the dye precursor and color developer react instantaneously to obtain a recorded image. No. 4160, Tokko Akira
It is disclosed in Publication No. 45-14039, etc. Such heat-sensitive recording materials have the advantages of being able to record with relatively simple equipment, being easy to maintain, and producing no noise. It is used in a wide range of fields such as automatic ticket vending machines, labels, and ticket vending machines. In particular, thermal recording labels are used for applications that require pasting after printing, such as parcode labels for POS (point of sale) systems, price display labels, and shipping/shipping labels. Especially at large mass retailers such as supermarkets and department stores, as well as chain specialty stores and restaurants.
The popularity of POS systems is remarkable. Its purpose is to aggregate and analyze product sales information in order to clearly understand consumer needs and formulate rational management strategies. The method of optically reading codes and OCR characters using scanners is currently rapidly growing. Therefore, various printing methods are currently being tried, and among them, the thermal recording method can be said to be the most excellent. This is because the printing method uses chemical or physical changes in substances due to heating to record images, and does not require development and fixing, nor does it require replenishment of printing ink. That is, it has many features such as being able to downsize and simplify the machine and speed up recording, and there is no need to worry about ink staining hands or products or ink fading. In addition, for reading barcodes, etc., which are colored images, it has been conventionally necessary to use He/Ne, which has red light with a wavelength of 633 nm.
Laser light is used, but recently semiconductor lasers have come into use. It can be directly modulated by current, can be miniaturized, is easy to use, is low cost, and because the oscillation wavelength is in the near-infrared range of 700 to 1,500 nm, there are fewer malfunctions due to dirt, so it is widely used. It is becoming popular. Therefore, it is desired to obtain colored images that can be read with a semiconductor laser also in heat-sensitive recording labels. However, in the conventional two-component thermosensitive recording material consisting of a leuco dye and a color developer, the absorption wavelength of a colored image is 550 to 620 nm on the long wavelength side even in a black coloring system.
Although it was possible to read with Ne laser light, it was not possible to read with a semiconductor laser with a near-infrared wavelength. On the other hand, as described in Shashin Kogyo Bessatsu Vol. 222 P. 58 (published by Shashin Kogyo Publishing Co., Ltd.), heat-sensitive recording materials that have an absorption wavelength in the near-infrared region include organic acid heavy metal salts or organic acid noble metal salts. , the other is an organic reducing agent,
Coloring systems using sulfur compounds and amino compounds are known. Some of this type of thermosensitive recording material has been commercialized using coloring systems such as long-chain fatty acid iron salt + polyhydric phenol, long-chain fatty acid silver salt + reducing agent, fatty acid aluminum salt + spiropyrans, etc. It is called a pigment-based thermosensitive recording material. (Problems to be Solved by the Invention) The heat-sensitive recording material of the present invention is located in the field of the above-mentioned pigment-based heat-sensitive recording material. Conventional pigment-based thermosensitive recording media have the advantage that colored images have an absorption wavelength in the near infrared region and have good storage stability. It has many problems such as not being black, not being able to be coated with water, and being expensive. It is an object of the present invention to provide a heat-sensitive recording material that solves many of the problems of conventional pigment-based heat-sensitive recording materials and retains its advantages. (Means for Solving the Problems) An object of the present invention is to combine an organic vanadium compound and a gallic acid ester represented by the following general formula (),
This can be achieved by providing on the substrate a heat-sensitive coloring layer containing as main components a water-soluble binder and a water-soluble binder. (In the formula, R represents an alkyl group having 3 to 18 carbon atoms, a cycloalkyl group, a phenyl group, or a benzyl group.) Examples of the organic vanadium compounds used in the present invention include vanadium stearate, vanadyl acetylacetonate, and pivalin. Examples include acid vanadium compounds, or organic vanadium compounds formed from an inorganic vanadium compound represented by the general formula () and a nitrogen-containing compound represented by the general formula () or (). The inorganic vanadium compound of the above general formula () is represented by the following formula. x・M ₂ O・y・V ₂ O.NH ₂ O ... () (In the formula, x and y are integers, and n is an integer from 0 to 18. Also, M represents a monovalent cation. ) Examples of monovalent cations corresponding to M in the general formula () include NH ₄ , Na, K, Li, etc. The nitrogen-containing compound of general formula () is represented by the following formula. (In the formula, R ₁ represents an alkyl group having 6 to 18 carbon atoms (which may have a branch), R ₂ is H or a benzyl group,
or represents an alkyl group having 1 to 4 carbon atoms, R ₃ , R ₄
is H or an alkyl group having 1 to 4 carbon atoms (R ₂ , R ₃ ,
R ₄ may be the same or different). ) Examples of this compound include hexylammonium chloride, 2-ethyl-hexyl dimethyl benzylammonium chloride, ethyldodecyldimethylammonium chloride, hexadecyldimethylbenzylammonium chloride, and hexadecyltrimethylammonium hydroxide. The nitrogen-containing compound of general formula () is represented by the following formula. (The above compound represents a hetero compound containing N such as a pyridine ring or a quinoline ring, and in the formula, R ₅ has 6 to 6 carbon atoms.
18 alkyl group or _-CH2 -O- _R1 or benzyl group or phenacyl group. R ₁ has 6 or more carbon atoms
18 alkyl groups (which may have branches) are shown. Examples of this compound include dodecylpyridium chloride, dodecylquinolinium chloride, and benzylpyridinium chloride. Organic vanadium compounds can be synthesized by various methods, but for example, an aqueous solution of an inorganic vanadium compound represented by the general formula () and an aqueous solution of a nitrogen-containing compound represented by the general formulas () and () are mixed at 5 to 30°C. , obtained as a precipitate by stirring for about 1 hour. In the present invention, the purpose of the organic vanadium compound can be achieved by adding the organic vanadium compound to the heat-sensitive coloring layer in an amount of 5 to 50% by weight of the total solid content. The gallic acid ester used in the present invention is represented by the general formula (). This purpose can be achieved by adding the ester in an amount of 5 to 50% by weight of the total solid content in the heat-sensitive coloring layer. Water-soluble binders include starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, styrene-maleic anhydride copolymer, ethylene-maleic anhydride copolymer, etc. Examples include water-soluble binders, latex-based water-soluble binders such as styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, and methyl acrylate-butadiene copolymers. In the heat-sensitive recording material of the present invention, main components which may be added as necessary in addition to the above-mentioned components will be specifically described. Examples of pigments include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, urea-formalin resin, and the like. In addition, higher fatty acid metal salts such as zinc stearate and calcium stearate, paraffin,
Waxes such as paraffin oxide, polyethylene, polyethylene oxide, stearamide, castor wax, etc., as sensitivity improvers, metaterphenyl, parabenzyl biphenyl, esters of hydroxynaphthoic acid, stearamide,
Examples thereof include tribenzylamine, naphthalene derivatives, dibenzyl terephthalate, and the like. Further examples include dispersants such as sodium dioctyl sulfosuccinate, ultraviolet absorbers such as benzophenone and benzotriazole, surfactants, and fluorescent dyes. Paper is mainly used as the substrate for the heat-sensitive recording material of the present invention, but various nonwoven fabrics, plastic films, synthetic papers, metal foils, etc., or composite sheets made of a combination of these may also be used as desired. The heat-sensitive recording material of the present invention is generally used in ordinary facsimile machines, printers, etc., and is also used in special applications for detecting near-infrared light. If a high preservability of the colored image is desired depending on the application, a protective layer may be laminated on the heat-sensitive recording layer in order to protect the uncolored area and the colored image area from the external environment. In this case, various water-soluble resins, latexes, and photocurable resins are used as the main components of the protective layer. Further, pigments, water resistant agents, water repellents, antifoaming agents, ultraviolet absorbers, etc. can be added as necessary. The heat-sensitive recording material of the present invention is manufactured by a manufacturing method similar to that of conventional dye-based heat-sensitive recording materials. Specifically, an organic vanadium compound and a gallic acid ester of the general formula () are separately ground and dispersed in an aqueous system using a sand grinder, attritor, ball mill, etc., and then
There are methods such as mixing the two to make a water-based paint, and microcapsulating both or one of the organic vanadium compound and the gallic acid ester of the general formula () and then mixing the two to make a water-based paint. (Example) Next, the present invention will be explained in more detail with reference to Examples. Example 1 Liquids A and B having the following compositions were separately dispersed using a sand grinder. Part A Vanadyl acetylacetonate 8 parts by weight Light calcium carbonate 20 〃 Zinc stearate 5 〃 Polyvinyl alcohol 12% solution 40 〃 Water 57 〃 Part B Stearyl gallate 30 parts by weight Stearamide 8 〃 Light calcium carbonate 20 〃 Polyvinyl alcohol 12% liquid 70〃Water 92〃Next, 130 parts by weight of liquid A, 220 parts by weight of liquid B, and 50 parts by weight of 12% polyvinyl alcohol were added and stirred to make a heat-sensitive coating liquid, and then 50g of this heat-sensitive coating liquid was added. The mixture was coated and dried on a high-quality paper of 7 g/m ² so that the coating weight after drying was 7 g/m ² , and then subjected to a calendering treatment to obtain a heat-sensitive recording material with a recording surface having a base smoothness of 500 seconds. Example 2 A thermosensitive recording material was obtained in exactly the same manner as in Example 1, except that a reaction product of sodium metavanadate and dodecylpyridinium chloride was used instead of vanadyl acetylacetonate. Example 3 A thermosensitive recording material was obtained in exactly the same manner as in Example 1, except that a reaction product of sodium metavanadate and cetylbenzyldimethylammonium chloride was used instead of vanadyl acetylacetonate in Example 1. . Comparative Example 1 A thermosensitive recording material was obtained in exactly the same manner as in Example 1 except that gallic acid was used instead of stearyl gallate in Example 1. Comparative Example 2 A thermosensitive recording material was obtained in exactly the same manner as in Example 1, except that methyl gallate was used instead of stearyl gallate in Example 1. Comparative Example 3 A thermosensitive recording material was obtained in exactly the same manner as in Example 1, except that ferric stearate was used instead of vanadyl acetylacetonate. Comparative Example 4 Liquid A: 3-(N-isoamyl-N-ethylamino)-6-
Methyl-7-anilinofluorane 5g Light calcium carbonate 28g Zinc stearate 5g Polyvinyl alcohol 12% solution 35g Water 52g Solution B: Benzyl parahydroxybenzoate 15g Terephthalic acid dibenzyl ester 5g Aluminum hydroxide 18g Polyvinyl alcohol 12% solution 35g Water 52g Next, add 125g of solution A, 125g of solution B, 50g of 12% polyvinyl alcohol solution, and 40g of water, mix, stir, and adjust to make a coating solution.Next, apply this coating solution to the surface of 50g/ ^m2 of high-quality paper. The coating was coated and dried so that the coating weight after drying was 7 g/m ² , and then subjected to a calendering treatment to obtain a heat-sensitive recording material with a recording surface having a base smoothness of 500 seconds. Evaluation The thermosensitive recording bodies obtained in Examples 1 to 3 and Comparative Rows 1 to 4 were evaluated as follows, and the results are shown in Table 1. (1) Skin density The optical density of the skin was measured using Macbeth RD918. (2) Color Density Printing was performed using COPiX6500 (manufactured by Toshiba), and the optical density of the colored image was measured using Macbeth RD918. (3) Image storage properties Colored images were stored at 50°C and 90% environment for one week. The optical density after storage was measured using Macbeth RD918. (4) Image water resistance Immerse the colored image in 20℃ tap water 2,
Saved time. Macbeth optical density after storage
Measured using RD918. (5) Image chemical resistance Hair liquid was dropped onto the colored image to check for discoloration. ○Does not erase color ×Erases color. (6) Near-infrared light reading Using a GaAs semiconductor laser (780 nm), we investigated whether barcodes could be read after printing. ○Can be read ×Cannot be read

[Table] (Effects of the Invention) The heat-sensitive recording material of the present invention can be coated with water thread, and as shown in Table 1, its colored image can be read by a semiconductor laser with near-infrared light. It can be seen that the image has excellent color development and storage stability.

Claims (1)

[Claims] 1. An organic vanadium compound and the following general formula ()
1. A heat-sensitive recording material, characterized in that a heat-sensitive coloring layer mainly composed of a gallic acid ester represented by the following formula and a water-soluble binder is provided on a substrate. (R represents an alkyl group having 3 to 18 carbon atoms, a cycloalkyl group, a phenyl group, or a benzyl group.)