JPH0326154B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides an ink for heat-sensitive recording media in which the thermosensitive recording ink layer has low plasticizer migration, and the fading of thermoplastic synthetic resin printed characters due to plasticizer migration is minimal. Regarding the composition. [Prior Art] Conventionally, heat-sensitive recording media using heat-sensitive recording ink containing a phenolic compound on the surface of a support and a binder containing a leuco dye that reacts with the phenolic compound and develops color under heating have been known. It is widely used in systems that use ticket issuing machines to issue train tickets, coupon tickets, etc., as well as in facsimile machines, printers for various measuring instruments, and the like. [Problems to be Solved by the Invention] However, in the above-mentioned conventional heat-sensitive recording medium, it is necessary to prevent the phenolic compound and the leuco dye, which reacts with the phenolic compound under heating to form a color, from reacting before thermal printing. Therefore, it is necessary to form an ink using a solvent that does not dissolve these substances, and such solvents are practically limited to aliphatic hydrocarbons and the like with low polarity. Therefore, the binder must also be soluble in aliphatic hydrocarbons.
For example, phenolic resin, coumaron resin, terpene resin, vinyltoluene/butadiene copolymer,
Vinyltoluene/acrylic ester copolymer,
Limited to cyclized rubber, etc. The binder of the conventional heat-sensitive recording ink layer described above cannot prevent the penetration of plasticizers used in synthetic resins, especially polyvinyl chloride resins, and when it comes into contact with substances containing such plasticizers, the plasticizers are removed. Due to penetration, the leuco dye or phenolic compound that is the coloring component is dissolved and eluted into the substance containing the plasticizer.
When the proportion of one of the color-forming components becomes too small, the acidity around the leuco dye decreases, and the leuco dye returns to a stable, colorless leuco form, causing the once colored characters to fade.
Another problem is that the plasticizer enters between the phenolic compound and the leuco dye, which causes the printed characters to fade and, in extreme cases, to disappear completely. For example, if a printed ticket is left in contact with a polyvinyl chloride resin product, the plasticizer will penetrate from the polyvinyl chloride resin product into the heat-sensitive recording ink layer of the ticket, so printing usually takes 2 to 3 hours at 40°C. Records will be erased. Therefore, it does not pose much of a problem when used for short-term tickets or various types of recording paper that do not require storage, but for long-term items such as railway commuter passes, polyvinyl chloride resin is used. If you keep it in your commuter pass holder, you will be inconvenienced by the problems mentioned above. Therefore, an object of the present invention is to provide a heat-sensitive recording ink for a heat-sensitive recording medium comprising a heat-sensitive ink layer that is difficult to penetrate with a plasticizer used in polyvinyl chloride resin or the like. [Means for Solving the Problems] In order to solve the above problems, the present inventors have conducted research and found that ``a phenolic compound is coated on the surface of a support by reacting the phenolic compound with the phenolic compound under heating. In an ink composition for a heat-sensitive recording medium having a heat-sensitive recording ink layer containing a color-forming leuco dye in a binder, the leuco dye is a fluoran-based leuco dye, and the binder is a polymethyl methacrylate resin, polyethyl A resin in which at least one of a methacrylate resin and a polybutyl methacrylate resin is dissolved in an aromatic solvent, and the phenolic compound and the leuco dye are insoluble in the aromatic solvent that dissolves the binder. The present invention was achieved by discovering the structure of "an ink composition for heat-sensitive recording media characterized by the following." [Function] As the support for the heat-sensitive recording medium comprising the heat-sensitive recording ink composition of the present invention, any of those used in conventional heat-sensitive recording media, such as paper, plastic, and composites thereof, can be used. In addition, if necessary, these supports may be provided with an appropriate primer layer for improving adhesive strength with the heat-sensitive recording ink layer described later. For example, when a polyester sheet is used as the support, a primer layer may be formed using a primer paint containing a polyester resin or vinyl chloride/vinyl acetate copolymer resin and isocyanate. Alternatively, when paper is used as a support, a primer layer similar to the above may be formed for the purpose of sealing to prevent ink from penetrating into the paper when forming a heat-sensitive recording ink layer or for improving adhesive strength. It's okay. Further, as the binder, which is one of the substances constituting the heat-sensitive recording ink of the present invention, at least one of polymethyl methacrylate resin, polyethyl methacrylate resin, and polybutyl methacrylate resin is used. The reason for using the above resins is that polymethyl methacrylate resin, polyethyl methacrylate resin, and polybutyl methacrylate resin are based on aromatic resins such as toluene and xylene that do not dissolve both of the coloring components (phenolic compounds and leuco dyes) described below. This is presumably because it is soluble in solvents and can prevent penetration of dioctyl phthalate, which is often used as a plasticizer. Further, by using at least one of the binders made of the above-mentioned resins, the water resistance of the formed heat-sensitive recording ink layer is improved and the film strength is also increased. Next, the phenolic compound and leuco paint, which are coloring components, will be explained. The phenolic compound used is one that is insoluble in the aromatic solvent that dissolves the binder made of the resin. Examples of such phenolic compounds include o-phthalic acid, dihydroxybenzoic acid, gallic acid, bisresorcinol ethylene ether, diresorcinol, β-
Resorcinic acid ethanolamide, methyl gallate, ethyl gallate, o-iodobenzoic acid, hydroxynaphthoic acid, acetoacetaminosalicylic acid, acetoacetamino-chloro-methylbenzenesulfonic acid, tricarbamylic acid, 2,4,6-
Trihydroxybenzoic acid or naphthol AS or its derivatives naphthol AS-BO, naphthol AS-BS, naphthol AS-D, naphthol AS-E, naphthol AS-G, naphthol AS
−LB, naphthol AS−OL, naphthol AS−
SW, naphthol AS-TR, naphthol AS-PH
etc., and one or more types of these can be used. The leuco dye that develops color by reacting with the above phenolic compound under heating must be colorless or light-colored in the binder before the reaction, and must be compatible with the aromatic solvent that dissolves the binder made of the above resin. Fluorane-based leuco dyes are used, which are insoluble and exhibit a coloring reaction when a phenolic compound is dissolved by heating and comes into contact with the leuco dye. Examples of fluorane-based leuco dyes include 1,2-
Benzo-6-diethylaminofluoran is mentioned. As explained above, the thermal recording ink composition of the present invention uses a solvent that dissolves the binder but does not dissolve the phenolic compound and the leuco dye.
That is, it is an ink made using only an aromatic solvent such as toluene or xylene. In the heat-sensitive recording ink having such a composition, in the ink state, the color-forming substance (leuco dye) and the acidic substance (phenolic compound) are dispersed in the solvent, and the color-forming reaction does not occur because they do not come into contact with each other through the binder. It has the effect of being difficult to occur. Furthermore, in order to improve the storage stability of the ink, the phenolic compound and the leuco dye are preferably formed into an ink separately in advance and mixed immediately before coating. In addition, when making ink, other additives such as dispersants, fillers, white pigments, waxes, colorants such as dyes and pigments, and surfactants may be added as necessary, or additives may be added to improve coating suitability. A diluent may be added. After forming the ink as described above, it is coated on the surface of the support by a known coating method, such as roll coating or gravure coating, so that the coating amount (dry basis) is 2 to 10 g/m ² . do. The heat-sensitive recording ink composition of the present invention can be used as a heat-sensitive recording medium due to the above-mentioned basic structure. Furthermore, the heat-sensitive recording medium made of the heat-sensitive recording ink composition of the present invention may be provided with the following protective layer that is provided in ordinary heat-sensitive recording media. As such a protective layer, polymethyl methacrylate resin, polyethyl methacrylate resin,
It is preferable to use a composition containing at least one type of polybutyl methacrylate resin as a main component, and 5 to 50 parts by weight of polyethylene wax or 5 to 50 parts by weight of Teflon powder per 100 parts by weight of these resins.
50 parts by weight, or both polyethylene wax and Teflon powder. Such a protective layer can be formed by dispersing polyethylene wax or Teflon powder in a resin solution in which the above resin is dissolved in a solvent. The ink may be prepared and applied using a known coating method. Further, a magnetic recording layer may be provided on a part of the support of the heat-sensitive recording medium, preferably on the back surface, and by doing so, a commuter pass for automatic ticket gates using a magnetic system can be obtained. Furthermore, predetermined fields and characters may be printed on the surface of the heat-sensitive recording ink layer of the heat-sensitive recording medium, and by doing so, the number of characters to be printed can be reduced and the printing time can also be shortened. However, the life of the recording head can also be extended. Furthermore, the heat-sensitive recording ink layer may be provided in the form of stripes or spots by gravure printing or the like, or it may be printed at different locations using leuco dyes with different coloring hues, and the coloring hue may be changed depending on the location on the support. You can do it like this. (Effects of the Invention) The heat-sensitive recording medium made of the heat-sensitive recording ink composition of the present invention has less plasticizer penetration than conventional ones and has a high film strength, so it can prevent printed characters from fading for a long time. This has the effect of saying. Therefore, the heat-sensitive recording medium made of the heat-sensitive recording ink composition of the present invention is suitable for uses such as commuter passes, coupon tickets, and other uses that require storage. [Example] Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples. Example 1 Solutions A and B having the following compositions were stirred for 1 hour using a stirrer containing glass beads to prepare. Fluorane-based leuco dye A: 3 parts by weight (Hodogaya Chemical, TH-106) Polymethyl methacrylate 30% toluene solution
...10 parts by weight (Paraloid A-11, manufactured by Rohm and Haas) Toluene ...5 parts by weight B liquid 2,4-dihydroxybenzoic acid ...3 parts by weight Polymethyl methacrylate 30% toluene solution
...10 parts by weight (Paraloid A-11 manufactured by Rohm & Birth) Toluene ...5 parts by weight The above liquid A, liquid B, toluene, and polyethylene wax 30% toluene dispersion in a ratio of 10:10:10:3 Mix it with a propeller mixer to make an ink, and immediately print it on high-quality paper (basis weight 200 g/m ² ).
This reverse roll coating was applied so that the dry coating amount was 5 g/m ² to obtain heat-sensitive recording paper. Example 2 A milky white polyester sheet (manufactured by Toray Industries, 188 μm thick) was used as a support, and a primer paint having the following composition was applied and dried to form a primer layer. Primer paint polyester resin...3 parts by weight (Toyobo Co., Ltd., Byron 200) PVC/vinyl acetate copolymer...2.5 parts by weight (Union Carbide Co., Ltd., VAGH) Isocyanate...2 parts by weight (Takeda Pharmaceutical Co., Ltd., Takenate D) -110N) Toluene: 30 parts by weight Methyl ethyl ketone: 20 parts by weight Next, liquids C and D having the following composition were mixed with A of Example 1.
It was prepared in the same manner as Solution and B. Fluorane-based leuco dye B liquid: 3 parts by weight (Hodogaya Chemical Co., Ltd., TH-106) Polymethyl methacrylate 30% toluene solution
...10 parts by weight (Mitsubishi Rayon, Dianal BR80) Toluene ...5 parts by weight D-liquid o-phthalic acid ...3 parts by weight polymethyl methacrylate 30% toluene solution
...10 parts by weight (manufactured by Mitsubishi Rayon, Dianal RB80) Toluene ...5 parts by weight The above liquids C, D and toluene were mixed in a ratio of 1:1:1, stirred with a propeller mixer to form the ink, and Lay it on the primer layer of the polyester sheet and apply it by three reverse roll coating so that the dry coating amount is 6g/ ^m2 ,
A thermosensitive recording layer was formed. Furthermore, a protective paint having the following composition was applied onto the above heat-sensitive recording layer by three-roll reverse roll coating so that the dry coating amount was 4 g/m ² .
A protective layer was formed. Protective paint polymethyl methacrylate 10% toluene solution
...10 parts by weight (Soken Chemical Co., Ltd., Thermorak M-16) Polyethylene wax 30% toluene solution
...0.3 parts by weight (manufactured by Asahi Denka, mark FC-113) Fluorine resin powder 50% toluene solution
...0.1 parts by weight (manufactured by Toyo Soda Kogyo, MOLD WIZ F57) Toluene ...3 parts by weight Comparative example 1 Liquids G and H having the following composition were mixed with 40 parts by weight using a ball mill.
It was prepared by kneading for hours. G liquid Fluorane leuco dye...1 part by weight (Hodogaya Chemical, TH-106) Stearamide...2 parts by weight 10% polyvinyl alcohol resin aqueous solution
3... Parts by weight (Nippon Gosei Kagaku Kogyo, Gohsenol NH20) Water... 4 parts by weight H liquid bisphenol A... 2 parts by weight Polyethylene wax 40% aqueous dispersion
...0.1 part by weight (Mitsui Petrochemicals, Chemipearl W100) 10% polyvinyl alcohol resin aqueous solution
...3 parts by weight Water ...4.9 parts by weight Above G liquid, H liquid and polyvinyl alcohol resin 30
% aqueous solution and water were mixed and stirred at a ratio of 10:20:20:20 (based on weight), and then the same procedure as in Example 1 was carried out to obtain a thermal recording paper for comparison. Comparative Example 2 Solutions I and J having the following compositions were prepared in the same manner as Solutions A and B in Example 1. Liquid I fluorane leuco dye...3 parts by weight (Hodogaya Chemical Co., Ltd., TH-106) Vinyltoluene/butadiene copolymer) 30% ethylcyclohexane solution...10 parts by weight (Gutdeyer Co., Ltd., Priorite VT) Ethylcyclohexane... ... 5 parts by weight J liquid Bisphenol A ... 3 parts by weight Vinyltoluene/butadiene copolymer 30% ethylcyclohexane solution ... 10 parts by weight (Guddoyer, Priorite VT) Ethylcyclohexane ... 5 parts by weight Above liquid I, Liquid J was mixed to form an ink, which was applied to a support with a primer layer provided thereon according to the procedure of Example 1 so that the dry coating amount was 6 g/m ² . Furthermore, a protective paint having the following composition was applied in the same manner as in Example 2, so that the dry coating amount was 4 g/m ² . Protective paint Vinyl toluene/butadiene copolymer 30% ethylcyclohexane solution...10 parts by weight Polyethylene wax (degree of polymerization 2000)
...1 part by weight Ethylcyclohexane 5 parts by weight In order to evaluate the plasticizer permeability of the heat-sensitive recording media obtained in each of the above Examples and Comparative Examples, the heat-sensitive recording media were printed under predetermined conditions, and then the printed portion was Table 1 shows the results of stacking polyvinyl chloride sheets (containing 24.4% dioctyl phthalate) and applying pressure, heating the whole to accelerate discoloration, and measuring the degree of discoloration over time using reflection density. show. Printing conditions Thin film thermal head used 1.2 mJ/dot (4 x 10 ^-4 cm ² ) Storage conditions Pressure 50 g/cm ² Temperature 40°C Density measurement Reflection densitometer, Kodatsu Kuratsuten No. 106
Using filter [table]

Claims (1)

[Scope of Claims] 1. An ink for a heat-sensitive recording medium having, on the surface of a support, a heat-sensitive recording ink layer containing in a binder a phenolic compound and a leuco dye that develops color by reacting with the phenolic compound under heating. In the composition, the leuco dye is a fluorane-based leuco dye, and the binder is at least one of polymethyl methacrylate resin, polyethyl methacrylate resin, and polybutyl methacrylate resin.
An ink for heat-sensitive recording media, characterized in that the resin is a resin in which a seed is dissolved in an aromatic solvent, and the phenolic compound and the leuco dye are insoluble in the aromatic solvent that dissolves the binder. Composition. 2 The above phenolic compound is o-phthalic acid,
Dihydroxybenzoic acid, gallic acid, bisresorcinol ethylene ether, diresorcinol, β
-Resorcinic acid ethanolamide, methyl gallate, ethyl gallate, o-iodobenzoic acid, hydroxynaphthoic acid, acetoacetaminosalicylic acid, acetoacetamino-chloro-methylbenzenesulfonic acid, tricarbamylic acid, 2,4,6-
The ink composition for a heat-sensitive recording medium according to claim 1, comprising one or more of trihydroxybenzoic acid, naphthol AS, or a derivative thereof.