JPH0572277B2 - - Google Patents

Description

[Detailed description of the invention]

(A) Industrial Application Field The present invention relates to a two-component color-forming heat-sensitive recording material, and particularly to a heat-sensitive recording material capable of producing a colored image that absorbs in the near-infrared region. (B) 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 color developer. By heating with a head, heat vent, laser light, etc., the dye precursor and developer react instantly.
This allows recorded images to be obtained, and is designated as Special Publication No. 43-4160.
It is disclosed in Japanese Patent Publication No. 14039/1983. These 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, including automatic ticket vending machines, labels, and train tickets. In particular, thermal recording labels are used for applications that require printing and pasting, such as barcode labels for POS (point of sale) systems, price display labels, and shipping/shipping labels. POS systems are becoming particularly popular in large-scale mass retailers such as supermarkets and department stores, as well as chain specialty stores and restaurants. 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 make the machine smaller and simpler, and speeding up recording, and there is no need to worry about ink staining hands or products or ink fading. In addition, when reading barcodes, etc., which are colored images, conventionally, He/Ne, which has red light with a wavelength of 633 nm, has been used.
Laser light is used, but recently semiconductor lasers have come into use. This is widely used because it can be directly modulated by current, can be miniaturized, is easy to use, is low cost, and has the advantage of being less likely to malfunction due to dirt because the oscillation wavelength is in the near-infrared range of 700 to 1500 nm. I've been doing it. Therefore,
It is desired to obtain a colored image that can be read with a semiconductor laser also in a heat-sensitive recording label. However, in the conventional two-component heat-sensitive 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, so He/Ne laser light cannot be used. Although it was possible to read it, it was not possible to read it using a semiconductor laser with a near-infrared wavelength. (C) Purpose of the Invention The purpose of the present invention is to provide a heat-sensitive recording material that can produce colored images that absorb in the near-infrared region, and another purpose is to provide a heat-sensitive recording material that has excellent color development and storage stability. It is to provide. (D) Structure of the Invention In a heat-sensitive recording material containing a normally colorless or light-colored dye precursor and a color developer as color-forming components, a fluorene compound represented by the following general formula () is used as the dye precursor; ()

[Formula] (In the formula, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ each represent a lower alkyl group.) 2,2'-thiobis(4,6-dichloro By using phenol) or 2,2'-thiobis(4-chlorophenol), the desired heat-sensitive recording material can be provided. The fluorene compound represented by the general formula () itself is a colorless to light-colored crystal and has no absorption in the near-infrared region, but it develops a color from blue to green by reaction with a color developer, and its colored image is Absorbs in the infrared. Specific examples of the fluorene compounds according to the present invention include 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6'-dimethylaminophthalide), 3-diethylamino-6-dimethylamino Fluorene-9-spiro-3'-(6'-dimethylaminophthalide), 3,6-bis(diethylamino)fluorene-9-spiro-3'-(6'-
dimethylaminophthalide), 3-dibutylamino-6-dimethylaminofluorene-9-spiro-
3'-(6'-dimethylaminophthalide), 3-dibutylamino-6-diethylaminofluorene-9-
spiro-3'-(6'-dimethylaminophthalide),
3,6-bis(dimethylamino)fluorene-9
-spiro-3'-(6'-diethylaminophthalide),
3-diethylamino-6-dimethylaminofluorene-9-spiro-3'-(6'-diethylaminophthalide), 3-dibutylamino-6-dimethylaminofluorene-9-spiro-3'-(6'-diethylaminophthalide) 3,6-bis(diethylamino)fluorene-9-spiro-3'-(6'-diethylaminophthalide), 3,6-bis(dimethylamino)fluorene-9-spiro-3'-(6' -dibutylaminophthalide), 3-dibutylamino-
6-diethylaminofluorene-9-spiro-
3'-(6'-diethylaminophthalide), 3-diethylamino-6-dimethylaminofluorene-9-
Examples include spiro-3'-(6'-dibutylaminophthalide). An electron-accepting compound is used as a color developer that causes the fluorene compound according to the present invention to develop color when heated, but there are few compounds that satisfy both color development and image storage properties, and 2,2'-thiobis(4,6- It was found that dichlorophenol) or 2,2'-thiobis(4-chlorophenol) has excellent color development and image storage properties. Specific examples of the color developer in the present invention are as follows: 2.
2'-thiobis(4,6-dichlorophenol) or 2,2'-thiobis(4-chlorophenol). The amount of each component constituting the heat-sensitive recording material of the present invention is determined based on 1 part by weight of the fluorene compound represented by the general formula () as the dye precursor, and 2,2'-thiobis(4,6-dichloro) as the color developer. It is preferred to use 0.1 to 6 parts by weight of phenol) or 2,2'-thiobis(4-chlorophenol). In the heat-sensitive recording material of the present invention, the main components that may be added as necessary in addition to the color-forming components will be specifically described. As binders, starches, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol,
Styrene-maleic anhydride copolymer, ethylene-
Examples include water-soluble binders such as maleic anhydride copolymers, latex-based water-soluble binders such as styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, and methyl acrylate-butadiene copolymers. 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, dispersants such as sodium dioctyl sulfosuccinate, ultraviolet absorbers such as benzophenone and benzotriazole, surfactants, and fluorescent Examples include dyes. Paper is mainly used as the support 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 can also be used as desired. The heat-sensitive recording material of the present invention is generally used for ordinary facsimile machines, printers, etc., and is also used for special applications that detect near-infrared light. When a high preservability of a colored image is desired depending on the application, for example when used for a label, 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, the main components of the protective layer include various water-soluble resins, latex,
A photocurable resin is used. Further, pigments, water resistant agents, water repellents, antifoaming agents, ultraviolet absorbers, etc. can be added as necessary. Further, for use as a label, an adhesive layer may be provided on the back surface so that it can be easily attached to another solid surface after printing. In this case, a release paper is provided on the adhesive layer. (E) Examples Next, the present invention will be explained in more detail using examples. Example 1 3,6-bis(dimethylamino)fluorene-
9-spiro-3'-(6'-dimethylaminophthalide)
20g was dispersed in a ball mill with 80g of a 1% polyvinyl alcohol aqueous solution. Separately, 50 g of 2,2'-thiobis(4,6-dichlorophenol) was dispersed in a ball mill along with 200 g of a 1% polyvinyl alcohol aqueous solution. After mixing these dispersions, add 250 g of a 40% dispersion of calcium carbonate, then add 40 g of a 25% dispersion of zinc stearate, 200 g of a 25% dispersion of stearic acid amide, and 625 g of an 8% aqueous polyvinyl alcohol solution and stir thoroughly. It was made into a coating liquid.
This coating liquid was applied onto a base paper having a basis weight of 55 g/m ² to a solid coating weight of 6 g/m ² and dried to obtain a heat-sensitive recording material. Example 2 2,2'-thiobis(4,6-dichlorophenol) in Example 1 was replaced with 2,2'-thiobis(4,6-dichlorophenol).
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that chlorophenol) was used. Comparative Example A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 4,4'-isopropylidene diphenol was used instead of 2,2'-thiobis(4,6-dichlorophenol) in Example 1. . Evaluation The heat-sensitive recording materials obtained in Examples 1 and 2 and Comparative Example were evaluated as follows, and the results are shown in Table 1. (1) Color density: Printing was performed under the conditions of 16.00 V and 3.0 milliseconds, and the optical density of the colored image was measured using Macbeth RD918. (2) Image water resistance: The colored image was immersed in tap water 2 at 20°C and stored for 20 hours. The optical density before and after storage was measured, and the image preservation rate was calculated from the following formula. Image preservation rate = Optical density after preservation / Optical density before preservation ×
100 (3) Near-infrared light reading: Using a GaAs semiconductor laser (780nm), we investigated whether the barcode could be read after it was printed.

[Table] (F) Effects of the Invention As shown in Table 1, the heat-sensitive recording material of the present invention has a color image that can be read by a semiconductor laser that emits near-infrared light, as well as improved color development and storage stability of the image. It can be seen that it is excellent.

Claims (1)

[Scope of Claims] 1. In a heat-sensitive recording material containing a normally colorless or light-colored dye precursor and a color developer as color forming components, the dye precursor is a fluorene compound represented by the following general formula (), and the dye precursor is a fluorene compound represented by the following general formula (). ) [Formula] (In the formula, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ each represent a lower alkyl group.) The color developer is 2,2'-thiobis(4,6- 1. A heat-sensitive recording material characterized in that it is 2,2'-thiobis(4-chlorophenol) or 2,2'-thiobis(4-chlorophenol).