JPH0362158B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a heat-sensitive recording material, and more particularly to a color developer for a heat-sensitive recording material that provides high-speed recording performance and stable recorded images.

[Prior Art] A thermosensitive recording material that utilizes a chemical reaction utilizes a color developing reaction between an electron-donating color former and an electron-accepting color developer to disperse each in the form of fine particles, and then binders and auxiliaries are added. When mixed and heated, one or both of them melt and come into contact, causing a chemical reaction and color development to obtain a recorded image. Ordinary heat-sensitive recording materials are coated on a support such as paper or film with colorless or light-colored dyes such as leuco dyes used as coloring agents, and acidic compounds such as phenolic compounds and organic acids used as color developers that develop color when heated. It is a color-forming system consisting of a substance and further provided with a heat-sensitive color-forming layer in which binders, fillers, sensitizers, and other auxiliary agents are dispersed.It is known from Japanese Patent Publication No. 45-14039 and is widely used. has been made into This type of heat-sensitive recording sheet obtains a recorded image through a chemical reaction between a color former and a color developer instantaneously when heated by a thermal head, so it requires more processing such as development and fixing than other recording materials. The device itself is relatively simple, records can be obtained in a short time, there is no noise generation or environmental pollution, and the cost is low. It is highly practical as a recording material and copying material for information and measuring instruments such as calculators and medical measuring instruments. In recent years, demands for higher speed and higher density recording have increased, and in addition to faster recording devices such as printers and facsimiles, the recording materials used also have excellent recording sensitivity and can be used at relatively low temperatures of around 70 to 80 degrees Celsius. It is required to have properties such as not developing color, and not causing dregs adhesion, stacking, pressure coloring, or head abrasion. Furthermore, this heat-sensitive recording material is also used for applications such as adhesive labels, and is becoming mainstream in the field of measuring labels. When heat-sensitive recording paper for adhesive labels used in this way comes into close contact with a stretch film made of polyvinyl chloride, the heat-sensitive recording layer absorbs plasticizers such as dioctyl adipate (DOA) and dioctyl phthalate (DOP) in the film. It may penetrate into the heat-sensitive color forming layer on the surface of the adhesive label and cause the recorded image area to fade over time. Particularly in the field of measuring labels, in addition to the above-mentioned plasticizer resistance, storage stability in the usage environment after application is required. That is, when applied to packaging items such as fresh vegetables and fish, mercury resistance is required, and when applied to packaging items for fried foods and other side dishes, oil resistance is required. Additionally, products that are displayed outdoors must be light resistant. Furthermore, take-out products from convenience stores and the like may be reheated in a microwave oven or the like, and may require high-temperature storage. It is difficult to satisfy all of these required characteristics with the current thermal recording paper for adhesive labels. A heat-sensitive recording material for adhesive labels for this purpose contains a color former made of a leuco dye on a support and a color developer that develops color when the leuco dye is heated, such as a color developer made of an organic acid or a phenol compound. It is known to have a heat-sensitive color forming layer and a water-soluble polymer layer as a protective layer on the heat-sensitive color forming layer. However, in the case of such heat-sensitive recording materials, although the storage stability against plasticizers is improved, the provision of the protective layer causes a drawback of poor thermal responsiveness. Furthermore, providing a protective layer causes disadvantages such as an increase in processing steps.

[Means to solve the problem]

The inventors of the present invention have made extensive studies to overcome these drawbacks, and have found that by incorporating specific para-hydroxythiobenzoic acid benzyl esters into the heat-sensitive coloring layer, the color-forming layer has excellent coloring properties and can be applied without the need for a protective layer. invented a heat-sensitive recording material in which the heat-sensitive coloring layer itself has excellent storage stability. The details will be explained below. That is, according to the present invention, in a heat-sensitive recording sheet in which a heat-sensitive color-forming layer is provided on one side of a support, the heat-sensitive color-forming layer is mainly composed of a color former and a color developer and a binder that cause the color former to develop. General formula () (However, R ₁ to _{R 3} are hydrogen, hydroxyl group, halogen, lower alkyl group having C ₁ to _{C 5} , lower alkoxy group, nitro group, cyano group, or acetyl group) Parahydroxythiobenzoic acid benzyl ester represented by The object of the present invention is to provide a heat-sensitive recording material characterized by containing the following. The thermal recording material in the present invention is capable of printing or recording images on the surface of its support by heating, and in addition to ordinary thermal paper for facsimiles and thermal paper for printers, if necessary, the back side By providing a pressure-sensitive adhesive layer or the like on the sheet, sheets that can be adhered to a solid surface, such as various price tag labels, measurement labels, name plate stickers, etc. are included. Examples of parahydroxythiobenzoic acid benzyl esters represented by the general formula () are:
Examples include those shown below. etc., and appropriate combinations thereof can also be used. It is also possible to further improve color development by using a color developer represented by the general formula () used in the present invention in combination with a color developer having a value other than the above. Examples of such color developers include: 4,4'-isopropyldene diphenol 4,4'-isopropyldene bis-(2-chlorophenol) 4,4'-isopropyldene bis-(2-methylphenol) 4 ,4'-isopropyldene bis-(2,6-dichlorophenol) 4,4'-isopropyldene bis-(2,6-dibromophenol) 4,4'-isopropyldene bis-(2,6-dimethylphenol) 4,4'-isopropylidene bis-(2-t-butylphenol) 4,4'-sec-butylidene diphenol 4,4'-cyclohexylidene bis-(2-methylphenol) 2,2'-thiobis- (4,6-dichlorophenol) P,P'-(1-methyl-7-hexylidene)diphenol 4-tert-butylphenol 4-tert-octylcatechol 4-phenylphenol 2,2'-methylenebis-(4- ethyl-6-t
-butylphenol) 2,2'-methylenebis-(4-methyl-6-t
-butylphenol) 2,2'-methylenebis-(4-t-butyl-3
Methylphenol) 4-Hydroxydiphenoxide 2,2'-dihydroxydiphenol α-naphthol β-naphthol Methyl-4-hydroxybenzoate Ethyl-4-hydroxybenzoate Propyl-4-hydroxybenzoate Benzyl-4-hydroxybenzoate 4,4 '-Butylidene bis(6-t-butyl-n
-cresol) 4,4'-butylidene bis(6-t-butyl-n
-methylphenol) 4,4'-thiobis(6-t-butyl-m-cresol) 2,2'dihydroxybenzophenone 4-hydroxy-acetonyl Novolac type phenolic resin 1,1,3-tris(2-methyl- Examples include 4-hydroxy-5-t-butylphenyl)butane alone or in combination. The color forming agent used in the present invention is usually a colorless or slightly pale leuco type such as triphenylmethane type, fluoran type, phenothiazine type, auramine type, or spiropyran type. For example, 3,3-bis(P -dimethylaminophenyl)
-6-dimethylaminophthalide 3,3-bis(P-dibutylaminophenyl)
Phthalide 3-dimethylamino-6-methoxyfluoran 3-dimethylamino-6-methyl-7-chlorofluoran 3-dimethylamino-5-methyl-7-dibenzylaminofluoran 3-dimethylamino-7-chlorofluoran Oran 3-dimethylamino-7-methoxyfluorane 3-dimethylamino-7-methylaminofluorane 3-dimethylamino-7-dibenzylaminofluorane 3-dimethylamino-7-(N-methylanilinofluorane) 3-dimethylamino-7-(orthochloro)anilinofluorane 3-dimethylamino-7,8-benzofluorane 3-dimethylamino-6-methyl-7-chlorofluorane 3-dimethylamino-6-methyl-7 -anilinofluorane 3-dimethylamino-6-methyl-7-P-butylanilinofluorane 3-dimethylamino-5-methyl-7-dibenzylaminofluorane 3-morpholino-5,6-benzolfluoran Oran 3-ethyl-6-methyl-7-anilinofluorane 2-anilino-6-diethylaminofluorane 3-(N-methyl-N-cyclohexylamino)
-6-Methyl-7-anilinofluorane Benzoylleucomethylene blue N-phenylrhodamine β-lactam Amidrhodamine β-saltone Benzo-β-naphthospiropyran 1,3,3-trimethyl-6'-chloro-8'-methoxy-indo Linobenzospiropyran 3-dibutylamino-7-orthofluoroanilinofluorane 2'-anilino-3'-methyl-6-(N-ethyl-N-isopentylamino)spiro(phthalide-
3,9-xanthene) 3-dibutylamino-7-orthochloroanilinofluorane 2-(3-chloropropylamino)-3-chloro-6-diethylaminospiro(xanthene-9,
Examples thereof include 3'-phthalide) 3-(N-ethyl-N-tetrahydrofurfuryl)-6-methyl-7-anilinofluorane alone or in combination. The binder used in the thermosensitive coloring layer of the present invention includes, for example, starch, modified starch, starch derivatives,
Casein, polyvinyl alcohol, polyvinyl alcohol modified products, polyvinyl alcohol derivatives,
Polyacrylamide, sodium polyacrylate, polyvinylpyrrolidone, methylcellulose, carboxylmethylcellulose, hydroxyethylcellulose, SBR, polyacrylic acid ester, styrene/maleic acid copolymer, saturated or unsaturated polyester resin, gelatin, etc. alone or in combination. Can be mentioned. In the formation of the heat-sensitive recording layer in the present invention, in addition to the leuco dye, color developer, and binder, the following various substances may be added as necessary. For example, talc, clay, silica, etc. to further improve writability, whiteness, statesking, etc.
White pigments such as titanium oxide, calcium carbonate, alumina, magnesia, barium sulfate, aluminum stearate, various waxes, higher fatty acid metal salts, higher fatty acid amides, etc. to improve color development, prevent staining, and prevent pressure coloring. These include various thermoplastic substances, as well as dispersants, wetting agents, antifoaming agents, etc. for improving dispersibility and coating suitability. Paper is generally used as a support in the present invention, but stickers such as plastic film can also be used.

【Example】

Examples and comparative examples of the present invention are shown below. Example 1 Dispersions A and B were prepared by mixing and dispersing the following components for 48 hours using a ball mill. (Liquid A) 3-(N-cyclohexyl-N-methylamino)-
6-Methyl-7-anilinofluorane 15 parts by weight 10% polyvinyl alcohol aqueous solution 50 〃 Water 35 〃 (Liquid B) Parahydroxythiobenzoic acid benzyl ester (Compound No. 1) 40 parts by weight Calcium carbonate 80 〃 Stearamide 40 〃 Zinc stearate 40 〃 Polyvinyl alcohol 10% aqueous solution 100 〃 Water 200 〃 Mix A and B solutions, add 400 parts by weight of 10% POVAL aqueous solution and mix to prepare a coating solution, and coat it on high-quality paper ( Apply it on one side of the paper (basis weight 50g/m ² ), dry it,
A heat-sensitive recording layer was formed with a coating amount of 7 g/m ² to obtain heat-sensitive recording paper. The surface smoothness of the obtained thermal recording paper
Supercalendar processing was performed to obtain a time of 200 to 300 seconds. Next, the label printer manufactured by Tokyo Electric Co., Ltd. (product name)
As a result of a printing test using HP9303), the printing density was high, there was no statesking, and there was no adhesion of scum. The shelf life test was also good. Example 2 A thermosensitive recording paper was obtained in the same manner as in Example 1 except that 3-dibutylamino-7-orthochloroanilinofluoran was used instead of the leuco dye in Solution A of Example 1. A color printing test was carried out in the same manner as in Example 1. As a result, the printing density was high, there was no staking, and there was no scum adhesion, which was good. The shelf life test was also good. Example 3 A thermosensitive recording paper was obtained in the same manner as in Example 1 except that 3-dibutylamino-7-(orthofluoroanilino)fluoran was used instead of the leuco dye in Solution A of Example 1. A color printing test was carried out in the same manner as in Example 1. As a result, the printing density was high, there was no staking, and there was no deposit of residue, which was good. It also performed well in a storage test. Example 4 The following components of liquid B' were mixed and dispersed in place of liquid B in Example 1, and otherwise the same procedure as in Example 1 was made to produce heat-sensitive recording paper, which was tested for color printing and storage stability. I conducted a test. (B′ solution) Parahydroxythiobenzoic acid benzyl ester
20 parts by weight 4,4 isopropylidene diphenol (bisphenol A) 20 Calcium carbonate 80 Stearamide 40 Zinc stearate 40 10% polyvinyl alcohol aqueous solution 100 Water 200 The resulting thermal recording paper has a print density of The coating was good, with no staining occurring, and no residue adhering. It also performed well in a storage test. Example 5 A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the following components of the B'' liquid were mixed and dispersed in place of the B liquid of Example 1. (B'' liquid) Parahydroxy Thiobenzoic acid benzyl ester
40 parts by weight 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane 10 〃 Calcium carbonate 80 〃 Stearamide 40 〃 Zinc stearate 40 〃 Polyvinyl alcohol 10% aqueous solution 100 〃 Water 190 The obtained thermal recording paper had a high print density, did not cause states king, and was in good condition with no residue attached. It also performed well in a storage test. Example 6 A thermosensitive recording paper was obtained in the same manner as in Example 1 except that the following components of B were mixed and dispersed in place of liquid B in Example 1. (Liquid B) Parahydroxythiobenzoic acid benzyl ester
40 parts by weight 4,4'-butylidene bis(6-t-butyl-3-
Methylphenol) 10 〃 Calcium carbonate 80 〃 Stearic acid amide 40 〃 Zinc stearate 40 〃 Polyvinyl alcohol 10% aqueous solution 100 〃 Water 190 〃 The obtained thermal recording paper has high printing density, does not cause states king, and is free from dust. It was in good condition with no adhesion. It also performed well in a storage test. Comparative Example 1 In place of the color developer of liquid B in Example 1, the following liquid B''''' prepared with bisphenol A as a color developer was used for mixing and dispersion, and the other conditions were the same as in Example 1. A thermosensitive recording paper was obtained using this method. (B′′′′ solution) 4,4′ isopyropylidene diphenol (bisphenol A) 40 parts by weight Calcium carbonate 80 〃 Stearic acid amide 40 〃 Zinc stearate 40 〃 Polyvinyl alcohol 10% aqueous solution 100 〃 Water 200 〃 Implementation A color print test was conducted in the same manner as in Example 1, and the print density was high and good, but the water resistance and alcohol resistance were poor in the storage test. Comparative Example 2 A thermosensitive recording paper was obtained in the same manner as in Example 1, except that benzyl parahydroxybenzoate was used instead of the color developer of liquid B in Example 1. A color printing test was conducted in the same manner as in Example 1, and the print density was high and good, but the water resistance and alcohol resistance in the storage test were poor. The evaluation results of these examples are shown in Table 1 together with comparative examples. The method for each test is as follows. Color density: Color is printed using a label printer, and the colored image is measured using a Macbeth densitometer (RD-514).
Measured at Background density: The non-printed area was measured using a Macbeth densitometer. Water resistance: Color printing was performed using a label printer, immersed in water at room temperature, and the density before and 15 hours after immersion was compared. Alcohol resistance: Color was printed using a label printer, immersed in Japanese sake (second grade) at room temperature, and the density before and 2 hours after immersion was compared. Debris adhesion: The amount of debris accumulated on the thermal head of the label printer was visually judged. Statesking: Tested for static noise during printing, printing problems, etc.

【table】

【table】

Claims (1)

[Scope of Claims] 1. In a heat-sensitive recording sheet in which a heat-sensitive color forming layer is provided on a support, the heat-sensitive color forming layer is mainly composed of a color forming agent and a color developer and a binder that cause the color forming agent to develop color, as the color developing agent: () (However, R ₁ to _{R 3} are hydrogen, hydroxyl group, halogen, lower alkyl group with carbon number of C ₁ to _{C 5} , lower alkoxy group,
A heat-sensitive recording material characterized in that a benzyl parahydroxythiobenzoic acid ester represented by the formula (representing a nitro group, a cyano group, or an acetyl group) is used.