JPH0480839B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to thermal recording paper with improved properties. Advances in recording devices due to advances in electronics have been remarkable, including thermal pen recorders for various measuring instruments,
Thermal recording paper is widely used in computer thermal printers, thermal automatic ticket vending machines, and facsimile machines. In particular, high-speed recording performance is required for information-related equipment such as facsimile machines.
The thermal recording paper used for this must also have the ability to quickly produce a dense recorded image. Thermal recording paper is made by coating a color forming agent and a color developer on a support, but in order for the thermal recording paper to have the above performance, the color developer must dissolve with a small amount of heat and cause a color reaction. is necessary. Among the phenol compounds that are often used as color developers, para-hydroxybenzoic acid esters, particularly para-hydroxybenzoic acid benzyl esters, are known as suitable color developers for high-speed thermal recording (Japanese Patent Application Laid-Open No. 1983-1972-1).
(See Publications No. 140483, No. 56-144193, No. 57-82089, and No. 57-107883). Thermal recording paper containing these color developers has many features such as good color development performance, high density and clear recorded images, and little background fog. However, the stability of the recorded image after color development is not necessarily sufficient, and it is known that fading and whitening phenomena occur in the color recorded image. The reason for this is not clear, but it is thought that the parahydroxybenzoate ester is detached and crystallized from the charge transfer complex of the color former and the parahydroxybenzoate ester, causing discoloration or whitening. In order to prevent this crystallization, methods of adding certain compounds are known, but satisfactory results have not always been obtained. In view of these circumstances, the present inventors conducted research and succeeded in obtaining a compound capable of inhibiting color fading or whitening phenomenon in thermosensitive recording paper. The present invention provides a colorless to light coloring agent, a color developer that causes this substance to develop color when heated, and a general formula (In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a hydrogen atom, a methyl group, or a group This is a thermosensitive recording paper having a thermosensitive layer containing an aromatic hydroxycarboxylic acid phenylmethyl ester represented by the formula (* indicates bonding with a phenyl group). The compound of the formula is a new compound that has not been described in any literature, and can be produced by using the ester reaction and etherification reaction described below. (1) General formula Phenyl methyl alcohol represented by (in the formula R ¹ has the above meaning) and the general formula A direct esterification reaction with a carboxylic acid represented by the formula (wherein T and R ² have the above-mentioned meanings). (2) General formula A dehydrohalogenation reaction between a halogenated phenylmethyl represented by the formula (wherein Z represents a halogen atom and R ¹ has the above-mentioned meaning) and an alkali salt of a compound of the formula. (3) Transesterification reaction between phenyl methyl alcohol of the formula and an alkyl ester of the compound of the formula. (4) A method in which a compound of the formula is reacted with an alkali salt of 2-hydroxy-naphthalene-6-carboxylic acid to carry out esterification and etherification reactions. (5) A method in which an alkali salt of nitrobenzoic acid is reacted with a compound of formula and the resulting product is etherified. Examples of compounds of the formula include 2-phenylmemethoxy-naphthalene-6-carboxylic acid phenylmethyl ester, 2-paramethylphenylmethoxy-naphthalene-6-carboxylic acid phenylmethyl ester, and 2-phenylmethoxy-naphthalene. -6
-Carboxylic acid-paramethyl-phenylmethyl ester, 2-paramethylphenylmethoxy-naphthalene-6-carboxylic acid-paramethyl-phenylmethyl ester, 4,4'-ethylenedioxy-bis-benzoic acid diphenylmethyl ester , 4,4′−
Examples include ethylenedioxy-bis-benzoic acid-di-(paramethyl)-phenylmethyl ester. When producing the thermal recording paper of the present invention, first, a color former, a color developer, and a compound of the formula are blended.
The mixing ratio is preferably 100 to 1000 parts by weight of the color developer to 100 parts by weight of the color former. The compound of the formula is preferably blended in an amount of 1 to 200 parts by weight per 100 parts by weight of the color developer. Colorless to light color formers include phthalide-based and fluoran-based leuco dyes, such as crystal violet lactone, benzoyl leucomethylene blue, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6- Methyl-7-chlorofluorane, 3-(N
-cyclohexyl-N-methylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-7-(ortho-chloroanilino)fluorane, 3-(N-ethyl-paratoluidino)-6-methyl-7-anilinofluorane Linofluorane, 3-diethylamino-7-[meta(trifluoromethyl)anilino]fluorane, 3-diethylamino-6-methyl-7-(ortho-para-dimethylanilino)fluorane, 3-pyrrolidino-6-methyl- Examples include 7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methylfluoran, and 3-cyclohexylamino-6-chlorofluorane. As a color developer, parahydroxybenzoic acid esters such as methyl parahydroxybenzoate, -ethyl, -propyl, -isopropyl, -butyl, -isobutyl, -hexyl, -benzyl, -phenethyl,
Examples include -phenyl and -naphthyl. These materials are atomized using water as a medium using a grinder such as a ball mill, attritor, or sand grinder, or a suitable emulsifying device, and various additive materials are added depending on the purpose to form a coating liquid. Additive materials include polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose,
Starches, styrene-maleic anhydride copolymer, vinyl acetate-maleic anhydride copolymer, styrene-
Binders such as butadiene copolymers, fillers such as kaolin, diatomaceous earth, talc, titanium oxide, calcium carbonate, magnesium carbonate, aluminum hydroxide, fatty acid metal salts such as zinc stearate, aluminum stearate, calcium stearate, oleic acid. Excipients such as zinc, waxes,
Examples include lubricants such as paraffin wax, cownabar wax, and polyethylene wax, benzophenone-based and triazole-based ultraviolet absorbers, water-resistant agents such as cryoxal, dispersions, and antifoaming agents. The thermosensitive recording paper of the present invention can be obtained by applying a coating solution containing these additive materials to a support such as paper or film. The heat-sensitive recording paper of the present invention has good color development, high-speed recording performance, and background stability, and furthermore, fading and whitening of recorded images are improved and stability is excellent. Example 1 Synthesis of 2-phenylmethoxy-naphthalene-6-carboxylic acid phenylmethyl ester 2-hydroxy-naphthalene-6-carboxylic acid
Add 470.5 g of dimethylformamide to 188.2 g (1.0 mol), 212.0 g (2.0 mol) of sodium carbonate, and 253.2 g (2.0 mol) of phenylmethyl chloride.
Heated at ℃ for 3 hours. After the reaction, dimethylformamide was distilled off, a toluene-water mixture was added, and the mixture was separated at 70°C. Next, the toluene layer was washed with alkali,
After washing with water, add toluene-water mixture again and
332 g of colorless crystals with a melting point of 96.7-98.0°C (yield 90%) are obtained by separating the toluene layer at ℃ and filtering it after cooling.
I got it. Elemental analysis value: C ₂₅ H ₂₀ O ₃ C H Theoretical value (%) 81.50 5.47 Experimental value (%) 81.41 5.51 Example 2 4,4'-ethylenedioxy-bis-benzoic acid-
Synthesis of diphenyl methyl ester 4,4'-ethylenedioxy-bis-benzoic acid-
1.32 g of dibutyltin oxide was added to 66.0 g (0.2 mol) of dimethyl ester and 86.4 g (4.0 mol) of phenylmethyl alcohol, and the mixture was heated at 190 to 200° C. for 2 hours while distilling off methanol. After the reaction, dibutyltin oxide was distilled off, and the resulting crude crystals were recrystallized from acetone to obtain 50.8 g (yield: 77%) of colorless crystals with a melting point of 108.5 to 110.2°C. Elemental analysis value: C ₃₀ H ₂₆ O ₆ C H Theoretical value (%) 74.67 5.43 Experimental value (%) 74.49 5.48 Example 3 Solution A (dye dispersion) 3-(N-cyclohexyl-N-methylamino)
-6-Methyl-7-anilinofluorane 4.0 parts 10% polyvinyl alcohol aqueous solution 9.2 parts Water 5.0 parts Solution B (Developer dispersion) Parahydroxybenzoic acid benzyl ester
6.0 parts 2-phenylmethoxy-naphthalene-6-carboxylic acid phenyl methyl ester 0.6 parts 10% polyvinyl alcohol aqueous solution 30.0 parts Each solution having the above composition was ground and mixed in a ball mill.
Next, a coating liquid was prepared by mixing 1.0 parts of liquid A and 4.0 parts of liquid B, and this coating liquid was applied to high-quality paper using a wire bar to obtain thermal recording paper (coating amount:
6g/ ^m2 ). Example 4 In place of 2-phenylmethoxy-naphthalene-6-carboxylic acid phenylmethyl ester in Solution B of Example 3, 2-paramethylphenylmethoxy-naphthalene-6-carboxylic acid-paramethyl-
A thermosensitive recording paper was obtained in the same manner as in Example 3 except that phenyl methyl ester was used. Example 5 Using 4,4'-ethylenedioxy-bis-benzoic acid diphenylmethyl ester instead of 2-phenylmethoxy-naphthalene-6-carboxylic acid phenylmethyl ester in Solution B of Example 3,
A thermosensitive recording paper was obtained in the same manner as in Example 3 in other respects. Comparative Example 1 A thermosensitive recording paper was obtained in the same manner as in Example 3 except that 2-phenylmethoxy-naphthalene-6-carboxylic acid phenylmethyl ester was not used in Solution B of Example 3. Comparative Example 2 4,4'-methylene-bis-(2,4'-methylene-bis-(2, A thermosensitive recording paper was obtained in the same manner as in Example 3 except that 6-tertiary butylphenol) was used. Test Example 1 For the three types of thermal recording papers of Examples 3 to 4 and Comparative Example 1, the background density and the image density when colored at 120°C were measured. In addition, heat-sensitive recording paper after color development is
℃ and humidity of 90% or 60℃ for 24 hours, and changes in background density and image density were measured. The results are shown in Table 1.

[Table] *: ○: Almost no change △: Discolored in spots

[Table] Test Example 2 After developing colors at 120°C for the three types of thermal recording papers of Examples 3 to 4 and Comparative Example 1, they were left for 24 hours under harsh conditions of 60°C and 90% humidity to observe changes in image density. It was measured. The results are shown in Table 2.

[Table] *: ○ means almost no change
x: Crystals precipitate white or are discolored in spots Test Example 3 The background density and the image density when colored at 120° C. were measured for the three types of thermal recording papers of Example 5 and Comparative Examples 1 and 2. In addition, heat-sensitive recording paper after color development is
℃ and 90% humidity for 24 hours, and changes in background density and image density were measured. The results are shown in Table 3.

[Table] *: ○: Almost no change ×: Crystals precipitate white or become mottled Discoloration

Claims (1)

[Scope of Claims] 1. A colorless or light-colored coloring agent, a coloring agent that causes this substance to develop color when heated, and a general formula (In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a hydrogen atom, a methyl group, or a group A thermosensitive recording paper having a thermosensitive layer containing an aromatic hydroxycarboxylic acid phenylmethyl ester represented by the formula (* indicates bonding with a phenyl group).