JPH085892B2 - Fluoran compound and thermosensitive recording material containing the compound - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fluoran compound useful as a color-forming compound used in a heat-sensitive recording material, and a heat-sensitive recording material containing the compound.

[Conventional technology]

Conventionally, colorless or light-colored electron-donating compounds (color-forming compounds) and organic or inorganic electron-accepting substances (developers)
Thermal recording using the color reaction with is widely used.

In this recording method, a fluoran compound is widely used as a color forming compound.

Conventionally, as a fluoran compound, for example, formula (A) ~
Formula (F), The compound of is known.

However, when the compound of the formula (A) is used in a heat-sensitive recording material, a mixture with a developer, for example, bisphenol A, develops a gray color or a black gray color by itself, and when it is applied to paper, it is gray or black. It has the drawback that only black-gray colored (ground stain) paper can be obtained.

Further, the compounds of the formulas (B) to (F) have a drawback that they are discolored to gray or brown due to humidity, light or heat, although a paper having a relatively high whiteness can be obtained immediately after coating.

Recently, thermal recording materials have been used not only indoors such as facsimiles but also outdoors and under more severe conditions such as prepaid cards typified by telephone cards and the like. It was Therefore, the thermal recording material is required to have further storage stability.

[Problems to be Solved by the Invention]

An object of the present invention is to provide a novel fluorane compound having excellent storage stability as a color-forming compound for a heat-sensitive recording material, and also to provide a method for producing this compound and a heat-sensitive recording material containing this compound. Is to provide.

[Means for solving the problem]

The present inventors have arrived at the present invention by searching various compounds in order to solve the above problems.

That is, the present invention is a fluoran compound represented by the formula (I), This compound has the formula (II) A benzoic acid derivative represented by the general formula (III) (Wherein R represents a lower alkyl group) and a diphenylamine derivative represented by the reaction, and a heat-sensitive recording material containing the fluorane compound.

The benzoic acid derivative of formula (II) used to prepare the fluorane compound of formula (I) of the present invention is typically
3-N-cyclohexyl-N-n-propylaminophenol and phthalic anhydride without solvent, or benzene,
It can be produced by reacting in a solvent such as toluene, xylene or tetrachloroethylene. During this reaction, a Lewis acid such as zinc chloride may be added.

Further, in the diphenylamine derivative represented by the general formula (III), in the general formula (III), R represents a lower alkyl group, and a specific example of the lower alkyl group is a methyl group or an ethyl group. it can. A methyl group is particularly preferable.

The fluoran compound of the formula (I) is a benzoic acid derivative of the formula (II) and a diphenylamine derivative of the general formula (III),
For example, it can be suitably produced as alkaline after reacting in the presence of a dehydrating condensing agent such as concentrated sulfuric acid, concentrated sulfuric acid added with fuming sulfuric acid, polyphosphoric acid, phosphorus pentoxide, or anhydrous aluminum chloride, more preferably in concentrated sulfuric acid. Dehydration condensation reaction is 0-100
A reaction temperature of 0 ° C is preferred, especially when the reaction is carried out in concentrated sulfuric acid, a temperature of 0 to 50 ° C is particularly preferred. The reaction time largely depends on the reaction temperature, but it is usually preferably several hours to 100 hours. After dehydration condensation, alkali treatment is usually carried out, but when alkali treatment is carried out, the pH is adjusted to 9 to 12 with potassium hydroxide, aqueous sodium hydroxide or the like.
The temperature is preferably 0 to 100 ° C. At this time, the alkali treatment may be performed in the coexistence of a solvent other than water, such as benzene or toluene.

In order to use the fluorane compound of the present invention in a heat-sensitive recording material, a fluorane compound of the formula (I) and a developer (for example, bisphenol A or a halide thereof, an alkylated product, dihydroxydiphenyl sulfone or a halide thereof, an alkylated hydroxybenzoic acid) are used. Acid esters, phenols such as hydroquinone monoethers, salicylic acid derivatives, salicylic acid amide derivatives, urea derivatives, organic developers such as thiourea derivatives, acid clay, attapulgite, activated clay, aluminum chloride, zinc bromide Binder (for example, polyvinyl alcohol or a modified product thereof, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, gum arabic, styrene-maleic anhydride copolymer salt, isobutene) in a fine aqueous dispersion of such an inorganic developer. Len - acrylic acid - such as a copolymer of maleic acid), pigment (talc, kaolin,
Calcium carbonate, etc., and if necessary, sensitizers (higher fatty acid amides, esters of aromatic carboxylic acids or sulfonic acids, aromatic or aromatic group-substituted aliphatic ethers or aromatic or aromatic group-substituted) Generally known sensitizers for heat-sensitive recording materials such as aliphatic hydrocarbons) and other additives (for example, ultraviolet absorbers, defoaming agents, etc.) are added to form a fine dispersion, and a suitable support (for example, paper, Plastic sheet,
It can be used as a heat-sensitive recording material by coating it on resin-coated paper or the like. Of course, it can be used without problems in a system using a solvent instead of an aqueous dispersion system.

The compound of formula (I) can be used alone as the color forming compound, and further, for adjusting the color of the color forming, for example, other color forming compounds such as triphenylmethane lactones, fluoranes and spiropyran. It is also possible to mix and use the classes as desired.

The melting point of the fluoran compound of formula (I) of the present invention is 257-2.
58 ° C., for example, the melting point of the known compound of formula (A) is 19
5 to 198 ° C., the melting point of the compound of formula (B) is 195 to 197 ° C., and the melting point of the compound of formula (C) is 124 to 126 ° C., which are extremely high.

Further, the compound of the present invention has extremely low solubility in various organic solvents (for example, hydrocarbon solvents such as benzene and toluene, esters such as ethyl acetate, ketones such as acetone). For example, the results of comparing the solubility in toluene with the compounds of formulas (A) to (F) are shown in Table 1.

The solubilities are shown in% by weight with respect to toluene at 25 ° C.

When the compound of the present invention having the above-mentioned properties is used in a heat-sensitive recording material, a heat-sensitive paper having high whiteness and free from background stain is obtained, and the storage stability (for example, moist heat resistance and solvent resistance) of the paper is very high. Are better. For example, Bisfer A is used as a color developer and the compound of formula (I) of the present invention is used as a color-forming compound.
Table 2 shows the results of a comparison between the heat-sensitive paper using the compound of Example 1 and the heat-sensitive recording paper using any of the compounds of the formulas (A) to (F) for the moist heat resistance and oil resistance of the background (uncolored portion). As shown.

In the moist heat resistance test, the thermal paper prepared by using each compound was kept at 60 ° C. in 90% relative humidity for 24 hours, and the stain of the paper was visually observed.

In the oil resistance test, the thermal paper was brought into contact with dioctyl phthalate and left for 1 week, and then the paper was visually observed for dirt.

Represents

The fluoran compound of the formula (I) of the present invention has the formula (A) to
The fluorane compound of the formula (F) is a structure different from the fluorane structure only in the substituent on the amino group at the 3-position,
In particular, it differs from the fluorane compound of the formula (B) only in the structure in which one methyl group on the amino group is converted into an n-propyl group, and as described above, the formula (A), the formula (B) and the formula (C 2) has a much higher melting point than that of the fluorane compound, and has a much lower solubility in an organic solvent than the fluorane compound of the formulas (A) to (F). When the fluorane compound of the formula (I) of the present invention having such properties is used in a heat-sensitive recording material, the storage stability of the heat-sensitive paper is greatly improved.

In particular, regarding the solubility in an organic solvent, generally, for example, when a methyl group is converted into a longer-chain alkyl group such as an n-propyl group, the solubility in an organic solvent, particularly a hydrocarbon solvent is increased. It is believed to be higher. However, comparing the solubilities of the fluorane compound of formula (I) and the fluorane compound of formula (A) of the present invention in toluene, the fluorane compound of formula (I) has the formula (A)
The solubility is much lower than that of
It's amazing.

Especially regarding the solubility in organic solvents, for example,
A compound of formula (E) in which the methyl group on the amino group of the compound of formula (B) is changed to an isoamyl group As described above, introduction of a longer-chain alkyl group is known to increase the solubility in an organic solvent, particularly a hydrocarbon solvent (for example, toluene) (for example, JP-A-54-34909). Gazette).

However, the fluorane compound of the formula (I) of the present invention having an n-propyl group on the amino group has the formula (B) and the formula (C).
And a fluoran compound of the formula (D), which has a feature that has not been found in the past that the solubility in toluene is extremely low, can be used as a color forming compound to provide a thermal recording paper having excellent storage stability. .

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 [Preparation of compound of formula (I)] 2- (4'-N-cyclohexyl-Nn-propylamino-2'-hydroxybenzoyl) benzoic acid [compound of formula (II)] 20 g of 100 ml After dissolving in concentrated sulfuric acid at 10 ℃,
11 g of 4-methoxy-2-methyldiphenylamine (a compound in which R is a methyl group in the general formula (III)) was added at the same temperature, and the mixture was stirred at 10 to 25 ° C. for 48 hours. 600 ml of reaction mixture
The solid that has precipitated is collected and washed with water, and then the solid is collected.
The mixture was added to 10% NaOH water (500 ml) and stirred at 60 to 70 ° C for 2 hours. The solid was filtered, washed with water, and then washed with 100 ml of isopropanol.

Furthermore, it is washed twice with toluene to obtain the desired 3-N-
20 g (69% yield) of cyclohexyl-Nn-propylamino-6-methyl-7-anilinofluorane was obtained as almost colorless crystals.

Melting point 257-258 ° C. The infrared absorption spectrum (KBr tablet) of this compound is shown in FIG. The powder X-ray diffraction pattern is shown in FIG.

Example 2 [Preparation of thermal recording paper using compound of formula (I)] 3-N-cyclohexyl-Nn-propylamino-6-methyl-7-anilinoflu of the present invention prepared in Example 1 Oran 10g, 10% polyvinyl alcohol aqueous solution 5g
A mixture of water and 37.5 g of water was atomized with a sand mill to a particle size of 3 μ. On the other hand, bisphenol A was similarly dispersed to obtain a 38% developer dispersion. 65.8 g of this color developer dispersion, the above 3
-N-cyclohexyl-N-n-propylamino-6-
Aqueous dispersion of methyl-7-anilinofluorane 50g, 60%
18.3 g of an aqueous dispersion of light calcium carbide, 88 g of a 100% polyvinyl alcohol aqueous solution and 51.9 g of water were mixed.

This mixed solution was applied to a white base paper using a wire rod No. 10 and then air-dried at room temperature to obtain a very white thermosensitive recording paper free of background stain. The heat-sensitive recording paper developed a slightly reddish black color very quickly when heated.

The storage stability (heat resistance, wet heat resistance, light resistance, etc.) of this color image was good.

When this thermosensitive recording paper was stored for 24 hours at 60 ° C and 90% relative humidity, the paper retained its whiteness immediately after coating and no scumming was observed. Also, after contacting the surface of the paper with dioctyl phthalate and storing it for 1 week,
No background stain on the paper was observed (Table 2).

Comparative Example In Example 2, 3-N-cyclohexyl-N-n
3-N-ethyl-N-ethylamino-6- instead of -propylamino-6-methyl-7-anilinofluorane
Methyl-7-anilinofluorane [compound of formula (A),
3-N-hexyl-N-methylamino-6-methyl-7
-Anilinofluorane [compound of formula (B)], 3-N-
Hexyl-N-ethylamino-6-methyl-7-anilinofluorane [compound of formula (C)], 3-N-hexyl-N-i-butylamino-6-methyl-7-anilinofluorane [ Compound of formula (D)], 3-N-hexyl-N
-I-heptylamino-6-methyl-7-anilinofluorane [compound of formula (E)] or 3-N-hexyl-
Using Nn-octylamino-6-methyl-7-anilinofluorane [compound of formula (F)], a heat-sensitive recording paper was prepared according to the method described in Example 2, and a moisture-heat resistance test and an oil resistance test were conducted. went. The results are shown in Table 2.

The coated surface of the thermal recording paper using the compound of formula (A) was already slightly soiled in gray immediately after coating.

[Brief description of drawings]

FIG. 1 shows the infrared absorption spectrum (KBr tablets) of the fluoran compound of formula (I). The vertical axis represents the transmittance, and the horizontal axis represents the wave number (cm ^-1 ). FIG. 2 shows the powder X-ray diffraction pattern of the fluoran compound of formula (I). The vertical axis represents the diffraction intensity, and the horizontal axis represents the diffraction angle (2
θ).

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Claims (2)

[Claims] 1. A formula (I) Fluoran compound represented by. 2. A heat-sensitive recording material containing a fluorane compound represented by the formula (I) according to claim 1.