JP2807903B2 - Leuco dye - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel leuco dye for image formation, and more particularly to a near-infrared absorbing leuco dye in heat-sensitive recording and pressure-sensitive recording.

[Conventional technology]

Recording materials using leuco dyes have been known for a long time, as shown in Japanese Patent Publication No. 45-14039, and are used as pressure-sensitive recording papers and heat-sensitive recording papers, and their use is increasing year by year.

Commonly used leuco dyes include, for example, triphenylmethane type, fluoran type, phenothiazine type, auramine type and the like. These dyes have various color tones and are properly used depending on the application. However, many of these dyes have been developed for the purpose of absorbing a color tone, that is, a visible region, and a near infrared region, that is, a dye.
At present, almost no dyes having an absorption in the range of 700 to 1000 nm have been developed. In recent years, as the use of semiconductor lasers has spread, there has been a movement to read recorded images such as barcodes with semiconductor lasers.
Thermal papers and the like are required to have absorption in the near infrared region.

In recent years, there have been several proposals regarding leuco dyes having absorption in the near infrared region and heat-sensitive and pressure-sensitive recording materials. For example, JP-A-51-121035, JP-A-57-167979, JP-A-58-167
Phthalide compounds containing one or two vinyl groups, such as those disclosed in JP-A-157779, JP-A-59-199757 and JP-A-60-199757.
Fluorene compounds such as those found in JP 226871
Fluoran compounds such as those found in US Pat.
There are sulfonylmethane compounds and the like as described in No. 0-231766.

[Problems to be solved by the invention]

However, although these compounds have absorption in the near infrared region, their strength is insufficient or their stability is poor. Also, its color tone is green,
When used for general recording materials, there has been a drawback that a leuco dye exhibiting a black color such as a fluoran compound must be used in combination in order to realize a strongly required black color.

Therefore, the present invention provides a color image in the near infrared region, particularly 700 to 9
An object of the present invention is to provide a novel leuco dye having strong absorption in the range of 00 nm and further exhibiting a blackish absorption in the visible region.

[Means for solving the problem]

According to the present invention, there is provided a leuco dye represented by the following general formula (I).

(Wherein, R _{1 to} R ₆ each represent the following.

R ₁ , R ₂ : lower alkyl group, cycloalkyl group, aralkyl group or aryl group. Further, R ₁ and R ₂ may be bonded to each other to form a ring, or may form a morpholine ring bonded via —O—.

R ₃ : a hydrogen atom, a lower alkyl group, an alkoxy group or an aralkyloxy group.

R ₄ and R ₅ : lower alkyl groups.

R ₆ : a hydrogen atom, a lower alkyl group, an alkoxy group or a halogen atom. In the general formula (I), specific examples of R ₁ and R ₂ include a lower alkyl group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group and an isobutyl group; a cycloalkyl group such as a cyclohexyl group An unsubstituted aryl group such as a phenyl group; a substituted aryl group substituted with a lower alkyl group such as a methyl group or an ethyl group or a dialkylamino group such as a dimethylamino group or a diethylamino group; an unsubstituted aryl group such as a benzyl group or a phenethyl group; A substituted aralkyl group; a substituted aralkyl group substituted with a lower alkyl group such as a methyl group and an ethyl group; and a heteroaliphatic functional group such as a piperidino group, a pyrrolidino group, and a morpholino group. Specific examples of R ₃ include a hydrogen atom; a lower alkyl group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group and an isobutyl group; a lower alkoxy group such as a methoxy group, an ethoxy group, a propoxy group and an isopropoxy group. Groups; aralkyloxy groups such as benzyloxy group and phenylethyloxy group; and R ₄ and R ₅ are lower alkyl groups such as methyl group, ethyl group, propyl group, isopropyl group, butyl group and isobutyl group. No. As a specific example of R ₆ ,
Hydrogen atom; lower alkyl groups such as methyl group, ethyl group, propyl group, and isopropyl group; methoxy group, ethoxy group,
An alkoxy group such as a propoxy group; and a halogen atom such as chlorine and bromine.

The leuco dye represented by the general formula (I) is a novel compound, usually a white to slightly yellow crystal, and can be easily synthesized according to the following reaction formula.

(Wherein R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , and R ₆ are the same as those described above) That is, a ketone derivative represented by the general formula (II) and an ethylene represented by the general formula (III) The derivative can be easily synthesized by dehydration condensation in the presence of a dehydration condensing agent.

In this case, acetic anhydride, propionic anhydride, phosphorus oxychloride, sulfuric acid, polyphosphoric acid, etc., and various Friedel-Crafts catalysts are used as the dehydrating condensing agent.

Further, the compound represented by the general formula (II) is obtained by converting various aromatic amine compounds and naphthalenedicarboxylic anhydride into
It can be easily obtained by reacting in the presence of a Friedel Crafts catalyst.

Further, the compound represented by the general formula (III) can be easily obtained by subjecting a benzophenone derivative to a Grignard reaction.

Specific examples of the leuco dye represented by the general formula (I) of the present invention include those shown in Table 1, but are not necessarily limited thereto.

To obtain a thermosensitive recording material using the leuco dye of the present invention, auxiliary components such as a leuco dye, a color former (electron-accepting compound) and a filler are each dispersed in an aqueous medium, and a mixed solution thereof is supported together with a binder. Apply and dry on body. This thermosensitive recording material is heated by a thermal head or the like, and a color image can be obtained by melting and contacting the leuco dye and the color former.

〔The invention's effect〕

The leuco dye of the present invention has a color-developing substance having strong absorption in a region of 700 to 900 nm, and it is possible to read a color by an image reader using a general-purpose semiconductor laser, and at the same time, a visible image is black. Has the advantage of being sharp due to the coloration.

〔Example〕

 Next, the present invention will be further described with reference to examples.

Example 1 [Synthesis of Compound of Specific Example No. (1)] 7.5 g of 2- (4'-diethylamino-2'-methoxybenzoyl) naphthoic acid and 1- (4-dimethylaminophenyl) -1- (4 (Chlorophenyl) ethylene (5.2 g), acetic anhydride (40 ml) is added, and the mixture is heated and stirred at 50 to 70 ° C. for 2 hours. After cooling, the reaction solution is poured into 200 ml of water, neutralized with an aqueous sodium hydroxide solution, and the precipitate is collected by filtration. Further, the precipitate is dissolved in 20 ml of concentrated hydrochloric acid, neutralized with an aqueous sodium hydroxide solution, and the precipitate is collected by filtration. Next, the precipitate was recrystallized from acetone to obtain white crystals. Yield 9.8 g, melting point 214
~ 221 ° C. The maximum absorption wavelength in acetic acid was 741 nm.

Example 2 Synthesis of Compound of Specific Example No. (2) 6.5 g of 2- (4'-diethylamino-2'-methoxybenzoyl) naphthoic acid and 1- (4-dimethylaminophenyl) -1-phenylethylene To 3.7 g, 30 ml of acetic anhydride is added, and the mixture is heated and stirred at 50 to 70 ° C for 2 hours. After cooling, the reaction solution is poured into 200 ml of water, neutralized with an aqueous sodium hydroxide solution, and the precipitate is filtered out. Next, the precipitate was recrystallized from acetone to obtain white crystals. Yield 9.0 g, melting point 210-215
° C. The maximum absorption wavelength in acetic acid was 730 nm.

Example 3 Synthesis of Compound of Specific Example No. (55) Instead of 1- (4-dimethylaminophenyl) -1-phenylethylene in Example 2, 1- (4-dimethylaminophenyl) -1- p-toluylethylene
Except that 3.6 g was used, 8 g of white crystals were obtained in the same manner as in Example 2. The melting point of this compound was 210-216 ° C, and its maximum absorption wavelength in acetic acid was 735 nm.

Example 4 Synthesis of Compound of Specific Example No. (3) Instead of 1- (4-dimethylaminophenyl) -1-phenylethylene in Example 2, 1- (4-dimethylaminophenyl) -1- 6.6 g of white crystals were obtained in the same manner as in Example 2, except that 3.8 g of (4-methoxyphenyl) ethylene was used. The melting point of this compound is 16
At 0-168 ° C, its maximum absorption wavelength in acetic acid was 732 nm.

Examples 5 to 22 Examples of various benzophenone derivatives represented by the general formula (II) and various ethylene derivatives represented by the general formula (III) are given in the same manner as in Example 1 by the same operation as in Example 1. Various compounds were synthesized. All are white to slightly yellow crystals, and the melting point and the maximum absorption wavelength in acetic acid are shown in Table 2.

Application Example 1 10 parts of the compound of Specific Example No. (1) synthesized in Example 1, 1
A mixture of 10 parts of a 0% aqueous polyvinyl alcohol solution and 30 parts of water is dispersed in a ball mill to prepare [Solution A]. Also, a mixture of 30 parts of 4,4'-diphenol sulfone, 20 parts of stearic acid amide, 20 parts of calcium carbonate, 35 parts of a 10% aqueous solution of polyvinyl alcohol, and 210 parts of water was dispersed in a ball mill and [liquid B] was dispersed. Prepare. Next, the [Solution A] and [Solution B] were mixed at a ratio of 1: 1 to prepare a coating solution, and the coating solution was applied on wood free paper and dried to prepare a thermosensitive recording material. This thermosensitive recording material is colored at 150 ° C. for 2 seconds,
The reflectance of the image and the background was measured with a reflection type spectrophotometer, the PCS value at 780 nm was obtained from the following equation, and the density of the image was measured with a Macbeth densitometer.

As a result, the color tone is green-black, Macbeth density is 1.10,
PCS value was 93.0%.

From these facts, it is clear that the leuco dye of the present invention is a substance whose color former exhibits a blackish coloration and at the same time has strong absorption in the near infrared region.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hisahiro Shimada 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Katsuhiro Nakata 1-2-2 Dojima, Kita-ku, Osaka-shi, Osaka No. 2 Inside Showa Kako Co., Ltd. (72) Kaoru Kodera 1-2-2 Dojima, Kita-ku, Osaka, Osaka Prefecture Inside of Showa Kako Co., Ltd. (72) Koji Ohara 1-2-2 Dojima, Kita-ku, Osaka, Osaka No. 2 Inside Showa Kako Co., Ltd. (72) Nobuo Akagi, Inventor 1-2-2 Dojima, Kita-ku, Osaka City, Osaka Prefecture Inside Showa Kako Co., Ltd. (56) References JP-A-60-73893 (JP, A) JP-A JP-A-2-289383 (JP, A) JP-A-63-165379 (JP, A) JP-A-64-24787 (JP, A) JP-A-63-4990 (JP, A) JP-A-64-29371 (JP , A) (58) Fields surveyed (Int. Cl. ⁶ , DB name) C09B 11/00-11/02 B41M 5/124-5/165 B41M 5/28-5/34 CA (STN)

Claims (1)

(57) [Claims] (1) General formula A leuco dye represented by (Wherein, R _{1 to} R ₆ each represent the following: R ₁ , R ₂ : a lower alkyl group, a cycloalkyl group, an aralkyl group, or an aryl group. Further, R ₁ and R ₂ are bonded to each other. R ₃ : a hydrogen atom, a lower alkyl group, an alkoxy group or an aralkyloxy group R ₄ , R ₅ : a lower alkyl group R ₆ : hydrogen atom, lower alkyl group, alkoxy group or halogen atom.)