JPH0621231B2 - Purification method of square lilium pigment - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for purifying squarylium pigments for improving electrophotographic properties.

2. Description of the Related Art Conventionally, as electrophotographic photoreceptors, inorganic photosensitive materials such as amorphous selenium, selenium alloy, cadmium sulfide, zinc oxide, etc., and organic photosensitive materials represented by polyvinylcarbazole and polyvinylcarbazole derivatives are widely known. .

In recent years, various types of organic photoconductors have been studied, and it has been reported that, in particular, a laminated type photoconductor having a charge generation layer and a charge transport layer has superior electrical characteristics to conventional ones.
As the charge generating material used in these photoreceptors, bisazos, trisazos, phthalocyanines, pyryliums, squaryliums, etc. are known, and as those having sensitivity from the visible region to the near infrared region, Pigments such as phthalocyanines, trisazos, and squaryliums have been reported. In particular, JP-A-49-105536
Also, the square liliums disclosed in JP-A-60-128453 and the like have excellent sensitivity from the visible region to the near-infrared region, and are therefore excellent as charge generating materials.

On the other hand, as a general purification method of organic pigments, a recrystallization method with an organic solvent, an acid pasting method with sulfuric acid, a reprecipitation method with an amine, a sublimation purification method and the like are known.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention By the way, when a square lilium pigment is used in an electrophotographic photoreceptor, even a small amount of impurities affects the charging property, dark decay, repeated stability, etc. However, many of the squarylium pigments having relatively high sensitivity have low solubility in solvents, and it has been difficult to achieve high purification. That is, in the recrystallization method using an organic solvent, the applicable range is very limited in terms of the solubility of the square lilium pigment, and a recrystallization solvent that can be applied particularly to a sparingly soluble square lilium pigment has not yet been found. . Further, the acid pasting method, the amine reprecipitation method and the sublimation purification method are hardly suitable for practical use in terms of stability and the like.

Therefore, an object of the present invention is to provide an electrophotographic photoreceptor having high sensitivity, high chargeability, low dark decay, low residual potential, and excellent stability for repeated use, and high purity. To provide a perfect square lilium pigment.

Means for Solving the Problems The above object of the present invention is achieved by dissolving a squarylium pigment in 2-chloroethanol, and recrystallizing or reprecipitating it for purification.

The square lilium pigment used in the present invention is represented by the following general formula (I).

[Wherein, R ₁ , R ₂ , R ₃ and R ₄ are each an alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted phenyl group, or (In the formula, R ₇ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms,
Hydroxyl group, alkoxy group having 1 to 4 carbon atoms, halogen atom,
A nitro group, a cyano group, a carboxyl group, an alkoxycarbonyl group having 1 to 4 carbon atoms or a trifluoromethyl group), and R ₅ and R
₆ is a hydrogen atom, a hydroxyl group, a methyl group, a halogen atom, a trifluoromethyl group, a carboxyl group, -NHCOR ₈ or -NHSO ₂ R ₉ (in the formula, R ₈ and R ₉ each have a substituent. And an alkyl group or a phenyl group). ] In particular, the square lilium pigment represented by the following general formula (II) is preferably used.

[Wherein R ₁₀ , R ₁₁ , R ₁₂ and R ₁₃ are each a methyl group, an ethyl group or (Wherein R ₁₆ represents a hydrogen atom, a methyl group, a hydroxyl group, a methoxy group, a fluorine atom, a chlorine atom, a bromine atom, a nitro group, a cyano group, a methoxycarbonyl group, an ethoxycarbonyl group or a trifluoromethyl group). R ₁₄ and R ₁₅ each represent a hydrogen atom, a hydroxyl group, a methyl group or a fluorine atom. ] Of the square lilium pigments represented by the general formula (I),
A left-right symmetrical squarerylium pigment having a four-membered ring can be easily synthesized from a square phosphoric acid and a corresponding aniline derivative by a known method. Further, a squarerylium pigment having a four-membered ring and asymmetrical left and right can be synthesized by the reaction shown in the following reaction formula.

The following are typical examples of the squarylium pigment represented by the general formula (I).

(1) 2,4-bis- [4 '(p-chlorobenzylmethylamino) phenyl] -1,3-cyclobutadiene-diylium-1,3-diolate (2) 2- (2'-fluoro-4' -Dimethylaminophenyl) -4- (2'-methyl-4'-dimethylaminophenyl) -1,3-cyclobutadiene-diylium-
1,3-diolate (3) 2,4-bis- (4'-ethylmethylaminophenyl) -1,3-cyclobutadiene-diylium-1,
3-diolate (4) 2,4-bis- (4'-dimethylaminophenyl) -1,3-cyclobutadiene-diylium-1,3
-Diolate (5) 2,4-bis- (2'-fluoro-4'-dimethylaminophenyl) -1,3-cyclobutadiene-diylium-1,3-diolate (6) 2,4-bis- (4 ′ -Dibenzylaminophenyl) -1,3-cyclobutadiene-diylium-1,3
-Diolate (7) 2- (2'-fluoro-4'-dimethylaminophenyl) -4- (2'-hydroxy-4'-dimethylaminophenyl) -1,3-cyclobutadiene-diylium-1,3- Dioleate (8) 2- (4'-dimethylaminophenyl) -4-
(2'-hydroxy-4'-dimethylaminophenyl)
-1,3-Cyclobutadiene-diylium-1,3-diolate (9) 2- (4'-dimethylaminophenyl) -4-
(2'-methyl-4'-dimethylaminophenyl)-
1,3-Cyclobutadiene-diylium-1,3-diolate (10) 2- (4'-dimethylaminophenyl) -4-
(4'-Dibenzylaminophenyl) -1,3-cyclobutadiene-diylium-1,3-diolate (11) 2- (2'-fluoro-4'-dimethylaminophenyl) -4- [4'- (P-Chlorobenzylmethylamino) phenyl] -1,3-cyclobutadiene-diylium-1,3-diolate (12) 2,4-bis (2'-hydroxy-4'-dimethylaminophenyl) -1,3 -Cyclobutadiene-diylium-1,3-diolate (13) 2,4-bis- (2'-methyl-4'-dimethylaminophenyl) -1,3-cyclobutadiene-diylium-1,3-diolate (14 ) 2,4-Bis- (3'-fluoro-4'-dimethylaminophenyl) -1,3-cyclobutadiene-diylium-1,3-diolate (15) 2,4-bis- [ ′-(P-Chlorobenzylmethylamino) -2′-fluorophenyl] -1,3-cyclobutadiene-diylium-1,3-diolate (16) 2- (2′-hydroxy-4′-dimethylaminophenyl) -4- [4 '-(p-chlorobenzylmethylamino) phenyl] -1,3-cyclobutadiene-diylium-1,3-diolate (17) 2- (2'-hydroxy-4'-dimethylaminophenyl) -4- [4 '-(p-chlorobenzylmethylamino) -2'-fluorophenyl] -1,3-cyclobutadiene-diylium-1,3-diolate (18) 2- (2'-fluoro-4' -Dimethylaminophenyl) -4- [4 '-(p-chlorobenzylmethylamino) -2'-hydroxyphenyl] -1,3-cyclobutadiene-diylium- , 3-diolate (19) 2- (2'-fluoro-4'-dimethylaminophenyl) -4- [4 '-(p-chlorobenzylmethylamino) -2'-fluorophenyl] -1,3-cyclo Butadiene-diylium-1,3-diolate (20) 2- (2'-fluoro-4'-dimethylaminophenyl) -4- (4'-dibenzylaminophenyl)-
1,3-Cyclobutadiene-diylium-1,3-diolate (21) 2- (2'-hydroxy-4'-dimethylaminophenyl) -4- (2'-methyl-4'-dimethylaminophenyl) -1 , 3-Cyclobutadiene-diylium-1,3-diolate (22) 2- (2'-fluoro-4'-dimethylaminophenyl) -4- (2'-methyl-4'-dimethylaminophenyl) -1, 3-cyclobutadiene-diylium-
1,3-diolate (23) 2- (4'-dimethylaminophenyl) -4-
(2'-fluoro-4'-dimethylaminophenyl)-
1,3-Cyclobutadiene-diylium-1,3-diolate (24) 2- (2 ', 6'-difluoro-4'-dimethylaminophenyl) -4- (2'-hydroxy-4'-dimethylaminophenyl ) -1,3-Cyclobutadiene-
Diylium-1,3-diolate (25) 2- (2 ', 6'-difluoro-4'-dimethylaminophenyl) -4- [4'-(p-chlorobenzylmethylamino) phenyl] -1,3- Cyclobutadiene-diylium-1,3-diolate (26) 2- (2 ', 6'-difluoro-4'-dimethylaminophenyl) -4- [4'-(p-chlorobenzylmethylamino) -2'- Hydroxyphenyl] -1,3
-Cyclobutadiene-diylium-1,3-diolate (27) 2- (2 ', 6'-difluoro-4'-dimethylaminophenyl) -4- [4'-(p-chlorobenzylmethylamino) -2 ' -Fluorophenyl] -1,3-
Cyclobutadiene-diylium-1,3-diolate In the present invention, the squarylium pigment represented by the general formula (I) is recrystallized or reprecipitated using 2-chloroethanol.

The recrystallization is carried out by dissolving the squarylium pigment in 2-chloroethanol, and the heating temperature at that time is preferably 60 ° C to 130 ° C (reflux temperature), and 100 ° C to 13 ° C.
0 ° C. is particularly preferred. 2-Chloroethanol may be used alone, or may be mixed with other solvent, for example, water, alcohol solvent such as ethanol, aromatic solvent such as toluene, halogenated hydrocarbon solvent such as trichloroethane. You may use. Further, an acid such as hydrochloric acid may be added.

The reprecipitation is carried out by dissolving the squarylium pigment in 2-chloroethanol and mixing it with a poor solvent, and the heating temperature at that time is the same as in the case of recrystallization. As the poor solvent, water, alcohol solvents such as ethanol, aromatic solvents such as toluene, halogenated hydrocarbon solvents such as trichloroethane, etc. are used. In addition, the ratio of the poor solvent at the time of reprecipitation is preferably in the range of 1/2 to 10 times the volume of 2-chloroethanol.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1 3,4-dihydroxy-3-cyclobutene-1,2-dione 10.0 g and N- (p-chlorobenzyl) -N-methylaniline 61.0 g were placed in a mixed solvent of 400 ml butanol and 200 ml toluene. The mixture was refluxed and reacted for 8 hours while removing the produced water. After allowing to cool, the resulting blue-green crystals were filtered off, washed with butanol, methanol and diethyl ether and dried to give 2,4-bis- [4 '(p-chlorobenzylmethylamino) having the following structural formula. Phenyl] -1,3-cyclobutadiene-diylium-1,3
-8.2 g of dioleate (exemplary compound (1)) (yield 38
%) Was obtained.

Next, 4.0 g of Exemplified Compound (1) was put in 400 ml of 2-chloroethanol, heated at reflux temperature for 20 minutes, filtered while hot, and the filtrate was allowed to cool, and the precipitated crystals were separated by filtration and purified. 3.5 g (yield 88%) of compound (1) was obtained.
The purified Exemplified Compound (1) had a crystal form different from the crystal form of the unpurified compound obtained by the above synthesis, and the X-ray diffraction of the powder was measured, and 2θ = 6 .4 °, 13.4 °, 17.6 °, 24.
A diffraction pattern having major diffraction peaks at 5 ° and 27.1 ° was shown.

Application Example 1 To 1 part by weight of the exemplified compound (1) purified by Example 1, 1 part by weight of polyvinyl butyral resin (BXL (registered trademark) manufactured by Sekisui Chemical Co., Ltd.) and 40 parts by weight of cyclohexanone were added, and the mixture was pulverized with a ball mill for 4 hours. The mixed dispersion was applied onto a polyester film (Metalmy (registered trademark) manufactured by Toray) on which aluminum was vapor-deposited using a bar coater, and dried to form a charge generation layer having a thickness of 0.2 μm.

N, N'-diphenyl-N, N 'is formed on the charge generation layer.
-Bis (3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine 1 part by weight, polycarbonate resin (manufactured by Teijin, Panlite (registered trademark)) 1 part by weight, tetrahydrofuran 10 parts by weight The resulting uniform solution was applied using a bar coater and dried to form a charge transport layer having a thickness of 15 μm, and an electrophotographic photoreceptor was prepared.

Next, the obtained electrophotographic photosensitive member was negatively charged by applying a corona discharge of -6 kV using an electrostatic copying paper tester (Kawaguchi Denki, Electrostatic Paper Analyzer, SP428), and then 2 After being left in the dark for a second, the photosensitive layer was irradiated with light using a tungsten lamp so that the illuminance on the surface was 5 lux.

The potential immediately after charging is Vo, and the potential after being left in the dark for 2 seconds is VDD
P, the exposure amount at which the surface potential becomes 1/2 of V DDP is E 1/2, 5
The surface potential after irradiating the light of looks for 10 seconds was set to VRP, and the same measurement was repeated 20 times.

The results are shown in Table 1.

Reference Example 1 Using the unpurified Exemplified compound (1) in Example 1, an electrophotographic photosensitive member was prepared in the same manner as in Application Example 1 and evaluated in the same manner. The results are shown in Table 2.

Example 2 4.0 g of the unexemplified exemplary compound (1) in Example 1 was put in 400 ml of 2-chloroethanol, and the mixture was refluxed at 20
Heat for 20 minutes, filter while hot, and immediately add methanol to the filtrate.
0 ml was poured and allowed to cool. The precipitated crystals were filtered out to obtain purified Example Compound (1) (3.6 g, yield 90%).

Application Example 2 Using the exemplified compound (1) purified by Example 2,
An electrophotographic photoreceptor was prepared in the same manner as in Application Example 1 and evaluated in the same manner. The results are shown in Table 3.

Example 3 25 g of 3,4-dichloro-3-cyclobutene-1,2-dione and 6.5 ml of boron trifluoride ethyl ether complex
Was dissolved in 30 ml of methylene chloride and N, N-dimethyl-m
-Mixed with 35 g of fluoroaniline and reacted for 16 hours at room temperature with stirring. After the reaction was completed, the mixture was diluted with dilute hydrochloric acid,
Then, it is washed with water, separated and purified by using column chromatography, and 3-chloro-4- (2'-fluoro-
4'-dimethylaminophenyl) -3-cyclobutene-
9.1 g (yield 72%) of 1,2-dione was obtained.

Then, this 3-chloro-4- (2'-fluoro-4 '
-Dimethylaminophenyl) -3-cyclobutene-1,
120 ml of acetic acid and 40 ml of water were added to 7.6 g of 2-dione, the mixture was refluxed for 2 hours, allowed to cool, and the precipitated crystals were separated by filtration and washed with water to give 3-hydroxy-4- (2'-fluoro-4'-.
Dimethylaminophenyl) -3-cyclobutene-1,2
-6.7 g (95% yield) of dione were obtained.

This 3-hydroxy-4- (2'-fluoro-
4'-dimethylaminophenyl) -3-cyclobutene-
1,2-dione (4.0 g) and N, N-dimethyl-m-toluidine (6.9 g) were put in 340 ml of butanol, and heated under reflux for 16 hours. After cooling, the resulting blue-green crystals were filtered off, washed with butanol, methanol and diethyl ether and dried to give 2- (2'-fluoro-4'-dimethylaminophenyl) -4- (2 '. -Methyl-4'-dimethylaminophenyl) -1,3-cyclobutadiene-diylium-1,3-diolate (Exemplified compound (2)) 4.
1 g (yield 68%) was obtained.

Next, 2.6 g of Exemplified Compound (2) was put in 260 ml of 2-chloroethanol, heated at reflux temperature for 10 minutes, filtered while hot, and the filtrate was allowed to cool, and the precipitated crystals were filtered off to obtain a purified compound. (2) 2.1 g (yield 81%) was obtained.

Application Example 3 Using the exemplified compound (2) purified by Example 3,
An electrophotographic photoreceptor was prepared in the same manner as in Application Example 1 and evaluated in the same manner. The results are shown in Table 4.

Reference Example 2 Using the unpurified Exemplified Compound (2) in Example 3, an electrophotographic photoreceptor was prepared in the same manner as in Example 2 and evaluated in the same manner. The results are shown in Table 5.

Example 4 Crude 2,4-bis- (4'-ethylmethylaminophenyl) -1,3-cyclobutadiene-diylium-
3.0 g of 1,3-diolate (Exemplified compound (3)) was added to 2
-Put in a mixed solvent of 25 ml of chloroethanol and 25 ml of ethanol, heat at reflux temperature for 10 minutes, filter while hot,
The filtrate was allowed to cool and the precipitated crystals were filtered off to obtain 2.7 g (yield 80%) of purified compound (3).

Application Example 4 Using the exemplified compound (3) purified by Example 4,
An electrophotographic photoreceptor was prepared in the same manner as in Application Example 1 and evaluated in the same manner. The results are shown in Table 6.

Reference Example 3 Using the unpurified Exemplified Compound (3) in Example 4, an electrophotographic photoreceptor was prepared in the same manner as in Application Example 1 and evaluated in the same manner. The results are shown in Table 7.

Examples 5 to 12 and Reference Examples 4 to 11 Exemplified compounds (4) to (11) were subjected to recrystallization treatment using 2-chloroethanol in the same manner as in Example 1 to obtain purified compounds. .

With respect to the purified Exemplified Compounds (4) to (11), an electrophotographic photoreceptor was prepared in the same manner as in Application Example 1 and evaluated in the same manner. The results are shown in Table 8. Further, using the exemplified compounds (4) to (11) not subjected to the recrystallization treatment, an electrophotographic photosensitive member was prepared in the same manner as in Application Example 1 and evaluated in the same manner. The results are shown in Table 9.

EFFECTS OF THE INVENTION Since the present invention has the above-mentioned constitution, it is possible to easily purify a squarerylium pigment which has been difficult to purify conventionally. Further, the square lilium pigment treated according to the present invention is suitable for use as a charge generating material in an electrophotographic photoreceptor, has high sensitivity, high chargeability, low dark decay and low residual potential. It is possible to form an electrophotographic photosensitive member which is low and has excellent stability against repeated use.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroyuki Tanaka 1600 Takematsu, Minamiashigara-shi, Kanagawa Fuji Xerox Co., Ltd. Takematsu business office (72) Inventor Hidemi Sudo 1600 Takematsu, Minamiashigara-shi, Kanagawa Fuji Xerox Co., Ltd. Takematsu business In-house

Claims (2)

[Claims] 1. A method for purifying a squarylium pigment, which comprises dissolving the squarylium pigment represented by the following general formula (I) in 2-chloroethanol and recrystallizing or reprecipitating it. [Wherein, R ₁ , R ₂ , R ₃ and R ₄ are each an alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted phenyl group, or (In the formula, R ₇ is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms,
Hydroxyl group, alkoxy group having 1 to 4 carbon atoms, halogen atom,
A nitro group, a cyano group, a carboxyl group, an alkoxycarbonyl group having 1 to 4 carbon atoms or a trifluoromethyl group), and R ₅ and R
₆ is a hydrogen atom, a hydroxyl group, a methyl group, a halogen atom, a trifluoromethyl group, a carboxyl group, -NHCOR ₈ or -NHSO ₂ R ₉ (in the formula, R ₈ and R ₉ each have a substituent. Represents an alkyl group or a phenyl group). ] 2. A square lilium pigment is represented by the following general formula (II):
The purification method according to claim 1, characterized in that: [Wherein R ₁₀ , R ₁₁ , R ₁₂ and R ₁₃ are each a methyl group, an ethyl group or (Wherein R ₁₆ represents a hydrogen atom, a methyl group, a hydroxyl group, a methoxy group, a fluorine atom, a chlorine atom, a bromine atom, a nitro group, a cyano group, a methoxycarbonyl group, an ethoxycarbonyl group or a trifluoromethyl group). R ₁₄ and R ₁₅ each represent a hydrogen atom, a hydroxyl group, a methyl group or a fluorine atom. ]