Oxo-titanylphthalocyanine crystal, method for producing the same, and electrophotographic photoreceptor

Abstract

The invention provides an oxo-titanylphthalocyanine crystal which is stable, is superior in dispersibility in a photoreceptive layer and efficiently contributes to improvements in sensitivity and charge retention rate of an electrophotographic photoreceptor when it is used as a charge generating agent, a method for producing the oxo-titanylphthalocyanine crystal, and an electrophotographic photoreceptor. The oxo-titanylphthalocyanine crystal has predetermined optical characteristics and thermal properties and is produced by a production method including the following steps (a) to (d): (a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in an acid to obtain an oxo-titanylphthalocyanine solution; (b) a step of adding the oxo-titanylphthalocyanine solution dropwise in a poor solvent to obtain a wet cake; (c) a step of washing the wet cake with an alcohol having 1 to 4 carbon atoms; and (d) a step of stirring the washed wet cake under heating in a nonaqueous solvent to obtain an oxo-titanylphthalocyanine crystal.

1 . An oxo-titanylphthalocyanine crystal having a maximum diffraction peak at a Bragg angle (2θ±0.2°)=27.2° in a CuKα characteristic X-ray diffraction spectrum and one peak in a temperature range from 270 to 400° C. other than the peak derived from vaporization of adsorbed water in differential scanning calorimetric analysis, the oxo-titanylphthalocyanine crystal being produced by a production method comprising the following steps (a) to (d):
 (a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in an acid to obtain an oxo-titanylphthalocyanine solution;   (b) a step of adding the oxo-titanylphthalocyanine solution dropwise in a poor solvent to obtain a wet cake;   (c) a step of washing the wet cake with an alcohol having 1 to 4 carbon atoms; and   (d) a step of stirring the washed wet cake under heating in a nonaqueous solvent to obtain an oxo-titanylphthalocyanine crystal.   
   
   
       2 . The oxo-titanylphthalocyanine crystal according to  claim 1 , wherein the production method comprises the following inspection steps (e) to (g) after the step (d):
 (e) a step of adding the oxo-titanylphthalocyanine crystal in an amount by weight of 1.25 parts based on 100 parts by weight of a mixed solvent of methanol and N,N-dimethylformamide (methanol:N,N-dimethylformamide=1:1 (by weight ratio)) to prepare a suspension;   (f) a step of filtering the suspension with a filter to obtain a filtrate; and   (g) a step of confirming that the absorbance of the filtrate for light having a wavelength of 400 nm is in a range from 0.01 to 0.08.   
   
   
       3 . The oxo-titanylphthalocyanine crystal according to  claim 1 , wherein the acid used in the step (a) is at least one type selected from the group consisting of concentrated sulfuric acid, trifluoroacetic acid and sulfonic acid. 
   
   
       4 . The oxo-titanylphthalocyanine crystal according to  claim 1 , wherein the poor solvent used in the step (b) is water. 
   
   
       5 . The oxo-titanylphthalocyanine crystal according to  claim 1 , wherein the alcohol having 1 to 4 carbon atoms which is used in the step (c) is at least one type selected from the group consisting of methanol, ethanol and 1-propanol. 
   
   
       6 . The oxo-titanylphthalocyanine crystal according to  claim 1 , wherein the wet cake was washed with the alcohol having 1 to 4 carbon atoms, and further washed with water in the step (c). 
   
   
       7 . The oxo-titanylphthalocyanine crystal according to  claim 1 , wherein the oxo-titanylphthalocyanine crystal has a maximum diffraction peak at a Bragg angle (2θ±0.2°)=27.2° in the CuKα characteristic X-ray diffraction spectrum measured after it is dipped in an organic solvent for 24 hours and no peak at 26.2°. 
   
   
       8 . A method for producing an oxo-titanylphthalocyanine crystal, the oxo-titanylphthalocyanine crystal having a maximum diffraction peak at a Bragg angle (2θ±0.2°)=27.2° in a CuKα characteristic X-ray diffraction spectrum and one peak in a temperature range from 270 to 400° C. other than the peak derived from vaporization of adsorbed water in differential scanning calorimetric analysis, the method comprising the following steps (a) to (d):
 (a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in an acid to obtain an oxo-titanylphthalocyanine solution;   (b) a step of adding the oxo-titanylphthalocyanine solution dropwise in a poor solvent to obtain a wet cake;   (c) a step of washing the wet cake with an alcohol having 1 to 4 carbon atoms; and   (d) a step of stirring the washed wet cake under heating in a nonaqueous solvent to obtain an oxo-titanylphthalocyanine crystal.   
   
   
       9 . The method for producing an oxo-titanylphthalocyanine crystal according to  claim 8 , the method comprising the following inspection steps (e) to (g) after the step (d):
 (e) a step of adding the oxo-titanylphthalocyanine crystal in an amount by weight of 1.25 parts based on 100 parts by weight of a mixed solvent of methanol and N,N-dimethylformamide (methanol:N,N-dimethylformamide=1:1 (by weight ratio)) to prepare a suspension;   (f) a step of filtering the suspension with a filter to obtain a filtrate; and   (g) a step of confirming that the absorbance of the filtrate for light having a wavelength of 400 nm is in a range from 0.01 to 0.08.   
   
   
       10 . An electrophotographic photoreceptor comprising a substrate and a photoreceptive layer containing a charge generating agent, a charge transfer agent and a binding resin, the photoreceptive layer being formed on the substrate, wherein
 the charge generating agent is an oxo-titanylphthalocyanine crystal having a maximum diffraction peak at a Bragg angle (2θ±0.2°)=27.2° in a CuKα characteristic X-ray diffraction spectrum and one peak in a temperature range from 270 to 400° C. other than the peak derived from vaporization of adsorbed water in differential scanning calorimetric analysis, the oxo-titanylphthalocyanine crystal being produced by a production method comprising the following steps (a) to (d):   (a) a step of dissolving a crude oxo-titanylphthalocyanine crystal in an acid to obtain an oxo-titanylphthalocyanine solution;   (b) a step of adding the oxo-titanylphthalocyanine solution dropwise in a poor solvent to obtain a wet cake;   (c) a step of washing the wet cake with an alcohol having 1 to 4 carbon atoms; and   (d) a step of stirring the washed wet cake under heating in a nonaqueous solvent to obtain an oxo-titanylphthalocyanine crystal.   
   
   
       11 . The electrophotographic photoreceptor according to  claim 10 , wherein the following relationship (1) is established between the reflection absorbance (A/−) of the photoreceptive layer for light having a wavelength of 700 nm, the film thickness (d/m) of the photoreceptive layer and the concentration (C/wt %) of the oxo-titanylphthalocyanine crystal in the photoreceptive layer.
     A·C   −1   ·d   −1 >1.75×10 −4   (1)