Hydroxygallium phthalocyanine crystal, process for producing the same, and electrophotographic photoreceptor containing the same

Hydroxygallium phthalocyanine crystals having intense diffraction peaks at Bragg angles (2.theta..+-.0.2.degree.) of 7.5.degree., 9.9.degree., 12.5.degree., 16.3.degree., 18.6.degree., 25.1.degree. and 28.3.degree. in CuK.alpha. characteristic X-ray diffractometry, a process for producing the same, and an electrophotographic photoreceptor containing the same are disclosed. The hydroxygallium phthalocyanine crystals are obtained by once preparing impurity-free hydroxygallium phthalocyanine having intense X-ray diffraction peaks at specific Bragg angles, followed by a solvent treatment for crystal transformation, in which the impurity-free crystals are prepared by using excess phthalocyanine ring-forming compound in the synthesis of starting gallium phthalocyanine or by removing insoluble matter from the acid paste of starting gallium phthalocyanine.

FIELD OF THE INVENTION 
This invention relates to a novel hydroxygallium phthalocyanine crystal 
useful as a photoconductive material, a process for producing the same, 
and an electrophotographic photoreceptor containing the same. 
BACKGROUND OF THE INVENTION 
In the field of electrophotographic photoreceptors, there has recently been 
an increasing demand to extend the photosensitive wavelength region of 
conventional organic photoconductive materials to a wavelength region of a 
semiconductor laser in the near infrared light region (780 to 830 nm) so 
as to make them applicable to a digital recording system, such as a laser 
printer. From this point of view, there have been reported photoconductive 
materials for semiconductor lasers, such as squarylium compounds as 
disclosed in JP-A-49-105536 and JP-A-58-21416, triphenylamine type 
tris-azo compounds as disclosed in JP-A-61-151659, and phthalocyanine 
compounds as disclosed in JP-A-48-34189 and JP-A-57-148745 (the term 
"JP-A" as used herein means an "unexamined published Japanese patent 
application"). 
In cases where an organic photoconductive material is used as a 
photosensitive material for semiconductor lasers, it is required to have a 
photosensitive wavelength region extended to a longer side and to provide 
a photoreceptor having satisfactory sensitivity and durability. None of 
the above-described conventional organic photoconductive materials 
sufficiently satisfies these requirements. 
In order to overcome the drawbacks of the conventional organic 
photoconductive materials, the relationship between their crystal form and 
electrophotographic characteristics has been studied. In particular, many 
reports have hitherto been made on phthalocyanine compounds. 
It is known that phthalocyanine compounds generally exhibit several 
different crystal forms depending on the process of synthesis or the 
process of treatment and that the difference in crystal form has a great 
influence on their photoelectric conversion characteristics. For example, 
known crystal forms of copper phthalocyanine compounds include .alpha.-, 
.pi.-, .chi.-, .rho.-, .gamma.-, and .delta.-forms as well as a stable 
.beta.-form. These crystal forms are known capable of interconversion by 
application of a mechanical strain, sulfuric acid treatment, organic 
solvent treatment, heat treatment, and the like as described, e.g., in 
U.S. Pat. Nos. 2,770,629, 3,160,635, 3,708,292, and 3,357,989. 
JP-A-50-38543 refers to the relationship between a crystal form of copper 
phthalocyanine and its electrophotographic characteristics. As for gallium 
phthalocyanine crystal forms, JP-A-1-221459 describes two crystal forms 
obtained by acid pasting. Further, the inventors of the present invention 
previously revealed that five crystal forms of hydroxygallium 
phthalocyanine exhibit excellent electrophotographic characteristics (see 
JP-A-5-263007). 
For the production of these crystals, a so-called acid pasting process as 
described in Bull. Soc. Chim., 23, France (1962) is adopted. That is, a 
starting gallium phthalocyanine compound is subjected to acid pasting to 
once obtain metastable hydroxygallium phthalocyanine, which is then 
subjected to a solvent treatment for transformation. 
Starting gallium phthalocyanine to be used in acid pasting includes 
chlorogallium phthalocyanine (see D.C.R. Acad. Sci., Vol. 242, p. 1026 
(1956), JP-B-3-30854 (the term "JP-B" as used herein means an "examined 
published Japanese patent application"), JP-A-1-221459, and Inorg. Chem., 
Vol. 19, p. 3131 (1980)), bromogallium phthalocyanine (see 
JP-A-59-133551), and iodogallium phthalocyanine (see JP-A-60-59354). 
However, hydroxygallium phthalocyanine having a specific crystal form which 
is prepared by usual acid pasting, even with the crystal form being equal, 
show variation in performance as a electrophotographic photoreceptor, such 
as sensitivity and a dark decay rate, and it has been difficult to obtain 
hydroxygallium phthalocyanine which provides stable image characteristics. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide hydroxygallium 
phthalocyanine having a novel crystal form which exhibits excellent 
characteristics required as a photoconductive material. 
Another object of the present invention is to provide a process for 
producing the hydroxygallium phthalocyanine crystals. 
A further object of the present invention is to provide an 
electrophotographic photoreceptor containing the hydroxygallium 
phthalocyanine crystals. 
The present inventors have conducted extensive investigations on production 
of hydroxygallium phthalocyanine crystals and, as a result, found that 
hydroxygallium phthalocyanine crystals having intense diffraction peaks at 
specific Bragg angles obtained by a specific process exhibit excellent 
characteristics as a photoconductive material, the process being 
characterized by such a manipulation that is added to the mode of 
preparing gallium phthalocyanine so as to prevent a starting gallium 
compound from remaining in a final product or such a manipulation that is 
added to the mode of acid pasting so as to remove an insoluble matter from 
an acid paste of gallium phthalocyanine. The present invention has been 
completed based on this finding. 
The present invention provides a process for producing hydroxygallium 
phthalocyanine crystals, which process comprises reacting a gallium 
compound with an excess of a compound forming a phthalocyanine ring to 
prepare gallium phthalocyanine, subjecting the resulting gallium 
phthalocyanine to acid pasting to obtain a hydroxygallium phthalocyanine 
crystal having intense diffraction peaks at Bragg angles 
(2.theta..+-.0.2.degree.) of 6.9.degree., 13.2.degree. to 14.2.degree., 
16.5.degree., and 26.4.degree. or of 7.0.degree., 13.4.degree., 
16.6.degree., 26.0.degree., and 26.7.degree. in CuK.alpha. characteristic 
X-ray diffractometry, and transforming the resulting crystal by a solvent 
treatment into hydroxygallium phthalocyanine crystals having intense 
diffraction peaks at Bragg angles (2.theta..+-.0.2.degree.) of 
7.5.degree., 9.9.degree., 12.5.degree., 16.3.degree., 18.6.degree., 
25.1.degree., and 28.3.degree. in CuK.alpha. characteristic X-ray 
diffractometry. 
The present invention also provides a process for producing a 
hydroxygallium phthalocyanine crystal, which process comprises removing an 
insoluble matter from an acid paste of gallium phthalocyanine in an acid 
pasting process to prepare a hydroxygallium phthalocyanine crystal having 
intense diffraction peaks at Bragg angles (2.theta..+-.0.2.degree.) of 
6.9.degree., 13.2.degree. to 14.2.degree., 16.5.degree., and 26.4.degree. 
or of 7.0.degree., 13.4.degree., 16.6.degree., 26.0.degree., and 
26.7.degree. in CuK.alpha. characteristic X-ray diffractometry, and 
transforming the resulting crystal by a solvent treatment into a 
hydroxygallium phthalocyanine crystal having intense diffraction peaks at 
Bragg angles (2.theta..+-.0.2.degree.) of 7.5.degree., 9.9.degree., 
12.5.degree., 16.3.degree., 18.6.degree., 25.1.degree., and 28.3.degree. 
in CuK.alpha. characteristic X-ray diffractometry. 
The present invention further provides a novel hydroxygallium 
phthalocyanine crystal prepared by the above processes and an 
electrophotographic photoreceptor containing these crystals as a 
photoconductive material.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is based on the finding that impurity in 
hydroxygallium phthalocyanine crystals gives great influences on 
electrophotographic characteristics. Crystals as synthesized often contain 
the starting gallium compound or intermediate products derived therefrom, 
which seem to form, in the subsequent operation such as acid pasting, 
GaO(OH), etc. which would cause reduction of electrophotographic 
characteristics. 
In one embodiment of the present invention, the starting gallium 
phthalocyanine, which is to be subjected to acid pasting, is prepared by 
using a compound forming a phthalocyanine ring in excess of a gallium 
compound thereby to suppress remaining of the gallium compound in the 
final product. In another embodiment of the present invention a step of 
removing an insoluble matter, such as GaO(OH), from acid paste of gallium 
phthalocyanine is added to an acid pasting process. By these manipulations 
there is provided a hydroxygallium phthalocyanine crystal having intense 
diffraction peaks at Bragg angles (2.theta..+-.0.2.degree.) of 
6.9.degree., 13.2.degree. to 14.2.degree., 16.5.degree., and 26.4.degree. 
or of 7.0.degree., 13.4.degree., 16.6.degree., 26.0.degree., and 
26.7.degree. in CuK.alpha. characteristic X-ray diffractometry, which are 
then transformed by a solvent treatment into a hydroxygallium 
phthalocyanine crystal having intense diffraction peaks at Bragg angles 
(2.theta..+-.0.2.degree.) of 7.5.degree., 9.9.degree., 12.5.degree., 
16.3.degree., 18.6.degree., 25.1.degree., and 28.3.degree. in CuK.alpha. 
characteristic X-ray diffractometry. 
In the first embodiment, gallium phthalocyanine is synthesized by using a 
compound forming a phthalocyanine ring in excess over an equivalent 
amount, e.g., 1.05 to 2 equivalents, preferably 1.05 to 1.4 equivalent, 
still preferably 1.1 to 1.25 equivalent, per equivalent of gallium. 
The compound forming a phthalocyanine ring includes phthalonitrile, 
3-methylphthalonitrile, 3,4-dimethylphthalonitrile, 
3-chlorophthalonitrile, 3,4-dichlorophthalonitrile, 3-nitrophthalonitrile, 
3,4-dinitrophthalonitrile, 3-cyanophthalonitrile, 
3,4-dicyanophthalonitrile, 2-methylphthalonitrile, 2-chlorophthalonitrile, 
2-nitrophthalonitrile, 2-cyanophthalonitrile, diminoisoindoline, 
5-methyldiiminoisoindoline, 5,6-dimethyldiiminoisoindoline, 
5-chlorodiiminoisoindoline, 5,6-dichlorodiiminoisoindoline, 
5-nitrodiiminoisoindoline, 5,6-dinitrodiiminoisoindoline, 
5-cyanodiiminoisoindoline, 5,6-dicyanodiiminoisoindoline, 
4-methyldiiminoisoindoline, 4-chlorodiiminoisoindoline, 
4-nitrodiiminoisoindoline, and 4-cyanodiiminoisoindoline. Phthalonitrile 
and diiminoisoindoline are preferred of them. 
The gallium compound includes gallium chloride, gallium bromide, gallium 
iodide, gallium fluoride, gallium trimethoxide, gallium triethoxide, 
gallium tripropoxide, and acetylacetonatogallium. 
It is particularly preferred to synthesize gallium phthalocyanine by 
starting with a gallium trialkoxide which is prepared in situ from, e.g., 
gallium chloride and sodium methoxide. 
The reaction between a gallium compound and excess phthalocyanine 
ring-forming compound is carried out at a temperature of 100.degree. to 
230.degree. C., preferably 140.degree. to 200.degree. C., for a period of 
3 to 48 hours, preferably 6 to 30 hours. 
The thus synthesized gallium phthalocyanine is subjected to acid pasting to 
obtain a hydroxygallium phthalocyanine crystal having intense diffraction 
peaks at Bragg angles (2.theta..+-.0.2.degree.) of 6.9.degree., 
13.2.degree. to 14.2.degree., 16.5.degree., and 26.4.degree. or of 
7.0.degree., 13.4.degree., 16.6.degree., 26.0.degree., and 26.7.degree. in 
CuK.alpha. characteristic X-ray diffractometry. 
Electrophotographic photoreceptors containing hydroxygallium phthalocyanine 
crystals prepared by starting with the hydroxygallium phthalocyanine 
crystals according to the first embodiment exhibit improved 
electrophotographic characteristics. This is probably because shortage of 
the phthalocyanine-forming compound due to decomposition, and the like is 
compensated for by the excess and therefore such compounds that might 
by-produce GaO(OH), etc. are prevented from remaining or being produced in 
the reaction system. 
Gallium phthalocyanine compounds which can be used as a starting material 
in the second embodiment of the present invention include chlorogallium 
phthalocyanine, bromogallium phthalocyanine, and iodogallium 
phthalocyanine. These gallium phthalocyanine compounds can be synthesized 
by known methods and are not limited in method of synthesis. The gallium 
phthalocyanine described in JP-A-6-73299, which is synthesized by using a 
gallium trialkoxide, is also useful. 
The acid pasting according to the present invention (common to the first 
and second embodiments) is carried out by dissolving or dispersing a 
gallium phthalocyanine compound in an acid to prepare an acid paste and 
adding the acid paste (i) to an aqueous alkali solution to obtain a 
hydroxygallium phthalocyanine crystal having intense diffraction peaks at 
Bragg angles (2.theta..+-.0.2.degree.) of 6.9.degree., 13.2.degree. to 
14.2.degree., 16.5.degree. and 26.4.degree. in CuK.alpha. characteristic 
X-ray diffractometry, or (ii) to a mixture of an aqueous alkali solution 
and an organic solvent to obtain a hydroxygallium phthalocyanine crystal 
having intense diffraction peaks at Bragg angles (2.theta..+-.0.2.degree.) 
of 7.0.degree., 13.4.degree., 16.6.degree., 26.0.degree. and 26.7.degree. 
in CuK.alpha. characteristic X-ray diffractometry. 
The acid to be used in acid pasting includes sulfuric acid, hydrochloric 
acid, hydrobromic acid, and trifluoroacetic acid. Concentrated sulfuric 
acid is preferred for its high dissolving power and ease of handling. 
Concentrated sulfuric acid is used in an amount 5 to 100 times, preferably 
15 to 40 times, the weight of gallium phthalocyanine. 
The organic solvent to be used in acid pasting includes alcohols, such as 
methanol; glycols, such as ethylene glycol, glycerin, and polyethylene 
glycol; ketones, such as acetone and methyl ethyl ketone; esters, such as 
ethyl acetate and butyl acetate; halogenated hydrocarbons, such as 
dichloromethane and chloroform; and aromatic hydrocarbons, such as toluene 
and xylene. The organic solvent is used in an amount 10 or less times, 
preferably 5 or less times, the volume of water. The alkali to be used 
includes sodium hydroxide, potassium hydroxide, sodium carbonate, 
potassium carbonate, ammonia, and various ammonium hydroxide salts. The 
mixture of an aqueous alkali solution and an organic solvent is used in an 
amount 1 to 100 times, preferably 3 to 20 times the volume of the acid 
paste of gallium phthalocyanine. 
The acid pasting is conducted at a temperature ranging from -15.degree. to 
100.degree. C. In using an organic solvent, a temperature lower than the 
boiling point of the solvent is recommended. 
In the second embodiment of the present invention, the acid paste is 
filtered through a filter insusceptible to corrosion of acid, such as a 
glass filter or a ceramic filter in order to remove impurity from the acid 
paste. Filtration is carried out by suction from the bottom of the filter, 
by pressuring from the top of the filter, or by both. The filtered acid 
paste is added dropwise to an aqueous alkali solution or a mixture of an 
aqueous alkali solution and an organic solvent with stirring while 
maintaining at a temperature of the boiling point or below, whereupon 
hydroxygallium phthalocyanine is produced. The acid paste may be filtered 
either prior to the dropwise addition or simultaneously with the addition. 
The resulting hydroxygallium phthalocyanine crystal is purified by washing 
with water and the like to give a hydroxygallium phthalocyanine crystal 
having intense diffraction peaks at Bragg angles (2.theta..+-.0.2.degree.) 
of 6.9.degree., 13.2.degree. to 14.2.degree., 16.5.degree., and 
26.4.degree. or of 7.0.degree., 13.4.degree., 16.6.degree., 26.0.degree., 
and 26.7.degree. in CuK.alpha. characteristic X-ray diffractometry. 
Electrophotographic photoreceptors containing hydroxygallium 
phthalocyanine crystals prepared from the hydroxygallium phthalocyanine 
crystals according to the second embodiment exhibit improved 
electrophotographic characteristics. This is probably because compounds 
that would have by-produced GaO(OH), etc. have been removed by filtration. 
The manipulation consisting of use of excess phthalocyanine ring-forming 
compound over a gallium compound in the synthesis of a starting gallium 
phthalocyanine compound and the manipulation consisting of removing an 
insoluble matter from an acid paste during acid pasting may be effected 
singly, or both of them may be effected in series. 
The thus obtained hydroxygallium phthalocyanine crystal is then subjected 
to solvent treatment. Solvent treatment induces crystal transformation to 
give a desired hydroxygallium phthalocyanine crystal having intense 
diffraction peaks at Bragg angles (2.theta..+-.0.2.degree.) of 
7.5.degree., 9.9.degree., 12.5.degree., 16.3.degree., 18.6.degree., 
25.1.degree., and 28.3.degree. in CuK.alpha. characteristic X-ray 
diffractometry. 
The solvent which can be used for the solvent treatment includes amides, 
such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, 
and 1,3-dimethyl-2-imidazolidinone; sulfoxides, such as dimethyl 
sulfoxide; and organic amines, such as morpholine and piperidine. The 
solvent used in the preparation of hydroxygallium phthalocyanine crystals 
may be a mixture of two or more of the above-enumerated solvents or a 
mixture of the above-enumerated solvent and water. 
The above-mentioned solvent treatment embraces not only an ordinary 
recrystallization treatment but other operations such as washing, wet 
grinding, immersion, and suspending with stirring. 
The solvent is used in an amount of 1 to 200 parts by weight, preferably 10 
to 100 parts by weight, per part by weight of hydroxygallium 
phthalocyanine. The treatment is carried out at a temperature of 0.degree. 
to 150.degree. C., preferably room temperature to 100.degree. C. The 
treatment may be conducted either by allowing the system to stand in an 
appropriate container or stirring the system. Further, the hydroxygallium 
phthalocyanine may be wet ground with the prescribed solvent by means of a 
ball mill, a mortar, a sand mill, a kneader, an attritor, etc. An 
inorganic compound, such as sodium chloride or sodium sulfate, or a 
grinding aid, such as glass beads, steel beads or alumina beads, may be 
used in wet grinding. 
The above-mentioned solvent treatment provides hydroxygallium 
phthalocyanine of novel crystal form having satisfactory crystal 
properties and a regular particle size. 
The electrophotographic photoreceptor according to the present invention in 
which the above-described hydroxygallium phthalocyanine crystals are used 
as a photoconductive material in the photosensitive layer thereof will be 
explained below. 
The photosensitive layer may have either a single layer structure or a 
laminate structure composed of a charge generating layer and a charge 
transporting layer. In the latter structure, the photosensitive layer 
comprises a conductive support having provided thereon a photosensitive 
layer composed of a lower charge generating layer and an upper charge 
transporting layer, in which the charge generating layer is formed of the 
hydroxygallium phthalocyanine crystals of the present invention and a 
binder resin. An undercoat layer is preferably provided between the 
photosensitive layer and the conductive support. 
The charge generating layer is formed by coating a conductive support with 
a coating composition prepared by dispersing the hydroxygallium 
phthalocyanine crystals in an organic solvent solution of a binder resin. 
Binder resins which can be used in the charge generating layer can be 
chosen from a broad range of insulating resins, such as a polyvinyl 
butyral resin and a polyvinyl formal resin. Solvents which can be used for 
dissolving the binder resin are preferably chosen from among those 
incapable of dissolving the undercoat layer. A suitable weight ratio of 
hydroxygallium phthalocyanine crystals to binder resin ranges from 40:1 to 
1:20. Dispersing of the hydroxygallium phthalocyanine crystals in the 
resin solution can be carried out in a usual manner by means of a ball 
mill, an attritor, a sand mill, etc. 
Coating can be effected by dip coating, spray coating, spinner coating, 
bead coating, wire bar coating, blade coating, roller coating, air knife 
coating, curtain coating, and the like. The thickness of the charge 
generating layer is suitably 0.05 to 5 .mu.m. 
The charge transporting layer is formed of an appropriate binder resin 
having dispersed therein a known charge transporting material, such as 
N,N'-diphenyl-N,N'-bis(m-tolyl)benzidine, 
4-diethylaminobenzaldehyde-2,2-diphenylhydrazone, and 
p-(2,2-diphenylvinyl)-N,N-diphenylaniline. 
The charge transporting layer is formed by coating a charge generating 
layer with a coating composition prepared from a charge transporting 
material and the same binder resin and solvent as used in the formation of 
a charge generating layer by the same coating means. A suitable weight 
ratio of charge transporting material to binder resin ranges from 10:1 to 
1:5. The charge transporting layer usually has a thickness of 5 to 50 
.mu.m. 
Where a photosensitive layer has a single layer structure, the 
photosensitive layer comprises a photoconductive layer in which the 
hydroxygallium phthalocyanine crystals of the present invention are 
dispersed in a charge transporting material and a binder resin. The charge 
transporting material and binder resin and the coating technique used here 
are the same as those used in the formation of a photosensitive layer 
having a laminate structure. A suitable weight ratio of charge 
transporting material to binder resin is about 1:10 to 10:1, preferably 
about 1:2 to 2:1, and a suitable weight ratio of hydroxygallium 
phthalocyanine crystals to binder resin is from about 1:100 to 5:1, 
preferably about 1:10 to 1:1. 
Any conductive support may be used as far as it is fit to use as an 
electrophotographic photoreceptor. 
If desired, an undercoat layer comprising a polyamide resin, a 
polycarbonate resin, a zirconium chelate compound, a titanyl chelate 
compound, etc. may be provided between the conductive support and the 
photosensitive layer in order to block injection of unnecessary charges 
from the conductive support into the photosensitive layer on charging of 
the photosensitive layer. 
If desired, the surface of the photosensitive layer may be covered with a 
protective (overcoat) layer. A protective layer functions to prevent the 
charge transporting layer of a photosensitive layer having a laminate 
structure from being chemically denatured on charging and also to improve 
mechanical strength of the photosensitive layer. 
The present invention will now be illustrated in greater detail with 
reference to Examples, but it should be understood that the present 
invention is not deemed to be limited thereto. Unless otherwise indicated, 
all the parts and percents are given by weight. 
EXAMPLE 1 
(a) In 75 ml of toluene was dissolved 10 parts of gallium chloride, and 33 
ml of a 28% methanolic solution of sodium methoxide was added thereto 
dropwise while cooling. After stirring for about 30 minutes, 33.5 parts of 
phthalonitrile (corresponding to 1.15 equivalent per equivalent of gallium 
chloride) and 150 ml of ethylene glycol were added thereto, followed by 
stirring at 180.degree. C. for 24 hours in a nitrogen atmosphere. The 
product was collected by filtration, washed successively with 
N,N-dimethylformamide and distilled water, and dried to give 27.8 parts of 
gallium phthalocyanine. 
(b) Ten parts of the gallium phthalocyanine prepared in (a) above were 
dissolved in 250 parts of concentrated sulfuric acid and stirred for 2 
hours. The resulting acid paste was added dropwise to an ice-cooled mixed 
solution consisting of 870 ml of distilled water and 530 ml of 
concentrated aqueous ammonia. The crystals thus precipitated were 
thoroughly washed with distilled water and dried to give 9 parts of 
hydroxygallium phthalocyanine crystals. The powder X-ray diffraction 
spectrum of the crystals is shown in FIG. 1. 
(c) One part of the hydroxygallium phthalocyanine crystals prepared in (b) 
above was milled in 15 parts of N,N-dimethylformamide together with 30 
parts of glass beads having a diameter of 1 mm for 24 hours. The crystals 
were separated, washed with n-butyl acetate, and dried at 50.degree. C. 
under reduced pressure of 20 Pa for 8 hours. Any residual solvent was 
removed to give 0.9 part of hydroxygallium phthalocyanine crystals. The 
powder X-ray diffraction spectrum of the crystals is shown in FIG. 2. 
EXAMPLE 2 
(a) In 75 ml of toluene was dissolved 10 parts of gallium chloride, and 33 
ml of a 28% methanolic solution of sodium methoxide was added thereto 
dropwise while cooling. After stirring for about 30 minutes, 29.1 parts of 
phthalonitrile (equivalent to gallium chloride) and 150 ml of ethylene 
glycol were added thereto, followed by stirring at 180.degree. C. for 24 
hours in a nitrogen atmosphere. The product was collected by filtration, 
washed successively with N,N-dimethylformamide and distilled water, and 
dried to give 28.0 parts of gallium phthalocyanine. 
(b) Ten parts of the gallium phthalocyanine prepared in (a) above were 
dissolved in 250 parts of concentrated sulfuric acid and stirred for 2 
hours. Any insoluble matter of the resulting acid paste was removed by 
filtration through a 1.5 .mu.m glass filter, and the filtrate was added 
dropwise to an ice-cooled mixed solution consisting of 870 ml of distilled 
water and 530 ml of concentrated aqueous ammonia. The crystals thus 
precipitated were thoroughly washed with distilled water and dried to give 
9 parts of hydroxygallium phthalocyanine crystals. The powder X-ray 
diffraction spectrum of the crystals was the same as that shown in FIG. 1. 
(c) The hydroxygallium phthalocyanine crystals prepared in (b) above 
subjected to the same solvent treatment as in Example 1(c) to obtain 0.9 
part of hydroxygallium phthalocyanine crystals. The powder X-ray 
diffraction spectrum of the crystals was the same as that shown in FIG. 2. 
COMATIVE EXAMPLE 1 
Ten parts of the gallium phthalocyanine obtained in Example 2(a) were 
dissolved in 250 parts of concentrated sulfuric acid and stirred for 2 
hours. The resulting acid paste as prepared was added dropwise to an 
ice-cooled mixed solution consisting of 870 ml of distilled water and 530 
ml of concentrated aqueous ammonia. The crystals thus precipitated were 
thoroughly washed with distilled water and dried to give 9 parts of 
hydroxygallium phthalocyanine crystals. The powder X-ray diffraction 
spectrum of the crystals was the same as that shown in FIG. 1. 
One part of the resulting hydroxygallium phthalocyanine crystals was milled 
in 15 parts of N,N-dimethylformamide together with 30 parts of glass beads 
having a diameter of 1 mm for 24 hours. The crystals were separated, 
washed with n-butyl acetate, and dried at 50.degree. C. under reduced 
pressure of 20 Pa for 8 hours. Any residual solvent was removed to give 
0.9 part of hydroxygallium phthalocyanine crystals. The powder X-ray 
diffraction spectrum of the crystals was the same as that shown in FIG. 2. 
The half-widths of the diffraction peak of the solvent-treated 
hydroxygallium phthalocyanine crystal at a Bragg angle 
(2.theta..+-.0.2.degree.) of 7.5.degree. in Example 2(C) and Comparative 
Example 1 were 0.420 and 0.435, respectively. This shows that the 
solvent-treated hydroxygallium phthalocyanine crystal of the present 
invention has excellent crystal properties. Further, when compared 
transmission electron microscope (TEM) photographs of the solvent-treated 
hydroxygallium phthalocyanine crystal in Example 2(C) and Comparative 
Example 1, it was measured that the solvent-treated hydroxygallium 
phthalocyanine crystal of Example 2(C) had more regular particle size than 
that of Comparative Example 1. 
EXAMPLE 3 
A solution consisting of 10 parts of a zirconium compound ("Orgatics ZC540" 
produced by Matsumoto Seiyaku K.K.), 1 part of a silane compound ("A 1110" 
produced by Nippon Unicar Co., Ltd.), 40 parts of isopropyl alcohol, and 
20 parts of butanol was applied to an aluminum support by dip coating and 
dried by heating at 150.degree. C. for 10 minutes to form an undercoat 
layer having a thickness of 0.2 .mu.m. 
One part of the hydroxygallium phthalocyanine crystals obtained in Example 
1 was mixed with 1 part of polyvinyl butyral ("S-Lec BM-S" produced by 
Sekisui Chemical Co., Ltd.) and 100 parts of n-butyl acetate, and the 
mixture was dispersed in a paint shaker together with glass beads for 1 
hour. The resulting coating composition was applied onto the undercoat 
layer by dip coating and dried by heating at 100.degree. C. for 10 minutes 
to form a charge generating layer having a thickness of about 0.2 .mu.m. 
In 20 parts of monochlorobenzene were dissolved 2 parts of a charge 
transporting material represented by formula (1): 
##STR1## 
and 3 parts of a polycarbonate resin comprising a repeating unit 
represented by formula (2): 
##STR2## 
and the resulting coating composition was applied to the charge generating 
layer by dip coating and dried by heating at 120.degree. C. for 1 hour to 
form a charge transporting layer having a thickness of 20 .mu.m. 
EXAMPLE 4 AND COMATIVE EXAMPLE 2 
An electrophotographic photoreceptor was prepared in the same manner as in 
Example 3, except for using, as a charge generating material, the 
hydroxygallium phthalocyanine crystals obtained in Example 2 or 
Comparative Example 1. 
Electrophotographic characteristics of the electrophotographic 
photoreceptors prepared in Examples 3 and 4 and Comparative Example 2 were 
evaluated by using a machine scanner as follows. The photoreceptor was 
charged to an initial surface potential of -800 V by a corona discharge 
under a high temperature and high humidity condition (28.degree. C., 85% 
RH). After 0.538 second, the dark decay potential V.sub.DDP (V) was 
measured to obtain a dark decay rate V.sub.DDR (V) (V.sub.DDR =V.sub.DDP 
-(-800)). Then, the photoreceptor was exposed to monochromatic light of 
780 nm which was isolated from light emitted from a tungsten lamp by means 
of a monochromator. The initial sensitivity dV/dE (kV.multidot.m.sup.2 
/J)) was measured. The results of these measurements are shown in Table 1 
below. 
TABLE 1 
______________________________________ 
V.sub.DDP V.sub.DDR 
dV/dE 
HOGaPc* 
(V) (V) (kV .multidot. m.sup.2 /J) 
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Example 3 Example 1 
-762 38 321 
Example 4 Example 2 
-760 40 311 
Compar. Compar. -752 48 325 
Example 2 Example 1 
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*HOGaPc: Hydroxygallium phthalocyanine 
As can be seen from Table 1, the hydroxygallium phthalocyanine crystals 
prepared by the process of the present invention are useful as a 
photoconductive substance to provide an electrophotographic photoreceptor 
having high sensitivity and a small dark decay rate. The photoreceptor 
prepared by using the crystals of the present invention exhibits excellent 
chargeability and stable electrophotographic characteristics and thereby 
affords excellent image characteristics when applied to semiconductor 
laser printers, etc. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.