Porous photoreceptor and method for manufacturing the same

A method for manufacturing a photoreceptor includes the steps of consecutively forming a transparent conductive layer, a photoconductive layer, insulation layer and an electrode layer on a transparent support member, covering the electrode layer with a photo-setting dry film having a mask pattern therein, and sand-blasting the electrode layer and the insulation layer through the mask pattern to form an array of pores in the electrode layer and the insulation layer. A porous layer having a uniform thickness and uniform arrangement of pores can be obtained.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
The present invention relates to a method for manufacturing a photoreceptor 
drum for use in a copying machine, a facsimile machine, a printer, or a 
like apparatus, and more particularly to a photoreceptor (hereinafter 
referred to as a "porous photoreceptor") having a surface formed as a 
porous layer, in which a large number of equally spaced fine pores are 
formed, and to a method for manufacturing the porous photoreceptor. The 
present invention also relates to a porous photoreceptor manufactured by 
such a method. 
(b) Description of the Related Art 
Conventionally, an electrophotographic process has been widely used as an 
image formation technology employed by copying machines, facsimile 
machines, printers, and like apparatus. The Carlson process (xerography) 
is a typical electrophotographic process, which includes six steps for 
printing, including electrification, exposure, development, transfer, 
fixing, and cleaning. Since a dedicated unit must be installed for each 
step, the entire system unavoidably becomes large-scaled. 
The inventors have disclosed an image recording method in Patent 
Publication No. JP-A-1997-204092 corresponding to U.S. Pat. No. 5,815,774, 
as a simplified electrophotographic process to replace the Carlson 
process. The disclosed method employs a porous photoreceptor composed of a 
photoreceptor and a porous insulation layer formed on the surface of the 
photoreceptor. An electrode is formed on the upper surface of the porous 
insulation layer. Conductive coloring particles are filled into pores 
formed on the thus-configured porous photoreceptor. The porous 
photoreceptor is exposed to light corresponding to print information, 
thereby selectively causing the coloring particles to move in the air 
toward an counter electrode and be thus transferred onto recording sheet 
located on the near side of the counter electrode. Since this method 
completes printing in three steps--a coloring particles filling step, an 
exposure and transfer step, and a fixing step, the associated equipment 
can be reduced in size. 
The above porous photoreceptor may be manufactured by the steps of forming 
pores in a sheet of the porous insulation layer by laser or drilling, and 
closely attaching the sheet onto the drum-shaped photoreceptor. However, a 
seam is formed between the abutting ends of the sheet and becomes apparent 
in the form of an image defect, thus impairing image quality. In the case 
of using a laser for forming the pores, the pores can be finely finished, 
and thus a high degree of image quality is obtained; however, mass 
productivity is rather poor with a resultant increase in cost of 
manufacture. In the case of forming the pores by mechanical means, such as 
by drilling, drilling must be repeated a tremendously large number of 
times. For example, when a porous layer having pores formed therein at a 
resolution of 200 dpi is to be formed on a cylindrical photoconductive 
layer having a length of 210 mm, which is the length of size A4 sheet, and 
a diameter of 30 mm, the number of pores to be formed becomes at least one 
million. Since only one pore can be formed by a single operation of 
drilling, drilling must be repeated at least one million times, which is 
not practical. 
To cope with the above problems, in Japanese Patent Application No. 
1997-317245, we have proposed a method for forming a porous layer in which 
a photo-setting liquid resin is used. 
The method includes the steps of applying the photo-setting liquid resin 
onto a photoconductive layer; causing the applied photo-setting liquid 
resin to be selectively set so as to establish contrast of set portions 
and unset portions in correspondence with desired patterns of pores; and 
eliminating the unset portions to thereby form a porous layer. However, 
the photo-setting liquid resin encounters difficulty in forming the porous 
layer to a uniform thickness. In addition, since the photo-setting liquid 
resin usually has high viscosity, the resin involves difficulty in 
handling during application thereof. 
In the printing method described in U.S. Pat. No. 5,815,774, image density 
is determined by the number of coloring particles contained in each of the 
larger number of pores. In order to contain a certain number of coloring 
particles in each pore, the diameter of the pore must assume at least a 
certain minimum value, or the depth of the pore must assume at least a 
certain minimum value, i.e., the thickness of the porous layer must assume 
at least a certain minimum value. The diameter of the pore is preferably 
decreased in order to improve resolution for printing a high-quality 
image. Accordingly, in order to obtain a certain image density, the depth 
of the pore, i.e., the thickness of the porous layer, is made to assume at 
least a certain minimum value. However, in the case of formation of a 
large number of through-pores in a photo-setting resin layer, with the 
increase in the thickness of the photo-setting resin layer, elimination of 
unset portions becomes more difficult, i.e., formation of pores becomes 
more difficult. 
As described above, formation of the porous layer is a key technology for 
the printing method described in U.S. Pat. No. 5,815,774. However, 
although a laser can process the porous layer to a high degree of fineness 
with resultant high image quality, employment of a laser has a drawback of 
high cost due to poor mass productivity. Formation of pores by mechanical 
means, such as by drilling, encounters difficulty in processing the porous 
layer to a high degree of fineness and is thus unsuited for formation of 
the porous layer. In the case of the method disclosed in Japanese Patent 
Application No. 1997-317245, formation of the porous layer to a uniform 
thickness is difficult because of employment of a liquid resin. The liquid 
resin involves difficulty in handling during application thereof and fails 
to meet a demand that the porous layer be formed to at least a certain 
minimum thickness in order to obtain high image density. 
SUMMARY OF THE INVENTION 
In view of the foregoing, an object of the present invention is to provide 
a method for manufacturing a porous photoreceptor at low cost in which a 
porous layer having a uniform thickness and having equally spaced pores 
formed therein is easily formed on a photoreceptor. 
It is another object of the present invention to provide a porous 
photoreceptor manufactured by such a method. 
The present invention provides, in a first aspect thereof, a method for 
manufacturing a porous photoreceptor comprising the steps of consecutively 
forming a transparent conductive layer and a photoconductive layer on a 
transparent support member, forming an insulator layer on the 
photoconductive layer, and jet-blasting minute particles onto the 
insulator layer through a mask pattern to form pores at least in the 
insulator layer. 
In accordance with the method of the first aspect of the present invention, 
the jet-blasting step provides an excellent porous layer having a uniform 
thickness and a pore structure in which the pores are arranged in a 
uniform pitch and have a uniform depth. 
The present invention also provides, in a second aspect thereof, a porous 
photoreceptor comprising a transparent support member, and a transparent 
conductive layer, a photoconductive layer and an electrode layer 
consecutively formed on the transparent support member, the 
photoconductive layer having a plurality of pores arranged on the 
photoconductive layer, each of the pores having a bottom within the 
photoconductive layer. 
In the porous photoreceptor of the second aspect of the present invention, 
porous layer has a uniform thickness and the pores are arranged at a 
uniform pitch thereon, resulting in an excellent porous photoreceptor 
providing a high printing quality. 
The present invention also provides, in a third aspect thereof, a method 
for manufacturing a porous photoreceptor comprising the steps of 
consecutively forming a transparent conductive layer and a photoconductive 
layer on a transparent support member, and jet-blasting minute particles 
onto the photoconductive layer through a mask pattern to form pores in the 
photoconductive layer. 
In the method according to the third aspect of the present invention, the 
porous photoreceptor according to the second aspect can be manufactured. 
The above and other objects, features and advantages of the present 
invention will be more apparent from the following description, referring 
to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will next be described in detail with 
reference to the drawings. FIG. 1 shows a porous photoreceptor 
manufactured by a method according to an embodiment of the first aspect of 
the present invention. In FIG. 1, the porous photoreceptor 100 includes a 
transparent support member 1, a transparent conductive layer 2 formed on 
the transparent support member 1, a photoconductive layer 3 formed on the 
transparent conductive layer 2, and a porous layer 4 made of an insulator 
formed on the photoconductive layer 3. The porous layer 4 has a top 
electrode 5 formed on the surface thereof. 
FIG. 2 is an enlarged schematic sectional view of the porous photoreceptor 
100 of FIG. 1. The transparent conductive layer 2 is formed by 
evaporation, dip coating, spray coating, or a like method. An undercoat 
layer may be formed between the transparent conductive layer 2 and the 
photoconductive layer 3. The photoconductive layer 3 is made of an 
inorganic or organic material. In the case of the photoconductive layer 3 
of an organic material, as shown in FIG. 2, the photoconductive layer 3 
includes a charge generation layer 31 formed on the transparent conductive 
layer 2 and containing a material for generation of charge carriers, and a 
charge transport layer 32 formed on the charge generation layer 31 and 
functioning to transport generated charges. The photoconductive layer 3 is 
formed by a known method employed for manufacture of an organic 
photoreceptor drum; for example, dip coating. 
FIG. 3 schematically shows a process for printing an image by use of the 
porous photoreceptor 100 of FIG. 1. In FIG. 3, a conductive roller 60 is 
spaced apart from the porous photoreceptor 100, and a recording sheet 7 
and an counter electrode 8 are spaced apart from the porous photoreceptor 
100 and are located downstream of the conductive roller 60 along the 
rotational direction of the porous photoreceptor 100. Conductive particles 
6 are fed onto the conductive roller 60 and are thinned into a thin 
conductive-particle layer 61 by a restriction blade 62. The counter 
electrode 8 is located on the far side of the recording sheet 7 with 
respect to the porous photoreceptor 100. 
A voltage is applied among the transparent conductor layer 2, the top 
electrode 5, and the conductive roller 60 so as to generate an electric 
field between the transparent conductor layer 2 and the conductive roller 
60 at a position where the porous photoreceptor 100 faces the conductive 
roller 60. The conductive particles 6 on the conductive roller 60 are 
electrified to negative polarity by the electric field and are attracted 
into pores formed in the porous layer 4. The conductive particles 6 
colliding against the top electrode 5 are electrified to positive polarity 
by the electric field and return to the conductive roller 60. Accordingly, 
the conductive particles 6 of negative polarity fill only the pores formed 
in the porous layer 4. The conductive particles 6 are contained in the 
pores such that the electric potential thereof becomes equal to that of 
the top electrode 5, so that the electric field of the surface of a 
particle layer approaches zero. Therefore, the filling conductive 
particles 6 are confined in the pores. 
In an image recording section where the porous photoreceptor 100 faces the 
recording sheet 7, a potential difference is established so as to generate 
an electric field directed from the transparent conductive layer 2 to the 
counter electrode 8. When the photoconductive layer 3 is irradiated with 
light emitted from a light source 110 in accordance with an image to be 
printed, the exposed portion of the photoconductive layer 3 increases in 
electric conductivity; consequently, charge established in the conductive 
particles 6 contained in the corresponding pores leak out through the 
photoconductive layer 3. 
As a result of the leakage of charge, the electric potential of the 
conductive particles 6 contained in the pores approaches that of the 
transparent conductive layer 2, so that an electric field is generated on 
the surface of the layer of the conductive particles 6. The conductive 
particles 6 located on the side of the top electrode 5 are electrified to 
positive polarity and move out of the corresponding pores to the recording 
sheet 7. The released conductive particles 6 attach onto the recording 
sheet 7, thereby forming an image thereon. As seen from the above 
description, the arrangement pitch of pores and the diameter of each pore 
directly determine image density. In order to obtain as high an image 
density as possible, the shape and arrangement of pores must be optimized 
so as to narrow the arrangement pitch of pores and to increase the pore 
diameter. For efficient printing on a recording sheet, it is preferred 
that an image be formed on a photoconductive layer of a cylindrical shape 
or a like shape and that the photoconductive layer be rotated for 
continuous printing. Therefore, a method for manufacturing a cylindrical, 
porous photoreceptor will next be described. 
The text includes descriptions in relation to the first to third aspects of 
the present invention. The first aspect of the present invention is 
directed to a method for manufacturing a porous photoreceptor, including 
the step of disposing on a photoconductive layer a porous layer in which 
pores are formed by jet-blasting or sandblasting. The second aspect of the 
present invention is directed to a porous photoreceptor in which pores are 
formed in a surface portion of a charge transport layer corresponding to 
the charge transport layer 32 of FIG. 4. The third aspect of the present 
invention is directed to a method for manufacturing a porous 
photoreceptor, including the steps of: forming a charge transport layer 
thicker than that formed in a conventional electrophotographic process; 
and forming pores in the charge transport layer by sandblasting. FIG. 4 is 
an enlarged schematic sectional view of the porous photoreceptor according 
to the second aspect or that manufactured by the method according to the 
third aspect. The first, second, and third aspects will next be described 
in detail with reference to the drawings. 
FIG. 5 illustrates a first step in manufacture of a dry film having a mask 
pattern for use in sandblasting which is common to the first and third 
aspects. A dry film 11 is used as a sheet resist. The present embodiment 
uses a negative photo-setting dry film of BF Series (product of Tokyo Ohka 
Kogyo Co., Ltd.) as a resist material of the dry film for use in 
sandblasting. The dry film 11 has a relatively small thickness of 50 .mu.m 
in order to facilitate formation of through-pores therein at fine pitches, 
which will be described later. In FIG. 5, a flat glass plate having a 
thickness of about 5 mm and good flatness, for example, is used as a glass 
support 10. A lower cover film is removed from the photo-setting dry film 
11 in preparation for attachment onto the glass support 10. The 
thus-prepared photo-setting dry film 11 is attached onto the glass support 
10 through application of heat and pressure by a thermal pressure roller 
12 (having a temperature of about 115.degree. C.) in such a manner as not 
to catch bubbles therebetween. Subsequently, an upper cover film 13 is 
removed from the dry film 11. A desired pore pattern may be formed on the 
dry film 11 through exposure effected by either method described below. 
Specifically, a mask on which a pore pattern is printed is placed on the 
dry film 11 so as to maintain close contact therewith. Then, the entire 
dry film 11 is subjected to exposure. Alternatively, a laser beam whose 
wavelength causes setting of the photo-setting dry film 11 is focused and 
scanned on the dry film 11 so as to effect exposure for formation of a 
pore pattern, without using a mask pattern. The former exposure method is 
simple; however, involves a drawback in that a mask must be remade each 
time a pore pattern is modified, which is uneconomical. The latter 
exposure method facilitates modification of a pore pattern through 
modification of pore pattern data to be output from a computer; however, 
involves a drawback in that outputting CAD data is time consuming, since 
scanning is performed on a pore-by-pore basis. The method to be used may 
be determined according to the shape or form of an object of exposure. 
The present embodiment employs the former exposure method using a mask. 
However, the latter exposure method using a laser may also be effectively 
employed. FIG. 6 is a partially enlarged top plan view of a patterned mask 
14. The patterned mask 14 is closely attached onto the dry film 11 through 
application of heat and pressure. The present embodiment uses the 
patterned mask 14 on which a pattern of slots as shown in FIG. 6 is 
printed. The thermal pressure roller 12 of FIG. 5 is used for closely 
attaching the patterned mask 14 onto the dry film 11 in order to prevent a 
failure in forming an exact image of the pattern on the dry film 11 and 
oxygen-induced desensitization of the photo-setting dry film 11, which 
might otherwise result from air caught therebetween. On the other hand, 
employment of the thermal pressure roller 12 causes reduction in the 
thickness of the dry film 11 due to heat and high pressure. For example, 
the thickness of the dry film 11 employed in the present embodiment 
decreases from 50 .mu.m to about 45 .mu.m. 
The dimensions and arrangement of patterns printed on the patterned mask 14 
are determined so as to correspond to those of pores formed on a porous 
photoreceptor manufactured by the method of the invention. The arrangement 
pitch of pores depends on the quality; particularly, the resolution, of an 
image to be printed by use of the porous photoreceptor. The shape of each 
pore and the wall thickness between pores depend on the number of 
conductive coloring particles filling each pore and a printing speed. FIG. 
6 exemplifies patterning on the patterned mask 14, and patterning is not 
limited thereto. The dry film 11 used in the present invention is of the 
negative type; in other words, an exposed portion becomes set through 
photocrosslinking and photopolymerization of a polymer chain. Thus, in 
FIG. 6, a light shield portion 15 corresponding to a pore is in the form 
of a black pattern so as not to permit transmission of light for exposure. 
FIG. 7 schematically illustrates the step of transferring a pore pattern of 
the mask onto the photo-setting dry film 11 through exposure. This step 
establishes contrast of set portions and unset portions on the dry film 
11. FIG. 8 illustrates the step of removing unset portions from the 
photo-setting dry film 11 which has undergone the exposure step, to 
thereby form through-pores in the dry film 11. Specifically, the dry film 
11 is immersed, for about 1 minute, in a developer 21 contained in an 
ultrasonic vibration generator 19 so as to form through-pores therein. The 
developer 21 is heated to a temperature of 30.degree. C. and is adapted to 
dissolve only the unset portions of the dry film 11. Alternatively, a 
high-pressure developer may be sprayed over the dry film 11 for selective 
development. Next, the developer is washed off the dry film 11 by use of 
pure water. Then, the dry film 11 is dried at a temperature of 60.degree. 
C. for 10 minutes in a thermostatic oven. Subsequently, the dry film 11, 
which serves as a sheet resist, is removed from the glass support 10. 
The thus-manufactured dry film 11 has a large number of through-holes 
formed uniformly therein and serves as a sheet resist used in common with 
the methods of the first and third aspects. The dry film 11 is resistant 
to abrasion exerted by abrasive grains sprayed under high pressure during 
sandblasting, which will be described later. Thus, being attached onto an 
object to be sandblasted, the dry film 11 serves as a mask during 
sandblasting. 
The first and third aspects are different in the methods used for 
manufacturing a porous photoreceptor. According to the first aspect, the 
insulation layer 4 is formed on the photoconductive layer 3 and is then 
sandblasted so as to form pores therein. A process for forming the 
insulation layer 4 on the photoconductive layer 3 will next be described. 
FIG. 9 is a schematic sectional partial view of a blank photoreceptor 100 
in which pores are not formed yet in the insulation layer 4. The 
insulation layer 4 has a thickness of about 100 .mu.m and is formed on the 
photoconductive layer 3. A layer of the top electrode 5 having a thickness 
of about 250 angstroms is previously formed on the surface of the 
insulation layer 4 through vacuum evaporation. The top electrode 5 may be 
formed through evaporation or electroless plating of metal, such as 
aluminum, gold, or bismuth, or ITO. The surface of the top electrode 5 may 
be coated with a conductive polymer. As described previously, the top 
electrode 5 has the following three functions: (1) to form a high electric 
field within the photoconductive layer 3; (2) to confine the conductive 
particles 6 in pores; and (3) to prevent adhesion of the conductive 
particles 6 onto the surface of the porous photoreceptor 100. Therefore, 
the top electrode 5 is an indispensable element. 
A thermosetting epoxy resin is used as material for the insulation layer 4 
for the following reasons: coating is easy to perform; adhesion to a base 
layer is excellent; shrinkage is hardly observed after setting; and 
suitable strength is exhibited after setting. The insulation layer 4 is 
formed in a manner similar to that for forming a charge transport layer 
constituting a photoconductive layer, as observed in a conventional method 
for manufacturing an electrophotographic photoreceptor. Specifically, a 
photoreceptor is dipped in a liquid coating of a thermosetting epoxy resin 
and is then pulled up at a constant rate to thereby coat the photoreceptor 
with a layer of the epoxy resin having a uniform thickness. Subsequently, 
the epoxy resin layer is set through application of heat. Alternatively, 
another polymer dissolved in a solvent may be applied onto the 
photoreceptor in a similar manner, followed by drying. A known coating 
method, such as blade coating, may also be employed. 
In the present embodiment, the charge generation layer 31 assumes a 
thickness of about 0.05 to 1 .mu.m, and the charge transport layer 32 
assumes a thickness of about 20 .mu.m. The charge generation layer 31 is 
made of n-type titanyl phthalocyanine and polyvinyl butyral described in, 
for example, Patent Publication No. JP-A-1991-9962. Material for the 
charge transport layer 32 is prepared by the steps of dissolving 
polycarbonate serving as a binder resin in a solvent, and adding to the 
resultant solution a charge transport material described in, for example, 
Patent Publication No. JP-A-1995-168376, in an amount of 20 to 40 wt %. 
The insulation layer 4 described above is sandblasted, as described later, 
so as to form pores therein, thereby obtaining a porous layer from the 
insulation layer 4. 
Next will be described a porous photoreceptor according to the second 
aspect. In the porous photoreceptor, pores are formed in a surface portion 
of the charge transport layer 32 constituting the photoconductive layer 3. 
FIG. 10 is a schematic sectional partial view of a blank photoreceptor in 
which pores are not formed yet in the photoconductive layer 3. The 
photoconductive layer 3 is composed of the charge generation layer 31 and 
the charge transport layer 32. As in the case of the first aspect, a layer 
of the top electrode 5 is previously formed on the surface of the charge 
transport layer 32 through evaporation of aluminum and assumes a thickness 
of about 250 angstroms. A material for the top electrode 5 and a method 
for forming the top electrode 5 are not limited thereto. The top electrode 
5 may be formed of other metal or conductive material by other method. 
In an actual printing process, when the photoconductive layer 3 is 
irradiated with light for exposure in accordance with print information, 
the charge generation layer 31 generates charges according to an amount of 
the exposure. The charge transport layer 32 is adapted to transport the 
thus-generated charges to the surface of the photoconductive layer 3, 
thereby neutralizing counter charges adhering to the surface and 
electrified to a polarity opposite to that of the generated charges, and 
thus eliminating charges from the surface. 
According to the second aspect, pores, the depth of each of which is less 
than the thickness of the charge transport layer 32, are uniformly formed 
in the surface portion of the charge transport layer 32, so that the 
surface portion functions as a porous layer. Usually, the charge 
generation layer 31 assumes a thickness of about 0.1 to 1 .mu.m, and the 
charge transport layer 32 assumes a thickness of about 5 to 50 .mu.m. In 
the second aspect, since the surface portion of the charge transport layer 
32 assumes the form of a porous layer, the charge transport layer 32 
assumes a larger thickness, specifically 100 to 150 .mu.m. 
The charge generation layer 31 is made of n-type titanyl phthalocyanine and 
polyvinyl butyral disclosed in, for example, Japanese Patent Application 
No. 1989-144889. Material for the charge transport layer 32 is prepared by 
the steps of dissolving in a solvent polystyrene which has higher hardness 
than that of polycarbonate and is abradable when sandblasted, and which 
serves as a binder resin; and adding to the resultant solution a charge 
transport material disclosed in, for example, Patent Publication No. 
JP-A-1995-168376, in an amount of 20 to 40 wt %. Polycarbonate may be used 
as the binder for abrasive grains of a certain type or a certain 
sandblasting pressure, which will be described later. 
The porous photoreceptor according to the second aspect and as described 
above is manufactured by the method of the third aspect. Specifically, the 
dry film 11, which serves as a sheet resist and in which through-holes are 
formed by the method described previously, is attached onto the charge 
transport layer 32. The charge transport layer 32 covered with the dry 
film 11 is subjected to sandblasting, which will be described layer, i.e., 
a stream of abrasive grains projected by compressed air is blown against 
the charge transport layer 32 via the dry film 11, thereby forming pores 
in the charge transport layer 32. 
As described above, the insulation layer 4 serving as the porous layer is 
formed on the photoconductive layer 3 by the method of the first aspect, 
or the surface portion of the photoconductive layer 3 is formed into the 
porous layer 4 by the method of the third aspect. Next will be described 
in detail a method for forming pores in the insulation layer 4, or the 
surface portion of the photoconductive layer by sandblasting through the 
dry film 11 serving as a sheet resist and attached thereto, or brought 
into contact therewith. 
FIG. 11 schematically illustrates a process of forming the porous layer 4 
by sandblasting in the method of the first or third aspect. A feed roller 
40 and a take-up roller 41 are rotated to feed the dry film 11, in which 
through-holes are formed by use of the patterned mask of FIG. 6 and which 
serves as a sheet resist, in the direction of the arrow. Tension rollers 
42 exert tension on the dry film 11 to prevent the dry film 11 from 
wrinkling and to exert an appropriate nip on the surface of contact 
between the dry film 11 and the insulation layer 4 or the charge transport 
layer 32. Nozzles 43 are arranged equally spaced in a line and in such a 
manner as to face the nip portion. 
A stream of abrasive grains 44 is projected by compressed air from each 
nozzle 43 and is blown against the insulation layer 4 or the charge 
transport layer 32 through pattern of the dry film 11. The projected 
abrasive grains 44 pass through the through-holes formed in the dry film 
11 and reach the insulation layer 4 or the charge transport layer 32 to 
thereby abrade the layer 4 or 32. The abrasive grains 44 are of silicon 
dioxide and are blown against a nip portion of a 5 mm width at a blast 
pressure of 4 kg/cm.sup.2 for 10 sec to 180 sec. Through optimization of 
such blasting conditions, the abrasive grains 44 may be of alumina, glass 
beads, or a like material used commonly for jet-blasting or sandblasting. 
A material for the abrasive grains 44 is determined according to the 
material and hardness of an object to be sandblasted. 
FIG. 12 illustrates a process for attaching the dry film 11 onto a blank 
photoreceptor in preparation for sandblast to be performed in a manner 
different from that of FIG. 11. The dry film 11 serving as a sheet resist 
is closely wound onto the metal-deposited insulation layer 4 or the charge 
transport layer 32 through application of heat and pressure in a manner 
similar to that of FIG. 5. The thermal pressure roller 12 heated to a 
temperature of about 115.degree. C. is rotated and pressed against the 
porous photoreceptor 100 with the dry film 11 held therebetween, while the 
porous photoreceptor 100 is rotated at a peripheral speed equal to that of 
the thermal pressure roller 12. The dry film 11 is then patterned with 
pre-determined holes to act as a sheet resist. Subsequently, the abrasive 
grains 44 are blown against the rotating photoreceptor 100 by use of a 
sandblaster equipped with the nozzles 43 arranged in parallel lines, 
thereby forming pores in the insulation layer 4 or the charge transport 
layer 32. 
Referring to FIG. 13, the nozzles 43 may be arranged all around the 
photoreceptor 100, so that the abrasive grains 44 are blown against the 
porous photoreceptor 100 along the entire circumference thereof. This 
method is preferable in that sandblasting time is shortened. The abrasive 
grains 44 and the blast pressure are similar to those employed in the 
sandblasting process of FIG. 11. After the elapse of a predetermined 
sandblasting time, formed pores are checked to see if they are as deep as 
desired; for example, 100 .mu.m deep. The dry film 11 is removed by 
pulling an end thereof. A release agent may be used for removing the dry 
film 11. 
A method for manufacturing a porous photoreceptor according to another 
embodiment of the present invention will next be described. The method 
includes the steps of applying a photo-setting liquid resin onto a charge 
transport layer or an insulation layer, which is to be formed into a 
porous layer covered with an electrode layer; forming a pattern on the 
applied photo-setting resin layer through exposure; and developing and 
drying the photo-setting resin layer to yield a resist layer. FIG. 14 is a 
view of a blank photoreceptor as viewed immediately after the 
photo-setting resin is applied thereto. In the present embodiment, the 
photo-setting liquid resin APR manufactured by Asahi Chemical Industry 
Co., Ltd. is used as a photo-setting resin 70. Since the photo-setting 
resin APR has high viscosity at room temperature, the resin APR is heated 
to a temperature of about 50.degree. C. so as to decrease viscosity. 
The thus-heated resin APR is uniformly applied onto the cylindrical charge 
transport layer 32 or the cylindrical insulation layer 4 to thereby yield 
a layer of the photo-setting resin 70 of a uniform thickness, followed by 
cooling. Subsequently, a pore pattern of FIG. 6 is transferred onto the 
photo-setting resin 70 through exposure effected by the method of FIG. 7. 
Then, the photo-setting resin 70 is subjected to development so as to 
remove unset portions, thereby forming pores therein. Subsequently, the 
photoreceptor is subjected to sandblast in which a stream of abrasive 
grains projected by compressed air is blown against the layer of the 
porous photo-setting resin 70, thereby forming pores in the charge 
transport layer 32 or the insulation layer 4. Then, the layer of the 
photo-setting resin 70 is removed in a manner described previously. 
FIG. 15 is a schematic view illustrating sandblasting of the blank 
photoreceptor of FIG. 14. According to the method of the present 
embodiment, a step of forming the resist layer, a step of sandblasting, 
and a step of removing the resist layer can be performed continuously 
while the photoreceptor is supported in place; in other words, a step of 
removing the dry film 11 from a glass support and a step of attaching the 
dry film 11 onto an object to be sandblasted are not involved. This method 
exhibits excellent mass productivity and is thus suited for manufacturing 
a large number of porous photoreceptors of the invention. 
The present invention yields the following effects. Whether the thickness 
of a photo-setting resin film used as sandblast resist is feasible depends 
on whether the photo-setting resin film of the thickness concerned is 
resistant to abrasive grains blown at high speed against the film. A thin 
photo-setting resin film is usable so long as the film exhibits such 
resistance. Thus, minute pores required for printing of high image quality 
can be easily formed in the photo-setting resin film, so that an image of 
high resolution can be printed. Since a top electrode layer is formed in 
advance before the step of forming pores, choking of pores is not involved 
in contrast to a method in which, after pores are formed in a layer formed 
on a photoreceptor, a top electrode layer is attached onto the porous 
layer. 
According to the first aspect, a porous layer may be made of any material 
so long as the material can be effectively abraded by abrasive grains and 
has an electrically insulating property. Thus, in contrast to a method in 
which a photo-setting resin is used as the porous layer, there is a good 
choice of materials for the porous layer. According to the second and 
third aspects, a surface portion of the charge transport layer 
constituting the photoconductive layer is adapted to function as the 
porous layer, thereby eliminating a step of attaching an insulation layer 
onto a photoreceptor. Therefore, a porous photoreceptor suited for mass 
production can be manufactured. 
Since the above embodiments are described only as examples, the present 
invention is not limited to the above embodiments and various 
modifications or alterations can be easily made therefrom by those skilled 
in the art without departing from the scope of the present invention.