Electrophotographic image forming method, apparatus and device unit

An electrophotographic photosensitive member having a surface layer comprising a bisphenol Z-type polycarbonate resin is charged by contact charging. The charged electrophotographic photosensitive member is then subjected to imagewise exposure to form an electrostatic latent image on the photosensitive member, the thus formed electrostatic latent image on the electrophotographic photosensitive member is developed. The electrophotographic photosensitive member shows good resistance to wearing and toner sticking when subjected to electrophotographic image formation including a contact charging process.

FIELD OF THE INVENTION AND RELATED ART 
The present invention relates to an electrophotographic image forming 
method, an electrophotographic apparatus and an electrophotographic device 
unit, respectively, using contact charging. 
In an electrophotographic process including steps of charging, exposure, 
development, transfer and cleaning applied to an electrophotographic 
photosensitive member, and a step of fixation to images, it has been an 
ordinary practice to effect charging with corona generated by applying a 
high voltage of 5-8 kilo-volts DC. 
In view of ozone and/or NOx generated at the time of corona discharge, a 
contact charging process free from generation of such gases has been 
proposed (Japanese Patent Laid-Open Application (JP-A) 57-178267, JP-A 
58-40566, etc.). In the contact charging process, an electrophotographic 
photosensitive member is charged by a charging member in contact with the 
photosensitive member, and the charging member is generally supplied with 
a DC voltage superposed with an AC voltage (JP-A 63-149668). 
In the contact charging process, the charging member is in direct contact 
with an electrophotographic photosensitive member, an excellent durability 
is required of the electrophotographic photosensitive member. 
Particularly, in case where an AC voltage is applied to the charging 
member, the electrophotographic photosensitive member is liable to suffer 
from noticeable surface deterioration, such as occurrence of pinholes. 
The surface deterioration of the electrophotographic photosensitive member 
is liable to lead to difficulties, such as toner sticking onto the surface 
or abnormal abrasion of the surface. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an electrophotographic 
image forming method including the use of a photosensitive member capable 
of showing excellent abrasion resistance, causing little toner sticking 
and supplying good images in combination with the contact charging 
process. 
A further object of the present invention is to provide an 
electrophotographic apparatus and an electrophotographic device unit 
suitable for application to such an image forming method. 
According to the present invention, there is provided an 
electrophotographic image forming method, comprising: 
a contact charging step for charging an electrophotographic photosensitive 
member having a surface layer comprising a bisphenol Z-type polycarbonate 
resin by contact charging, 
an imagewise exposure step for subjecting the charged electrophotographic 
photosensitive member to imagewise exposure to form an electrostatic 
latent image on the photosensitive member, and 
a development step for developing the electrostatic latent image on the 
electrophotographic photosensitive member. 
According to another aspect of the present invention, there is provided an 
electrophotographic apparatus, comprising: 
an electrophotographic photosensitive member having a surface layer 
comprising a bisphenol Z-type polycarbonate resin, 
a charging member for charging the electrophotographic photosensitive 
member in contact with the electrophotographic photosensitive member, 
imagewise exposure means for imagewise exposing the charged 
electrophotographic photosensitive member to form an electrostatic latent 
image thereon, and 
developing means for developing the electrostatic latent image on the 
electrophotographic photosensitive member. 
According to a further aspect of the present invention, there is provided 
an electrophotographic device unit, comprising: 
an electrophotographic photosensitive member having a surface layer 
comprising a bisphenol Z-type polycarbonate resin, and 
a charging member for charging the electrophotographic photosensitive 
member in contact with the photosensitive member. 
These and other objects, features and advantages of the present invention 
will become more apparent upon a consideration of the following 
description of the preferred embodiments of the present invention taken in 
conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
In the electrophotographic image forming method according to the present 
invention, an electrophotographic photosensitive member having a surface 
layer comprising a bisphenol Z-type polycarbonate resin (in a sense of 
including derivatives having benzene rings capable of having a 
substituent) is used and charged by a charging member disposed in contact 
with the photosensitive member and supplied with a voltage (this process 
being referred to herein as "contact charging (process)"). 
The surface layer of an electrophotographic photosensitive member refers to 
a photosensitive layer when the photosensitive member has a single 
photosensitive layer, a layer in the photosensitive layer remotest from an 
electroconductive support when the photosensitive layer is a 
laminated-type one, and a protective layer when the photosensitive layer 
has such a protective layer on the photosensitive layer. 
FIG. 1 shows an embodiment of the image forming apparatus according to the 
invention. Referring to FIG. 1, a charging member 1 is disposed to contact 
the outer peripheral surface of an electrophotographic photosensitive 
member 12 in the form of a drum rotating in the direction of an arrow A to 
charge the photosensitive member to a prescribed voltage of a positive or 
negative polarity. The charging member 1 may be supplied with a positive 
or negative DC voltage which may preferably be in the range of -2000 volts 
to +2000 volts. It is possible to superpose an AC voltage with the 
above-mentioned DC voltage. The AC voltage superposed with the DC voltage 
may preferably have a peak-to-peak voltage of at most 4000 volts. The AC 
voltage can also have such an amplitude so as to provide pulse voltages in 
superposition with the DC voltage. The superposition of an AC voltage can, 
however, cause an abnormal sound due to vibration of the charging member 
and the photosensitive member in some cases. 
The charging member 1 can be instantaneously supplied with a prescribed 
voltage or can be supplied with a gradually increasing voltage so as to 
protect the photosensitive member. 
The charging member 1 may be rotated in a direction identical to that of 
the photosensitive member 12 as shown in FIG. 1, or may be rotated in a 
reverse direction or disposed un-rotated so as to rub the outer surface of 
the photosensitive member. Further, the charging member 1 can be provided 
with a function of cleaning residual toner on the photosensitive member 12 
so as to omit a cleaning means 10. 
The charged photosensitive member is then illuminated with image light 6 
from an imagewise exposure means (not shown), such as slit exposure means 
or laser beam scanning exposure means. As a result, an electrostatic 
latent image corresponding to the image light is sequentially formed on 
the periphery of the photosensitive member 12. The latent image is then 
developed with a toner by a developing means 7, and the resultant toner 
developed image is sequentially transferred by a transfer charging means 8 
to a recording material 9 which is supplied from a paper supply (not 
shown) to between the photosensitive member 12 and the transfer charging 
means 8 in synchronism with the rotation of the photosensitive member 12. 
The recording material 9 having thereon a transferred image is then 
separated from the photosensitive member surface and supplied to an image 
fixing means (not shown) where the transferred image is fixed to provide a 
copy product, which is then discharged out of the apparatus. 
The surface of the photosensitive member 12 after the transfer subjected to 
removal of residual toner by a cleaning means to be cleaned and then 
subjected to a discharge treatment by a pre-exposure means 11, followed by 
repetitive image formation. 
It is possible to combine a plurality among the above-mentioned components 
of the electrophotographic apparatus, such as the photosensitive member 
and the developing means, to constitute a device unit which can be 
detachably mountable to a main assembly of the electrophotographic 
apparatus. For example, an electrophotographic device unit may be 
constituted, as shown in FIG. 2, by disposing at least a photosensitive 
member 12, a charging member 1 and a developing means 12 in a casing 20, 
so that the device unit can be detachably mountable to (i.e., attached to 
or released from, as desired) the apparatus main assembly by using a guide 
means, such as a guide rail in the apparatus main assembly. The cleaning 
means 10 may be disposed in the casing 20, as shown, or disposed outside 
the casing 20, as desired. Further, it is also possible to dispose at 
least a photosensitive member 12 and a charging member 1 in a first casing 
21 to form a first electrophotographic device unit, and dispose at least a 
developing means 7 in a second casing 22 to form a second 
electrophotographic device unit, so that the first and second device units 
can be detachably mountable to the main assembly of the 
electrophotographic apparatus. In the embodiments shown in FIGS. 2 and 3, 
a charging member 23 is used as a transfer charging means. The charging 
member 23 may have a structure similar to that of the charging member 1. 
The charging member 23 as the transfer charging means may preferably be 
supplied with a DC voltage of 400-2000 volts. FIGS. 2 and 3 show a fixing 
means 24 omitted from showing in the embodiment of FIG. 1. 
The bisphenol Z-type polycarbonate resin constituting the surface layer of 
the electrophotographic photosensitive member 12 may preferably be one 
represented by the following formula (I) 
##STR1## 
wherein R.sub.1 -R.sub.8 independently denote hydrogen, halogen, alkyl 
group capable of having a substituent, alkenyl group capable of having a 
substituent and aryl group capable of having a substituent. The alkyl or 
alkenyl group as group R.sub.1 -R.sub.8 may preferably have 1-4 carbon 
atoms. The aryl group (which can be a combination of a plurality of 
R.sub.1 -R.sub.8) may preferably be one providing a benzene nucleus, which 
can be fused with a benzene nucleus in the main chain. Examples of the 
substituent which can be possessed by the alkyl, alkenyl or aryl group may 
include bromine, chlorine, fluorine, methyl, ethyl, propyl and vinyl. The 
bisphenol Z-type polycarbonate resin used in the present invention may 
preferably have a viscosity-average molecular weight of 30,000-80,000, 
more preferably 30,000-60,000. The bisphenol Z-type polycarbonate resin 
having a molecular weight in the prescribed range may provide a solution 
having an appropriate viscosity suitable for application or coating and 
provide the surface layer with optimum mechanical properties inclusive of 
a strength. 
The weight-average molecular weight refers to a value based on measurement 
based on the solution viscosity method (JIS K6719). 
The electrophotographic photosensitive member used in the present invention 
may have a so-called single layer-type photosensitive layer which 
comprises a charge-generating substance and a charge-transporting 
substance in a single layer, or a lamination-type photosensitive layer 
which includes in lamination a charge generation layer containing a 
charge-generating substance and a charge transport layer containing a 
charge-transporting substance. However, in order to better satisfy various 
properties required of an electrophotographic photosensitive member, it is 
preferred to use the latter photosensitive member including the lamination 
photosensitive layer. 
Preferred examples of the charge-generating substance may include: azo 
pigments, quinone pigments, quinocyanine pigments, perylene pigments, 
indigo pigments, azulenium slat pigments, oxytitanium phthalocyanine, 
copper phthalocyanine, selenium-tellurium, pyrylium dyes, and thiopyrylium 
dyes. In case of a photosensitive layer of the lamination type, the charge 
generation layer may be formed by vapor-deposition, or by application of a 
solution of the charge-generating substance together with binder resin and 
a solvent prepared by dispersion or dissolution by means of a homogenizer, 
an ultrasonic disperser, a ball mill, a vibrating ball mill, a sand mill, 
attritor or a roll mill. The charge-generating substance and the binder 
resin may preferably be blended in a weight ratio of 1:5-5:1, more 
preferably 1:2-3:1. The charge generation layer may preferably be formed 
in a thickness of at most 5 .mu.m, more preferably 0.05-2 .mu.m. 
The charge-transporting substance may be an electron-transporting substance 
or a hole-transporting substance. Examples of the electron-transporting 
substance may include: electron-attracting substances, such as chloroanil, 
tetracyanoethylene, tetracyano-quinodimethane, 
2,4,5,7-tetranitro-9-fluorenone, 2,4,5,7-tetranitroxanthone, and 
2,4,8-trinitrothio-xanthone; and polymerized derivatives of these 
electron-attracting substances. 
Examples of the hole-transporting substance may include: hydrazones, such 
as p-pyrrolidino-benzaldehyde-N,N-diphenylhydrazone, and 
p-diethyl-benzaldehyde-3-methylbenzthiazoline-2-hydrazone; pyrazolines, 
such as 
1[pyridyl(2)]-3-(p-diethyl-aminostyryl)-4-methyl-5-(p-diethylaminophenyl)p 
yrazoline, 
1-phenyl-3-(p-diethylaminostyryl)-4-methyl-5-(p-diethylaminophenyl)pyrazol 
ine, and spiropyrazoline; styryl compounds, such as 
a-phenyl-4-N,N-diphenylaminostilbene, 
N-ethyl-3-(d-phenylstyryl)-carbazole, 9-dibenzylaminobenzylidene-9H-fluore 
none, and 5-p-ditolylaminobenzylidene-5H-dibenzo[a,d]cyclo-heptene; 
thiazole compounds, such as 
2-(p-diethyl-aminostyryl)-6-diethylaminobenzothiazole; triarylmethane 
compounds, such as bis(4-diethylamino-2-methylphenyl)phenylmethane; 
polyarylalkanes, such as 1,1,2,2-tetrakis 
(4-N,N-diethylamino-2-methylphenyl)-ethane; triphenylamine, 
poly-N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, 
polyvinyl-acridine, poly-p-vinylanthracene, pyrene-formaldehyde resin, and 
ethyl carbazole-formaldehyde resin. 
In addition to the organic charge-transporting substances described above, 
it is also possible to use an inorganic substance, such as selenium, 
selenium-tellurium or cadmium sulfide. 
Particularly effective examples of the charge-transporting substance may 
include the following: 
##STR2## 
In case of a photosensitive layer of the lamination type, the charge 
transport layer may be formed by dissolving a charge-transporting 
substance as described above together with a binder resin in a solvent to 
form a solution, followed by application and drying of the solution. The 
charge-transporting substance and the binder resin may preferably be 
blended in a weight ratio of 3:1-1:3, further preferably 2:1-1:2. The 
charge transport layer may preferably be formed in a thickness of 5-40 
.mu.m, further preferably 10-30 .mu.m. 
A photosensitive layer of the single layertype may be formed by dissolving 
or dispersing a charge-generating substance and a charge-transporting 
substance as described above in a solvent to form a coating liquid, 
followed by application and drying of the coating liquid. 
The binder resin constituting a photosensitive layer other than the surface 
layer or a surface photosensitive layer in combination with the bisphenol 
Z-type polycarbonate resin may for example comprise: polyvinyl butyral, 
polyvinyl benzal, polyalkylate, polycarbonate, polyester, phenoxy resin, 
cellulose resins, acrylic resins, polyurethane, acrylonitrile-styrene 
copolymer, polyacrylamide, polyamide or chlorinated rubber. 
Particularly, the binder resin for the charge generation layer may 
preferably comprise, e.g., polyvinyl butyral, polyvinyl benzal, 
polyallylate, polycarbonate, polyester, phenoxy resin, cellulose resin, 
acrylic resin, polyurethane. The binder resin for the charge transport 
layer may preferably comprise, e.g., acrylic resin, polyallylate, 
polyester, polycarbonate, polystyrene, acrylonitrilestyrene copolymer, 
polyacrylamide, polyamide, or chlorinated rubber. 
The electrophotographic photosensitive member used in the present invention 
may be provided with a protective layer, as desired, on the photosensitive 
layer. The protective layer may for example comprise: polyethylene 
polypropylene, polyvinylidene chloride, polystyrene, 
Poly-.alpha.-methylstyrene, polymethyl methacrylate, polycarbonate, or 
methyl methacrylate-styrene copolymer. 
In the protective layer, it is possible to add an 
electroconductivity-imparting substance, such as a charge-transporting 
substance as descried above or electroconductive particulate in order to 
reduce the residual potential characteristic of the resultant 
photosensitive member. Examples of the electroconductive particulate may 
include: powder, flake and short fiber of metals, such as aluminum, 
copper, nickel and silver; electroconductive metal oxides, such as 
antimony oxide, indium oxide and tin oxide; polymeric electroconductive 
substances, such as polypyrrole, polyaniline or polymeric electrolytes; 
carbon black, carbon fiber and graphite powder. 
The protective layer may preferably have a thickness of 0.2-15 .mu.m in 
view of the residual potential characteristic and desired durability, 
particularly preferably 0.5-15 .mu.m in view of the film strength and the 
image forming characteristic. 
The bisphenol Z-type polycarbonate resin is used as a binder resin in the 
surface layer, and may preferably constitute 50-100 wt. %, particularly 
70-98 wt. %, of the binder resin of the surface layer. 
The photosensitive layer or protective layer may be formed by a coating 
method, such as dip coating, spray coating, spinner coating, curtain flow 
coating, roller coating or gravure coating of a coating liquid using a 
solvent, such as tetrahydrofuran, dioxane, cyclohexanone, benzene, 
toluene, xylene, monochlorobenzene, dichloromethane, dichlorobenzene or a 
mixture of these. For producing an electrophotographic photosensitive 
member in the form of a drum effectively and accurately in a large mass, 
the dip coating method may be the best. 
The electrophotographic photosensitive member used in the present invention 
may have an electroconductive support, which may comprise a support 
structure of an electroconductive material, such as aluminum, aluminum 
alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, 
titanium, nickel, indium, gold, or platinum. Further, it is also possible 
to constitute an electroconductive support as a support of plastic or 
paper coated with an electroconductive layer of aluminum, aluminum alloy, 
indium oxide, tin oxide, indium-tin-oxide, or a support of a plastic 
material comprising an electroconductive polymer. 
It is possible to optionally dispose an undercoating layer having a barrier 
function and an adhesive function between the electroconductive support 
and the photosensitive layer. The undercoating layer may for example be 
formed of casein, polyvinyl alcohol, nitrocellulose, ethyleneacrylic acid 
copolymer, polyvinyl butyral, phenolic resin, polyamide, polyurethane, 
gelatin, or aluminum oxide. The undercoating layer may preferably be 
formed in a thickness of 0.1-10 .mu.m, particularly 0.1-5 .mu.m. In order 
to prevent the occurrence of interference fingers due to scattering in the 
case of laser light as a source of image light, it is sometimes effective 
to dispose an optional electroconductive layer on the electroconductive 
support, preferably below the undercoating layer. The optional 
electroconductive layer may be formed by dispersing electroconductive 
powder, such as carbon black, metal particles or metal oxide particles in 
an appropriate binder resin. The optional electroconductive layer may have 
a thickness of 5-40 .mu.m, preferably 10-30 .mu.m. 
The contact charging member 1 may have any shape inclusive of a roller as 
shown in FIGS. 1-3, a brush, a blade, a belt, or a flat sheet. The 
roller-shaped charging member 1 may preferably have a structure comprising 
a bar-shaped electroconductive core member surroundingly coated 
sequentially with an elastic layer, an electroconductive layer, and a 
resistance layer. 
The electroconductive core member may for example comprise a metal, such as 
iron, copper or stainless steel, or an electroconductive resin, such as a 
carbon-dispersed resin or a metal particledispersed resin. 
The elastic layer is a layer which is rich in elasticity and low in 
hardness. The elastic layer may preferably have a thickness of at least 
1.5 mm, further preferably at least 2 mm, particularly preferably 3-13 mm. 
The elastic layer may preferably comprise, e.g., chloroprene rubber, 
isoprene rubber, EPDM rubber, polyurethane rubber, epoxy rubber, or butyl 
rubber. 
The electroconductive layer may preferably have a volume resistivity of at 
most 10.sup.7 ohm.cm, further preferably at most 10.sup.6 ohm.cm, 
particularly preferably 10.sup.-2 -10.sup.6 ohm.cm. 
The electroconductive layer may preferably be thin so as to transmit the 
softness of the lower elastic layer to the upper resistance layer and may 
preferably have a thickness of at most 3 mm, further preferably at most 2 
mm, particularly preferably 20 .mu.m -1 mm. 
The electroconductive layer may comprise, e.g., a vapor-deposited metal 
film, an electroconductive particle-dispersed resin, or an 
electroconductive resin. The vapor-deposited metal film may for example be 
formed by vapor deposition of a metal, such as aluminum, indium, nickel, 
copper or iron. The electroconductive particle-dispersed resin may for 
example comprise a resin, such as polyurethane, polyester, vinyl 
acetate-vinyl chloride copolymer or polymethyl methacrylate containing 
electroconductive particles of, e.g., carbon, aluminum, nickel or titanium 
oxide, dispersed therein. The electroconductive resin may for example 
comprise quaternary ammonium salt-containing polymethyl methacrylate, 
polyvinylaniline, polyvinylpyrrole, polydiacetylene, or polyethyleneimine. 
The resistance layer is formed to have a higher resistivity than the 
electroconductive layer and may preferably have a volume resistivity of 
10.sup.6 -10.sup.12 ohm.cm, particularly 10.sup.7 -10.sup.11 ohm.cm. The 
resistance layer may for example comprise a semiconductive resin or an 
electroconductive particledispersed insulating resin. Examples of the 
semiconductive resin may include ethyl cellulose, nitrocellulose, 
methoxymethylated nylon, ethoxymethylated nylon, copolymer nylon, 
polyvinylpyrrolidone, casein, and mixtures of these resins. Examples of 
the electroconductive particledispersed insulating resin may include: 
insulating resins, such as polyurethane, polyester, vinyl acetate-vinyl 
chloride copolymer and polymethacrylic acid containing electroconductive 
particles of, e.g., carbon, aluminum, indium oxide or titanium oxide, in a 
relatively small amount so as to control the resultant resistivity. 
The resistance layer may preferably have a thickness of 1-500 .mu.m, 
particularly 50-200 .mu.m. 
The flat sheet-shaped charging member may be formed by disposing an 
electroconductive layer and a resistance layer on an elastic layer. In 
this case, no electroconductive core member may be used. 
The blade-shaped charging member may be formed by disposing an elastic 
layer and a resistance layer on a metal sheet. 
The brush-shaped charging member may be formed by radially disposing 
electroconductive fiber so as to surround the periphery of an 
electroconductive core metal with an adhesive layer disposed therebetween, 
or by disposing electroconductive member on a surface of a metal sheet 
with an adhesive layer disposed therebetween. 
The electroconductive fiber may preferably have a volume resistivity of at 
most 10.sup.8 ohm.cm, further preferably at most 10.sup.6 ohm.cm, 
particularly preferably 10.sup.-2 -10.sup.6 ohm.cm. Each filament of the 
electroconductive fiber may preferably be sufficiently thin so as to 
retain the softness and may preferably have a diameter of 1-100 .mu.m, 
further preferably 5-50 .mu.m, particularly preferably 8-30 .mu.m. The 
electroconductive fiber may preferably have a length of 2-10 mm, 
particularly 3-8 mm. 
The electroconductive fiber may for example comprise an electroconductive 
particle-dispersed resin or an electroconductive resin as described above. 
The electroconductive fiber may also comprise carbon fiber. 
EXAMPLES 
Hereinbelow, the present invention will be described based on Examples, 
wherein "parts" refer to "parts by weight". 
Example 1 
An Al cylinder having an outer diameter of 80 mm and a length of 360 mm was 
used as a support. The Al cylinder was coated with a paint having the 
following composition by dipping, followed by heatcuring at 140.degree. C. 
for 30 min. to form a 18 .mu.m-thick electroconductive layer. 
______________________________________ 
Tin oxide-coated titanium oxide powder 
10 part(s) 
Titanium oxide powder 10 parts 
Phenolic resin 10 parts 
Silicone oil 0.001 parts 
Methanol/ethyl cellosolve (= 1/1) 
20 parts 
______________________________________ 
Then, the electroconductive layer was coated by dipping with a solution of 
3 parts of N-methoxymethylated nylon and 3 parts of copolymer nylon in a 
solvent mixture of 65 parts of methanol and 30 parts of n-butanol to form 
a 0.5 .mu.m-thick undercoating layer. 
Separately, 4 parts of bisazo pigment of the following structural formula, 
2 parts of polyvinyl butyral resin ("Eslec BLS" (trade name), mfd. by 
Sekisui Kagaku K.K.) and 100 parts of cyclohexanone, were subjected to 
dispersion for 20 hours in a sand mill containing 1 mm-dia. glass beads. 
The resultant dispersion was diluted with 100 parts of methyl ethyl ketone 
to form a dispersion liquid for charge generation layer, which was then 
applied by dipping onto the above-formed undercoating layer to form 0.2 
.mu.m-thick charge generation layer. 
##STR3## 
Then, 10 parts of Compound Example (3) as charge-transporting substance 
described hereinbefore and 10 parts of a bisphenol Z-type polycarbonate 
resin of the following formula having a viscosity-average molecular weight 
of 40,000 were dissolved in a solvent mixture of 50 parts of 
monochlorobenzene and 10 parts of dichloromethane to form a paint, which 
was then applied by dipping onto the above-formed charge generation layer 
to form a 20 .mu.m-thick charge transport layer, thus preparing an 
electrophotographic photosensitive member. 
##STR4## 
A commercially available electrophotographic image-forming apparatus 
("NP-3525", mfd. by Canon K.K.) was remodeled by replacing the 
photosensitive member with the above-prepared electrophotographic 
photosensitive member, disposing a roller-shaped contact charging member 
in contact with the photosensitive member and replacing the silicone 
rubber-made cleaning blade with a urethane rubber-made cleaning blade. The 
contact charging member was prepared by coating the periphery of a 
stainless steel-made cylindrical bar having a diameter of 5 mm and a 
length of 350 mm with an electroconductive urethane rubber in a thickness 
of 7.5 mm and a width of 330 mm. The electroconductive urethane rubber was 
prepared by dispersing 4 parts of electroconductive carbon in 100 parts of 
urethane rubber. The charging member showed a volume resistivity of 
10.sup.6 ohm.cm. 
The above-remodeled electrophotographic apparatus was subjected to a 
durability test of successively copying on 5000 sheets of recording paper 
in an environment of a temperature of 35.degree. C. and a relative 
humidity (RH) of 70%. In the durability test, the charging member was 
supplied with -1500 volts DC, the copying sheets were supplied at a rate 
of 200 mm/sec., and the performances of the apparatus were evaluated by 
the number of recording sheets after which 10 or more black spots other 
than the normal image occurred on a recording sheet due to toner sticking 
onto the photosensitive member during the durability test and the abrasion 
amount (reduced thickness) of the photosensitive member after the 
durability test. The results of the evaluation are shown in Table 1 
appearing hereinafter. 
Example 2 
An electrophotographic photosensitive member was prepared in the same 
manner as in Example 1 except that the bisphenol Z-type polycarbonate 
resin was replaced by a bisphenol Z-type polycarbonate resin of the same 
structure but having a viscosity-average molecular weight of 32,000. 
The electrophotographic photosensitive member thus produced was evaluated 
otherwise in the same manner as in Example 1. The results of the 
evaluation are also shown in Table 1. 
Example 3 
An electrophotographic photosensitive member was prepared in the same 
manner as in Example 1 except that the bisphenol Z-type polycarbonate 
resin was replaced by a bisphenol Z-type polycarbonate resin of the same 
structure but having a viscosity-average molecular weight of 48,000. 
The electrophotographic photosensitive member thus produced was evaluated 
otherwise in the same manner as in Example 1. The results of the 
evaluation are also shown in Table 1. 
Example 4 
An electrophotographic photosensitive member was prepared in the same 
manner as in Example 1 except that the bisphenol Z-type polycarbonate 
resin was replaced by a mixture of a bisphenol Z-type polycarbonate resin 
of the following structural formula (A) having a viscosity-average 
molecular weight of 80,000 and polydimethylsiloxane of the following 
formula (B) having a viscosity-average molecular weight of 80,000. 
##STR5## 
The electrophotographic photosensitive member thus produced was evaluated 
otherwise in the same manner as in Example 1. The results of the 
evaluation are also shown in Table 1. 
Example 5 
An electrophotographic photosensitive member was prepared in the same 
manner as in Example 1 except that the bisphenol Z-type polycarbonate 
resin was replaced by a bisphenol Z-type polycarbonate resin of the same 
structure but having a viscosity-average molecular weight of 90,000. 
The electrophotographic photosensitive member thus produced was evaluated 
otherwise in the same manner as in Example 1. The results of the 
evaluation are also shown in Table 1. 
Example 6 
An electrophotographic photosensitive member was prepared in the same 
manner as in Example 1 except that the bisphenol Z-type polycarbonate 
resin was replaced by a bisphenol Z-type polycarbonate resin of the same 
structure but having a viscosity-average molecular weight of 22,000. 
The electrophotographic photosensitive member thus produced was evaluated 
otherwise in the same manner as in Example 1. The results of the 
evaluation are also shown in Table 1. 
Example 7 
An electrophotographic photosensitive member was prepared in the same 
manner as in Example 1 except that the bisphenol Z-type polycarbonate 
resin having a viscosity-average molecular weight of 20,000. The 
photosensitive member was further coated by dipping with a 3 .mu.m-thick 
protective layer comprising the bisphenol Z-type polycarbonate resin 
having a viscosity-average molecular weight of 32,000 used in Example 2 
and Compound Example (3) as charge-transporting substance used in Example 
1 in a weight ratio of 2:1. 
The electrophotographic photosensitive member thus produced was evaluated 
otherwise in the same manner as in Example 1. The results of the 
evaluation are also show in Table 1. 
Example 8 
An electrophotographic photosensitive member was prepared in the same 
manner as in Example 7 except that the binder resin for constituting the 
protective layer was replaced by a 9:1 (by weight) mixture of the 
bisphenol Z-type polycarbonate resin having a viscosity-average molecular 
weight of 32,000 and the polydimethylsiloxane bisphenol used in Example 4. 
The electrophotographic photosensitive member thus produced was evaluated 
otherwise in the same manner as in Example 1. The results of the 
evaluation are also show in Table 1. 
Comparative Example 1 
An electrophotographic photosensitive member was prepared in the same 
manner as in Example 1 except that the bisphenol Z-type polycarbonate 
resin was replaced by bisphenol A-type polycarbonate resin having a 
viscosity-average molecular weight of 20,000. 
The electrophotographic photosensitive member thus produced was evaluated 
otherwise in the same manner as in Example 1. The results of the 
evaluation are also shown in Table 1. 
TABLE 1 
______________________________________ 
Number of sheets until 
Abrasion 
occurrence of black spots 
amount 
(.times. 1000) (.mu.m) 
______________________________________ 
Example 1 no black spots 0.8 
2 4.1 1.0 
3 3.8 0.5 
4 3.1 0.7 
5 4.9 2.8 
6 3.5 3.9 
7 2.8 0.3 
8 3.0 0.3 
Comp. Ex. 1 0.8 7,1 
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