Electrophotographic photosensitive member with cured cyclized rubber binder

In an electrophotographic photosensitive member having a photoconductive layer composed of a photoconductive material and a binder, improvement wherein said binder is a curable rubber.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a photosensitive member for use in 
electrophotography. 
2. Description of the Prior Art 
The electrophotographic photosensitive member takes various constructions 
for obtaining a predetermined characteristics or in accordance with the 
kind of the electrophotographic processes to be applied. Representative 
photosensitive member for the electrophotography is such one that is 
provided with a photoconductive layer on a substrate or such one that is 
provided with an insulating layer on the surface of the photoconductive 
layer, both types being used widely. The photosensitive member consisting 
of the substrate and the photoconductive layer is used for image formation 
by the most common electrophotographic processes including electric 
charging, image exposure, image development, and, depending on necessity, 
image transfer. As to the photosensitive member having the insulative 
layer thereon, such insulative layer is provided for the purposes of 
protecting the photoconductive layer, improving the mechanical strength of 
the photosensitive member, improving the dark decay characteristic, or 
being applied to a particular electrophotographic process, or further 
preventing pollutions. Representative examples of the photosensitive 
member having such insulative layer and the electrophotographic process 
using the photosensitive body having such insulative layer thereon are 
disclosed, for example, in U.S. Pat. No. 2,860,048, Japanese patent 
publications Nos. 16429/1966, 15446/1963, 3713/1971, 23910/1967, 
24748/1968, 19747/1967, 4121/1961, and so on. 
The electrophotographic photosensitive member is liable to be damaged 
inasmuch as it is subjected to various electrical and mechanical impacts 
such as corona charging process, image developing process, cleaning 
process, and so forth. It is also liable to lower its charge sustaining 
capability on account of moisture. Therefore, when the electrophotographic 
photosensitive member undergoes such damages time and again, the quality 
of the image to be formed thereon becomes remarkably deteriorated. In 
particular, when the photoconductive layer is composed of a binder and a 
photoconductive material (various resins being used as the binder), its 
durability is also poor. Also, the image to be formed on the 
electrophotographic photosensitive member is poorer in its tonality than 
the image formed by use of ordinary photographic emulsion. 
In the photosensitive member having the insulative layer, when the layer is 
formed on the photoconductive layer, it becomes necessary for the 
photosensitive member to be excellent in its durability so that the 
insulative layer of a desired mechanical strength may be formed thereon 
without disturbing the composition of the photoconductive layer. For this 
purpose, when the insulative layer is formed by, for example, application 
of a liquid resin, the photoconductive layer should not be of such quality 
that is dissolved in the solvent of the liquid resin. 
In view of the foregoing, there has so far been strong demands for the 
electrophotographic photosensitive member excellent in durability against 
electrical and mechanical impacts, moisture resistance, tonality, and so 
forth. However, it has been difficult to provide such electrophotographic 
photosensitive member excellent in these various characteristics. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an 
electrophotographic photosensitive member excellent in its electrical and 
mechanical durability. 
It is another object of the present invention to provide an 
electrophotographic photosensitive member excellent in moisture 
resistance. 
It is still another object of the present invention to provide an 
electrophotographic photosensitive member excellent in tonality. 
It is other object of the present invention to provide an 
electrophotographic photosensitive member which causes the least memory 
phenomenon, hence no ghost image. 
It is still other object of the present invention to provide an 
electrophotographic photosensitive member excellent in its toner transfer 
efficiency. 
The electrophotographic photosensitive member according to the present 
invention is characterised in that it has a photoconductive layer composed 
of a curable rubber as a binder and a photoconductive material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The electrophotographic photosensitive member according to the present 
invention does not undergo the dielectric breakdown due to the corona 
charging, but forms very clear reproduction image. In case the 
electrophotographic photosensitive member is subjected to the 
electrophotographic processes to form an image at the initial stage, 
followed by subsequent formation of other imgage, a part of the 
electrostatic charge corresponding to the initially formed image remains 
at the time of the subsequent image formation. This phenomenon is called 
the "memory phenomenon." As this memory phenomenon becomes intense, there 
emerges a ghost image. The electrophotographic photosensitive member 
according to the present invention is less in such memory phenomenon, 
hence no ghost image appears. Further, since the electrophotographic 
photosensitive member of the present invention is difficult to be affected 
by moisture, its charge sustaining capability is satifactory and a stable 
image formation can be realized. Furthermore, the electrophotogaphic 
photosensitive member according to the present invention is excellent in 
its tonality of the reproduced image, and also exhibits effective 
reproducibility of an image in an intermediate tone. It has also good 
toner transfer efficiency to thereby be able to form an image of high 
image contrast. In addition, the photoconductive layer of the 
electrophotographic photosensitive member according to the present 
invention is excellent in its mechanical strength, heat-resistance, 
solvent-resistance, hardness, and adhesivity to the substrate, which 
contribute to improvement in the durability of the photosensitive member. 
Further, since the photoconductive layer of the electrophotographic 
photosensitive member of the present invention is excellent in its 
heat-resistance as mentioned above, it is possible to render the 
insulative layer provided on the photoconductive layer by a film forming 
method to be more durable by heat-setting. Such solvent-resistance and 
heat-resistance of the photoconductive layer are particularly effective in 
manufacturing a seamless drum-shaped photosensitive member. In the 
formation of the photoconductive layer, the other kind of resin material 
may be used, depending on necessity, together with the curable rubber. 
The curable rubber to be used in the present invention is such one that 
produces bridge-connection, or cross-linking, by imparting thereto an 
energy such as heat, light, electron beam, etc. so as to change the same 
to that having a three-dimensional chemical structure with reduced rubber 
elasticity, and hardened becomes. The curable rubber forms the 
photoconductive layer in its cured state. In the case of using a cyclized 
rubber, however, the photoconductive layer can be effectively formed in 
its uncured state. For the curable rubber used in the present invention, 
various sorts of curable rubber available in general market can be used. 
Representative examples of such curable rubber are: cyclized butadiene 
rubber, isoprene rubber, isobutylene-isoprene rubber, butyl rubber, 
butadiene rubber, butadiene-styrene rubber, nitrile rubber, chloroprene 
rubber, chlorinated polyethylene rubber, fluorinated rubber, 
chloro-sulfonated polyethylene rubber, silicone rubber, and others. In 
particular, the cyclized rubber is excellent as the curable rubber. The 
cyclized rubber has within its molecule the cycle structure, examples of 
which are cyclized butadiene rubber, cyclized isoprene rubber, cyclized 
natural rubber, triazine rubber, and so on. 
Besides the photosensitive member is manufactured by forming the 
photoconductive layer directly on the substrate, it may be fabricated by 
first forming a curable rubber layer on the substrate, on which rubber 
layer the photoconductive layer is subsequently formed. It may also be 
fabricated in such a manner that the curable rubber layer is formed on the 
photoconductive layer, on which rubber layer the substrate is provided. 
Thickness of the curable rubber layer may be properly determined. Usually, 
it is from 0.1 to 10 microns, or more preferably from 0.1 to 5 microns. 
The content of the curable rubber to form the photoconductive layer ranges 
from 0.5 to 50 parts by weight with respect to 100 parts by weight of the 
photoconductive material, or more preferably, from 10 to 30 parts by 
weight. 
For the photoconductive material, there may be used arbitrarily inorganic 
materials such as ZnO, CdS, TiO.sub.2, CdSe, Se, SeTe, SeAs, etc., and 
organic materials such as phthalocyanine, polyvinyl carbazole, anthracene, 
polyvinyl pyrene, polyvinyl anthracene, etc. 
As to the photosensitive member having the insulative layer, there may be 
appropriately used various kinds of resin materials to form such 
insulative layer. Examples of these resin materials are: organic 
insulative substances such as polyethylene, polyester, polypropylene, 
polystyrene, polyvinyl chloride, polyvinyl acetate, acrylic resin, 
polycarbonate, silicone resin, fluorinated resin, epoxy resin, urethane 
resin, melamine resin, and so on. 
For more readily forming the insulative layer, coating of such insulative 
layer is more excellent than its adhesion to the photoconductive layer. 
The coating method is effective in forming a seamless insulative layer on 
the drum-shaped photosensitive member. From such standpoint, use of a 
curable resin is more effective than the use of other kind of resins. 
For the particularly appropriate curable resin, there can be enumerated 
acrylic resin, urethane resin, polyester resin, epoxy resin, melamine 
resin, silicone resin, and so on. Thickness of the insulative layer is 
usually set in a range of from 0.1 to 100 microns, and more preferably 
from 0.1 to 50 microns. It is also possible that, at the time of forming 
the photoconductive layer, such layer is formed by the coating method so 
that no granular photoconductive material remain on the surface of the 
formed photoconductive layer, whereby the surface part thereof may be 
rendered the insulative layer. 
The substrate may be formed from any appropriate material such as stainless 
steel, copper, alumimum, tin, and other metal plates, as well as paper, 
sheet, resin film, and other sheet material. The substrate may be 
dispensed with as the case may be. 
Thickness of the photoconductive layer, though depending on the kind and 
characteristics of the photoconductive substance to be used, may generally 
range from 5 to 100 microns, and more preferably from 10 to 50 microns or 
so. 
In order to enable those skilled persons in the art to understand fully the 
present invention, the following examples are presented. It should however 
be noted that the present invention is not limited to these examples 
alone. 
EXAMPLE 1 
15 parts by weight of curable cyclized butadiene rubber (produced and sold 
by Japan Synthetic Rubber Co., Ltd. under a trade name "CBR") as the 
binder and 1 part by weight of diazo curing agent were added to and well 
mixed with 100 parts by weight of CdS powder. The mixture was passed for 
five times through a roll mill device having a gap of 40 microns for 
perfect mixing of the CdS powder and the binder. Thereafter, viscosity of 
the mixture was adjusted to 800 cps by the use of methylethyl ketone. 
Then, a cylindrical substrate made of aluminum was immersed in this 
viscosity-adjusted liquid and drawn up at a speed of 30 mm/min., after 
which this cylindrical substrate was heat-treated for 30 minutes at 
150.degree. C. to cure the liquid coating, thereby forming the 
photoconductive layer of 50 microns in thickness. The thus formed 
photoconductive layer was found to be insoluble in ketone solvents and to 
have a heat-resistance of about 200.degree. C. It was also found out that 
hardness of the binder was higher than "3H" in pencil hardness (determined 
in accordance with Japanese Industrial Standard (JIS) No. K-5401), and its 
adhesivity to the substrate was satisfactory. 
The obtained photoconductive layer was immersed in a diluted liquid of 
photo-curing type acryl urethane resin (manufactured and sold by Kansai 
Paint Co., Ltd. under a trade name of "SONNE"), the viscosity of which was 
so adjusted by methylethyl ketone solvent as to become 90 cps, and drawn 
up at a speed of 30 mm/min. After this, the photoconductive layer was 
subjected to light irradiation by a 4 kw mercury lamp for 5 minutes to 
cure the resin, thereby forming the insulative layer of 10 microns thick. 
The above-mentioned operation was repeated for three times to form the 
insulative layer of 30 microns thick on the photoconductive layer. It was 
observed at the time of forming the insualative layer that no pentration 
of the insulative-layer-forming-resin into the photoconductive layer, 
hence no deterioration in the characteristics of the photoconductive 
layer. 
The thus obtained photosensitive member was subjected to the 
electrophotographic processes consisting of the primary d.c. positive 
corona charging, the secondary a.c. corona discharging simultaneous with 
image exposure, the overall surface exposure, the wet-type image 
development with negative toner, the image transfer to an image transfer 
medium, and the cleaning by a blade, after which it was examined for its 
dielectric breakdown resistance, moisture resistance, memory phenomenon, 
tonality, and durability. 
The dielectric breakdown was examined by measuring white dots to occur in 
the image formed on the image transfer medium where no toner adheres when 
the photosensitive member undergoes the dielectric breakdown. The 
measurement of the white dot members was conducted after the 
electrophotographic processes had been repeated for 1,000 times. The 
memory phenomenon was examined by measuring the residual potential of the 
image formed by the first electrophotographic processes and that of the 
image formed by the subsequent second electrophotographic processes, in 
which the "image exposure" in the secondary a.c. corona discharging 
simultaneous with image exposure was changed to the "overall surface 
exposure." The moisture resistance was examined by measuring the contrast 
potential of the electrostatic image to be formed when the 
electrophotographic processes were conducted at 25.degree. C. and 60% RH 
(Relative Humidity) and that of the electrostatic image to be formed when 
the electrophotographic processes were conducted after the photosensitive 
member had been left in the atmosphere at 35.degree. C. and 85% RH for 24 
hours. The tonality was examined by measuring the distinguishable number 
of step-wedges in 10 stages used as the original, when they are 
reproduced. The durability of the photosensitive member was examined by 
measuring the number of revolution of the drum-shaped photosensitive 
member until a part of the insulative layer or the photoconductive layer 
thereof was exfoliated as the result of the repeated electrophotographic 
processes. 
For the sake of comparison, the same measurements as mentioned above were 
conducted on the photosensitive members using, in place of the curable 
cyclized buadiene rubber as the binder for the photoconductive layer, 
polyethylene, polypropylene, polyester, copolymer of vinyl chloride and 
vinyl acetate, polystyrene, acrylic resin, and epoxy resin. The results 
are as shown in the following Table 1. 
TABLE 1 
______________________________________ 
Number 
of White 
Resi- 
Dots dual Humidity 
per Poten- Resistance 
Tonal- 
Dura- 
Binder 1500 cm.sup.2 
tial 60% 85% ity bility 
______________________________________ 
Curable 
Cyclized 
Butadiene 0 3 V 650V 630V 10 50,000 
Rubber or above 
Polyethylene 
10 20 V 670V 630V 7 2,000 
Polypropylene 
8 30 V 640V 570V 7 2,500 
Solvent-soluble 
Polyester 4 20 V 650V 600V 7 20,000 
Copolymer of 
Vinyl Chloride 
3 10 V 650V 620V 8 38,000 
and Vinyl 
Acetate 
Polystyrene 
10 40 V 680V 590V 7 1,500 
Acrylic Resin 
7 40 V 670V 580V 7 2,500 
Epoxy Resin 
6 50 V 660V 550V 6 15,000 
______________________________________ 
From the above Table 1, it is recognized that the photosensitive member 
according to the present invention is very excellent in all of its 
properties. 
Also, in the present embodiment, the results of measurements on the 
photosensitive member having the photoconductive layer formed with curable 
cyclized butadiene rubber which was not yet cured were as follows: number 
of white dot . . . 2, ewsidual potential . . . 10 V; moisture resistance . 
. . 660 V (60%) and 600 V (85%); tonality . . . 8; and durability . . . 
20,000 and above. These results were also excellent. 
EXAMPLE 2 
In substitution for the curable cyclized butadiene rubber (trade name 
"CBR") used in Example 1 above, the following curable cyclized rubbers A 
through E were used to form the photosensitive members, and the 
measurements were conducted in the exactly same manner as in Example 1, 
the results of which were found to be also excellent. Even when these 
curable cyclized rubbers were used for forming the photosensitive members 
without curing treatment, their durability, dielectric breakdown 
resistance, tonality, moisture resistance, etc. were found to have been 
improved. 
A. Curable cyclized rubber (manufactured and sold by Japan Synthetic Rubber 
Co., Ltd. under a trade name "CLBR") --curing conditions: 180.degree. C. 
for 20 mins. 
B. Curable cyclized isoprene rubber (manufactured and sold by Eastman Kodak 
under a trade name of "Kodak Thin Film Resist KTFR")--curing conditions: 
light irradiation for 5 mins. by a high pressure mercury lamp. 
C. Curable cyclized polyisoprene rubber (manufactured and sold by Tokyo 
Ohka Kogyo Co., Ltd. under a trade name of "OMR")--curing conditions: 
150.degree. C. for 30 mins. 
D. Curable cyclized natural rubber (manufactured and sold by Fuji Chemicals 
Industrial Co., Ltd. under a trade name of "Fuji Super Resist 
FSR")--curing conditions: 180.degree. for 20 mins. 
E. Curable cyclized natural rubber (manufactured and sold by Hoechst Co., 
Ltd. under a trade name of "ALPEX CK450")--curing conditions: 160.degree. 
C. for 30 minutes. 
EXAMPLES 3 to 9 
The dielectric breakdown resistance, memory phenomenon, moisture 
resistance, tonality, and durability of the photosensitive members 
manufactured by use of the undermentioned resine Ex. 3 to 9 in place of 
the cyclized butadiene rubber (for the photoconductive layer) and the 
photocuring type acryl urethane resin (for the insulative layer) in 
Example 1 were examined. The results were favorable. The numerical figures 
for the temperature and time in the parenthesis indicate the curing 
conditions of the curable rubber. 
(EXAMPLE 3) 
Photoconductive layer: Curable polyisoprene rubber (manufactured and sold 
by Kureha Chemical Industries Co., Ltd. under a trade name of "KURARAY") 
(160.degree. C., 40 mins.) 
Insulative layer: Photo-curing type acrylic resin (manufactured and sold by 
Toa Gosei Chemical Industry Co., Ltd. under a trade name of "ARONIX") 
(EXAMPLE 4) 
Photoconductive layer: Curable polynitrile-butadiene rubber (manufactured 
and sold by Mitsui Toatsu Chemicals, Inc. under a trade name of 
"POLYLUCK") (150.degree. C., 30 mins.) 
Insulative layer: Photo-curing type polyester resin (manufactured and sold 
by Nippon Polyurethane Industry Co., Ltd. under a trade name of 
"DESMOPHENE") 
(EXAMPLE 5) 
Photoconductive layer: 80 % of curable silicone rubber (manufactured and 
sold by Toray Silicone Co., Ltd. under a trade name of "SH432") and 20% of 
epoxy resin (manufactured and sold by Shell Chemical Co., Ltd. under a 
trade name of "EPIKOTE") (170.degree. C., 30 mins.) 
Insulative layer: Thermo-setting melamine resin (manufactured and sold by 
Nippon Soda Co., Ltd. under a trade name of "SUPER BECKAMINE 5-820") 
(EXAMPLE 6) 
Photoconductive layer: 
Curable acryl rubber (manufactured and sold by Nippon Zeon Co., Ltd. under 
a trade name of "HYCAR 4021") (160.degree. C., 20 mins.) 
Insulative layer: Thermo-setting epoxy-modified silicone resin 
(manufactured and sold by Shinetsu Kogaku Co., Ltd. under a trade name of 
"ES1002-T") 
(EXAMPLE 7) 
Photoconductive layer: 90% of curable ethylenepropylene rubber 
(manufactured and sold by Sumitomo Chemicals Co., Ltd. under a trade name 
of "ESPRENE-EPPM") and 10% of polyester (manufactured and sold by Toyobo 
Co., Ltd. under a trade name of "VYLON 200") (160.degree. C., 20 mins.) 
Insulative layer: Photo-curing type acryl resin (manufactured and sold by 
Tokyo Ohka Kogyo Co., Ltd. under a trade name of "PHOTOFIX") 
(EXAMPLE 8) 
Photoconductive layer:: Curable ethylene-propylene rubber (manufactured and 
sold by Sumitomo Chemicals Co., Ltd. under a trade name of "ESPRENE-EPPM") 
(140.degree. C., 40 mins.) 
Insulative layer: Thermo-setting epoxy-modified silicone resin 
(manufactured and sold by Shinetsu Kogaku Co., Ltd. under a trade name of 
"ES1001") 
(EXAMPLE 9) 
Photoconductive layer: Curable Polysulfide rubber (manufactured and sold by 
Toray Thiokol Co., Ltd. under a trade name of "THIOKOL") (150.degree. C., 
30 mins.) 
Insulative layer: Thermo-setting urethane-modified silicon resin 
(manufactured and sold by Shinetsu Kogaku Co., Ltd. under a trade name of 
"KR302) 
EXAMPLE 10 
The photosensitive member having no insulative layer provided thereon was 
subjected to the electrophotographic processes comprising primary d.c. 
negative charging to render its surface potential to be 700 V, image 
exposure, latent image formation, wet-type image development with positive 
toner, image transfer to an image transfer paper, and cleaning by a blade, 
after which it was examined for various properties such as the dielectric 
breakdown resistance, memory phenomenon, moisture resistance, tonality, 
durability, charge sustaining capability, and toner transfer ratio in the 
same manner as in Example 1. 
The charge sustaining capability was examined by measuring the surface 
potential of the photosensitive member after 10 seconds' lapse from its 
charging with 700 V. The toner transfer ratio was examined by measuring 
the ratio of transfer of the total toner adhered onto the photosensitive 
member, when the toner image formed on the photosensitive member was 
electrostatically transferred to the image transfer paper. The results are 
as shown in the following Table 2. From the results, the photosensitive 
member is found to be very excellent in the above properties. 
TABLE 2 
__________________________________________________________________________ 
Number of 
White Dots Humidity Charge 
Toner 
per Residual 
Resistance Sustaining 
Transfer 
Binder 1500 cm.sup.2 
Potential 
60% 
85% 
Tonality 
Durability 
Capability 
Ratio 
__________________________________________________________________________ 
Curable Cyclized 
Butadiene 
0 3 V 670V 
650V 
10 50,000 
690V 90% 
Rubber or above 
Polyethylene 
9 20 V 630V 
570V 
7 2,500 670V 85% 
Polypropylene 
8 30 V 640V 
580V 
7 3,000 630V 85% 
Solvent-Soluble 
Polyester 
5 25 V 650V 
600V 
8 10,000 
680V 85% 
Copolymer of 
Vinyl Chloride 
2 10 V 640V 
610V 
8 15,000 
650V 85% 
and Vinyl 
Acetate 
Polystyrene 
10 40 V 640V 
560V 
7 2,000 590V 75% 
Acrylic Resin 
8 40 V 640V 
550V 
7 2,500 600V 60% 
Epoxy Resin 
7 50 V 650V 
540V 
6 15,000 
610V 60% 
Urethane 
Resin 7 40 V 650V 
570V 
6 3,500 620V 65% 
Polyvinylidene 
Fluoride 8 30 V 640V 
480V 
7 3,000 620V 80% 
__________________________________________________________________________