Substrate for electrophotographic photoconductor and electrophotographic photoconductor using the same

A substrate for an electrophotographic photoconductor having an anodic oxidation film on the surface is subjected to two-step sealing treatment in which the substrate is sealing treated with nickel fluoride as a sealing agent, and then with nickel acetate as a sealing agent. Therefore, an electrophotographic photoconductor using the substrate for an electrophotographic photoconductor is small in charge potential difference between the first turn and the second turn and after, and does not generate a fogged image defect or the like even without preliminary charging before printing.

This application is based on Patent Application No. 09-191,150 filed Jul. 
16, 1997 in Japan, the content of which is incorporated hereinto by 
reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an aluminum substrate for an 
electrophotographic photoconductor, where a surface thereof is covered 
with an anodized aluminum film. Also, the present invention relates to an 
electrophotographic photoconductor using the aluminum substrate. 
2. Description of the Related Art 
Heretofore, technical advances in electrophotography have been made in the 
field of copier machines and recently have been applied in the field of 
laser printers and so on. The laser printers provide excellent image 
qualities and allow high speed and quiet printing operations in comparison 
with those of the conventional impact printers. Thus, most of the present 
recording devices, such as printers and copiers, adopt the 
electrophotographic technologies. A photoconductor to be provided in each 
of those recording devices is prepared by forming a photoconductive layer 
on a conductive substrate. Inorganic materials (e.g., selenium, zinc 
oxide, arsenic-selenium alloy, and cadmium sulfide) have been used for the 
conventional photoconductive layers. Recently, however, most of the 
photoconductive layers are prepared by using organic materials instead of 
inorganic materials because of: 
(1) a wide choice of the organic materials; 
(2) an advantage in total expenditure including manufacturing costs; 
(3) the possibility of obtaining a novel photoconductor having excellent 
properties which are far superior to those of the inorganic one; and so 
on. 
It is now common practice to make a photoconductor as a structure having 
functionally separated layers. That is, as shown in FIG. 2, the 
photoconductor comprises an under-coating layer 2, a charge-generation 
layer 3, and a charge-transport layer 4, which are stacked on a substrate 
1 in that order. A single-layered type structure shown in FIG. 1 is used 
in some rare cases, where a layer 5 formed on a substrate 1 performs a 
double function. 
For preparing the photoconductor having the functionally separated layers, 
materials to be applied on a surface of the substrate to form the 
under-coating layer as a first layer may be grouped into two types. The 
first one includes resin materials such as polyamide and melamine resins 
and the second one includes materials that make an anodized aluminum film 
on an aluminum substrate by means of anodic oxidation. In general, the 
latter type is more reliable under the conditions of high temperature and 
high humidity. 
In the current trend of advanced information technology, the need for a 
multi-functional copier have been increased. The multi-functional copier 
may have a plurality of functions such as a facsimile function and a 
printer function in addition to a function of the conventional copier. 
Therefore, a digital copier is becoming a leading part as a 
multi-functional copier in the current trend of advanced information 
technology. The digital copier is designed to combine the conventional 
analog copier technology with the technologies of laser printer, LED 
printer, and so on, permitting the digitization of images. 
Various materials can be considered in a photoconductor to be used in the 
laser printer or the LED printer. Among them, phthalocyanines are selected 
as materials of exceedingly sensitive to wavelengths generated by the 
laser and the LED, and thus they are often used in a charge-generation 
layer. Generally, the phthalocyanines are chemically stable, easy to 
synthesize, and obtainable at a comparatively low cost. 
Using the known digital copier, where a photoconductor comprises 
phthalocyanine in its charge-generation layer, causes problems with a 
developed photographic image. A fog can be observed on the image after the 
first rotation of the photoconductor in the digital copier, while this 
kind of the trouble is almost trivial in the case of using the 
conventional laser or LED printer. Comparing with the results of the first 
rotation, furthermore, we can confirm that this kind of deficient image 
quality is reduced after the second rotation and substantially eliminated 
after the third rotation of the photoconductor. 
The digital copier adopts a reverse development scheme which is generally 
used in the laser printers and the LED printers, so that it has been 
confirmed that the fogged image after the first rotation is substantially 
due to an electrostatic charge failure of the photoconductor. 
Comparing with the results of the first rotation of the photoconductor 
before and after the process of continuously making about 100,000 copies 
of a predetermined material to experience electrical fatigue and letting 
it stand for about 30 to 60 minutes, the severity of the fog after the 
process becomes more worse than the severity of the fog before the 
process. 
In laser printers and LED printers, we can observe the phenomenon of 
generating the potential difference between the charge potential at the 
first rotation and the charge potential at the second or later rotation. 
Thus, it is possible to redesign the process so that any rotations except 
the first one responsible for an image formation. In order to fill market 
needs for speeding up the first copy, accelerating the recovering time 
from a power-saving mode, and so on, there is the demand for designing the 
process so as to include the step of forming an image as a result of the 
first rotation. In this case, however, some modifications including a 
preliminary charging may be made. For attaining such a process design, 
however, the best possible solution is to reduce the difference between 
the potential at the first rotation and the potential at the second 
rotation in the photoconductor from the viewpoint of cost advantage and 
device simplification. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an electrophotographic 
photoconductor in which the difference between a charge potential at the 
first rotation and a charge potential at the second or later rotation is 
negligibly small and, as a result, a fog or the like is not generated even 
without performing a preliminary charging before the process of image 
formation. 
In a first aspect of the present invention, there is provided a method for 
making a substrate for an electrophotographic photoconductor comprising 
the steps of: 
forming an anodic oxidation film on the surface of an aluminum substrate; 
performing a first sealing treatment with nickel fluoride as a sealing 
agent at a specific temperature to the aluminum substrate with the anodic 
oxidation film formed thereon; and 
performing a second sealing treatment with nickel acetate as a sealing 
agent at a specific temperature to the aluminum substrate with the anodic 
oxidation film formed thereon and treated by the first sealing treatment 
with nickel fluoride as a sealing agent. 
Here, concentration of the sealing agent comprising nickel fluoride may be 
0.8 to 20 g/l, preferably 1.2 to 10 g/l. 
The specific temperature in the first sealing treatment may be 10 to 
35.degree. C., preferably 20 to 30.degree. C. 
Concentration of the sealing agent comprising nickel acetate may be 1.5 to 
15 g/l, preferably 5.0 to 10 g/l. 
The specific temperature in the second sealing treatment may be 70 to 
95.degree. C., preferably 80 to 90.degree. C. 
In a second aspect of the present invention, there is provided a substrate 
for an electrophotographic photoconductor, comprising: 
an aluminum substrate; and 
an anodic oxidation film formed on the aluminum substrate; 
wherein the aluminum substrate with the aluminum anodic oxidation film 
formed thereon is treated by a first sealing treatment with nickel 
fluoride as a sealing agent and then treated by a second sealing treatment 
with nickel acetate as a sealing agent. 
Here, concentration of the sealing agent comprising nickel fluoride may be 
0.8 to 20 g/l, preferably 1.2 to 10 g/l. 
The first sealing treatment may be performed at a temperature of 10 to 
35.degree. C., preferably 20 to 30.degree. C. 
Concentration of the sealing agent comprising nickel acetate may be 1.5 to 
15 g/l, preferably 5.0 to 10 g/l. 
The second sealing treatment may be performed at a temperature of 70 to 
95.degree. C., preferably 80 to 90.degree. C. 
In a third aspect of the present invention, there is provided an 
electrophotographic photoconductor having at least a substrate and a 
photosensitive layer laminated on the substrate, wherein 
the substrate comprises an aluminum substrate, the aluminum substrate 
having an anodic oxidation film formed thereon, the aluminum substrate 
with the anodic oxidation film being treated by a first sealing treatment 
with nickel fluoride as a sealing agent, and then treated by a second 
sealing treatment with nickel acetate as a sealing agent. 
Here, concentration of the sealing agent comprising nickel fluoride may be 
0.8 to 20 g/l, preferably 1.2 to 10 g/l. 
The first sealing treatment may be performed at a temperature of 10 to 
35.degree. C., preferably 20 to 30.degree. C. 
Concentration of the sealing agent comprising nickel acetate may be 1.5 to 
15 g/l, preferably 5.0 to 10 g/l. 
The photosensitive layer may contain phthalocyanine as a charge generation 
substance. 
The above and the other objects, effects, features and advantages of the 
present invention will become more apparent from the following description 
of embodiments thereof taken in conjunction with the accompanying drawings 
.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
A substrate for electrophotographic photoconductor and a photoconductor 
using such a substrate of the present invention will be described in 
detail. 
The substrate for electrophotographic photoconductor of the present 
invention can be obtained by the process of properly performing sealing 
treatments after applying an anodic oxidation process on an aluminum-base 
material. The anodic oxidation process deposits an oxidized aluminum film 
on the material and can be carried out by, for example, the process 
including the steps shown in Table 1. 
TABLE 1 
______________________________________ 
Treat- Liquid 
Step ment temp Conc. 
No. Details time (.degree. C.) 
Chemical used 
(g/l) 
______________________________________ 
1 Degreasing 4.0 min 60 Degreasing 30 
agent 
(e.g. TO- 
CLEAN 101) 
2 Water washing 
1.0 min Pure water 
3 Water washing 
1.0 min Pure water 
4 Neutralization 
1.0 min Nitric acid 
70 
5 Water washing 
1.0 min Pure water 
6 Water washing 
1.0 min Pure water 
7 Anodic 23.5 min 20 Sulfuric acid 
180 
oxidation 
8 Water washing 
1.0 min Pure water 
9 Water washing 
1.0 min Pure water 
10 Water washing 
2.5 min Pure water 
11 First-step 2.0 min 25 Nickel fluoride 
2 
pit sealing (e.g. TOP-SEAL 
L-100) 
12 Water washing 
1.0 min Pure water 
13 Second-step 
10.0 min 85 Nickel acetate 
8 (40 
pit sealing (e.g. TOP-SEAL 
ml/l) 
H298) 
14 Water washing 
1.0 min Pure water 
15 Water washing 
1.0 min Pure water 
16 Water washing 
1.0 min Pure water 
17 Hot water 2.0 min 65 Pure water 
washing 
18 Drying 4.0 min 70 Hot air drying 
______________________________________ 
The process includes two sealing treatments: Step No. 11 and Step No. 13 in 
Table 1. The first-step sealing treatment (Step No. 11) is performed using 
nickel fluoride as a sealing agent. The concentration of nickel fluoride 
is preferably 0.8 to 20 g/l, more preferably 1.2 to 10 g/l at a 
temperature of preferably 10 to 35.degree. C., more preferably 20 to 
30.degree. C. On the other hand, the second-step sealing treatment (Step 
No. 13) is performed using nickel acetate as a sealing agent. The 
concentration of nickel acetate is preferably 1.5 to 15 g/l, more 
preferably 5.0 to 10 g/l at a temperature of preferably 70 to 95.degree. 
C., more preferably 80 to 90.degree. C. If the sequence of these sealing 
treatments is reversed, the resulting photoconductor does not show any 
advantage of the present invention because it has poor electrical 
properties and provides an image with visual defects, such as fog or the 
like. If an additional sealing treatment with pure water at 80 to 
90.degree. C. for 5 to 20 minutes is performed after the nickel fluoride 
sealing (i.e., double-sealing treatment), another problem is caused when 
these steps are performed in the commercial-scaled continuation process. 
The problem is that a water bath for the sealing treatment using pure 
water tends to be contaminated with the other agents and so on, leading to 
the generation of image defects such as fog. Thus, the double sealing 
treatment cannot attain the advantages of the present invention. 
We are now describing an electrophotographic photoconductor as a preferred 
embodiment of the present invention. The photoconductor uses the substrate 
described above as a substrate. 
The photoconductor of the present embodiment may be of having a structure 
of single-layer type or functionally-divided layer type. The former 
structure is shown in FIG. 1, while the latter structure is shown in FIG. 
2. Each of the photoconductor in the figures has a photosensitive layer 5 
on a substrate 1. In FIG. 2, however, the photosensitive layer 5 is 
further divided into functionally different layers. In the following, only 
a negative-charged photoconductor with a functionally-divided 
photosensitive layer will be described in detail. However, it is needless 
to say that it will become apparent to those skilled in the art that the 
respective detailed description is applicable also to the single-layer 
type photoconductor shown in FIG. 1. 
Referring again to FIG. 2, the negative-charged photoconductor is in the 
type of having a functionally-divided layer structure. The photosensitive 
layer 5 is laminated on the substrate 1 through an undercoating layer 2 
and consists of a charge generation layer 3 and a charge transport layer 4 
which are laminated in that order, resulting in a 
functionally-distinguished multi-layer structure. 
The substrate 1 acts as an electrode of the photoconductor and 
simultaneously as a substrate of other respective layers. The substrate 1 
is provided as an aluminum substrate which may be any of cylindrical, 
plate, and film forms. The aluminum substrate has an anodized aluminum 
film on its surface. 
The charge generation layer 3 may be formed by vacuum deposition of an 
organic photoconductive substance or by coating a material that contains 
particles of organic photoconductive substance dispersed in a resin 
binder. The charge generation layer 3 is responsible for receiving light 
to generate electric charges. It is important that the charge generation 
layer 3 has the high efficiency of charge generation and simultaneously 
has the desirable charge injection properties into the charge transport 
layer 4, that is, the charge injection is to exhibit small electrical 
field dependence and to be efficient even at low electrical field. A 
charge generation substance of the charge generation layer 3 may be 
selected from the group consisting of metal-free phthalocyanine compounds; 
phthalocyanine compounds having, at their center, a metal such as tin, 
zinc, or copper, or an oxide of one of these metals, or a metal 
coordinated with chlorine atom or the like. Among these substance, a 
suitable one can be selected according to the wavelength band of exposure 
light source for image formation and to the photosensitivity required for 
the photoconductor. The amount of the phthalocyanine compound to be used 
is 5 to 500 parts by weight, preferably 10 to 100 parts by weight, with 
respect to 10 parts by weight of the resin binder. 
Since the charge generation layer 3 is sufficient to have only a charge 
generation function, the film thickness is generally within a range to 
obtain a necessary photosensitivity and is designed as thin as possible, 
generally less than 5 .mu.m, preferably less than 1 .mu.m. The charge 
generation layer 3 mainly comprises a charge generation substance which 
can be mixed with a charge transport substance or the like. As a binder 
for the charge generation layer, such polymers as polycarbonate, 
polyester, polyurethane, polyamide, epoxy, polyvinylbutyral, phenoxy, 
silicone, methacrylic ester, or copolymers thereof, and halogenated or 
cyanoethylated compounds thereof can be used in appropriate combinations. 
The charge transport layer 4 is a coated film comprising an organic charge 
transport substance dispersed in a resin binder. The charge transport 
layer 4 maintains the charge of the photoconductor as an insulator layer 
in a dark place, while it transfers the charge infected from the charge 
generation layer when it receives light. For resin binders for the charge 
transport layer, polymers and copolymers of polycarbonate, polyester, 
polystyrene, and methacrylic ester are used, which are important to have a 
compatibility with charge transport substances in addition to mechanical, 
chemical and electrical stabilities and adhesiveness. In the charge 
transport layer 4, any of distyryl compounds, diamine compounds, hydrazone 
compounds, stilbene compounds and the like are used as a charge transport 
substance. The amount of the compound is 20 to 200 parts by weight, 
preferably 30 to 150 parts by weight, with respect to 100 parts by weight 
of the resin binder. 
Film thickness of the charge transport layer 4 is preferably 3 to 50 .mu.m, 
more preferably 15 to 40 .mu.m, to maintain a practically effective 
surface potential. 
For the purpose of improving sensitivity, reducing residual potential, 
improvement of environmental resistance or stability to harmful light, or 
the like, an electron accepting substance, an antioxidant, a light 
stabilizer, or the like can be added to the undercoating layer, the charge 
generation layer, and the charge transport layer as necessary. 
Further, on the above photosensitive layer, a surface protective layer may 
be provided for the purpose of improving the environmental resistance and 
mechanical strength. The surface protective layer is desirably one which 
does not substantially disturb transmission of light. 
In the following, the present invention will be described in detail with 
reference to the embodiments. 
Embodiments 1 to 4 (Two-Step Sealing) 
After a cylindrical aluminum substrate (JIS 6063 material) was cut using a 
lathe into desired dimensions, degreasing was carried out with a 
degreasing agent (TOCLEAN 101, 30 g/l/60.degree. C., 2 minutes: from 
Okuno Chemical Industries Co., Ltd.), and thoroughly washed with water to 
remove the degreasing agent. After that, the aluminum substrate was 
subjected to anodic oxidation (current density 1.0 A/dm.sup.2, 
electrolytic voltage 13.5 to 14.0 V) in sulfuric acid (180 g/l, 20.degree. 
C., 25 minutes) to obtain an anodic oxidation film thickness of 7 .mu.m. 
A first step sealing treatment was carried out using nickel fluoride 
(TOP-SEAL L-100: from Okuno Chemical Industries Co., Ltd.) in a 
concentration of 2 g/l for 2 minutes. Then, a second step sealing 
treatment was carried out using nickel acetate (TOP-SEAL H298, 40 ml/l: 
from Okuno Chemical Industries Co., Ltd.) in 4 conditions at temperatures 
of 60.degree. C., 70.degree. C., 80.degree. C., and 90.degree. C. for 8 
minutes. 
After that, the substrate was subjected to ultrasonic washing 2 times with 
hot pure water and 2 times with pure water, respectively. Then, it was 
further subjected to hot air to obtain an aluminum substrate (hereinafter 
referred to as "raw cylinder") complete with formation of the anodic 
oxidation film. 
Next, the thus obtained raw cylinder was washed with an alkaline washing 
agent (CASTROL 450: from Castrol Co., Ltd.) in a concentration of 2 weight 
%, rinsed with pure water, washed with hot pure water at 65.degree. C., 
and dried. Next, as the charge generation layer, 10 parts by weight of 
titanyl phthalocyanine and 10 parts by weight of resin binder 
(polyvinyl-butyral (BM-2 from Sekisui Chemical Co., Ltd.) were dispersed 
in 980 parts by weight of tetrahydrofuran to obtain a coating liquid, 
which was dip coated and then dried at 100.degree. C. for 30 minutes to 
form a charge generation layer having a film thickness of about 0.2 .mu.m. 
Next, 100 parts by weight of hydrazone compound and 100 parts by weight of 
polycarbonate resin (TOUGHZET B-500: from Idemitsu Kosan Co., Ltd.) were 
dissolved in 900 parts by weight of dichloromethane to prepare a coating 
solution, which was dip coated and then dried at 100.degree. C. for 60 
minutes to form a charge transport layer having a film thickness of about 
25 .mu.m, thereby obtaining an organic lamination type photoconductor. 
Embodiments 5 to 8 (Two-Step Sealing) 
In the stage of sealing treatment in the process of forming anodic 
oxidation films of embodiments 5 to 8, treatment was made in the same 
conditions respectively as in Embodiments 1 to 4, except that 
concentration of nickel fluoride (TOP-SEAL L-100: from Okuno Chemical 
Industries Co., Ltd.) was 4 g/l in Embodiments 5-8. 
Comparative Examples 1 and 2 (One-Step Sealing) 
In the stage of sealing treatment in the process of forming anodic 
oxidation film, sealing treatment of only a single step was carried out 
with nickel acetate (TOP-SEAL H298, 40 ml/l: from Okuno Chemical 
Industries Co., Ltd.) in two conditions at temperatures of 60.degree. C. 
and 80.degree. C. for 8 minutes. Other conditions were the same as in 
Embodiment 1. 
Comparative Examples 3 and 4 (One-Step Sealing) 
In the stage of sealing treatment in the process of forming anodic 
oxidation film, sealing treatment of only a single step was carried out 
with nickel fluoride (TOP-SEAL L-100: from Okuno Chemical Industries Co., 
Ltd.) in a concentration of 2 g/l in two conditions of for 2 minutes and 
10 minutes. Other conditions were the same as in Embodiment 1. 
Comparative Examples 5 and 6 (One-Step Sealing) 
In the stage of sealing treatment in the process of forming anodic 
oxidation film, sealing treatment of only a single step was carried out 
with nickel fluoride (TOP-SEAL L-100: from Okuno Chemical Industries Co., 
Ltd.) in a concentration of 4 g/l in two conditions of for 2 minutes and 
10 minutes. Other conditions were the same as in Embodiment 1. 
Each of the thus prepared photoconductors was equipped on a digital copier 
modified for measurement of surface potential of the photoconductor, 
evaluated a difference in charge potential between the first turn and the 
second turn at an initial time and after making 100,000 copies, and the 
image was evaluated. 
The evaluation results are shown in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Initial After 100,000 sheets copying 
First step Second step 
First 
Second First 
Second 
pit sealing pit sealing 
turn 
turn 
Charge turn 
turn 
Charge 
Nickel fluoride 
Nickel acetate 
charge 
charge 
pot. 
Image 
charge 
charge 
pot. 
Image 
Temp. Conc. 
Time 
Temp. 
Conc. 
Time 
pot. 
pot. 
dif. 
evalu- 
pot. 
pot. 
dif. 
evalu- 
(.degree. C.) 
(g/l) 
(min) 
(.degree. C.) 
(g/l) 
(min) 
(V) (V) (V) ation 
(V) (V) (V) ation 
__________________________________________________________________________ 
Em.1 
Room 
2 2 60 5 8 -520 
-532 
12 good 
-535 
-550 
15 good 
Em.2 
Room 
2 2 70 5 8 -540 
-551 
11 good 
-535 
-548 
13 good 
Em.3 
Room 
2 2 80 5 8 -545 
-553 
8 good 
-543 
-552 
9 good 
Em.4 
Room 
2 2 90 5 8 -550 
-555 
5 good 
-540 
-550 
10 good 
Em.5 
Room 
4 2 60 5 8 -530 
-540 
10 good 
-534 
-549 
15 good 
Em.6 
Room 
4 2 70 5 8 -540 
-549 
9 good 
-540 
-552 
12 good 
Em.7 
Room 
4 2 80 5 8 -545 
-551 
6 good 
-543 
-551 
8 good 
Em.8 
Room 
4 2 90 5 8 -550 
-554 
4 good 
-544 
-549 
5 good 
Co. 
-- -- -- 60 5 8 -510 
-551 
41 x -492 
-542 
50 x 
Ex.1 
Co. 
-- -- -- 80 5 8 -520 
-550 
30 x -500 
-545 
45 x 
Ex.2 
Co. 
Room 
2 2 -- -520 
-545 
25 x -487 
-547 
60 x 
Ex.3 
Co. 
Room 
2 10 -- -520 
-550 
30 x -491 
-546 
55 x 
Ex.4 
Co. 
Room 
4 2 -- -520 
-545 
25 x -484 
-550 
66 x 
Ex.5 
Co. 
Room 
4 10 -- -535 
-559 
24 x -500 
-549 
49 x 
Ex.6 
__________________________________________________________________________ 
In the table, image evaluation results are indicated as follows. 
good: fogged image defect is not observed. 
x: fogged image defect is observed. 
As can be seen from the above results shown in Table 2, by performing 
two-step sealing treatment when forming the aluminum anodic oxidation film 
as in Embodiments 1 to 8, a difference in potential between the first turn 
and second turn at the initial time and after making 100,000 copies in a 
digital copier was remarkably reduced to 15 V or less compared to 
Comparative Examples 1 to 6 performing one-step sealing treatment. 
Furthermore, no fogged image defect was noted in the image, thus obtaining 
a good result. 
As described above, with the present invention, in a digital copier, 
difference in charge potential is small between the initial time of 
operation and after an actual print fatigue, and a good image is obtained 
without degradation of other characteristics of the photoconductor even by 
a process without preliminary charging. 
The present invention has been described in detail with respect to various 
embodiments, and it will now be apparent from the foregoing to those 
skilled in the art that changes and modifications may be made without 
departing from the invention in its broader aspects, and it is the 
intention, therefore, in the appended claims to cover all such changes and 
modifications as fall within the true spirit of the invention.