U.S. patent number 3,879,199 [Application Number 05/348,370] was granted by the patent office on 1975-04-22 for surface treatment of arsenic-selenium photoconductors.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Michael P. Trubisky.
United States Patent |
3,879,199 |
Trubisky |
April 22, 1975 |
Surface treatment of arsenic-selenium photoconductors
Abstract
A method of improving the electrical characteristics of an
arsenic-selenium photoconductive layer is disclosed which comprises
coating the surface of said layer with a specific thickness of an
organic material which is selected from the group consisting of a
mixture of vinyl chloride and vinyl acetate, chloranil, the
tributylamine salt of styrene-methacrylic acid,
2,4,7-trinitro-9-fluorene, p-benzoquinone, naphthylamine,
hexachlorobenzene, polyvinyl carbazole, N-vinyl carbazole,
N-N-dimethylallylamine anthracene, aniline hydrochloride,
mesitylene and phenoxy resins. Coating with these materials
prevents surface charges contained on the photoconductive layer
from injecting into the bulk of the photoconductor, thereby
reducing the dark discharge characteristics of the
photoconductor.
Inventors: |
Trubisky; Michael P. (Fairport,
NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
26899510 |
Appl.
No.: |
05/348,370 |
Filed: |
April 5, 1973 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
204477 |
Dec 3, 1971 |
|
|
|
|
888030 |
Dec 24, 1969 |
|
|
|
|
Current U.S.
Class: |
430/58.05;
430/67; 430/64; 430/85; 430/58.25; 430/58.65; 430/58.7; 430/58.6;
430/58.35 |
Current CPC
Class: |
G03G
5/0436 (20130101); G03G 5/14739 (20130101); G03G
5/14708 (20130101); G03G 5/1473 (20130101); G03G
5/14734 (20130101); G03G 5/14726 (20130101) |
Current International
Class: |
G03G
5/147 (20060101); G03G 5/043 (20060101); G03g
005/00 () |
Field of
Search: |
;96/1.5,1.5C
;117/201,215,218 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
44-3674 |
|
Feb 1969 |
|
JA |
|
43-16198 |
|
Jul 1968 |
|
JA |
|
Other References
Regensburger, "Optical Sensitization Of Charge Carrier Transport In
Poly(N-Vinyl carbazole)," Photochemistry and Photobiology, Vol. 8,
Nov. 1968, pp. 429-440. .
Dessauer et al., Xerography and Related Processes, 1965, pp.
108-109..
|
Primary Examiner: Torchin; Norman G.
Assistant Examiner: Miller; John R.
Parent Case Text
BACKGROUND OF THE INVENTION
This application is a continuation-in-part of application Ser. No.
204,477, filed Dec. 3, 1971, now abandoned which in turn is a
continuation-in-part of my previous application, Ser. No. 888,030,
filed Dec. 24, 1969 now abandoned.
Claims
What is claimed is:
1. A xerographic plate which consists essentially of a supporting
electrically conductive substrate, a photoconductive layer
consisting essentially of an arsenic-selenium alloy having an
arsenic content from about 0.5 to 50 percent by weight of said
alloy overlaying said substrate, with said photoconductive layer
being overcoated with an electrically insulating, thin film of a
material selected from the group consisting of; a mixture of 90
weight percent vinyl chloride and 10 weight percent vinyl acetate,
chloranil, the tributyl amine salt of styrenemethacrylic acid,
2,4,7-trinitro-9-fluorene, p-benzoquinone, naphthylamine,
hexachlorobenzene, polyvinyl carbazole, N-vinyl carbazole,
N-N-dimethylallylamine, anthracene, aniline hydrochloride,
mesitylene, and phenoxy resins, said film having a thickness of
between about 25 to 2,000 Anstrom Units.
2. The plate of claim 1 wherein said alloy has an arsenic content
in an amount of about 40 percent by weight of said alloy.
3. The plate of claim 1 wherein said alloy has an arsenic content
in an amount of about 20 percent by weight, of said alloy.
4. The plate of claim 1 wherein said alloy has an arsenic content
in an amount of about 16 percent weight of said alloy.
5. The plate of claim 1 wherein said alloy has an arsenic content
in an amount of about 0.5 percent by weight of said alloy.
Description
In the art of xerography, a photosensitive element containing a
photoconductive insulating layer is first uniformly
electrostatically charged in order to sensitize its surface. The
plate is then exposed to an image of activating electromagnetic
radiation such as light, X-ray, or the like, which selectively
dissipates the charge in the illuminated areas of the
photoconductive insulator while leaving behind a latent
electrostatic image in the non-illuminated areas. This latent
electrostatic image may then be developed and made visible by
depositing finely divided electroscopic marking particles on the
surface of the photoconductive insulating layer. This concept was
originally disclosed by Carlson in U.S. Pat. No. 2,297,691, and is
further amplified and described by many related patents in the
field.
The use of vitreous selenium, as taught by Bixby in U.S. Pat. No.
2,297,907, introduced to commercial xerography a photoconductor
capable of holding and retaining an electrostatic charge for
relative long periods of time when not exposed to light. In
addition, vitreous selenium exhibits relatively good sensitivity to
light as compared to other photoconductive materials and has
sufficient strength and stability to be reused hundreds or even
thousands of times.
U.S. Pat. Nos. 2,803,542 to Ullrich and 2,822,300 to Mayer et al
both disclose improvements over vitreous selenium by the
incorporation of elemental arsenic in amounts ranging from less
than 1 percent to about 50 percent by weight. The addition of
arsenic has been found to increase the stability of selenium with
regard to crystallization, and additionally provides increased
spectral response in the yellow-red band of the electromagnetic
spectrum to which vitreous selenium is relatively insensitive.
In a typical xerographic cycle, a given plate is charged in the
dark to a particular potential called the "acceptance potential."
After the plate has been charged, a certain percentage of the
acceptance potential is lost in the absence of light. This loss in
apparent surface voltage is called "dark discharge" or "dark
decay." If the dark discharge becomes a significant percentage of
the initial acceptance potential, it can be seen that only a
portion of the initially accepted potential will eventually be
available for development of a latent electrostatic image after the
plate has been exposed to a pattern of light. It can therefore be
seen that the dark discharge for a given xerographic plate should
preferably be kept at a relatively low level in order that a
maximum amount of voltage be available for the development of the
electrostatic image. In modifying or improving the properties of
selenium through the use of alloy additions of arsenic as taught by
the Ullrich and Mayer et al patents disclosed above, the
advantageous properties imparted by the arsenic addition have been
found useful and essential in certain types of xerographic imaging,
such as rapid cycling in which multiple copies are made in a
relatively short period of time. One characteristic of
photoconductors in the arsenic-selenium system, however, is that
the addition of arsenic does result in an increased dark discharge
over that exhibited by vitreous selenium. Although the dark
discharge level for most arsenic-selenium alloys is not at a level
to render it unsuitable for use in reusable xerography, the
reduction or improvement of the dark discharge characteristic is a
goal which would afford greater versatility with regard to use, and
result in greater electrical efficiency because of the increased
electrical potential available for development.
OBJECTS OF THE INVENTION
It is, therefore, an object of this invention to provide a method
of reducing dark discharge in photoreceptors of the
arsenic-selenium system.
It is a further object of this invention to provide a method of
improving the electrical characteristics of arsenic-selenium
photoconductive alloys.
It is yet another object of this invention to provide a xerographic
plate which exhibits improved electrical characteristics.
It is a further object of this invention to provide a novel method
of improving the electrical characteristics of an arsenic-selenium
photoconductive layer.
BRIEF DESCRIPTION OF THE INVENTION
The foregoing objects and others are accomplished in accordance
with this invention by providing a method of decreasing the dark
discharge characteristics of photoconductors of the
arsenic-selenium system by coating the photoconductor surface with
a thin film of an organic material which is selected from the group
consisting of a mixture of vinyl chloride and vinyl acetate,
chloranil, the tributylamine salt of styrenemethacrylic acid,
2,4,7-trinitro-9-fluorene, p-benzoquinone, naphthylamine,
hexachlorobenzene, polyvinyl carbazole, N-vinyl carbazole,
N-N-dimethylallylamine, anthracene, aniline hydrochloride,
mesitylene and phenoxy resins. By coating the photoconductor
surface with a thin film of the organic materials noted above,
surface charges which are contained on the photoconductor are
prevented from injecting into the bulk of the photoconductor. This
results in a significant decrease in the dark discharge
characteristic of treated plates as compared to untreated plates.
The resultant decrease in dark discharge of the coated
arsenic-selenium photoconductor plate is further characterized by
an increased electrical potential a short time after charging, and
a decreased charging current which results in overall greater
electrical efficiency.
DETAILED DESCRIPTION OF THE INVENTION
As stated above, suitable organic materials which have been found
to be effective in decreasing the dark discharge of
arsenic-selenium photoconductors when applied within a specific
thickness range, include organic materials which are selected from
the group consisting of a mixture of vinyl chloride and vinyl
acetate, chloranil, the tributylamine salt of styrenemethacrylic
acid, 2,4,7-trinitro-9-fluorene, p-benzoquinone, naphthylamine,
hexachlorobenzene, polyvinyl carbazole, N-vinyl carbazole,
N-N-dimethylallylamine, anthracene, aniline hydrochloride,
mesitylene and phenoxy resins. By application of the organic
material as a film having a thickness between about 25 to 2000
Angstrom Units over the surface of the photoconductor, acceptable
reduction in dark discharge of the photoconductor occurs without
any adverse effects on the xerographic efficiency of the
photoconductor.
It has been determined that the organic material must be in the
form of a layer overlying the photoconductor with a thickness of
between about 25 to 2,000 Angstrom Units to result in acceptable
dark discharge rates with photoconductors of the arsenic-selenium
type. If this layer or film thickness falls below about 25 Angstrom
Units, no substantial reduction in dark discharge rate occurs,
while if the layer thickness exceeds about 2,000 Angstrom Units
then it becomes difficult to discharge the photoconductive layer
upon exposure to illumination because of residual potential buildup
across the coating which cannot easily be dissipated by an erase
lamp. It should also be recognized in this regard, that the organic
film or layer which is applied in the instant invention should not
be confused with thicker organic overcoatings which are used
primarily to protect photoconductive surfaces from abrasion, such
as are illustrated by U.S. Pat. Nos. 2,860,048 and 3,146,145 to
Deubner and Kinsella, respectively. Furthermore, the organic
materials of the instant invention which comprise the coating
should not be confused with photoconductor overcoatings of
insulators such as hydrocarbons, or insulating resins such as
polystyrenes which are also used to protect photoconductors, since
these materials are not effective in reducing dark discharge rates
of arsenic-selenium photoconductors.
The surface treatment of the arsenic-selenium alloy may comprise
the application of the particular organic material in the form of a
dilute solution of the material in any appropriate solvent. Typical
solvents for the above organic materials include methyl isobutyl
ketone, benzene, methyl alcohol, cyclohexane and isopropyl alcohol.
In general, the organic material is diluted to a relatively weak
solution in an appropriate solvent. Concentrations of from about
0.01 to 1.0 weight percent of the organic material have proven
particularly satisfactory. Suitable techniques for applying the
organic solution include dip or draw coating, swabbing the solution
on the photoconductive surface by hand with absorbant cotten or
cloth, applying with an applicator such as a squeegie, immersing
for a few seconds in a bath of the solution, spraying or by
rolling. Other means of applying the appropriate organic solution
to the arsenic-selenium surface would occur to those versed in the
art.
Arsenic-selenium alloys falling within the scope of the instant
invention include arsenic in a concentration of about 0.5 to 50
percent by weight with the balance substantially selenium. The
alloy is amorphous or vitreous in form and may be used in any
conventional xerographic type application. U.S. Pat. Nos. 2,803,542
to Ullrich, 2,822,300 to Mayer et al and 3,312,548 to Straughan
illustrate suitable arsenic-selenium alloys, methods of
preparation, and the utility intended for the method and product of
the instant invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following examples further specifically define the present
invention with respect to a method of surface treating and testing
an arsenic-selenium alloy layer. The examples and data below are
intended to illustrate various preferred embodiments of the instant
invention.
EXAMPLE I
A plate comprising a 40 micron layer of a 20 weight percent arsenic
- 80 weight percent selenium alloy is formed by vacuum deposition
on a polyethyleneimine interface contained on an aluminum substrate
by the method set forth by Straughan in U.S. Pat. No. 3,312,548.
The substrate is maintained at about 65.degree.C during vacuum
deposition with a vacuum of about 10.sup.-.sup.6 Torr. The final
plate was sectioned into two parts designated sections "A" and "B,"
respectively, and rested in the dark overnight. Xerographic
properties of the two sections were determined to be similar. The B
section was then surface treated by dip coating with a 1 percent
solution of N, N-dimethylallylamine in isopropyl alcohol. The plate
was immersed in the coating bath for about one minute to form a
dried coating thickness of several hundred Angstrom Units. The
plates were again dark rested overnight (for about 18 hours) and
retested the following day. Under identical charging conditions,
the surface potential measured 1-1/2 seconds after charging was
determined to be 220 volts for the untreated A section and 310
volts for the treated B section. This difference in surface
potential is attributed to the reduced dark discharge of the
treated plate.
EXAMPLE II
A second plate comprising a 40 micron layer of a 40 weight percent
arsenic -- 60 weight percent selenium alloy is deposited at
175.degree.C on a chromic acid cleaned aluminum substrate using the
method of Example I. The plate was then cut into sections
designated A and B, and dark rested (for about 18 hours) overnight.
The xerographic properties of the two sections were determined to
be similar. The B section was then surface treated with a 1 percent
solution of PKHH phenoxy polymer in 2-butoxyethanol (available from
Union Carbide under the Tradename Bakelite PKHH). The plates were
again dark rested overnight and retested the following day. The
acceptance potential was determined to be 50 volts for the
untreated A section and 95 volts for the treated B section. The
charging conditions and results are similar to those of Example
I.
EXAMPLE III
A series of 17 plates comprising a 40 weight percent arsenic -- 60
weight percent selenium alloy were made by vacuum deposition to the
following specification using the method set forth in Example
I:
1. Eleven plates (Nos. 1-11) comprise a 40 micron layer of the
arsenic-selenium alloy deposited on an aluminum substrate at about
180.degree.-200.degree.C.
2. Six plates (Nos. 12-17) comprise a 15 micron layer of
arsenic-selenium alloy on a gold coated glass substrate at a
deposition temperature of about 25.degree.C.
The plates were first sectioned into two parts. One section of each
plate was designated "Control" and not treated. The second section
of each plate was treated with a 1 weight percent organic solution
of the instant invention by dip coating the section in an organic
solution for about 1 to 2 minutes to form a dired coating about
several hundred Angstroms thick on the surface of the
arsenic-selenium photoconductor. The plates were rested in the dark
overnight and were then electrically tested by first charging to a
field of about 15 volts/micron of photoconductor thickness. The
dark discharge was then determined in both the rested condition and
after cycling. The results of the testing are shown in Table I. The
plates are numbered 1-17, with the untreated section designated
"Control" and the treated section designated as such.
TABLE I
__________________________________________________________________________
SURFACE TREATMENT OF 40% As - 60% Se PHOTOCONDUCTOR
__________________________________________________________________________
DARK RESTED CYCLED ** DARK DISCHARGE DARK DISCHARGE PLATE NO.
TREATMENT IN 5 SEC. (%) IN 5 SEC.
__________________________________________________________________________
(%) 1 (Control) None 30 28 1 (Treated) 1% VYNS in
methylisobutylketone 5 15 (A mixture of 90% vinyl chloride and 10%
vinyl acetate available from Union Carbide under the 2 (Control)
None 30 27 2 (Treated) 1% chloranil in methylisobutylketone 9 24 3
(Control) None 28 39 3 (Treated) 1% tributylamine salt of
styrene-methacrylic acid in 18nzene 33 4 (Control) None 68 65 4
(Treated) 1% chloranil in methylisobutylketone 13 31 5 (Control)
None 100 100 5 (Treated) 1% 2,4,7-trinitro-9-fluorene in benzene 74
90 6 (Control) None 100 86 6 (Treated) 1% p-benzoquinone in methyl
alcohol 62 47 7 (Control) None 43 49 7 (Treated) 1% naphthylamine
in methyl alcohol 26 40 8 (Control) None 97 76 8 (Treated) 1%
hexachlorobenzene in benzene 65 69 9 (Control) None 82 65 9
(Treated) 1% polyvinylcarbazole in cyclohexane 27 47 10 (Control)
None 50 83 10 (Treated) 1% polyvinylcarbazole in cyclohexane 6 20
11 (Control) None 96 100 11 (Treated) 1% n-vinyl carbazole in
benzene 50 81 12 (Control) None 40 65 12 (Treated) 1%
N,N-dimethylallylamine in isopropyl alcohol 17 23 13 (Control) None
77 68 13 (Treated) 1% anthracene in benzene 44 54 14 (Control) None
86 91 14 (Treated) 1% aniline-hydrochloride in methyl alcohol 56 62
15 (Control) None 83 95 15 (Treated) 1% VYNS in
methylisobutylketone 6 12 16 (Control) None 60 82 16 (Treated) 1%
N-vinylcarbazole in benzene 10 28 17 (Control) None 65 86 17
(Treated) 1% mesitylene in methyl alcohol 45 39
__________________________________________________________________________
* The dark discharge in the rested condition is determined by
charging a given dark rested plate to the appropriate potential in
the dark and measuring the voltage loss in 5 seconds with an
electrometer probe. The ratio of the voltage lost in 5 seconds to
the initial charged potential i the percentage of dark discharge.
** The cycled dark discharge is determined by charging a given dark
reste plate to the appropriate potential in the dark followed by
discharging th plate by exposure to a cool while fluorescent erase
lamp. This cycle is repeated 20 times. The dark discharge is then
determined as the ratio of the voltage loss in 5 seconds to the
initial charged potential as set forth above.
EXAMPLE IV
A series of 9 additional plates are made by the method of Example
I. These plates are number 18-26, respectively, and are made to the
following specifications:
1. Plates 18, 19 and 20 comprise a 30 micron layer of a 0.5 weight
percent arsenic -- balance selenium layer deposited on an aluminum
substrate held at 55.degree.C during vacuum deposition.
2. Plates 21, 22 and 23 comprise a 30 micron layer of a 5 weight
percent arsenic -- balance selenium layer deposited on an aluminum
substrate held at 55.degree.C during vacuum deposition.
3. Plates 24, 25 and 26 comprise a 50 micron layer of a 16 weight
percent arsenic -- balance selenium layer deposited on an aluminum
substrate held at 150.degree.C during vacuum deposition.
One plate of each of the above three groups (Plates 18, 21 and 24,
respectively) was designated a "Control" plate and was not treated
by the process of the instant invention. The remaining plates were
dip coating by the technique set forth in Example III to form an
organic coating several hundred Angstroms thick on the surface of
the arsenic-selenium photoconductive layer. All plates were dark
rested overnight, and were charged to a field of about 12
volts/micron of photoconductor thickness for plate 18-23 and about
8 volts/micron for plates 24-26. The dark discharge in 5 seconds
was then determined for each plate.
TABLE II ______________________________________ SURFACE TREATMENT
OF 0.5, 5.0 AND 16.0% As - Se ALLOYS
______________________________________ DARK RESTED DARK DISCHARGE
-PLATE NO. SURFACE TREATMENT IN 5 SEC. (%)
______________________________________ 18 (Control) None 14 19
(Treated) 1 wt% Polyvinyl Carbazole in methylene chloride 5 20
(Treated) 1 wt% PKHH Phenoxy Polymer in 2-butoxyethanol 3 21
(Control) None 39 22 (Treated) 1 wt% Polyvinyl Carbazole in
methylene chloride 6 23 (Treated) 1 wt% PKHH Phenoxy Polymer in
2-butoxyethanol 7 24 (Control) None 33 25 (Treated) 1 wt% Polyvinyl
Carbazole in methylene chloride 14 26 (Treated) 1 wt% PKHH Phenoxy
Polymer in 2-butoxyethanol 10
______________________________________
The dark discharge is determined in the same manner as described
for the values listed in Table I.
As shown by the examples, and the data contained in Tables I and
II, the dark discharge of plates treated by the process of the
instant invention is markedly lower than that for the untreated
plates. It can therefore be seen that the instant invention results
in a method of significantly increasing the amount of surface
voltage available for the development of photoconductors of the
arsenic-selenium system.
Although specific components and proportions have been stated in
the above description of the preferred embodiments of the instant
invention, other suitable materials and procedures such as those
listed above, may be used with similar results. In addition, other
materials and changes may be utilized which synergize, enhance, or
otherwise modify the instant invention. It should be understood
that the organic coatings of the instant invention may be formed on
the surface of the arsenic-selenium photoreceptor by a wide range
of techniques other than those previously suggested. For example,
the organic material may be incorporated as a component in the
conventional cascade development process, or optionally, as a
component in a liquid development system. It is also contemplated
that the organic material may be simply applied in a separate
intermediate step at some point in the conventional xerographic
cycling of an arsenic-selenium drum.
Other modifications and ramifications of the present invention
would appear to those skilled in the art upon reading the
disclosure. These are intended to be within the scope of this
invention.
* * * * *