U.S. patent number 3,907,650 [Application Number 05/332,044] was granted by the patent office on 1975-09-23 for photosensitive binder layer for xerography.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Heinz W. Pinsler.
United States Patent |
3,907,650 |
Pinsler |
September 23, 1975 |
Photosensitive binder layer for xerography
Abstract
A process for applying a photoconductive layer to a flexible
nickel or nickel-coated substrate by initially subjecting a nickel
sheet or belt to an acid etching bath followed by anodizing
treatment in an electrolytic bath to obtain at least two
intermediate metal oxide layers such as nickel oxide layers having
superior adhesive and charge-injection-blocking characteristics;
and a flexible photoreceptor element with such structure which is
especially useful for high-speed xerographic copy work.
Inventors: |
Pinsler; Heinz W. (Brighton,
NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
23296484 |
Appl.
No.: |
05/332,044 |
Filed: |
February 12, 1973 |
Current U.S.
Class: |
430/131; 205/216;
430/65; 216/108; 216/34; 148/255; 205/188; 430/63 |
Current CPC
Class: |
G03G
5/102 (20130101); G03G 5/144 (20130101) |
Current International
Class: |
G03G
5/10 (20060101); G03G 5/14 (20060101); C25D
011/34 (); C09K 013/04 (); G03C 003/36 (); G03G
005/04 () |
Field of
Search: |
;204/32R,34 ;252/79.2
;156/18 ;148/6.14R,6.15R ;117/34 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Edmundson; F. C.
Attorney, Agent or Firm: Crowe; John E. O'Sullivan; James P.
Ralabate; James J.
Claims
What is claimed is:
1. In a process for producing a photoreceptor element comprising a
nickel or nickel-coated substrate and a photoconductive layer
joined in good blocking and charge-injection preventing contact
with the substrate through at least two intermediate nickel oxide
blocking layers arranged between the substrate and the
photoconductive layer the improvement comprising
microetching and chemically oxidizing the nickel or nickel-coated
substrate with a composition comprising an inorganic acid selected
from the group consisting of phosphoric acid, sulfuric acid and
hydrochloric acid, in the presence of at least one of palladium
chloride, chloroplatinic acid, or ferric sulfate;
anodically oxidizing the resulting microetched chemically oxidized
substrate; and
depositing a selenium-containing photoconductive layer upon the
treated substrate to obtain the desired photoreceptor element.
2. The process of claim 1 wherein the anodizing step is effected by
glow discharge.
3. The process of claim 1 wherein the anodizing step is effected by
immersing the substrate as an anode in an electrolytic bath until
its potential, as measured against a saturated calomel electrode,
has a maximum value of about 0.85 volt.
4. The process of claim 1 wherein the microetching step is effected
with an etching bath comprising phosphoric acid and chloroplatinic
acid.
5. The process of claim 1 wherein the microetching step is effected
with an etching bath comprising phosphoric acid and palladium
chloride.
6. A process for producing a photoreceptor element comprising a
nickel or nickel-covered substrate and a selenium-containing
photoconductive layer joined in good blocking contact through at
least two intermediate blocking layers arranged between said
substrate and the applied photoconductive layer, comprising
a. microetching the nickel or nickel-coated substrate with an
etching composition comprising
1. an inorganic acid solution containing at least one of phosphoric
acid, sulfuric acid, or hydrochloric acid,
2. a balance of 0% up to about a catalytic amount of at least one
of palladium chloride or chloroplatinic acid based on the total
amount of catalyst utilized in steps (a) and (b), and
3. from 0% up through about 10% by weight of a water soluble alkali
metal halide or iron sulfate; about 8% - 10% of the metal sulfate
being utilized in the absence of platinum or palladium
catalyst;
b. anodically oxidizing the washed microetched and oxide-coated
substrate by immersing and treating as an anode in an electrolytic
bath until the potential of the resulting etched double oxide
coated electrode as measured against a saturated calomel electrode
changes from a negative value to a value not exceeding about 0.85
volt; and
c. depositing a selenium-containing photoconductive layer upon a
surface of the treated and washed substrate to obtain the desired
element.
7. A process according to claim 6 in which the clean substrate is
treated with a pre-etch and wash solution containing 0% up to a
catalytic amount of at least one of palladium chloride or
chloroplatinic acid.
8. The process of claim 7 wherein the initial acid treatment of
step is effected with a phosphoric acid solution or a hydrochloric
acid solution in the presence of about 0% - 0.1% by weight of
palladium chloride or chloroplatinic acid.
9. The process of claim 6 wherein the microetching step is effected
with an etching bath comprising phosphoric acid and potassium
chloride.
10. The process of claim 6 wherein the anodizing step is effected
in an acidic electrolytic bath containing an alkali metal chromate
salt solution as an electrolyte.
11. The process of claim 6 wherein the selenium-containing
photoconductive layer comprises a cadmium selenide, a gallium
triselenide, an arsenic triselenide, an antimony-selenium or a
selenium-arsenic-halogen-alloy.
12. The process of claim 6 wherein the microetching step is
effected with an etching bath comprising sulfuric acid and ferric
sulfate.
Description
This invention relates to fast, highly flexible photoreceptor
elements and to a process for obtaining such elements comprising a
nickel or nickel-coated substrate, particularly of the belt type,
having a photoconductive layer strongly affixed thereto and joined
in good blocking and charge injection-preventing contact with the
substrate through the utilization of at least two intermediate
nickel oxide blocking layers arranged between the substrate and the
photoconductive layer.
In the xerographic art, a photoconducting insulating layer is first
given a uniform electrostatic charge in order to sensitize its
surface. The layer is then exposed to an image as defined by
electromagnetic radiation, such as light, which selectively
dissipates the applied charge in the illuminated areas of the
photoconducting insulating layer while leaving behind a latent
electrostatic image in the non-illuminated areas. The latent
electrostatic image may be developed and made visible by deposited
finely divided electroscopic marking particles on the surface of
the photoconductive layer. This concept was originally described by
Carlson in U.S. Pat. No. 2,297,691 and is further amplified and
described by many related patents in the field.
Conventionally, a xerographic photoreceptor plate includes a
supporting conductive base or substrate which is generally
characterized by the ability to accommodate the release of electric
charge upon exposure of the photoconductive member to activating
radiation such as light. Usually, this substrate must have a
specific resistivity of less than about 10.sup.10 ohm-cm,
preferably less than about 10.sup.5 ohm-cm and have sufficient
structural strength to provide mechanical support for a
photoconductive member.
The conventional xerographic plate also normally has a
photoconductive insulating layer overlaying the conductive base or
substrate. Photoconductive layers may comprise a number of
materials known in the art. For example, selenium-containing
photoconductive material such as vitreous selenium, or selenium
modified with varying amounts of arsenic are found suitable. In
general, however, such photoconductive layer must have a specific
resistivity greater than about 10.sup.10 ohm-cm in the absence of
illumination and preferably at least 10.sup.13 ohm-cm. In addition,
the resistivity should drop at least several orders of magnitude in
the presence of activating radiation or light. This layer should
also support an electrical potential of at least about 100 volts in
the absence of radiation and customarily may vary in thickness from
about 10 to 200 microns.
A photoconductive layer having the above configuration, normally
will exhibit some reduction in potential or voltage leak even in
the absence of activating radiation. This phenomenon is known as
"dark decay" and will vary somewhat with usage of a photoreceptor.
The existence of the problem of "dark decay" is well known and has
been controlled to some extent by incorporation of thin barrier
layers such as dielectric material between the base or substrate
and the photoconductive insulating layer. U.S. Pat. No. 2,901,348
to Dessauer et al utilizes a film of aluminum oxide (Ex. 25 to 200
angstroms) or an insulating resin layer, such as a polystyrene (Ex.
0.1 to 2 microns) for this purpose. With some limitations, such
barrier layers function to allow the photoconductive layer to
support a charge of high field strength while minimizing charge
dissipation in the absence of illumination. When activated by
illumination, however, the photoconductive layer should still
become conductive and permit a migration of the existing charges
through the photoconductive layer in the radiation or
illumination-struck areas.
In addition to the electrical requirements of a barrier layer, it
is necessary that all photoreceptor layers also meet certain
requirements with regard to mechanical and chemical properties.
These requirements become particularly important when one attempts
to utilize xerographic processes in modern automatic copiers
operating at high speeds. For such purpose it has been found very
useful to utilize photoreceptors in the form of endless belts (ref.
U.S. Pat. No. 3,691,450).
While belt-type photoreceptors have the advantage of greater speed
for xerographic copying purposes, there are also serious technical
problems inherent in their use. For example, high speed
machine-cycling conditions demand strong adhesion between a
photoconductive layer and the underlying substrate compared with
the slower aluminum photoreceptor drum which does not substantially
flex.
It is also very important that any interface between the
electrically conductive supporting substrate and the
photoconductive layer be chemically stable since changes at this
point will have a substantial effect on the electrical properties
of the photo-receptor.
In searching for suitable photoreceptor materials it has been found
that nickel or nickel-coated substrates are useful. Seamless belts
of this material have satisfactory mechanical and chemical
properties and can be readily produced by techniques known to the
art.
Unfortunately, however, belts of this material also have some
limitations or deficiencies. For example, it is difficult to find
suitable blocking layers for controlling "charge-injection" while
still avoiding a flaking off or spalling of the photoconductive
layer.
The concept of "charge-injection" is known and recognized, in that
electrical currents far in excess of ohmic currents can provably be
drawn through insulators from the electrodes, (ref. Physical Review
97 No. 6, 1538, 1955; Rose, "Concepts In Photoconductivity and
Allied Problems", Interscience Publishers, John Wylie and Sons,
1963). The phenomenon is sometimes analogized to a vacuum diode in
which the cathode thermally emits electrons into the vacuum and a
space charge is built up between the cathode and the anode. Where
an insulator is involved, the carrier concentration exceeds the
equilibrium concentration whenever charge is injected from the
electrodes. The flowing electrical current, in such case, is
space-charge-limited, and greater than the normal ohmic current is
expected with equilibrium carrier concentrations. The magnitude of
such space-charge-limited current is difficult to predict (in any
case) because of the presence and effect of traps on charge
transport through a photoconductive material. Generally speaking,
charge injection can and should be prevented or at least limited to
assure chargeability of the photoconductor and by dark discharge.
Mere thickness of insulating layer alone, however, will not provide
a suitable answer since an intolerable residual voltage can be
built up if an insulating layer becomes too thick.
It is possible to prevent or at least to limit charge injection
through the careful choice of interface materials having a work
function such that they form a blocking layer with the
photoconductive layer. In this context the term "work function" is
defined as
a difference in energy level between electrons present in a
particular material and those calculated at infinite distance in
vacuo; i.e., a binding energy.
Within the above definition, an electron blocking contact is formed
for xerographic purposes whenever the electronic work function of
the metal substrate is larger than that of the over-lying
photoconductive insulator layer. If, on the other hand, the
electronic work function of the substrate is smaller than the
photoconductive insulator, electrons are injected into the
system.
In attempting to determine the efficiency of a particular interface
from the relative work functions of the joining materials, it has
been found that small amounts of adsorbed impurities on surfaces
forming interface materials will also cause substantial changes in
work function. Unfortunately, this can happen when amorphous
selenium or selenium alloys are utilized in a photoconductive
layer. In fact, such material customarily includes small amounts of
chlorine and arsenic (ref. "Xerography and Related Processes"; J.
H. Dessauer and H. E. Clark). The injection of electrons from an
interface area will dark-discharge a photoreceptor when the
photoconductor surface is charged positively and a negative
electric counter charge is induced at the substrate.
It is further noted that a material which conducts only holes can
also be employed as an electron blocking interface, provided it is
deposited as a thin layer between the photoconductive layer and the
charge-conducting substrate. Such material includes, for instance,
chlorine- and arsenic-rich selenium.
It is an object of the present invention to obtain improved
flexible photoreceptor elements for xerographic copying purposes,
in which a nickel or nickel-coated charge conductive substrate
layer and a photoconductive layer, particularly a
selenium-containing photoconductive layer are strongly bonded
without loss of charge-injection-blocking properties.
It is a further object of the present invention to obtain
photoconductive layers affixed to a nickel or nickel-coated
substrate by chemically stable flex-proof bonding which is easily
applied.
It is a still further object of the present invention to obtain,
prepare and employ an efficient metal oxide blocking contact
suitable for use with a nickel-selenium alloy interface of a
flexible belt-type photoreceptor component.
These and other objects of the instant invention are accomplished
by microetching a nickel or nickel-coated substrate such as
metallized paper or metallized plastic belt with an etching
composition an inorganic acid, inclusive of phosphoric, sulfuric,
or composition comprising acid, or combination thereof, in the
presence of at least one of palladium chloride, chloroplatinic acid
or ferric sulfate. This step is followed by anodizing the resulting
microetched chemically oxidized substrate, preferably by immersing
the substrate as an anode in an electrolytic bath and/or by glow
discharge such as described, for instance, by Ignatov in J. Chimie
Physique, 54 (1957) pg. 96 et seq.
When prepared by the first method it is found advantageous to
immerse the substrate as an anode in an electrolyte bath until its
potential, as measured against a saturated calomel electrode, has a
maximum value of about 0.85 volt.
The substrate is then further treated by depositing a suitable
photoconductive layer, particularly a selenium-containing
photoconductive layer of one of the usual type upon the treated
substrate to obtain the desired photoreceptor element.
Preferably, nickel or nickel-covered substrate suitable for use in
photoreceptor elements within the present invention, are kept free
of surface contaminants other than necessary additives such as
dopants. This pre-condition can be easily obtained through the use
of one or more cleaning steps wherein the substrate is initially
immersed for a brief period into a cleaning bath. Suitable cleaners
for such purpose are sold commercially, and are exemplified, for
instance, by "Mitchell Bradford No. 14 Cleaner" and by "Mobil Acid
Cleaner". The cleaned and well-rinsed substrate is optionally
further treated with a pre-etch acid wash solution, preferably one
containing an inorganic acid solution such as hydrochloric acid or
phosphoric acid, and additionally containing 0% up to about a
catalytic amount of at least one of palladium chloride or
chloroplatinic acid. For such purpose "a catalytic amount" is
usefully defined as the concentration of palladium chloride or
chloroplatinic acid sufficient to substantially accellerate a
combined etching and chemical oxidation reaction at the surface of
the nickel substrate when the washed substrate is subsequently
exposed to the required etching and oxidizing composition.
Generally speaking, a satisfactory concentration of catalyst in a
pre-etch acid wash solution (when used) varies from about 0.01% -
0.10% by weight of solution, and the corresponding acid
concentration can usefully, although not exclusively, vary from
about 15% - 55% by weight.
When desired, the full catalytic amount of platinum or palladium
can be supplied by inclusion of one or both in (a) the pre-etch
acid wash solution, (b) in the etching composition, or (c) in both
the wash solution and etching composition. In each case, however, a
total solution concentration of about 0.01% - 0.10% by weight is
found sufficient to assure an adequate catalytic deposition on the
nickel belt surface, provided proper temperature and time
conditions are met. By way of example, a pre-etch acid washing step
is preferably carried out at a temperature range of about
15.degree.C - 85.degree.C, for a period of about 1-5 minutes.
The microetching step, on the other hand, can be usefully carried
out at a somewhat higher temperature range of about 20.degree.C -
110.degree.C and for a period of about 2-15 minutes. Where
increased concentration and/or differences in temperature are
permitted, however, the treatment time can be varied somewhat
without substantially affecting the desired properties.
Generally speaking, a suitable etching solution for purposes of the
present invention can comprise
1. an inorganic acid solution containing at least one of phosphoric
acid, sulfuric acid or hydrochloric acid;
2. a balance of 0% up to about a catalytic amount of at least one
of palladium chloride or chloroplatinic acid based on the total
amount of catalyst utilized in the acid wash and micro etching
steps, and
3. from 0% up through about 10% by weight of a water soluble alkali
metal halide or metal sulfate.
In addition to the optional inclusion of catalyst, the etching bath
used in the present invention can usefully include a water soluble
alkali metal halide or a metal sulfate salt exemplified by KCl and
Fe.sub.2 (SO.sub.4).sub.3. A concentration range of from 0% up
through about 10% by weight of such metal salts is found useful,
provided at minimum of about 8% - 10% by weight of the metal
sulfate such as Fe.sub.2 (SO.sub.4).sub.3 is utilized in the
absence of either platinum or palladium catalyst in the acid
washing and etching baths.
The amount of inorganic acid or acids present in the etching
composition can usefully vary, a concentration of about 10% - 60%
by weight being suitable, and a concentration of 10% - 25% by
weight being preferred for purposes of the present invention. The
presence of phosphoric acid in this etching composition is a
further preferred embodiment of the present invention.
After exposure to the etching composition, such as by dipping, the
washed microetched and oxide-coated substrate is subject to an
anodizing step by immersing and treating as an anode in an
electrolytic bath until the potential of the electrode as measured
against a saturated calomel electrode changes from a negative value
to a value not exceeding about 0.85 volt. In this step a second
oxide coat is applied over the previous chemically-applied metal
oxide coat on the nickel substrate. For the purpose of applying
such additional coat it is convenient, for instance, to immerse the
substrate (i.e., the belt) as an anode in an electrolytic bath with
a chromate salt solution as electrolyte. This bath can usefully
operate at an applied current of about 3-10m A/cm.sup.2 until the
anode potential (with current cut off and measured against a
saturated calomel electrode) has the maximum potential value
indicated above. This step is most efficiently carried out at a
current density of about 5-10mA/cm.sup.2 and for a period varying
from about 1-15 minutes.
Suitable electrolytes for the electrolytic bath include, for
instance, a 5-15% solution (by weight) of Na.sub.2 Cr.sub.2
O.sub.7, K.sub.2 Cr.sub.2 O.sub.7, Na.sub.2 CrO.sub.4, K.sub.2
CrO.sub.4 or H.sub.2 CrO.sub.4, at room temperature up to about
95.degree.C, and preferably about 50.degree.C through 95.degree.C.
The parameters of (1) temperature (2) electrolyte concentration and
(3) current density are inversely related to the anodizing
treatment time for purposes of obtaining a suitable second oxide
layer on the belt.
In addition to, or as an alternative to, the above-described step,
it is also found useful to lay down a nickel oxide layer by glow
discharge techinque. Here the nickel substrate is made the anode
under partial vacuum, with a current density of about 3 .times.
10.sup..sup.-5 A/cm.sup.2 and a voltage (cathode) of about 2.5 K.V.
for a period of about 1-5 minutes. This technique is modified and
described in detail in Vol. 54 of J. Chimie Physique, (supra).
After washing, a photoconductive layer, preferably a
selenium-containing photoconductive layer, is deposited upon a
surface of the treated and washed substrate to complete the major
components of the photoreceptor element. For this purpose it is
found convenient to utilize selenium-containing photoconductor
material and techniques as described, for instance, in U.S. Pat.
Nos., 2,753,278, 2,970,906, 3,312,548 and 3,490,903; a particularly
suitable technique involves sealing selenium, arsenic and a halogen
in a container under heat to form a homogeneous material, which is
then applied onto a cooled substrate by evaporation from a lined
crucible under vacuum. Suitable photoconductive layers applicable
to the present invention include, for instance, a cadmium selenide,
a gallium triselenide, an arsenic triselenide, an
antimony-selenium- or selenium-arsenic-halogen layer. Also included
are photoconductive layers containing Tellurium, Germanium and
Bismuth.
The following examples specifically demonstrate preferred
embodiments of the present invention without limiting it
thereby.
EXAMPLE I
A. A stain-free nickel alloy test belt identified as A-1, having a
thickness of about 4.5 mil (0.0045 inch), a width of 5 inches and a
circumference of 65 inches, is cleaned with an aqueous solution
containing 10% by weight of "Mitchell Bradford No. 14 Cleaner",
water rinsed in deionized water for about 2 minutes, immersed in an
acid wash solution (10% by volume 85.5% H.sub.3 PO.sub.4) for 1
minute, and then immersed for 10 minutes at 60.degree.C in an
etching bath containing 18g/liter KCl, 150 ml/liter of 85.5%
H.sub.3 PO.sub.4, and 0.21g/liter of 10% chloroplatinic acid
(H.sub.2 PtCl.sub.6.6H.sub.2 O) as a catalyst. The belt is then
rinsed, dried and evaluated (Table I).
B. An identical nickel test belt identified as A-2 is treated as in
procedure "A" (supra) with the exception that the rinsing step in
deionized water prior to microetching is extended to a full 5
minutes.
The results obtained in Steps A and B are examined microscopically
and Gloss measurements made in the usual way in accordance with the
following descriptions, and reported in Table I.
Microscopic Examination -- The morphology of the etched nickel foil
is examined by a scanning electron microscope and an optical
microscope, applying ultramicrotome techniques to obtain vertical
cross sections of the foils.
Gloss Measurements -- Any change of the surface structure of the
nickel belt is noticeable by a change in reflectivity. The gloss
value is measured with a Hunter Lab D16-75 gloss meter which
measures the relative reflectance of treated and untreated surfaces
using a 75.degree. incident light beam.
Table I ______________________________________ Sample Belt
Observation ______________________________________ A-1 A gray
uneven oxide layer is obtained on the belt surface. Etching not
consistent. Gloss = 10% reflectance A-2 A uniform gray-black oxide
layer is observed on a good microetched belt surface. Gloss = 3%
reflectance ______________________________________
The above results suggest considerable sensitivity to contamination
when chloroplatinic acid is used as a catalyst.
EXAMPLE II
A nickel test belt identical with the one used in Example I, and
identified as A-3 is treated as in Example I A except that a
PdCl.sub.2 catalyst is utilized by immersing the belt in a pre-etch
acid wash solution containing 0.25g/liter PdCl.sub.2 and 300
ml/liter of concentrated HCl. The micro etching step is then
carried out for 5 minutes in a bath containing 650 ml/liter of
85.5% H.sub.3 PO.sub.4 and 80 g/liter of KCl; with evolution of
some chlorine by-product. The microetched belt is then rinsed and
dried as in Example I and evaluated (Table II) before further
treatment.
EXAMPLE III
A nickel test belt identical with those used in Examples I-II, and
identified as A-4, is immersed for 5 minutes at about 75.degree.C
in an agitated alkaline solution containing 10% by weight of a
commercial cleaner (Mitchell Bradford No. 14 Cleaner), rinsed for 2
minutes in deionized water then cleaned once more in a commercial
cleaning solution (1/12 strength Mobile Acid Cleaner), rinsed for 2
minutes in deionized water, dipped into an acid wash solution (300
ml/liter of concentrated HCl) for 30 seconds, dipped into an acid
solution containing 0.25 g/liter PdCl.sub.2 and 300 ml/liter of
concentrated HCl for 10 seconds, then etched in a KCl-free etching
bath containing 650 ml/liter of 85.5% H.sub.3 PO.sub.4 ; the
microetched belt is then subject to the usual rinsing and drying
steps as in Examples I-II and evaluated (Table II) before further
treatment.
EXAMPLE IV
Four nickel test belts identical with those used in Examples I-IV,
and identified as A 5-8, are cleaned and rinsed in deionized water
as in Example I then immersed (without a pre-etch acid wash) in an
etching solution containing 184 g/liter of Fe.sub.2
(SO.sub.4).sub.3 and 97.5 g/liter of H.sub.2 SO.sub.4 at
85.degree.C. After treating the four belts in the etching bath for
varying periods of time, they are removed, rinsed and dried as in
Example I and evaluated (Table II) before further treatment.
Table II
__________________________________________________________________________
(Step 1) Belt Cat. Pre-etch Etch Time Observation and Gloss No.
Bath(s) Bath (min.) Test
__________________________________________________________________________
A-3 PdCl.sub.2 Yes, with H.sub.3 PO.sub.4 5 Ex.* etching and oxide
Cat. KCl layer. Gloss=2% reflec- tance. Cl.sub.2 evolved. A-4
PdCl.sub.2 Yes, with H.sub.3 PO.sub.4 5 Ex.* etching and oxide Cat.
layer. Gloss=3% reflec- tance. No Cl.sub.2 evolved. A-5 -- NO
H.sub.2 SO.sub.4 2 G.* etching and oxide Fe.sub.2 (SO.sub.4).sub.3
layer. Gloss=7% reflec- tance. A-6 -- " " 2 Vg.* etching and oxide
layer. Gloss=3% reflec- tance. A-7 -- " " 5 Ex.* etching and oxide
layer. Gloss=2% reflectance. A-8 -- " " 5 Vg.* etching and oxide
layer. Gloss=3% reflectance.
__________________________________________________________________________
*Ex. = Excellent Vg. = Very Good G. = Good
EXAMPLE V
A stain-free nickel test belt identical with those used in the
preceeding examples and identified as A-9 is cleaned and rinsed,
then microetched at 60.degree.C for 10 minutes. Both the acid wash
and etching baths are identical with Example II except that the
etching solution contains 650 ml/liter of a 7:1 by volume of
concentrated H.sub.3 PO.sub.4 /HCl solution. The etched nickel belt
is otherwise treated identically with Example II. The microetching
and the oxide layer on the belt is found to be of comparable
quality to that obtained in Examples II and III (i.e., A 3-4).
EXAMPLE VI (Control)
A stain-free nickel test belt identical with those used in the
preceeding examples, and identified as A-10, is cleaned and rinsed,
then oxidized at 110.degree.C for 7 minutes in an etching bath
consisting essentially of 650 ml/liter of concentrated H.sub.3
PO.sub.4 solution. The oxidized nickel belt has a dull appearance
and is evaluated as "G" (see Table II footnote).
EXAMPLE VII
A. Samples from test belts A 1-9 of Examples I-IV are next treated
for 10 minutes in an electrolytic bath containing sodium chromate
solution as electrolyte (10% by weight at pH6), operating at
90.degree.C with a current density of 5 mA/cm.sup.2. After
treatment, the test belts are rinsed with deionized water, air
dried, and then mounted onto a circular rotatable mandril and
coated in a vacuum chamber (5 .times. 10.sup..sup.-4 Torr) over a
stainless steel crucible containing a heated selenium alloy
consisting of about 99.67% selenium, 0.33% arsenic and about 30
parts per million chlorine at a temperature of about 280.degree.C
for 40 minutes. During this period the mandril is constantly
rotated at about 6 revolutions per minute to obtain an external
photoconductor surface having a uniform thickness of about 50 .mu..
Each belt is then tested for mechanical and electrical properties
and the results reported in Table III.
B. Test belt A-10 of Example VI (the Control) is directly coated
with a selenium photoconductive layer as in Example VII without the
prior 10 minute treatment in an electrolytic bath. This belt is
then tested for mechanical and electrical properties as in Example
VII A and the results reported in Table III.
For testing purposes the following guidelines and definitions are
generally applicable in evaluating the results obtained:
Cold Test -- The flexible coated photoreceptor belt is mounted over
two 5-inch cardboard inserts and placed in a storage box and held
at -28.8.degree.C for 4 hours. To pass the test, the
photoconductive coating must remain intact without cracking or
spalling.
Shock Test -- A photoreceptor belt, while still in a storage box,
is dropped from a 42 inches height onto a supporting floor. To pass
the test the belt must remain intact and be substantially
undamaged.
Flex Test -- Each belt is mounted on a tri-roller assembly adapted
to rotate the belt over each roller at about 43.degree.C. The belt
is cycled for 1000 cycles in 30 minutes. The test is repeated (with
5 minute hiatus) for 30,000 cycles or until the belt structurally
fails. To pass this test the belt must complete 30,000 cycles
without exhibiting cracks which are visible to the eye.
Mandrel Test -- The belt is bent three times over a cylinder having
a 11/4 inches diameter at Room Temperature and then checked for
cracks in the substrate and layers applied thereto.
Electrical Dark Discharge Test -- The photoreceptor belt is charged
at 900 volt in the dark and the potential checked after 3 seconds.
A dark decay or voltage loss of 12% or less is acceptable for
general xerographic purposes.
Vc. Determination Test -- An electrical charge is added stepwise to
a photoreceptor surface in the dark and it is determined at what
voltage the charging behavior of the photoreceptor begins to
substantially deviate (by 40 volts) from the desired (linear)
charging characteristics. A maximum voltage of 900 volts - 950
volts is considered fair, 950 volts - 1100 volts is good, 1100 -
1500 volts is very good and 1500 - 1600 volts is considered
excellent.
Print Test -- About 50 square inches of photoreceptor are dark
charged at 900 volts and developed without light exposure after
about 20 seconds using fine powdered toner. The presence of light
or dark spots or a visible pattern is attributed to uneven dark
discharge of the photoreceptor attributable to non-uniformities of
the interface.
Table III
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Belt Mandrel Cold and Shock Flex Electrical Vc Print (coated) Test
Test (-28.8.degree.C) Test Dark Dis- Test Test (1.25" charge Test
Diam) <12% 3 Sec.
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A-1 Passed Passed Failed Passed -- Failed A-2 " " Passed " 1100v.
Passed 30,000 cycles A-3 " " " " 1560v. " A-4 " " " " 1560v. " A-5
" " Failed " -- Failed A-6 " " Passed " -- Passed A-7 " " " " -- "
A-8 " " " " -- " A-9 " " " " 1500v. " A-10 Failed " Failed "
(900v.) " (control)
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EXAMPLE VIII
A test belt identified as A-11 is prepared as in Example III and
then the etched and coated belt is subject to Glow Discharge
treatment for 2 minutes at a chamber pressure of about 70 .mu.
mercury (100 mA with substrate cathode voltage of 2.5 kv). The
treated belt is then coated with a selenium photoconductive layer
on a rotating mandrel for 40 minutes as in Example VII. The
electrical and mechanical properties of the belt are found to be
comparable to those of belts A-3 and A-4 (Table III).
While the above Examples are directed to preferred embodiments of
the invention, it will be understood that the invention is not
limited thereby.
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