Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF_T~E INVENTION
This invention relates bD improved photoreceptors - -
utilizing flexible substrates and relatively brittle heavy
ionizable inorganic photocond~ctive material, the photoreceptor
being obtained in accordance with an oxidation-ion-deposition
process.
Photoreceptors, particularly those related to the
xerographic copying, traditionally comprise a photoconductive
insulating layer such as an ionizable element or alloy thereof
exemplified by selenium (amorphous or trigonal) and selenium ;-
alloys such as a selenium-arsenic alloy with varying amounts
of a halogen. Such materials are customàrily applied in charge
blocking contact to a supporting metal-or metal-covered charge-
conductive substrate. Suitable substrates for such purpose
include, for instance, aluminum, steel, nickel, brass, NESA~
glass or corresponding metal-coated polymeric materials.
~hotoreceptors comprising at least the above compon-
ents are ger.erally given a uniform electrostatic charge and the ~ ~
sensitized surface then exposed to an image pattern deined by ~ -
an electromagnetic radiatîon, such as light. Light impingement
results in a selective dissipation of the initial applied -~
char~e leaving a positive electrostatic image. The electro-
static image is then customarily developed by applying oppositely -
charged electroscopic marking particles onto the charge-bearing
photoreceptor surface.
The above basic concept was originally described by
C. Carlson in U.S. Patent 2,297,691, issued October 6, 1~42
and has been since amplified and redescribed in many related
patents in the field. Generally speaking, however, photo-
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conductive layers suitable for carrying out the above functions
have a specific resistivity of about 10l - 10l3 ohm-cm, in
the ahsence of i]lumination. In addititon, their resistivity
must drop at least several orders of magnitude where exposed
to an activating radiation such as light.
Photoreceptors meeting the above criteria also normally
exhibit some loss in applied charge, even in the absence of
light exposure. This phenomenon is known as "dark decay" and
will vary somewhat with sensitivity and with usage of the photo- ;
receptor. The existence of the problem of "dark decay" is well
~nown and has been controlled to a substantial extent by incor- -~
poration of thin barrier layers such as a dielectric film be- ;
tween the base or substrate and the photoconductive insulating
layer. U~S. Patent 2,901,348 of ~. Dessauer et al issued
August 25, 1959 utilizes a film of aluminum oxide Df about 25
to 200 angstrom or a .1 - 2J~ insulating resin layer, such as a
polystyrene for such purpose~ With some limitations, these
barrier layers function to allow the photoconductive layer to
support a charge of high field strength while minimizing "dark
decay". When activated by illumination, however, the photocon-
ductive layer and barrier layer must become sufficiently con-
ductive to permit substantial dissipation of the applied charge `~;~
in light-struck areas within a short period of time.
In addition to the above-indicated electrical re-
quirements, it is also becoming increasingly important that
photoreceptors meet rather stringent requirements with regard
to mechanical properties such as flexibility and durability.
Such additional criteria become particularly important in modern
automatic copiers operating a~ high speeds where the photo~
receptor is in the form of an endless flexible belt. While
belt~type photoreceptors have many advantages, there are also
serious technical problems inherent in their use. For example,
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high speed machine cycling conditions require particularly ~-
strong adhesion between the photoconductive layer and the
underlying substrate. Unfortunately, however, some of the
most sensitive and efficient photoconductive materials are
relatively brittle as films and do not generally adhere well
to flexing metal substrates having a good charge blocking
contact. It is very important that any interface between the
electrically conductive supporting substrate and the photo~
- conductive layer be stable and strongly adherent to both since ; ;
changes at this point will have a substantial effect on the
electrical properites of the photoreceptor.
The above problems have been considered and resolved
to a substantial extent in a process described in a copending
Canadian application filed on June 10, 1974, by Lewis B.
Leder, John C. Schottmiller and Harold H. Schroeder entitled
"Improved Photoreceptor Fabrication"-Serial No. 226,579, filed
May 8, 1975 wherein the subs~rate (cathode) is initially
bombarded by non-metallic ions under a DC glow discharge in
the presence of air or an inert rare gas containing at least
1% by volume available oxygen. This step is then followed
or overlapped by further exposure of the substrate (cathode)
with a mixture of non-metallic high energy cations o~ an inert
gas-such as nitrogen or argon, uncharged vaporized photocon-
ductive material and-high energy ions of the photoconductive
material. While the above-described process represents a
substantial technical br~akthrough in utilizing the more
efficient brittle photoconductors in flexible belt-type
photoreceptors, there still remains room for substantial
improvement. In particular, the production of high energy
photoconductive catlons in a glow discharge for bombardment
purposes is relatively in~fficient (up to 5~ ion production at
best) and requires expensive electrical equipment of limited
capacity to maintain a suitable electrical field.
SI~M~RY OF THE NVENTION
In accordance with one aspect of this invention there
is provided a method for obtaining flexible photoreceptors having
improved durability and adhesion between a metal- or metal- :
coated substrate thereof, and a photoconductor layer thereof
containing inorganic photoconductive material in charge block-
ing contact with the substrate, comprising exposing clean oxide-
coated substrate to a vapor cloud containing photoconductive
material from a grounded or floating donor source, said vapor :
cloud comprising both uncharged photoconductive material and high
energy ions of photoconductive material from a glow discharge~ .
the high energy ions being substantially obtained by heating the ~:
donor source to effect vaporization o~ photoconductive material ~
and bombarding the resulting vapor cloud with electrons and/or ` `~ :
gas ions in ~he g].ow discharge. ;~
In accordance with another aspect of this invention
- there is provided a method for obtaining flexible photoreceptors
having improved durability and adhesion between components thereof --~
and containing a metal- or metal-coated substrate and a photoconduc- ~-
tor layer of an inorganic photoconductive element or alloy thereof
in charge blocking contact with the substrate, comprising initially
bombarding a grounded or floating substrate with electrons and gas
ions under glow discharge in the presence of air or a mixture of ~.
oxygen with at least one inert non-metallic ion-forming gas; and
exposing the resulting oxidized substrate to a vapor cloud contain-
3~ ing photoconductor material from a grounded or floating donor source,
said cloud comprising unchaxged photoconductive material and high
energy ions from a glow discharge, the high energy ions being
obtained by heating the photoconductor donor source to effect
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vaporization, and bombarding the resulting vapor cloud with elec-
trons and/or gas ions in the glow discharge.
This invention also relates to flexible photoreceptors
produced by the foregoing methods.
While numerous modifications are possible, the initial
step of obtaining a clean-oxidized substrate is most conveniently
obtained by first bombarding the grounded or floating substrate
with electrons and gas ions created under glow discharge in the
presence of air or a mixture of oxygen with at least one inert
non-me~allic ion-forming gas such as nitrogen, argon, xenon, etc.,
and then exposing the resulting oxidized substrate to a high
energ~ ion-containing photoconductor vapor cloud as descri~ed above.
In any case, most suitable photoreceptors include
at least one thin oxide charge blocking layer in general
accordance with U.S. Patent 2,901,348 or as otherwise obtained. ~-
When flexible metal belts such as nickel belts are used as
substrates, however, special chemical treatment is sometimes
required in order to obtain a suitable intermediate charge
blocking layer. ~ -
Depending upon the nature o~ the substrate, plus
tha charge, shape, and positioning of the electrode, the
important step o exposure of oxide-coated substrate to the vapor
cloud can be effected subsequently or e~en in conjunction with
- , -
at least part of the initial substrate cleaning and oxidation
bombardment step provided electrical rather than chemical
pre-treatment is utilized.
Suitable subskrates for purposes of the present
in~ention can usefully include relatively thin layers or metal
oils of copper, steel, brass, aluminum, zinc, nickel or
corresponding metal-coated flexible polymeric bases such as
a coated polyethylene terephthalate. Of particular interest are
aluminum-coated polyethylene terephthalate belts and nickel belts.
Photoconductive material suitable for use in the
instant process generally includes inorganic ionizable elements
':
such as selenium, selenium alloys inclusive of alloys of selenium
with tellurium, germanium, antimony, bismuth and arsenic and/or one
or more halogens such as chlorine, bromine, or iodine. Such photo-
conductive ma~erials are obtainable, for instance, by subjecting
selenium plus small amount of arsenic, etc., and halogen to heat.
Satisfactory adhesion of brittle inorganic photoconductor
material such as above defined, to flexible metal substrates as
above defined can now be satisfactorily accomplished more easily
and with better results in accordance with specific embodiments of
the present invention.
The initial bombardment of the grounded or floating sub-
strate with electrons and ions of a non-metallic gas to clean and
oxidize is best carried out, for instance, by evacuating a suit-
able modi~ied vacuum coater down to a pressure of about 5 x 10 5
Torr or better and then backfilling to about 5 - 30 microns
pressure. A pressure of about 10 - 20 microns is generally prefer- ^-
. .
red, however, for this purpose. While air under reduced pressureis acceptable, it is also found convenient to utilize various
alternative mix~ures of positive ion-producing and oxidizing gases
at comparable pressures. Such include, for instance, argon-oxygen,
argon-air, argon-CO2, or a mixture of pure nitrogen and oxygen, -
etc., provided the amount of available oxygen for initial oxida-
tion of the substrate is not less-than about 1% by volume of the -~
available gases, and provided a glow discharge can be maintained. ~ `
This invention will become more apparent from the
following detailed description taken in conjunction with the draw-
ings in which Figures lA - lF schematically illustrate methods and
equipment for carrying out the instant invention.
In accordance with the present invention, it is also
found that the initial ion bombardment of a grounded substrate is
best carried out directly under a "glow bar" (Figures IA and IC)
such as an aluminum cathode and a potential up to about 5000 v and
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at about 3500 - 5000 volts, depending upon the type and pressure
of gas used to form the bombarding ions. While a "glow bar"
is preferred, other known means of producing a glow discharge
can be used as alternatives or supplemental sources. Such
sources can include, for instance, a high voltage hot filament
or electron gun.
Prior to or immediately after completion of a period
of time sufficient to lay down an oxide barrier layer of about
10 - 200 angstrom thickness and heat the substrate to a temperature
of about S5 - 80C. (about 5 - 20 minutes and preferably 8 - 10
minutes under conditions indicated above), the grounded oxide-
bearing substrate is exposed to bombardment by a cloud comprising
uncharged and ionic photoconduct.ive particles evolved from
the heated photoconductor source, the vapor cloud obtained
therefrom having been exposed to electron- or indirectly to
gaseous-ion bombardment to obtain a minor amount of ions of
the evaporant photoconductor material. In such situation, the
multaneous overlapping substrate bombardment by non-metallic
ions such as argon or nitrogen will tend to displace more loosely
adherent condensed photoconductive particles already laid down
on the substrate in favor of ionic photoconductor particles
having much greater velocity and energy content than the vaporized
uncharged photoconductor~material. This occurs despite the
relatively low concentrations of photoconductor ions obtained
relative to the total amount of thermally created-photoconductive
particles.
For p~rposes of the present invention, deposition onto
the clean oxidized substrate is best effected by separately heating
the photoconductor donor source to a temperature between room
temperature and the maximum evaporation temperature of the
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photoconductive material. For such purpose, the preferred
temperature range (1) favors maximum vapor concentration and
field conditions commensurate with maintenance of a glow
discharge pressure proximate to the heated photoconductor source
and the substrate, and (23 favors the highest possible conversion
of uncharged to charged (ions) p~otoconductor material to effect
the impaction of the largest possible concentration of high
energy photoconductor particles onto the substrate.
While various arrangements of electrodes and donor
sources are acceptable for this purpose, the most promising to
date are shown in diagrammatic cross-section (ref. Figures
IB, ID, IF).
One particularly preferred arrangement utilizes at
least one negative high voltage electrode such as a rod or wire
conveniently mounted on insulators between the donor source
such as a heated crucible and the substrate. Such an arrangement
can include, for instance, one or more electrodes above and
in parallel long axial arrangement with respect to at least
one heated photoconductor-material-containing crucible boat.
In the case of a plurality of crucible boats this can also
include an electrode above each lip or shared between and
above the lips of adjacent crucibles in a coater (ref. Fig. IC - IF).
; . Another suitable arrangement for obtaining high energy
ions of photoconductive matexial requires aiming at least one
glow bar into the vapor cloud produced by the donor source
~ref. Fig. IB).
In addition to the above-described physical arrangement
of the coating components it is also important in some embodiments
that an adequate concentration of ions be maintained along with
charged photoconductive particles.
,, ~ .,.
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As a practical matter, the initial treatment of a
metal substrate (ref. Fig. IA, IC, IE) is best effected in an
atmospheric pressure of about 5 - 30 microns, the amount of oxygen
pxesent being not less than about 1% by volume of available gases.
In the subsequent photoconductor deposition step (ref. Fig. IB, ID,
IF), however, it is sometimes desirable to increase the amount
of vacuum to about 5 x 10 5 Torr or better and then backfill
the coating chamber with up to about 1 - 30 microns of argon,
nitrogen, xenon or similar relatively inert gases.
In order to effectively raise the vapor pressure of
the photoconductive material for deposit onto the oxidized
substrate, the photoconductor source is conveniently heated by
a number of different ways. Such include, for instance,
resistance heating of one or more crucibles or boats containing
the photoconductor material, the use of an electron beam or
gun directed at the unvaporized photoconductor material of the
donor source, or even by ion beam heating of the photoconductor
material. In any case, the optimum temperatures will vary with
1 the photoconductive material, the distance between source and
i ~ubstrate and the atmospheric composition and pressure utilized.
1. .
! By way of example, a crucible temperature up to about
350 C. and pre~exably about 180 C. - 300C. is found adequate
or vaporizing selenium and most of the known selenium alloys
under a pressure up to about 30 microns.
During the period of photoconductor deposition onto
the clean oxide-coated substrate, it is essential that a glow
discharge be maintained for the purpose of creating high energy
photoconductor ions without seriously limiting the rate and area
of deposition of the photoconductive material onto the substrate.
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As previously indicated, th~ relationship of the
electrodes and other essential components for carrying out the
inventive process are very generally represented in diagrammatic
cross-section in Figures IA - IE. In Figure IA, in particular,
the elements (aj and (d) respectively represent a metal substrate
and a photoconductor donor source (i.e. a crucible containing
photoconductor material "M") within a vacuum coater (not shown);
element (b) represents one or more aluminum glow bars (cathode)
aimed at the substrate and preferably activated under an atmos-
pheric pressure af about 10 - 20~u to effect the heating and
oxidation of the substrate as desired. The step, as described,
is conveniently effected by initial exposure of the substrate
(a) to a high voltage glow bar discharge of about 3000 - 5000 v.
The next step is conveniently represented in diagrammatic
cross-section by Figure IB in wh:ich ~al) represents the oxidized
metal substrate, ~d) represents the photoconductor source but
lacking some photoconductor matexial (M) due to evaporation,
and elements (c) and tf) respectively represent a negative glow
bar and a positive target electrode. These two figures represent
a dynamic situation in which the first glow bar ~Figure IA)
i5 turned off after establishing a clean oxidized substrate and
one or more high voltage glow bars (c) activated to establish a
negative glow region bet.ween (c) and (f) for the purpose of
producing high energy photoconductor ions from the heated
crucible (d). Alternatively, the second step can be achieved
by altering th~ position or aim of glow bar (b) in Figure IA
provided a grounded target electrode such as (f~ is provided.
A ground metal wall of the vacuum coater can act in the capacity.
In carrying out the described second step, the pressure inside the
vacuum coater is preferably kept at about 10 - 20 microns and the
donor crucible (d) preferably heated to about 180-300C. as before
to obtain an adequate vapor cloud of photoconductor material.
In any case, the second step is carried out so that the glow
(ionization of the non-metallic gas atmosphere) occurs in a
convenient location to intercept vaporized photoconductor material
somewhere between the donor crucible and the substrate.
After a period sufficient to deposit about .5 - l~/o
of the desired photoconductor matarial (i.e. about 2 - 5 minutes),
the glow bar(s) are turned off, the pressure is lowered to
5 x 10-5 Torr or better, and vapor deposition of the photo~
conductor material is optionally allowed to proceed by evaporation-
condensation in the usual manner to obtain a total photoconductor
coating of about 40 - 60JU on the substrate. In most cases,
a relatively minor amount (about 1 - 5% by weight) of the
evaporant is ionized for deposit:ion on the substrate.
Whi?e air under reduced pressure is preferred for
purposes of the above-described process, it is also possible
to utilize argon or similar inert gases provided at least 1%
by volume of oxyyen is present in the initial oxidation step.
By effecting the second deposition stage (ref. Figure
I~) in the presence o~ positive non-metallic ions such as nitrogen
or argon, it is possible to displace a substantial amount of
accompanying low-energy-deposited photoconductor material
from the substrate in favor of the available charged high energy
photoconductor ions. The efficiency of this process can be improved
either by allowing the substrate to "float" (not connected to
ground) or by applying a low voltage (100 - 500 volt~ negative
potential to the substrate.
Successful impact deposition, therefore, often requires
a balance between removal and deposition rate so as to obtain
a net coating action. The time required to obtain an adequate
photoconductive layer will laryely depend on these factors~
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As earlier noted, the chief advantage of depositing
ionized vitreous photoconductor on a metallic substrate is
realized in improved adhesion and improved interface electrical
properties, it is necessary only to deposit a fraction of the
entire photoconductor thickness in the high energy ionic state.
Generally speaking, about .5 - 10% is sufficient, with the
balance of the deposition comple~ed by more conventional vacuum
deposition techniques at about 5 x 10 5 Torr. If desired,
however, the entire photoconductive layer may be deposited in
the mode as above described.
A further modification of the procedure outlined above,
-and one which is particularly noteworthy with respect to
reduced power demands, is again diagrammatically represented
in diagrammatic cross-section in Fi~ures IC, ID, IE and IF
in which elements (a2) and (a4) respectively represent a pre-
cleane~ metal substrate or base such as nickel or aluminum which
is then initiaily heated and oxidized by glow bars (b2) and (b3)
undèr partial vacuum (Figures IC and IE) or by other standard
means. Crucible boats (d2) and (d3), contain suitable amounts
o~ photoconductive material "M" and are equipped with heating
means (not shown) and conveniently positioned beneath substrates
(a2) and (a3) in convenient parallel axial arrangement to an
ion plating rod or wire electrodes (g2) and (g3) of solid or
tubular construction of convenient diameter which are activated
by negative high voltage under reduced pressure ~Figures ID and IF~
to effect a glow discharge area between crucibles (d2) and (d3)
and the corresponding oxidized substrates (a3) or (aS). Just prior
to or in conjunction with the glow discharge, the heating means
of crucibles (d2) and (d3) are activated to vaporize the photo-
i conductive material and to obtain desired high energy photo-
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4LS
conductive ions (M ) as well as uncharged p~otoconductive material
~m) for impact with the oxidized substrate. Both the substrates
and the crucibles can be conveniently grounded as shown or the
substrate can be permitted to float. In addition, the ion plating
rods need not be equidistant from each crucible, particularly
where a plurality of substrates are being treated in a single
coater ~ref. Fig. IE and IF).
While various sized rods or wires and various materials
and distances can be utilized to obtain an adequate ion-forming
glow discharge, it is found particularly useful to use a 1/16"
- 1/2" diameter solid stainless steel, aluminum or tungsten rod
of indeterminate length, suspended about o25ll - 4" above one
or more 5" to 100" crucibles in parallel arrangement and about
2" - 30" below the substrate~s) to be coated. Other combinations
of spacing are possible depending upon the pressure, rod diameter
and crucible temperature, etc.
Referring more specifically to the procedures represented
in Figures IC - IFt when the substrate is at a suitable temperature
or depositing photoconductor material thereon, the glow bar
i~ turned off as previously described with respect ~o Figures IA
- IB and a glow discharge instituted by activating the ion plating
rod (g2) or (g33 under an atmosp~lere of about 5 - 20 u.
Simultaneously, crucible (d2) or (d3) àre stepwise heated up to
about 180C~ to 350C. and held at this range (i.e. depending
on the photoconductive material used) for about 1 - 10 minutes;
t~e glow discharge is then terminated by cutting off the current.
Subsequent coating of photoconductor material by simple evaporation-
condensation is optionally carried out at a somewhat lower
pressure ~5 x 10-4 Torr or better) at suitable crucible temperature
in the manner previously indicated.
Although the thickness of the p~otoconductive layer
obtained is positively correlated to the negative voltage
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applied to the rod-shaped ion-plating rod or wire, as above
described, optimal results are obtained with an AC or DC voltage
of from about 1 - 4 KV, and preferably at about 2.5 KV, having a
maximum current of about 20 to 25 ma and a minimum of about .2
to .5 ma with a 1/8" x 15" solid aluminum plating rod. Under
such conditions the plating rod will become hot enough to avoid
deposition of any appreciable amount of selenium at the end of
~he run.
In a planetary system of rotating substrates above
several 100" long chains of crucibles having one plating rod/chain,
it is found practical to utilize a maximum current of only about
167 ma/chain and a minimum current of about 6 ma/chain to obtain
durable flexible photoconductor coating(s~ on the corresponding
substrates or bases. The results obtained indicate that a fully
adeguate supply of high energy photoconductor -ions are produced.
The following examples specifically demonstrate preferred
embodiments of the present invention without limiting it thereby.
EXAMPLE I
A nickel alloy test belt identified as A-l and having
a thickness of 4.5 mil (.0045"), a length of 10" and a diameter
of 4.75" is cleaned with a hot aqueous solution containing 10%
by weight of "Mitchell Bradford ~14 Cleaner" and then rinsed
in deionized water for about 2 minutes. i~
Sample belt A-l is mounted on a grounded or floating
rotatable mandrel in a vacuum coater about 6" away from grounded
or floating stainless steel crucibles equipped with resistive
heating means and containing a photoconductor selenium alloy
consisting essentially of about 99~5/O selenium and .5% arsenic.
Two high voltage glow bars (up to 5000 v) are mounted about
3" from the test belt, the first (GBl) being directed essentially
at the belt in the 10 o'clock position and the second (GB2)
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is mounted at similar distance but at about 5 o'clock relative
to the belt as center and directed substantially at the interspace
between the substrate belt and the stainless steel crucibles.
After evacuating to 5 x 10 5 Torr and backfilling the coater
with 20 micron air pressure, negative 3000 volts is applied
to the first glow bar !GBl) for about 10 minutes to heat and
oxidize the bel~. The first glow bar voltage is then turned
off, coater pressure thereafter lowered to about 15 microns,
the crucible heated up to 280 C., and the second glow bar (GB2)
~3500 volts) turned on for about 10 minutes. The second glow
bar is then turned off and straight vapor dep~sition permitted
to proceed at reduced pressure ~S x 10-5 Torr) for about 25
minutes to obtain a total uniform photoconductor coating about
50 microns thick. During both steps, the mandrel is constantly
rotated at about 10 revolutions per minute to obtain uniform
exposure. The belt is then cooled, removed from the coater,
tested for electrical properties and flex, and the results
reported in Table I infra.
; EXAMPLE_II
Two nickel test belts of essentially iaentical size
and shape as test belt A-l, and identified as A-2 through A-4
;are cleaned as in Example I and coated as follows:
Belt A 2 i~ coated as in Example I except that a
30 ~ backfiLl of oxygen t5% by volume3 and argon (95% by volume3
i~ utilized in place of air during the initial heating and
oxidation o~ the belt under the first glow bar (GBl) and partial
coating under the second glow bar.
Belt A 3 (control) i5 treated identically as A-l in
I Example I except that the second step (i.e., the initial
I deposition of photoconductor material onto the oxidized substrate)
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is effected for 35 minutes at 5 x 10 5 Torr without utilization
of a glow bar~ After depositing about S0 microns of the photo-
conductive material, the belt is cooled~ removed from the coater,
tested as in ~xample I and reported in Table I.
EXAMPLE III
Example I is repeated using respectively stainless
steel, aluminum and brass test belts of the same dimensions
as A-l and comparable test results are obtained.
TABLE I
: Test Belt Capacitive 1 20 Second Mandrel Test*
. Charge Dark (1 1/2" diameter)
_ ~v/u) Decay ._ . _
A-l 23 20 P `
......... ~ __ _ _
~-2 21 16 P
.. , . ~_~_ ._. _ .... ... _
A-3 24 17 F
_ _ _ __~ _ _
*P = pass ~no cracks or spalls observed)
: F = fail (one or more cracks or spalls observed)
Belt bent once around a 1 1/2" pipe at room temperature.
EXAMPLE IV (Control~
Two nickel test belts identical to those used in
Examples I-II and identified respectively as A-4 and A-5 are
cleaned and rinsed as in Example I. Belt A-4 is then mounted
on a rotating mandrel (10 rev/min) and placed in a vacuum coater
at 5 x 10 5 Torr in convenient proximity over a 15" resistance-
heated ~loating crucible boat ccntaining a selenium alloy (99.5%
-17-
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,,,,~, ,,, .. " ~. ., - ~
, . . . . . .
As - .5% As), which is raised stepwise to a temperature of
3Q0C. and held at this temperature for about 20 minutes. The
belt and coater are then cooled to ambient conditions and the
treated belt removed and tested for electrical properties and
flex. The results are reported in Table II below.
EXPMPLE V
Belt A-5 is similarly mounted on a mandrel in a vacuum
coater over a 15" grounded resistance heated crucible boat of
identical dimensions and containing the same composition selenium
.. _ . . ......... . . . . ..
- alloy as in Example IV. A bare 1/8" x 15" solid aluminum rod
is mounted on insulators 2" above the crucible in parallel axial
alignment to its long axis and 6" from the mounted test belt
(ref. Figures ~IC - ID). An aluminum glow bar is also positioned
to~one side for preliminary electron bombardment of the substrate
in the manner of Figure IC to first heat and uniformly oxidize
the test belt. The coater is pwnped down to lOJ~ pressure and
'the belt initlally exposed to the aluminum glow bar for 10 minutes
f~llowed by heating of the crucible to 230C. and simultaneous
activation of the bare solid aluminum rod at 2.5 KV DC to obtain
an approximate rod shaped glow discharge. After 3 minutes, the
current is turned off and the coating continued for 20 minutes
as a simple evapo~ation-condensation step to give the desired
thickness. ~he coater is then permitted to cool to ambient
condition. The belt is removed, tested as before and the results
reported in Table II.
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TABLE II
`
¦ Test Belt Capacitive 20 Second i Mandrel Test*
. iCharge Dark I (1 1/2'l diameter)
` !(V/u~ DeCay I
l (v/sec) ,
, , _ _ .~ . _ _ .
. A-4 21 17 F
. tControl~ I
. . _ _
. A-5 ~
.
~ P = pass (no cracks or spalls observed)
: ~ = fail (one or more cracks or spalls observed)
When belt bent once around a 1 I!2" pipe at room temperature.
- - ---~`~ EXAMPLE VI ~- ~ ~~~ ~ `` ~
Two aluminum test belts identified as A-6 and A-7 and
. having the same dimensions as test belts used in the previous
'examples are cleaned and washed as before and then moun~ed side
by side on a rotatable mandrel above two 15" crucibles containing
-: the same photoconductive material as in Example V. Thxee I/2~
hollow (1/8 " id) stainless steel tubes are mounted on insulators
2", 3" and 2" respectively above the lips o~ the two crucibles
as ion plating rods in the manner shown schematically in Figures
IE and IF. The rods, in turn, are arranged a maximum of about
S ~ ,"~ 0~ below the exposed bottom plane of the aluminum belts beiny ~:
treated. The test belts are exposed to glow bars to heat and ;
oxidize the surface and then bombarded with both uncharged vaporized
~:
photoconductor material and ionized vaporized photoconductor
material in the manner of Example V at 1.8 KV DC for each rodA
After 3 minutes, the current is turned off and coating permitted
to continue for 20 minutes as a simple evaporation-condensation :
~19-
'r~ ~ .. . . . .
1~4~
. .
~tep and then the coater and test belts allowed to cool to ambient
conditions for xemoval and testing as in Example V. ~he resulting
coated belts are tested for flex as before and the results
reported in Table III.
EXAMPLE VII
Example VI i~ repeated with identical test belts A-8
and A-9 using three 1/16" bare stainless steel tubes of the
preceeding Example and in general accordance with Figures IE
and IF. The wires~ however, are uniformly arranged in parallel,
1" above each crucible lip rather than staggered as in the
preceeding Example. After oxidation and deposition steps are
completed,-the belts are cooled, removed and tested as in
Example VI. The flexibility and integrity of the coated belt
is found to be comparable to that obtained with belts A-6 and A-7.
,
TABLE III
Test Belt Mandrel Test* ~¦
_ .... _
` ~-6 P
.. . , _ _ . ...
A-7 P .
__ -- . .
A-8 P
_ _ _ _
_' -
~ .
*P = pass (no cracks or spalls observed when belt is
bent once around a 1 1/2" pipe at room
temperature)
While the above Examples are directed to preferred
embodiments of the invent.ion, it will be understood that the
invention is not limited thereky.
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