Coater hardware and method for obtaining uniform photoconductive layers on a xerographic photoreceptor

A method and device for obtaining uniform vapor deposition of one or more inorganic metallic photoconductive materials onto a substrate by importing under vacuum a slow translational movement of one or more heated crucibles and/or of the substrate being coated.

This invention relates to a device and method for obtaining a more uniform 
vapor deposition of inorganic metallic coating material such as 
photoconductive material onto a suitably prepared receiving surface such 
as a substrate by varying the position of the vapor source with respect to 
the receiving surface. 
BACKGROUND 
It is customary in the xerographic art to form an electrostatic latent 
image on a photoreceptor drum or plate comprising a charge conductive 
backing such as, for example, a metallic or metal coated surface having a 
photoconductive insulating layer applied thereto in good charge blocking 
contact. A suitable device for this purpose comprises, for example, an 
aluminum plate having a thin layer of vitreous selenium and an aluminum 
oxide and/or polymeric interlayer. Such a plate is characterized by being 
capable of accepting a suitable electrostatic charge and of quickly and 
selectively dissipating a substantial part of the charge where light is 
exposed. In general, such photoreceptors are sensitive to light in the 
blue-green spectral range. 
While selenium containing photoconductive elements are usefully employed in 
commercial xerography, there is room for substantial improvement in 
photoconductive properties such as the range of spectral response, heat 
and charge stability, etc. These can be improved by the addition of 
various photoconductive alloys, alloying elements or other types of 
additives (ref. U.S. Pat. Nos. 2,803,542 and 2,822,300). For example, the 
addition of various amounts of arsenic can result in a broader range of 
spectral sensitivity and improve overall photographic speed and stability. 
Suitable alloys or homogeneous mixtures of elemental selenium with other 
metals suitable for this purpose can also be incorporated into the usual 
photoconductive material by conventional vacuum evaporation techniques. 
For example, additional inorganic coating materials can be placed in open 
or shuttered crucibles in a vacuum during an initial coating step. The 
xerographic substrate upon which the photoconductive material is to be 
deposited is conveniently placed above or in some other convenient 
location with respect to the potential coating vapor source. After the 
container has been evacuated to a suitable pressure (about 5 .times. 
10.sup..sup.-5 Torr), the vessel containing photoconductive material 
and/or additive is then heated by suitable means known to the art such as 
by electric resistance heating elements to promote vaporization of the 
material. At least some of the vaporized material then condenses on the 
relatively cool substrates; such a deposition process normally requires a 
period of about 15-60 minutes, depending upon the amount of substrate 
surface to be coated and the desired thickness of coating material. 
From time to time it is also found desirable to apply profile 
concentrations of one or more photoconductive components or separate 
layers of different photoconductive materials to obtain a particular 
desired spectrum of characteristics. In such case, the respective 
photoconductive materials or alloys are most conveniently applied to 
substrates or bases by coevaporation techniques, in which predetermined 
amounts of the respective photoconductive materials or alloys are placed 
in separate crucibles or in subdivided crucibles and exposed or heated in 
a predetermined sequence under vacuum. One very useful modification for 
this purpose involves coating in the presence one or a plurality of 
elongated crucibles heated by electrical heating elements or by other 
conventional means, the crucibles being subdivided into a plurality of 
compartments or bins, each capable of carrying different amounts and kinds 
of coating materials depending upon the desired final concentration. 
Another useful modification involves the formation of one or more trains 
of small crucibles temporarily connected to each other and containing 
various photoconductive materials. Both arrangements are found to be very 
useful in coating a plurality of substrates simultaneously with a 
plurality of components. 
Unfortunately, however, the use of such crucibles separated by baffles or 
end walls also presents serious technical problems insofar as it is 
difficult to control surface irregularities and achieve consistency during 
batch coating. This is found to be due largely to variation in the 
geometric relation of substrates to crucible bins and particularly 
attributable to the presence of crucible end walls or baffles. Such 
coating irregularities, in turn, usually cause unacceptable variations in 
electronic properties both between and within the individual 
photoreceptors being batch produced. 
It is an object of the present invention to develop a method and equipment 
for efficiently and evenly batch coating one or more receiving surfaces or 
prepared substrates with one or more coating materials or components 
thereof. 
It is also an object of the present invention to minimize or avoid 
irregularities when batch coating one or more inorganic photoconductive 
materials onto prepared xerographic substrates in a vacuum coater. 
A still further object relates to obtaining an improved method for 
improvement quality of batch coated xerographic photoreceptors containing 
one or more photoconductive components. 
THE INVENTION 
The above and other objects are achieved in accordance with the present 
invention wherein receiving surfaces, inclusive of xerographic substrates 
or bases, are batch coated with at least one vaporizable coating material 
or component thereof and applied under vacuum from one or more evaporation 
crucibles containing a plurality of subdivisions delimited by baffles or 
end plates and crucible walls, and arranged in convenient proximity to the 
receiving surfaces. 
The process as envisioned requires the steps of heating one or more 
material-containing crucibles simultaneously or in sequence while moving 
at least one of said (a) crucibles or said (b) receiving surfaces in a 
translational manner along parallel planes with respect to each other. 
A particularly suitable batch coating device within the scope of this 
invention for achieving the above objects and described process (i.e. 
vacuum coating vaporizable coating materials or components thereof onto 
receiving surfaces) comprises, in combination, 
a. one or more evaporation crucibles arranged within a vacuum coater in 
convenient proximity to receiving surfaces to be coated, said crucibles 
being elongated and having a plurality of subdivisions delimited by 
baffles or end plates and crucible side walls; 
b. mounting means for movably holding receiving surfaces in the same or 
parallel planes within the vacuum coater in convenient proximity to the 
crucibles and coating material; 
c. supporting means for movably supporting one or more crucibles in the 
same or parallel planes within the vacuum coater at points below the 
mounted receiving surfaces; 
d. heating means arranged for separately or concurrently vaporizing coating 
material from all or subdivisions of each crucible as desired; and 
e. means for moving one or both of said crucibles and said receiving 
surfaces within the vacuum coater in a translational manner during 
coating. 
The device, as described, is best utilized for coating coating material or 
components thereof onto mounted receiving surfaces by heating one or more 
of the crucibles under vacuum and moving at least one of said (1) 
crucibles and said (2) receiving surfaces in translational movement along 
parallel planes with respect to each other.

In particular, FIG. 1 is illustrative of a suitable embodiment of the 
present invention wherein base member 15 and rails 13 as well as a 
rotatable or rotating reciprocating spindle 8 are affixed or conveniently 
mounted within a vacuum coater capable of achieving an atmospheric 
pressure to about 5 .times. 10.sup..sup.-5 Torr in general accordance with 
known coating procedures. Such general procedure and vacuum coating 
techniques are described, for instance, in U.S. Pat. Nos. 2,753,278, 
2,970,906, 3,311,548 and 3,490,903. Removable elongated evaporation 
crucibles exemplified by 9 are subdivided by baffles or end plates 12 for 
holding individual coating compositions or components thereof 10 and 
equipped with resistance heating elements 11 plus sliding means 14 adapted 
for a back and forth translational movement along a plane within the 
coater. Actuation means (not shown) permit movement of crucible 9 back and 
forth along rails 13 during coating and, if desired, a reciprocating as 
well as a rotational movement of spindle 8. 
One or more receiving surfaces demonstrated as drums of suitable structural 
integrity, here shown in the form of mountable drums, 7 are mounted on a 
metal spindle 8 in convenient proximity to crucible 9. As noted above, the 
mounted receiving surface or drum can optionally also move in a 
translational manner as well as rotate about the axis corresponding to 
spindle 8. 
FIGS. 2-5 relate to various modifications of self-heating crucibles showing 
parts corresponding to FIG. 1 including crucibles 9B-9E), sliding means 
14A-14D, coating materials 10A-10D and electrical heating elements 
11B-11E. The later elements can be usefully eliminated, if desired, 
provided the crucible itself comprises a material having sufficient 
resistivity to act as the heating element. 
FIG. 6 exemplifies a further modification within the scope of the present 
invention in which a crucible 9A containing resistance heating means 11A 
is mounted on a base 20 containing means 21-24 for imparting a rotational 
translating movement of said crucible in convenient proximity to receiving 
surfaces shown as a plurality of drums 7A removably mounted on a rotatable 
spindle 8A having the dual ability to axially rotate and, if desired, to 
move back and forth in an axial translational direction, the long axis of 
the crucible being generally parallel with the drum axis or spindle 8A. 
Generally speaking, a receiving surface for purposes of the present 
invention is inclusive of surfaces of plates, flexible belts, drums, 
sheets, webs or miscellaneous-shaped objects, the only limitation being 
that the object being coated be sufficiently stable when exposed to heats 
of vaporization and condensation of the coating material utilized, and 
that the coating material adequately adhere in stable condition to the 
surface being coated. In this connection, it is noted that xerographic 
substrates or base plates such as stainless steel, aluminum, copper, 
brass, nickel, chromium, metal coated glass or the like having suitable 
oxide or other intermediate blocking layers and also charge or hole 
transport layers, if desired, are well suited for covering in the above 
manner. 
The coating materials 10 -10E of FIGS. 1-6 represent one or more separate 
coating materials or components of coating materials of metallic or 
non-metallic types, the principle criterion being that the materials being 
applied have a sufficiently high vapor pressure under heat and a vacuum 
(up to about 5 .times. 10.sup..sup.-5 Torr in the case of a 
photoconductive material) to evaporate and condense onto the desired 
receiving surface within a reasonable time and without undesired chemical 
changes to the coating material or the receiving surfaces. 
Photoconductive materials being applied in the present manner are 
preferably although not exclusively inorganic photoconductive materials or 
additives thereof. Suitable materials for coating within the present 
invention can also include vaporizable monomeric materials for, in situ, 
polymerization onto a substrate as well as amorphous selenium, various 
selenium alloys with arsenic and/or tellurium, etc., and optional halogens 
or sensitizing dyes such as disclosed in U.S. Pat. No. 3,532,496. Such 
materials can be conveniently placed in adjacent subdivisions of each 
crucible in sequence below each drum, belt, or plate, etc., to be coated 
or some even applied in separate adjacent crucibles of a stationary or 
nonstationary type. 
The spindle 8, 8A, end plates 12, 12A, rails 13, and comparable or 
equivalent means (FIG. 6, No. 21-24) are preferably although not 
exclusively of stainless steel. 
For purposes of the present invention it is also useful to include 
evaporation crucibles of steel, ceramic or comparable materials or either 
conventional open boat or of a tube type. Such include, for instance, 
modified crucibles which avoid the risk of spattering of coating material 
such as described in U.S. Pat. Nos. 3,748,090 and 3,746,502. 
It has also been found that the method and device above exemplified and 
described is best carried out when one or more crucibles are moved in long 
axial direction with respect to a plurality of stationary receiving 
surfaces, particularly xerographic substrates or bases although the 
receiving surfaces, or both crucibles and receiving surfaces, can be moved 
out of sync to assure adequate coverage. In any case, the movement with 
respect to the crucibles and receiving surfaces is that of a relative 
translational motion during deposition. For this purpose, one or more 
crucibles (or receiving surfaces) can be slowly moved with respect to a 
plurality of receiving surfaces (or crucibles) as above described, the 
movement of each crucible (or receiving surface) being about 1/4 to about 
2 times the long axial distance of a crucible subdivision, preferably 
being unidirectionally displaced about 1 inch to 6 inches and completing 
each cycle of movement in about 5 - 60 seconds and particularly 5 - 10 
seconds. 
A further advantageous arrangement involves arranging the receiving 
surfaces in the form of drums axially rotatably mounted convenient to at 
least one crucible, the long axis of each drum being arranged parallel and 
above the long axis of each crucible.