The general field of the invention comprises sputtering apparatus and more particularly the invention is concerned with apparatus for sputtering a photoconductive or similar coating onto a seamless belt or cylinder whereby to achieve a continuous substrate member of plastic or metal having such a photoconductive coating on its surface.
In recent times a technique has developed for the sputtering of electrophotographic film which is a meter or more in width and several hundred meters long through the use of sputtering methods and apparatus disclosed in U.S. Pat. Nos. 3,829,373; 3,884,787; 3,905,887; 4,013,539 and 4,026,787
The sputtering which is effected by this apparatus comprises the deposit of material by establishing an electrical plasma condition in a pressure vessel between a target or cathode of the material which is to be deposited and an anode upon which the material is to be deposited. A high energy r.f. source of power is coupled to the target and anode and an inert gas such as argon is introduced into a low pressure chamber provided in the pressure vessel which houses the target and anode. The argon is ionized and heavy ions bombard the target thereby causing molecules of the target material to be driven out of the target. At least an electric field between the target and the anode causes the particles or molecules to be driven to the anode and deposited there. A substrate member of some material, usually an insulating polyester or other polymer sheeting, as disclosed in the above described patents, overlies the anode whereby the material that is driven from the cathode, i.e., sputtered from the target, will deposit on the substrate member. This deposit can be built up to thicknesses which depend upon the conditions in the chamber, the materials involved, the time of the sputtering and other parameter such as power, temperature, gas pressure, etc.
The particular kind of apparatus which is discussed in the above mentioned patents and the apparatus which is described herein are intended to be used for the deposit of a microcrystalline coating of a photoconductive material such as cadmium sulfide or the like having unusual properties. The material itself and the special conditions of its manufacture are disclosed in U.S. Pat. No. 4,025,339.
This invention is especially concerned with the deposit of this type of microcrystalline photoconductive material upon cylindrical or belt-shaped substrate members for use in different kinds of imaging apparatus, for example, convenience or office copiers, printing plate makers, printing presses and the like. Although adaptable to the deposit of the material upon substrate members of plastic, the invention has especial application to the deposit of the photoconductive material upon substrate members comprising sleeves of flexible metal.
The substrate members which are of importance insofar as the practical application of the invention herein is concerned comprise seamless thin-walled metal cylinders of nickel, copper or other metal which are formed by electrodeposition. U.S. Pat. Nos. 2,287,122 and 3,354,519 disclose this type of cylinder and the methods of making the same. The cylinder which is to be coated according to the invention is imperforate rather than foraminous as used heretofore inasmuch as ink or dye is to be transferred through the medium of the photoconductive coating on the exterior of the cylinder rather than by expressing the ink through the wall of the cylinder by doctor means.
The problems of coating a cylinder of this kind include principally maintaining the wall precisely in position while it is passing through the plasma produced by the conditions in the chamber to achieve a precisely uniform coating. Using a drum for mounting the cylinder or mounting a belt within the sputtering apparatus and driving the drum is one solution to the problems which arise. This invention proposes another solution which admirably solves several of the difficulties which attach to the use of a drum of the same diameter as the interior diameter of the cylinder or the belt formed into a cylinder for sputtering.
The invention provides structure to enable the belt or cylinder to be easily mounted on the anode; structure which maintains the belt or cylinder under tension at all times; structure which enables a single sputtering apparatus to accommodate cylinders or belts of a variety of different diameters; and a type of sputtering apparatus which occupies less floor space than one which utilizes a single drum for mounting the cylinder or belt.
For the purpose of this specification and claims, the word "sleeve" will be used as generic to both a cylinder and a belt.