US3536481A - Electrolytic process of forming a xerographic belt - Google Patents

Description

Oct. 27, 1970 3,536,481

ELECTROLYTIC PROCESS OF FORMING A XEROGRAPHIC BELT Filed June 12, 1967 w. a. HESPENHEIDE ET AL 2 Sheets-Sheet 1 FIG. 2

ma y

INVENTORS WI LBUR G. HESPENHE'DE FIG. 3

. no a JUGLE nrronwsrs 06.27, 1970 w. G. HESPENHEIDE ETAL 3,536,481

ELECTROLYTIC PROCESS OF FORMING A XEROGRAPHIC BELT Filed June 12, 1967 2 Sheets-Sheet 2 INVENTORS WILBUR G. HESPENHEIDE BY ON JUGLE D M A. yum

ATTORNEYS United States Patent 3,536,481 ELECTROLYTIC PROCESS OF FORMING A XEROGRAPHIC BELT Wilbur G. Hespenheide, Webster, and Don Barton Jugle,

Penfield, N.Y., assignors to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed June 12, 1967, Ser. No. 645,178 Int. Cl. G03g 5/00 US. Cl. 96-1 1 Claim ABSTRACT OF THE DISCLOSURE A flexible endless xerographic belt and the method of making and using it. The belt comprises an electrically conductive substrate having a uniformly smoothened seam of high bonding strength formed by the reception of a metal electrolytically deposited along a channel defined by edges on the ends of the substrate, a mandrel supporting said substrate ends, and an insulating mask selectively superimposed in overhanging relationship therewith. A layer of photoconductive insulating material is deposited on a surface of the substrate.

BACKGROUND OF THE INVENTION This invention relates in general to xerography and in particular to xerographic plates, a xerographic process using such plates and to a process for the production of such plates.

In the xerographic process as described in US. Pat. 2,297,691 to Chester F. Carlson, a base plate of relatively low electrical resistance such as metal, paper, etc. having a photoconductive insulating surface coated thereon, is electrostatically charged in the dark. The charge coating is then exposed to a light image. The charges leak off rapidly to the base plate in proportion to the intensity of light to which any given area is exposed, the charge being substantially retained in non-exposed areas. After such exposure, the coating is contacted with electroscopic marking particles in the dark. These particles adhere to the areas where the electrostatic charges remain forming a powder image corresponding to the electrostatic image. The powder image can then be transferred to a sheet of transfer material resulting in a positive or negative print, as the case may be, having excellent detail and quality. Alternatively, when the base plate is relatively inexpensive as in the case of paper, it may be desirable to fix the powder image directly to the plate itself.

As discussed in Carlson, photoconductive insulating coatings comprise anthracene, sulfur, or various mixtures of these materials such as sulfur with selenium, etc., to thereby form uniform coatings on the base material. These materials have a sensitivity largely limited to the shorter wave lengths and have a further limitation of being only slightly light sensitive. Consequently, there has been a continuing eifort to produce improved photoconductive insulating materials.

The discovery of the photoconductive insulating properties of highly purified vitreous selenium has resulted in this material becoming the standard in commerical xerography. The photographic speed of this material is many times that of the prior art photoconductive insulating materials. Such a plate is characterized by being capable of receiving a satisfactory electrostatic charge and selectively 6 dissipating such a charge when exposed to a light pattern.

3,535,481 Patented Oct. 27, 1970 In commercial applications, selenium is generally deposited upon a rigid backing material, such as a rigid cylindrical drum which is readily adapted for automatic operation. More recently, a flexible belt, such as the one shown in US. Pat. 3,146,688 to Clark et al., has been contemplated as the supporting substrate for the deposited photoconductive insulating material. Such a system offers a substantially increased reproduction surface thereby permitting increased speed in the reproduction of copies from an original.

Unfortunately, an endless belt-type flexible xerographic member, while advantageous in one sense, has not proven entirely satisfactory. The principal reason is that the photoconductive insulating layer does not respond well in the area of the belt seam. More specifically the seam tends to fail after repeated flexing and does not have an equivalent radius of curvature to that of the remainder of the belt. As a result there has been an adverse elfect on the properties of the overlying photoconductive insulating layer.

SUMMARY OF THE INVENTION It is therefore an object of this invention to improve endless flexible electrophotographically reusable plates having high quality reproduction sensitivity uniformly over the surface thereof. Another object of this invention is to produce an endless flexible foil joined at a seam wherein the metallurgical structure of its foil surrounding the seam is not adversely affected.

Still another object is to provide a novel xerographic process wherein a reusable flexible xerographic plate is utilized which has exceptional mechanical strength and photoconductive response under normal conditions of xerographic machine operation.

Yet another object of this invention is to ensure formation of a smooth seam along the edges of a strip joined by electrodeposition of a metal wherein the need for a dressing operation of the seam prior to deposition of an overlying layer is minimized.

Another object of this invention is to maintain a uniform radius of curvature for a flexible endless belt when subjected to repeated flexing at applied loads.

The foregoing objects and others as will become apparent are accomplished, generally speaking, by precleaning a conductive substrate in the form of a strip and then joining the ends thereof by electrolytic deposition of a metal therebetween by selectively flowing an electrolyte solution along a seam to be formed. The seam formed is smooth and flat and has mechanical properties as good as or better than the remainder of the strip. More than this the need for dressing down the surface of the seam prior to deposition of an overlying layer is minimized.

In accordance with the invention metal forms the most suitable material for the conductive backing strip or substrate. However, a high conductivity is not required and almost any structurally satisfactory material which is more conductive than the photoconductive insulating layer can be used. Materials having electrical resistivities about 10 ohm-centimeters are generally satisfactory for the supporting substrate of this invention although it is more desirable to use materials of less than about 10 ohmcentimeters. Suitable backing materials include brass, aluminum, copper, nickel, zinc, chromium, steel, stainless steel, paper, plastic, glass or other sheets having a conductive coating thereon, as of tin oxide (NESA glass), noncoated conductive plastics, rubbers, etc. The strip desirably has a thickness ranging from about .003 inch to .010 inch for flexing with a high reliability and strength.

The first step in the method is the preparation of the strip. This is most important if a good bond at the seam is to be obtained. The ends of the strip are abrasively cleaned as by being passed between bufiing wheels which advantageously have a surface free of organic fats. A typical abrasive is a water slurry of aluminum oxide or other suitable inorganic materials. The abrasive cleaning removes oily films and smoothens sheared edges so that maximum adhesion can be attained during electro-deposition as will be understood. Other suitable cleaning processes as are known to those in the electrochemical arts may be used. Typical ones are electrolytic cleaning in alkaline or acid solutions, immersion etching, rinsing, etc. It should be understood that cleaning may be accomplished prior to assembly of the strip in a plating jig or alternatively in a flow-type system in communication with the plating jig.

The next step is the making of a smooth and fiat seam by the electrodeposition of a metal along the ends of the strip. Typical electrodeposited metals are nickel, copper, iron, chromium, zinc, and the precious metals. A preferred metal is nickel because of a wide range of mechanical properties available by controlling parameters during electrodeposition. Any suitable electrolytic nickel plating solution may be employed for this purpose. Aqueous solutions containing a metal cation and nickel sulphamate are preferred because of the rapid and uniform deposition achieved. A typical aqueous nickel sulphamate solution is as follows:

Material: Parts by vol. or wt.

Nickel sulphamate concentrate in water fluid oz./gal. 44-77 Nickel chloride oz./gal. 0.5-6 Boric acid oz./gal. 4-6

Other suitable plating solutions may be employed. Typical examples are set forth in US. Pat. 2,318,592.

The electrolyte solution is heated to a temperature of about 50 C. before introducing it into a special plating jig in which the strip ends are positioned for joining by electrodeposition of a metal mentioned above.

The plating jig comprises an anode which is advantageously made of the metal being deposited and two cathodes. One cathode takes the form of the strip ends being joined. The other cathode is a flat mandrel supporting the strip ends. In this manner it is possible to achieve flatness and uniformity on a first side of the seam. Flatness and smoothness on the other side of the seam are ensured in a manner to be described hereinafter. The anode and cathode are connected to a power source to establish a current density ranging from about 100 to about 800 amps per square foot across the seam area.

The cathode mandrel may be made from any suitable material. Typical materials are stainless steel, chromium, titanium, and prolytic graphite. The cathode mandrel material is desirably cleaned and otherwise treated to insure adherence of the electrodeposited metal onto the strip material being joined.

In accordance with the invention the seam formed is smooth and flat on both sides. In order to achieve this condition the deposition rate of metal at the edge of the seam is controlled. To this end a mask is selectively positioned in the flow path of the electrolyte to overhang the channel defined by the strip ends and the cathode mandrel. The precise position of the mask relative to the strip edges is dependent upon such factors as viscosity of the electrolyte, density, flow rate, and current density. This relationship is conveniently established by a formula for the Reynolds number N of the electrolyte along the seam which can be expressed as follows:

where L is the characteristic linear dimension of the apparatus through which the flow is taking place;

V is the linear velocity; p is the density; and a is the absolute viscosity.

It has been found that for N of less than about 2200 the mask overhang should approximately equal the strip thickness for thicknesses already mentioned above. Where N is greater than about 2200 the ratio of overhang to thickness is in the range of about 1 to 2.

It is believed that the arrangement of mask overhang in relation to the strip edges establishes a region of reduced electrolyte flow thereby lessening deposition rates at the seam edges where electric fields are normally higher. Additionally, it has been found that the current density and plating rate at the ends of the strip is reduced because they are at a greater distance through the solution from the anode. It should be noted that seam widths ranging from about 2 to about 30 times the strip thickness have been found to work well with this mask overhang. For best results the plating zone should be about /21 inch longer than the strip so that uniform flow conditions are assured at the edge of the seam. Any excess deposition of metal can be sheared off afterwards so that a smooth edge results.

The mask can be made of any suitable material. A preferred material is glass because of its strength, wettability by the electrolyte, and insulative characteristics. A glass found to work especially Well is manufactured under the trademark Chemcor, manufactured by Corning Glass Works, Corning, NY.

The last step in the method of producing the endless flexible xerographic belt is the deposition of a photoconductive insulating layer on the conductive substrate. Any suitable material, such as vitreous selenium and deposition process can be used as these do not form a part of the present invention. Many suitable processes for deposition are described in the patents to Mangali et al., 2,657,- 152; to Bixby et al., 2,753,278; and to Bixby, 2,970,906. In general, the photoconductive layer is deposited through vacuum evaporation of selenium onto a backing plate held at a temperature of at least about 20 C., and generally in the range between 40 C. and C. and preferably on the order of about 50 C. The deposition of the selenium layer is halted when the layer has reached the desired thickness such as, for example, on the order of about 10 to 200 microns, preferably about 20 to 50 microns. Deposition is normally conducted under pressure conditions on the order of less than about 1 micron of mercury.

BRIEF DESCRIPTION OF THE DRAWINGS A clearer understanding of the invention will be had from the following description when read in connection with the accompanying drawings wherein:

FIG. 1 is a schematic view of apparatus for forming a smooth seam along edges of a foil strip according to the present invention;

FIG. 2 is a cross-sectional view of the jig taken along line 22 in FIG. 1 and illustrating details of the anode, cathode, and mask;

FIG. 3 is a cross-section view similar to FIG. 2 of a preferred embodiment of the plating jig; and

FIG. 4 is an exploded isometric view of the plating jig shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 there is shown seam forming apparatus which includes a container 10 filled with an electrolyte solution 11, such as the nickel plating solution described above. Container 10 has a heating element 12 located in the bottom for controlling the temperature of the solution. Solution 11 is circulated through conduit 13 by a pump 14 through a plating jig 16 comprising an anode 20 and a cathode 22. After passing through the jig solution is received into container which also serves as a reservoir. Connected across the anode and cathode is a variable source of DC potential 24 for regulating the current flow between the anode and cathode. Desirably conduit tubing 13 and associated fittings should be made of a suitable material so that organic contamination of the system is minimized. Polyvinyl chloride tubing and Teflon fittings are suitable for this purpose.

Anode 20, which is made of metal to be deposited, has a channel 26 formed at its bottom portion overlying the ends of a foil strip 30 along which a seam is to be formed. The electrolyte flows along the seam which is enclosed from the atmosphere to achieve a high linear flow rate thereby accelerating deposition.

Foil strip 30 is positioned with its ends extending parallel on top of cathode 22 which serves as a mandrel on which the seam is formed. It should be noted that with the flatness of cathode mandrel 22 a flat and smooth seam on the side of the mandrel is assured. The foil strip ends are held in position during electrodeposition by any suitable means, such as by locating pins 31 (FIG. 4) on the cathode mandrel which are received by holes formed in the strip ends.

To control deposition of metal at the strip edges and ensure smoothness throughout the seam a pair of masking members is selectively positioned to overlie the edges along the length of the seam. It should be noted that the masking member edges overhang the strip edges by a predetermined distance 11. This distance h varies with the Reynolds number of the electrolyte as well as the thickness of the strip as mentioned above. It is believed that the mask overhang establishes a region of reduced electrolyte flow thereby lessening deposition around the seam edges where electric fields are normally higher.

A resilient pad 38 positioned between anode 20 and mask 35 forms a seal between them. Pad 38 is made from any suitable material such as silicone rubber.

FIGS. 3 and 4 show a preferred embodiment for the plating jig in which one or more metal chips to be deposited and conductive plates are substituted for the solid anode structure of FIG. 2. Conductive plates 60 are embedded in the side walls of a housing 61 which is made from any suitable electrically insulating material, such as silicone rubber. Typical materials for the plates, which desirably do not chemically react with the electrolyte, are titanium, platinum, and prolytic graphite.

Supported between plates 60 is an elongated metal chip 62 which furnishes metal ions to the solution. It should be noted that as in the embodiment of FIG. 2 a pair of masking members 35 is positioned to overhang the edges of a foil strip 30 by a distance it. A metal frame 68 embedded in housing 61 serves to form a rigid structure through which a sufficient force may be applied to effect a liquid seal on either side of the strip. In this manner an endless flexible belt is formed with a smooth and flat seam on each side.

The following examples are given to enable those skilled in the art to more clearly understand and practice the invention. They should not be considered as a limitation upon the scope of the invention but merely as being illustrative thereof.

EXAMPLE I A brass foil strip .004 inch thick and 11 /2 inches wide is clamped with ends spaced .120 inch apart between a nickel anode and stainless steel cathode in a plating jig such as that shown in the FIG. 2. The channel formed in the anode 20 is about A; of an inch wide with a height of about of an inch. A glass mask is positioned to overhang the foil edges by .004 inch. A cleaning solution consisting of 10% hydrochloric acid and 90% water is pumped through the jig for 3 minutes. After this, water is pumped through the jig for 30 seconds for rinsing away the cleaning solution. A nickel sulphamate electrolyte solution having a specific gravity of 1.20 at 50 C. and a viscosity of 3.0 centipoise is pumped through the cell at a rate of 270 ft./min. for about 10 to 15 seconds until air bubbles are eliminated. A DC potential is then applied to the cell in reverse polarity with a positive charge on the cathode 22 and a negative charge on the anode 20 for about 15 seconds at a current density of amps per square foot to etch the foil so that maximum adhesion can be obtained. After a 15 second interval for etching, the polarity was then switched with the anode 20 being changed to positive and the cathode 22 being changed to negative. After approximately 40 minutes pumping was stopped and the foil strip removed from the jig. The belt seam insofar as detected was uniformly smooth and did not vary from the thickness of the foil strip. The belt was passed over a flcxure test for over 300,000 flexings, and was given tensile test for strengths of over 60,000 lbs./sq. inch with no change in physical properties as far as could be determined.

EXAMPLE II A seam for an endless flexible substrate was made in a manner similar to Example I, except that stainless steel foil was substituted in place of the brass foil and cleaning solution ASTM B-254-53 was utilized. As far as could be determined, the results were the same.

EXAMPLES III AND IV A 40 micron layer of vitreous selenium is vacuum deposited over the endless belts of Examples I and II under conditions mentioned above. It was found that the xerographic belt has superior flexing properties and the electrical properties are substantially equivalent to those of standard selenium plates. Excellent xerographic copies are obtained with this flexible belt.

The term nickel as used herein is not meant to restrict the composition to chemically or even commercially pure nickel since various impurities or alloying elements may be present sometimes to a considerable extent without impairing the utility of the device. Nickel, therefore, is to be understood to mean that which is composed largely of nickel or which owes its physical characteristics largely to this metal.

While the invention has been described with reference to preferred embodiments thereof it will be understood by those skilled in the art that various changes in the form and details may be made without departing from the true spirit and scope of the invention. Further, provided the advantageous results of this invention are not adversely affected, additional operations may be formed to achieve this, the herein disclosed results, while in certain circumstances, certain operations may be deleted as will be apparent to those skilled in the arts. Numerous modifications may be made to adapt a particular situation or material to the teachings of the herein disclosed invention. All such additions, deletions, modifications, etc. are considered to be within the scope of the present invention.

What is claimed is:

1. A process for producing continuous xerographic reproduction comprising placing an electrostatic charge on a chargeable surface of a flexible endless xerographic member comprising an electrically conductive substrate having a thickness ranging from about .003 inch to about .010 inch joined at a smooth seam of high bonding strength, said seam being formed by the reception of a metal electrolytically deposited along a channel defined by edges on the ends of said substrate, a mandrel supporting said substrate ends, and an insulative mask overhanging said substrate edges by a predetermined extent ranging from about one to about two times the thickness of said substrate, said joined substrate supporting a photoconductive insulating layer having a thickness ranging from about 20 microns to about 60 microns on which charge is retained, selectively dissipating electrostatic charge from the surface of the photoconductive insulating layer by exposing the layer to a light image thereby creat- 7 8 ing a latent electrostatic image on the surfaces of said 3,146,688 9/1964 Clark et a1. 355-11 photoconductive layer, and developing said latent electro- 3,396,092 10/1968 Moyer et a1. 204-29 static image with electroscopic marking material.

GEORGE F. LESMES, Primary Examiner References Cited 5 M. B. WITIENBERG, Assistant Examiner UNITED STATES PATENTS 2,318,592 5/1943 Cupery 204 49 2,569,367 9/1951 Bradner et a1. 74-232

Images