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.

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 __________________________________________________________________________ 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. __________________________________________________________________________ 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) __________________________________________________________________________

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.

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.