US3914126A - Nickel oxide interlayers for photoconductive elements - Google Patents

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

United States Patent Pinsler Oct. 21, 1975 [54] NICKEL OXIDE INTERLAYERS FOR 3,511,661 5/1970 Rauner et al. 96/86 PHOTOCONDUCTIVE ELEMENTS 3,684,572 8/1972 Taylor [17/213 Inventor: Heinz W. Pinsler, Brighton, N.Y.

Xerox Corporation, Stamford, Conn. j

Filed: Feb. 8, 1974 Appl. No.: 440,907

Related US. Application Data Division of Ser. No. 332,044, Feb. 12, 1973.

Assignee:

References Cited UNITED STATES PATENTS 12/1946 Peters ..117/200 2/1949 Stockdale 117/230 Primary ExaminerRoland E. Martin, Jr.

Assistant ExaminerJ. L. Goodrow Attorney, Agent, 0r FirmJohn E. Crowe; James J. Ralabate; James P. OSullivan [57] 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.

6 Claims, N0 Drawings NECKEL UXTDIE TNTlERLAt ERS FQR PHQTUCGNDUCTTVE ELEMENTS This is a division of application Ser. No. 332,044, filed Feb. 12, 1973.

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" ohm-cm, preferably less than about 10 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 ohmcm in the absence of illumination and preferably at least 10 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 a dielectric material between the base or substrate and the photoconductive insulating layer. U.S. Pat. No. 2,901,348 to Dessauere't al utiiizes a film of aluminum oxide (Ex. 25 to 200 angstroms) or an insulating resin layer, such as polystyrene (Ex. 0.1 to 2 microns) for this purpose. With some limirations, 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 photoreceptor.

In searching for suitable photoreceptor materials it has been found that nickel or nickel-coated substrates are useful. Seamless belts of this material have satifactory 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 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 insure chargeability of the photoconductor and by dark discharge. Merethickness 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 overlying photoconductive insulator layer. If, on the other hand, the electronic work function of the substrate is smaller than the photocon' ductive 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 layerbetween the photoconductive layer and the chargeconducting substrate. Such material includes, for instance, chlorineand 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 nickelcoated charge conductive substrate layer and a photoconductive layer, particularly a selenium-containing photoconductive layer are strongly bonded without loss of charge-injection-blocking properties.

I It is a further object of the present invention to obtain photoconductive layers affixed to a nickel or nickelcoated 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 nickelcoated substrate such as metallized paper or metallized plastic belt with an etching composition comprising an inorganic acid, inclusive of phosphoric, sulfuric or hydrochloric 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.

um-containing photoconductive layer of one of the usual type upon the treated substrate to obtainthe desired photoreceptor element.

Preferably, nickel or nickel-covered substrate suit-' able 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 suchpurpose are sold commer-' cially, and are exemplified, for instance, by Mitchell Bradford No. 14 Cleaner and by Mobil .Acid Cleaner. The cleaned and well-rinsed substrate is op tionally 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 l a pre-etch acid wash solution (when used) varies from corresponding acid concentration can usefully, although not exclusively, vary from about 15% to 55% by weight.

When desired, the full catalytic amount of platinum or palladium can be supplied byinclusion 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 15C 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 20C l 10C and for a period of about 2-15 minutes. Where increased concentrationand/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 up through about l0%'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 (SO A concentration range of from 0% up through about 10% by weight of such metal salts is found useful, provided a minimum of about 8% 10% by weight of the metal sulfate such as Fe (SO,,) 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.

Afte 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 chemi- Cally-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 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 -1OmA/cm 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 Cr- O K Cr O Na- CrO K CrO or H CrO at room temperature up to about 95C, and preferably about 50C through 95C. 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 abovedescribed step, it is also found useful to lay down a nickel oxide layer by glow discharge technique. Here the nickel substrate is made the anode under partial vacuum, with a current density of about 3 X A/cm and a voltage (cathode) of about 2.5 K.V. for a period of about l-5 minutes. This technique is modified and described in detail in V0]. 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, U.S. Pats. Nos. 2,753,278,'2,970,906, 3,312,548 and 3,490,903;

a particularly suitable technique involves sealing sele- L nium, arsenic and a halogen in a container under .heat

to form ahomogenous 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 seleniumarsenic-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;

I EXAMPLE'I A. A stain-free nickel alloy test beltidentified as A-l, having a thickness of about 4.5 mil (0.0045inch), a width of 5 inches and a circumference of 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 PO for 1 minute, and then immersed for 10 minutes at 60C in an etching bath containing l8g/liter KCl, 150 ml/liter of 85.5% H PO and 0.2lg/liter of 10% chloroplatinic acid (H PrCl 6H 0) 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 4 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 incident light beam.

good microetched belt surface. Gloss 3% of 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 catalyst is utilized by immersing the belt in a pre-etch acid wash solution containing 0. 25g/liter PdCl and 300 ml/liter of concentrated l-ICl. The micro etching step is then carried out for 5 minutes ina bath containing 650 ml/liter of85.5% H PO and 80 g/liter of KCl; with evolution of some chlorine byproduct. The microetched belt is then rinsed and dried as in Example I and evaluated (Table 11) before further treatment.

EXAMPLE III A nickel test belt identical with those used in Examples HI, and identified as A-4, is immersed for minutes at about 76C in an agitated alkaline solution containing 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 Mobil Acid Cleaner), rinsed for 2 minutes in deionized water, dipped into an acid wash solution (300 ml/liter of concentrated I-ICl) for v30 seconds, dipped into an acid solution containing .25 g/liter PdCl and 300 ml/liter of concentrated HCl for 10 seconds, then etched in a KC]- free etching bath containing 650 ml/liter of 85.5%'

H PO the microetched belt is then subject to the usual rinsing and drying steps as in Examples 1-11 and evaluated (Table II) before further treatment.

EXAMPLE IV For nickel test belts identical with those used in Ex+ amples I-IV, and identified as A5-8, are cleaned and rinsed in deionized water as in Example I then immersed (without a preetch acid wash) in an etching solution containing 184 g/liter of Fe (SO.,) and 97.5 g/liter of H 80, at 85C. 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.

EXAMPLE v1 (Control) A stain-free nickel test belt identical with those used in the preceeding examples, and identified as A40, is

cleaned and rinsed, then oxidized at 110C for 7 minutes in an etching bath consisting essentially of 65.0 ml/liter of concentrated H PO 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 pl-I6), operating at 90C with a current density of 5 mA/cm After treatment, thetest belts are rinsed with deionized water, air dried, and

, then mounted onto a circular rotatablemandriland coated in a vacuum chamber (5 X 10* 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 280C for minutes. During this period the mandril is constantly at about 6 revolutions per minute to obtain an external photoconductor sur- Table II (Step 1) Belt No. Cat. Pre-etch Etch Time Observation and Gloss Bath(s) Bath (min.) Test A-3 PdCl Yes, with H PO, 5 Ex.* etching and oxide Cat. KCl layer. Gloss=2% reflectance. Cl evolved A-4 PdCl Yes, w/Cat. H PO 5 Ex.* etching and oxide layer. Gloss=3% reflectance. No C1 evolved.

A-5 NO H 80 2 G.* etching and oxide Fe (SO.), layer. Gloss=7 reflectance.

A-6 2 Vg.* etching and oxide layer. Gloss=3% reflectance.

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 rectly coated with a selenium photoconductive layer as 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 C for 10 minutes. Both the acid wash and etching baths are iden-,

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. 1

For testing purposes the following guidelines and definitions are generally applicable in evaluating the results obtained:

Cold Test The flexible coated photoreceptor belt 1 I is mounted over two 5-inch cardboard inserts and placed in a storage box and held at -28.8C 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 inch 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 as- What is claimed is:

1. A photoreceptor element comprising a nickel or nickel-coated substrate and a photoconductive layer joined in good blocking and charge-injection preventsembly adapted to rotate the belt over each roller at ing contact with the substrate through at least two inabout 43C. The belt is cycled for 1000 cycles in 30 termediate nickel oxide blocking layers arranged bemmlltes- T test repeated (with 5 minute a s) for tween the substrate and the photoconductive layer, ob- 30,000 cycles or until the belt structurally fails. To pass i d b h process comprising thistest the belt must complete 30,000 cycles w tho microetching the nickel or nickel-coated substrate exhlbltmg cracks Whlch are Ylslble to the with an etching composition comprising an inor- Mandrel T i belt bent three Over a ganic acid selected from the group consisting of Cylmder havmg a mch dlametef at Room p phosphoric acid, sulfuric acid and hydrochloric ture and then checked for cracks in the substrate and acid, in the presence of at least one of palladium layers PP 15 chloride, chloroplatinic acid, or ferric sulfate;

Elctrlcal Dark Dlscharg? Test The Photoreceptor anodizing the resulting microetched chemically oxibelt is charged at 900 volt in the dark and the potential dized Substrate. and gg aftler 3 seconds' i decay :1 voltage a depositing a photoconductive layer upon the treated O 0 or e55 accepta e or gener Xerograp 1c substrate to obtain the desired photoreceptor elepurposes. mem

Vc. Determination Test An electrical charge is added stepwise to a photoreceptor surface in the dark 2. The photoreceptor element of claim 1 wherein the and it is determined at what voltage the charging bephotoconductive layer is a selenium-containing photohavior of the photoreceptor begins to substantially deconductive layer. viate (by 40 volts) from the desired (linear) charging characteristics. A maximum voltage of 900 volts 950 3. A photoreceptor element comprising a nickel or volts is considered fair, 950 volts l 100 volts is good, nickel-covered substrate and a selenium-containing l 100 1500 volts is very good and 1500 1600 volts photoconductive layer joined in good blocking contact is considered excellent. through at least two intermediate blocking layers ar- Print Test About 50 square inches of photorecepranged between said substrate and the applied phototor are dark charged at 900 volts and developed withconductive layer, obtained by the process out light exposure after about 20 seconds using fine a. microetching the nickel or nickel-coated substrate powdered toner. The presence of light or dark spots or with an etching composition comprising a visible pattern is attributed to uneven dark discharge 1. an inorganic acid solution containing at least one of the photoreceptor attributable to non-uniformities of phosphoric acid, sulfuric acid, or hydrochloric of the interface. acid,

Table III Belt Mandrel Cold & Shock Flex Electrical Vc Print (coated) Test Test (28.8C) Test Dark Dis- Test Test (1.25" charge Test Diam) 12% 3 Sec.

A-l Passed Passed Failed Passed Failed A 2 Passed l 100v. Passed 30.000 cycles 156W A4 I560 A 5 Failed Failed A-6 Passed Passed A9 150W A 1 0 Failed Failed (900v.)

(control) EXAMPLE VH1 2. a balance of 0% up to about a catalytic amount A test belt identified as A-l l is prepared as in Exam- While the above Examples are directed to preferred embodiments of the invention, it will be understood that the invention is not limited thereby.

of at least one of palladium chloride or chloroplatinic acid based on the presence of a total amount of catalyst in effecting step (a), and

3. from 0% up through about 10% by weight of a water soluble alkali metal halide or metal sulfate; about 8% 10% of the metal sulfate being utilized in the absence of platinum or.palladium catalyst;

b. anodizing the washed microetched and oxidecoated substrate 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 not exceeding about 0.85 volt; and

S. A photoreceptor element of'claim 2 wherein the microetching step is effected with an etching bath comprising phosphoric acid and chloroplatinic acid.

6. A photoreceptor element of claim 1 wherein the microetching step is effected with an etching bath comprising phosphoric acidand palladium chloride.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3, 914, 126

DATED October 21 1975 age 1 of 2 |NV ENTOR(S) Heinz W. Pinsler It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[SEAL] Column 2 line 34, "satifactory" Column 5, line 20, "Afte" should be After--.

Column 6, line 53, "3% of" omit the "of" Column 7, at the end of Table II, "g.=Good" should be G 0 0 Column 7, line 64, "conccentrated" should be --concentrated-.

Column 8, line 28, insert rotatedbetween "constantly and "at".

Column 9, line 63, "40 seconds" Columns 5 and las shown on the attached sheet should be added but will apply to the Grant only.

Sixth Day of July 1976 A ttes t:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner uj'PaIents and Trademarks should be --40 minutes.

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. ln 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 overlying photoconductive insulator layer. if, on the other hand, the electronic work function of the substrate is smaller than the photoconductivc 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 ofelectrons 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, chlorineand 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 nickelcoated 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 nickelcoated 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 nickelcoated substrate such as nietallized paper or metallized plastic belt with an etching composition comprising an inorganic acid, inclusive of phosphoric, sulfuric or hydrochloric acid, or combination thereof, in the pres ence 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 lgnatov in J. Chimie Physique, 54 (i957) pg. 96 et seq.

Page 2 of 2 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. v

The substrate is then further treated by depositing a suitable photoconductive layer. particularly a seleniuni-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.l0% by weight of solution, and the corresponding acid concentration can usefully, although not exclusively, vary from about 15% to 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 cata' lytic 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 prefe rably carried out at a temperature range of about 15C 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 20C l 10C and for a period of about 2-l5 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 i. 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

Claims (8)

1. A PHOTORECEPTOR ELEMENT COMPRISING A NICKEL OR NICKELCOATED SUBSTRATE AND A PHOTOCONDUCTIVE LAYER JOINTED 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, OBTAINED BY THE PROCESS COMPRISING MICROETCHING TE NICKEL OR NICKEL-COATED SUBSTRATE WITH AN ETCHING COMPOSITION COMPRISING AN INOGANIC ACID SELECTED FROM THE GROUP CONSISTNG OF PHOSPHORIC ACID, SULFURIC ACID AND HYDROCHLORIC ACID, IN THE PRESENCE OF AT LEAST ONE OF PALLADIUM CHLORIDE, CHLOROPLATINIC ACID, OR FERRIC SULFATE, ANODIZING TE RESULTING MICROETCHED CHEMICALLY OXIDIZED SUBSTRATE, AND DEPOSITING A PHOTOCONDUCTIVE LAYER UPON THE TREATED SUBSTRATE TO OBTAIN THE DESIRED PHOTORECEPTOR ELEMENT.

2. The photoreceptor element of claim 1 wherein the photoconductive layer is a selenium-containing photoconductive layer.

2. a balance of 0% up to about a catalytic amount of at least one of palladium chloride or chloroplatinic acid based on the presence of a total amount of catalyst in effecting step (a), and

3. from 0% up through about 10% by weight of a water soluble alkali metal halide or metal sulfate; about 8% - 10% of the metal sulfate being utilized in the absence of platinum or palladium catalyst; b. anodizing the washed microetched and oxide-coated substrate 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 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.

3. 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, obtained by the process a. microetching the nickel or nickel-coated substrate with an etching composition comprising

4. The photoreceptor of claim 3 wherein clean nickel or nickel-coated substrate is treated with a pre-etch acid solution additionally containing 0% up to about a catalytic amount of at least one of palladium chloride or chloroplatinic acid prior to the microetching step.

5. A photoreceptor element of claim 2 wherein the microetching step is effected with an etching bath comprising phosphoric acid and chloroplatinic acid.

6. A photoreceptor element of claim 1 wherein the microetching step is effected with an etching bath comprising phosphoric acid and palladium chloride.