IL39655A - Xerographic photoreceptor interface - Google Patents

Description

ηκ ^Βΐρ · an Alios D'»a'a new Xerographic photoreceptor interface XEROX CORPORATION XD 3666 This invention relates in general to xerography, and in particular, to an improved interfacial layer for a -xerographic -member. i I . ■ ' I " In the -art of xerography, a xerographic plate containing a photoconducting insulating layer is first given a uniform electrostatic charge in order to sensitize its surface. The plate is then exposed to an image of activating electromagnetic radiation, such as light, which selectively dissipates the charge in the illuminated areas pf the photoconductive insulator 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 electro- scopic marking particles on the surface of the photoconductive layer. This concept was originally described by Carlson in.

U.S. Patent 2,297,691 and is further amplified and described by many related patents in the field.

Conventionally, a xerographic member or plate normally includes a conductive base or support which is generally characterized by the ability to conduct electricity for charging or sensitization of a composite member and to accomodate the release of electric charge upon exposure of the member to activating radiation such as light. Generally, this conductive support must have a specific resistivity of less than about ^? ohm-cm, and usually less , than about- 10- ■ -ohm-cm. The conductive support should also have sufficient structural strength to provide mechanical support for the photosensitive member thus making it readily adaptable for xerographic machines suitable for commercial . use .

The 'conventional xerographic plate normally has a photoconductive insulating layer overlaying a conductive support. The photoconductor may comprise any suitable material known in the art. For example, vitreous selenium, or selenium modified with. varying amounts of arsenic is one example of one suitable reusable photoconductor which has wide use in commercial xerography. In general, the photoconductive layer must have a specific resistivity greater than, about 10 ohm-cm 13 in the absence of illumination and preferably at least 10 ohm-cm The resistivity should drop at least several orders of magnitude in the presence of activating radiation or light. In general, the photoconductive layer should support an electrical potential of at least about 100 volts in the absence of radiation and may vary in thickness from about 10 to 200 microns.

.' A plate having the above configuration, normally under dark room conditions, exhibits a reduction in potential or voltage leak in the absence of activating radiation which is known -as "dark decay"' and exhibits a variation in electrical performance upon repetitive cycling which is described in the art as "fatigue". The problem of "dark decay" and "fatigue" are well known in the art and have been remedied by the incorporation in the plate structure of a barrier layer which comprises a thin dielectric material only a fraction of the thickness of the photoconductive layer. This barrier or interfacial layer is inter-disposed between' the conductive substrate and the photoconductive insulating layer. U.S. Patent 2,901,348 to Dessauer et al contemplates such a layer and suggests the use of a thin layer or film of aluminum oxide in a thickness range of about 25 to 200 angstroms; or an insulating resin layer, such as polys yrep: in the order of about 0,1 to 2 microns in thickness. These barrie layers function to allow the photoconductive layer to support a in the absence of illumination. When activated by illumination, the photoconductive layer becomes conductive, thereby causing a migration of the appropriate charges through said photocon-.ductive layer and the appropriate dissipation of charge in the radiation or illumination struck areas.

In addition to the electrical requirements- of a barrier layer, it is also necessary that such a layer meet certain requirements with regard to mechanical properties such as "photoreceptor adhesion and overall flexibility. For example, when using a. flexible photoreceptor, such as a continuous belt, both the photoconductor and interface must be properly matched so as to have the. required electrical characteristics and rlechanical stability. It has been demonstrated that after a i great deal of flexing, many interfaces tend to spall or crack, resulting in the flaking off or spal-ling of. sections of the photoreceptor rendering it no longer suitable for use in xerography. Therefore, there is a continuing need for improved barrier layers which meet both the required electrical characteristics and mechanical properties for use in applications in which a flexible xerographic member. or belt is used.

It is, therefore, an object of the invention to provide a new and improved photoreceptor barrier layer which overcomes the above noted disadvantages . . .

It is another object of this invention to provide a photoreceptive member which exhibits outstanding electrical characteristics and mechanical properties.

It is another object of this invention to provide an improved interfacial barrier layer. , in accordance with this invention by providing a photoconductive φ member which exhibits outstanding electrical characteristics and mechanical properties, and which includes a novel interfacial barrier layer which comprises a polycarbonate resin and a poly urethane resin. More specifically, the interfacial layer comprises either a polymer blend or mixture of a polycarbonate and a polyurethane which is sandwiched between a photoconductive insulating layer and a supporting substrate. . One of the advantages of this interfacial composition is that the combination of properties which include tensile strength, elongation, modulus of elasticity, adhesive properties, and electrical characteristics exceed the properties of the individual polycarbonate or polyurethane resins when used separately.' The present invention will be more fully understood of embodiments upon consideration of the following, disclosure/of the invention, especially when taken in conjunction with the accompanying drawing wherein: the single figure represents a schematic illustration of one embodiment of a xerographic member in accordance with the present invention.

In the drawing, reference character 10 illustrates one embodiment of an improved photoreceptor device of the instant device. Reference character 11 designates a support member which is preferably an electrically conductive material. The support nickel, may comprise a conventional metal such as brass, aluminum, steel, . The support may also be of any convenient thickness, rigid or flexible and in any suitable form such as a sheet, web, cylinder, or the like. The support may comprise other materials such as metalized paper, plastic sheets covered with a thin , or chromium v » a thi conductive layer of e romium JO» tin oxide/. A preferred substrate for use in the instant invention comprises an endless flexible seamless xerographic belt which comprises nickel, and which is formed by the method described in German Offenlegungsschrif 2,103,322. " The substrate 11 is overlayed with an organic inter-facial layer 12, which comprises a polymer blend or. mixture of a polycarbonate and a polyurethane resin. In general, the ratio by weight of the polycarbonate to polyurethane resin should be kept within about 1 to 1 and 7 to 1..· Polyurethane concentrations of less than 13 percent by weight (7 to 1 ratio) do not have mechanical properties suitable for use in the instant invention, while concentrations- of polyurethane over about 50 percent by weight are undesirable in that high concentrations of polyurethane are believed to present fabrication or coating problems. Although high molecular weight polycarbonates (casting resins) are preferred (those having a molecular weight averaging from about 75,000 to 100,000) any suitable polycarbonate resin may be used. The polyurethane resins are of the type referred to as saturated, thermoplastic, polyester-based. ■ ,* Typical polycarbonates suitable for use in the instant invention comprise MakrolOn 7505Z, and Makrolon 9005Z, available from Bayer Dyestuffs and Chemicals Ltd.; Merlon M50-Natural, Merlon M50-1010 Clear Tint, and Merlon 1,000 pdr, all available from Mobay Chemical Company; Lexan 125 and Lexan 155, available from General Electric Co., Chemical Materials Dept.

The typical polyurethane resins suitable for use in the instant invention include Vithane TPU123, available from Goodyear Tire and Rubber Co., Chemical Division; and Estane 5703, available from B. F. Goodrich Chemical company. technique. For example, the appropriate proportions of poly-;^' carbonate and .polyurethane resins are normally dissolved in a solvent and the resih solution coated onto a supporting substrate. The solvent is then allowed to evaporate leaving a flash dried coating contained on the supporting substrate. Residual solvents are then driven off by oven drying at 150 to 300°F for about 5 minutes. Typical coating techniques which are suitable for forming the interfacial layer include spray coating, draw coating, dip. coating, or flow coating. In general, the dried thickness of the interfacial layer should be about .0.5 to 3.0 microns.

Thicknesses less than about 0.5 microns are undesirable, in that they do not give a uniformly thick layer, are porous and do not uniformly cover substrate roughness. In' addition, they are .difficult to charge and tend to leak electrical charge. Thicknesses above about 3.0 microns result in ηση-cha ge dissipation. In general, the composite resistivit of interfacial layer ranges 11 1 ■from about 10 to 10 · ohm-cm.

In addition to the above polycarbonate and polyurethane resins , .other additives may be added to the mixture. These ' additives include small amounts of conductive or photoconductive pigments such as copper phthalocyanine, zinc oxide (electrography grade) , cadmium .sulfoselenide , and metal-free phthalocyanine.

In general these additives are used to control the resistivity of the interfacial barrier layer, and in some cases are even believed to improve the' mechanical properties of layer.

Although the exact structure of the interface has not been clearly defined, at low concentrations of polyurethane, in the range of about 13 weight percent to 35 weight percent, the structure of the interfacial layer appears to comprise a polyblend of spherical polyurethane particles contained in a surrounding polycarbonate matrix. The size of the spherical polyurethane phase or particles appears to increase with an increase in A preferred application of the instant invention includes the use -of the instant interface -on a flexible endless. belt which may typically comprise a conductive material such as nickel or brass. In addition to the required electrical characteristics, it is essential that the ihterfacial layer of the instant invention have a high degree of flexibility and forms a satisfactory adhesive and cohesive interface .between the photoconductive layer and the supporting substrate.

Photoconductive insulating layer 13 overlays interfacial layer. 12.· The photoconductor may comprise any suitable photo-conductive insulator which is compatible with the insulating resins and forms an adherent layer which properly bonds the photoconductive layer to the substrate. Suitable photoconductive materials include vitreous selenium or selenium alloyed with materials such as. arsenic, antimony, tellurium, sulfur, bismuth and mixtures, thereof . A preferred photoconductor comprises a' vitreous alloy of selenium containing arsenic in an amount from about 0.1 to 50 percent by weight. The thickness of the photoreceptor layer is not particularly critical and may range from about 10 to.200 microns. In general, thicknesses in the range from about 20 to 80 microns are particularly satisfactory for use in conventional xerography. The photoreceptor layer may be prepared by any suitable technique. A preferred technique includes vacuum evaporation wherein the appropriate material or alloy is evaporated over the interfacial layer. In general, a selenium or selenium-arsenic alloy layer thickness of about 60 microns is · obtained when vacuum evaporation is continued for about 1 hour -5 at a vacuum of 10 Torr. at a crucible temperature of about 280°C. U.S. Patents 2,803,542 to Ullrich; 2,822,300 to Mayer et al, 2,901,348 to Dessauer et al and 2,753,278 to Bixby all illustrating vacuum evaporation techniques which are suitable in the formation of selenium or selenium alloy layers of the instant invention. ^ In order to gain added sensitivity when using selenium-arsenic layers, a halogen dopant such as chlorine or iodine, may be added in order to improve the . electrical characteristics. This concept is more fully described by U.S. Patent ... . . . . ... ... . . t 3,312*548 to Straughan. - • The following Examples further specifically describe the present invention with respect to a method of making a photoreceptor member having an interfacial barrier layer.

The percentages in this specification, Examples and claims are by weight unless otherwise stated. ' The Examples below are intended to illustrate various preferred embodiments of the instant invention.

EXAMPLE 1 A coating solution for forming an organic interfacial barrier layer is prepared as follows: 76.8 grams of polycarbonate resin (Merlon M-50, available from Mobay Chem.

Co.). is dissolved in 1280 milliliters of ethylene dichloride solvent. A second solution is made containing 16 grams of copper phthalocyanine (available from Hercules Inc., Imperial De partment) dispersed in 1540 milliliters of p-dioxane solvent.

A-third solution is made comprising 19.2 grams of polyurethane resin (TPU 123 available from Go'odyear Tire and Rubber Co., Chemical Division) diluted In 625 milliliters of cyclohexanon solvent. The copper phthalocyanine pigment is added to the dioxane the ethylene dichloride-polycarbonate solution. This solution is milled in a pebble mill jar for 16 hours.

The polyurethane resin is dissolved in the cyclohexanone solvent,' filtered one pass through a Sethco recirculating cartridge filter, one pass through a Gelman 0.2 micron absolute filter, then added to and mixed with the polycarbonate - copper phthalo-cyanine solution. Tetrachloroethylene solvent is then added to the above mixture to control the solution viscosity and drying rate for spraying. This mixture is then coated onto a continuous flexible nickel belt .0045 inches thick, approximately 16.5 inches wide and 65 inches in circumference by spray coating using an air atomized spray process with a Binks electrostatic spray gun. The coating is then allowed to dry, as described previously, Ipo form a thickness of about 1.5 microns. This results, in the formation of an interfacial layer which contains a ratio of 4 parts by weight polycarbonate resin to 1 part by weight of polyurethane resin, and about 14 weight percent, copper phthalocyanine .

The coated nickel substrate is then mounted onto a -circular mandrel and inserted in a vacuum chamber. An alloy source containing about 99.67 'weight percent selenium and .33% weight percent arsenic and containing 30 parts per million chlorine, is inserted in a stainless steel crucible beneath the coated nickel substrate. During vacuum evaporation the substrate is rotated about its longitudinal axis at a rate of about 6 to 12 revolutions per minute. The vacuum chamber -4 is evacuated to a vacuum of about 5 x 10 Torr. The crucible' containing the selenium-arsenic alloy is then heated to a temperature of about 300°C and evaporation continued for about 40 minutes resulting in vitreous selenium-arsenic alloy photoreceptor being coated over the interfacial layer in a thickness of about 60 microns. At the end of this time, the vacuum chamber ■ EXAMPLES II-XXI y Twenty .additional coated flexible nickel belts are prepared by the method of Example I containing various types of resin interfaces. These, belts are designated belts 2-21, respectively. Belts 2 to' 13. contain various ratios of'; polycarbonate to polyurethane : Belts 14 and 15 comprise a 100% polyester interface; belts 16, 17, 18. and 19 contain 100% polyurethane interfacial layers; while belts 20 and 21 contai 86 weight percent polycarbonate and 14 weight percent copper phthalocyanine . The photoconductive layer is a 60 micron layer of about 99.7% selenium-.3% arsenic and the interface layers are about 1 to 2 microns in thickness.

Each of belts 1-21 are tested under three conditions as follows : Cold Test - The flexible coated photoreceptor belts are mounted over two five-inch cardboard inserts and placed in a storage box and held at -20° F for four hours. To pass the test, the photoconductor coating must remain intact without cracking or spalling. .. .

Shock Test - The photoreceptor belts, while still in a storage box, are dropped from a 42" height onto a supporting floor. To pass the test the photoreceptor layer must remain intact and the belt substantially undamaged.

Flex Test - Each belt is then mounted on a tri-roller assembly adapted to rotate the belt over each roller. Ambient-temperature is 110 °F and the belts are cycled for 1000 cycles in 30 minutes and then rested for five minutes. This test is' repeated for 30 ,000 cycles · unless the belt fails before the end of 30,000 cycles. To pass the test the belt must complete 30,000 cycles without exhibiting cracks which are visible to the eye.

Each of. belts 1-21," made by Examples, I-XXI are tested - T A B L E Belt No. (Example) Type C 1 I Poly-Poly 4:1 (270°F) P 2 II *Poly-Poly 8:1 (270°F) P 3 III Poly-Poly 8:1 (270°F) P 4 IV Poly-Poly 8:1 (160°F.) P V Poly-Poly 8:1 (160°F) P 6 VI Poly-Poly 8:1 (270°F) P 7 VII Poly-Poly 8:1 (270°F) P 8 VIII Poly-Poly 8:1 (270°F) P 9 IX Poly-Poly 6:1 (270°F) P X Poly-Poly 6:1 (270°F) P 11 XI . Poly-Poly 4:1 (270°F) P 12 XII Poly-Poly 4:1 (270°F) P XIII Poly-Poly 4:1 (270°F) P 14 XIV Polyester (100%) (270°F) • 15 XV Polyester (100% (270°P) 16 XVI Estane "5705 (100% Polyurethane) 270°F F 17 XVII Estane 5705 (100% Polyurethane) 270°F F 18 XVIII Estane 5705 (100% Polyurethane) 270°F F 19 XIX Estane 5705 (100% Polyurethane) 270°F F ' 20 XX Polycarbonate (100%) 270°F 21 XXI Polycarbonate (100%) 270°F F * Poly-Poly represents the weight ratio of polycarbonate to pol represents thousands of cycles.

Where a blank exists for a test for a given belt, it should be understood. that the particular test was not conducted. The temperature listed for each belt is that which is used to dry off the residual solvent. It can be seen from the results set forth in the Table that those belts containing the polycarbonate-polyurethane · interfaces falling within the ratio set forth in the specification, passed all of the three tests without failure. These are belts 1,9,10,11,12 and 13. Belts 2,3,4,5,6,7 and 8, which are ,at the minimum concentration for the polyurethane, exhibit marginal properties in that three of the seve.i belts failed to pass the flex test. Belts 14 and 15, which are made of polyeste resin, illustrate that single organic materials normally do not exhibit outstanding properties, and both •failed the fle test. Belts 16, 17, 18 and 19, which comprise 100 percent polyurethane do not exhibit outstanding properties in that all four belts failed the cold test. In addition, belts 17. and 19 also failed the flex test. Belts 20 and 21, which comprise only the polycarbonate resin which contains about 14 weight percent copper phtbalocyanine, either failed the flex test or the cold test. Polycarbonate alone is not · suitable for use as a barrier layer in that its resistivity 17 of- 10 ohm-cm. is too insulating.

Although specific components and proportions have been stated above in the above description of the preferred embodiments of this invention, other suitable procedures and materials such as those listed above, may also be used with similar results.

Other modifications and ramifications of the present invention would appear to those skilled in the art upon reading the disclosure. These are also intended to be within the

Claims (10)

1. · A xerographic member which comprises an electrically conductive substrate, having thereon an interfacial barrier layer which comprises a polymer blend or mixture of a polycarbonate and polyuretbane resin in a ratio of about 7 to 1 parts by weight polycarbonate to 1 part by weight polyuretbane, the interfacial barrier layer having a thickness of about 0.5 to 3*0 microns, and a photoconduotive insulating layer having a thickness of about 10 to 200 microns overlaying said barrier layer*

2. · A member accordin to Claim , wherein the member is in the form of an endless flexible belt.

3. · A member according to Claim 2, wherein the belt substrate is made of nickel, brass, aluminium or stainless steel.

4. · A member according to any of Claims 1 to 3j wherein said barrier layer contains a phthalocyanine.

5. member according to Claim 4» wherein the phthalocyanine is selected from copper phthalocyanine and metal-free phthalocyanine·

6. A member according to any of Claims 1 to 5, wherein the photoconductor comprises a vitreous alloy of selenium and arsenic.

7. · A member according to Claim 6, wherein the arsenic is present in an amount of about 0*1 to about 0 percent by weight, with the balance substantially selenium. 39655/2 t

8. A member according to Claim 7, wherein the photoconduetive layer comprises about 99*67 weight percent selenium and 0.33 weight percent arsenic*

9. · A member according to any of Claims 6 to 8, wherein the selenium-arsenic photoconductor contains a chlorine dopant.

10. A member according to an of Claims 1 to 5, wherein the photoconduetive layer comprises vitreous selenium* EH:mz