EP0919877B1

EP0919877B1 - Process for producing electrophotographic photosensitive member

Info

Publication number: EP0919877B1
Application number: EP98309737A
Authority: EP
Inventors: Tomohiro Kimura; Yoichi Kawamorita; Shintetsu Go; Hideaki Nagasaka
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1997-12-01
Filing date: 1998-11-27
Publication date: 2004-02-18
Anticipated expiration: 2018-11-27
Also published as: DE69821728D1; CN1241730A; DE69821728T2; KR19990062682A; CN1222833C; KR100312951B1; EP0919877A1

Description

Electrophotographic photosensitive members are constituted basically of a photosensitive layer on which a latent image is formed by electrostatic charging and exposure to light and a substrate on which the photosensitive layer is provided.
Meanwhile, electrophotographic photosensitive members are required to have sensitivities, electric properties and optical characteristics in accordance with electrophotographic processes applied.
They are also required to have an environmental stability in any environment of from low temperature/ low humidity to high temperature/high humidity which is good enough to well exhibit their performances.
Faulty images are exemplified typically by image lines, black spots in white background areas, white spots in black background areas, background fog in white background areas, and also interference fringes caused by factors such as surface shape of substrates and uneven layer thickness of photosensitive members in the case of apparatus such as digital copying machines and laser beam printers in which exposure is effected using a light source having a single wavelength. Accordingly, in the manufacture of photosensitive members, some countermeasures must be taken in advance so that these faulty images do not occur.
As a factor having a great influence when such faulty images occur, there can be given the surface state of a substrate.
Substrates having not been treated at all after molding usually do not necessarily have any surface state as it is which is most suited for photosensitive members. Hence, problems caused by the surface state may occur in many instances.
To solve such problems, methods of approach have hitherto been proposed, as exemplified by a method in which the surface of an aluminium substrate is subjected to chromating to form a chromated chemical conversion coating, as disclosed in Japanese Patent Application Laid-Open Nos. 54-12733 and 57-62056; a method in which a boehmite coating is formed on the surface of an aluminium substrate, as disclosed in Japanese Patent Application Laid-Open Nos. 58-14841 and 64-29852; and a method in which the surface of an aluminium substrate is oxidized forcedly by high-temperature treatment to form an oxidized film, as disclosed in Japanese Patent Application Laid-Open No. 57-29051.
With regard to, e.g., the method of chromating, substrates having a certain degree of performance can be obtained. However, since the treating solutions contain chromium, it is very difficult to dispose of waste liquor, and also this is not preferable in view of environmental safety.
With regard to the boehmite treatment, the crystal state of the surface can not be said to be suited for substrates of electrophotographic photosensitive members. It can be effective to a certain degree with regard to electrophotographic performance, but, with regard to images, no satisfactory image quality has been achieved because the surface structure and shape are unsuited. Thus, under existing circumstances, those satisfying all performances have not been available.
What is aimed by the above surface treatment is that the film formed on the substrate surface prevents any non-uniformity from being caused in electrophotographic performances and images by electric charges injected locally from the substrate to the photosensitive layer.
As a method of preventing such local charge injection so as to cause no faulty images, a method is available in which the surface of an aluminium substrate is subjected to anodizing to provide a layer of aluminium oxide (e.g. Japanese Patent Application Laid-Open Nos. 2-7070 and 5-34964).
This method is a good method in order to attain such an aim. However, in order to form the layer uniformly without causing any uneven layer thickness on the substrate surface, it must be formed in a certain larger thickness, and a thickness of about 5 or 6 µm or more under usual conditions for its formation. Hence, the layer must be formed in a much larger thickness than the thickness actually required as a charge injection blocking layer, resulting in an increase in cost.
Accordingly, it is here intended to provide an electrophotographic photosensitive member having good electrophotographic properties, that causes no faulty images in any environment of from low temperature/low humidity to high temperature/high humidity, and which also may less cause potential variations. In particular, it is intended to provide a process by which such an electrophotographic photosensitive member can be produced with ease, at a low cast and stably.
As a result of studies made in order to solve the problems discussed above, the inventors have discovered that it is a very effective means to form on the substrate an insoluble coating or film with specific composition by applying specific chemical conversion treatment to the substrate surface, i.e. by chemical reaction between an aluminium substrate used in the electrophotographic photosensitive member and an aqueous acid solution containing a specific metal element, without use of any electrical external force. This is effective in view of the advantages that an electrophotographic photosensitive member having excellent properties can be obtained, and the cost and environment can be made very less adversely affected, and further the production apparatus can be made simpler than in the anodizing.
The present invention provides a process of producing an electrophotographic photosensitive member, comprising the steps of:
subjecting, without applying any electrical external force, an aluminium substrate to chemical conversion with an aqueous acid solution containing a salt of titanium or a salt of zirconium; and
forming a photosensitive layer thereon.
In the accompanying drawings:
Fig. 1 schematically illustrates an example of the construction of an electrophotographic apparatus having a process cartridge having an electrophotographic photosensitive member; and
Fig. 2 is a graph showing compositional ratio of elements constituting the surface portion of an aluminium substrate subjected to chemical conversion.
An electrophotographic photosensitive member produced by the process of the present invention has an aluminium substrate and a photosensitive layer provided thereon, and the substrate contains aluminium, oxygen and titanium, or aluminium, oxygen and zirconium, at its surface portion underlying the photosensitive layer.
The above electrophotographic photosensitive member can be obtained by subjecting the aluminum substrate to chemical conversion with an aqueous acid solution containing a salt of titanium or a salt of zirconium, and thereafter forming the photosensitive layer.
The chemical conversion referred to in the present invention is treatment where a substrate is brought into contact with a specific solution to form on the substrate a coating having specific composition, without applying any electrical external force as in anodizing.
Metals of the metal salts used in the present invention are titanium and zirconium. The aluminium substrate having a chemical conversion coating of the present invention in which any one of titanium and zirconium is present together with aluminium and oxygen has very good properties as a substrate for electrophotographic photosensitive members.
The salt of titanium and the salt of zirconium may preferably be fluorine compounds. The salt of titanium may include titanium hydrofluoric acid, a sodium salt, potassium salt or ammonium salt thereof, and titanium sulfate. The salt of zirconium may include zirconium potassium fluoride and zirconium sulfate.
The aqueous acid solution may preferably contain the metal salt in a concentration of from 0.01 to 2 g/liter as weight of metal.
The aqueous acid solution may also preferably contain fluorine ions in a concentration ranging from 0 to 10 g/liter. Within this range, etching reaction may appropriately take place on the substrate surface and a uniform coating can be formed with ease.
The aqueous acid solution of the present invention may preferably have a pH adjusted within the range of from 1.0 to 5.5 using ammonia or sodium hydroxide. If it has a pH below 1.0, the etching reaction may take place violently to make it difficult to obtain a good coating. If it has a pH above 5.5, the coating may be formed at so low a rate that only a thin coating can be obtained, making it difficult to obtain a remarkable effect of the present invention.
In the present invention, in view of an advantage that the reaction takes place stably, the aqueous acid solution may preferably be heated to 30 to 90°C when used.
As methods for bringing the substrate into contact with the aqueous acid solution, either method of dipping and spraying may be used. Dipping is preferred in view of production efficiency.
The substrate having been subjected to the chemical conversion is used after it is washed and dried.
The composition of the substrate surface portion in the present invention is measured by the Auger electron ray spectroscopy, and is defined to be the one within the range of from the uppermost surface to a depth of 5 nm (50 Å).
In the present invention, the titanium or zirconium may be contained in an amount ranging from 4 to 100 atom%.
The chemical conversion coating containing titanium or zirconium, formed on the substrate surface may preferably have a total layer thickness of 1 pm or smaller, and more preferably 5 nm (50 Å) or larger. If the coating is in a layer thickness larger than 1 µm, electric charges can escape with difficulty in excess to tend to cause an increase in residual potential or cause ghost. If it is in a layer thickness smaller than 5 nm (50 Å) (5 × 10^-3 µm), remarkable effects of the present invention may be obtained with difficulty.
In the present invention, in view of corrosion resistance and adhesion of coating films, the aqueous acid solution may preferably further contain a phosphoric acid, a phosphate, a tannin or a tannic acid.
The phosphoric acid and phosphate may include phosphoric acid or a sodium, potassium or ammonium salt thereof, and pyrophosphoric acid, tripolyphosphoric acid, hexametaphosphoric acid or a sodium salt or potassium salt thereof. Also, organic phosphoric acid compounds may be used as exemplified by phytic acid, nitrodiethanolethylene phosphonic acid, 2-hydroxyethylmethacryl-1-acid phosphonic acid, 2-ethylhexyl acid phosphonic acid and ethane-1-hydroxy-1,1-diphosphonic acid.
The phosphoric acid or phosphate in the aqueous acid solution may preferably be in a concentration ranging from 0.05 to 50 g/liter in terms of phosphate ions. Within this range, an especially uniform and good chemical conversion coating can be formed and also the treating solution can have an especially good stability.
The tannin or tannic acid may include quebracho tannin, depside tannin, Chinese tannic acid, Turkish tannic acid, hamamelitannic acid, chebulinic acid, sumac tannin, Chinese gallotannin and ellagitannin.
The tannin or tannic acid in the aqueous acid solution may preferably be in a concentration ranging from 0.1 to 10 g/liter.
In the present invention, the aqueous acid solution may preferably contain hydrofluoric acid, borofluoric acid, hydrosilicofluoric acid or a salt of any of these. These compounds have the function to etch the substrate surface when the substrate is subjected to chemical conversion, and hence a very uniform chemical conversion coating can be formed.
From the foregoing, it is preferable for the chemical conversion coating of the present invention to contain phosphorus and fluorine.
There are no particular limitations on the aluminium substrate so long as it comprises aluminium, which may include pure aluminium and aluminium alloys such as Al-Mn, Al-Mg, Al-Cu, Al-Si, Al-Mg-Si and Al-Cu-Si types. Stated more specifically, aluminium of 6000 types such as JIS A6063 and aluminium of 3000 types such as JIS A3003 may be used. There are also no particular limitations on its shape. It may preferably be in the form of a drum.
The photosensitive layer of the electrophotographic photosensitive member used in the present invention will be described below.
Constitution of the photosensitive layer in the present invention is grouped roughly into a single-layer type in which a charge-generating material and a charge-transporting material are contained in the same layer and a multi-layer type having a charge generation layer containing a charge-generating material and a charge transport layer containing a charge-transporting material.
An electrophotographic photosensitive member having the multi-layer type photosensitive layer will be described below.
The photosensitive layer may be constituted in the manner that the charge generation layer and the charge transport layer are layered on the substrate in this order or conversely the charge transport layer and the charge generation layer are layered in this order.
The charge transport layer is formed by coating a coating solution prepared by dissolving a charge-transporting material such as a polycyclic aromatic compound having a biphenylene, anthracene, pyrene or phenanthrene structure, a nitrogen-containing cyclic compound such as indole, carbazole, oxadiazole or pyrazoline, a hydrazone compound or a styryl compound in a resin having film forming properties, followed by drying.
The resin having film forming properties may include polyesters, polycarbonates, polystyrenes, polymethacrylates and polyarylates.
The charge transport layer may preferably have a layer thickness of from 5 to 40 µm, and preferably from 10 to 30 µm.
The charge generation layer is formed by coating a dispersion prepared by dispersing a charge-generating material such as an azo pigment such as Sudan Red or Dyan Blue, a quinone pigment such as pyrene, quinone or anthanthrone, a quinocyanine pigment, a perylene pigment, an indigo pigment such as indigo or thioindigo or a phthalocyanine pigment in a resin such as polyvinyl butyral, polystyrene, or polyvinyl acetate or acrylate, followed by drying, or formed by vacuum deposition of the above pigment.
The charge generation layer may preferably have a layer thickness of 5 µm or smaller, and more preferably from 0.1 to 3 µm.
The single-layer type photosensitive layer is formed by coating a coating fluid prepared by dispersing and dissolving the charge-generating material and the charge-transporting material in the resin, followed by drying.
Such a photosensitive layer may preferably have a layer thickness of from 5 to 40 µm, and more preferably from 10 to 30 µm.
In the present invention, a subbing layer having the function as a barrier and the function of adhesion may be provided between the support and the photosensitive layer. The subbing layer is formed by coating a solution prepared by dissolving casein, polyvinyl alcohol, nitro cellulose, ethylene-acrylic acid copolymer, alcohol-soluble polyamide, polyurethane or gelatin, followed by drying.
The subbing layer may preferably have a layer thickness of from 0.1 to 3 µm.
In the present invention, a protective layer may be provided on the photosensitive layer.
The protective layer may be constituted of a material including polyester, polyacrylate, polyethylene, polystyrene, polybutadiene, polycarbonate, polyamide, polypropylene, polyimide, polyamide-imide, polysulfone, polyacrylic ether, polyacetal, phenol, acrylic, silicone, epoxy, urea, allyl, alkyd, butyral, phenoxy, phosphazene, acryl-modified epoxy, acryl-modified urethane and acryl-modified polyester resins.
The protective layer may preferably have a layer thickness of from 0.2 to 10 µm.
In the above respective layers, a lubricant such as polytetrafluoroethylene, polyvinylidene fluoride, fluorine type graft polymer, silicone type graft polymer, fluorine type block polymer, silicone type block polymer or silicone oil may be incorporated in order to improve cleaning performance and wear resistance.
Additives such as an antioxidant may further be added for the purpose of improving weatherability.
In the protective layer, conductive powder such as conductive tin oxide or conductive titanium oxide may be dispersed for the purpose of resistance control.
Fig. 1 schematically illustrates the construction of an electrophotographic apparatus having a process cartridge having an electrophotographic photosensitive member.
In Fig. 1, reference numeral 1 denotes a drum type electrophotographic photosensitive member which is rotatingly driven around an axis 2 in the direction of an arrow at a given peripheral speed. The photosensitive member 1 is uniformly electrostatically charged on its periphery to a positive or negative, given potential through a primary charging means 3. The photosensitive member thus charged is then exposed to light 4 emitted from an exposure means (not shown) for slit exposure or laser beam scanning exposure. In this way, electrostatic latent images are formed successively on the periphery of the photosensitive member 1.
The electrostatic latent images thus formed are subsequently developed by toner by the operation of a developing means 5. The toner-developed images formed by development are then transferred successively by the operation of a transfer means 6, to the surface of a transfer medium 7 fed from a paper feed section (not shown) to the part between the photosensitive member 1 and the transfer means 6 in the manner synchronized with the rotation of the photosensitive member 1.
The transfer medium 7 which has received the images is separated from the surface of the photosensitive member, is led through an image fixing means 8, where the images are fixed, and is then printed out of the apparatus as a copied material (a copy).
The surface of the photosensitive member 1 from which images have been transferred is brought to removal of the toner remaining after the transfer, through a cleaning means 9. Thus, the photosensitive member is cleaned on its surface, further subjected to charge elimination by pre-exposure light 10 emitted from a pre-exposure means (not shown), and then repeatedly used for the formation of images. When the primary charging means 3 is a contact charging means making use of a charging roller, the pre-exposure is not necessarily required.
The apparatus may be constituted of a combination of plural components integrally joined as a process cartridge from among the constituents such as the above electrophotographic photosensitive member 1, primary charging means 3, developing means 5 and cleaning means 9 so that the process cartridge is detachably mountable to the body of the electrophotographic apparatus such as a copying machine or a laser beam printer. For example, at least one of the primary charging means 3, the developing means 5 and the cleaning means 9 may be integrally supported in a cartridge together with the photosensitive member 1 to form a process cartridge 11 that is detachably mountable to the body of the apparatus through a guide means such as a rail 12 provided in the body of the apparatus.
In the case when the electrophotographic apparatus is used as a copying machine or a printer, the exposure light 4 is light reflected from, or transmitted through, an original, or light irradiated by the scanning of a laser beam, the driving of an LED array or the driving of a liquid crystal shutter array according to signals obtained by reading an original through a sensor and converting the information into signals.
The electrophotographic photosensitive member may be not only applied in electrophotographic copying machines, but also widely applied in the fields where electrophotography is applied, e.g., laser beam printers, CRT printers, LED printers, liquid-crystal printers and laser beam engravers.
The present invention will be described below in greater detail by giving Examples.

Example 1

An aluminium cylinder of 29.92 mm in outer diameter, 28.5 mm in inner diameter and 254 mm in length was prepared.
An aqueous acid solution (trade name: PALCOAT 3753, available from Nihon Parkerizing Co., Ltd.; pH: 3.8) containing phytic acid as an organic phosphoric acid and titanium hydrofluoric acid and titanium ammonium fluoride as salts of metals was kept at a temperature of 40°C, and the abovealuminium cylinder was immersed in this aqueous acid solution to make chemical conversion for 1 minute, which was then washed with pure water, followed by air-drying. The chemical conversion coating thus formed was in a layer thickness of 20 nm (200 Å).
Next, 4 parts by weight of oxytitanium phthalocyanine, 2 parts by weight of polyvinyl butyral resin (trade name: BX-1, available from Sekisui Chemical Co. Ltd.) and 34 parts by weight of cyclohexanone were dispersed for 8 hours by means of a sand mill, followed by addition of 60 parts by weight of tetrahydrofuran to make up a charge generation layer coating dispersion.
This dispersion was dip-coated on the aluminium cylinder having been subjected to chemical conversion, followed by drying with heating at 95°C for 10 minutes to form a charge generation layer with a layer thickness of 0.2 µm.
Next, a solution prepared by dissolving 50 parts by weight of a triarylamine compound represented by the following formula and 50 parts by weight of bisphenol-Z polycarbonate resin in 400 parts by weight of monochlorobenzene was dip-coated on the charge generation layer, followed by drying with heating at 110°C for 1 hour to form a charge transport layer with a layer thickness of 20 µm.

- Evaluation -

The surface portion of the substrate having been subjected to chemical conversion, washing and drying was examined by elementary analysis using a scanning Auger electron ray spectroscope while making argon ion etching from the uppermost surface in the depth direction of the substrate. As the result, aluminum, titanium and oxygen were detected as main constituent elements. Their graphic representation is given in Fig. 2. In the present Example, the relationship between depth and sputter time is 11 nm/min (110 Å/min) in terms of SiO₂. This value is appropriately changeable.
The compositional ratio of elements at the uppermost surface of the substrate and a depth of 5 nm (50 Å) from the uppermost surface is shown in Table 1 as elementary percentage regarding the amount of aluminium element as 100.
As can be seen from these results, the chemical conversion coating on the substrate surface comprises an oxidized aluminium coating in which titanium has been incorporated. As the result of analysis, nitrogen, fluorine, phosphorus and so forth are detected as other elements contained. These elements are considered to be those originally contained in the phosphoric acid and fluorine compound in the aqueous acid solution used when the chemical conversion is made, and incorporated in the chemical conversion coating.
Next, the electrophotographic photosensitive member obtained was left for 48 hours in environment of normal temperature/normal humidity (23°C, 60%RH), high temperature/high humidity (32.5°C, 85%RH) or low temperature/low humidity (15°C, 10%RH), and thereafter set in a commercially available laser beam printer of a reverse development system to reproduce solid white images in each environment.
The state of background fog in the solid white images thus formed was visually evaluated. The results are shown in Table 2.
Simultaneously, values of dark-area potential and light-area potential were measured in each environment. The results are shown in Table 2.

Example 2

An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that a solution (trade name: PALCOAT 3756, available from Nihon Parkerizing Co., Ltd.; pH: 3.2) containing tannic acid, an ammonium salt and zirconium fluoride and zirconium sulfate as salts of metals was used as the aqueous acid solution for chemical conversion.
Evaluation was made similarly. The results are shown in Tables 1 and 2. The chemical conversion coating was in a layer thickness of 15 nm (50 Å).

Example 3

An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that a solution (trade name: PALCOAT 3753T, available from Nihon Parkerizing Co., Ltd.; pH: 3.2) containing phytic acid and containing zirconium hydrofluoric acid and zirconium ammonium fluoride as salts of metals was used as the aqueous acid solution for chemical conversion. Evaluation was made similarly. The results are shown in Tables 1 and 2. The chemical conversion coating was in a layer thickness of 18 nm (180 Å).

Example 4

An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that a solution (trade name: ALUSURF 301N-1, available from Nihon Paint Co., Ltd.; pH: 4.0) containing phosphoric acid and containing zirconium fluoride and a sodium salt of zirconium hydrofluoric acid as salts of metals was used as the aqueous acid solution for chemical conversion. Evaluation was made similarly. The results are shown in Tables 1 and 2. The chemical conversion coating was in a layer thickness of 30 nm (300 Å).

Comparative Example 1

An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that the chemical conversion was not carried out. Evaluation was made similarly. The results are shown in Table 2.

Comparative Example 2

Ammonia water with a concentration of 0.3% was prepared, and this was heated to 95°C.
In this heated ammonia water, the same aluminium cylinder as that used in Example 1 and having not been subjected to chemical conversion was immersed to make surface treatment, followed by drying to form a boehmite coating on the cylinder surface.
An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that this aluminium cylinder was used instead. Evaluation was made similarly. The results are shown in Table 2.

Comparative Example 3

Chemical conversion was carried out by immersing an aluminium cylinder for 1 minute in, in place of the aqueous acid solution of the present invention, a chromium phosphate type solution for chemical conversion (trade name: ALUCHROME 3701, available from Nihon Parkerizing Co., Ltd.) kept at 30°C, containing neither titanium nor zirconium, to form a chromate type chemical conversion coating on the surface of the cylinder.
An electrophotographic photosensitive member was produced in the same manner as in Example 1 except that this aluminium cylinder was used instead. Evaluation was made similarly. The results are shown in Table 2.

Claims

A process of producing an electrophotographic photosensitive member, comprising the steps of:

subjecting, without applying any electrical external force, an aluminium substrate to chemical conversion with an aqueous acid solution containing a salt of titanium or a salt of zirconium; and

forming a photosensitive layer thereon.
The process of claim 1, wherein the salt of titanium and the salt of zirconium are fluorine compounds.
The process of claim 1 or claim 2, wherein said aqueous acid solution has a pH of from 1.0 to 5.5.
The process of claim 1, 2 or 3, wherein said aqueous acid solution has a temperature of from 30°C to 90°C.
The process of any of claims 1 to 4, wherein said aqueous acid solution further contains at least one compound selected from the group consisting of a phosphoric acid, a phosphate, a tannin and a tannic acid.
The process of any of claims 1 to 5, wherein said aqueous acid solution further contains at lest one compound selected from the group consisting of hydrofluoric acid, borofluoric acid, hydrosilicofluroic acid and a salt of any of these.