Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2002-08-07
2004-06-01
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S058700, C430S059600
Reexamination Certificate
active
06743557
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a positively working single-layer organic photoreceptor which can be mounted on high-resolution electrophotographic equipment of liquid (or wet) development system.
BACKGROUND OF THE INVENTION
Electrophotographic image-forming apparatus have been widely spreading chiefly in offices as printers, copiers, facsimiles, etc. for their capability of high speed processing and high image quality.
Broadening of application of the electrophotographic image-forming techniques particularly in the fields of instruments having color output capability and light-duty printers has been of recent interest. Accordingly, electrophotographic image-forming technology realizing high resolution, high gradient and high speed has been being actively researched and developed, and market development of image-forming apparatus reflecting the results of the researches and developments is being undertaken.
Coping with such a market trend, improvements along the researches and developments have been added to a photoreceptor, which may be said to be the heart of this type of image-forming apparatus, particularly an organic photoreceptor.
This kind of organic photoreceptors are roughly divided into layered or dual-layer ones comprising a charge generating layer (CGL) having a charge generation function and a charge transport layer (CTL) having a charge transport function and single-layer ones having a photosensitive layer having both a charge generation function and a charge transport function.
The former type of organic photoreceptors comprise a cylindrical conductive substrate made of aluminum, etc. on which a CGL and a CTL are stacked in this order. Their application is generally limited to negatively charging image-forming apparatus in nature of the organic material. The latter type construction comprises a cylindrical conductive substrate of aluminum, etc. on which a single-ply photosensitive layer is provided and is mainly applied to positively charging image-forming apparatus which, in principle, easily provide high resolution.
When a semiconductor laser having a wavelength of 700 to 800 nm or a light-emitting diode having a wavelength of 600 to 700 nm is used as an exposure light source, both the single-layer and the layered photoreceptors often contain such photoconductive materials as phthalocyanine compounds, particularly metal-free phthalocyanine pigments and titanyl phthalocyanine pigments as a charge generating material (CGM).
Layered photoreceptors of separate function type in which a CTL is superposed on a CGL have been widely put into practical use for their electrophotographic characteristics and durability. However, because the CTL used in this type of photoreceptors chiefly contains a hole transport material (HTM) by material limitation, most of these photoreceptors adopt a negative charging layer configuration fit for negative charging electrophotographic processing.
Compared with positive corona discharge, negative corona discharge used in negative charging image-forming apparatus is less stable and generates more ozone, the powerful oxidizing action of which gives adverse influences to the photoreceptor and the working environment.
While a positive charging system generating less ozone is an effective choice to solve these problems, a positive charging organic photoreceptor required for this system is generally less sensitive than negative charging organic photoreceptors. Therefore, a positive charging organic photoreceptor with high sensitivity has been sought for. Because a positive charging photoreceptor has the charge generating function predominantly in the vicinity of its surface, the distance of electrons' movement to the photoreceptor surface necessary to form an electrostatic latent image is shorter than that in a negative charging photoreceptor. As a result, a positive charging photoreceptor is characterized by high resolution.
Various layer configurations have been proposed for a photosensitive layer of a positive charging photoreceptor, including a layered type having a CGL on a hole transport layer (HTL) and a single-layer type having a layer containing both a charge generating material (CGM) and a charge transport material (CTM). Positive charging layered type photoreceptors are behind negative charging layered type photoreceptors in practical application because they have a thin CGL on their surface and therefore involve the problem of poor durability. Positive charging single-layer photoreceptors tend to be inferior to negative charging layered photoreceptors in electric characteristics such as sensitivity as stated above. This problem is due to because none of the available electron transport materials (ETMs) is equal or superior to available hole transport materials (HTMs) in mobility.
In recent years, a large number of ETMs and electrophotographic photoreceptors using them which deserve attention have been proposed or reported in JP-A-1-206349, JP-A-4-360148, Denshi Shashin Gakkaishi, vol. 30 (1991), pp. 266-273, JP-A-3-290666, JP-A-5-92936, Proceedings of Pan-Pacific Imaging Conference/Japan Hardcopy '98, Jul. 15-17th, 1988, JA Hall, Tokyo, Japan, pp. 207-210, JP-A-9-151157, Proceedings of Japan Hardcopy '97, Jul. 9-11th, 1998, JA Hall, Tokyo, Japan, pp. 21-24, JP-A-5-279582, JP-A-7-179775, Proceedings of Japan Hardcopy '92, July 6-8th, JA Hall, Tokyo Japan, pp. 173-176, and JP-A-10-73937.
Further, single-layer photoreceptors having a combination of the HTM and the ETM disclosed in JP-A-5-150481, JP-A-6-130688, JP-A-9-281728, JP-A-9-281729, and JP-A-10-239874 have been noted for their high sensitivity, and part of them have been put to practical use.
On the other hand, electrophotographic apparatus are classified according to the development system into those for dry development and those for wet (liquid) development. The wet development system uses a liquid developer comprising charged toner particles dispersed in a dielectric medium, usually a petroleum isoparaffinic solvent such as Isopar (available from Exxon Chemicals). A photoreceptor having thereon an electrostatic latent image formed by exposure processing is dipped in or brought into contact with the liquid developer. Whereupon, the toner is electrophoretically adhered to the latent image in an electric field produced between the photoreceptor and a separately provided development electrode thereby to visualize the latent image. The toner used in the liquid development system has a smaller particle size (0.1 to 1 &mgr;m) than that used in the dry development system (3 to 10 &mgr;m) and a larger total surface area and thereby gains greater toner charge. As a result, toner image disturbances hardly occur, and the edge effect is reduced. Thus, the liquid development system is characterized by providing images of high resolution and good gradation reproduction and is particularly suitable for full color image formation.
Since the photoreceptor is dipped in a petroleum paraffinic solvent as mentioned above, the photosensitive layer must be resistant to this solvent. Because organic photoreceptors generally used in dry development are not sufficiently resistant to the solvent of this kind, they would undergo not only considerable deterioration in appearance but elution of the CTM dispersed therein into the solvent, resulting in serious reduction of electrical and optical characteristics. Therefore, inorganic photoconductive substances such as selenium and amorphous silicon have been of frequent use to make a solvent-resistant photoreceptor for use in the liquid development system.
With the recent development of organic photoreceptors, a solvent-resistant photoreceptor comprising a poly(2,6-dimethoxyanthracene-9,10-diol alkanedicarboxylic acid ester) resin has been proposed in JP-A-4-358157. The proposed photoreceptor is a negative charging layered photoreceptor having a solvent-resistant overcoat. The problem of harmful ozone generation due to negative corona discharge is still involved. It has therefore been keenly demanded to develop a positive
Fuji Electric Imaging Device Co. Ltd.
Goodrow John
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