Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
1999-06-03
2001-05-01
Martin, Roland (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S059500, C430S083000, C540S141000
Reexamination Certificate
active
06225015
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a oxytitanium phthalocyanine (to be abbreviated as “TiOPc” hereinafter) and a process for the production thereof, and it also relates to an electrophotographic photoreceptor to which it is applied.
PRIOR ART
In recent years, electrophotography is not only used in the field of copying machines, but also it now has come into wide use in the fields of a printing plate, a slide film and a microfilm where photography has been conventionally used. Further, studies are being made on the application of electrophotography to a high-speed printer using a laser, an LED or a CRT as a light source. In recent years, studies have also began concerning the application of photoconductive materials to uses other than the electrophotographic photoreceptor, such as electrostatic recording elements, sensor materials and an EL devices. A photoconductive material and an electrophotographic photoreceptor using the same are therefore being demanded to satisfy higher levels in wider fields of applications. For an electrophotographic photoreceptor, inorganic photoconductive materials such as selenium, cadmium sulfide, zinc oxide and silicon have been known and widely studied to put them into practical use. These inorganic materials have various advantages and at the same time have various disadvantages. For example, selenium has defects that production conditions with it are severe and that it is easily crystallized due to heat or mechanical impact. Cadmium sulfide and zinc oxide are poor in humidity resistance and durability. It is pointed out that silicon has poor chargeability and difficulty of production. Further, selenium and cadmium sulfide also involve toxicity problems.
In contrast, organic photoconductive materials have advantages that they are excellent in film-formability and flexibility, that they are light in weight and excellent in transparency and that they are feasible for designing a photoreceptor to light in a wide wavelength region according to a proper sensitizing method. For these reasons, practical use thereof is gradually attracting attention.
Meanwhile, a photoreceptor for use in electrophotography is required to satisfy the following general basic properties. That is, (1) it is to have a high chargeability to corona discharge in a dark place, (2) it is to be free of much leakage of an obtained charge in a dark place (small dark decay), (3) it is to readily dissipate a charge on irradiation with light (small light decay), and (4) it is to be free of residual charge after irradiation with light.
However, as organic photoconductive materials, photoconductive polymers including polyvinylcarbazole have been so far studied in various ways, while these are not necessarily satisfactory in film formability, flexibility and adhesion and cannot be said to fully have the above basic properties as a photoreceptor.
Organic low-molecular-weight photoconductive compounds can give a photoreceptor excellent in film formability, adhesion and mechanical properties such as flexibility by selecting a binder for forming the photoreceptor, while it is difficult to find out a compound suitable for retaining high-sensitivity properties.
For overcoming the above problems, there have been developed organic photoreceptors having higher sensitivity properties imparted by using different materials which separately have charge generation function and a charge transportation function. These photoreceptors called a function-separation type has a feature in that materials suitable for individual functions can be selected from a broad range of materials, and a photoreceptor having predetermined performances can be easily produced, so that studies have been extensively under way.
Of these materials, various materials such as phthalocyanine pigments, squarilium dyes, azo pigments and perylene pigments have been studied as a material having the role of charge generation. Above all, azo pigments have been studied in various ways and practically have been in wide use since they can have diversified molecular structures and can be expected to show a high charge generation efficiency. However, it has not yet been clear what relationships are there between the molecular structure and the charge generation efficiency of the azo pigments. Under the circumstances, a huge volume of studies have been made on syntheses thereof to find out optimum structures, while there have not yet been obtained any azo pigments which satisfy demands of the above basic properties and high durability as a photoreceptor.
In recent years, further, laser beam printers having advantages of a high speed, a high-quality image and non-impact properties by using laser beam in place of conventional white light are widely used together with advanced data processing systems, and it is accordingly desired to develop materials which can comply with requirements therefor. Of laser beams, a semiconductor laser, which has been and is increasingly applied to a compact disc, an optical disc, etc., in recent years and has been remarkably technically developed, is actively applied to the field of printers as a compact and highly reliable light source material. In this case, the wavelength of the light source is approximately 780 nm, and it is therefore intensely desired to develop a photoreceptor having high-sensitivity properties to light having a long wavelength of approximately 780 nm. Under the circumstances, developments of photoreceptors using phthalocyanines having light absorption in a near infrared region are actively under way.
Not only phthalocyanines differ in absorption spectrum, photoconductivity, etc., depending upon central metals, but also phthalocyanines having an identical central metal differ in the above various properties depending upon crystal forms, and it is reported that phthalocyanines having specific crystal forms are selected for an electrophotographic photoreceptor.
For example, concerning TiOPc, JP-A-61-217050 discloses an &agr;-form TiOPc having main diffraction peaks at Bragg angles of 7.6°, 10.2°, 22.3°, 25.3° and 28.6° in X-ray diffraction spectrum, and JP-A-62-67094 discloses a &bgr;-form TiOPc having main diffraction peaks at Bragg angles of 9.3°, 10.6°, 13.2°, 15.1°, 15.7°, 16.1°, 20.8°, 23.3°, 26.3° and 27.1°. However, these phthalocyanines fail to fully satisfy required high properties.
JP-A-1-17066 discloses a Y-form TiOPc which has diffraction peaks at 9.5°, 9.7°, 11.7°, 15.0°, 23.5°, 24.1° and 27.3° and exhibits relatively good sensitivity. For the synthesis in the above crystal form, JP-A-63-20365 discloses a method in which an aqueous suspension of &agr;-form TiOPc treated by acid pasting is subjected to crystal transformation in a chlorinated benzene solvent. JP-A-3-35245 discloses a method in which an aqueous suspension of amorphous TiOPc is subjected to crystal transformation in the presence of o-dichlorobenzene or 1,2-dichloroethane. In view of environmental pollution problems in recent years, such as the incidence of dioxin, the use of the chlorinated benzene is undesirable.
As a production method using no halogen substance, JP-A-3-35064 discloses a crystal transformation method in the presence of cyclohexanone, tetrahdyrofuran or cyclohexanol, and JP-A-3-134065 discloses a crystal transformation method in the presence of an aromatic hydrocarbon such as toluene or xylene or monoterpene solvent such as terpinene, myrcene or limonene. However, TiOPc obtained by any one of these methods shows a low sensitivity.
Further, an electrophotographic photoreceptor formed of any one of the above phthalocyanines has a defect that the chargeability thereof is poor at the step of development after the charging procedure in the first round of an image forming process is finished and the chargeability is stabilized only in the second round and thereafter. This phenomenon is related to a standing period of time after the process of image formation such as charging and exposure. There is observed a tendency that the chargeability in the first round come to be poor with an incre
Horiuchi Tamotsu
Okaji Makoto
Sato Michihiko
Suruga Kazuyuki
Martin Roland
Mitsubishi Paper Mills Ltd.
Nixon & Vanderhye
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