Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1998-04-29
2002-05-07
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S524000, C428S035700, C428S323000
Reexamination Certificate
active
06383639
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charging member for developing an electrostatic latent image which is used to develop an electrostatic latent image formed by an electrostatic recording method in electrophotography, a method for manufacturing the charging member and an electrostatic latent image developer, image forming apparatus and image forming method using the charging member.
2. Description of the Related Art
When conventionally developing an electrostatic latent image formed by an electrostatic recording method, a charging member is used to impart an appropriate amount of positive or negative charge to a toner. Particularly in the case of using a two-component developer, a coated carrier coated with a resin which is the charging member is used. However, the use of the two-component developer causes problems such as a reduction in charge amount at high temperature and humidity, an extreme increase in charge amount at low temperature and humidity, and also gradual deterioration of charge controllability due to contamination of the surface of a carrier by toner components, e.g. a binder resin, charge controlling agent, and external additives. In order to solve such problems, a coated carrier is used in which the carrier is produced by coating a core material (hereinafter called “carrier core” or simply called “core” as the case may be) with such as a fluorine-based polymer, silicone-based polymer, silicone oil, which has a low surface energy, and is superior in environmental stability and surface contamination resistance to conventional materials. In recent years, carriers have been proposed which are coated with a fluorine-based polymer as disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 49-51950: 57-99653 and 60-202451; with a silicone-based polymer as disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 60-19156: 62-121463: 61-110159 and 61-110160; and with a resin containing silicone oil or the like as disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 3-46669: 3-46670: 3-46671 and 5-72814.
These carriers, however, require further improvements. They have insufficient adhesiveness to the carrier core, insufficient wear resistance of a resin coating layer, and show poor environmental stability due to large variations in the initial charge values and the spread of the charge distribution of a toner at high temperature and humidity or at a low temperature and humidity, particularly, due to reduction in charge amount at high temperature and humidity, or an extreme increase in the amount of charge at a low temperature and humidity. Carriers coated with an amide-type polymer are also proposed as described in Japanese Patent Application Laid-Open (JP-A) Nos. 3-217857 and 3-219263, but these carriers still require further improvements in environmental stability and charging properties since amino groups in the resin are used for the crosslinking reaction.
Further, a carrier produced by coating a core material with a phenol resin is used to improve the durability of the carrier. This carrier, however, has insufficient charging properties because a phenol resin with no substituent group is generally used.
On the other hand, as a developing sleeve, a metal sleeve such as aluminum and stainless steel (SUS) or an elastic sleeve such as silicone rubber, NBR and EPDM have been used.
However, control of initial charging of a toner is difficult due to the low charging ability of these developing sleeves themselves, and further, an amount of low charged toner or reversely polarized toner increase with the increase in the number of copies sheets due to the deterioration of the toner and contamination of the developing sleeve arising from long term use, thereby resulting in the easy occurrence of problems such as increase in fog or reduction of image density.
In order to solve these problems, many attempts have been made to increase the toner charge in the initial stage. For instance, the surface of the developing sleeve has been coated with a charge control material exhibiting charge with the polarity opposite to that of the toner. In order to assist the charging properties of a toner with a negative charge, trial methods in which the developing sleeve is coated with a resin exhibiting positive charging properties such as an acrylic resin and nylon resin and the like, or in which the developing sleeve is coated with the above mentioned resins or other resins having non-charging-properties, e.g. a phenol resin, containing a positive charge control agent such as a quaternary ammonium salt and the like, have been tried. Particularly the phenol resin has high mechanical strength, wear resistance and durability and is hence a desirable material to coat the developing sleeve therewith.
However, though these developing sleeves certainly assist in promoting the charging speed of the toner and in increasing the charge amount of the toner in the initial stage, the developing sleeves possess poor environmental stability, and problems such as reductions in image density and generation of ghost images due to excessive charge in the vicinity of the surface thereof and duplication of charged layers arise, especially at low temperature and humidity.
Further, when coating the developing sleeve with a phenol resin containing a positive charge control agent, neither durability nor environmental stability can be sufficiently imparted when only phenol resin is used, even if environmental stability is high.
An attempt to coat the surface of the developing sleeve with a silicone resin containing an aminosilane coupling agent is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 1-147478. The attempt to coat the surface of the developing sleeve with a resin having a functional group containing a nitrogen atom such as an amino group is surely effective for increasing charge. However, reduction in charge amount may occur for extremely long term use even in thus method and thus such problems still has to be solve for obtaining a stable image quality.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the above drawbacks in prior art. An object of the present invention is to provide a highly durable charging member which ensures rapid charging, prevents a reduction in the charge amount at a high temperature and humidity, and prevents a extreme increase in the charge amount at a low temperature and humidity, provides a carrier capable of preventing a developer from deteriorating due to peeling of the coating from the core, and from deteriorating due to spent carrier caused by aging of the toner. The object also includes providing a method for manufacturing the charging member as well as providing an electrostatic latent image developer, an image forming apparatus and an image forming method each using the charging member. The present inventors have conducted extensive studies to solve the above problems, and found that these problems can be solved by using a phenol resin possessing the specific structure, shown below.
According to a first aspect of the present invention, there is provided a charging member comprising a resol-type phenol resin having at least one structural unit selected from the group consisting of structural units represented by the structural formulas (I) to (VIII):
wherein X1 to X6 in the structural formula (I), X1 to X8 in the structural formula (II) or X1 to X10 in the structural formulas (III) to (VIII) represent at least two bonding groups, one or more OH groups, one to four —[(CH
2
)
p
NR
1
R
2
] groups, the remainder represent a hydrogen atom, a halogen atom or an alkyl or an alkoxy group having 1 to 6 carbon atoms, wherein R
1
and R
2
each independently represents an alkyl group having 1 to 10 carbon atoms and p denotes an integer from 0 to 10.
According to another aspect of the present invention, there is provided a developing sleeve comprising a coating layer applied to the outer peripheral surface of a cylinder support, the coating layer composed of
Fuji 'Xerox Co., Ltd.
Hess Bruce H.
Oliff & Berridge, P.C.
Shewareged B.
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