Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-10-20
2002-12-31
Dote, Janis L. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S111350, C430S137130, C525S328800, C525S375000
Reexamination Certificate
active
06500595
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a carrier for use in a developer for developing an electrostatic latent image formed by electrophotography, electrostatic printing, electrostatic recording or the like image forming method. More particularly, the present invention relates to a carrier for use in a two-component developer for developing an electrostatic latent image. In addition, the present invention relates to a method for manufacturing the carrier, and coating liquid used for the method.
2. Discussion of the Background
In electrophotography, an image forming method is typically used in which an electrostatic latent image formed on a photoreceptor or an electrostatic recording material using any one of various known methods such as electrophotography, electrostatic printing, electrostatic recording or the like image forming method is developed with a developer to form a visible image. A two component developer in which a carrier and a toner are mixed and agitated so that the carrier and toner are frictionally charged, is typically used as the developer. In this case, a proper amount of a positive or negative charge is imparted to the toner.
Carriers is broadly classified into coated carriers in which the surface of a core material is covered with a cover layer and a non-coated carrier having a core material with no cover layer. In recent years, various coated carriers have been typically used because of having good durability.
Properties requisite for carriers are as follows:
(1) to stably impart proper charge properties such as proper charge quantity and charge quantity distribution to a toner: and
(2) to stably maintain good charge properties for a long period of time:
In order to have such requisite properties, it is needed for the carriers to have proper electric properties such as electric resistance. In addition, it is needed for the carriers to have good resistance to changes of environmental conditions such as temperature and humidity, and good resistance to impact and abrasion to stably maintain good charge imparting properties for a long period of time. In attempting to obtain such a good coated carrier, various coated carriers have been proposed.
As to the developing method, methods using a magnetic brush are typically used. Magnetic brush developing methods using a two component developer tend to cause the following problems:
(1) image density decreases due to deterioration of the charge properties of the developer;
(2) images having fogging are produced;
(3) unclear images and/or uneven images are produced because the images include carrier particles (namely the carrier in the developer adheres to an image bearing member as well as the toner in the developer); and
(4) the quantity of the carrier decreases due to the carrier adhesion;
The charge properties of a developer including a coated carrier and a toner tend to deteriorate when one or more constituents of the toner in the developer adhere to the cover layer of the coated carrier (this problem is hereinafter referred to as a spent toner problem), or when the cover layer of the coated carrier is peeled therefrom due to stresses which are caused when mixed,.rubbed and fed in a developing unit together with the toner.
In addition, when a coated carrier having an uneven cover layer is used for a developer, the resultant produced images tend to have fogging particularly when a supplemental toner is added to the developer or a toner concentration of the developer is high, or when environmental conditions such as temperature and humidity change. In particular, when one or more constituents of the toner in the developer adheres to the cover layer of the coated carrier, and thereby the surface of the carrier is contaminated (i.e., spent toner problem), the charge properties of the developer deteriorate.
Therefore, in order to develop a developer having a long life, a carrier, which has a proper structure and/or includes a proper material so as not to cause the spent toner problem or so as not to be influenced by the spent toner problem, is needed.
In attempting to avoid such deterioration of charge properties of a developer including a coated carrier and a toner, the following methods have been proposed:
(1) the hardness of the resin layer formed on the carrier is enhanced such that the resin layer so that the cover layer does not peel the carrier surface;
(2) the surface energy of the resin formed on the carrier in the developer is decreased to avoid adhesion of the toner constituents to the carrier surface (i.e., to avoid the spent toner problem); and
(3) a combination of the methods (1) and (2).
With respect to the method (1), Japanese Laid-Open Patent Publication No. 62-262057 discloses a carrier in which an iron oxide powder serving as a core material is coated with a resin composition which is produced by crosslinking a copolymer having a carboxyl group and/or a hydroxyl group and a melamine resin, to improve the life of the carrier and to improve the image density. Japanese Laid-Open Patent Publication No. 62-262057 discloses a carrier in which a core material is coated with a resin composition which is produced by crosslinking a thermoplastic resin having a hydroxy group which is not reacted and an alkoxylated melamine resin, to improve fluidity, resistance to high humidity and toner releasability of the resultant carrier. In addition, Japanese Laid-Open Patent Publication No. 2-79862 discloses a carrier in which a core material is coated with a resin composition which is produced by crosslinking an acrylic resin and a melamine resin, to improve durability and weather resistance of the resultant carrier. Further, Japanese Laid-Open Patent Publication No. 5-216281 discloses a carrier in which a core material is coated with an acrylic resin composition which is crosslinked using a melamine formaldehyde resin, to improve durability, heat resistance and weather resistance of the resultant carrier.
However, carriers including a melamine resin have a drawback such that the charge quantity of the carrier decreases under high temperature and high humidity conditions.
With respect to the method (2), Japanese Laid-Open Patent Publications Nos. 60-186844 and 64-13560 have disclosed carriers which are coated with a silicone resin or a fluorine-containing resin, to avoid the spent toner problem. When a silicone resin is used, the silicone resin should be sufficiently crosslinked to avoid the spent toner problem. The sufficiently-crosslinked silicone resin is brittle, and therefore the resin film tends to peel from the coated carrier. If a silicone resin is properly crosslinked, the cover layer is easily abraded, resulting in occurrence of the spent toner problem and deterioration of the charge properties of the carrier when these carriers are used for a long period of time.
Japanese Laid-Open Patent Publication No. 60-201360 discloses a carrier in which a core material is coated with a resin composition in which 100 parts by weight of a resin to be coated is mixed with 0.1 to 20 parts by weight of guanamine, a guanamine derivative, or a guanamine condensation product, to impart good charge imparting ability to the resultant carrier. However, the carrier cannot maintain good charge properties for a long period of time.
In attempting to improve these drawbacks, Japanese Laid-Open Patent Publication No. 8-6307 discloses a carrier which is coated with a thermosetting resin which is produced by crosslinking a guanamine resin and another resin having a functional group which can react with the guanamine resin, wherein the concentration of the guanamine resin is 40% or greater. However, the resistance of the carrier to the spent toner problem is not satisfactory although the resistance of the carrier to changes of environmental conditions and the hardness of the cover layer are good.
Because of these reasons, a need exists for a carrier for an electrophotographic developer, which can maintain good charge imparting ability without causing the spent toner problem even when used
Asahina Yasuo
Mochizuki Satoshi
Suzuki Kohsuke
Suzuki Tomomi
Dote Janis L.
Ricoh & Company, Ltd.
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