Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-09-22
2001-05-29
Goodrow, John (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S137170
Reexamination Certificate
active
06238836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrostatic image developer which is employed in electrophotographic methods, electrostatic recording methods, and electrostatic printing methods.
This application is based on Japanese Patent Application No. Hei 10-271250 filed in Japan, the content of which is incorporated herein by reference.
2. Description of Related Art
Various electrophotographic methods have been disclosed in, for example, U.S. Pat. No. 2,297,691, Japanese Patent Application, Second Publication No. Sho 42-23910, and Japanese Patent Application, Second Publication No. Sho 43-24748; commonly, an electrostatic latent image is formed on an electrostatic latent image bearing medium such as a photoconductive photosensitive medium or the like by means of charge or light exposure, and then this electrostatic latent image is developed using a toner composition containing a colorant in a binder resin, and the resulting toner image is transferred to a support medium such as transfer paper or the like and fixed, and a visible image is thus formed.
Furthermore, a large number of developing methods are known among electrophotographic methods; these can be broadly classified into two-component developing methods which employ, as a developer, a mixture of toner and a carrier comprising microparticles (20-500 micrometers) of, for example, iron powder, ferrite, nickel, glass, or the like, and single-component developing methods which employ a developer comprising only toner.
Representative examples of the two-component developing methods include the cascade method disclosed in U.S. Pat. No. 2,618,552, and the magnetic brush method disclosed in U.S. Pat. No. 2,874,063. In these methods, functions such as the agitation, conveyance, charging, and the like of the developer are apportioned to the carrier, so that the functional separation between the carrier and the toner is made clear. For this reason, the control of the charge of the toner and the formation of the developer layer are comparatively easy, and the method is capable of high speed, so that it is presently widely employed.
In recent years, in concert with the development of the information society, there have been increasing requirements for improvement in the quality of printed images, increase in recording speed, greater density, long term storage stability, and the like, in a variety of fields such as electrophotography, electrostatic recording, and electrostatic printing, and there has been a great desire for improvements in the characteristics of toner for recording electrostatic latent images on non-printing media. In particular, in toners employed in two-component developers which are used in high speed printing, the strength of the toner with respect to friction with the carrier, and stable fixing behavior in a broad range of temperatures in heat roller fixing methods, are important characteristics, and these characteristics are very frequently dependent on the characteristics of the binder resin which is employed in the toner composition.
Among single-component developing methods, for example, U.S. Pat. No. 4,336,318 discloses a magnetic single-component developing method for conducting development using an electrically insulating magnetic toner. In this method, a charge is introduced into the toner as a result of the frictional charge between the toner particles and the toner-bearing medium and the toner thin film forming member, or as a result of the frictional charge between the toner particles themselves, and an electrostatic latent image is deposited on the photosensitive medium.
This developing method does not employ a carrier, and does not require a device for controlling the mixing ratio between the carrier and the toner, so that it is advantageous in that the developing apparatus has a small size.
In this method, in order to form the magnetic brush of the toner on a metal sleeve, it is necessary to provide the appropriate magnetic characteristics to the toner itself, and for this reason, it is absolutely necessary that magnetic materials such as magnetite, ferrite, and the like be contained in the toner. The amount of these magnetic materials contained varies somewhat depending on the developing conditions and type of materials; however, an amount within a range of 30-60% by weight is common.
Accordingly, the fact that the proportion of binder resin which is contained in the toner powder is small in comparison with that in a two-component developing toner is disadvantageous from the point of view of the fixation properties. As a result of these circumstances, the development of a binder resin which is capable of exhibiting sufficient fixation properties even when the proportion of binder resin contained is low in a magnetic single-component developing method has been keenly desired.
On the other hand, in order to solve the problems in the single-component developing method employing magnetic toner in this manner, a non-magnetic single-component developing method has been proposed which does not require that the toner have magnetic properties. Various apparatuses have been devised employing such a method; in many of these, toner is deposited on a developing sleeve or the like by means of static electric power, and the toner is then conveyed to a latent image surface and developed.
In non-magnetic single-component developing methods, an electrophotographic powdered toner is employed which contains, as required components, a binder resin, a colorant, and a charge control agent; the binder resin employed in this method is, like the binder resin employed in other developing methods, required to have stability with respect to static electricity, durability during continuous printing, and stable fixing behavior over a wide range of temperatures.
The binder resins for toner which have been investigated include, for example, polystyrene, styrene-acrylic ester copolymer, styrene-butadiene copolymer, polyester, epoxy resin, polybutyral, xylene resin, coumarone-indene resin, and the like, and various proposals have been made for the design of such resins depending on the use thereof.
Generally, characteristics which are required in binder resins include a variety of characteristics such as charge, fixation characteristics, and the like; in particular, in binder resins which are employed in toner used in heat roller fixation, an improvement in the fixation properties with respect to the transfer paper, and the anti-offset properties with respect to the heat roll is required. In heat roller fixation, the toner particles which are electrostatically deposited on the transfer paper are fused by means of a passage through the pressurized and heated hot rollers, and are fixed on the transfer paper. When the surface temperature of the rollers is too low at this time, the toner particle layer as a whole is not sufficiently heated, and only that surface which comes into contact with the heated rollers is softened and deposited on the heated rollers. The toner on the transfer paper side is not softened, so that no adhesion force is produced, and as a result, almost all of the toner layer on the transfer paper moves to the fixing roller without being fixed on the transfer paper. This is termed a cold offset.
On the other hand, when the temperature on the roller surface is too high, the viscosity of the molten toner decreases, and in concert with this, the internal cohesive force of the molten toner layer also decreases precipitously and becomes less than the force of adhesion to the heating roller. As a result, the molten toner layer is ruptured and moves both to the transfer paper and to the fixing roller. This is termed the hot offset, and is a cause for the contamination of the heating roller. The toner deposited on the heat roller is retransferred to the transfer paper and causes contamination of parts other than the image, so that the quality of printing declines.
What is meant by anti-offset properties is the ability of the toner at certain temperatures to avoid giving ris
Aoki Norio
Gambayashi Hideki
Kogawara Toshiro
Nakamura Masanobu
Shimane Yoshinori
Armstrong Westerman Hattori McLeland & Naughton LLP
Dainippon Ink & Chemicals Inc.
Goodrow John
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