Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2000-10-25
2003-10-21
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...
C430S109300, C430S110300, C430S111400, C430S124300, C430S125320
Reexamination Certificate
active
06635398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a dry toner used in recording processes that utilize electrophotography, electrostatic recording, magnetic recording and toner-jet recording, and an image forming method which employs such a dry toner. More particularly, the present invention relates to a toner used in image-forming apparatus utilizable in copying machines, printers, facsimile machines and plotters, and an image forming method which employs such a toner. The present invention also provides a process for producing the toner.
2. Related Background Art
A number of methods are conventionally known as electrophotography as disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publications Nos. 42-23910 and 43-24748 and so forth. In general, copied images are obtained by forming an electrostatic latent image on a photosensitive member by utilizing a photoconductive material and by various means, subsequently developing the electrostatic latent image by the use of a dry toner (hereinafter call to “a toner”) to form a toner image, transferring the toner image to a transfer medium such as paper or film, followed by fixing by the action of heat, pressure, heat-and-pressure, or solvent vapor.
As methods by which the electrostatic latent image is rendered visible, developing methods such as cascade development, magnetic brush development and pressure development are known in the art. Another method is also known in which, using a magnetic toner and using a rotary sleeve provided with a magnet at the core, the magnetic toner is caused to fly across the sleeve and a photosensitive member by the aid of an electric field.
One-component development systems require no carrier such as glass beads or iron powder required in two-component development systems, and hence can make developing assemblies themselves small-sized and light-weight. Also, since in the two-component development systems the concentration of toner in carrier must be kept constant, a device for detecting toner concentration so as to supply the toner in the desired quantity is required, resulting in a large size and weight for the developing assemblies. In the one-component development system, such a device is not required, and hence the developing assemblies can commonly be made relatively light-weight.
As printers, LED printers or LBP printers are prevailing in the recent market. As a trend of techniques, there is a tendency toward higher resolution. More specifically, those which hitherto have a resolution of 300 or 600 dpi are being replaced by those having a resolution of 1,200 or 2,400 dpi. Accordingly, with such a trend, the developing systems are now required to achieve a high minuteness. Copying machines have also made progress to have higher functions, and hence they trend toward digital systems. In this trend, chiefly employed is a method in which electrostatic latent images are formed by using a laser. Hence, the copying machines also trend toward a high resolution and, like the printers, it has been sought to provide a developing system with higher resolution and higher minuteness.
In order to achieve such higher resolution and higher minuteness, it is required to make toners have a smaller particle diameter. However, making toners have a smaller particle diameter results in a great scattering of the chargeability of toner particles, and how to control it becomes important in order to achieve such an object.
For example, Japanese Patent Application Laid-Open No. 4-276762 discloses a proposal of a toner comprising toner particles produced by polymerization and having an average particle diameter of 3 to 8 &mgr;m to the surfaces of which specific carbon black has been made to adhere. When images are reproduced using such a toner provided on particle surfaces with a material capable of controlling chargeability, the carbon black kept adhering to particle surfaces may, e.g., come off upon paper feed of about 5,000 sheets or more to cause a great variation of charging performance of toner, resulting in an insufficient charging stability.
A proposal for imparting charging stability from the viewpoint of materials is also disclosed in, e.g., Japanese Patent Application Laid-Open No. 6-242631. However, as a result of image evaluation actually made by a method disclosed in this publication, there has proved to be room for further improvement in respect of resolution.
In order to make the charging performance of toner uniform, a method is also employed in which a toner on a toner-carrying member is regulated by a strong force by means of a toner thickness regulation member. Where the toner is regulated by a strong force, the toner tends to deteriorate because of friction to tend to cause a lowering of image quality as images are reproduced on a larger number of sheets.
Accordingly, it becomes necessary to enhance the strength of toner. This can commonly be solved by making binder resin of toner have a higher glass transition temperature or introducing a cross-linking component into the binder resin to enhance modulus of elasticity in the region of temperature not higher than the glass transition temperature of the toner. As the result, however, the fixing temperature at the time of image formation must be set high, or, in the case of heat roller fixing, the pressure applied to the roller must be set a little high. This may cause difficulties such that power consumption increases in accordance with necessary heat energy and roller contamination and wind-around offset may occur very frequently.
In order to lower the fixing temperature on the other hand, a method is available in which the binder resin is made to have a low glass transition temperature or have less cross-linking component. Such a method, however, is not preferable because it may cause the difficulties as stated above or may further cause a lowering of blocking resistance during storage of toners.
Various methods and apparatus are also proposed with regard to processes by which toner images are fixed to sheets such as paper and film. At present, a method most commonly used is a pressure heating method using a heating roller or using a stationary heat-generating heater through a heat-resistant film.
The pressure heating method using a heating roller is a method in which the toner image surface of a fixing target sheet is brought into pressure contact with the surface of a heating roller having a releasability to the toner and the fixing target sheet is passed therethrough under pressure contact. In this method, the heating-roller surface and the toner image on the fixing target sheet come into contact under application of a pressure, and hence a very good thermal efficiency can be achieved when the toner image is fixed onto the fixing target sheet, and rapid fixing can be effected.
In this fixing method, however, the heating-roller surface and the toner image come into contact in a molten state under application of a pressure, and hence part of the toner image may adhere and transfer to the fixing-roller surface, which may again transfer to the subsequent fixing target sheet to tend to contaminate the fixing target sheet, which is what is called an offset phenomenon. Such an offset phenomenon is greatly affected by fixing speed and fixing temperature. Accordingly, it is commonly attempted to set the surface temperature of the fixing roller relatively low in the case of fixing at a low speed and set the surface temperature of the fixing roller relatively high in the case of fixing at a high speed so that the quantity of heat imparted to the toner from the heating roller to fix the toner image can always be controlled at a constant level to keep the offset phenomenon from occurring.
The toner on the fixing target sheet is formed in some layers as toner layers. Hence, especially in a system where the fixing is at a high speed and the fixing roller has a high surface temperature, the uppermost toner layer coming in contact with the heating roller and the lowermost toner layer coming in contact with the fixing target sheet
Chiba Tatsuhiko
Hashimoto Akira
Komoto Keiji
Kukimoto Tsutomu
Canon Kabushiki Kaisha
Dote Janis L.
Fitzpatrick ,Cella, Harper & Scinto
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