Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-09-06
2003-05-06
Chapman, Mark A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108700, C430S137140
Reexamination Certificate
active
06558864
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner for developing an electrostatic image, which is used in developing electrostatic latent images with a developer in electrophotography or in an electrostatic recording process, etc., to a method for producing it, and also to an electrostatic image developer, a method for forming an image and an image forming apparatus.
2. Description of the Related Art
Visualization of image information via electrostatic images in electrophotography or the like is now utilized in various fields. In electrophotography, electrostatic latent images are formed on a photoreceptor through static charging and exposure to light, then they are developed with a toner-containing developer, and the resulting toner images are transferred and fixed on recording media, on which the images are thus visualized.
The developer to be used therein includes a two-component developer that contains a toner and a carrier, and a mono-component developer of a magnetic or non-magnetic toner alone. For producing the toner, generally employed is a kneading and grinding method that includes melting and kneading a thermoplastic resin along with a pigment, a charge control agent and a release agent such as wax, cooling the resulting mixture, then grinding it, and classifying the resulting particles. To the toner, optionally added are inorganic or organic particles, which adhere to the surfaces of the toner particles to thereby improve the flowability and the cleanability of the toner. The method is effective for producing high-quality toners, but involves some problems such as those mentioned below.
In such an ordinary kneading and grinding method, the morphology and the surface structure of the toner particles produced could not be controlled, and they delicately vary depending on the grindability of the starting materials used and on the condition employed in the grinding step. In the method, therefore, it is difficult to obtain toner particles having a specifically defined morphology and a specifically defined surface structure. In addition, in the kneading and grinding method, the starting materials to be used are limited. Concretely, the resin colorant dispersion to form a toner must be brittle so that it can be well ground in an economic device. However, if the resin colorant dispersion is too brittle, the toner containing it will release fine powder in a development unit, when having received mechanical shear force in the unit, and, as the case may be, the toner morphology will be often changed. This will have some negative influences on the function of developers. For example, in a two-component developer, fine powder of the toner will adhere to and solidify on the surfaces of carrier particles to thereby much deteriorate the chargeability of the developer; and in a mono-component developer, the particle size distribution of toner particles will be broadened, and, as a result, the toner will scatter and its morphology will change to worsen its ability to develop images, whereby the quality of the images developed will be lowered. In case where a large quantity of a release agent such as wax is added to prepare a toner, the release agent is often exposed out on the surfaces of the toner particles, depending on the type of the thermoplastic resin combined with it, and this is problematic. In particular, in a combination of a resin which contains an increased amount of a high-molecular component so as to increase its elasticity and which is therefore difficult to grind, and a brittle wax such as polyethylene, polyethylene will be readily exposed out on the surfaces of toner particles. This will be favorable in point of the releasability in toner fixation and of the cleanability of non-transferred toner from photoreceptors, but the polyethylene having been exposed out on the toner surfaces will readily move owing to external force applied thereto, and will soil development rollers and photoreceptors and or will contaminate carrier particles, whereby the reliability in image formation will be lowered.
For amorphous toner, its flowability could not be increased to a satisfactory level even when a flowability improver is added thereto. In that case, fine particles existing on the surfaces of the toner particles will move to the recesses of the surfaces owing to the mechanical shear force that may be applied to the toner particles in a duplicator, whereby the flowability of the toner will be time-dependently lowered; or the flowability promoter will be embedded inside the toner particles whereby the developability, the transferability and the cleanability of the toner will be worsened. In case where the toner recovered in a cleaning zone in a duplicator is returned to the development unit therein, the quality of the images formed will be further worsened. If the amount of the flowability promoter in the toner is increased so as to solve the problems, peppers will appear on photoreceptors, and the promoter particles will much scatter.
Recently, some methods have been proposed for controlling the morphology and the surface structure of toner particles. For example, one method proposed in Japanese Patent Laid-Open Nos. 282752/1988 and 250439/1994 is for producing toner through emulsion polymerization combined with condensation. This includes separately preparing a dispersion of resin particles formed through emulsion polymerization, and a dispersion of a colorant in a solvent, mixing them to form condensed masses of which the size corresponds to the size of the toner particles to be produced, and heating and melting them to form toner particles. According to the method, the toner morphology can be controlled in some degree and the chargeability and the durability of the toner produced can be improved. However, since the inner structure of the toner particles produced therein is nearly uniform, the method is still problematic in that the releasability of the sheet on which toner images are fixed is not good and the transparency in OHP output is not stable.
As so mentioned hereinabove, toner must stably exhibit its capability even under various types of mechanical stress in electrophotography. For this, too much exposure of a release agent out of the surfaces of toner particles must be prevented, the surface hardness of toner particles must be increased not detracting from the fixability of toner, the mechanical strength of toner must be increased, and both the chargeability and the fixability of toner must be ensured.
High-quality images are much desired these days. In particular, high-precision color images are desired, for which the particle size of toner particles is reduced more and more. However, if the size of conventional toner particles having an ordinary particle size distribution is reduced, fine toner powder will increase. Such fine toner powder is problematic in that it contaminates carrier particles and soils photoreceptors, and it scatters. For these reasons, it has heretofore been difficult to realize high image quality and high reliability even though the size of toner particles is reduced. To solve the problem, it is important to realize a sharp particle size distribution of toner particles and to reduce the particle size thereof.
In recent digital full-color duplicators and printers, a color image original is separated into B (blue), R (red) and G (green) through individual color filters, then latent images of dots each having a diameter of from 20 to 70 &mgr;m are formed, corresponding to the original, and they are developed with toners of Y (yellow), M (magenta), C (cyan) and Bk (black) through subtractive color mixture. As compared with conventional monochromatic image-forming machines, a larger quantity of toners must be transferred in such full-color image-forming machines, and in addition, toners corresponding to small-size dots of latent images must be used therein. To that effect, it is more important that the toners for latent images of such small-size dots meet the requirements of uniform chargeability, durab
Ishiyama Takao
Kadokura Yasuo
Maehata Hideo
Matsumura Yasuo
Sato Shuji
Chapman Mark A.
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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