Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making developer composition
Reexamination Certificate
1998-01-21
2001-01-23
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making developer composition
C430S110100, C430S111400
Reexamination Certificate
active
06177224
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electrophotographic toner for use in electrophotographic recording methods adopted by, for example, electrostatic copy machines and laser printers.
BACKGROUND OF THE INVENTION
In the past, electrophotographic methods based on application of the Carlson process have been widely used in image formation using toner. Devices adopting the Carlson process are usually provided with a photoreceptive drum, the surface of which is a photoreceptive layer, around which are provided, in order, a charger, an exposure device, a developer, a transfer device, a fixing device, a cleaner, and a charge eliminator.
The Carlson process will be described below.
In this process, first, in a dark environment, the surface of the photoreceptive drum is given a uniform charge by the charger.
Next, the exposure device projects the image of an original onto the surface of the photoreceptive drum, thus eliminating the charge in the areas onto which the light is projected, and forming an electrostatic latent image on the surface of the photoreceptive drum.
Next, toner from the developer, which has a charge of reverse polarity with respect to the photoreceptive drum, is affixed to the electrostatic latent image, thus forming a visible image in toner.
Then, a recording material such as paper is laid over this visible toner image, which is transferred to the recording material by giving the recording paper a charge of reverse polarity with respect to the toner by corona discharge from the reverse side of the recording material.
The toner image is then fixed to the recording material by means of heat and pressure applied by the fixing device, yielding a permanent image.
Toner which remains on the photoreceptive drum without being transferred to the recording material is removed by the cleaner. The electrostatic latent image on the photoreceptive drum is then eliminated by the static eliminator.
Then, successive image formation can be performed by repeating the foregoing process, beginning with charging of the photoreceptive drum.
Toner used in Carlson-process-based electrophotographic methods performs the function of a colored powder to form a visible image, and the functions of carrying a charge and attachment to the recording material. Since toner performs these multiple functions, it is often difficult for a toner to satisfy each of these functions equally well. Sometimes there are problems with image density, at other times problems with preservation, and so on.
In order to solve these problems, additives are often added to the toner to stabilize properties such as preservation, fluidity, and chargeability.
Japanese Examined Patent Publication No. 33698/1988 (Tokukosho 63-33698) discloses a method of manufacturing a developing agent which aims to make effective use of the various properties of toner by achieving the optimum mix of toner and additives.
Here, the additives are in the form of fine particles, but fine particles of this kind are generally found in the form of large secondary particles formed by aggregation of the fine primary particles. For this reason, attempting to provide a toner with desired characteristics usually becomes a question of how finely the aggregates (secondary particles) of additive can be broken down and uniformly dispersed throughout the toner in the optimum state.
Accordingly, the manufacturing method disclosed above adopts as a standard for the optimum state of uniform dispersal of the additives in the toner a mixing time which is 70% of the mixing time at which chargeability of the toner shows a first order singular point. However, depending on the type of additive, there are cases in which the charging level of the additive is lower than that of the toner particles themselves. For this reason, the aggregates of additive cannot be sufficiently broken down by relying solely on the foregoing indicator, and this may make it impossible to obtain desired characteristics.
SUMMARY OF THE INVENTION
The present invention was created in view of the foregoing problems, and its object is to provide an index for setting a mixing time which maximizes the effects of additives, and to provide a toner with desired characteristics.
In order to achieve the foregoing object, a method of manufacturing electrophotographic toner according to the present invention includes the step of:
mixing at least toner particles and an additive for a predetermined mixing time to produce an electrophotographic toner;
the predetermined mixing time being set within a range from a first mixing time through a second mixing time;
the first mixing time being a mixing time at which chargeability of the electrophotographic toner, which changes according to the duration of mixing of the toner particles and the additive, shows a singular point, and the second mixing time being a mixing time at which preservation of the electrophotographic toner, which also changes according to the duration of mixing, shows a singular point.
In general, chargeability and preservation of a toner change according to a predetermined mixing time, which is the actual duration of mixing of toner particles and additives at the time of manufacture. Accordingly, the foregoing method achieves the optimum balance between chargeability and preservation by means of the simple method of adjusting the mixing time so that it is within a range from a first mixing time, at which toner chargeability shows a singular point, through a second mixing time, at which toner preservation shows a singular point.
In other words, the first and second mixing times are used as indices for setting the predetermined mixing time. In this way, by achieving good chargeability, a toner having superior characteristics with regard to image density, fogging density, and scattering can be easily obtained.
Furthermore, by also achieving good preservation, the toner obtained shows little blocking even after a long period of storage, and has superior fluidity. Accordingly, by setting the predetermined mixing time within a range from the first mixing time, at which chargeability shows a singular point, through the second mixing time, at which preservation shows a singular point, a toner with balanced improvement of characteristics with regard to image density, scattering, fogging density, and fluidity can be provided.
In order to achieve the object mentioned above, another method of manufacturing electrophotographic toner according to the present invention includes the steps of:
preparing a mixture of materials by mixing a composite of materials containing at least a binding agent, a pigment, and a charge control agent;
preparing a melted, kneaded mixture by melting and kneading the mixture of materials;
performing grinding classification of the melted, kneaded mixture to obtain toner particles having a predetermined particle diameter; and
adding at least an additive to the toner particles and mixing for a predetermined mixing time to produce an electrophotographic toner;
the predetermined mixing time being set within a range from a first mixing time through a second mixing time;
the first mixing time being a mixing time at which chargeability of the electrophotographic toner, which changes according to the duration of mixing of the toner particles and the additive, shows a singular point, and the second mixing time being a mixing time at which preservation of the electrophotographic toner, which also changes according to the duration of mixing, shows a singular point.
Setting the toner particle materials and manufacturing method as specified in the foregoing method results in further improvement of the effect obtained when the predetermined mixing time is set as specified above, namely, balanced improvement of characteristics with regard to image density, scattering, fogging density, and fluidity.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the dra
Imafuku Tatuo
Morinishi Yasuharu
Nagahama Hitoshi
Nakamura Tadashi
Ogawa Satoshi
Conlin David G.
Dike, Bronstein, Roberts and Cushman LLP
Dote Janis L.
Neuner George W.
Sharp Kabushiki Kaisha
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