Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
2001-04-26
2002-12-10
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Post imaging process, finishing, or perfecting composition...
C430S108800, C430S120400
Reexamination Certificate
active
06492084
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner for use in electrophotographic copying machines, facsimile apparatus, and printers, and an image formation method using the toner.
2. Discussion of Background
Conventionally, thermal image fixing is often used for fixing toner images.
According to the principle of thermal toner image fixing, a toner to be fixed has to be softened or melted by the heat applied thereto by an image fixing unit. Furthermore, the softened or melted toner has to be embedded in the fibers of paper by the pressure applied thereto by the image fixing unit, or has to be caused to adhere to the fibers with the adhesive force generated at the surface of the softened or melted toner.
In light of the toner fixing mechanism mentioned above, the melting point or softening point of a resin for use in the toner is required to be equal to or lower than the image fixing temperature set by the image fixing unit.
In recent years, there is an increasing demand for energy saving from the viewpoint of environmental protection. The energy that can be used in the image fixing unit is now being restricted.
In practice, in order to reduce the energy required for image fixing, there is no choice but to lower the image fixing temperature that is set in the image fixing unit. To cope with an image fixing unit with a lowered image fixing temperature, there is necessarily no choice but to employ a resin with a lower melting point as the resin for use in the toner. However, the resin with a low melting point tends to readily soften, so that toner particles containing the above-mentioned resin readily cause a blocking problem. Further, the mutual action between the toner particles and additives externally added to the toner particles changes with time because of the adhesion of the surface of the toner particles, thereby causing changes in the characteristics of toner. The result is that the preservation stability of the toner is impaired.
Furthermore, the toner prepared using the above-mentioned resin is so soft and adhesive that even in a developer unit, there occurs a so-called spent phenomenon with the deposition of the toner on the surface of a carrier to use up the carrier. Further, the toner causes the problem of adhering in the form of a film to the surface of a development roller, which phenomenon is referred to as the toner filming, and the toner also has the problem of being easily deposited on a developer blade in the developer unit.
Furthermore, after the completion of image fixing, image-bearing sheets unfavorably stick to each other, depending on the environmental conditions, which is referred to as a blocking phenomenon.
In addition to the above, another problem occurs in the preparation of the toner using a conventional resin with a low melting point. Namely, it is difficult to efficiently pulverize the toner, and the toner easily sticks to the inner wall of a pulverizer, because the resin is excessively soft.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a toner for use in electro-photography, from which the conventional problems of the prior art have been eliminated, which has a lower image fixing temperature than that of a conventional toner, thereby achieving the saving of energy, and also has the following characteristics:
1. Having excellent storage stability
2. not reacting with externally added additives and causing no changes in the characteristics with time
3. Not causing the spent phenomenon, toner filming, and deposition
4. Imparting excellent preservability to materials printed with the toner
5. Having excellent grindability
A second object of the present invention is to provide an image formation method using the above-mentioned toner.
The inventor of the present invention has discovered an image fixing system capable of carrying out image fixing by using in a toner (1) a resin having such a melting point that is higher than the lowest temperature in image fixing, and (2) a wax having such a melting point that is lower than the lowest temperature in image fixing. In this case, the wax serves as a solvent or a plasticizer when heated to the melting point of the wax or to a temperature above the melting point of the wax, so that the resin is dissolved on a molecular level in the wax, and the image fixing can be carried out at a temperature that is lower than the melting point of the resin, with the resin being softened or dissolved in the wax.
Based on this knowledge, the inventor of the present invention has also discovered that image fixing can be carried out using a toner comprising a cyclized rubber with a high melting point. Further, when the cyclized rubber is used in combination with a wax which has a melting point by far lower than that of the cyclized rubber, image fixing can be achieved at a temperature near the melting point of the wax. Thus, the inventor has found a toner for use in electrophotography capable of energy saving.
In the present invention, the melting point of the cyclized rubber indicates a softening point thereof measured by a flow tester method. Furthermore, in the present invention, the melting point of the wax indicates a temperature at which the crystals of the wax mostly become amorphous and transparent. Namely, the concept of the term “melting point” used in the present invention is different from that of the glass transition temperature (Tg) measured by the DSC method, or from that of a top peak in an endothermic curve. For example, in the case of cyclized isoprene, the measurement by use of the DSC method indicates an endothermic peak at a temperature in a range of from 50° C. to 80° C. However, practically, the cyclized isoprene is clearly in a solid state at temperatures of about 100° C.
The first object of the present invention can be achieved by a toner comprising a coloring agent, and a binder which comprises a binder resin comprising a cyclized rubber.
In the above toner, the cyclized rubber may be contained in an amount of 10 wt. % or more of the total amount of the binder resin.
In the above toner, it is preferable that the cyclized rubber have a cyclization degree of 40% or more.
Furthermore, in the above toner, the binder may further comprise a wax, which dissolves therein the cyclized rubber when heated to the melting point of the wax or above. The wax servers as a solvent for the cyclized rubber.
Furthermore, in the above toner, it is preferable that the composition ratio of the wax to the cyclized rubber (the wax: the cyclized rubber) be (97:3) to (5:95) on a weight basis.
In the above toner, the melting point of the wax is lower than the melting point of the cyclized rubber.
It is preferable that the wax have a melt viscosity of 1 to 10,000,000 centipoise at 150° C.
It is also preferable that the wax have a penetration of 0 to 20 at 25° C.
It is preferable that the wax comprise at least one wax component selected from the group consisting of paraffin wax, microcrystalline wax, olefin wax, and oxidized wax or be selected from the group of the above-mentioned waxes.
The toner of the present invention is fixable at a temperature equal to or lower than the melting point of the cyclized rubber.
The second object of the present invention can be achieved by an electrophotographic image formation method, using the above-mentioned toner.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The toner for use in electrophotography of the present invention will now be explained in more detail.
In the present invention, as a main binder, there is employed a cyclized rubber which has a high melting point and excellent preservability, and high resistance to occurrence of the spent phenomenon, toner filming, and deposition on the developer blade.
The binder for use in the toner may further comprise a wax. In this case, the cyclized rubber is dissolved in the wax. The cyclized rubber dissolved in the wax is then solidified and used as the toner.
When the thus prepared toner is subjected to thermal image fixing, the cyclized rubber is dissolv
Goodrow John
Ricoh & Company, Ltd.
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