Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Post imaging process – finishing – or perfecting composition...
Reexamination Certificate
1999-12-17
2001-05-22
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...
C430S110100, C399S222000
Reexamination Certificate
active
06235441
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a positively chargeable toner for use in a recording method, such as electrophotography, electrostatic recording, magnetic recording and jet recording, and an image forming method and an image forming apparatus including development of an electrostatic latent image with the toner.
Hitherto, a large number of electrophotographic processes have been known, inclusive of those disclosed in U.S. Pat. Nos. 2,297,691; 3,666,363; and 4,071,361. In these processes, in general, an electrical or electrostatic latent image is formed on a photosensitive member comprising a photoconductive material by various means, then the latent image is developed with a toner, and the resultant toner image is, after being transferred onto a transfer material such as paper etc., via or without via an intermediate transfer member, as desired, fixed by heating, pressing, or heating and pressing, or with solvent vapor to obtain a copy or print carrying a fixed toner image. According to necessity, residual toner remaining on the photosensitive member without transfer is cleaned by various methods. The above steps are repeated for successive image formation.
For complying with varying market demands in recent years, such as complex functions and personal use, such an image forming system or apparatus is severely required to be smaller in size and lighter in weight, and exhibit higher speed and higher reliability. As a result, a toner used therein is required to exhibit further higher performances.
For example, as means for fixing a toner image onto a transfer(-receiving) sheet such as paper, various systems or devices have been developed including a heat-pressure fixing system using heating rollers as a currently most popular one. In the heat-pressure fixing system using hot rollers, a fixation sheet carrying a toner image is caused to pass over and in contact with a heating roller surfaced with a material exhibiting a releasability to a toner thereby fixing the toner image onto the fixation sheet. In this fixation scheme, as the heating roller surface and the toner image on the fixation sheet contact each other, a very good heat efficiency is attained for malt-attaching the toner image onto the fixation sheet to afford quick fixation.
In the heating roller fixation scheme frequently used heretofore, however, in order to obviate a fixation failure caused by a temperature change of the heating roller due to passage of fixation sheets and other external factors and also the so-called offset phenomenon of the toner being transferred onto the heating roller, it is necessary to maintain the heating roller within an optimum temperature range, thus requiring an increased heat capacity of the heating roller which leads to a larger power consumption, an increase in size of image forming apparatus and a temperature increase in the apparatus.
Accordingly, various means have been proposed heretofore for the purpose of preventing toner attachment onto the fixing roller surface or improving the low-temperature fixing performance. For example, it has been practiced to form a roller surface of a material exhibiting good releasability to a toner, such as silicone rubber or fluorine-containing resin and coat the roller surface with a liquid (offset preventing liquid) exhibiting good releasability, such as silicone oil, for the purpose of preventing offset and fatigue of the roller surface material. This method is very effective for the prevention of toner offset but requires a device for supplying the offset-preventing liquid, thus still involving a problem of requiring a complicated fixing device leading to an increase in size of the entire apparatus.
Accordingly, the realization of an effective fixing method which can also accomplish good fixation of toner image onto transfer sheets and offset prevention, owes very much to improvement in toner performances in addition to improvements in fixing devices as mentioned above.
In other words, for the purpose of offset prevention, it is desired to develop a toner exhibiting a broad fixable temperature range and good anti-offset characteristic rather than relying on the supply of an offset-preventing liquid. From this viewpoint, it has been practiced to increase the releasability of the toner per se by adding a waxy material, such as low-molecular weight polyethylene or low-molecular weight polypropylene, capable of sufficiently melting under heating. This is effective for offset prevention but on the other hand results in increased agglomeratability and unstable chargeability of the toner, thus being liable to cause a lowering in developing performance during continuous image formation. Accordingly, various trials have been made in order to improve the binder resin performances as another approach.
For example, it is known to increase the glass transition temperature (Tg) or molecular weight of the binder resin in the toner so as to increase the melt viscoelasticities of the toner in order to prevent the offset. In the case of improving the anti-offset characteristic according to this method, however, the fixability is liable to be lowered while the developing performance is not so much adversely affected, thus resulting in lowering in fixability at low temperatures as required in high-speed fixation or economization of energy consumption, i.e., inferior low-temperature fixability.
In order to improve the. low-temperature fixability of a toner, it is necessary to lower the melt-viscosity of the toner thereby increasing the contact area with the fixation sheet, so that the binder resin used for this purpose is required to have a lower Tg or lower molecular weight.
As is understood from the above, the low-temperature fixability and the anti-offset characteristic are contradictory in some respects, so that it is difficult to develop a toner simultaneously satisfying these properties.
For solving the above problem, Japanese Patent Publication (JP-B) 51-23354 has disclosed a toner comprising a moderately crosslinked vinyl polymer through use of a crosslinking agent and a molecular weight-adjusting agent. In addition, there have been proposed many toners comprising blends of vinyl polymers having various Tg, molecular weights and gel contents.
Such a toner comprising a crosslinked vinyl polymer or gel content exhibits excellent anti-offset characteristic. However, in the case of using a crosslinked vinyl polymer as a starting material for providing a toner containing such a component, the polymer causes a very large internal friction and receives a large shearing force during the melt-kneading stop for toner production. For this reason, the molecular chains are severed in many cases to result in a toner having a lower melt-viscosity, which adversely affects the anti-offset performance.
For solving the above problem, Japanese Laid-Open Patent Application (JP-A) 55-90509, JP-A 57-178249, JP-A 57-178250 and JP-A 60-4946 have proposed toners containing a crosslinked polymer formed by using a carboxyl acid-containing group and a metal as toner starting materials and reacting these materials under heating during the melt-kneading
JP-A 61-110155 and JP-A 61-110156 have disclosed a reaction of a binder comprising a vinyl resin monomer and a special monoerter compound as essential components with a polyvalent metal compound to form crosslinkages via the metal.
JP-A 63-214760, JP-A 63-217362, JP-A 63-217363 and JP-A 63-217364 disclose a toner composition comprising a binder resin including a low-molecular weight fraction containing a carboxyl group, a high-molecular weight fraction and a polyvalent metal ion forming a crosslinkage with the carboxylic group formed by adding a dispersion liquid of a metal compound to a solution product of solution polymerization to cause the crosslinking reaction under heating.
JP-A 2-168264, JP-A 2-235069, JP-A 5-173363, JP-A 5-173366 and JP-A 5-241731 disclose a toner binder composition containing a low-molecular weight component and a high-molecular weight component having specified molecula
Fujikawa Hiroyuki
Fujimoto Masami
Kobori Takakuni
Tanikawa Hirohide
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Goodrow John
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