Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-12-12
2004-06-01
Lee, Susan (Department: 2852)
Electrophotography
Image formation
Transfer
C399S250000, C399S302000, C399S308000, C399S348000
Reexamination Certificate
active
06745002
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a liquid-development electrophotographic apparatus which uses a nonvolatile, high-viscosity, high-concentration liquid toner.
BACKGROUND ART
As an electrophotographic apparatus operating by the steps of generating an electrostatic latent image on a photosensitive body (a photosensitive drum), causing toner to be attracted to the electrostatic latent image, transferring the toner onto paper or the like, and fixing the transferred toner, a dry-type apparatus, which uses a powder toner, is widely used.
However, a powder toner involves the following problems: toner particles scatter; and since toner particles have a relatively large particle size of 7 &mgr;m to 10 &mgr;m, resolution is low.
Thus, when high resolution is required, a liquid-development-type apparatus, which uses a liquid toner, is used for the following reason. A liquid toner has a small toner particle size of about 1 &mgr;m and exhibits a large electrostatic-charge capacity. Thus, a toner image is unlikely to be disturbed, and high resolution can be achieved.
FIG. 13
shows the overall configuration of a conventional liquid-development-type electrophotographic apparatus (disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 2000-56575). In
FIG. 13
, a photosensitive drum
10
is electrostatically charged by means of a charger
21
. Subsequently, the photosensitive drum
10
is exposed to light by means of an exposure unit
22
, whereby an electrostatic latent image is formed. A prewetting unit
23
applies silicone oil to the surface of the photosensitive drum
10
. Reference numeral
26
denotes a blade for scraping off residual development toner, and reference numeral
27
denotes a destaticizer.
Developing units
24
corresponding to yellow, magenta, cyan, and black are provided and use as a liquid developer a nonvolatile, high-viscosity, high-concentration liquid toner. A developing roller supplies the liquid developer onto the photosensitive drum
10
while causing toner particles contained in the liquid developer to adhere to the photosensitive drum
10
according to an electric field established between the same and the photosensitive drum
10
.
An intermediate transfer roller
15
transfers color toners one by one from the photosensitive drum
10
according to an electric field established between the same and the photosensitive drum
10
. A heating unit
28
heats the surface of the intermediate transfer roller
15
to thereby melt the toners adhering to the intermediate transfer roller
15
. Heating by the heating unit
28
is performed after all color toners have been transferred onto the intermediate transfer roller
15
. A pressure roller
19
is adapted to fix on a printing medium the toners which are melted on the intermediate transfer roller
15
by means of the heating unit
28
.
When the intermediate transfer roller
15
transfers toner particles from the photosensitive drum
10
according to an electric field established between the same and the photosensitive drum
10
, there must be removed oil which is composed of excessive prewetting liquid and carrier in a developed toner layer and which, together with toner particles, is transferred from the photosensitive drum
10
to the intermediate transfer roller
15
. For effecting the removal, the illustrated apparatus employs an oil-removing roller
25
on the intermediate transfer roller
15
.
A carrier solvent to be used in the liquid-development electrophotographic apparatus is intended to prevent scattering of toner particles, which assume a particle size of about 1 &mgr;m, as well as to uniformly disperse toner particles through electrification of the toner particles. In development and electrostatic transfer processes, the carrier solvent serves as a “bridge” to facilitate movement of toner particles, which is effected by means of electric-field action.
In a liquid-development printer process, the carrier solvent is a component necessary for storage of toner, transport of toner, formation of a toner layer, development, and electrostatic transfer of toner. However, during and after the step of fixation of toner on a paper medium, the carrier solvent is a component unnecessary for obtainment of good picture quality. Thus, at present, in many liquid developers (liquid toners) a volatile insulating liquid is used as a carrier solvent. However, a liquid developer which uses a nonvolatile carrier solvent is developed in consideration of fixation of toner within apparatus due to volatilization of a carrier, and effects of a volatile carrier on the human body and the environment. An example of such a liquid developer is an HVS (High-Viscosity Silicone) toner.
In some cases, a liquid-development toner which uses a nonvolatile carrier solvent may involve the following problem: the carrier solvent cannot be volatilized during melting of toner through application of heat to the liquid toner and, particularly during fixation of toner or melt transfer of a toner image, hinders development of adhesion of a molten toner onto a paper medium, resulting in a failure to attain satisfactory picture quality and fixation strength with respect to a toner image transferred onto the paper medium.
In some cases, a system that employs melt transfer of an image formed through superposition of toners from an intermediate transfer body to a paper medium may involve the following problem: a toner image on the intermediate transfer body may become spottedly frizzy during application of heat for melting the toners. This problem is related to the relation among releasability of the surface of the intermediate transfer body, viscosity (fluidity) of molten toners, and wettability of a carrier solvent.
Thus, a nonvolatile carrier solvent must be removed to the greatest possible extent before a step of fixing toner on a paper medium is started. However, before a heating step, a limit is imposed on removal of a carrier solvent filling gaps present among toner particles.
Therefore, a “hot carrier removal” process is effective for removal of a carrier solvent. According to the process, residual carrier trapped in gaps present among toner particles is caused to float on toner particles during melting of toner through application of heat, and the floating carrier is removed. Specifically, in a printer apparatus whose printing operation involves remaining of a nonvolatile carrier solvent within a toner image formed on an intermediate transfer body, the carrier solvent (a liquid component) is separated through utilization of integration of toner particles (a resin component) during melting of toner particles by application of heat as well as through utilization of strong electric-field-induced force of toner particles electrically activated by temperature rise. In application of an electric field to a molten toner in the course of heating, influence of heat on roller members and mutual influence for other process conditions must be considered. However, prior art techniques fail to sufficiently consider these factors in determination of control conditions.
Since color toners are transferred on a single-color basis from the photosensitive drum
10
to the intermediate transfer roller
15
, a color toner which has already been transferred onto the intermediate transfer roller
15
passes, before heating, a contact portion between the photosensitive drum
10
and the intermediate transfer roller
15
. If the color toner contains excessive prewetting liquid and carrier, the excessive prewetting liquid and carrier are collected and flow at the contact portion between the photosensitive drum
10
and the intermediate transfer roller
15
, causing disturbance of an image and affecting heating and melting of a toner layer in the course of fixation. As mentioned previously, the illustrated configuration can remove excessive prewetting liquid or carrier liquid.
However, the illustrated configuration must be such that sufficient cooling is achieved at the contact portion between the photosensitive drum
10
and the intermediate
Hongawa Hironaga
Hongo Masanobu
Ichida Motoharu
Inamoto Akihiko
Miyamoto Satoshi
Lee Susan
PFU Limited
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