Electrophotography – Image formation – Development
Reexamination Certificate
2001-05-07
2002-10-15
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Development
C399S237000
Reexamination Certificate
active
06466756
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a liquid-toner-development-type electrophotographic apparatus. More particularly, the invention relates to a liquid-toner-development-type electrophotographic apparatus in which a toner layer on an intermediate transfer member is melted through application of heat to separate a carrier solvent and a solid component from each other, and the carrier solvent is then removed.
BACKGROUND ART
1. Prior Art
A conventionally known liquid-toner-development-type electrophotographic apparatus uses as a liquid developer a highly viscous liquid toner composed of a liquid carrier (oil) and solid particles, such as pigment, which are dispersed in the liquid carrier (as disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 11-65290). A powder toner involves the following problems: toner particles scatter; and toner particles have a relatively large particle size of 7 &mgr;m to 10 &mgr;m, resulting in poor resolution. By contrast, a liquid toner has a small toner particle size of about 1 &mgr;m and can hold a large amount of electrostatic charge. Thus, a toner image is unlikely to be disturbed, and high resolution can be achieved.
FIG. 4
shows the overall configuration of a conventional liquid-toner-development-type electrophotographic apparatus. In
FIG. 4
, a photosensitive drum
10
is electrostatically charged at about 700 V by means of a charger
11
. Subsequently, the photosensitive drum
10
is exposed to light by means of an exposure unit
12
, whereby an electrostatic latent image is formed such that an exposed portion assumes an electric potential of about 100 V. A prewetting unit
13
applies silicone oil having a viscosity of about 20 cSt to the surface of the photosensitive drum
10
, to a thickness of 4 &mgr;m to 5 &mgr;m.
Developing units
14
corresponding to yellow, magenta, cyan, and black are provided and use as a liquid developer a nonvolatile toner of high viscosity and high concentration having a toner viscosity of 400 mPa·S to 4000 mPa·S and a carrier viscosity of 20 cSt. A developing roller supplies the liquid developer while being in contact with the photosensitive drum
10
, in such a manner as to maintain a two-layer structure composed of a toner layer on the developing roller and a prewetting liquid film on the photosensitive drum
10
, to thereby cause 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 member
15
is biased at about −500 V to thereby transfer toner particles thereto from the photosensitive drum
10
in the order of yellow, magenta, cyan, and black according to an electric field established between the same and the photosensitive drum
10
. A backup roller
20
is adapted to fix on printing paper the toner which is present on the intermediate transfer member
15
and is melted by means of a heating unit
18
. The heating unit
18
heats a portion of the surface of the intermediate transfer member
15
at a position located upstream of the backup roller
20
.
A carrier solvent used in liquid development 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 electrophotographic process, the carrier solvent is a component necessary for storage of toner, transport of toner, formation of a toner layer, and electrostatic transfer of toner. However, during and after the step of fixation of toner on paper medium, the carrier solvent is a component unnecessary for obtainment of good picture quality. Thus, at present, a volatile insulating liquid is used as a carrier solvent in many liquid developers (liquid toners). However, 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 electrophotographic apparatus which uses a liquid developer using a nonvolatile carrier solvent; for example, an HVS (High-Viscosity Silicone) toner, as shown in
FIG. 4
, is developed.
In some cases, a liquid-development toner using 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 thermal 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.
As mentioned previously, the intermediate transfer member
15
must be heated by appropriate heating means located outside or inside the same. However, this configuration involves the following problems: since the intermediate transfer member
15
is heated at all times, the photosensitive drum
10
is heated, with a resultant deterioration in photosensitive properties; since, during removal of a carrier, a toner image is in a molten state through exposure to heat, the toner image is disturbed due to adhesion to a carrier-removing roller, resulting in an impairment in picture quality; and in a process of superposing toner images, a toner image which has previously been electrostatically transferred is in a molten state through exposure to heat and is thus disturbed during contact with the photosensitive drum, resulting in an impairment in picture quality.
2. Related Art
To solve the above problems, the present applicant filed with the Japanese Patent Office a patent application for a liquid-toner-development-type electrophotographic apparatus comprising a cooling roller for eliminating influence of heating of an intermediate transfer member on a photosensitive drum and means for removing excessive carrier at a position located upstream of a heating position where a toner layer on the intermediate transfer member is melted through application of heat (Japanese Patent Application No. 11-26960 filed on Feb. 4, 1999).
FIG. 3
shows heating and cooling mechanisms proposed in the above filed application. In
FIG. 3
, toner particles transferred from a photosensitive drum
10
to an intermediate transfer belt
24
are melted through application of heat. The molten toner is transferred onto a printing medium, such as paper, in a single operation. At this time, a backup roller
20
abuts a heating roller
25
under pressure so as to fix the molten toner onto the medium, such as printing paper.
The intermediate transfer belt
24
is looped around a plurality of tension rollers
26
and
27
, the heating roller
25
, and the cooling roller
23
. A carrier-removing roller
21
is disposed in contact with the surface of the intermediate transfer belt
24
at a position located upstream of a position where the intermediate transfer belt
24
comes into contact with the heating roller
25
. A bias potential is applied to the carrier-removing roller
21
while a conductive roller
19
located in opposition to the heating roller
25
is grounded, thereby removing excessive carrier as well as prewetting liquid without exerting an electrical influence on other processes, such as electrostatic transfer and thermal transfer. However, excessive carrier solvent cannot be completely removed.
Various proposals have been put forth for removing as much carrier solvent as possible from a toner image on the photosensitive drum or the intermediate transfer member. However, in the case of a nonvolatile oil, removing almost all nonvolatile oil trapped between toner particles is nearly impossible.
DISCLOSURE OF THE INVENTION
When toner particles, or a solid component of toner, are melted and integrated through applicatio
Hongawa Hironaga
Ichida Motoharu
Inamoto Akihiko
Miyamoto Satoshi
Moto Satoru
Brase Sandra
PFU Limited
Staas & Halsey , LLP
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