Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-11-17
2002-05-14
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Transfer
C399S302000, C430S047300
Reexamination Certificate
active
06389260
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image forming device including: toner image forming means for forming a toner image dealing with both colors and a black color to form color or monochromatic (black and white) images, respectively; an intermediate transfer belt onto which the toner image of the respective colors or the black color formed by the toner image forming means is transferred; and transfer means for transferring the toner image on the intermediate transfer belt onto a recording medium, and in particular to a color image forming device which is suitably miniaturized and can realize high image quality, further including a plurality of the toner image forming means per color, and arranging respective toner image forming means by a tandem method, while having the intermediate transfer belt for transferring the toner image.
BACKGROUND OF THE INVENTION
Conventionally, major color image forming devices such as a color photocopying machine and a color printer have an arrangement in which a plurality of developing devices are provided, each of which forms a visible image (toner image) of a different color, and these toner images are eventually transferred one over another onto the same recording paper (transfer paper).
Generally, the color image forming device having the plurality of the developing devices is roughly classified into two types: a single photoreceptor type (or a single drum type); and a tandem type (multiple-step drum type).
First of all, in the single photoreceptor type color image forming device, a color image is formed by switching and successively operating the plurality of the developing devices capable of developing respective colors with respect to one photoreceptor drum. As a plurality of colors usually used therefor are, for example, the four colors of yellow (hereinafter referred to as “Y”), magenta (“M”, hereinafter), cyan (“C”, hereinafter) and black (“Bk”, hereinafter).
However, in the single photoreceptor type color image forming device, an image forming process (exposing, developing and transferring) is repeated for every color of the plurality of colors. For example, in the case of forming the color image with the four colors above, four developing devices are switched to be successively operated, so as to repeatedly perform image forming process for four times with respect to the photoreceptor drum.
Accordingly, in order to form one color image per one recording paper, four times a duration of time for image formation is necessary, thus requiring a considerable length of time for a whole image forming process. Therefore, in the single photoreceptor type color image forming device does arise a problem of the less counts of print per unit time, i.e., a slow image formation rate.
On the other hand, a tandem type color image forming device is made up of a plurality of toner image forming means having the photoreceptor drum and the developing device, each of which deals with each of the plurality of colors (four colors, for example), while juxtaposing these plurality of the toner image forming means per each color.
The following will describe one example of the tandem type color image forming device. For example, sequentially from an upper-stream side of a transport direction of a recording paper transport path for transporting recording paper which is a recording medium, respective image forming stations (toner image forming means) per respective colors of Y, M, C and Bk (black) are juxtaposed in a row (tandem), and in addition, a fixing device is provided on a downstream side of the recording paper transport path for these four image forming stations.
In the foregoing arrangement, first, recording paper which is static-absorbed with respect to the recording paper transport path is carried to the image forming station. Next, the toner images of the respective colors formed on respective photoreceptor drums are successively transferred one over another onto the recording paper. Thereafter, the recording paper after the transfer is carried to the fixing device in which fusion-pressurization fixation (fixing by applying heat and pressure) is performed on the toner image yet to be fixed on the recording paper, thus forming a color image on the recording paper.
Thus, in the tandem type color image forming device, the toner images of respective colors are formed by the image forming stations (toner image forming means) which are provided per color, and therefore, virtually, only a single step of the image forming process is required. Therefore, on a simple calculation, about four times a processing rate can be realized compared with the single photoreceptor type, and the problem of the slow image formation rate in the single photoreceptor type is cleared, thereby making it possible to realize a faster color image forming process.
Further, since, in the tandem type, as many photoreceptors and developing devices as types of color to be formed are needed, problems arise in terms of (i) an increase in the number of components, (ii) complication of manufacturing steps, and (iii) a rise in manufacturing costs. However, in recent years, an internal device has been miniaturized and composed in a unit (become a set device). This prevented the manufacturing steps from becoming more complicated and requiring higher costs, and the internal device has become relatively inexpensive. Accordingly, as far as the color image forming devices are concerned, the tandem type has been becoming the mainstream thereof, taking the place of the single photoreceptor type.
In the tandem type, however, the plurality of the image forming stations each of which is provided for each color are all set to be sequentially juxtaposed from the upper-stream side of one phase of the recording paper transport path. Accordingly, this causes the recording paper to be carried through as many transport paths as the plurality of the image forming stations. As a result, the transport path becomes long, which raises such a problem that the size of the tandem type color image forming device increases more than the single photoreceptor type.
Recently, therefore, there have been proposed various color image forming devices having the purpose of settling problems arisen in the single photoreceptor type and the tandem type, respectively. Typical techniques include color image forming devices disclosed, for example, in {circumflex over (1)} Japanese Unexamined Patent Publication No. 169175/1987 (Tokukaisho 62-169175 published on Jul. 25, 1987), {circumflex over (2)} Japanese Unexamined Utility Model Publication No. 5157/1991 (Jitsukaihei 3-5157 published on Jan. 18, 1991), {circumflex over (3)} Japanese Patent No. 2907944 (Publication No. Tokukaihei 4-13161 published on Jan. 17, 1992), {circumflex over (4)} Japanese Unexamined Patent Publication No. 341617/1993 (Tokukaihei 5-341617 published on Dec. 24, 1993) and {circumflex over (5)} Japanese Unexamined Patent Publication No. 271107/1995 (Tokukaihei 7-271107 published on Oct. 20, 1995).
First, the technique {circumflex over (1)} relates to a tandem type color image forming device, and as shown in
FIG. 7
, in an image forming section are juxtaposed four image forming stations
102
a,
102
b,
102
c
and
102
d
each of which deals with each color of Y, M, C or Bk, and besides, an intermediate transfer medium
103
having the shape of a belt is provided so that it commonly opposes to photoreceptor drums (not shown) in these image forming stations
102
a
through
102
d.
In other words, the four image forming stations
102
a
through
102
d
are disposed side by side on an upper side of the color image forming device, while on a lower side is disposed the intermediate transfer medium
103
. The intermediate transfer medium
103
is rotatable in a direction of an arrow in the drawing.
In the foregoing arrangement, toner images having respective colors of Y, M, C and Bk are superimposed on a surface of the intermediate transfer medium
103
. Thereafter, the toner images thus superimposed is transferred by a transfer device
104
onto
Fukudo Naoki
Fukunaga Keizo
Kataoka Hiroshi
Kido Eiichi
Masuda Jitsuo
Pendegrass Joan
Sharp Kabushiki Kaisha
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