JPH01209471A - Electrophotographic image forming device - Google Patents

Abstract

PURPOSE:To eliminate the necessity of reversing and feeding a transfer sheet and to form images on its both sides rapidly without enlarging a device by fixing the images after transcribing them on both sides of the sheet. CONSTITUTION:A first image on a transfer belt 7 is charged electrostatically to polarity the same as the transfer belt 7 by an electrostatic charge means 10. When a transfer sheet 26 is supplied between the transfer belt 7 and a contact roller 14, the surface potential of the transfer sheet 26 is controlled by the contact roller 14, and the first image on the transfer belt 7 is transcribed on one side of the transfer sheet 26. Then this transfer sheet 26 moves to the contact part of a photosensitive body 5 with the transfer belt 7, and a second image which is formed on the photosensitive body 5 is transcribed on the other side of the transfer sheet 26 owing to the difference of the surface potentials among the transfer belt 7, the transfer sheet 26 and the photosensitive body 5. In this way, the images are formed on both sides of the transfer sheet 26 by transcribing the images on both sides of the sheet 26 and fixing them. Thus the images on both sides of one sheet can be formed rapidly and the device can be miniaturized by avoiding the necessity of reversing and feeding the transfer sheet 20 to put it.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is applicable to electrophotographic image forming devices such as copying machines and printers, and is particularly applicable to transferring developed images on a photoreceptor and a transfer belt to transfer paper at once. The present invention relates to an electrophotographic image forming apparatus that can obtain double-sided images.

(Prior art) In conventional copying machines, in order to obtain a double-sided image, the first image formed on the photoreceptor is transferred and fixed onto one side of transfer paper, the transfer paper is turned over, and the next image is transferred and fixed. A common method was to transfer and fix the second image formed on the photoreceptor to the other side of the transfer paper.

On the other hand, Japanese Patent Publication No. 54-28740 discloses a WJ image forming apparatus which includes a photoreceptor and a transfer roller or a transfer belt and transfers images onto both sides of a transfer sheet at once.

Although the principle is the same whether a transfer roller or a transfer belt is used, in the case of using a transfer belt, as shown in FIG. The polarity of the toner of the first image on the transfer belt 32 is reversed by the toner polarity reversing charger 34, and the toner of the first image on the transfer belt 32 is transferred to
The transfer charger 33 simultaneously transfers the image and the second image formed on the photoreceptor 31 onto both sides of the transfer paper 35 supplied between the photoreceptor 31 and the transfer belt 32, and then fixes the image on the transfer sheet 35. has been done. 36 is a charger for tacking the transfer paper 35 to the transfer belt 32.

(Problem to be solved by the invention) However, in the conventional method of performing transfer and fixing twice, it is necessary to provide another paper passage path to reverse and feed the transfer paper after transfer and fixation, which makes the device For example, there were problems in that the volume increased by 30 to 40% and the cost increased significantly by 7. Additionally, there is the problem that heat curls occur on the transfer paper during the first fixing process, which tends to cause poor paper feeding during the second transfer/fixing process, and since the paper is passed twice, it takes time to form images on both sides. was there.

On the other hand, in the method disclosed in the above-mentioned publication, since the transfer is performed on both sides of the transfer paper at the same time, the above-mentioned problem can be solved, but with the transfer paper interposed between the photoreceptor and the transfer belt, Since the transfer from the transfer belt to the transfer paper and the transfer of the PIS2 image from the photoconductor to the transfer paper are performed simultaneously using the same transfer charger, the transfer is easily affected by the quality and thickness of the transfer paper. There is a problem that transfer defects are likely to occur.

In view of the above-mentioned problems, the present invention is capable of forming double-sided images without increasing the size of the device or causing poor paper feeding, and has a fast double-sided image forming speed, and is not affected by the quality or thickness of the transfer paper. The object of the present invention is to provide an electrophotographic image forming apparatus that can stably obtain proper images.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a means for selectively forming a regular image and a mirror electrostatic latent image on a photoreceptor, and a dielectric layer on the surface of a conductive base material. a transfer belt comprising a body layer and capable of transferring a developed image developed on a photoreceptor; a charging means for charging the transfer belt; It is characterized by comprising a conductive contact roller that can be separated and is grounded via a charge injection circuit.

(Function) According to the above configuration, the first image formed on the photoreceptor is
Since the transfer belt is charged by the charging means, the first image on the transfer belt is transferred to this transfer belt due to the difference in surface potential between the transfer belt and the photoreceptor, and then the first image on the transfer belt is charged by the charging means to the same polarity as the transfer belt. Then, when a transfer paper is supplied between the transfer belt and the contact roller, the surface potential of this transfer paper is controlled by the contact roller, so that the first image on the transfer belt is transferred to one side of the transfer paper, and then The transfer paper moves to the contact area between the photoreceptor and the transfer belt, and the second image formed on the photoreceptor is transferred to the other side of the transfer paper due to the surface potential difference between the transfer belt, the transfer paper, and the photoreceptor. Images can be formed on both sides of the transfer paper by transferring images to both sides of the transfer paper and then fixing these images.

Therefore, there is no need to turn the transfer paper over and pass it through, making it possible to form double-sided images at high speed and downsizing the apparatus, and since the images are transferred and fixed on both sides, paper passing failures due to heat curling do not occur.

Furthermore, since the first and second images are transferred to the transfer paper separately at the close contact roller position and the photoreceptor position, they are less affected by the quality and thickness of the transfer paper, making it easier to print the correct image. Obtainable.

(Embodiment) An embodiment in which the present invention is applied to a copying machine capable of double-sided copying will be described below with reference to FIGS. 1 to 5.

In FIG. 1, reference numeral 1 denotes a document table plus on which a document is placed, and is movable in the horizontal direction in the figure. 2 is a light source that illuminates the original; 3 is an optical system such as a convergent light transmission array that projects the image of the original onto the photoreceptor 5; and 4 is a prism that switches the image projected onto the photoreceptor 5 into a normal image and a mirror image. , it is movable between a position inserted in the optical path and a retracted position. A developing device 6, a transfer belt 7, a photoreceptor cleaner 8, an eraser 9, a charging charter 10, etc. are arranged around the photoreceptor 5 in the direction of rotation of the photoreceptor 5 from the exposed portion of the projected image. There is.

As shown in FIG. 2, the transfer belt 7 has a polystyrene base material (electrical resistance of 106 Ωell or less) 11 having a thickness of 600 μta as a conductive base material and containing carbon black as a conductive filler. It is composed of a dielectric type belt on which a polybutylene layer 12 having a thickness of 50 .mu.III ('11 resistance resistance' of 4 Ωcm or more) is formed. The transfer belt 7 is an endless belt wound between a driven roller 13a on the upper side of the paper passing path and a driving roller 13b on the lower side so that the upper surface thereof forms a substantially horizontal paper passing path. It is composed of

A conductive contact roller 14 made of metal or conductive rubber is disposed above the driven roller 13a of the transfer belt 7. This contact roller 14 is in close contact with the transfer belt 7.
They are configured to be separable and are grounded via a charge injection circuit 15.

As the charge injection circuit 15, as shown in FIG. 5(a), (1+)
, as shown in (c), a resistance 2 of several 10 to several 100 MΩ
3. Barista 24 and 100 baristas of several 100 to 1ooov
A bias power supply 25 of ~-1000V or the like can be used.

A static elimination charger 1G, a belt cleaner 17, and a belt charger 18 are arranged below the transfer belt 7 along the rotational direction of the transfer belt 7. Further, a conductive backup roller 19 is provided so as to face the belt crease 17 with the transfer belt 7 in between, and is grounded.

On the transfer paper discharge side of the transfer belt 7, an upper fixing roller 220 and a lower fixing roller 21 are arranged with a paper passing path in between. 22 is the heater lamp.

Next, the operation will be explained.

First, the operation when performing double-sided copying will be explained with reference to FIG.

First, with the prism 4 interposed on the optical path as shown, 11 originals are placed on the document table plus 1, and the document table plus 1 is moved from right to left in the figure and charged to -500V. A normal power-saving latent image is formed on the photoreceptor 5. The latent image on the photoreceptor 5 is developed with toner by a developing device 6 with a developing bias of 1150 cm.

This first toner image is transferred onto the dielectric layer 12 of the transfer belt 7, which is charged to -1200V by a belt charger 18 to which a voltage of -5.5KV is applied. At this time, the contact roller 14 is separated from the transfer belt 7. The first toner image on the transfer belt 7 passes through the belt cleaner 17 without being cleaned. After the first toner image has passed, the belt cleaner 17 cleans by pressing the belt again. When the first toner image passes through the belt charger 18, the belt charger 18 is turned on, and the fjSl toner image is charged to the same polarity as the transfer belt 7.

Next, with the prism 4 retracted from the optical path, place a Pf42 original on the document glass 1, and place the document on the document glass 1.
is moved from left to right in the figure to form a mirror a-electronic latent image on the charged photoreceptor 5. The latent image on the photoreceptor 5 is transferred to the developing device 6.
The image is developed with toner to form a second toner image.

In this case, the ends of the first toner image that has rotated once on the transfer belt 7 and the second toner image on the photoconductor 5 are aligned at the position where the photoconductor 5 and the transfer belt 7 contact each other, so that the same sides are aligned. It is being Further, a timing roller (not shown) is used to move the transfer paper 26 so that the edge of the transfer paper 26 corresponds to the edge of the toner image.
is fed.

When feeding the transfer paper 26, the contact roller 14 is brought into close contact with the transfer belt 7, and the transfer paper 26 fed between them has a potential at least lower than the potential of the photoreceptor 5 due to charge being injected from the contact roller 14. Number 100 ■ high, -700~
The potential is -800 cm, and the toner image of fjS1 on the transfer belt 7 is transferred to the lower surface of the transfer paper 26 due to the surface potential difference with the transfer belt 7.

Furthermore, when the transfer belt 7 rotates and the transfer paper 26 reaches the contact portion between the transfer belt 7 and the photoreceptor 5, the second
The toner image is transferred onto the upper surface of the transfer paper 20 due to the surface potential difference between the photoreceptor 5, the transfer belt 7, and the transfer paper 26.

In addition, when the contact roller 14 is directly grounded, the surface potential of the transfer paper 26 becomes a value almost close to the surface potential of the photoreceptor 5, and the transfer performance is poor when the transfer paper is thick paper or at high temperature. significantly reduced.

In this way, the toner images are transferred to both sides, and the transfer paper 26 discharged from the transfer belt 7 is fed between the upper and lower fixing rollers 20 and 21 whose temperature is controlled at approximately 185° C., and is fixed simultaneously on both sides.

Next, the operation when performing one-sided copying will be explained with reference to FIG.

With the prism 4 retracted from the optical path as shown in the figure, place the original on the platen glass 1, move the platen plus 1 from left to right in the figure, and place a mirror image of the electrostatic potential on the photoreceptor 5. form an image. The latent image on the photoreceptor 5 is developed with toner by a developing device 6 to form a toner image.

Next, a transfer paper 26 is fed between the transfer belt 7 charged by the belt charger 18 and the contact roller 14 so that the edge of the toner image corresponds to the edge of the transfer paper 26, and the photoreceptor 5 and (The toner image is transferred onto this transfer paper 26 due to the surface potential difference between the photo belt 7 and the VT photo paper 26. Then, the transfer belt 7
The toner image is conveyed toward the fixing rollers 20 and 21, and the one-sided copying is completed.

Next, the operation when performing composite copying will be explained with reference to FIG.

With the prism 4 interposed on the optical path as shown in the figure, place the first original on the document table plus 1, move the document table plus 1 from the cloth to the left in the figure, and place it on the photoreceptor 5. A normal e-electronic latent image is formed.The latent image on the photoreceptor 5 is developed with toner by a developing device 6.This first toner image is transferred onto a transfer belt 7 charged by a belt charger 18. The belt cleaner 17 is transferred and rotates once without being cleaned by the belt cleaner 17. The belt cleaner 17 is kept in its pressure contact even after the toner image of !@1 has passed. Also, the belt charger 18 is When the first toner image passes, it is turned off and the close contact roller 14 is also separated.

Next, the document table places a second document on the lath 1, forms a second toner image in the same way as the first toner image, and
The image is transferred onto the transfer belt 7. In this case, the first toner image that has rotated once on the transfer belt 7 and pPJ2 on the photoreceptor 5
The toner images are synchronized so that they correspond appropriately to each other at the position where the photoreceptor 5 and the transfer belt 7 contact each other. Note that since the electrical resistance of the conductive layer 12 of the transfer belt 7 is quite large, its surface potential will hardly attenuate in the time it takes for the transfer belt 7 to rotate twice. The belt cleaner 17 is not pressed against the belt cleaner 17 until the toner image No. 2 passes through the belt cleaner 17, and after the toner image passes through the belt cleaner 17, it is pressed against the belt cleaner 17.

Further, while the first and #S2 toner images pass through the belt charger 18, the belt charger 18 is turned on to charge the toner to the same polarity as the transfer belt 7.

Thereafter, the transfer paper 26 is fed by a timing roller (not shown) so that the edge of the transfer paper 26 corresponds to the edge of the toner image. During this paper feeding, the contact roller 14 is brought into close contact with the transfer belt 7, and the lower surface of the transfer paper 26 fed between them is
Due to the surface potential difference with the transfer belt 7, the composite toner images of the first and ptIJ2 on the transfer belt 7 are transferred. During this composite copying, the close contact roller 14 may be directly grounded. In this way, the composite toner image is transferred to the lower surface of the transfer belt 7.
The transfer paper 26 discharged from the transfer paper 26 is fixed by a fixing row 221 at the lower part, and a composite image is obtained.

Incidentally, if a plurality of developing devices 6 are provided and the colors of the first toner image and the second toner image are changed, a composite image of a plurality of colors can be obtained.

Further, the selection of each copying operation of double-sided copying, single-sided copying, and composite copying is performed using a selection switch provided on a control panel (not shown).

Although the above embodiment shows an example in which the present invention is applied to a copying machine, it can be similarly applied to a printer.

Effects of the Invention According to the electrophotographic image forming apparatus of the present invention, since the image is transferred and fixed on both sides of the transfer paper as described above, there is no need to reverse the transfer paper and feed it, and it is possible to print double-sided images at high speed. Moreover, it can be formed without increasing the size of the apparatus, and there is no possibility of paper feeding failure due to heat curl. Moreover, according to the present invention, since the first image and the second image are transferred to the transfer paper separately at the contact roller position and the photoreceptor position,
It is not easily affected by the quality or thickness of the transfer paper, and exhibits great effects such as being able to easily obtain appropriate images.

[Brief explanation of the drawing]

Figures 1 to 5 show an embodiment in which the figures 5 and 5 are applied to a copying machine, in which Figure 1 is a schematic configuration diagram showing the state during double-sided copying, Figure 2 is a partially enlarged sectional view of the transfer belt, and Figure 3 The figure is a schematic configuration diagram showing the state during single-sided copying, FIG. 4 is a schematic configuration diagram showing the state during composite copying, and FIGS. 5(a), (b), (
c) is a circuit diagram showing an example of a charge injection circuit, and FIG. 6 is a schematic configuration diagram of a conventional example. 1... Document platen glass 4... Prism 5... Photoreceptor 7... Transfer belt 11. ..... Conductive base material 12 ..... Dielectric layer 14 ..... Contact roller 15 ..... Charge injection circuit 18...Belt charger 26...Transfer paper agent Patent attorney Masaru Ishihara Figure 5 (a) (b) (c) Figure 6 235 2^3 Fua small F, ya, to -2

Claims (1)

[Claims] (1) A means for selectively forming a positive image and a mirror electrostatic latent image on a photoreceptor; a transfer belt capable of transferring the transfer belt, a charging means for charging the transfer belt, and a conductive contact between the charging means and the photoreceptor that is capable of contacting and separating from the transfer belt and is grounded via a charge injection circuit. An electrophotographic image forming apparatus equipped with a roller.