JPS60181762A - Two-color image forming device - Google Patents

Abstract

PURPOSE:To prevent toner for forming the 2nd image forming toner from sticking on a thin line part and an edge part of the 1st image and causing color mixture by using a specific corona discharger when a photosensitive body is secondarily charged electrostatically to the opposite polarity of primary electrostatic charge while the 1st visual image is left formed on the photosensitive body. CONSTITUTION:A secondary electrifier 12 consists of a conductive shield member 20, corona wire 21, corona ion flow control screen 22, corona generating power source 23, and bias power source 24. The screen 22 consists of a conductor part 25 extending in parallel to the corona wire 21 and an insulating part 26 which covers it, and the conductor part 25 is connected to the power source 24. When a voltage is impressed from the power source 23 to the corona wire 21, the surface of the insulating part 26 is charged electrostatically positively with corona ions and the conductor part 25 is grounded through the power source 24, so electric power shown by a broken line arrow is generated at a thin gap part of the screen 22 and corona ions 27 advance in the normal direction of the photosensitive body 10. Thus, color mixture due to the toner for forming the 2nd image is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer using electrophotographic technology, and particularly relates to a two-color image forming apparatus.

[Prior art and its problems]

2. Description of the Related Art A corona discharger conventionally used for secondary charging with a polarity opposite to primary charging, particularly in a two-color image forming apparatus using a bipolar photoreceptor, will be described with reference to the drawings.

Figure 1 shows a conventional corona discharger, with corona wire 1
A charging voltage composed of a conductive shield 2 and a conductive shield 2 is applied to the corona wire 4.1 to ionize the surrounding air. This ionized gas travels from the opposing pole toward the conductive head of the photoreceptor according to its polarity, and charges the photoreceptor 3 provided on the conductive head. However, the corona ion flow generated from this corona discharger is radial as shown in FIG. When secondary charging with opposite polarity is performed using an electric device, corona ions of opposite polarity will concentrate in areas with large potential contrast such as etched areas and thin line areas of the first image, and the amount of charge in these areas will increase during the second development. There has been a problem in that the toner for the first image and the toner for the second image are mixed with each other at the time of the second development.

In order to solve this problem, a corona discharger as shown in Figure 2 was proposed.

This corona discharger is composed of a corona wire 1, a conductive shield 2, and an insulating slit member 4. It is designed to be released from the inside of the body.

Although this corona discharger improves the straightness of the corona ion flow to some extent, it only narrows the so-called emission angle of corona ions, so it is still a two-color image forming device using a bipolar photoreceptor. When used for reverse polarity secondary charging, it was not possible to completely prevent color mixing at the edges and thin line areas of the first image that occurs during development of the second image.

Figure 3 shows how a conventional corona discharger is used in a two-color image forming apparatus.
FIG. 3 is a process model diagram when used in a secondary charger.

In step (a), the bipolar photoconductor P is primarily charged with a predetermined polarity. Next, in step (b), the manuscript OR,
The first g@light of (two-color image A-13 on white background C) is transmitted through a filter that blocks the A color and transmits the B color. The step (c) is the first development, in which the A color toner is attached. The step (d) is secondary charging with the opposite polarity to the primary charging, but as mentioned above, secondary charging; Since the corona ions of one charge concentrate on the edge part of the first image where the potential contrast is large, the potential of the A color toner adhesion area is also reversed to negative, which is the polarity of the secondary charge, and that potential is B It reaches the bias level during color development.

As a result, as shown in (B), after performing the second exposure through a filter that blocks at least the A color, when performing the second development with the A color toner, 8 colors are applied to the area that has already been developed with the A color. Toner gets on top of the paper, causing color mixing.

This tendency is remarkable in the thin line portions and edge portions of the first image, and all of the above-mentioned conventional techniques have this drawback.

Moreover, in the conventional technology shown in FIG. 2; Since the corona ions that contribute to the 11 charge are only the ions emitted from the slit portion of the slit member 4, there is also a drawback that the charging efficiency is poor.

[Purpose of the invention]

In view of the above-mentioned conventional drawbacks, the present invention provides a corona ion flow control screen that is disposed at or near the opening for corona ion irradiation, so that toner for forming the second image adheres to the fine line portions and etched portions of the first image. It is an object of the present invention to provide a two-color image forming apparatus equipped with a corona discharger that does not cause so-called color mixing.

[Key points of the invention]

In order to achieve the above two objects, the present invention performs primary charging with a predetermined polarity, and performs the primary charging on a photoreceptor on which a first latent image or a first developed image is still formed by image exposure, development, etc. The method is characterized by using a corona discharger in which a corona ion flow control screen is disposed at or near an opening for irradiating corona ions in order to perform secondary charging of opposite polarity.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 is a block diagram of a two-color image forming apparatus according to the present invention.

The two-color image forming apparatus includes a photoreceptor 10, a primary charger 11, a secondary charger 12, and a first developer 13 as its peripheral devices.
, a second developing device 14, an exposure section 15, a polarity matcher 16, a transfer device 17, a cleaner 18, an eraser lamp 19, and the like.

FIG. 5 shows an example of the configuration of the secondary charger 12 used in the present invention.

The secondary charger 12 includes a conductive shield member 20, a corona wire 21, a corona ion flow control screen 22, a corona generation power source 23, and a bias power source 24.

The opening of the shield member 20 has a width of 20 to 30 mm, and the corona wire 21 is made of a tungsten wire or a gold-plated tungsten wire with a wire diameter of 5 to 80 μm. In addition, the corona wire 21 has
A predetermined voltage is applied from the corona generation power source 23.

The corona ion flow control screen 22 is disposed at or near the opening of the shield member 20, as shown in FIG. 5, and is connected to a bias power source 24.

Further, as shown in FIG. 6, the corona ion flow control screen 22 includes a plurality of conductor portions 2 extending parallel to the corona wire 21.
5, and an insulating part 26 coupled to the corona wire side of the conductor part 25, and the plurality of conductor parts 25
is connected to the screen bias power supply 24.

Ion flow control screen 22 configured as shown below.
When a voltage of, for example, about 5000V to 6000V is applied to the corona wire 21 from the corona generation power supply 23,
The corona ions generated thereby positively charge the corona wired side of the ion flow control screen 22, that is, the surface of the insulating section 26.

At this time, the conductor portion 2 of the corona ion flow control screen 22
5 is grounded via the screen bias power supply 24, so that lines of electric force are generated in the gap between the ion flow control screens 22 as shown by broken arrows in FIG.

The subsequent corona ions 27 are accelerated along the direction of the generated electric lines of force and travel at high speed toward the photoreceptor 10 from the normal direction thereof, as shown in FIG. Therefore, the corona ions 27
Since it moves straight, the whole can be uniformly shifted to the positive side while maintaining the contrast of the potential formed by the first electrostatic latent image.

Next, an example of a two-color image forming process using the above-mentioned secondary charger will be described. First, as shown in FIG. 8(a), the surface of the photoreceptor 10 is uniformly negatively charged by the primary charger 11. give Next, when an optical image of the original 28 (having a red part R and a black part BK on a white background part W) is exposed through or without the red filter 8a, the red corresponding area and the white background corresponding area on the photoreceptor 10 are The surface potential decreases significantly due to light attenuation, but in the black corresponding area, the first electrostatic latent image remains at its initial level without light attenuation, and the first electrostatic latent image is shown in Fig. 8fb.
) is formed as shown in FIG.

Next, when this primary electrostatic latent image is developed with a first developing device holding black toner, the positively charged black toner 29 adheres only to the black corresponding portion of the photoreceptor IO, as shown in FIG. do. Here, it is important to make sure that the potential of the black corresponding area after black development is almost the same as before development, and to maintain the potential difference between the black corresponding area and the red corresponding area or white background corresponding area to an appropriate level. This is very important in preventing the red toner 30 from adhering to the black corresponding portion of the photoreceptor 10 as well. For this purpose, the resistance of the developer during development of the first color, i.e., the resistance of the developer if it is a -component developer, and the resistance of the carrier or the developer containing carrier and toner if it is a two-component developer. It needs to be sufficiently high. In other words, if the resistance of the developer during black development is low,
The electric charge in the black corresponding area leaks to the developing device side through the developer and the potential decreases.Conversely, charge is injected into the white background corresponding area or red corresponding area from the developing device side and the potential increases, so the black corresponding area The potential difference between the black background corresponding part and the white background corresponding part or the red corresponding part becomes smaller, and if secondary charging is performed without any measures, the potential difference between the black background corresponding part and the white background corresponding part or the red corresponding part will further decrease.

For this reason, when the resistance of the developer is 10<9> Ωcm or more, there is almost no potential drop due to charge leakage in the black corresponding area, and no variation in potential occurs in the white background or red corresponding areas.

Next, the secondary charger 1 of the corona ion flow control screen
When a positive secondary charge with a polarity opposite to that of the primary charge is applied to the surface of the photoreceptor 10 by using 2, the potential polarity of the area corresponding to the white background and the area corresponding to the red color is reversed and becomes positive, as shown in the figure (d+). Although it is charged, since the black corresponding portion is originally held at a high potential of negative polarity, its surface potential decreases to zero level due to positive charging.

That is, in this secondary charging process, the potentials of the white background corresponding area and the red corresponding area, which had decreased to zero level on the negative polarity side due to optical attenuation, are reversed to a higher positive potential to enable development. In addition, it is of course possible to lower the potential of the black corresponding area to a sufficiently lower potential level than the developable potential, but conventionally, the electric field contrast of the first image with the surrounding area is particularly high. Positive corona ions of opposite polarity due to secondary charging concentrate and flow into black thin lines and edge areas, and their potential is raised to the opposite polarity, and the red toner 30
In contrast, in the present invention, the corona discharge current of the secondary charger flows into the surface of the photoreceptor 10 from the direction normal to the surface of the photoreceptor 10.
In addition, since the speed is fast, the straightness is high, and it is possible to prevent corona ions from concentrating on one part, so it is possible to prevent red 1 to ner from adhering to fine lines and edges of the first image.

In the present invention, a corona ion flow control screen is used to
Since the subsequent charging is performed, a potential contrast sufficient to prevent the toner for the second image from adhering to the thin line portions, edge portions, etc. of the first image can be obtained.

After this secondary charging is completed, image exposure of the document 28 is performed again in synchronization with the formation of the first electrostatic latent image through the cyan filter 8b that blocks the red light component.
As shown in 1, the potential of the white background area is greatly reduced due to optical attenuation, but since the red area is not exposed to light, the potential of the red area is not attenuated by light and maintains the potential level at the time of secondary charging. , a second electrostatic latent image is formed with charges remaining only in the red-corresponding portion (FIG. 2(e)). Next, when this second electrostatic latent image is developed with a red developing device, the negatively charged red toner 30 adheres only to the red corresponding portion, as shown in ff) of the figure. Therefore, on the photoconductor 10, the black corresponding area is developed with the positively charged black toner 29, and the red corresponding area is developed with the negatively charged red toner 30, so that the two-color toner is developed with the negatively charged red toner 30. All images are formed fAY brightly and with sufficient density.

This photoreceptor 1 (IJ2) transfers the two-color toner image to a transfer device 17.
By transferring the image onto a transfer paper and fixing it, a final two-color image is obtained. At this time, an electrostatic transfer method, a pressure transfer method, a thermal transfer, etc. can be adopted as a transfer method, but in the case of an electrostatic transfer method, the two-color image on the photoreceptor IO is correctly transferred as described above. Since the two toners each have a negative charge, it is necessary to reverse the charge of one of the toners using a polarity combiner prior to transfer. For example, if the polarity of the first charge toner in the red corresponding area is reversed to positive polarity using a corona discharger, the toner image can be transferred all at once by applying negative polarity charge from the back side of the transfer paper during transfer. can.

In the two-color image forming apparatus of the present invention, as described above, the toner for forming the second image does not adhere to the fine line portions and edge portions of the first image, and the red and black images are clear and have sufficient density. You can make a two-color copy of .

Note that the shape of the :JL:lnion flow control screen is not limited to parallel lines, and the same effect can be obtained even if it is in the form of a grid, t)x lines, or concentric circles. Further, the cross-sectional shape is not limited to a circular shape, but may be rectangular as shown in FIG. 9, for example.

Corona ion flow control screen is a conductive plate with many fine holes, such as iron, aluminum, copper, etc.
It may also be a plate with a thickness of about 0.01 to 1.0 mm coated with a photosensitive resist to a thickness of 30 to 200 μm, the hole pattern burnt out, and etched with a suitable chemical solution.

In addition, insulator resin was applied to one side of a net-like braided wire made of the above material by spraying to a thickness of 30 μm to 20 μm.
It may be coated with a thickness of 0 μm, or it may be a plastic mesh coated with a suitable metal deposited on one side in a thickness of several μm to several + several μm.

The size of these holes and the density of the holes are determined depending on various conditions such as the latent image potential, exposure, and development of the two-color image forming process used in the present invention.

Further, the shape of the hole may be any shape such as circular, polygonal, irregular, etc., but in the case of a circular shape, good results were obtained when i\ was 1 mm or less.

In addition, the set voltage applied to the conductor part of the corona ion flow control a11 screen varies depending on the configuration, shape, effective diameter of the holes, etc. of the screen, but generally speaking, if a voltage with the opposite polarity to that of corona ions is applied, the corona ion flow will be reduced. Ions are absorbed into the conductor portion, resulting in low ion passage efficiency.

Furthermore, if an unnecessarily high voltage of the same polarity is applied, the passage of ions is blocked due to lines of electric force generated between the screens, and the ion passage efficiency is similarly reduced.

Generally, for a mesh screen of 16 to 300 mesos, when the corona ions are positive, the applied voltage is 1000 V to 3
000V is good.

It is more effective to make the distance between the ion flow control screen and the photoreceptor surface as close as possible.

However, if they are brought too close together, spark discharge will occur between the surface of the photoreceptor and the conductor portion 25.

Therefore, in the configuration of the above embodiment, the distance between the conductor part of the corona ion flow control screen and the surface of the photoreceptor is 1 mm to 5 mm.
It is desirable to set it between mm.

FIG. 9 shows another embodiment of the invention. The corona ion flow control screen 22 has a rectangular cross section, and the conductor portion 2
5 and an insulating section 26.

The ion flow control screen configured as described above also achieved the same effects as the screen configured as described above.

FIG. 10 shows another embodiment of the present invention, which differs from the above embodiment in that the insulation part of the corona ion flow control screen is provided not only on the corona wire side but also on the photoreceptor side. are doing. That is, the corona control screen 31 of this embodiment is composed of a conductor section 32 and insulating sections 33 and 34 provided on both upper and lower surfaces of the conductor section 32.

The corona ion flow control screen 31 configured as described above can suppress spark discharge between the photoconductor surface and the conductor section 32 by the insulating section 34 on the photoconductor side. The distance r between and the photoreceptor surface
411 can be set even smaller. Of course, this corona ion flow control screen 31 differs from the above-described corona ion flow control screen 22 only in that the insulating section is provided not only on the corona wire side but also on the photoreceptor side. Similarly, it can be configured in various ways.

As another application process, the surface of a bipolar photoreceptor is uniformly negatively charged, and then imagewise exposed through a red filter to form a first electrostatic latent image. After positively charging other parts other than the first electrostatic latent image forming part, image exposure is performed again through a cyan filter to form a second electrostatic latent image, and the first electrostatic latent image and the second electrostatic latent image are formed. Even in a two-color image forming apparatus in which two electrostatic latent images are sequentially developed and visualized using developing units each having toner of each color, such as black and red, which are charged with opposite polarities, the secondary charging according to the present invention can be performed in the same way. has the effect of

Further, in each of the embodiments described above, a voltage applying power source was used for screen bias, but the conductor portion of the corona ion flow control screen may be grounded via a resistor or the like. In this case, corona ions flow into the conductor section, producing a voltage corresponding to the resistance.

Further, the resistance value of the intervening resistor can be arbitrarily selected depending on the shape of the screen, charging voltage setting, etc.

Furthermore, the screen may be composed of the conductor section alone.

〔Effect of the invention〕

According to the two-color image forming apparatus of the present invention equipped with the corona discharger configured as described above, the corona discharge current is electrically accelerated by the control screen, and the corona discharge current is accelerated from the normal direction to the photoreceptor surface. Since the flow becomes a parallel flow, the straightness is improved, and the corona does not flow concentratedly into areas where the potential difference with respect to the corona wire on the photoreceptor is large, so that a large positive and negative potential difference can be obtained after secondary charging.

Therefore, not only can color mixture be prevented, but also the image density of the second color can be sufficiently reproduced.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a conventional corona discharger, FIG. 2 is a configuration diagram of another conventional corona discharger, and FIG. 3 is a configuration diagram showing a conventional corona discharger.
FIG. 4 is a process model diagram of a two-color image forming process using a conventional corona discharger, and FIG. 5 is a block diagram of a two-color image forming apparatus for carrying out the present invention. FIG. 6 is an explanatory diagram showing the control state thereof, FIG. 7 is a diagram showing the operating state of corona ions in the case of the present invention, and FIG. 8 is a diagram showing the secondary charging device of the present invention. FIGS. 9 and 10, which are process model diagrams of the two-color image forming process, are block diagrams showing other embodiments of the present invention. 8... Red filter, 10... Photoreceptor, 11...
・Primary 4() electric appliance, 12...Secondary charger, 13.
...First developer, 14...Second developer, 15...
Exposure section, 1G... polarity matcher, 17... transfer device,
18...Cleaner, 19...Eraser lamp,
20...Shield Sun/Month, 21...''1'J Nasoiya, 22.31...Ion flow control screen, 23...Power source for corona generation, 24...Power source for bias, 2-. 5.32...
・Conductor part, 26° 33.34... Thread color ttff 1st generation 27... Corona ion, 28... Manuscript, 29
...Black toss -130...Red toner. Patent Applicant Casio Needle Calculator Co., Ltd. ID Co., Ltd. Representative Patent Attorney Yoshi Osuga 2 Figure 1 Figure 2 Figure 4 Figure 5 Figure 6 Figure 6 Figure 7 Figure 8 (b) Mouth Ear eco, 10

Claims (6)

[Claims] (1) Perform primary charging with a predetermined polarity, and apply a secondary 11) charge of opposite polarity to the primary charging on the photoreceptor on which the first latent image or first developed image is formed by imagewise exposure, development, etc. A two-color image forming apparatus characterized in that a corona discharger is used in which a corona ion flow control screen is disposed at or near an opening for corona ion irradiation. (2) The two-color image forming apparatus according to claim 1, wherein the corona ion flow control screen is comprised of a conductive member and an insulating member. (3) The two-color image forming apparatus according to claim 2, wherein the insulating member is provided on a surface of the conductive portion facing the solar ion generating portion. (4) The two-color image forming apparatus according to claim 2, wherein the insulating member is provided on the surface of the conductive member on the corona ion generating section side and the surface on the photoreceptor side, respectively. (5) The two-color image forming apparatus according to any one of claims 2 to 4, wherein the conductive member is grounded via a bias power source. (6) The two-color image forming apparatus according to any one of claims 2 to 4, wherein the conductive member is grounded via a resistor.