JP2603129B2 - Two-color image forming apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming apparatus such as an electrophotographic copying machine,
In particular, an image to be formed can be displayed in two colors.
The present invention relates to a color image forming apparatus.

2. Description of the Related Art At present, an electrostatic recording method using electrophotography is widely applied to a printer as a terminal device of information equipment such as a computer, a facsimile, and a CAD.

These printers use laser beams, LEDs, LCDs
An information signal is written as an electrostatic latent image on a photoconductor (electrostatic latent image carrier) by, for example, and the electrostatic latent image is visualized by a developing device. Then, the visible image is transferred to a transfer paper. Furthermore, the transferred image is fixed on transfer paper to obtain a recorded image.
In general, the recorded image was a single color such as black.

However, for example, when calculating values or data values are formed in a color different from the format color, or when a part of a drawing output by CAD is formed in another color to distinguish images in multiple colors,
The image becomes clear and the content becomes easy to understand. Thus, discriminating images in multiple colors is an effective means for better understanding information. Therefore, conventionally, an image forming method for forming a multicolor image by an electrostatic recording method has been proposed. Hereinafter, a basic two-color image among multicolor images will be described.

The method of forming the two-color image is performed as follows. That is, as shown in FIG. 5, a photosensitive drum (electrostatic latent image carrier) 1 having a photoconductive layer coated on a conductive substrate is charged to a charger 2.
To form a first latent image by exposing with a first information signal 3 by a light emitting element such as a laser, and visualizing the first latent image by a first developing device 4 (hereinafter referred to as a first latent image).
Color development). Next, after the photosensitive drum 1 is recharged by the recharger 7, the photosensitive drum 1 is exposed to the second information signal 5 and
Is visualized by the second developing device 6 (hereinafter, referred to as second color development). The visualized toner images are transferred to transfer paper 9 by a transfer charger 8, and then fixed by a fixing device 10. Also, the photosensitive drum 1
The upper transfer residual toner is cleaned by the cleaning device 11, and the residual surface charge is removed by an eraser lamp (not shown).

By the way, in such a two-color electrophotographic apparatus, the toner visible image of the first color on the photosensitive drum 1 adheres to the photosensitive drum 1 due to the effect of the reflection force. There is a problem that the toner of the first color is mixed into the second developing device during the two-color development. to solve this problem,
For the first color development, a two-component magnetic brush development method using a developer composed of a non-magnetic toner and magnetic particles (carrier) is said to be suitable. In the case of the two-component magnetic brush developing method, the amount of charge of the toner is higher than that of the one-component developing method using a magnetic toner, so that the mirroring force with the photosensitive drum also works so strongly, and the above-described problem hardly occurs. is there. Also, 1
If the color toner image is recharged with the same polarity as the polarity of the toner, the charge amount of the toner increases, the adhesion between the toner layer and the photosensitive drum increases, and the toner of the first color becomes the second color. It is possible to more effectively prevent mixing in the developing device. However, since a small amount of carrier adheres to the photosensitive drum and adversely affects the image, conventionally, a carrier collection roller 13 is provided to collect the carrier on the photosensitive drum.

Next, regarding the developing method of the second developing device, it is preferable to adopt a non-contact developing method in order not to disturb the toner image of the first color on the photosensitive drum. The jumping development method used is said to be suitable.

The first and second developing devices used for the above-described image formation include a sleeve and a magnet roller as a developer carrier, and the sleeve and the magnet roller are arranged in a longitudinal direction, for example, at a sixth position. It was configured as shown in the figure.

That is, as can be understood with reference to FIG. 6, the photosensitive drum 1 as a latent image carrier is provided on both ends of the sleeves 41 and 61 as the developer carrier in the first and second developing devices. Spacer rollers 45 and 65 are rotatably arranged as contact members for keeping the gap between the sleeves 41 and 61 at a predetermined value, for example, about 50 to 500 μ. Is made of high-density polyethylene, fluororesin, or the like having excellent wear resistance. Furthermore, gears 46 and 66 for driving the sleeves 41 and 61 are provided on one end of the sleeves 41 and 61, and magnet rolls 42 included in the sleeves 41 and 61 are provided on the other end.
Shafts 42a, 62a for fixing 62 protrude.

The first and second developing devices configured as described above are operated according to a predetermined process, and a latent image formed on the photosensitive drum is developed by a magnetic brush developing method, a jumping developing method, or the like.

Problems to be Solved by the Invention Here, in order to perform the first color development, as described above,
A two-component developing method comprising a carrier and a non-magnetic toner is preferable. However, during printing by repeating the above-described image forming process, the carrier is discharged from the end of the developer application area on the sleeve of the first developing device. A small amount of the toner is leaked and adheres to the photosensitive drum, and the carrier adhered to the photosensitive drum is trampled by the space roller 65 of the second developing device.
Of the conductive substrate (usually, aluminum is used), and the shaved powder is used as the sleeve of the second developing device 6.
There is a case where a problem arises that the liquid crystal enters between the photosensitive drum 1 and the photosensitive drum 1 and causes leakage of the developing bias. In order to solve this problem, conventionally, a carrier collecting device for collecting the carrier leaked from the first developing device is provided between the first developing device and the second developing device in the vicinity of the photosensitive drum 1. As described above, there is a method of providing the roller 13, but this method has a disadvantage that the image forming apparatus becomes large-scale and the cost increases.

Accordingly, the present invention has been made in order to solve the above-mentioned drawbacks, and an object of the present invention is to form a two-color image through a predetermined process and leak as a latent image carrier from the first developing device. The developer carrier attached to the photosensitive drum is significantly reduced, and the spacer roller of the second developing device arranged to maintain a predetermined gap with the photosensitive drum is prevented from stepping on the carrier attached to the photosensitive drum. Accordingly, an object of the present invention is to provide a two-color image forming apparatus capable of obtaining a two-color image of good image quality without adversely affecting the operations of the photosensitive drum and the developing device.

Means for Solving the Problems The above object is achieved by a two-color image forming apparatus according to the present invention. That is, in summary, the present invention forms two types of latent images by performing exposure based on different image signals on a uniformly charged latent image carrier, and forms a second latent image corresponding to each latent image. In a two-color image forming apparatus that develops a two-color image by performing development with a first developing device and a second developing device, the developing device includes a developer carrier that is outside the developer application area of the developer carrier of the first developing device. A magnetic force on the surface of the latent image carrier in a portion opposed to the latent image carrier is provided in the second developing device in order to make contact with the latent image carrier while maintaining a predetermined gap. A two-color image forming apparatus in which a contact member is provided.

According to the present invention, the magnetic force on the surface of the photosensitive drum outside the developer application area of the sleeve as the developer carrier of the first developing device and at the opposing portion between the sleeve and the photosensitive drum as the latent image carrier is 300 G or less. A spacer roller as a contact member provided in the second developing device for contacting the photosensitive drum was provided in the region of, and was brought into contact with the photosensitive drum, thereby leaking from the first developing device and adhering to the photosensitive drum. This solves the conventional problem that the carrier is stepped on by the space roller of the second developing device, thereby scraping the photosensitive drum, thereby leaking the developing bias.

Embodiments Hereinafter, the present invention will be described based on one embodiment with reference to the accompanying drawings.

FIG. 2 is a schematic sectional explanatory view of one embodiment of the two-color image forming apparatus according to the present invention. Referring to FIG.
The color image forming apparatus includes a photosensitive drum 1 as a latent image carrier rotatable in an arrow direction (clockwise direction). Along the rotation direction of the photosensitive drum 1, the charger 2, the first exposure device 3, the first developing device 4, the recharger 7, the second exposure device 5,
Second developing device 6, transfer charger 8, cleaning device 11
, Respectively, are sequentially arranged.

The image forming process of the two-color image forming apparatus having such a configuration will be briefly described below.

That is, when forming a two-color image, first, the surface of the photosensitive drum 1 is
After that, the surface of the photosensitive drum is exposed to, for example, a laser beam corresponding to the first image signal from the first exposure device 3 to form a latent image corresponding to the first image information. The first latent image is visualized by a first developing device 4 using a developer comprising a carrier (magnetic particles) and a non-magnetic toner.

Next, in order to form a second color image, the surface of the photosensitive drum is uniformly recharged by the recharger 7, and then, similarly to the formation of the first color image, the surface of the photosensitive drum is subjected to the second exposure. Exposure is performed by, for example, a laser beam corresponding to the second image signal from the device 5 to form a latent image corresponding to the second image information. The second latent image is formed by using a developer made of a magnetic toner. Second
The developing device 6 visualizes the image by, for example, jumping development. At this time, ie, when shifting from the formation of the first image to the formation of the second image, the first image is formed while the image forming process is repeatedly performed. Since the carrier may leak from the end of the developer application area on the sleeve 41 of the developing device 4 and adhere to the photosensitive drum 1, the attachment of this carrier onto the photosensitive drum will be described below with reference to FIG. Details will be described.

Referring to FIG. 1, there is shown a first developing device 4 of a two-color image forming apparatus of the present invention used for the above-described image formation, and the first developing device includes a sleeve as a developer carrier. 41 and a magnet roller 42 are provided.

FIG. 1 shows a developing section A (sleeve 41) formed by a sleeve 41 and a magnet roller 42 of the developing device 4, a developer application area D thereof, and a developing pole of the magnet roller 42.
FIG. 3 is a diagram showing the relationship of magnetic force on the surface of the photosensitive drum 1 in a portion where the surface and the photosensitive drum 1 are opposed to each other) as viewed from the longitudinal direction.

As will be readily understood with reference to FIG.
Ideally, the developer is applied only to the developer application area D on the surface of the sleeve 41 shown in FIG. 1, but the sleeve 41 is rotating and the magnet roller 42 In practice, it is usually set to be about 2 to 5 mm longer than the end of the developer application area D so that stable application of the developer is performed at the end of the area D. Since the magnetic binding force exists outside the developer application area D,
Although small, it is inevitable that the carrier adheres to the surface of the sleeve 41 outside the developer application area D.

Further, the length of the magnet roller 42 is changed to the developer application area D.
Even if the length is the same, as shown in FIG. 1, the magnetic force at the end of the magnet roller 42 gradually decreases, so that the magnetic force also exists outside the developer application area on the surface of the sleeve 41. Similarly, the phenomenon that the carrier adheres to the outside of the developer application area D is inevitable.

The carrier adhering to the outside of the developer application area D on the sleeve 41 in this manner is a magnetic force constrained on the surface of the sleeve 41 by the magnet roller 42, a centrifugal force separating from the surface of the sleeve 41, and a force between the sleeve 41 and the photosensitive drum 1. The antagonism of Coulomb force or the like caused by the carrier itself acting on both sides having an electric charge determines whether the carrier remains on the sleeve 41 or adheres to the photosensitive drum 1.

Here, as the carrier, for example, a fluorine-coated ferrite insulating carrier having a particle size of about 60 μm is used, the sleeve 41 is 20 mm in diameter, the rotation speed is 80 rpm, and the photosensitive drum 1 in the developer application area D in the developing section A is used. Magnetic force of 1000G
(Gauss), an experiment was conducted to observe the adhesion state of the carrier on the sleeve 41 and the photosensitive drum 1. When the magnetic force was 600 G or more outside the developer application area D, most of the carrier was observed. Is restrained on the sleeve 41, and a very small amount of carrier adheres to the photosensitive drum 1, and the magnetic force is reduced.
On the other hand, in the region of 600 G to 300 G, only a small amount of carrier is constrained on the sleeve 41, and most of the carrier adheres to the photosensitive drum 1. Further, in the photosensitive drum, in the region where the magnetic force was 300 G or less, the carrier did not adhere on the sleeve 41 or the photosensitive drum 1. This is because when the carrier leaks from the developer application area D to the outside of the developer application area,
In the magnetic field of 600 G to 300 G, almost all of the leaked carrier adheres to the photosensitive drum 1, and acts as a kind of buffer band. The magnetic field of 300 G or less outside (see the arrow in FIG. 1) This is probably because the region P) does not leak. In addition, the above magnetic force, using a probe SAB4-1802, Gauss meter 640 manufactured by FW Bell, the distance between the measurement surface of the probe and the sleeve 41 was adjusted to the distance between the photosensitive drum and the sleeve. Value to the photosensitive drum 1
The upper magnetic force.

Next, the above-described experiment was performed by changing the magnetic force on the photosensitive drum 1 in the developer application area D in the developing section A to 800 G and 600 G. In the case of the magnetic force of 800 G, similar to the case of the magnetic force of 1000 G, Outside the developer application area D, in an area having a magnetic force of 600 G or more, the carrier adheres to the sleeve 41 and the magnetic force is 600 to 300
In the region G, the carrier adhered to the photosensitive drum 1, and at a magnetic force of 300 G or less, no carrier adhered to either the sleeve 41 or the photosensitive drum 1. The magnetic force on the photosensitive drum 1 in the developer application area D in the developing section A is 600 G
When the photosensitive drum 1 is in the
A magnetic force of 600 G or more is preferable because some carrier adhesion occurs on the upper side.

Further, in the above experiment, the rotational speed of the sleeve 41 was set to 70
rpm, and the magnetic force on the photosensitive drum 1 in the developer application area D in the developing section A was set to 1000 G. Outside the developer application area D, in the area where the magnetic force was 700 G or more, the carrier leaked from the developer application area D was Most of the carrier is constrained by the sleeve 41 or more. In the region of the magnetic force of 700 to 300 G, most of the leaked carrier adheres to the photosensitive drum 1, and in the region of the magnetic force of 300 G or less, the carrier adheres to both the sleeve 41 and the photosensitive drum 7. Was not seen.

In the above experiment, the sleeve 41 and the photosensitive drum 1 were used.
If the gap between the photosensitive drum 1 and the sleeve 41 is too small, the developer in the developing section A will be retained. If the gap is too large, the image will stick or When the solid portion is easily swept by a carrier brush, that is, a magnetic brush, and is extremely large, the magnetic pole configuration of the magnet roller 42 required to obtain a magnetic force of 600 G or more on the photosensitive drum 1 becomes difficult. The gap between the sleeve 1 and the sleeve 41 is preferably set within a predetermined range, and the gap is about 100 to 600 μm.
The degree is preferred.

The developing pole S ₁ of the magnet roller 42 is too distant from the position facing the photosensitive drum 1, the carrier brush at the developing portion A of on the sleeve 41, i.e. the magnetic brush,
The photosensitive drum 1 and the sleeve 41, becomes the sleep state, so disadvantageous to carrier adhesion, developing pole S ₁ as shown in FIG. 3, the peak of the radial magnetic forces photosensitive drum It is desirable that the distance is set to be within ± 30 ° from the opposing position.

As described above, in the developing section where the sleeve 41 of the first developing device 4 and the photosensitive drum 1 are opposed to each other and outside the developer application area, in the region where the magnetic force on the photosensitive drum 1 is 300 G or less, the photosensitive drum 1 On top of 1, no carrier adheres,
The spacer roller 65 of the second developing device 6 is provided in this region as a contact member, and is brought into contact with the photosensitive drum 1 so that the spacer roller 65 as the contact member is moved to the developer application area of the first developing device 4. The carrier leaking from the end D and adhering to the photosensitive drum 1 is not stepped on, so that there is no problem of shaving the surface of the photosensitive drum 1.

In the above embodiment, the sleeve 61 of the second developing device 6 is used.
The spacer roller 65 as a contact member for maintaining the gap between the photosensitive drum 1 and the photosensitive drum 1 at a predetermined value has been described. However, the present invention makes contact with the photosensitive drum 1 so as to maintain the above-mentioned purpose, that is, to maintain the predetermined gap. Any material may be used as long as it is disposed in the space, for example, instead of the spacer roller 65, a sheet-shaped spacer roller may be used, and a sheet of a fluororesin, polyethylene terephthalate, or polyimide having excellent wear resistance is used. be able to.

Next, another embodiment of the two-color image forming apparatus according to the present invention will be described below with reference to FIG.

FIG. 4 shows an improved modification of the magnetic pole pattern on the surface of the photosensitive drum by the magnet roller of the first developing device in another embodiment of the two-color image forming apparatus of the present invention.

With the configuration as in the above-described embodiment, the photosensitive drum 1 leaks from the end of the developer application area D of the first developing device 4.
The spacer roller 65 of the second developing device 6 trampled on the carrier adhered thereon, thereby preventing the photosensitive drum 1 from being scraped. However, the carrier was extremely consumed from the first developing device 4 during repeated printing. In this case, there arises a problem that a new carrier must be replenished to the first developing device 4. This embodiment is designed to solve such a problem relating to the consumption of the carrier, and its purpose is to minimize the leakage of the carrier from the end of the developer application area D of the first developing device 4. It is.

For this purpose, in this embodiment, the magnet roller 42 is magnetized so as to take the magnetic pole pattern shown in FIG. 4, that is, the developing pole of the magnet roller 42 is moved out of the developer application area D, as shown in FIG. By having the magnetic force maximum point as shown in (1), the carrier leaking from the end of the developer application area D is captured at the magnetic force maximum point, so that the carrier leakage can be reduced as much as possible. Becomes It should be noted that the maximum point of the magnetic force must be provided outside the developer application area D in order to prevent the developer application in the developer application area D from being disturbed. Need to be longer,
Conversely, if it is too weak, the effect of trapping carriers will not be produced, so it is appropriate to set the magnetic force difference to a magnetic force of about 20 to 200 G.

Effects of the Invention As described above, according to the two-color image forming apparatus of the present invention, the latent image carrier in the opposed portion between the developer carrier and the latent image carrier of the first developing device of the two-color image forming apparatus By contacting the spacer roller of the second developing device with the region where the magnetic force of the developing pole measured on the surface is 300 G or less, the developing roller leaks from the end of the developer application area of the first developing device and is on the latent image carrier. Problems such as abrasion of the surface of the latent image carrier caused by stepping on the attached carrier by the spacer rollers or leakage of a developing bias applied between the developer carrier and the latent image carrier can be solved. .

Further, by configuring the developing pole of the first developing device to have a maximum point outside the developer application area, it is possible to reduce the amount of carrier leaking from the first developing device and adhering to the latent image carrier. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a sleeve of a first developing device, a magnet roller and a spacer roller, and a magnetic force on a photosensitive drum surface in a developing section generated by a developer application area and a developing pole of the magnet roller. FIG. 2 is a schematic configuration diagram of one embodiment of a two-color image forming apparatus according to the present invention. FIG. 3 is a diagram showing the relationship between the photosensitive drum and the developing pole of the first developing device. FIG. 4 is a diagram showing a magnetic pole pattern on the surface of the photosensitive drum by the magnet roller of the first developing device in another embodiment of the two-color image forming apparatus according to the present invention. FIG. 5 is a schematic configuration diagram of an example of a conventional two-color image forming apparatus. FIG. 6 is an arrangement diagram of a sleeve, a magnet roller, and a spacer roller of a developing device used in a conventional two-color image forming apparatus. 1: photosensitive drum 4: first developing device 6: second developing device 41, 61: sleeve 65: spacer roller D: developer application area

Claims (4)

(57) [Claims] A first developing device corresponding to each of the latent images, forming two types of latent images on a uniformly charged latent image carrier based on different image signals; Second
In a two-color image forming apparatus that develops a two-color image by performing development with a developing device, a two-color image forming apparatus is provided outside the developer application area of the developer carrier of the first developing device, and between the developer carrier and the latent image carrier. The magnetic force on the surface of the latent image carrier in the facing portion is 300 G
A two-color image forming apparatus, wherein a contact member provided in the second developing device is provided in the following area so as to contact the latent image carrier while maintaining a predetermined gap. 2. The two-color image forming apparatus according to claim 1, wherein the first developing device is a two-component developing device using a mixture of magnetic particles and toner as a developer. 3. The developer carrier of the first developing device is non-magnetic and has a magnet roller inside, and the developing roller of the magnet roller has a developing pole of 600 G or more. 2. The two-color image developing apparatus according to claim 1, wherein the image is located within ± 30 [deg.] From an image facing the carrier. 4. The device according to claim 1, wherein a magnet roller is disposed in the developer carrier of the first developing device, and a developing pole of the magnet roller has a maximum point outside a developer application area. Color image forming apparatus.