JP3480779B2 - Multicolor image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus for transferring a toner image formed by an electrophotographic method by a contact transfer apparatus, and more particularly to improving the quality of an image formed.

[0002]

2. Description of the Related Art When a toner image formed on the surface of a photoconductor is transferred onto a recording paper by using a contact transfer device having a transfer belt or a transfer roller, recording is performed by the transfer belt or the transfer roller. Since the paper is pressed against the photoconductor, the gathering force between the toners in the transfer area increases, and an abnormal image called a so-called insect bite print, in which the central portion of the character image is not transferred, is likely to occur. This phenomenon is particularly prominent in thick paper and OHP sheets because the transfer electric field is reduced due to the thickness of the recording paper itself together with the pressure of pressing the recording paper against the photoconductor. As a method for preventing the occurrence of such an abnormal image and forming a high-quality image, there is a method of increasing the voltage applied to the transfer device. Further, as a method of increasing the charging efficiency in corona transfer, preventing the occurrence of an abnormal image, and forming a high-quality image, for example, JP-A-57-82862 or JP-A-6-62862.
As disclosed in Japanese Laid-Open Patent Publication No. 3-292164, a method is used in which a pre-transfer charger is provided and the toner image formed on the photoconductor is recharged before transfer. A similar method is also applied to the roller transfer method, which is contact transfer, as disclosed in, for example, JP-A-3-
No. 102382 is disclosed.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 4-3179, after exposing the photoconductor charged by the first charging means, the first developing means develops with the first color, and thereafter, In a two-color image forming apparatus which exposes a photoreceptor charged by two-charging means and develops a second color by a second developing means to form a two-color image, the first developing on the upstream side in a single-color image forming mode. When a monochromatic image is formed using the means, the charged photoconductor is discharged by the second charging means to improve the transfer efficiency.

[0004]

When the voltage applied to the transfer device is increased as described above, transfer defects in a wide area, such as abnormal images called so-called prints, occur due to electric leakage or discharge at the transfer entrance. There is a fear that a too high applied voltage cannot be applied, and it cannot be said that this is a sufficient countermeasure. Further, the method of providing a pre-transfer charger and recharging the toner image formed on the photoconductor before transfer to increase charging efficiency requires a dedicated charger, resulting in cost increase.

Further, in the two-color image forming apparatus, when a single-color image is formed by using the first developing means on the upstream side in the single-color image forming mode, the charged photoreceptor is discharged by the second charging means. Causes a charge having a polarity opposite to that of the developing toner charging polarity, and when the contact transfer device is used, the above-mentioned problem of abnormal image becoming more prominent occurs.

The present invention has been made in order to solve the above drawbacks, and an object thereof is to obtain a multicolor image forming apparatus capable of forming an image of good quality by using a contact transfer device with a simple structure. To do.

[0007]

SUMMARY OF THE INVENTION A multicolor image forming apparatus according to the present invention comprises a charging device for charging a rotating photoconductor, an exposure unit for exposing the charged photoconductor surface, and a latent image on the exposed photoconductor surface. A plurality of sets of developing devices for developing the toner in the rotation direction of the photoconductor, forming a single-color or multicolor toner image on the surface of the photoconductor, and transferring the formed toner image to recording paper by a contact transfer device. In a color image forming apparatus, when a monochromatic image is formed, the toner image formed on the surface of the photoconductor is
A developing device on which the toner image is formed before being transferred to recording paper.
Of the charging device provided on the downstream side of the photosensitive member in the rotation direction of the photosensitive member.
Charging the electric potential higher than the charging potential during multicolor image formation
Recharge the photoconductor on which the toner image is formed by setting the potential
It is characterized by

A second multicolor image forming apparatus according to the present invention develops a charging device that charges a rotating photoconductor, an exposure unit that exposes the charged photoconductor surface, and a latent image on the exposed photoconductor surface. Multi-color image formation in which a developing device and a plurality of sets with respect to the rotation direction of the photoconductor are formed, a monochromatic or multicolor toner image is formed on the photoconductor surface, and the formed toner image is transferred to recording paper by a contact transfer device. In the apparatus, the cohesion of the toner used in each of the developing devices is set to decrease from the upstream side to the downstream side in the rotation direction of the photoconductor, and the monochromatic image is formed on the photoconductor surface. Record toner image
A developing device that has formed the toner image before transfer to paper
The charging voltage of the charging device installed on the downstream side of the rotating direction of the photoconductor
The charging potential is higher than the charging potential when forming a multicolor image.
And recharge the photoconductor on which the toner image is formed.
Is characterized by.

[0009]

[0010]

Further, the toner formed on the surface of the photoconductor
It is preferable to have a recharge mode selection switch for selecting a mode for recharging the image.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a first charging device and a first exposure unit for exposing the surface of a charged photoreceptor to the upstream side in the rotational direction of a photoreceptor rotating clockwise are provided. The apparatus includes a second charging device, a second exposing unit that exposes the charged surface of the photoconductor, and a second developing device downstream of the first developing device in the rotation direction of the photoconductor. A belt transfer device is provided on the downstream side of the second developing device.
The first developing device uses a black toner having a high cohesion degree, for example, and the second developing device uses a red toner having a low cohesion degree, for example, to form a black-red two-color image or a single-color image. To do. The second developing device maintains a minute gap with the photoconductor only when developing a red toner image, and separates from the photoconductor when forming a black toner monochromatic image.

When forming images of two colors of black and red, a black toner image is formed on the surface of the photoconductor by the first charging device, the first exposure section and the first developing device. An image of a red toner is formed on the surface by the second charging device, the second exposure unit, and the second developing device. The formed two images of black and red are transferred onto a recording paper by a belt transfer device.

Further, in the case of forming a monochromatic image of only the black toner by the first developing device, a grit potential different from that in the two-color image formation is applied to the second charging device and the black toner is applied.
By recharging the formed photoreceptor, the transfer resistance due to the gathering force between toners in the transfer area is reduced to enhance the transfer force, and it is possible to prevent the occurrence of an abnormal image called so-called insect bite print, Transfer a different image to the recording paper.

The recharging by the second charging device is performed when the manual feeding using thick paper or the like is selected or when the recharging mode selection switch of the operation unit is selected, and the power consumption and the ozone are reduced. Reduce the occurrence.

Further, a black toner having a high degree of cohesion is used for the first developing device provided on the upstream side in the rotational direction of the photoconductor, and the cohesion degree is used for the second developing device on the downstream side in the rotational direction of the photoconductor. The second charging device is driven only when a monochrome toner image of a black toner having a high cohesion is transferred to a thick paper using a small red toner, and a high quality image is always formed.

[0017]

1 is a block diagram showing an embodiment of the present invention. As shown in the figure, the image forming apparatus includes a photosensitive member 1 that rotates clockwise, a first charging device 2 that charges the photosensitive member 1, a first exposure unit 3 that exposes the surface of the charged photosensitive member 1 and an exposure unit. A first developing device 4 for developing the latent image on the surface of the photoconductor 1 is provided on the upstream side in the rotation direction of the photoconductor 1, and is exposed on the downstream side of the first developing device 4 in the rotation direction of the photoconductor 1. A second charging device 5 for charging the body 1, a second exposure unit 6 for exposing the surface of the charged photoreceptor 1 and a second developing device 7 for developing a latent image on the exposed surface of the photoreceptor 1 are provided. ing. A belt transfer device 9 having a bias roller 8 is provided on the downstream side of the second developing device 7. First developing device 4
Is a black toner, and the second developing device 7 is a red toner. This second developing device 7 can be moved with respect to the photoconductor 1 by a solenoid 10 and a spring 11 so as to maintain a minute gap with the photoconductor 1 only when developing a red toner image.

In the image forming apparatus having the above-mentioned structure,
When forming a color image, the surface of the photoconductor 1 uniformly charged by the first charging device 2 is irradiated with laser light from the first exposure section 3 to form a negative-positive latent image. To be done. The formed latent image is developed by the first developing device 4 to form a first image by the black toner on the surface of the photoconductor 1. Then, the second charging device 5 recharges the photoconductor 1 including the image portion and the non-image portion of the black toner, and the second exposure portion 6 performs the second exposure to perform negative exposure. An image is formed. This latent image is developed by the second developing device 7 to form a second image by the red toner. The black-red two-color image formed on the surface of the photoconductor 1 is transferred to the recording paper 12 by the belt transfer device 9 to which a voltage is applied by the bias roller 8. When forming a black-red two-color image in this way, the second
The conditions for recharging by the charging device 5 of the above are as follows: prevention of color mixture development of the red toner on the image portion of the black toner and introduction of the black toner into the second developing device 5 using the red toner. The second charging device 21 and the second charging grid potential applying device 22 are set so that the inside of the second developing device 5 is not contaminated. For example, the potential of the first charging device 2 is -850.
V, the potential of the first exposure is -100V, the bias voltage of the first developing device 4 is -550V, and a black toner image is formed, and the second charging device 5 biases the second developing device 7. When the voltage is -750V, it was obtained by an experiment so that the above condition is satisfied, and the recharge potential of the image portion of the black toner is -800 to
The second charging grid potential applying device 21 is set to −900V, and the second charging grid potential applying device 22 is set to −900V. Then, the potential of the second exposure is set to -100V, and the red toner
Second development is performed.

In the image forming apparatus for forming a two-color image of black and red as described above, when a single color image of only the black toner is formed by the first developing device 4, the second charging device 5 is usually used.
The second exposure unit 6 and the second developing device 7 are not driven to form an image, and the manual paper feed selection setting device 24 is used to form the recording paper 1.
The second charging device 5 is driven only when the second manual feed is selected. This is because when a contact transfer device such as the belt transfer device 9 is used, the recording paper 12 is pressed against the photoconductor, so that the gathering force between the toners in the transfer area is increased and the central portion of the character image is not transferred. An abnormal image called iwayu insect eating print occurs, and this phenomenon is particularly noticeable on thick paper. Since thick paper or the like in which such insect-feeding prints are problematic can be used only by manual feeding, the insect charging prints are not generated by driving the second charging device 5 during manual feeding. To do so.

Therefore, when 55K plain paper is used as the recording paper 12 and when 135K thick paper is used,
FIG. 2 shows a situation in which a so-called insect bite print is generated when a monochromatic image of only black toner is formed when a postcard is used. As shown in FIG. 2, the insect-eating prints did not occur on the 55K plain paper when the second charging device 5 was not driven, but the insect-eating prints occurred on the 135K thick card or postcard. . Therefore, when a monochromatic image of only black toner is formed, the second charging device 5 is driven and the image formed by changing the grit potential is examined.
When the grit potential of is -900V, it is 1 with 55K plain paper.
No worm-eating prints were produced on the 35K cardboard, but some worm-eating prints were produced on the postcards. In addition, the second charging device 5
When the grit potential of is set to -1050V, it becomes the same as 55K plain paper.
Insect-eating prints did not occur on either the 135K cardboard or the postcards. Therefore, the second charging grid potential applying device 2
Grit potential −90 when forming a two-color image of black and red on 2
Grit potential when forming a monochrome image with 0 V −1000
Two types of V are set in advance, single-color image formation is selected, and the recording paper 12 is set by the manual paper feed selection setting device 24.
When the manual feed is selected, the control device 23 sets the recharge potential set in the second charging charge applying device 21 and the grit potential −1000V set in the second charging grid potential applying device 22 to the second value. Output to the charging device 5.

In this manner, the grid potential of the second charging device 5 is set to a potential different from that of the two-color image forming mode, and recharging is performed to enhance the transfer force, and the recording paper 12 of the insect bite print is printed. It is possible to prevent an image from being formed. At this time, a black toner which becomes a problem when forming a two-color image
The development that enters the second developing device 7 does not cause any particular problem whether the second developing device 7 is separated from the photoconductor 1.

Further, the second charging device 5 is driven only when the monochromatic image formation is selected and the manual paper feed is selected, and when the plain paper is conveyed by the normal conveyance path and the image is formed, the second charging device 5 is formed. Since the charging device 5 is not driven, power consumption and ozone generation can be reduced.

Further, in the above-described embodiment, the case where the second charging device 5 is driven when the monochromatic image formation is selected and the manual feeding is selected is explained. However, the recharging mode is selected in the operation section. If the switch 25 is provided and the second charging device 5 is driven even when the recharging mode selection switch 25 is operated, the second charging device 5 can be driven at any time. It is possible to improve the quality and obtain a high quality image.

Further, as shown in the above embodiment, a black toner having a high aggregation degree of, for example, 20 to 25% is used for the first developing device 4 provided on the upstream side in the rotation direction of the photoconductor 1. Photoconductor 1
When a red toner having a small cohesion degree of, for example, 5 to 10% is used in the second developing device 7 on the downstream side in the rotation direction of, the recharging before transfer is not required when a monochromatic image of the red toner is formed. Also, it is possible to form an image free from insect bites on both 55K plain paper and 135K thick paper and postcard.
This is because when the degree of aggregation is small as in the red toner, the transfer resistance due to the aggregation between the toners is small. This increases the additive amount of the external additive of the black toner and increases the cohesion degree to, for example, 15
It could be confirmed from the fact that an image free from insect-eating prints can be formed even if it is reduced to about 10%. Therefore, a black toner having a high degree of aggregation is used for the first developing device 4 provided on the upstream side in the rotation direction of the photoconductor 1, and the black toner is aggregated on the second developing device 7 on the downstream side in the rotation direction of the photoconductor 1. By using the red toner having a small degree, when the second charging device 5 is driven only when the monochrome image of the black toner is transferred to the thick paper,
A high quality image can always be formed.

Although the above embodiment has been described with respect to the image forming apparatus for forming a two-color image, it can be similarly applied to an image forming apparatus for forming a three-color or four-color image.

[0026]

As described above, the present invention has a plurality of sets of charging devices, exposure units, and developing devices in the rotational direction of the photoconductor to form a monochromatic or multicolor toner image on the photoconductor surface. In a multicolor image forming apparatus that transfers the formed toner image onto a recording sheet by a contact transfer device, when a monochromatic image is formed, the surface of the photoconductor on which the monochromatic toner image is formed is rotated. Since it is recharged by the charging device provided on the downstream side of the direction, and then transferred to the recording paper by the contact transfer device, the transfer force in the transfer area can be increased, and an abnormal image called so-called insect bite print is generated. This makes it possible to transfer a high-quality image onto recording paper.

Further, when the photoreceptor on which the monochromatic toner image is formed is recharged, the charging device on the downstream side for recharging is given a different condition from that for the multicolor image formation, and recharged. It is possible to transfer a high-quality image onto recording papers having different thicknesses.

Further, when manual feeding using thick paper or the like is selected, or when the recharging mode selection switch of the operation unit is selected, the photoreceptor on which a monochromatic toner image is formed is recharged. By doing so, it is possible to reduce power consumption and ozone generation and form a high-quality image.

Further, a toner having a high aggregation degree is used for the developing device provided on the upstream side in the rotation direction of the photoconductor, and a toner having a low aggregation degree is used for the developing device on the downstream side in the rotation direction of the photoconductor. Thus, by recharging only when a toner monochromatic image having a high degree of cohesion is transferred to thick paper or the like, it is possible to always form a high quality image without newly providing a transfer device for recharging.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state of a bug-eating print when transferred onto different types of recording paper.

[Explanation of symbols]

1 photoconductor 2 First charging device 3 First exposure unit 4 First developing device 5 Second charging device 6 Second exposure unit 7 Second developing device 9 Belt transfer device 21 Second Charging Charge Applying Device 22 Second charging grid potential applying device 23 Control device 24 Manual feed selection setting device 25 Retransfer mode selection switch

Claims (3)

(57) [Claims] 1. A charging device for charging a rotating photoconductor,
A plurality of sets of an exposure unit for exposing the charged surface of the photoconductor and a developing device for developing the latent image on the surface of the exposed photoconductor are provided in the rotating direction of the photoconductor, and a monochromatic or multicolor toner image is formed on the surface of the photoconductor. Before transferring the toner image formed on the surface of the photoconductor to the recording paper in a multicolor image forming apparatus that transfers the formed toner image onto the recording paper by the contact transfer device. To form the toner image
A belt provided downstream of the developing device in the rotational direction of the photoconductor.
The charging potential of the electronic device from the charging potential during multicolor image formation.
Set the charging potential to a large value and set the photoreceptor on which the toner image is formed.
A multicolor image forming apparatus which is recharged . 2. A charging device for charging a rotating photoconductor,
A plurality of sets of an exposure unit for exposing the charged surface of the photoconductor and a developing device for developing the latent image on the surface of the exposed photoconductor are provided in the rotating direction of the photoconductor, and a monochromatic or multicolor toner image is formed on the surface of the photoconductor. In a multicolor image forming apparatus in which the toner image formed on the recording medium is transferred to a recording sheet by a contact transfer device, the cohesion degree of the toner used in each of the developing devices is changed from the upstream side to the downstream side in the rotation direction of the photoconductor. When a monochromatic image is formed, the toner image formed on the surface of the photoconductor is transferred to the recording paper before the toner image is formed.
Provided on the downstream side of the developing device in the rotation direction of the photoconductor
The charging potential of the charging device is the charging potential when forming a multicolor image.
A photosensitive member on which a toner image is formed with a higher charging potential
A multicolor image forming apparatus characterized by recharging the body . 3. The multicolor image forming apparatus according to claim 1, further comprising a recharge mode selection switch for selecting a mode for recharging the toner image formed on the surface of the photoconductor.