JPH08166703A - Image forming device - Google Patents

Abstract

PURPOSE: To efficiently separate and remove admixed toner electrified to the opposite polarity of toner to be used and to prevent fog. CONSTITUTION: An image forming device forms a two-color toner image on a photoreceptor 1 by forming positive and negative electrostatic latent images, one higher and the other lower than an arbitrary reference potential within the same-polarity electrification potential on the photoreceptor 1, and by developing the electrostatic latent images by means of a first developing device 4 and a second developing device 6 having a first toner 5 and a second toner 7, respectively, of different colors and electrification polarities. This device uses the developer satisfying the relationship of T1<C<T2 (wherein T1 is the first toner, C is first and second carriers, and T2 is the second toner) in an electrification series consisting of the toners T1 and T2 and the carriers C. The image forming device is capable of removing ingress toner by forming an electrostatic latent image to which the ingress toner is attached in a non- recording area on the photoreceptor 1 and by applying the developing devices 4 and 6 development bias voltages by which only the ingress toner is attached to it. This image forming device is equipped with a means for controlling the rotating speed of a motor which rotates a developing roll.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a toner, and more particularly to an apparatus for removing a first toner mainly mixed in a second developing machine in two-color printing.

[0002]

2. Description of the Related Art Positive and negative electrostatic latent images are formed above and below an arbitrary reference potential on a photoconductor having the same polarity, and the electrostatic latent images have different colors and different charging polarities. first,
In an image forming apparatus that develops two color toner images on a photoconductor by developing with first and second developing machines having a second toner, there is a problem that the first toner mixes in the second developing machine. is there. More specifically, the first toner image on the photoconductor formed by the first developing machine is scraped off by the magnetic brush of the second developing machine during the second development and mixed in the second developing machine. When the first toner is mixed in the second developing machine, the mixed first toner has a reverse polarity, so that the first toner is developed from the second developing machine to the background area (hereinafter referred to as fog), and the image quality is deteriorated. The first toner mixed in or rubbing against the second carrier or the second toner changes the charge amount of the first toner or the second toner. It became polar and the second image was mixed.

To solve the above-mentioned problems, there are conventional methods for removing mixed toner, such as Japanese Patent Laid-Open Nos. 59-214049 and 5-150604.

Japanese Patent Laid-Open No. 59-214049 discloses an image forming apparatus in which a separation roll is provided in the second developing machine and a high voltage is applied to the separation roll to separate and remove the first toner mixed in the second development machine. And the charging series of toner and carrier is T1 <C
<T2, where T1 is the first toner, C is the first and second carriers, and T2 is the developer satisfying the second toner.

In Japanese Patent Laid-Open No. 59-214049, since the separation roll is provided, it is possible to suppress the occurrence of fogging due to the mixed first toner. Further, since the developer in which the charge series of the toner and the carrier satisfies the above formula is used, the mixed first toner is rubbed with the second carrier and the second toner, and the charge amount of the first toner and the second toner is changed. Since there is almost no change, the first toner mixed in the second developing device can be efficiently removed, and thus the color mixture of the second image can be suppressed.
However, since the separation roller is provided in the second developing machine, a high voltage is required, and there is a problem that the developing apparatus becomes large and the cost increases.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 5-150604, a latent image for removing the oppositely charged toner is formed on a non-recording area of a photoconductor,
A method for removing the oppositely charged toner is proposed.

Japanese Unexamined Patent Publication (Kokai) No. 5-150604 discloses a Japanese Unexamined Patent Publication (Kokai) No. 59-
Unlike the 214049 publication, since no separation roll is used,
Although the problems of upsizing and cost increase are solved,
A problem occurs when the method of Japanese Patent Application Laid-Open No. 5-150604 is applied to an image forming apparatus that forms two color toner images on a photoconductor by using first and second toners having different charging polarities and different colors. Normally, the rotation speed of the developing roller of the second developing machine is the rotation speed of the developing roller of the second developing machine so as not to scrape the first toner image with the magnetic brush of the second developing machine to reduce the first image density. Is set to be slow (peripheral speed ratio to the photoconductor is 1.1 to 2.0). Since the rotation speed of the developing roll of the second developing machine is slow, the amount of the second developer conveyed is small. Since the second developer is conveyed in a small amount, the efficiency of removing the first toner, which is the reverse charge mixed in the second developing machine in the non-recording area, is low, and there is a problem that fog occurs in the recording area. It was

[0008]

The above-mentioned conventional examples, Japanese Patent Laid-Open Nos. 59-214049 and 5-150604, have the following problems.

In Japanese Patent Laid-Open No. 59-214049, there are problems that the developing machine becomes large and the cost increases.

Further, in Japanese Unexamined Patent Publication No. 5-150604, the efficiency of removing the first toner, which is the opposite charge and mixed in the second developing machine in the non-recording area, is low, and fog occurs in the recording area. was there.

An object of the present invention is to form a positive type or negative type electrostatic latent image above and below an arbitrary reference potential within a charging potential of the same polarity on a photoconductor, and to form different colors on the electrostatic latent image. An image forming apparatus that forms a two-color toner image on a photoconductor by developing with first and second developing machines having first and second toners having different charging polarities, and a charging series of toner and carrier is T1. <C <
T2 (T1 is first toner, C is first and second carrier, T
2 is a second toner), and a developing bias voltage is applied to the developing machine so that an electrostatic latent image to which the mixed toner is attached is formed on the non-recording area of the photoconductor and only the mixed toner is attached. In an image forming apparatus capable of removing the mixed toner applied, the mixed toner charged opposite to the toner to be used is efficiently separated and removed without using a separation roll or a high voltage power source, and fogging is prevented. An object is to provide an image forming apparatus that suppresses occurrence.

[0012]

In order to achieve the above object, the present invention forms a positive or negative electrostatic latent image above and below an arbitrary reference potential within a charging potential of the same polarity on a photoconductor. Then
Each of the electrostatic latent images has a different color and a different charging polarity.
An image forming apparatus that develops with a first and a second developing machine having a second toner to form a two-color toner image on the photoconductor, and the charging series of the toner and the carrier is T1 <C <T2 (T1 is the first One toner, C is a first and second carrier, and T2 is a second toner), and a means for forming an electrostatic latent image to which the mixed toner is attached to the non-recording area of the photoconductor, A means for applying a developing bias voltage such that only the mixed toner adheres to the developing roll, and a motor control means for controlling the rotation speed of the motor for rotating the developing roll are provided for the motor for rotating the developing roll. Characterize.

[0013]

In the non-recording area of the photoconductor, the motor control means rotates the rotation speed of the motor for rotating the developing roll, that is, the rotation speed of the developing roll faster than the rotation speed of the photoconductor in the recording area. As a result, the transport amount of the developer in the developing device increases in the non-recording area of the photoconductor, so that the mixed toner is efficiently removed without using a separation roll or a high voltage power source.

[0014]

Embodiments of the present invention will be described below with reference to FIGS. 1, 2 and 3. FIG. 1 shows an example of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic configuration diagram of the first and second developing machines. FIG. 3 shows a state of the electrostatic latent image formed on the photoconductor 1 and the first developing bias 46 and the second developing bias 66.
The rotation speed 47 of the first developing roll 42 and the rotation speed 67 of the second developing roll 62 are shown. The horizontal axis represents the position in the circumferential direction on the photoconductor 1, and the vertical axis represents the magnitude of the surface potential and the rotation speed of the developing roll. In the case of a printer that prints on cut sheets, there is always an area that is not printed between recording sheets, so on the photosensitive member 1, the recording area a where the toner image is transferred onto the recording sheet, the recording sheet and the recording sheet There is a non-recording paper area b corresponding to the space.

In FIG. 1, the photoconductor 1 rotating in the clockwise direction is uniformly charged, for example, positively by the charger 2. Next, the laser beam 3 modulated by the two image information is irradiated to simultaneously form two electrostatic latent images of positive type and negative type above and below the reference potential V ₀ .

The positive type electrostatic latent image is normally developed by the negatively charged black first toner 5 of the first developing device 4,
The negative electrostatic latent image is reversely developed by the positively charged red second toner 7 of the second developing device 6. A developer satisfying T1 <C <T2 (T1 is the first toner, C is the first and second carriers, and T2 is the second toner) is used as the charge series of the toner and the carrier.

In FIG. 2, the first developing roll 42 and the second developing roll 62 rotate to convey the first developer 45 and the second developer 65 to the surface of the photoreceptor 1.

The first developing machine 4 is controlled by the first developing machine control means 41. The first developing machine control means 41 includes a second developing bias control means 43 and a first developing bias power source 48.
And a first motor control means 44 and a first motor 49. The first developing bias control means 43 controls the first developing bias power source 48 to control the value of the first developing bias 46. The first motor control unit 44 controls the rotation speed of the first motor 49 that rotates the first developing roll 42, and controls the rotation speed of the first developing roll 42.

Similarly, the second developing machine 6 is controlled by the second developing machine control means 61. Second developing machine control means 6
Reference numeral 1 includes a second developing bias control means 63, a second developing bias power source 68, a second motor control means 64, and a second motor 69.

The second developing bias control means 63 controls the second developing bias power source 68 to control the value of the second developing bias 66. The second motor control means 64 controls the second developing roll 6
The number of rotations of the second motor 69 that rotates 2 is controlled, and the rotation speed of the second developing roll 62 is controlled.

The formation of a two-color image will be described with reference to FIG. In the recording area a, positive and negative electrostatic latent images are formed above and below the surface potential V ₀ , and the first developing bias power source 48 controlled by the first developing bias control means 43.
Applies a first bias 46 of V ₁ indicated by the solid line to the first developing machine 4, and the first developing roll 42 is driven by the first motor 49 controlled by the first motor control means 44. It is rotating at the rotation speed of V11 shown by the solid line.

Further, the second developing bias power source 68 controlled by the second developing bias control means 63 causes the second developing device 6 to have a second bias 66 of V ₂ indicated by a broken line.
The second developing roller 62 is rotated by the second motor 69 controlled by the second motor control means 64 at the rotation speed of V22 indicated by the broken line. Developing roll 6
The rotation speed of 2 is set so that the first toner image already formed on the surface of the photoconductor 1 is not scraped off by the second magnetic brush to reduce the density, and the first toner image is not disturbed. The roll is rotating slower than the rotation speed of the roll 42.

The first developing device 4 deposits the first toner 5 on the positive latent image potential V ₁ ′. The second developing machine 6 deposits the first toner 7 on the negative latent image potential V ₂ ′. The two-color toner image 8 thus formed on the surface of the photoconductor 1 is positively charged by the toner charging device 9 to make the polarities uniform, and then the transfer device 1
0 is electrostatically transferred to the recording paper 11 all at once. After that, the residual electrification on the surface of the photoconductor 1 is erased by the eraser 12,
Further, the residual toner is removed by the cleaner 13 to remove the photoconductor 1.
To reuse. The toner image on the recording paper 11 is fixed on the fixing device 14
Is thermally fixed in.

In the two-color image forming apparatus, since the black first toner image is already formed on the surface of the photoconductor 1 when developing by the second developing device 6, the first toner image on the surface of the photoconductor 1 is formed. The toner 5 is scraped off by the magnetic brush of the second developing device 6 and is mixed into the second developing device 6. Since the charging series of the toner and the carrier is T1 <C <T2, the mixed first toner 51 in the second developing device 6 is negatively charged even if it is rubbed with the second carrier and the second toner 7. I am maintaining. Further, when the residual toner cannot be completely cleaned, the second toner 7 is mixed into the first developing device 4. The charging series of toner and carrier is T1 <C <T
2, the mixed second toner 71 in the first developing device 4
Maintains positive charge even when it is rubbed with the first carrier and the first toner 5.

The mixed toner removing process will be described in detail below.

In the non-recording area b, positive and negative electrostatic latent images are formed as in the recording area a. However, this electrostatic latent image is for adhering the mixed toner and has nothing to do with the image information. In this non-recording area b, the developing bias value of each of the first developing machine 4 and the second developing machine 6 and the rotation speed of the developing roll are changed.

The value of the first developing bias 46 applied to the first developing machine 4 is V ₁ ′ and the value in the recording area a by the first developing bias power source 48 controlled by the first developing bias control means 43. Set higher than the value V ₁ . As a result, the negatively charged black first toner 5 does not adhere to the electrostatic latent image, but the positively charged mixed second toner 71 adheres to the negative electrostatic latent image portion. Further, the first developing roll 42 is driven by the first motor 49 controlled by the first motor control means 44 to have a speed V11 faster than V11.
Rotate at 1 speed. By doing so, the transport amount of the first developer increases, the adhesion amount of the mixed toner 71 on the photoconductor 1 increases, and the mixed toner removal efficiency improves.

Similarly, the value of the second developing bias 66 applied to the second developing device 6 is set to the second developing bias control means 63.
By the second developing bias power source 68 controlled to
It is set lower than V ₂ ′ and the value V ₂ in the recording area a. As a result, the positively charged red second toner 7 does not adhere to the electrostatic latent image, but the negatively charged mixed first toner 51 adheres to the positive electrostatic latent image portion. Further, the second developing roller 62 is rotated by the second motor 69 controlled by the second motor control means 64 at a speed V222 which is faster than V22. By doing so, the transport amount of the second developer is increased, the amount of the mixed toner 51 attached to the photoconductor 1 is increased, and the mixed toner removal efficiency is improved.

When the rotational speed of the developing roll is increased in the non-recording area b, the rotational speed of the developing roll is so high as to prevent the scattering of the developer or the scattering of the carrier due to the saturation magnetization of the carrier and the magnetic force of the magnet roll. Needless to say, set.

These mixed toners adhering to the non-recording area b of the photoconductor 1 are positively charged by the toner charger 9 to make the polarities uniform, and then removed by the cleaner 13.

The non-recording area b is the recording paper 11 during continuous printing.
The non-recording area b is the area between the recording papers 11 and 11 in other words, it is the time during which no printing is performed. However, the image forming apparatus may be controlled so that the image forming apparatus performs the image mixing removing process at the end of printing, or the image forming apparatus may be turned on to perform the image mixing removing process. By doing so, the mixed toner can be removed more effectively.

In this way, the mixed toner is prevented from accumulating inside the first and second developing machines, and fogging in the recording area is suppressed. Further, since a removing roll and a removing bias power source for removing the mixed toner are not required, it is possible to provide a small-sized image forming apparatus at low cost.

[0033]

EFFECTS OF THE INVENTION Positive and negative electrostatic latent images are formed above and below an arbitrary reference potential on the photoconductor of the same polarity, and electrostatic latent images of different colors and different charging polarities are formed. first,
An image forming apparatus which develops by a first and a second developing machine having a second toner to form a two-color toner image on a photoconductor,
Toner is mixed in the non-recording area of the photoconductor using a developer satisfying the charge series of T1 <C <T2 (T1 is the first toner, C is the first and second carriers, and T2 is the second toner). In an image forming apparatus capable of removing the mixed toner, which forms an electrostatic latent image to which the toner should be attached, and applies a developing bias voltage to the developing machine so that only the mixed toner is attached, to a motor for rotating the developing roll, Since the motor control means for controlling the number of rotations of the motor for rotating the developing roll is provided to rotate the developing roll in the non-recording area of the photosensitive member faster than the rotating speed in the recording area of the photosensitive member, The developer transport amount increases. Therefore, the mixed toner charged opposite to the toner to be used is efficiently separated and removed without using a separation roll or a high-voltage power source,
An image forming apparatus capable of suppressing the occurrence of fogging can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an image forming apparatus to which the present invention is applied.

FIG. 2 is a block diagram of a developing machine of an image forming apparatus to which the present invention is applied.

FIG. 3 is an explanatory diagram of a potential of a photoconductor, a bias potential, and a developing roll rotation speed according to an embodiment of the invention.

[Explanation of Codes] 46 ... First developing bias, 47 ... First developing roll rotation speed, 66 ... Second developing bias, 67 ... Second developing roll rotation speed.

Claims (2)

[Claims] 1. A positive or negative electrostatic latent image is formed above and below an arbitrary reference potential within a charging potential of the same polarity on a photosensitive member,
Each of the electrostatic latent images has a different color and a different charging polarity.
In an image forming apparatus that develops with a first and a second developing device having a second toner to form a two-color toner image on the photoconductor, the charging series of the toner and the carrier is T1 <C <T2 (T
1 is a first toner, C is a first and second carrier, and T2 is a second toner), and an electrostatic latent image to which mixed toner is to be attached is formed on the non-recording area of the photoconductor. An image forming apparatus comprising: a unit, a unit for applying a developing bias voltage to the developing roll so that only the mixed toner adheres, and a unit for controlling the rotation speed of a motor for rotating the developing roll. 2. The motor control means according to claim 1, wherein the motor control means sets a rotational speed of a motor for rotating the developing roll, that is, a rotational speed of the developing roll in a non-recording area of the photoconductor, in a recording area of the photoconductor. Image forming apparatus that rotates at a speed higher than the rotation speed in.