JP2003295554A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent image failure due to toner melt sticking to a photoreceptor in a final image forming part in a cleaner-less tandem type image forming apparatus. <P>SOLUTION: In the cleaner-less tandem type image forming apparatus, metal soap is contained in developer in a final process of an image forming part. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleanerless image forming apparatus. More specifically, the developer (toner) remaining on the image carrier after the transfer step is removed and collected from the image carrier by cleaning at the same time in the developing device by cleaning at the same time, and is reused to remove the cleaning device. System image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a transfer type image forming apparatus such as a copying machine, a printer or a facsimile using an electrophotographic system has a photosensitive member which is a rotary drum type image carrier, and the photosensitive member has a predetermined size. A charging device (charging step) for uniformly charging to polarity / potential, an exposure device (exposure step) as an information writing means for forming an electrostatic latent image on the charged photoreceptor, and a charging device formed on the photoreceptor. A developing device (developing process) that visualizes an electrostatic latent image with toner that is a developer, a transfer device (transfer process) that transfers the toner image from a photoconductor surface to a transfer material such as paper, and a photoconductor after the transfer process. It consists of a cleaning device (cleaning process) that removes a little residual toner on the top to clean the surface of the photoconductor, and a fixing device (fixing process) that fixes the toner image on the transfer material. Electrophotographic process (charging, exposure, development, transfer and cleaning) is applied is subjected to image formation.

The toner remaining on the photoconductor after the transfer process is removed from the photoconductor surface by the cleaning device and collected in the cleaning device to become waste toner, but such a toner is used in view of environmental protection and effective use of resources. It is desirable not to produce waste toner.

Therefore, there is an image forming apparatus in which the transfer residual toner, so-called waste toner, collected by the cleaning device is returned to the developing device for reuse.

Further, the cleaning device is abolished, and the transfer residual toner on the photoconductor after the transfer process is removed / collected from the photoconductor by "simultaneous development cleaning" in the developing device to reuse the image. There is a forming device.

Simultaneous development cleaning is performed by cleaning the transfer residual toner on the photoconductor after transfer during the subsequent developing process, that is, by continuously charging and exposing the photoconductor to form an electrostatic latent image. During the process of affirming the development of the image, the fog removal bias (fog removal potential difference Vback which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photoconductor) causes the toner to be developed on the surface of the photoconductor which should not be developed with toner (non-image area). The transfer residual toner present in (1) is collected in the developing device.
According to this method, the residual toner after transfer is collected by the developing device and reused for the development of the electrostatic latent image in the subsequent steps, so that the waste toner is eliminated and the troublesomeness during maintenance is reduced. You can Further, the cleanerless structure is advantageous for downsizing the image forming apparatus.

[0007]

A) As described above,
In a cleanerless-type image forming apparatus that removes and collects residual toner remaining on the photoconductor after the transfer process in a developing device through cleaning and cleaning at the same time, the charging device of the photoconductor contacts the photoconductor to clean the surface of the photoconductor. In the case of the contact charging device that performs the charging process, when the transfer residual toner on the photoconductor passes through the charging part, which is the contact nip part between the photoconductor and the contact charging device, the charge polarity of the transfer residual toner becomes normal. The toner having the opposite polarity adheres to the contact charging device and contaminates the contact charging device with more than allowable amount of toner, resulting in poor charging.

That is, although the toner as a developer is small in quantity, there is a mixture of toners whose charge polarity is originally reversed to the opposite polarity from the normal polarity. Further, there are some toners whose charge polarity is regular polarity and whose charge polarity is reversed due to the influence of transfer bias or peeling discharge, and those whose charge amount is reduced by reducing the charge amount.

Therefore, the transfer residual toner is a mixture of toner having a normal charge polarity, reverse toner having a reverse polarity, and a toner having a small charge amount, and the reverse toner and the toner having a small charge amount are used as the photoconductor. It easily adheres to the contact charging device when passing through the charging part which is the contact nip part of the contact charging device.

B) Further, in order to remove and collect the transfer residual toner on the photosensitive member by cleaning the developing device at the same time as the developing device, the transfer residual toner on the photosensitive member is carried to the developing unit through the charging unit. It is necessary that the charging polarity is normal and that the charging amount is the charging amount of the toner capable of developing the electrostatic latent image on the photoconductor by the developing device. Reversed toner and toner having an unsuitable charge amount cannot be removed / collected from the photoconductor by the developing device, resulting in defective images.

C) The toner adhered to the contact charging device of the above a) is mixed in that it is carried from the transfer section to the charging section and has a regular charge polarity, a reverse polarity, and a small charge amount. The transfer residual toner on the photoconductor is charged to the normal polarity by the toner charge amount control means so that the charge polarity is aligned to the normal polarity and the charge amount is made uniform, which can be prevented.

However, the transfer residual toner charged by the toner charge amount control means in order to prevent the toner from adhering to the contact charging device is larger than the charge amount of the toner capable of developing the electrostatic latent image on the photoconductor. Therefore, it is difficult for the developing device to be removed / collected by simultaneous cleaning with development. In such a case, the toner remaining on the photoconductor overlaps with the next image, resulting in a defective image.

In order to prevent such image defects, a transfer residual toner equalizing means is installed upstream of the photosensitive member of the toner charge amount control means, and the charge amount of the transfer residual toner is controlled to collect the toner in the developing device. Was efficiently performed, and image stains due to poor collection were eliminated.

In a four-color tandem type color image forming apparatus using such a cleanerless image forming apparatus, particularly, an image forming apparatus in which the color of the final image forming portion is black (hereinafter referred to as Bk-st) is used. When paper durability is applied, B
The phenomenon that the photosensitive member of k-st was fused by the toner and the fused portion was blocked from exposure and the image was blanked. Further, even when the paper passing durability was performed with a mixed image of a color image and a monochrome image, the Bk-st photoconductor was fused with the toner and the image was blank.

Therefore, the present invention relates to a cleanerless type image forming apparatus in which the transfer residual developer on the image bearing member after the transfer step is removed and collected by cleaning at the same time as development, and is reused. It is a system that prevents the adhesion of the agent and efficiently collects the transfer residual developer by the developing means. Even if the paper passing durability is advanced, the toner on the Bk-st photoconductor of the final image forming portion The purpose is to eliminate image blank areas due to fusion.

[0016]

The present invention is an image forming apparatus having the following configuration.

(1) An image carrier having a plurality of color image forming sections, a charging means for charging the surface of the image carrier, and an information writing means for forming an electrostatic latent image on the charged image carrier.
In a cleanerless image forming apparatus, which has a developing unit that supplies a developer to the electrostatic latent image to visualize the electrostatic latent image, and a transfer unit that transfers the visualized developer image to a transfer material,
An image forming apparatus characterized in that a developer in an image forming section in a final step contains a metallic soap.

(2) The image forming apparatus according to (1), wherein the toner in the developer in the image forming section in the final step is black.

(3) The image of (1) or (2), characterized in that the metal soap is contained in an amount of 0.05 to 0.5 parts by weight based on 100 parts by weight of the developing toner. Forming equipment.

(4) The image forming apparatus of (1) to (3), wherein the metallic soap is zinc stearate powder.

(5) A developer charge amount control means which is located upstream of the charging means and downstream of the transfer means as the cleanerless means, and which charges the developer on the developer surface on the image carrier surface. A residual development which is positioned upstream of the developer charge amount control means and downstream of the transfer means, and which makes uniform the residual developer image remaining on the surface of the image carrier after transferring the developer to the transfer material. The image forming apparatus according to any one of (1) to (4), further including a uniform agent image forming means.

(6) The image forming apparatus according to any one of (1) to (5), wherein the charging means is contact charging.

(7) An image forming apparatus according to any one of (1) to (6), characterized in that an oscillating electric field is applied to the charging means.

(8) The image forming apparatus according to (1) to (7), wherein the information writing means is an exposing means.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) An image forming apparatus (image recording apparatus) according to an embodiment will be described below.

FIG. 1 is a schematic structural model diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process, a contact charging type, an anti-development image type, a cleanerless type, and a maximum sheet size of A3 size.

(1) Overall Schematic Configuration of Printer a) The image carrier 1 is a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. This photosensitive drum 1 is a negatively chargeable organic photoconductor (OPC), has an outer shape of 50 mm, and has a center axis of 100 mm / se.
It is rotationally driven counterclockwise as indicated by an arrow at a process speed (peripheral speed) of c.

In the photosensitive drum 1, as shown in the layer structure model of FIG. 2, an undercoat layer for suppressing the interference of light on the surface of the aluminum cylinder (conductive drum substrate) 1a and improving the adhesiveness of the upper layer. 1b, a photocharge generation layer 1c, and a charge transport layer 1d are applied in this order from the bottom.

B) The charging device 2 is a contact charging device (contact charging device) as a charging device for uniformly charging the peripheral surface of the photosensitive drum 1, and this example is a charging roller (roller charging device).

The charging roller 2 is rotatably held at both ends of a cored bar 2a by bearing members (not shown), and is biased toward the photosensitive drum by a pressing spring 2e so that the surface of the photosensitive drum 1 is supported. They are pressed against each other with a predetermined pressing force, and are rotated by the rotation of the photosensitive drum 1. The pressure contact portion between the photosensitive drum 1 and the charging roller 2 is a charging portion (charging nip portion) a.

The core metal 2a of the charging roller 2 has a power source S1.
By applying a charging bias voltage of a predetermined condition, the peripheral surface of the rotary photosensitive drum 1 is contact-charged with a predetermined polarity and potential. In this example, the charging bias voltage for the charging roller 2 is a DC voltage (Vdc) and an AC voltage (V
ac) is an oscillating voltage that is superimposed.

More specifically, DC voltage: -500V AC voltage; frequency f1000Hz, peak-to-peak voltage Vpp1
This is an oscillating voltage in which 400 V and a sine wave are superimposed, and the peripheral surface of the photosensitive drum 1 is uniformly contact-charged to −500 V (dark potential Vd).

The longitudinal length of the charging roller 2 is 320 mm, and the core metal (support member) 2a is formed as shown in the layer structure model diagram of FIG.
It has a three-layer structure in which a lower layer 2b, an intermediate layer 2c, and a surface layer 2d are sequentially laminated from the bottom to the outer periphery. The lower layer 2b is a foam sponge layer for reducing charging noise, and the surface layer 2d is a protective layer provided to prevent leakage even if there is a defect such as a pinhole on the photosensitive drum 1. .

More specifically, the specifications of the charging roller 2 of this example are as follows. a. Core metal 2a; stainless round bar with a diameter of 6 mm b. Lower layer 2b; carbon dispersed foam EP
DM, specific gravity 0.5 g / cm ³ , volume resistance value 10 ² to 10
⁹ Ωcm, layer thickness 3.0 mm, length 320 mm c. Intermediate layer 2c; carbon-dispersed NBR rubber, volume resistance value 10 ²
-10 ⁵ Ωcm, layer thickness 700 μm d. Surface layer 2d; tin oxide and carbon dispersed in fluorine resin resin resin Volume resistance value 10 ⁷ to 10 ¹⁰ Ωcm, surface roughness (JIS standard 10-point average surface roughness Ra) 1.5 μm, layer thickness 10 μm
In FIG. 2, 2f is a charging roller cleaning member, which is a flexible cleaning film in this example. The cleaning film 2f is arranged in parallel with the longitudinal direction of the charging roller 2 and has one end fixed to a supporting member 2g that reciprocates a certain amount in the longitudinal direction, and is connected to the charging roller 2 on the surface near the free end side. Arranged to form a contact nip. The supporting member 2g is driven by a drive motor of the printer through a gear train to reciprocate a predetermined amount in the longitudinal direction, and the charging roller surface layer 2d is rubbed with the cleaning film 2f. As a result, contaminants (fine toner, external additives, etc.) on the surface of the charging roller 2d are removed.

C) The information writing means 3 is an exposure device as an information writing means for forming an electrostatic latent image on the surface of the photosensitive drum 1 which has been charged, and this example is a laser beam scanner using a semiconductor laser. . A laser beam modulated in accordance with an image signal sent to the printer side from a host process such as an image reading device (not shown) is output, and the uniformly charged surface of the rotary photosensitive drum 1 is subjected to laser scanning exposure at the exposure position b. L (image exposure). The laser scanning exposure L lowers the potential of the surface of the photosensitive drum 1 irradiated with the laser beam, so that electrostatic latent images corresponding to the scanned and exposed image information are sequentially formed on the surface of the rotating photosensitive drum 1. Go.

D) The developing means 4 is a developing device (developing device) as a developing means for supplying the developer Z (toner) to the electrostatic latent image on the photosensitive drum 1 to visualize the electrostatic latent image. Is a reversal developing device of a two-component magnetic brush developing system.

4a is a developing container. Reference numeral 4b is a non-magnetic developing sleeve, and the developing sleeve 4b is rotatably arranged in the developing container 4a with a part of the outer peripheral surface thereof exposed to the outside. 4c is a magnet roller fixed non-rotatably and inserted in the developing sleeve 4b, 4d is a developer coating blade, 4e is a two-component developer housed in the developing container 4a, and 4f is a bottom part in the developing container 4a. The developer agitating member 4g provided is a toner hopper, and contains replenishment toner.

The two-component developer 4e in the developing container 4a is a mixture of toner and magnetic carrier, and is a developer stirring member 4f.
Is stirred by. In this example, the magnetic carrier has a resistance of about 10 ¹³ Ωcm and a particle size of 40 μm. The toner is negatively charged by friction with the magnetic carrier.

The developing sleeve 4b is arranged facing the photosensitive drum 1 so that the closest distance (referred to as S-Dgap) to the photosensitive drum 1 is maintained at 350 μm and is close to the photosensitive drum 1. The portion where the photosensitive drum 1 and the developing sleeve 4a face each other is the developer c. The developing sleeve 4b is rotationally driven in the developing portion c in the direction opposite to the traveling direction of the photosensitive drum 1. On the outer peripheral surface of the developing sleeve 4b, a part of the two-component developer 4e in the developing container 4a is adsorbed and held as a magnetic brush layer by the magnetic force of the magnet roller 4c in the sleeve, and is rotatably conveyed as the sleeve rotates. A predetermined thin layer is formed by the developer coating blade 4d, and the surface of the photosensitive drum 1 is brought into contact with the developing portion c to appropriately rub the surface of the photosensitive drum. A predetermined developing bias is applied to the developing sleeve 4b from the power source S2. In this example, the developing bias voltage for the developing sleeve 4b is an oscillating voltage obtained by superimposing a DC voltage (Vdc) and an AC voltage (Vac). More specifically, DC voltage: -350V AC voltage: 1600
It is an oscillating voltage in which V is superimposed.

Thus, the toner in the developer coated on the surface of the rotating developing sleeve 4b as a thin layer and conveyed to the developing section c becomes an electrostatic latent image on the surface of the photosensitive drum 1 by the electric field due to the developing bias. Correspondingly and selectively adhering, the electrostatic latent image is developed as a toner image. In the case of this example, toner adheres to the exposed bright portion of the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed.

At this time, the charge amount of the toner developed on the photosensitive drum is -25 μC / g.

The thin developer layer on the developing sleeve 4b which has passed the developing portion c is returned to the developer reservoir portion in the developing container 4a as the developing sleeve continues to rotate.

In order to maintain the toner concentration of the two-component developer 4e in the developing container 4a within a predetermined substantially constant range, the toner concentration of the two-component developer 4e in the developing container 4a is, for example, an optical toner (not shown). Detected by the density sensor, the toner hopper 4g is drive-controlled according to the detected information, and the toner in the toner hopper is replenished to the two-component developer 4e in the developing container 4a. The toner supplied to the two-component developer 4e is stirred by the stirring member 4f.

E) Transfer means / fixing means 5 is a transfer device, and in this example is a transfer roller. The transfer roller 5 is pressed against the photosensitive drum 1 with a predetermined pressing force, and the press contact nip portion is the transfer portion d. A transfer material (transferred member, recording material) P is fed to the transfer section d from a paper feed mechanism section (not shown) at a predetermined control timing.

The transfer material P fed to the transfer portion d is nipped and conveyed between the rotating photosensitive drum 1 and the transfer roller 5, and during that time, the transfer roller 5 is supplied to the transfer roller 5 from the power source S3 and the negative polarity of the toner is the normal charging polarity. In this example, +2 kV is applied to transfer the transfer portion d.
The toner images on the surface of the photosensitive drum 1 are sequentially electrostatically transferred to the surface of the transfer material P that is nipped and conveyed.

The transfer material P which has received the toner image transferred through the transfer portion d is sequentially separated from the surface of the rotary photosensitive drum 1 and conveyed to a fixing device 6 (for example, a heat roller fixing device) to fix the toner image. The image is received and output as an image-formed product (print, copy).

(2) Cleanerless System and Toner Charge Amount Control The printer of this example is cleanerless, and is dedicated to removing a small amount of transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P. No cleaning device provided. The transfer residual toner on the surface of the photosensitive drum 1 after the transfer is carried to the developing portion c through the charging portion a and the post-exposure portion b as the photosensitive drum 1 continues to rotate, and is simultaneously cleaned (collected) by the developing device 3 for developing. Is done (cleanerless system).

In the present embodiment, the developing sleeve 4b of the developing device 4 is rotated in the developing portion c in the direction opposite to the traveling direction of the surface of the photosensitive drum 1 as described above. It is advantageous for collecting the residual toner.

Since the transfer residual toner on the surface of the photosensitive drum 1 passes through the exposure portion b, the exposure process is performed on the transfer residual toner. However, since the amount of transfer residual toner is small, a great influence does not appear.

However, as described above, the transfer residual toner has a normal charging polarity, a reverse charging polarity (reversing toner),
Some toners having a small charge amount are mixed, and the reversal toner and the toner having a small charge amount adhere to the charging roller 2 when passing through the charging portion a, so that the charging roller is contaminated more than an allowable amount and charged. It will cause defects.

Further, in order to effectively perform the simultaneous cleaning of the transfer residual toner on the surface of the photosensitive drum 1 by the developing device 3, the charging polarity of the transfer residual toner on the photosensitive drum carried to the developing section c is set. It is necessary that the polarity is normal and that the amount of charge is the amount of charge of the toner that can develop the electrostatic latent image on the photosensitive drum by the developing device. Inverted toner and toner having an unsuitable charge amount cannot be removed / collected from the photosensitive drum by the developing device, resulting in defective images.

Also, with the recent diversification of user needs,
The continuous printing operation of images having a high printing rate such as photographic images causes a large amount of transfer residual toner at one time, which further aggravates the above problems.

Therefore, in the present embodiment, the transfer residual toner (residual developer image) is made uniform in order to make the transfer residual toner on the photosensitive drum 1 uniform at the position downstream of the transfer portion d in the photosensitive drum rotation direction. A charging unit 8 is provided, and the charging polarity of the transfer residual toner is a regular polarity at a position downstream of the transfer residual toner equalizing unit 8 in the photosensitive drum rotation direction and upstream of the charging unit a in the photosensitive drum rotation direction. A toner (developer) charge amount control means 7 is provided for making the polarity negative.

By providing the transfer residual toner uniforming means 8, the pattern transfer residual toner on the photosensitive drum 1 which is carried from the transfer portion d to the toner charge amount control means 7 has a large amount even if the toner amount is large. Since the toner is dispersed and distributed on the surface of the photosensitive drum 1 and is not patterned, the toner is prevented from concentrating on a part of the toner charge amount control means 7, and the transfer charge residual toner of the toner charge amount control means 7 is entirely normalized. The polarity charging process is always sufficiently performed to effectively prevent the transfer residual toner from adhering to the charging roller 2. Generation of a ghost image of the transfer residual toner image pattern is strictly prevented.

In the present embodiment, the transfer residual toner equalizing means 8 and the toner charge amount control means 7 are brush-like members having an appropriate conductivity, and are arranged by bringing the brush portion into contact with the surface of the photosensitive drum 1. It is set up. Reference numeral f is a contact portion between the transfer residual toner uniformizing means 8 and the surface of the photosensitive drum 1. Reference numeral e is a contact portion between the toner charge amount control means 7 and the surface of the photosensitive drum 1.

The transfer residual toner equalizing means 8 is grounded, and the toner charge amount controlling means 7 is applied with a negative voltage from the power source S4.

The transfer residual toner remaining on the photosensitive drum 1 after the transfer of the toner image to the transfer agent P in the transfer portion d is made uniform by the transfer residual toner equalizing means 8 by the subsequent rotation of the photosensitive drum 1.
To the contact portion f between the photosensitive drum 1 and the transfer drum, and the toner is once sucked by the transfer residual toner equalizing means 8. Here, since the amount of toner that the transfer residual toner equalizing means 8 can hold is limited, after the saturation state is reached, the toner is gradually released and adhered to the surface of the photosensitive drum 1 and conveyed. The toner attachment state on one surface, that is, the distribution of the toner attached to the photosensitive drum 1 surface is made uniform.

The transfer residual toner on the surface of the photosensitive drum uniformized by the transfer residual toner equalizing means 8 continues to the photosensitive drum 1.
Rotation reaches the contact portion e between the toner charge amount control means 7 and the photosensitive drum 1, and the transfer residual toner on the photosensitive drum 1 passing through the toner charge amount control means 7 has a negative polarity whose charge polarity is normal polarity. Are aligned with.

By aligning the charge polarity of the transfer residual toner to the negative polarity which is the normal polarity, when the surface of the photosensitive drum 1 is charged from above the transfer residual toner by the charge a located further downstream, The mirror power on the drum 1 is increased, and the transfer residual toner is prevented from adhering to the charging roller 2.

For this reason, the amount of charge required for the transfer residual toner needs to be 2.2 times or more as compared with the amount of toner charge at the time of development.

FIG. 3 shows the relationship between the voltage applied to the toner charge amount control means 7 and the toner charge amount after passing through the toner charge control means 7. When no voltage is applied to the toner charge amount control means 7, as described above, the transfer residual toner is affected by the negative toner of the image portion, the positive toner of the non-image portion, and the positive voltage of the transfer. Since the toner includes the toner whose polarity is reversed to the positive polarity, the charge amount is indefinite. Further, it can be seen that by applying a voltage to the toner charge amount control means 7, the toner charge amount after passing through the toner charge amount control means 7 is increased and is saturated at a certain value or more. In the toner used in this embodiment, the charge amount when saturated was −90 μC / g.

Next, before the transfer residual toner enters the charge amount a,
FIG. 4 is a graph showing the relationship between the transfer residual toner charge amount and the adhesion amount to the charging roller 2 when the transfer residual toner amount is 1.
Shown in. It can be seen that the adhesion amount is decreased by increasing the charge amount of the transfer residual toner. Further, at this time, the occurrence of a poorly charged image due to the adhesion of the transfer residual toner to the charging roller 2 occurred at a charge amount of the transfer residual toner of −55 μC / g or less.

Therefore, in order to prevent the transfer residual toner from adhering to the charging roller 2 and suppress the occurrence of a poorly charged image, the charge amount of the transfer residual toner is compared with the toner charge amount at the time of development. It turns out that it is necessary to double or more.

In the present embodiment, the voltage applied to the toner charge control means 7 is -800 V, and the charge amount of the transfer residual toner after passing through the toner charge amount means 7 is -70 μC / g.
And

Next, the recovery of the transfer residual toner in the developing step will be described.

As described above, the developing device 4 is of a cleanerless type in which the transfer residual toner is cleaned simultaneously with the development.
As described above, the developed toner charge amount on the photosensitive drum 1 is −25 μC / g in this embodiment. Table 1 shows the relationship between the transfer residual toner and the amount of charge for collecting by the developing device 4 under the developing conditions in the present embodiment.

[0067]

[Table 1]

The toner charge amount for collecting the transfer residual toner on the photosensitive drum 1 by the developing device 4 is 0.5 to 1.8 as compared with the toner charge amount (-25 μC / g) at the time of development.
It needs to be doubled.

However, as described above, in order to prevent the toner from adhering to the charging roller 2, the transfer residual toner largely negatively charged to −70 μC / g by the toner charge amount control means 7 is developed. In order to recover in No. 4, it is necessary to remove the charge.

Here, the relationship between the toner charge amount after the toner on the photosensitive drum 1 having the charge amount of −70 μC / g after passing through the charge roller 2 and Vpp of the AC voltage applied to the charge roller 2 is shown in FIG. Shown in. It can be seen that power is being received as Vpp of the alternating voltage is increased.

The charging roller 2 is charged with an AC voltage (frequency f1000 Hz, in order to charge the peripheral surface of the photosensitive drum 1).
By applying Vpp1400V), the transfer residual toner is subjected to AC charge removal. Therefore, the charging portion a
After passing through, the toner charge amount is −30 μC / g. In the developing process, the untransferred toner on the photosensitive drum 1, which should not be developed with the toner, is caused by the developing device 4 due to the above reason.
Will be collected.

In this way, the charge amount of the transfer residual toner on the photosensitive drum 1 carried from the transfer part d to the charging part a is adjusted to the negative polarity of the normal polarity by the toner charge amount control means 7 and transferred by the charging process. While preventing the residual toner from adhering to the charging roller 2, the charging roller 2 charges the photosensitive drum 1 to a predetermined potential, and at the same time, the toner charging amount control means 7 is charged to a negative polarity of normal polarity. By controlling the charge amount of the transfer residual toner to an appropriate charge amount by which the developing device 4 can develop the electrostatic latent image on the photosensitive drum, the transfer device can efficiently collect the transfer residual toner.

In the four-color tandem type color image forming apparatus (see FIG. 6) using such a cleanerless image forming apparatus, particularly when the image forming apparatus which is Bk of the final image forming section is used for paper passing durability, The Bk-st photoconductor was fused with the toner, and the fused portion had a phenomenon that the exposure was blocked and the image was blank. When paper passing durability is performed with a color image having an image ratio of 5% for each color, other image forming apparatuses (Y-st, Ms
In t and C-st), image defects due to toner fusion did not occur up to 30,000 sheets, whereas in Bk-st, white spots due to toner fusion occurred after 3000 sheets. In addition, if the ratio of the number of color images and black monochromatic images is 1: 5 (black monochromatic mode),
When paper passing durability is performed with a color image with an image ratio of 5% for each color,
In Y-st, M-st and C-st, image defects due to toner fusion did not occur up to 100,000 sheets, whereas in Bk-s
At t, white spots due to toner fusion occurred on 5000 sheets.

Toner fusion to the photosensitive member is caused by the friction of the nip portion between the contact charging member and the photosensitive member and the AC vibration when the transfer residual toner passes between the contact charging member and the photosensitive member. Fuse on the body. Usually, even if the toner is fused on the photoconductor as described above, if the photoconductor cleaner is provided, the toner fusion portion is scraped off by the cleaning effect of the cleaner, and the image defect due to the toner fusion hardly occurs.

However, as described above, in the case of an image forming apparatus that does not have a photoconductor cleaner, since there is no member for positively polishing the photoconductor, the toner once fused on the photoconductor is not removed, and the paper is not passed. As the durability progresses, the toner fusion portion further grows. Due to the toner adhesion portion that has grown until the exposure is completely blocked, the potential there does not drop to a predetermined potential even when exposed, and appears as white spots on the image.

When a large amount of reverse toner is present on the photoconductor, especially when retransfer toner from the upstream image forming apparatus is present on the photoconductor, the transfer residual toner equalizing means 8 and the toner charge amount control means 7 are provided. However, it is not possible to control the charge amount to a normal amount, and the reversal toner is rotated along with the photoconductor by the contact charging member, which further aggravates the toner fusion. That is, in the tandem image forming apparatus as in the present embodiment, the toner is more likely to be fused to the last station.

Further, the color image forming apparatus does not output all color images but uses color images and monochrome images separately. That is, only in Bk-st, the time for the toner to pass between the photoconductor and the charging member becomes much longer than in other stations, and in Bk-st, fusion easily occurs.

In the present embodiment, the cleanerless image forming apparatus of such a four-color tandem system and the image forming apparatus having the final image forming portion of Bk are used, and zinc stearate is added to the toner in the Bk-st developer. The powder was externally added. As a result of diligent research, it has been found that external addition of a metal soap powder such as zinc stearate to the toner increases the releasability of the toner particles themselves and makes it difficult for the toner to fuse to the photoreceptor.

[0079]

[Table 2]

0.01% zinc stearate as shown in Table 2.
As a result of externally adding 0.8 parts to 0.8 parts and carrying out paper passing at an image ratio of 5%, a defective image is generated due to the white spot phenomenon due to toner fusion when the external addition amount is less than 0.05. It has been found.

However, when zinc stearate was externally added in an amount of more than 0.5 parts, transfer defects (hereinafter referred to as mottled spots) in which the image was partially rounded off were generated (see Table 2). When the developing container is filled with a large amount of zinc stearate, a plurality of toner particles are agglomerated, and the toner agglomerates have a small friction area per magnetic particle with the magnetic particles, and the toner is normally charged to the toner. The amount becomes smaller. When such toner aggregates are developed and transferred to the photoreceptor,
Since the charge amount is small, it is difficult to attract the transfer bias having the opposite polarity to the toner, and as a result, only that portion is not transferred.

When zinc stearate is externally added to the toners of all stations, the level of toner fusion is significantly improved. For example, as shown in FIG. 7A, zinc stearate is externally added to the first image forming portion. In this case, when the color of the downstream image forming portion is transferred onto the toner developed and transferred in the first image forming portion, only a part of the particles of zinc stearate externally added to the toner of the first image forming portion has a resistance. It has risen, and it becomes difficult for the next toner to be transferred onto it. As a result, when a color such as a secondary color is formed, local transfer failure occurs (FIG. 7-2).

When zinc stearate is externally added only to the final image forming portion as in the present embodiment, there is no toner transferred onto it, and normally, a secondary color is formed so that colors are superposed. Sometimes Bk toner is not used.

As described above, in the tandem type cleanerless image forming apparatus, when zinc stearate is externally added to the Bk toner of the final image forming portion, the image defect due to the white spot due to the toner fusion does not occur, and the image defect is 5%. A good image was maintained up to 30,000 sheets in terms of durability of color image passing of image ratio and durability of color and monochrome mixed sheet passing.

(Other Embodiments) 1) The transfer residual toner equalizing means 8 and the toner charge amount controlling means 7 are brush-like members in the embodiment, but may be brush rotating bodies, elastic roller bodies, sheet-like members, or the like. Can be a member of the form

2) The image bearing member has a surface resistance of 10 ⁹ to 10 10.
^It may be a direct injection type having a charge injection layer of ¹⁴ Ω · cm. Even when the charge injection layer is not used, the same effect can be obtained even when the charge transport layer is in the above resistance range. Surface volume resistance is about 10 ¹³ Ω
An amorphous silicon photoconductor having a size of cm may be used.

3) As the flexible contact charging member, in addition to the charging roller, a fur brush, felt, cloth or the like having a shape and material can be used. Moreover, more appropriate elasticity, conductivity, surface property, and durability can be obtained by combining various materials.

4) As the waveform of the alternating voltage component (AC component, voltage whose voltage value changes periodically) of the oscillating electric field applied to the contact charging member and the developing member, a sine wave, a rectangular wave, a triangular wave or the like can be appropriately used. Is. It may be a rectangular wave formed by periodically turning on / off the DC power supply.

5) In addition to the laser scanning means of the embodiment, the image exposing means as the information writing means on the charged surface of the photoconductor as the image carrier is, for example, digital exposure using a solid light emitting element array such as an LED. It may be a means. It may be an analog image exposure means using a halogen lamp, a fluorescent lamp or the like as a document illumination light source. In short, what is necessary is just to form an electrostatic latent image corresponding to image information.

6) The image carrier may be an electrostatic recording dielectric or the like. In this case, after uniformly charging the dielectric surface,
The charged surface is selectively neutralized by a neutralizing means such as a neutralizing needle head or an electron gun to write and form an electrostatic latent image corresponding to target image information.

7) The toner developing system / means for the electrostatic latent image is arbitrary. The reversal development method or the regular development method may be used.

Generally, in the method of developing an electrostatic latent image, a non-magnetic toner is coated on a developer carrying member such as a sleeve by a blade or the like, and a magnetic toner is coated on a developer carrying member. A method for developing an electrostatic latent image by applying it to the image carrier in a non-contact state by coating with a magnetic force and developing the electrostatic latent image on the developer carrying member as described above. A method in which a coated toner is applied to an image carrier in a contact state to develop an electrostatic latent image (one-component contact development) and a method in which a magnetic carrier is mixed with toner particles is used as a developer (two-component development). Used as a developer) to be conveyed by magnetic force and applied to the image carrier in a contact state to develop an electrostatic latent image (two-component contact development), and the above two-component developer to the image carrier. Applied in a non-contact state It is roughly divided into four types of methods (2-component non-contact development) for developing the latent image.

8) The transfer means is not limited to the roller transfer of the embodiment, but may be blade transfer, belt transfer, other contact transfer charging system, or non-contact transfer charging system using a corona charger. .

[0094]

EFFECT OF THE INVENTION By adopting the following constitution as the image forming apparatus in the present invention, stable and favorable image formation can be continuously carried out.

(1) An image carrier having a plurality of color image forming units, a charging unit for charging the surface of the image carrier, and an information writing unit for forming an electrostatic latent image on the charged image carrier.
In a cleanerless image forming apparatus, which has a developing unit that supplies a developer to the electrostatic latent image to visualize the electrostatic latent image, and a transfer unit that transfers the visualized developer image to a transfer material,
Image forming apparatus characterized in that the developer in the image forming section in the final step contains metal soap (2) The toner in the developer in the image forming section in the final step is black (1) Image forming device.

(3) The image of (1) or (2), characterized in that the metal soap is contained in an amount of 0.05 to 0.5 parts by weight based on 100 parts by weight of the developing toner. Forming equipment.

(4) The image forming apparatus according to (1) to (3), wherein the metal soap is zinc stearate powder.

(5) A developer charge amount control means which is located upstream of the charging means and downstream of the transfer means as the cleanerless means, and which charges the developer on the developer surface on the image carrier surface. Residual development that is located upstream of the developer charge amount control means and downstream of the transfer means and that uniformizes the residual developer image remaining on the surface of the image carrier after transferring the developer to the transfer material. The image forming apparatus according to any one of (1) to (4), further including a uniform agent image forming means.

(6) The image forming apparatus according to (1) to (5), wherein the charging means is contact charging.

(7) The image forming apparatus according to any one of (1) to (6), characterized in that an oscillating electric field is applied to the charging means.

(8) The image forming apparatus according to (1) to (7), characterized in that the information writing means is an exposing means.

[Brief description of drawings]

FIG. 1 is a schematic configuration model diagram of an image forming apparatus according to an embodiment.

FIG. 2 is a layer configuration model diagram of a photosensitive drum and a charging roller.

FIG. 3 is a diagram showing the relationship between the voltage applied to the toner charge amount control means and the charge amount of transfer residual toner.

FIG. 4 is a diagram showing a relationship between a charge amount of transfer residual toner and a toner adhesion amount on a charging roller.

FIG. 5 is a relationship diagram between a toner charge amount after passing through a charging roller and Vpp of an applied AC voltage.

FIG. 6 is a schematic diagram of a four-color tandem type image forming apparatus according to an embodiment.

FIG. 7 is a transfer failure model diagram when zinc stearate is externally added to the upstream image forming unit.

[Explanation of symbols]

1 Photosensitive drum (image carrier) 2 charging roller 3 Laser beam scanner 4 Developing device 5 Transfer roller 6 fixing device 7 Toner charge amount control means (developer charge amount control means) 8 Transfer residual toner uniformizing means (residual developer uniformizing means) S1 to S4 Bias voltage application power supply

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/08 507 G03G 15/08 507B 21/00 507L 9/08 361 F term (reference) 2H005 AA08 AA21 CB08 EA07 2H077 AA37 AC16 AD06 AD13 AD18 AD36 EA03 EA24 GA13 2H134 GA01 GB02 HF13 KG01 KG03 KG07 KH01 KH04 KJ02 MA02 MA11 2H200 FA02 GA12 GA14 GA16 GA23 GA34 GA47 GA57 GB25 HB12 H45B25 HB12 H45B25 HB22 H47B25 HB22 H47B25 HB22 H47B25 HB22 H47BB LA29 LB02 LB08 LB14 MA03 MA04 MA08 MA12 MA14 MA20 MB04 MC06 NA02 NA06 NA09 NA10 2H300 EB04 EB07 EB12 EF02 EF08 EF14 EG02 EG05 EG08 EG09 EH16 EJ09 EJ30 EJ35 EJ43 EJ47 EJ50 EJ52 EK03 EL03 EL05 EM03 GG29 GG37 GG41 HH17 HH22 HH35 KK03 KK07 KK14 MM05 MM25 NN01 PP06 PP07 PP09 PP10

Claims (8)

[Claims] 1. An image carrier having a plurality of color image forming sections, a charging unit for charging the surface of the image carrier, an information writing unit for forming an electrostatic latent image on the charged image carrier, and a static unit. In a cleanerless image forming apparatus, which has a developing unit for supplying a developer to the electrostatic latent image to visualize the electrostatic latent image and a transferring unit for transferring the visualized developer image to a transfer material, An image forming apparatus, wherein the developer in the image forming section contains metal soap. 2. The image forming apparatus according to claim 1, wherein the toner in the developer in the image forming section in the final step is black. 3. The image forming apparatus according to claim 1, wherein the metal soap is contained in an amount of 0.05 to 0.5 parts by weight based on 100 parts by weight of the developing toner. 4. The image forming apparatus according to claim 1, wherein the metallic soap is zinc stearate powder. 5. The cleanerless means is located upstream of the charging means and downstream of the transfer means,
A developer charge amount control means for charging the developer on the surface of the image bearing member, and a transfer material which is located upstream of the developer charge amount control means and downstream of the transfer means. 2. A residual developer image uniformizing means for uniformizing the residual developer image remaining on the surface of the image carrier after being transferred to the image carrier.
~ 4 image forming apparatus. 6. The image forming apparatus according to claim 1, wherein the charging unit is contact charging. 7. The image forming apparatus according to claim 1, wherein an oscillating electric field is applied to the charging unit. 8. The image forming apparatus according to claim 1, wherein the information writing unit is an exposing unit.