JPH08248777A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device having a large diameter of a photoreceptor which uses a supporsing method of a multicolored toner and to obtain such an image forming device that a stable image of high quality can be formed on a recording sheet, good separation performance is obtd. and ozone is little produced. CONSTITUTION: This image forming device contains an electrifying means to electrify an image carrier, an exposing means to form an electrostatic latent image on the image holding body, a developing means to develop the latent image to form a toner image, a transfer means to transfer the toner image to a transfer material, and a separating means to separate the transfer material to which the toner image is transferred from the image holding body surface. The separating means includes at least an electrostatic separating means in a superposed electric field of DC bias and AC bias. A sawtooth electrode 19 as a separating electrode is disposed to face the image carrier. The sawtooth electrode 19 is designed in such a manner that the angle α between the peak line direction of the top of the sawtooth and the carrying direction of the transfer material ranges in 10 deg. to 60 deg. and that the width L of the electrode in the transfer direction of the transfer material is 1=70mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus having improved separation means for separating a transfer material onto which a toner image has been transferred from the surface of an image carrier.

[0002]

2. Description of the Related Art A toner image formed on the surface of an image carrier (hereinafter also referred to as a photoconductor) is a transfer material (hereinafter also referred to as recording paper).
It is transferred onto the above by various transfer means. As one of various transfer means, a method of transferring a toner image onto a recording paper by a transfer electrode as a corona electrode is often used. However, the method using corona discharge of the transfer electrode has an environmental problem due to the generation of ozone because a high voltage is used, and it is necessary to take measures against discharge to other devices and circuits in the device because of the high voltage. Therefore, in recent years, a method using a transfer roller has been used as a transfer means.

The method using a transfer roller has a merit that ozone is less generated and transfer efficiency is improved because a voltage lower than that of the transfer electrode as a corona electrode is used, but the transfer roller exposes the recording paper to light. It has the problem of sagging against the body and making separation a little difficult.

[0004]

As a method of separating recording paper when a transfer roller is used, a recording material that is a transfer material is used with a small drum diameter of a photosensitive member that is an image carrier. There is a method in which a photosensitive drum having a small diameter, for example, a diameter of about 30 mm is used, and the recording paper is peeled off from the photosensitive drum having the small diameter and separated. However, this method is good for single-color toner, but there is a problem that the size of the image is limited in the image formation by the method of superposing multi-color toner.

Therefore, the diameter of the photosensitive drum is, for example, 80 m.
In an image forming apparatus using a photoconductor drum having a large diameter of m-th order, for example, as shown in FIG.
A method is considered in which the recording paper P is attracted to the separation belt 191 and is peeled off from the photoconductor drum 10 by using. However, in this case, the peeling discharge is apt to occur, which causes problems such as image disturbance and a transfer memory which affects the subsequent image formation on the photosensitive drum.

As another method, as shown in FIG. 5B, a method of using a sawtooth-shaped separation electrode 192 having a small thickness, for example, a thickness of about 0.1 mm is considered. In this case, compared to a separation electrode having a corona type electrode, there is an advantage that ozone is less generated, but it is difficult to uniformly remove the electric charge, a problem such as image loss in an image, and a paper jam due to poor recording paper separation performance ( Jam) is likely to occur.

The present invention has been made to solve the above problems. That is, in an image forming apparatus having a large diameter of a photoconductor by a multicolor toner superposition method, high quality image formation can be stably obtained on recording paper, and separation performance is good,
An object is to provide an image forming apparatus that generates less ozone.

[0008]

The above-mentioned object is to provide a charging means for uniformly charging an image carrier, an image exposing means for forming an electrostatic latent image on the image carrier, and the electrostatic latent image. Developing means for developing a toner image to form a toner image, transfer means for electrostatically transferring the toner image onto a transfer material, and separating means for separating the transfer material on which the toner image is transferred from the surface of the image carrier. In the image forming apparatus having the above-mentioned, the separation means has at least an electrostatic separation means under an electric field in which an alternating current bias is superimposed on a direct current bias, and a sawtooth electrode is provided as a separation electrode on a surface facing the image carrier. In the saw-shaped electrode, the angle between the ridgeline of the tip of the saw-tooth and the transfer direction of the transfer material is 10 ° to 60 °, and the width of the electrode in the transfer material transfer direction is 1 mm to 70 mm. Reached by an image forming device characterized by It is made.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, the structure and operation of a color printer which is an example of an image forming apparatus according to the present invention will be described with reference to FIG.

In this color printer, toner images of respective colors sequentially formed on an image bearing member are superposed on each other, and then transferred at one time on a recording paper at a transfer portion to form a color image, and thereafter, an image is separated by a separating means. It is a color image forming apparatus of the type that is peeled from the surface of a carrier.

In FIG. 1, 10 is an image bearing member, which is a photosensitive drum or a photosensitive belt. The photosensitive drum here is Se, AS ₂ Se ₃ , a-Si, OP.
A material such as C (organic photoreceptor) is used. Especially as OPC used here, JP-A 64-17066, JP-A-2-183258, and JP-A-2-183.
No. 265, Y described in JP-A-3-128973
It is preferable to use type titanyl phthalocyanine or polycrystalline titanyl phthalocyanine. And the above-mentioned O
A PC photosensitive member (organic photosensitive member) is formed by coating on a drum substrate, and is grounded and driven and rotated clockwise in the drawing. Reference numeral 12 denotes a scorotron charger, which applies a uniform charge of V _{H to} the peripheral surface of the photosensitive drum 10 by corona discharge by a grid and a corona discharge wire whose potential is held at V _G. Prior to charging by this scorotron charger 12,
In order to eliminate the history of the photoreceptor until the previous printing, the peripheral surface of the photoreceptor is neutralized by exposure by a PCL (pre-charging static eliminator) 11 using a light emitting diode or the like.

After the photosensitive drum 10 is uniformly charged, the image exposing means 13 performs image exposure based on the image signal.
The image exposure means 13 is a means for performing a main scan in which an optical path is bent by a reflection mirror 134 through a polygon mirror 131, an fθ lens 132, and a cylindrical lens 133 which rotate using a laser diode (not shown) as a light emitting source. A latent image is formed by (sub scanning). In this embodiment, the character portion is exposed, and the character portion has a lower potential V _L.
To form a reverse latent image.

Around the periphery of the photosensitive drum 10, a developing device 14 (14Y) containing a developer containing toner such as yellow (Y), magenta (M), cyan (C), black (K), and a carrier, respectively. , 14M, 14C, 14K), and first, the development of the first color yellow is carried out by the developing sleeve 141 which has a magnet built therein and rotates while holding the developer. The developer consists of a carrier in which ferrite is used as a core and is coated with an insulating resin around it, and a toner whose main component is polyester and pigments according to the color and charge control agents, silica, titanium oxide, etc. are added. The agent is 100 μm on the developing sleeve 141 by the layer forming means.
Is regulated to a layer thickness of 600 μm (developer) and is transported to the development area.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.2 m, which is larger than the layer thickness (developer).
as 1.0mm from m, AC bias and V of V _AC during this time
_DC bias of DC is superimposed and applied. V _DC and V _H ,
Since charging of the toner is the same polarity, the toner given the opportunity to leave from the carrier by V _AC is not adhere to a portion of the high V _H of potential than V _DC, the lower V _L portion of potential than V _DC Adhesion and visualization (reversal development) are performed.

After the visualization of the first color is completed, the process proceeds to the image forming process of the magenta of the second color, and the scorotron charger 12 again.
Uniform charging is performed, and a latent image based on the image data of the second color is formed by the image exposure unit 13. At this time, the charge elimination by the PCL 11 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Once again, V is applied over the entire surface of the photosensitive drum 10.
A latent image similar to that of the first color is formed on the portion of the photoconductor having the _H potential and the image of the first color is not developed, but development is performed again on the portion having the image of the first color. In the portion to be performed, the latent image of V _M ′ is formed due to the light shielding by the toner of the first color and the electric charge of the toner itself, and V _DC
And development is performed according to the potential difference between V _M ′ and V _M ′. In the overlapping portion of the images of the first color and the second color, the development of the first color is V _L
When the latent image of is formed, the balance between the first color and the second color is lost, so the exposure amount of the first color is reduced and V _H > V _M > V
_It may be an intermediate potential that becomes _L.

An image forming process similar to that for the magenta of the second color is performed for the cyan of the third color and the black of the fourth color, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 10.

On the other hand, one sheet of transfer material (recording paper) P that has been unloaded from the paper feed cassette 15 via the half-moon roller 16 is temporarily stopped, and is transferred by the rotation operation of the paper feed roller 17 when the transfer timing is adjusted. Is fed to the area.

In the transfer area, the transfer roller 18 is pressed against the peripheral surface of the photosensitive drum 10 in synchronization with the transfer timing,
The supplied recording paper P is sandwiched and the multicolor image is transferred at once. The contact pressure of the transfer roller 18 at this time is
20 g / cm to 80 g / cm per unit length of 8 is preferred.

Next, the recording paper P is discharged almost simultaneously by the separation electrode 19, separated from the peripheral surface of the photosensitive drum 10 and conveyed to the fixing device 20, where a heat roller (upper roller) 201 and a pressure roller (lower roller) 202. After the toner is fused by heating and pressurizing, the toner is ejected to the outside of the apparatus through the paper ejection roller 21. The transfer roller 18 and the separation electrode 19 are retracted and separated from the peripheral surface of the photosensitive drum 10 after the recording paper P has passed,
Prepare for the next toner image formation.

On the other hand, the photosensitive drum 10 from which the recording paper P is separated
Removes and cleans the residual toner by pressing the blade 221 of the cleaning device 22, and again receives the charge removal by the PCL 11 and the charge by the charger 12 to start the next image forming process. The blade 221 immediately moves after cleaning the surface of the photoconductor and retracts from the peripheral surface of the photoconductor drum 10.

Next, an embodiment of the present invention will be described with reference to FIGS.

FIG. 2 is a partially enlarged view showing the relative positional relationship of the separation electrode according to the present invention with respect to the photosensitive drum, the transfer roller and the like. FIG. 3 is an enlarged view of the separation electrode, (A) is a plan view, and (B) is a front view.

2 and 3, the photosensitive drum 10 is a photosensitive drum having a diameter of 120 mm. When the toner image is transferred onto the recording paper P, the transfer roller 18 is brought into pressure contact with the photosensitive drum 10 in synchronization with the transfer timing onto the recording paper P, as described with reference to FIG.
It should be noted that the transfer roller is always in a pressure contact state during printing of the single color toner. The voltage of the transfer roller 18 is + 3k.
Enables application of DC bias voltage from V to 4kV 20
A transfer roller of the type in which a DC current of μA is passed and the surface of the transfer roller is cleaned by a blade is used. Separation electrode 19 provided immediately downstream of the transfer roller 18.
Is 1.0 mm to 1.5 m between the photosensitive drum 10 and
It is installed with a gap C of m.

The upper surface of the separation electrode 19 has a saw-like shape as shown in the drawing, and an angle α is provided between the ridgeline direction of the tips of the saw-like teeth and the conveying direction of the recording paper P which is the transfer material. ing. The width L of the separation electrode 19 which is the sawtooth electrode in the conveyance direction of the recording paper P has a certain width. And the separation electrode 19, the charge of the electrostatic separation method of the voltage obtained by superimposing a DC bias voltage and a 1kHz AC voltage at 5 kV _pp from 2 kV _pp of + 1 kV from -1.2kV has become possible application.

Table 1 shows the results of Examples and Comparative Examples conducted under the following conditions.

As recording paper, 16 lb paper from Jamestown was used, and the paper was passed 1000 times each. The environmental conditions are as follows.

HH: 30 ° C. 80% RH NN: 20 ° C. 50% RH LL: 10 ° C. 20% RH Then, α is the angle formed by the ridge line direction of the serrated teeth and the conveying direction of the recording paper P, and L is the separation. The width of the electrode 19 in the transport direction of the recording paper P, V _DC is the DC bias voltage of the separation electrode 19, V _DC
ACp-p is the AC voltage of the separation electrode 19, and J is the number of paper jams (jams).

[0029]

[Table 1]

As can be seen from the above examples and comparative examples, the angle α and the width L of the separation electrode 19 are such that the angle α is 20 ° to 50 °.
When the width L is between 15 mm and 50 mm, the paper jams, so-called jam does not occur even once, and the separation performance is very good. This is because even in the case of a sawtooth electrode, the ridgeline of the tip of the sawtooth is inclined with respect to the conveyance direction of the recording paper P, and the width L of the sawtooth electrode has a certain width. It is considered that this is because the electric discharge in 10 in the longitudinal direction becomes uniform, which enables uniform charge removal. Therefore, the problem of image omission does not occur and high quality image formation is possible.

FIG. 4 is a sectional view of a color printer showing another embodiment of the image forming apparatus to which the invention is applied. In addition, about the code | symbol used in drawing, the same code | symbol is attached | subjected to the part which has the same function as FIG. Further, the points different from the above embodiment will be described. Around the photosensitive belt (image carrier) 103 wound around the driving roller 101 and the driven roller 102 and rotatable, a scorotron charger 12, an image exposure unit (semiconductor laser light scanning device) 13, and a developing device 14Y. , 14M,
14C, 14K, a transfer roller 18, a separation electrode 19, and a cleaning device 22 are provided.

The radius of curvature is at least 4 near the separation site.
Since the photosensitive belt 103 of 0 mm or more has a problem in separability, a saw-shaped electrode is used as a separating electrode under an electric field in which a DC bias and an AC bias are superposed as in the above, so that a jam does not occur. High-quality image formation can be stably obtained.

Then, the present inventor has further studied and found that good results are obtained when the angle α is 10 ° to 60 ° and the width L is 1 mm to 70 mm. Also, the present invention
It is preferable that the photosensitive drum 10 has a drum diameter of 80 mm or more or the photosensitive belt 103 has a radius of curvature of 40 mm or more and is used for color image formation of a multicolor toner superposition method.

[0034]

According to the present invention, in an image forming apparatus having a large diameter of a photosensitive drum or a large radius of curvature of a photosensitive belt for forming a color image by a multicolor toner superposition method, there is a problem that an image is missing on recording paper. It is possible to stably form a high-quality image without causing any trouble. Furthermore, it is possible to provide an image forming apparatus that does not cause a paper jam (jam), has a good separation performance, generates a small amount of ozone, and is good as an environmental measure.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a partially enlarged view around a separation electrode according to the present invention.

FIG. 3 is an enlarged view of a separation electrode according to the present invention.

FIG. 4 is a configuration diagram of another image forming apparatus according to the present invention.

FIG. 5 is a view of a separation means of a conventional example.

[Explanation of symbols]

 10 Photoconductor drum 103 Photoconductor belt 18 Transfer roller 19 Separation electrode α Angle L Width P Recording paper

Claims (5)

[Claims] 1. A charging unit for uniformly charging an image carrier, an image exposing unit for forming an electrostatic latent image on the image carrier, and a toner image formed by developing the electrostatic latent image. In the image forming apparatus, there is provided: a developing unit for performing electrostatic transfer, a transfer unit for electrostatically transferring the toner image onto a transfer material, and a separating unit for separating the transfer material transferred with the toner image from the surface of the image carrier. The separating means has an electrostatic separating means under an electric field in which at least a DC bias is superimposed on an AC bias, and a sawtooth electrode is disposed as a separating electrode on a surface facing the image carrier, and the sawtooth electrode is a sawtooth electrode. The angle formed by the ridge line direction of the tooth tip and the conveying direction of the transfer material is 10 ° to 60 °, and the width of the electrode in the conveying direction of the transfer material is 1 mm to 70 mm.
An image forming apparatus characterized in that 2. The image forming apparatus according to claim 1, wherein the image carrier has a drum shape and a drum diameter is 80 mm or more. 3. The image forming apparatus according to claim 1, wherein the image carrier has a radius of curvature of at least 40 mm in the vicinity of the separation portion of the transfer material. 4. The image forming apparatus according to claim 1, wherein the transfer unit is a transfer roller. 5. The image forming apparatus according to claim 1, 2, 3 or 4, wherein the image forming apparatus forms a color image of a multicolor toner superposition method.