JPH06148954A - Electrophotographic method and image forming device - Google Patents

Abstract

PURPOSE:To efficiently transfer a toner image on a photosensitive body onto an image receiving paper, to prevent the constitution of a device from being complicated and to reduce the generation of ozone. CONSTITUTION:An electrical conductive elastic transfer roller 5 is brought into contact with the photosensitive body 1 by prescribed pressure. A magnetic field is formed at a nip part by actuating a magnet 6 whose width is equal to or wider than the contact width (nip) of the body 1 and the roller 5 from the back surface of the base material of the body 1. When the toner image on the body 1 is transferred onto the image receiving paper 9, an AC voltage and a DC voltage are superimposed and impressed on the roller 5. Then, toner 11 is vibrated by the AC voltage and transferred on the paper 9 from the body 1 by the DC voltage by resisting to magnetic force of the inside of the body 1. This is because the toner 11 is more easily attached on the surface of the paper 9 than the surface of the body 10. By such a method, an excellent image without toner scattering, void and surface fogging can be obtained. Besides, the impressing voltage can be lowered and the ozone is hardly generated. Moreover, the toner 11 on the surface of the roller 5 is also transferred on the body 1 by the vibration by the AC voltage and the magnetic force and removed, and the constitution of the device is simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a facsimile,
The present invention relates to a printer, and more particularly, to an electrophotographic system and its image forming apparatus.

[0002]

2. Description of the Related Art In recent years, electrophotographic apparatuses have been shifting from the purpose of office use to personal use, and have been downsized.
There is a demand for a technology that realizes maintenance-free operation. Small printers intended for personal use are expected to be placed in a corner of a desk or used in a general household, and may meet conditions such as maintenance and low ozone emissions. It becomes a point of popularization.

A printing process of an electrophotographic copying machine or printer will be described. First, the photoreceptor is charged to form an image. As a charging method, a corona discharger which has been widely used in the past is used, and in recent years, a photoreceptor is applied by a contact-type charging method in which a conductive roller is directly pressed against the photoreceptor in order to reduce ozone generated. Charge the surface uniformly. After the photoconductor is charged, in the case of a copying machine, the copy original is irradiated with light and the reflected light is irradiated onto the photoconductor through a lens system. Alternatively, in the case of a printer, an image signal is sent to a light emitting diode or a laser diode as an exposure light source to form a latent image on the photoconductor by turning the light ON-OFF. When a latent image (high or low surface potential) is formed on the photosensitive member, the photosensitive member is pre-charged with colored toner (5 μm to 15 μm in diameter).
It is visualized by (μm position). The toner adheres to the surface of the photoconductor according to the level of the surface potential of the photoconductor, and is electrically transferred to the copy sheet. That is, the toner is charged positively or negatively in advance, and a charge having a polarity opposite to the polarity of the toner is applied from the back surface of the copy sheet and is electrically attracted. Up to now, a corona discharger has been widely used as the charge applying method as in the charging method, but in recent years, a transfer device using a conductive roller has been put into practical use in order to reduce ozone generation.

FIG. 4 shows U of Japanese Unexamined Patent Publication No. 48-69524.
SP2,807,233, JP-A-3-15558
4 is a schematic diagram showing a configuration of a toner image transfer device disclosed in Japanese Patent Publication No. 4 or the like. FIG. In FIG. 4, 20 is a transfer roller made of foamed or solid rubber and adjusted to a medium resistance of about 10 ⁷ Ω, 21 is a power supply for applying voltage to the transfer roller, 22 is a photoconductor, and 23 is Receiving paper (copy paper), 2
4 is toner. The operation of the transfer device configured as described above will be described.

An image is formed on the surface of the photoconductor 22 by the toner described above. Now, it is assumed that the polarity of the photoconductor 22 is negative and the polarity of the toner 24 is positive. The transfer roller 20 is in contact with the photoconductor 22 with a predetermined pressing force. The image receiving paper 23 is supplied to the contact point between the photoconductor 22 and the transfer roller 20, and is pressed against the photoconductor 22 by the transfer roller 20 and comes into contact with the toner 24. Toner 24 on the transfer roller 20
Since the negative voltage opposite to the polarity of is applied from the power supply device 21, the toner 21 is transferred onto the image receiving paper 23. Since the transfer roller 20 is in contact with the image receiving paper 23, the voltage applied from the power supply 21 can be as low as several hundred to 3000V. Image receiving paper 2
3 passes through the contact point between the photoconductor 20 and the transfer roller 22 and is conveyed to a fixing unit (not shown). Image receiving paper 23 and transfer roller 2
When the width of 0 is different, especially when the copy width (image width) is larger than the image receiving paper 23, the transfer roller 20 causes the toner 24
To get dirty. Immediately after this, when copying is performed with the transfer roller 20 and the image receiving paper 23 having substantially the same width, the back surface of the image receiving paper 23 is soiled by the toner 24 adhering to the transfer roller 20. To prevent this, at a time when the toner 24 is not involved in copying, a voltage having the same polarity (positive in this case) as that of the toner 24 is applied to the transfer roller 20 so that the toner 24 attached to the surface of the transfer roller 20 is applied to the photoconductor 22. A method of returning it can be used (Japanese Patent Laid-Open No. 51-9840, etc.).

[0006]

The above-mentioned transfer method has the following problems. 1. Occurrence of Fog Due to Transfer As described above, the polarity opposite to the toner polarity is applied to the transfer roller. In a copying machine, this is a developing method (a regular developing method; toner adheres to the surface charge of the photoconductor) in which the white background portion of the original becomes white, and the same polarity as the charge polarity of the photoconductor is applied to the transfer roller. On the other hand, when a light emitting diode or a laser diode is used as a light source for a printer or the like, a developing method in which the exposed portion becomes a character (reversal developing method; toner adheres to the surface of the photosensitive member where there is no electric charge) is used. The charging polarity and the toner polarity are the same, and a voltage opposite to that of the toner is applied to the transfer roller. For this reason, since the transfer roller and the photoconductor directly contact with each other in a portion without the image receiving paper, normally,
The photoconductor is charged to the opposite polarity to the one that charges the photoconductor. This appears as a transfer memory on the image (because of insufficient charge, it causes background fog). In particular, in recent years, the diameter of the photoconductor has been reduced in order to reduce the size of the apparatus. Therefore, the photoconductor needs to rotate several times to obtain one image, and this effect is likely to occur. 2. Dirt on the backside of the image-receiving paper (copy paper) Dirt on the backside of the image-receiving paper is (1) when the image-receiving paper is jammed inside the machine during copying. (2) A case where the copy width (image width) and the image receiving paper width are different from each other (especially, copy width> image receiving paper width), and then copy width ≦ image receiving paper width. (3) Usually, it does not occur often, but when copying irregular size paper. Etc. Regarding (1) and (2), a method of applying a voltage having the same polarity as the toner polarity to the transfer roller afterwards and returning the toner adhering to the transfer roller to the photoconductor is used.
It is not possible to deal with the case where the copying with different widths of the image receiving paper is continuously performed in (2) to (3). Especially, when the device is downsized and used by an unfamiliar user, these troubles are assumed. Contamination on the back side of the image receiving paper may cause jamming of the image receiving paper in the toner fixing process that continues after the transfer process, which not only impairs the reliability of the entire apparatus but also requires a power supply for cleaning the transfer roller. Furthermore, switching of the high-voltage power source is required, and the device becomes complicated. 3. Missing characters and lines When the toner on the photoconductor is transferred to the image receiving paper by using the transfer roller, the transfer roller is in contact with the photoconductor at a predetermined pressure. For this reason, in areas where toner is concentrated, such as characters and lines, the pressure is higher than in areas where there is no toner, and toner particles agglomerate, causing so-called "middle voids" that are not transferred to the image receiving paper. In particular, it tends to occur in the case of a thick image receiving paper. 4. Toner Scattering Around Characters The transfer of the toner on the photoconductor to the image receiving paper is carried out by the attraction between the charged electric charge of the toner and the electric charge opposite to the charged electric charge of the toner applied from the outside. However, since the insulating property of the toner is high, the electric charge is likely to concentrate on a portion of the image receiving paper where the toner does not exist. As a result, the toner is likely to be scattered around the characters where no toner exists.

In view of the above problems, the present invention provides a transfer method and an image forming apparatus that generate less ozone and are easy to maintain.

[0008]

In order to solve the above problems, the present invention provides an electrophotographic method and an image forming apparatus characterized by the following configurations.

According to the present invention, an electrostatic latent image carrier that contains and moves a fixed magnet, a developer reservoir, a magnetic developer, a developing device for developing the magnetic developer, and a position facing the fixed magnet. An electrode roller installed in the electrophotographic apparatus, wherein the force for transferring the developer image on the electrostatic latent image carrier to the image receiving paper is the magnetic force generated by the fixed magnet. The electrophotographic method is a resultant force of an electrostatic force connecting between the electrostatic latent image holding member and the electrode roller.

Further, the present invention is the electrophotographic method, wherein the electrostatic force is an electrostatic force generated by applying a pulsating voltage to the electrode roller.

The present invention also relates to 1. 1. an electrostatic latent image holder that contains a fixed magnet and moves; 2. developing means for developing a magnetic developer on the surface of the electrostatic latent image carrier; To be placed at a position facing at least a part of the fixed magnet, to sandwich the image receiving paper between the electrostatic latent image holding member and to transfer the magnetic developer image on the electrostatic latent image holding member. 3. The conductive electrode of 4. An image forming apparatus, comprising: a pulsating voltage generating means for applying a pulsating voltage to the conductive electrode to transfer the magnetic developer image onto the image receiving paper.

Furthermore, the present invention is an image forming apparatus in which the conductive electrodes are roller-shaped. Further, the present invention is an image forming apparatus having a configuration in which a roller-shaped conductive electrode is in contact with an electrostatic latent image holding member.

Further, the present invention is the image forming apparatus, wherein the pulsating current voltage generating means is a voltage generating means for generating a voltage in which a direct current voltage is superimposed on an alternating current voltage.

[0014]

The transfer of the toner on the photosensitive member to the image receiving paper is carried out by the attraction of the charge of the toner and the charge opposite to the charge of the toner applied from the outside.

However, since the toner has a high insulating property, the electric charge is likely to concentrate on the portion of the image receiving paper where the toner does not exist. The inventors have used a magnetic developer as a toner, have a magnetism generating means included in a cylindrical photoconductor, and transfer the toner to an image receiving paper by electrostatic force while holding the toner by a magnetic field. It has been found that the toner can be prevented from scattering around the characters even if the charge is nonuniform due to the presence or absence.

Further, the force acting on the toner adhered according to the electric charge (latent image) on the surface of the photoconductor is roughly classified into an electrostatic force attracting the electric charge of the photoconductor and the toner charge and a mechanical force acting on the photoconductor surface and the toner surface. . The size of the two is said to be antagonistic although the electrostatic force is somewhat large. The inventors have conducted experiments in which toner containing a magnetic material on the surface of a photoconductor is transferred to an image receiving paper. (1) Mechanical force acting between the surface of the photoconductor and the toner can be weakened by slight vibration. (2) Toner Is designed to transfer by applying the phenomenon that it is more likely to adhere to the surface of the image receiving paper than to the surface of the photoconductor, and when an AC voltage with a sinusoidal waveform centered at 0V is applied to the transfer roller described above, the amplitude (voltage It was found that the toner is transferred to the image receiving paper by slight vibration with a maximum value and a minimum value difference of 500 V and a frequency of 50 Hz.

However, if the vibration becomes too large due to the electric charge of the toner, the toner is scattered around the transferred image, and the image quality is significantly impaired. The inventors believe that the toner image is disturbed by the application of an AC voltage to a slight gap existing immediately before or immediately after reaching the contact portion (nip portion) between the photosensitive member and the transfer roller (FIG. 5, FIG. 5
In the figure, 26 is a pulsating current generating power source, and a fixed magnet is arranged inside the photoconductor (the inside of the cylindrical photoconductor) to hold the toner from the inside of the photoconductor and guide the toner to the above-mentioned nip portion (Fig. 6. In FIG. 6, 25 is a magnet disposed on the back surface of the electroconductive substrate of the photoconductor), and a good image was obtained without scattering. Further, by superposing a slight DC voltage on the AC voltage in order to cancel the magnetic force provided inside the photoconductor, a transfer performance equivalent to that at the time of DC application transfer was obtained. By applying the above-mentioned pulsating voltage to the transfer roller, the applied voltage at the time of transfer can be kept low, and even if the transfer roller comes into direct contact with the photoconductor, the photoconductor is not charged by the transfer roller (main charging And cause fog) and less ozone. By applying this pulsating flow, the toner vibrates slightly, but the toner particles are less likely to aggregate due to the pressure applied by the transfer roller. In addition, since the magnetic force inside the photoconductor acts during transfer and during non-transfer, it also vibrates the unnecessary toner adhering to the transfer roller (mechanical force on the transfer roller surface and the toner surface). (Cut off), attract toner to the photoconductor, and clean the transfer roller. This eliminates the need for a cleaning power source, and eliminates the need to switch the transfer / cleaning power source.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram of an image forming apparatus (electrophotographic apparatus) of an embodiment according to the present invention.

(Embodiment 1) 1 is a photoreceptor as an electrostatic latent image holding member, in which a phthalocyanine-based pigment is dispersed in a resin as a charge generating layer on a conductive base material. As the charge transport layer, an organic photoconductor was used in which hydrazone was mixed with a resin so that the thickness of the photoconductive layer was 20 μm.

2 is a corona discharge device for charging the photoreceptor 1.
Reference numeral 3 is an exposure device for performing image exposure on the photoconductor, and 4 is a developing device for visualizing the latent image after exposure, which is a photoconductor for attaching toner, which is a magnetic developer, to the photoconductor 1. 1, a fixed magnetic field generating magnet 4a and a collecting roller 4b made of a conductive member for applying a voltage to collect excess toner other than the image portion. Reference numeral 5 denotes a transfer roller set so as to come into contact with the photoconductor 1. The transfer roller 5 is an elastic roller in which conductive rubber is provided around a shaft made of conductive magnetic metal. The pressing force applied to the photoconductor 1 is 0 to 2000 g, preferably 500 to 1000 g per transfer roller 5 (about 216 mm). This was measured from the product of the spring coefficient and the amount of contraction of the spring for pressing the transfer roller 5 against the photosensitive member 1. The contact width with the photoconductor is about 0.5mm-5m
m. The rubber hardness of the transfer roller 5 is measured by Asker C (measurement using block pieces, not roller shape).
At 80 degrees or less, preferably 30 to 40 degrees. Reference numeral 6 denotes a magnet disposed inside the conductive base material of the photoconductor 1 having a surface magnetic flux density of about 1000 Gs (× 10 ⁻⁴ Wb / m ² ).
The width of the magnet 6 is preferably larger than the contact width (nip) between the photoconductor 1 and the transfer roller 5.

Reference numeral 7 is a thrusting guide made of a conductive member for introducing the image receiving paper to the transfer roller 5, and 8 is a conveying guide in which the surface of the conductive member is insulation-coated. The plunge guide 7 and the transport guide 8 are grounded directly or through a resistor. Reference numeral 9 is an image receiving paper, 10 is a cleaning device for cleaning the toner remaining on the surface of the photoconductor 1 after transfer, and 11 is toner. Reference numeral 12 is a voltage generating power supply for applying a voltage to the transfer roller 5.

Specifically, the outer diameter of the photoconductor 1 is 30 mm,
As the conductive base material, a negatively charged organic photoreceptor having a thickness of 1 mm was used.
The transfer roller 5 used was one in which a conductive urethane elastomer having a foaming property was provided around a shaft having a diameter of 6 mm to have a resistance value of 10 ⁷ Ω (an electrode was provided on the shaft and the surface, and 500 V was applied to both electrodes). The outer diameter of the entire transfer roller 5 is 16.4 mm,
The hardness of Asker C was 40 degrees. The transfer roller 5 was brought into contact with the photoconductor 1 by pressing the shaft of the transfer roller 5 with a metal spring. The pressing force was about 1000 g. Photoconductor 1
The magnet 6 disposed inside the conductive base material is fixed on the axis of the photoconductor 1 so that the magnet surface is along the base material of the photoconductor 1 so as not to contact the base material of the photoconductor 1. At 10 mm,
Approximately 200 Gs (× 10 ^-4 Wb / m ² ) on the surface of photoconductor 1
And the magnetic pole was N. The toner 11 as the magnetic developer has an average particle diameter of about 12 μm and is negatively charged.

The operation will be described using the apparatus described above. The surface of the photoconductor 1 is negatively charged by using the corona discharge device 2.
After charging, the developing device 4 visualizes the latent image formed by the surface charges of the photoconductor 1 by the exposure device 3. To visualize the image, a toner as a magnetic developer is attached to the surface of the photoconductor 1 by the magnet 4a contained inside the base material of the photoconductor 1. When the reversal developing method in which a developing bias similar to the surface potential of the photoconductor 1 is applied to the collecting roller 4b, the photoconductor surface potential of the portion exposed by the exposure device 3 becomes low, and this portion is negatively charged. The toner adheres and the toner in the non-image area where the surface potential of the photoconductor is high is collected by the collecting roller 4b. At the same time that the photoconductor 1 reaches the contact position of the transfer roller 5, the image receiving paper 9 is supplied to the contact portion between the photoconductor 1 and the transfer roller 5. A DC voltage of about +2000 V is applied to the transfer roller 5,
The magnetic force of the magnet 6 is overcome to be transferred to the image receiving paper 9. At the time of transfer, the toner is restrained by the magnetic force of the magnet 6 and the toner is transferred to the image receiving paper 9 by electrostatic force, so that a good image can be obtained without toner scattering. The transferred image passes through the conveyance guide 8 and a fixing device (not shown), and the toner 11 is fixed on the image receiving paper 9. In addition to the scattering of the toner 11 around the characters, there was no background fog or hollow characters in the images, and the images had good maximum image density and were good.

(Embodiment 2) FIG. 2 shows a schematic diagram in the case of transfer using pulsating flow at the time of transfer. The used photoconductor, corona discharge device, exposure device, developing device, transfer roller and the like are made of the same members as in FIG. 1, and the setting conditions of magnets and the like contained in the photoconductor are also the same. In FIG. 2, reference numeral 13 is a pulsating flow generating power supply device.
The pulsating current voltage has a voltage waveform of a sine wave, a rectangular wave, or the like, a frequency of 30 to 500 Hz, and an amplitude of about 200 to 100 between peaks.
A DC voltage may be superimposed at 0V. FIG. 3 shows the voltage waveform used in this example. A sine wave with a frequency of 50 Hz was used by superimposing a DC voltage of +500 on an AC voltage of 500 V with a peak-to-peak voltage.

Next, the operation will be described. The procedure is the same as in Example 1 until an image is formed on the photoreceptor with toner. At the same time when the photoconductor 1 reaches the contact position of the transfer roller 5, the transfer material 9 is supplied to the contact portion between the photoconductor 1 and the transfer roller 5.
The above-mentioned pulsating voltage is applied to the transfer roller 5,
At the transfer nip portion (contact portion between the photoconductor 1 and the transfer material 9), the toner 11 is vibrated by the pulsating flow. The toner 11 is more likely to adhere to the paper transfer material 9 than the surface of the photoconductor 1, and the toner 11 released from the surface of the photoconductor 1 due to vibration has a DC voltage component in the pulsating flow (the polarity of the toner 11 is negative). The DC voltage component is positive) The force is transferred to the transfer material 9 by overcoming the force of the magnet 6 arranged inside the photoconductor 1. The transferred image passes through the impression guide 8 and a fixing device (not shown), and the toner 11 is fixed on the transfer material 9. Image is toner 1 around the text
There was no scattering of 1, no fog on the ground, and no blanking of characters, and a satisfactory maximum image density was obtained.

(Comparative Example) A DC voltage was applied to the transfer roller 5 instead of applying a pulsating current voltage without enclosing the magnetism generating means inside the photoreceptor 1. The resistance of the transfer roller 5 and the pressing force applied to the photoconductor 1 were the same as those in the above-described embodiment. The DC voltage to be applied was determined to be approximately +2000 V so that the maximum image density on the image would be equivalent to that in the above example. For comparison, when the surface potential of the photoconductor 1 after transfer is monitored, it is approximately +100 V when pulsating current is applied and +50 V when direct current is applied.
After cleaning the toner 11 remaining on the photoconductor 1 with the cleaning device 10 and then comparing the surface potential of the photoconductor 1 after being charged by the corona discharge device 2, the pulsating current is applied to the transfer roller 5. The voltage was about 100 V lower when DC was applied than when. Since the charging potential of the photoconductor 1 is low, the background fog is increased when a direct current is applied to the transfer roller 5, and uneven density is conspicuous in the halftone image.

[0027]

As described above, according to the present invention, an electrostatic latent image holding member including a fixed magnet and moving, a developer reservoir, a magnetic developer, a developing device for developing the magnetic developer, and An electrophotographic method used in an electrophotographic apparatus having a fixed magnet and an electrode roller installed at a position facing the fixed magnet, wherein the force for transferring the developer image on the electrostatic latent image holding member to an image receiving paper is An electrophotographic method, which is a resultant force of a magnetic force generated from a fixed magnet and an electrostatic force connecting the electrostatic latent image holding member and the electrode roller. Alternatively, a good transferred image can be obtained by using an electrophotographic method characterized in that the electrostatic force is an electrostatic force generated by applying a pulsating voltage to the electrode roller.

As described above, by applying a magnetic field to the transfer nip and applying a pulsating voltage to the transfer roller,
Since the toner vibrates, the mechanical force acting between the photoconductor and the toner can be reduced, and the transfer can be performed under a low voltage condition. A pulsating voltage that extends around the transfer nip can be prevented by a magnet disposed inside the photoconductor. As a result, an image without toner scattering, background fogging, and voids can be obtained. Further, a power supply for cleaning the toner adhered on the surface of the transfer roller is not required, and the device structure can be simplified.

[Brief description of drawings]

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

FIG. 2 is a schematic configuration diagram of an image forming apparatus according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a pulsating voltage waveform applied to a transfer roller according to an embodiment of the present invention.

FIG. 4 is a schematic diagram for explaining the operation of a conventional transfer device.

FIG. 5 is a schematic diagram showing that toner is vibrating under the influence of pulsating voltage around a photoconductor and a transfer roller nip when a pulsating voltage is applied to the transfer roller.

FIG. 6 is a diagram showing a structure in which a magnet disposed inside a photoconductor holds toner on the surface of the photoconductor, and even if a pulsating voltage is applied to the transfer roller, the toner vibrates around the nip of the photoconductor and the transfer roller under the influence of the pulsating voltage. Schematic showing that there is nothing

[Explanation of symbols]

 1 Photoconductor 5 Transfer Roller 6 Magnet 12 Voltage Generation Power Supply 13 Ripple Voltage Generation Power Supply

Claims (6)

[Claims] 1. An electrostatic latent image carrier that contains a fixed magnet and moves, a developer reservoir, a magnetic developer, a developing device for developing the magnetic developer, and a position opposed to the fixed magnet. An electrophotographic method for use in an electrophotographic apparatus having an electrode roller, wherein the force for transferring the developer image on the electrostatic latent image carrier to the image receiving paper is the magnetic force generated by the fixed magnet, and An electrophotographic method which is a resultant force of an electrostatic force connecting between the electrostatic latent image holder and the electrode roller. 2. An electrophotographic method, wherein the electrostatic force is an electrostatic force generated by applying a pulsating voltage to the electrode roller. 3. 1. An electrostatic latent image holder that includes a fixed magnet and moves; 2. developing means for developing a magnetic developer on the surface of the electrostatic latent image carrier. It is installed at a position facing at least a part of the fixed magnet, and holds the image receiving paper between the electrostatic latent image holding member and
And a conductive electrode for transferring the magnetic developer image on the electrostatic latent image carrier, An image forming apparatus, comprising: a pulsating voltage generating means for applying a pulsating voltage to the conductive electrode to transfer the magnetic developer image onto the image receiving paper. 4. The image forming apparatus according to claim 3, wherein the conductive electrode has a roller shape. 5. The image forming apparatus according to claim 4, wherein the roller-shaped conductive electrode is in contact with the electrostatic latent image holding member. 6. The image forming apparatus according to claim 3, wherein the pulsating current voltage generating means is a voltage generating means for generating a voltage in which a direct current voltage is superimposed on an alternating current voltage.