JPH0815962A - Image-forming device - Google Patents

Abstract

PURPOSE:To provide an image-forming device which ensures stable, uniform electrification over a long period of time even in the use of a DC electrification bias. CONSTITUTION:The hardness of the rubber of an electrifying roller 4 is 40-50 degrees, a cleaning roller 5 disposed behind the electrifying roller 4 is a brush roller made by wrapping a fiber brush round a shaft, and the both ends of the shaft projecting from the cleaning roller 5 stretch beyond the both ends of the shaft of the electrifying roller 4. Also, the total pressure which a photosensitive drum 1 receives from the electrifying roller 4 and cleaning roller 5 is 250-600g on the sides of the shaft ends of the electrifying roller. Further, the photosensitive drum 1 can rotate following the electrifying roller 4 by obtaining the driving force of the roller 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an electrophotographic system including a charging step of uniformly charging a photosensitive member through a direct-current charging voltage applied to the charging roller while arranging the charging roller in contact with the photosensitive member. The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or an image forming apparatus applied as a process cartridge of these devices.

[0002]

2. Description of the Related Art Conventionally, process means for exposing, developing, transferring, cleaning (removing residual toner), discharging, and charging are arranged on the outer peripheral surface of a photosensitive drum, and an image is formed by a predetermined electrophotographic process. Electrophotographic devices based on the so-called Carlson process are well known.

The charging means used in this type of device is generally a corotron system in which a high voltage is applied to a thin tungsten wire to perform corona discharge, or a conductive roller is charged with a voltage of several hundreds of volts to contact and charge a photosensitive drum. (Japanese Patent Application Laid-Open No. 5-297690, etc.), charging is performed while further applying a voltage to a conductive brush to bring the brush into contact with a photosensitive drum, and a brush in which magnetic particles are attached to a conductive sleeve in which a magnet is inserted. A so-called particle charging method has also been proposed in which a magnetic brush is rubbed against a photosensitive drum and a charging bias is applied to a group of magnetic particles through a sleeve to carry out charging (JP-A-59-133569).

However, the corotron method has many environmental problems in terms of safety, such as the use of high voltage and the generation of ozone, and the method of using a charging brush or charged particles causes a long period of time due to brush abrasion or particle deterioration. Therefore, it is difficult to uniformly charge the photoconductor. Therefore, while the charging roller is in contact with the photoconductor, charging is performed while applying a charging bias on the photoconductor drum via the charging roller.
A so-called charging roller system has been drawing attention, and in such a charging roller system, there are a system using an alternating voltage for a charging bias and a system using a DC voltage. Since an oscillating electric field is formed in the air in the separated area of the drum to charge it, ozone is likely to be generated due to a minute discharge phenomenon. The film thickness is reduced, and the charging roller fluctuates depending on the environmental conditions such as the temperature and humidity inside the machine. Therefore, it is advantageous to use the DC bias in order to precisely control the charging bias in consideration of these fluctuation conditions.

[0005]

However, when an alternating voltage is applied, as described above, an oscillating electric field is formed in the air in the separated area for charging, so that the charging roller and the photosensitive drum are not charged. The contact state (nip) of is not particularly a problem, but in the case of DC bias, the roller /
Since the charging current flows to the photoconductor side through the nip formed between the drums, the adhesion of the roller to the drum side is strongly required.

For this reason, particularly in the charging method using the DC bias, the charging roller is formed by using the conductive rubber. However, even if such a conductive rubber is used, the rubber hardness of the roller is increased. If it is hard, the adhesion cannot be obtained, and if it is too soft, the rubber component of the roller elutes, causing contamination of the drum.

For this reason, the hardness of the conductive rubber roller may be determined by an experiment to find preferable adhesion and hardness at which the rubber component is not eluted, but the charging roller slips through the toner cleaning means in contact with the photosensitive drum. In order to remove silica, paper dust, etc. adhering to the surface of the charging roller,
A charging cleaner is placed in contact with the opposite side of the charging position.

The charging cleaner is formed in the shape of a blade or a roller. However, in both cases, cleaning is performed on the opposite side of the nip position with the photosensitive drum while applying a contact pressure to the charging roller. In addition, when the non-uniform pressure is easily applied to the charging roller through the cleaner, and the linear velocity ratio between the cleaner and the charging roller is different,
Vibrations such as chattering generated at the cleaning position may be transmitted to the nip position.

Generally, the rotation of the charging roller is configured so that the charging roller is driven and rotated by the driving of the photosensitive drum. With such a structure, not only the backlash of the conduction gear between the photosensitive drum and the charging roller but also other vibrations are likely to occur, and in particular, the cleaning means is disposed in contact with the back side of the charging roller. The cleaning has a braking function. In other words, the driving force on the photosensitive drum side and the braking force from the cleaning unit cause chattering, that is, minute vibration, in the rotation of the charging roller, which further improves the adhesion at the nip position. descend.

The present invention has been made in view of the above-mentioned drawbacks of the prior art.
An object of the present invention is to provide an image forming apparatus capable of stable and uniform charging for a long period of time even when a DC charging bias is used.

[0011]

According to the first aspect of the present invention, first, the rubber hardness of at least the surface layer side of the charging roller is set to 30 to 50 degrees.
It is preferably set in the range of 40 to 50 degrees, and a cleaning roller having a hardness lower than that of the charging roller is disposed in contact with the back side of the charging roller so that the biasing pressure generated by the cleaning roller causes the photosensitive drum of the charging roller to contact with the photosensitive drum. Make sure that the contact pressures between them are not uneven. As a result, only the rubber hardness of the charging roller can affect the adhesiveness between the cleaning roller and the photosensitive member while minimizing the effect of noise on the cleaning roller side, which enables accurate contact. In this case, by configuring the cleaning roller as a brush roller having a fiber brush wound around a shaft, the biasing pressure applied to the charging roller by the cleaning roller can be substantially zero, and thus the rubber of the charging roller can be reduced. It is possible to further prevent uneven contact pressure between the charging roller and the photoconductor drum while maintaining the adhesion due to the hardness. The reason for setting at least the rubber hardness on the surface layer side here is that all the rubber layers are 30 to 50.
Degree, preferably in the range of 40 to 50 degrees, for example, even when a single-layer conductive rubber layer is formed by changing the molecular weight distribution or the degree of crosslinking in the rubber layer radial direction, only the rubber hardness on the surface layer side is within the above range. I hope

Also in the second aspect of the present invention, the rubber hardness of at least the surface layer side of the charging roller is set in the range of 30 to 50 degrees, preferably 40 to 50 degrees, and the charging roller is disposed in contact with the back side of the charging roller. Both shaft ends of the cleaning roller are configured to protrude from the shaft end of the charging roller, and the total pressure of the charging roller including the cleaning roller toward the photosensitive drum is 250 to 60 on the charging roller shaft end side.
The feature is that it is set to be 0 g.
As a result, the cleaning roller is configured so as to protrude from the shaft end of the charging roller, so that a uniform pressure is applied to the charging roller to improve the adhesion between the charging roller and the photoconductor, and in particular, the charging roller including the cleaning roller is charged. The total pressure of the roller toward the photosensitive drum is 250 at the end of the charging roller shaft.
By setting the weight to be up to 600 g, more accurate contact can be achieved.

According to a third aspect of the present invention, the cleaning roller, which is disposed in contact with the back side of the charging roller, has both shaft ends protruding from the shaft end of the charging roller, and the cleaning roller has a fiber brush as a shaft. A brush roller wound around the cleaning roller suppresses the load applied to the charging roller as much as possible. Further, the charging roller shaft is movable toward the center of the photosensitive drum shaft, and pressure is applied to both ends of the roller shaft. Is set so that the total pressure to the photosensitive drum side is 250 to 600 g at the charging roller shaft end side. As a result, the load applied to the charging roller on the cleaning roller side is suppressed as much as possible, thereby minimizing the noise effect of the cleaning roller and improving the adhesion between the charging roller and the photoconductor, and especially including the cleaning roller. By setting the total pressure of the charging roller to the photosensitive drum side to be 250 to 600 g on the charging roller shaft end side, more accurate contact can be achieved.

According to a fourth aspect of the invention, in order to prevent chattering in the rotation of the charging roller due to the driving force on the photosensitive drum side and the braking force from the cleaning means side, the photosensitive drum is driven by the driving force of the charging roller. In addition to being rotatable, the cleaning roller is composed of a brush roller formed by winding a fiber brush around a shaft, and preferably both shaft ends of the cleaning roller protrude from the shaft end of the charging roller. According to this invention, since the cleaning roller having a braking function is constituted by the brush roller, no braking force is generated, and the driving force is also constituted by the charging roller itself. It is possible to completely suppress chatter due to rotation.

The first to fourth inventions are all aimed at obtaining an image forming apparatus capable of stable and uniform charging for a long period of time even when a DC charging bias is used. Therefore, it is obvious that an invention having more preferable effects can be formed by combining the first invention, the second invention, the third invention, and the fourth invention as appropriate.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; However, the dimensions, materials, shapes, relative positions and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely examples, unless otherwise specified. Not too much.

FIG. 1 shows an image forming apparatus to which the present invention is applied.
In particular, a basic configuration diagram of the process unit around the photosensitive drum 1 of the printer is shown, and the charge removing unit 2 including the LED unit 8, the developing unit 60, the transfer roller 7, the cleaning blade 3, and the eraser along the drum rotation direction (clockwise). , The charging roller 4 is arranged, and as is well known, the static eliminating means 2
After the charge is removed by, the exposure latent image is written by the LED unit 8 on the photoconductor drum 1 uniformly charged by the charging roller 4, and the toner image is visualized by the developing unit 60 by reversal development of the exposure latent image. After the toner image is transferred onto the recording medium 10 by the transfer roller 7, the residual toner is removed by the cleaning blade 3. The residual toner removed by the cleaning blade 3 is stored in a waste toner bottle (not shown) by a screw (not shown).

Next, the respective process means will be described. The photoconductor drum 1 is an OPC drum 1 (organic photoconductor) having a diameter of 30φ and a negative charging polarity, and is configured to be rotatable at a predetermined peripheral speed in the arrow direction. The film thickness (total thickness of GGL, CTL, etc.) of the photoconductor layer of the photoconductor drum 1 is set to 25 μm, and a photoconductor having high viscoelasticity is used for the CTL layer. Further, it is preferable to use a defectless photoconductor in which irregularities are regulated on the coated surface of the photoconductor.

As is well known, the LED units 8 are LEs arranged in rows.
Consists of an LED head with D elements arranged and a focusing lens,
An exposure latent image corresponding to image information is writable on the photosensitive drum 1.

The developing unit 60 comprises a developing container 61 containing a multi-component developer consisting of a carrier and toner, and a developing roller 62 containing a fixed magnet assembly (not shown). A -450V direct current developing bias power source 65 is connected to perform the development by low electric field reversal developing.

The carrier is composed of carrier mother particles in which a magnetic material is uniformly dispersed in a binder resin, and conductive fine particles are fixed on the surface of the carrier mother particle. The magnetic force thereof is 5 kOe (Oersted). The maximum magnetization in a magnetic field is 55 to 80 emu / g, the average central particle size of the carrier is 3
A developer having a particle size distribution containing 5 wt% or more and 15 wt% or more of particles of 35 μm or less is used.

Ordinary high-resistance or insulating toner is used as the toner. For example, a binder resin, a colorant, a charge control agent, an offset preventive agent and the like are added with a magnetic material to have an average central particle size of 5 to 15 μm. It is configured as a front and rear magnetic toner, and the proper mixing ratio of the carrier and the toner is set to, for example, 85 to 90:15 to 10% by weight.

The transfer roller 7 has a resistivity of 10 ⁵ Ω · cm.
The following conductive elastic roller, specifically, a urethane rubber roller is used, and the transfer bias 70 is set to +250 V, which is the polarity opposite to the polarity of the surface potential of the photoconductor 1a and the toner image charge.

On the other hand, the cleaning blade 3 has a plate-shaped polyurethane elastomer material having a wedge-shaped cross section attached to a support member (not shown), and the tip corner portion of the cleaning blade 3 has the photosensitive drum 1 at its tip.
It is arranged so as to come into contact with the substantially linear contact.

The charging roller 4 is driven to rotate in synchronism with the photosensitive drum 1 and has a resistivity of 1 by adding a conductive component around the roller shaft 41 composed of a 6φ solid stainless steel shaft.
A polyurethane rubber 42 set to 0 ⁷ Ω · cm or less is molded, the surface is polished and shaped into a 12φ roller shape, which is formed by performing nylon resin coating on the surface. The roller surface roughness is set to Rz <4 μm. Further, as will be described later, if the surface rubber layer is in the rubber hardness range, the surface layer of the rubber layer 42 of the charging roller 4 may be subjected to a curing treatment, if necessary. The molecular weight distribution and the degree of crosslinking may be changed in the radial direction from the charging roller shaft 41 toward the rubber surface layer.

A cleaning roller 5 is disposed in contact with the back side of the charging roller 4. As shown in FIG. 2B, the cleaning roller 5 has a surface of a roller shaft 52 coated with a rubber layer 51, and then has a cord-like body 50 made of a chemical fiber material on the surface thereof, preferably a large-diameter wool-like chemical. A filament or a string-like body 50 in which long fibers are planted on the surface is spirally wound from the central position in different circumferential directions, and by the rotation of the cleaning roller 5, the adhered matter attached to the roller 5 is removed. It is formed to be movable from the center side toward the shaft end side.

The winding pitch is not particularly limited, but if the winding pitch is set so as to be too inclined with respect to the direction orthogonal to the axis, efficient movement becomes impossible. Therefore, 10 to 60 ° with respect to the direction orthogonal to the axis, It is preferable to set it at about 10 to 45 °. The diameter of the cleaning roller 5 is preferably set to be slightly smaller than the diameter of the charging roller 4.

The periphery of the back side of the cleaning roller 5 and the charging roller 4 is, as shown in FIG.
The paper dust, which is surrounded by 0 and trapped from the charging roller 4 side by the rotation of the cleaning roller 5, moves toward the shaft end side from the center side by the fibrous cord-like body 50 wound in the spiral shape, and then charged. The cleaning roller 5 is further moved from the shaft end of the roller 4 to both shaft ends of the cleaning roller 5, and is then recovered in the recovery container 40 as needed. In this embodiment, the drum contact width of the charging roller 4 is set to be smaller than the axial length of the cleaning roller 5, as will be described later.

FIG. 3 shows the construction of the bias circuit for carrying out the charging and development, 30 is a high-voltage power supply circuit for supplying a DC voltage V of 1200 V to the voltage adjusting circuit, 31 is a voltage adjusting circuit, and each circuit is a voltage adjusting circuit. charging bias voltage and assembly adjustment for adjusting a developing bias voltage Boriyu - arm and user adjustment Boriyu - comprises a beam, the Boriyu - roller shaft of the charging roller 5 and the charging bias V _t, which is adjusted by the beam through the correction resistor And a developing bias is applied to the developing roller 62, respectively. In this case, the charging bias is configured so that a voltage of 800 to 1000 V is applied to the charging roller 4 and a charging current of about 3 to 6 μm flows. The developing bias is 350 to 45.
A voltage of 0 V is applied to the charging roller 4 and about 170 to 17
It is configured so that a developing current of 3 μm flows.

The bias voltage / current relationship is preferably set as follows. Voltage: Development bias Vg> Charging bias Vt Current: Charging current It << Development current Ig High-voltage power supply current I = It + Ig

The length in the direction of each drum of the above apparatus structure is as shown in FIG. In this embodiment, the width of each device is defined by the following formula (1). A>B> (D, G) ≧ H> E (1) A: Photoconductive layer forming width of the photosensitive drum B: Cleaning blade drum contact width D: Charging roller 4 drum contact width E: Maximum image forming area Width G: Transfer roller H: Development roller In this case, the transfer roller 7 and the development sleeve 6 may have the same length. The relationship between the drum contact width D of the charging roller 4 and the shaft length F of the cleaning roller 5 is defined by the length of the following formula 2) as described above. F> D ... 2)

FIG. 6 shows the structure of the drive system around the charging roller 4, which is transmitted from the shaft gear M ₁ of the motor M to the shaft gear 4A of the charging roller 4 via the relay gear 59 and then to the shaft gear 4A. The shaft gear 1A of the photoconductor drum 1 is meshed with the photoconductor drum 1 so that the photoconductor drum 1 is driven to rotate in synchronization with the rotation of the charging roller 4. The shaft gear 4A of the charging roller 4 meshes with the shaft gear 5A of the cleaning roller 5 via relay gears 58,58.

In this case, the cleaning roller 5
The direction of rotation of the cleaning roller 5 may be either the rotation in the forward direction or the rotation in the against direction with respect to the charging roller 4 at the contact position with the charging roller 4.
And the charging roller 4 have different peripheral velocities, and the relative peripheral velocity difference is set to a range of 1.1 to 3, preferably 1.1 to 1.5, and more preferably 1.1 to 1.2. Is good. Therefore, in order to set the relative peripheral speed difference to the range of 1.1 to 1.2, the two relay gears 58, 58 are interposed and the cleaning roller 5 is forwardly rotated with respect to the charging roller 4, that is, the charging roller. The rotation direction is set counterclockwise with respect to the clockwise direction of 4.

The charging roller 4 is, as shown in FIG.
The charging roller shaft 41 is fitted in the guide groove 20A provided in the drum supporting frame 20, and springs 49 are used at both ends of the roller shaft 41 to move the pressure toward the center of the photosensitive drum shaft 1a. Energize. On the other hand, the cleaning roller 5 and the charging roller 4 are controlled by the housing of the collection container 40 of the charging roller so that the distance between them is constant. As a result, only the cord-like body 50 of the cleaning roller 5 comes into contact with the charging roller 4 so that the load applied to the charging roller 4 by the cleaning roller 5 becomes zero as much as possible. As a result, the load of the cleaning roller 5 is not applied to the photosensitive drum 1, and the total pressure of the charging roller 4 to the photosensitive drum 1 side is determined only by the load of the spring 49. In this embodiment, the load of the spring 49 is set so that the total pressure on the photosensitive drum side at the end of the charging roller shaft 41 is 300 g.

Next, in order to confirm the effect of the present invention, the polyurethane rubber 42 constituting the charging roller 4 is made to have different molecular weight distributions and cross-linking degrees, and the rubber hardness of the rubber layer is Asker-C.
In measurement, 20 ° to 30 ° (Comparative Example 1), 40 to 50 °
(Example 1), a device set at 60 to 70 ° (Comparative Example 2) was incorporated into the apparatus and printed on 10,000 sheets. In Comparative Example 1, the rubber component of the charging roller 4 was eluted. Contamination of the drum occurred, and uneven charging occurred in Comparative Example 2. However, in Example 1, neither contamination of the drum nor uneven charging occurred, and a good image was formed.

In this embodiment, the charging roller 4 has a length of 226.
mm, the distance from the roller end to the spring pressure contact position is 7.2
The recording sheet of A4 size can be charged by setting it to mm. Then, in the above state, the charging roller 4 is used by using Example 1 in which the rubber hardness of the rubber layer is set to 40 to 50 °.
The spring pressure of the spring 49 applied to both ends of the
(Comparative Example 3), 300 g (Example 1), and 700 g (Comparative Example 4) were different from each other, and the charged state was confirmed. In Comparative Example 3 in which the spring pressure was 200 g, uneven charging occurred and the spring pressure was 7%.
At 00 g, the voltage on both sides of the charging roller 4 becomes higher than that at the central portion, and uneven charging in the axial direction also occurs.

Next, the spring pressure of the spring 49 is set to 200.
The fibrous cord-like body 5 of the above-mentioned Example is added to Comparative Example 3 set to g.
Instead of 0, a cord-like body 50 formed of a soft rubber having a surface coated with fluororubber or a fluororesin is wound in the same manner as described above, and a predetermined pressure is applied to the charging roller 4 to set the cleaning roller 5 in place. Using the apparatus (Example 2) in which the total pressure of the charging roller 4 including the charging roller 4 on the photosensitive drum side was set to 400 g on the charging roller shaft end side, the charged state was grasped, and the preferable electrified state could be grasped. Next, in the case of the second embodiment, when the relay gear 59 of the drive motor of the shaft gear 1A of the photosensitive drum 1 is meshed with the photosensitive drum 1 drive / charging roller 4 driven / cleaning roller 5 driven, the charging roller No chattering occurred in No. 4 and a preferable charged state could not be obtained.

[0038]

As described above, according to the present invention, it is possible to obtain an image forming apparatus capable of stable and uniform charging for a long period of time even when a DC charging bias is used. It has various remarkable effects.

[Brief description of drawings]

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

FIG. 2 is a front view showing a configuration of a charging roller and a cleaning roller of FIG. 1 and an enlarged view thereof.

FIG. 3 shows a configuration of a bias circuit for performing charging and development shown in FIG.

FIG. 4 is a schematic diagram in which the width and the like of a photosensitive drum, a charging roller, and a cleaning roller of the apparatus shown in FIG. 1 are defined.

FIG. 5 shows a state in which a charging roller and a photosensitive drum are fitted together.

6 shows a configuration of a drive system around a charging roller 4 of the apparatus shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 1A Shaft gear of photoconductor drum 4 Charging roller 43 Charging bias power source 4A Shaft gear of charging roller 41 Charging roller shaft 5 Cleaning roller 5A Shaft gear of cleaning roller 50 Fiber brush 49 Spring

Claims (6)

[Claims] 1. A charging step of arranging a charging cleaning means on the back side of a charging roller arranged in contact with a photosensitive member and applying a DC charging voltage to the charging roller to charge the photosensitive member. In the image forming apparatus, the charging roller is constituted by providing a conductive rubber layer having a rubber hardness of at least the surface layer side of the rubber layer provided around the charging roller shaft of 30 to 50 degrees, preferably 40 to 50 degrees. An image forming apparatus characterized in that a cleaning roller having a hardness smaller than that of the charging roller is arranged in contact with the back side of the charging roller. 2. The image forming apparatus according to claim 1, wherein the cleaning roller is a brush roller formed by winding a fiber brush around a shaft. 3. A charging step of arranging a charging cleaning means on the back side of a charging roller arranged in contact with a photosensitive member and applying a DC charging voltage to the charging roller to charge the photosensitive member. In the image forming apparatus, the charging roller is constituted by providing a conductive rubber layer having a rubber hardness of at least the surface layer side of the rubber layer provided around the charging roller shaft of 30 to 50 degrees, preferably 40 to 50 degrees. The cleaning roller, which is disposed in contact with the back side of the charging roller, has both shaft ends protruding from the shaft end of the charging roller, and the total pressure of the charging roller including the cleaning roller toward the photosensitive drum is An image forming apparatus characterized in that the charging roller shaft end side is set to have a weight of 250 to 600 g. 4. A charging step of arranging a charging cleaning means on the back side of a charging roller arranged in contact with a photosensitive member and applying a DC charging voltage to said charging roller to charge the photosensitive member. In the image forming apparatus, the cleaning roller, which is disposed in contact with the back side of the charging roller, is composed of a brush roller having a fiber brush wound around the shaft, and the load applied to the charging roller by the cleaning roller is suppressed as much as possible. Furthermore, the charging roller shaft is made movable toward the center of the photosensitive drum shaft, and pressure is applied to both ends of the roller shaft so that the total pressure on the photosensitive drum side becomes 250 to 600 g at the charging roller shaft end side. Image forming apparatus characterized in that 5. A charging step of arranging a charging cleaning means on the back side of a charging roller arranged in contact with the photoconductor, and applying a DC charging voltage to the charging roller to charge the photoconductor. In an image forming apparatus, a brush roller is formed by winding a fiber brush around a cleaning roller, which is configured so that the photosensitive drum is driven to rotate by the driving force of the charging roller and is in contact with the back side of the charging roller. Image forming apparatus characterized by comprising 6. The image forming apparatus according to claim 1, wherein both shaft ends of the cleaning roller are configured to protrude from a shaft end of the charging roller.