JPH1090978A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of eliminating white spots and void as defects especially seen when a character printing factor is low for dot pictures or the like and suppressing damaging of an electrostatic latent image carrier caused by overcurrents or the occurrence of pinholes. SOLUTION: An image forming device comprises a cylindrical electrostatic latent image carrier 11 and a brush-like charged body 15 contacted with the electrostatic latent image carrier 11, and image data is exposed so as to form an electrostatic latent image on the surface of the electrostatic latent image carrier 11 provided with electric charge by the charged body 15. The charged body 15 includes at least one brush unit 26U composed of a first brush 26a positioned in the rotational direction upstream side of the electrostatic latent image carrier 11 and a second brush 26b positioned in the downstream side thereof, and the amount of electric charge provided from the first brush 26a to the electrostatic latent image carrier 11 is set smaller than that provided from the second brush 26b to the electrostatic latent image carrier 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image on recording paper, and more particularly, to an image forming apparatus for forming an electrostatic latent image on a surface of an electrostatic latent image carrier charged by a charging member. The present invention relates to an image forming apparatus including a forming unit.

[0002]

2. Description of the Related Art A conventional image forming apparatus using an electrophotographic process such as a copying machine, a facsimile, an electrophotographic apparatus, or an electrostatic printer is known. In an image forming apparatus, a cylindrical electrostatic latent image carrier (photoconductor drum)
Is charged to form an electrostatic latent image, charged toner is supplied to the surface of the electrostatic latent image carrier, and the charged toner is attached to the electrostatic latent image to form a toner image (development). Thereafter, while feeding the recording paper in synchronization with the rotation of the electrostatic latent image carrier, a bias voltage having a polarity opposite to that of the toner is applied from the back side of the recording paper, so that the toner on the electrostatic latent image carrier is The image is transferred onto the recording paper. Further, the unfixed toner image is fixed on the recording paper by the fixing mechanism.

In order to charge an electrostatic latent image carrier, a scorotron which performs corona discharge from a wire electrode is generally used. Scorotron uses several k for corona discharge
v high voltage must be applied to the electrodes, the cost of the high-voltage power supply increases, and the ozone generated by the discharge adversely affects the human body and the environment, or the electrostatic latent image carrier and its surroundings There is a problem that the rollers are easily damaged.

[0004]

A developing device using a brush as a charged body is known (Japanese Patent Laid-Open No. 5-100544).
Reference). In a device using a brush-like charged body, such as the developing device of the publication, a low voltage of about 1 kv is generally applied to the nip portion which forms a contact portion between the electrostatic latent image carrier and the brush-shaped charged body. Can be applied to charge the electrostatic latent image carrier. In the developing device, the above problem in the scorotron can be solved, but a new problem occurs.

That is, in a developing device using a brush-like charged body, each bristle constituting the brush is almost in point contact with the electrostatic latent image carrier, so that the uncharged electrostatic latent image carrier Abnormal discharge is likely to occur when a large electric field is suddenly applied to the body, and white spots and white spots, which are defects, are remarkable especially in an image with a low printing rate such as a halftone dot image. Frequency, or the frequency of occurrence of damage or pinholes of the electrostatic latent image carrier due to overcurrent.

[0006] In a developing device using a brush-like charged member, the amount of charged charge and the charged potential applied to the electrostatic latent image carrier are determined by the electric resistance of the charged member itself or the charged member and the electrostatic latent image. Although greatly dependent on the contact resistance between the carrier and the carrier, the electric resistance value is easily affected by the environment such as the contact area and the temperature and humidity, and the charge amount and the charge potential vary greatly. For this reason, the image density is not stable, the halftone image is scattered, or
Problems such as fogging on the recording paper occur. Further, in the developing device, since the brush tips and antinodes of each brush are brought into contact with the electrostatic latent image carrier to be charged, charging unevenness such as sweeping unevenness in the rotation direction of the electrostatic latent image carrier is generated. For example, when a halftone image is printed, a linear sweeping unevenness image is formed in the running direction of the recording paper. Further, as the image is formed, shaving powder of the electrostatic latent image carrier or toner (fogging toner) remaining on the surface of the electrostatic latent image carrier accumulates on the brush of the charged body, so that the toner is used at the start of use. The charging ability is remarkably different from that near the end of the life, and the charging potential of the electrostatic latent image carrier may fluctuate in a range of 50 V or more.

In view of the above, the present invention eliminates white spots and white spots which are remarkably observed when a printing rate of a halftone dot image or the like is low when charged by a brush-like charging member, and eliminates electrostatic latent due to overcurrent. An object of the present invention is to provide an image forming apparatus capable of suppressing damage to an image carrier and occurrence of pinholes. Further, the present invention, at the time of charging by the brush-like charged body,
It is an object of the present invention to provide an image forming apparatus capable of stabilizing a charge amount and a charging potential, preventing charging unevenness such as sweeping unevenness, and improving deterioration of charging characteristics due to brush contamination.

[0008]

In order to achieve the above object, an image forming apparatus according to the present invention comprises a cylindrical electrostatic latent image carrier, and a brush-like charging device which comes into contact with the electrostatic latent image carrier. And an image forming apparatus that forms an electrostatic latent image by exposing image data on a surface of the electrostatic latent image carrier to which a charge is applied by the charged body. At least one set of a brush unit including a first brush located on the upstream side in the rotation direction of the latent image carrier and a second brush located on the downstream side, and the amount of charge provided to the electrostatic latent image carrier from the first brush Is smaller than the amount of charge given to the electrostatic latent image carrier from the second brush.

According to the image forming apparatus of the present invention, the electric charge is applied to the electrostatic latent image carrier in a stepwise manner, and the electric field generated when the electrostatic latent image carrier comes into contact with the charged body. Can be changed in a stepwise manner, so that the electric field condition is improved without causing a problem such as abrupt change or non-uniformity and local increase. This prevents the occurrence of white spots or white spots when the printing rate such as a halftone dot image is low, and the occurrence of damage or pinholes on the electrostatic latent image carrier due to overcurrent.

Preferably, the first brush and the second brush of the brush unit are supported by a single conductive support extending in a direction parallel to a rotation axis direction of the electrostatic latent image carrier, and have an electric resistance. Configured as brushes with different values. Alternatively, instead of this, the first of the brush units
The brush and the second brush are connected to the other end of each of the first resistor and the second resistor each having one end connected to a common power supply, and are configured as brushes having the same electric resistance value.

It is desirable that the charging bias of the charging member is controlled at a constant voltage. According to this, the charged potential on the surface of the electrostatic latent image carrier can be kept constant, so that, for example, the applied potential fluctuates and a high bias voltage is applied, such as occurs during constant current control, and the electrostatic latent image is charged. Problems such as damage to the image carrier can be suppressed. Therefore, there is no uneven charging,
Stable and uniform charging potential and surface charge amount of the electrostatic latent image carrier can be obtained, and a small charging potential on the electrostatic latent image carrier, which was a disadvantage at the time of charging by the brush-like charging body It is possible to improve the phenomenon that fogging easily occurs due to unevenness, or the deterioration of the charging characteristics due to brush contamination.

[0012]

The present invention will be described in more detail with reference to the drawings. FIG. 1 is a sectional view of an image forming unit in an image forming apparatus according to an embodiment of the present invention in a direction perpendicular to the rotation axis of an electrostatic latent image carrier, and FIG. FIG. 3 is a front view from the image carrier side, and FIG.
It is sectional drawing regarding the III-III line.

As shown in FIG. 1, the image forming section includes a developing device 12, an electrostatic latent image carrier (photosensitive drum) 11, and a cleaner from the upstream side to the downstream side in the transport direction of the recording paper 17. The units 13 are arranged in order.

The electrostatic latent image carrier 11 is an organic photoconductor (OP
C) a cylindrical photoconductive material formed in a cylindrical shape,
The recording paper 17 rotates clockwise in the figure at a peripheral speed of 114 mm / sec about a rotation axis 11a orthogonal to the transport direction of the recording paper 17.
This corresponds to a print speed of 24 PPM in an A3 size electrophotographic printer. A brush-shaped charging member 15 is provided above the electrostatic latent image carrier 11, and a brush-shaped transfer member 16 is provided below the electrostatic charging member 15.
Are arranged.

The developing device 12 is disposed to face the electrostatic latent image carrier 11, and includes a toner hopper 20 containing a stirring member 21, a toner supply member 25, and a toner carrier 22 on a recording paper. A thin layer forming member 23 is provided along the transfer direction and slides on the surface of the toner carrier 22 to form a toner layer.

The toner carrier 22 is made of, for example, a metal roller such as stainless steel or aluminum and an elastic material such as silicone, nitrile-butadiene copolymer, and urethane rubber provided on the outer periphery thereof and having conductivity. Become. The elastic portion of the toner carrier 22 is
In consideration of the contact pressure with the electrostatic latent image carrier 11, the rubber hardness is set to 30 to 40 ° using a JIS A hardness tester. Also,
The electric resistance value between the roller surface of the toner carrier 22 and the rotation axis indicates a leak to the electrostatic latent image carrier 11 due to low resistance,
In addition, it is desirable that the resistance is set to 10 ⁵ to 10 ⁶ Ω in consideration of a decrease in development efficiency and fog due to high resistance. The particle diameter of the negatively chargeable polyester toner 19 used in the present embodiment is about 7 to 8 μm. Toner carrier 2
The ten-point average surface roughness Rz of 2 is preferably 7 μm or less in order to uniformly charge the toner 19.

The thin layer forming member 23 can be formed of a spring material made of a thin metal plate such as stainless steel and phosphor bronze.
Alternatively, it can be formed by applying a silicone rubber to a contact portion with the toner carrier 22.

The brush-shaped charging member 15 has a shape extending in the width direction of the recording paper 17, that is, in the direction of the rotation axis of the electrostatic latent image carrier 11 (the direction of arrow B in FIG. 2). As shown in FIGS. 2 and 3, the charged body 15 has a set of brush units 26 </ b> U, a conductive polyester spinning base cloth 27 on which the brush units 26 </ b> U are planted, and a base cloth 27 attached thereto. A conductive metal support plate (conductive support) 29 made of SUS, SUM, aluminum or the like. A DC constant-voltage power supply 37 is connected to the metal support plate 29.

The brush unit 26U is made of conductive fibers such as rayon or nylon provided with conductivity by carbon black powder.
Are provided in eight rows along the rotation direction (the direction of arrow A in FIG. 1). The eight rows of conductive fibers forming the brush unit 26U are composed of the first brush 26a and the second brush 26a each having four rows having different electric resistance values depending on the content of the carbon black powder.
And a brush 26b. First brush 26a
Is located upstream of the second brush 26b in the rotation direction of the electrostatic latent image carrier 11, and has an electric resistance value of the second brush 26b.
Is set to be larger than the electric resistance value. That is, the first and second brushes 26a and 26a having different electrical resistance values
b is located on the upstream side and the downstream side in the rotation direction of one metal support plate 29 extending in the rotation axis direction of the electrostatic latent image carrier 11.

In this embodiment, the brush unit 2
The conductive fiber constituting 6U has a weave degree of 600D / 10
OF (600 denier / 100 filaments.
100 fibers of 6 denier form a conductive system of 600 denier per fiber). Each of the conductive fibers constituting the brush unit 26U is implanted in a line in the folded state on the base cloth 27 (see FIG. 4).
It is set to 4000 F / inch and the length is set to 5 mm. The distance between the metal support plate 29 and the electrostatic latent image carrier 11 is set to 4 mm.
Is compressed by about 1 mm in contact with the electrostatic latent image carrier 11. The first brush 26a and the second brush 26b are 1k
v, a different electric resistance value within a range of 1 × 10 ⁴ to 1 × 10 ⁶ Ω between the metal support plate 29 and the composite resistance value of the two. Is 1 × 1
It is set to be 0 ⁴ to 1 × range of 10 ⁵ Omega.

The image forming apparatus having the above configuration operates as follows. First, when a predetermined switch is operated, a charging bias voltage of −1000 to −1600 V is applied to the charging member 15 from the DC constant-voltage power supply 37, and the electrostatic latent image carrier 11 is charged by the charging member 15. Start rotating while rotating. At this time, the surface potential of the electrostatic latent image carrier 11 is about -700V. In a state where the electrostatic latent image carrier 11 is uniformly charged by the charging member 15, the surface of the electrostatic latent image carrier 11 is exposed by exposing image data from a light source (not shown) such as a laser. An electrostatic latent image is formed.

In the developing device 12, while the toner 19 contained in the toner hopper 20 is stirred by the stirring member 21 rotating in the counterclockwise direction in FIG. 1, the toner carrier 22 is rotated by the toner supply member 25 rotating in the counterclockwise direction. Supplied to The toner carrier 22 rotates counterclockwise, and the toner 19 supplied to the carrier 22 is triboelectrically charged by the thin-layer forming member 23 and the height thereof is regulated. It is made into a uniform thin layer. The charged toner 19 adhered as a thin layer on the toner carrier 22 is transferred to the nip portion between the toner carrier 22 and the electrostatic latent image carrier 11 according to the rotation of the toner carrier 22, and Due to an electric field based on the potential difference between the surface potential of the toner carrier 22 and the bias voltage applied to the toner carrier 22, the toner adheres to the electrostatic latent image on the surface of the electrostatic latent image carrier 11 to form a toner image.

The toner image on the electrostatic latent image carrier 11 is moved to a portion facing the transfer member 16 as the carrier 11 rotates. Then, the recording paper 17 fed by a transport mechanism (not shown) is inserted into the nip portion between the electrostatic latent image carrier 11 and the transfer body 16 in synchronization with the rotation of the electrostatic latent image carrier 11. In this case, a bias voltage having a polarity opposite to that of the toner 19 is applied from the back surface of the recording paper 17. As a result, the toner image on the surface of the electrostatic latent image carrier 11 starts to move to the recording paper 17 side, and the electrostatic latent image carrier 11 is continuously rotated.
All of the toner images on the surface of the electrostatic latent image carrier 11 are
Transcribed above. The recording paper 17 is transferred to a pressure bonding mechanism (not shown) on the downstream side in the transport direction with the unfixed toner image adhered to the surface thereof, and pressed to fix the toner image.

At the time of charging, the electrostatic latent image carrier 11
High-resistance first brush 26 located on the upstream side in the rotational direction of
a has a low resistance second brush 26b located on the downstream side.
Therefore, the amount of electric charge given to the electrostatic latent image carrier 11 from the first brush 26a is smaller than the amount of charge given to the electrostatic latent image carrier 11 from the second brush 26b. As a result, the electric charge required for charging is gradually increased from the uncharged portion on the upstream side to the downstream side of the electrostatic latent image carrier 11, so that the electrostatic latent image carrier 11 and the electrostatic latent image carrier 11 are charged. Body 15
The electric field at the time of contact changes stepwise.

Therefore, when the electrostatic latent image carrier 11 comes into contact with the first brush 26a and the second brush 26b, the state of the electric field changes abruptly depending on how the brush hits, or becomes non-uniform and locally. It is good without becoming large in size. Thereby, since abnormal discharge is eliminated, when a printing rate such as a halftone dot image is low, white spots are generated or a white spot image is generated. Further, since the charging member 15 is composed of a multi-layer brush, a uniform charging potential and surface charge on the electrostatic latent image carrier 11 can be obtained.

In the present embodiment, since the charging bias of the image forming unit is controlled at a constant voltage, the applied potential fluctuates as in the case of controlling the electrostatic latent image carrier 11 with a constant current. Applying a high bias voltage suppresses problems such as damage to the electrostatic latent image carrier 11 and occurrence of pinholes on the surface of the carrier. Thereby, the electrostatic latent image carrier 1 is stable and uniform without charging unevenness.
A charge potential and a surface charge amount of 1 can be obtained. Therefore, in the image forming apparatus according to the present invention, the disadvantage of the conventional apparatus in which fog is apt to occur due to minute unevenness of the charging potential on the electrostatic latent image carrier 11 at the time of charging using the brush-like charging body is also improved. .

Next, a second embodiment of the image forming apparatus will be described with reference to FIG. In the present embodiment, a brush unit 26U composed of first and second brushes 26a and 26b having substantially the same electric resistance value as the first embodiment is provided on the upstream side in the rotation direction of the electrostatic latent image carrier 11 in the rotation direction. Two sets are arranged side by side with the downstream side. That is, the first brushes 26a having a high resistance value and the conductive brushes 26 having a low resistance value are alternately arranged in two rows. With such a configuration, the same effect as in the device of the first embodiment can be obtained.

A third embodiment of the image forming apparatus will be described with reference to FIG. In the present embodiment, the brush-shaped charged body is divided into two in the rotation direction of the electrostatic latent image carrier 11, and there are differences in the structure of the charged body and the electrical equipment around the charged body. Are the same as in the first embodiment.

In the present embodiment, as shown in FIG. 6, a brush-shaped charging member 31 is provided with first electric resistance values equal to each other.
The brush 33a and the second brush 33b are used. First
The brush 33a and the second brush 33b form a set of brush units 33U, and include a first conductive support 32a and a second conductive support 32b extending in the rotation axis direction of the electrostatic latent image carrier 11. Each is supported. First conductive support 32
a and the DC constant-voltage power supply 37, and between the second conductive support 32 b and the DC constant-voltage power supply 37, respectively, the first resistor 35 and the second resistor 36 having different electric resistance values from each other. Is connected. The electric resistance of the first resistor 35 is set to be larger than the electric resistance of the second resistor 36. According to this configuration, the same effect as that of the image forming apparatus of the first embodiment can be obtained.

If the first resistor 35 and the second resistor 36 have very large resistances compared to the electric resistance of the brush unit 33U, the first resistor 35 and the second resistor 36 can be controlled under constant voltage control.
Even if the resistance of the charger 31 fluctuates due to environmental fluctuations, the charging current is almost determined by the resistors 35 and 36. That is, the change in the charging current is reduced, and the change in the surface charge amount of the electrostatic latent image carrier 11 and the change in the charging potential due to the environment are suppressed. Even if a pinhole or the like occurs in the electrostatic latent image carrier 11, the current flowing between the charging body 31 and the electrostatic latent image carrier 11 is regulated, so that an overcurrent flows and a brush or static It is possible to prevent problems such as damage to the electro-latent image carrier 11 from increasing.

[0031]

EXAMPLE 1 A combination of a first brush 26a having an electric resistance of 1 × 10 ⁶ Ω and a second brush 26b having an electric resistance of 8 × 10 ⁴ Ω was used to form the charging member 15 shown in FIG. Formed. 1st brush 2
6a is composed of four rows of conductive fibers having a high resistance value, the second brush 26b is composed of four rows of conductive fibers having a low resistance value,
In addition, the combined resistance value of the first brush 26a and the second brush 26b is set to about 7 × 10 ⁴ Ω. In this configuration, the charging potential of the electrostatic latent image carrier 11 was −710 V when −1050 V was applied as the charging bias voltage.

Using the charging member 15 having the above structure,
Running printing was performed on the recording paper 17. As a result, white spots, white streaks, black streaks, and the like caused by the brush were not observed in an image having a small printing rate such as a halftone dot, and the printing quality was good.

On the other hand, the charged member has a resistance value of 5 × 10
^In the case of using a ⁴ Ω conventional brush, the charging potential of the electrostatic latent image carrier 11 when a charging bias voltage of −1050 V is applied becomes −705 V. In the image, white spots or white or black streaks, which are considered to be caused by a brush, were observed.

Example 2 The electric resistance of each of the first brush 33a and the second brush 33b was set to an equal resistance of 1 × 10 ⁵ Ω to form the charging member 31 shown in FIG. The first resistor 35 on the upstream side in the rotation direction of the electrostatic latent image carrier 11 has an electric resistance of 100 M
The second resistor 36 on the downstream side has an electric resistance value of 10 MΩ.

When the charging member 15 having the above structure is used and a charging bias voltage of -1400 V is applied, the charging potential of the electrostatic latent image carrier 11 becomes -700 V, which is caused by the brush in 6000 sheets of running print. No white spots, white streaks, or black streaks were found in the halftone dot image.
In particular, when the first resistor 35 and the second resistor 36 have a higher electric resistance value than the first brush 33a and the second brush 33b, the image quality such as image density and fog due to environmental fluctuations is better. Did not appear, and the printing result was good.

As described above, the present invention has been described based on the preferred embodiments (examples).
It is not limited only to the configuration of the above embodiment,
An image forming apparatus in which various modifications and changes have been made from the configuration of the above embodiment is also included in the scope of the present invention.

[0037]

As described above, according to the image forming apparatus of the present invention, the electric field when the electrostatic latent image carrier comes into contact with the charged body is changed stepwise, so that the state of the electric field rapidly changes. It does not change or become non-uniform and locally large, so that it is good. As a result, white spots and white spots that are remarkably observed when the printing rate of a halftone dot image or the like is low can be eliminated, and damage to the electrostatic latent image carrier due to overcurrent and generation of pinholes can be suppressed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view in a direction orthogonal to a rotation axis of an electrostatic latent image carrier showing an image forming unit in an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a front view of a brush-shaped charging member used in the image forming section of FIG. 1 as viewed from an electrostatic latent image carrier.

FIG. 3 is a cross-sectional view of the charged body of FIG. 2 taken along line III-III.

FIG. 4 is an enlarged side view showing conductive fibers of the brush-like charged body of FIG. 2;

FIG. 5 is a front view showing another embodiment of the brush-shaped charging member viewed from an electrostatic latent image carrier.

FIG. 6 is a cross-sectional view of an image forming unit according to a second embodiment of the present invention in a direction orthogonal to a rotation axis of an electrostatic latent image carrier.

[Explanation of symbols]

 Reference Signs List 11 electrostatic latent image carrier 11a rotating shaft 15, 31 brush-like charged body 26a, 33a first brush 26b, 33b second brush 26U, 33U brush unit 27 base fabric 29 metal support plate (conductive support) 32a first 1 conductive support 32b second conductive support 35 first resistor 36 second resistor 37 constant voltage power supply

Claims (4)

[Claims] 1. An electrostatic latent image carrier, comprising: a cylindrical electrostatic latent image carrier; and a brush-shaped charger, which is in contact with the electrostatic latent image carrier. An image forming apparatus that forms an electrostatic latent image by exposing image data to a surface of the image forming apparatus, wherein the charged member is located on a first brush located on an upstream side in a rotation direction of the electrostatic latent image carrier and on a downstream side. At least one set of brush units comprising a second brush, wherein an amount of charge given to the electrostatic latent image carrier from the first brush is smaller than an amount of charge given to the electrostatic latent image carrier from the second brush. An image forming apparatus comprising: 2. The first brush and the second brush of the brush unit are supported by one conductive support extending in a direction parallel to a rotation axis direction of the electrostatic latent image carrier, and have an electric resistance value. Are configured as mutually different brushes.
An image forming apparatus according to claim 1. 3. The first brush and the second brush of the brush unit are connected to one end of each of a first resistor and a second resistor each having one end connected to a common power supply, and have an electric resistance value. The image forming apparatus according to claim 1, wherein the image forming apparatuses are configured as mutually equal brushes. 4. The image forming apparatus according to claim 1, wherein a charging bias of the charging member is controlled at a constant voltage.