JPH0792752A - Image forming device - Google Patents

Abstract

PURPOSE:To stabilize potential at which an image carrier is charged so as to enable images of good qualify to be obtained by rotating the image carrier for a predetermined time when no image is formed, and charging the surface of the image carrier using a contact charging means. CONSTITUTION:A bias is applied to a charging brush 4 from a DC constant voltage source, and the overall surface of a photoconductor 1 is uniformly charged to minus by the charging brush 4, and a developing machine 2 causes a toner to be fused to an electrostatic latent image formed by an exposure means 5, to form a toner image on the photoconductor 1. In order to stabilize the initial condition of service in which such contact charging is employed, when a process unit is mounted on the machine, it is first determined whether or not the process unit is new. When the process unit is new, initializing action in which a predetermined bias is applied to the charging brush 4 while the photoconductor 1 is rotated without operating a transfer means is performed for a predetermined period of time (one minute or so). Charging potential in the initial condition is thus stabilized and the quality of images enhanced.

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 such as an electrophotographic apparatus.

[0002]

2. Description of the Related Art In an electrophotographic apparatus, there is a step of uniformly charging a photoconductor, and the uniformity of charging determines the uniformity of image density. It is very important for printing with high image quality. Further, even if one image can be uniformly charged, there is a problem in that the charging potential changes and the image density changes depending on the environment or repeated printing. That is, the environment and the stability of charging against repeated printing are also very important for high-quality printing.

In recent years, a scorotron charging device which is excellent in charging uniformity and stability has been widely used. The scorotron charging device may cause fatigue of the photoreceptor due to repetition,
Even if the corona discharge becomes a little unstable due to the environment or wire contamination, it has the characteristic of aligning the surface potential of the photosensitive member with the potential of the grid. However, the scorotron charger uses corona discharge, and has a problem that a large amount of ozone is generated because an excessive charging current is passed. If the concentration of ozone in the air increases, it will damage the respiratory system of the human body.

On the other hand, a charging roller as disclosed in Japanese Patent Laid-Open No. 168667/1988 and a Japanese Patent Laid-Open No. 62-2699 / 1987.
Japanese Patent Laid-Open No. 75-75 discloses a charging method that uses a contact charging device such as brush charging, in which the amount of ozone generated is extremely small. Although the charging roller has the same charging uniformity as that of a scorotron charging device, it has a complicated structure, requires mechanical accuracy, and is expensive. On the other hand, although the charging brush is similar in price to the scorotron charging device, the charging brush is inferior to the scorotron charging device in terms of uniformity of charging, and there is a problem that a streak image is likely to occur in a halftone image.

In contact charging of a charging roller, a charging brush or the like, deterioration of charging performance due to aging of the charging member often poses a problem. FIG. 2 shows the change over time in the charging potential of the brush charger. As is apparent from FIG. 2, the surface potential is changed by about 150 V at the start of printing and after 2 minutes, and the image density is greatly changed between them, which is a problem.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus capable of obtaining an image of good quality by stabilizing the charging potential on the surface of an image carrier. is there. Another object of the present invention is to provide a method of manufacturing a contact charging member that can obtain an image of good quality by stabilizing the charging potential on the surface of an image carrier.

[0007]

The present invention (Claim 1) includes:
Contact charging means for charging the surface of the image carrier, electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier, and developing means for developing the electrostatic latent image to form a developer image. A transfer means for slidingly contacting the transfer material in contact with the image carrier to transfer the developer image to the transfer material, and the contact charging without operating the transfer means for a predetermined time during non-image formation. An image forming apparatus comprising: an aging means for performing an aging operation of charging the surface of the image carrier by the means.

According to the present invention (claim 2), a contact charging means for charging the surface of the image carrier, an electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier, and the electrostatic latent image forming means. Developing means for developing the latent image to form a developer image, transfer means for slidingly contacting the transfer material in contact with the image carrier to transfer the developer image to the transfer material, and a predetermined means for non-image formation An image forming apparatus comprising: an aging means for performing an aging operation, in which the surface of the image bearing member is charged by the contact charging means without operating the transfer means for a certain period of time. Alternatively, a unit including the contact charging means is configured to be attachable / detachable, the contact charging means or the unit is mounted, and the detecting means for detecting whether the mounted contact charging means or the unit is new, and the detecting means. Fitted by When touching the charging means or unit detects that a new, the d - d by managing means -
An image forming apparatus is further provided with a means for performing a cleaning operation.

Further, according to the present invention (claim 3), a contact charging means for charging the surface of the image carrier, an electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier, and the electrostatic latent image forming means. Developing means for developing the latent image to form a developer image, transfer means for slidingly contacting the transfer material in contact with the image carrier to transfer the developer image to the transfer material, and a predetermined means for non-image formation Aging means for performing an aging operation for charging the surface of the image carrier by the contact charging means without operating the transfer means for a period of time, and the contact charging means for charging the surface of the image carrier. Charging current detecting means for detecting the charging current, and when the current value detected by the charging current detecting means is within a predetermined range, the aging operation to the image forming operation on the transfer material is performed. And a means for migrating Providing that the image forming apparatus.

Furthermore, the present invention (claim 4) provides a contact charging means for charging the surface of the image bearing member, an electrostatic latent image forming means for forming an electrostatic latent image on the charged image bearing member, and the electrostatic latent image forming means. Developing means for developing the electrostatic latent image to form a developer image, transfer means for slidingly contacting the transfer material in contact with the image carrier to transfer the developer image to the transfer material, and non-image forming means Aging means for performing an aging operation, in which the contact charging means charges the surface of the image carrier without operating the transfer means for a predetermined time, and the contact charging means charges the surface of the image carrier. Charging current detecting means for detecting the charging current and a developing bias applied to the developing means when the current value detected by the charging current detecting means falls within a predetermined range. Image forming operation based on the developing bias To provide an image forming apparatus characterized by comprising a means for changing to the developing bias for.

Further, the present invention (Claim 5) further comprises a step of removing impurities adhering to the brush-like member by subjecting the brush-like member to an electrification treatment by electrification or a discharge. A method of manufacturing a contact charging member is provided.

[0012]

The image forming apparatus of the present invention (Claim 1) performs an aging operation in which the surface of the image bearing member is charged by the contact charging means without operating the transfer means for a predetermined time during non-image formation. It is equipped with aging means. Therefore, in particular, when a new contact charging means is used, the aging operation is performed by the aging means at the time of non-image formation, whereby the charging potential in the initial state is stabilized and the image quality is improved. .

The image forming apparatus of the present invention (Claim 2) is configured such that a contact charging unit or a unit including the contact charging unit is detachably attached together with the above-mentioned aging unit. And a detecting means for detecting whether or not the attached contact charging means or unit is new, and an aging means when the contact charging means or unit attached is detected by this detecting means. -Means for performing a closing operation. Therefore, it is possible to automatically perform the aging operation when mounting a new contact charging unit or a unit including the unit.

In the image forming apparatus of the present invention (claim 3), in addition to the aging means described above, a charging current detecting means for detecting a charging current for the contact charging means to charge the surface of the image carrier, and the charging means. And a means for shifting from an aging operation to an image forming operation on the transfer material when the current value detected by the current detecting means falls within a predetermined range. This takes advantage of the fact that the charging current is in proportion to the surface potential of the image carrier, the surface potential is stabilized by the aging operation, and the aging operation is completed when the surface potential reaches a predetermined value. It is what makes me. Therefore, it is possible to prevent the aging operation for a longer time than necessary.

In the image forming apparatus of the present invention (claim 4), in addition to the above-mentioned aging means, a charging current detecting means for detecting a charging current for the contact charging means to charge the surface of the image carrier, and this charging. When the current value detected by the current detecting means falls within a predetermined range, the developing bias applied to the developing means is changed from the developing bias during the aging operation to the developing bias for the image forming operation. And means. By controlling the developing bias by detecting the charging current in this manner, excessive adhesion of the developer during the aging operation and adhesion of the developer on the non-image portion during the image forming operation can be prevented.

A method of manufacturing a contact charging member according to the present invention (claim 5) comprises a step of removing impurities adhering to the brush-like member by subjecting the brush-like member to an electrification treatment by energization or discharge. There is. As a result, the charging potential in the initial state is stabilized and the image quality is improved without performing the above-described aging operation after the contact charging member is attached to the image forming apparatus.

When the power of the machine is turned on, the charging device is replaced, the printer is aged for a predetermined time, or printing is performed after the charging current from the charging device reaches a predetermined value, or the developing bias is changed according to the charging current value. Is changed, or by performing energization treatment in the manufacturing process of the charging member, stable charging is performed. A high-quality image can be obtained by performing stable charging with a stable charging potential and adjusting the bias even when the charging potential is unstable.

[0018]

FIG. 1 shows the structure of an image forming apparatus according to an embodiment of the present invention. This image forming apparatus is a laser printer having an A4 size and a resolution of 400 dpi, and shows a printing speed of A4: 5 sheets / minute and a process speed of 30 mm / sec. In the figure, reference numeral 100 indicates a process unit, in which the photoconductor 1, the developing device 2, the cleaner 3, and the charging brush 4 are included. The diameter of the photoreceptor is φ24 mm, and the developing device 3 is a non-magnetic contact one-component developing device.

A bias is applied to the charging brush 4 by a DC constant voltage power source. The entire surface of the photoconductor 1 is uniformly negatively charged by the charging brush 4. After that, an electrostatic latent image is formed by the exposure unit 5, and toner is attached to the latent image by the developing device 2 (reverse development), so that a toner image is formed on the photoconductor 1. The paper P is conveyed from the paper cassette 7 and is in close contact with the photoconductor in the contact nip between the transfer brush 6 and the photoconductor 1. By the bias applied to the transfer brush 6, the toner image is transferred to the paper P in the above-mentioned nip. Paper P with unfixed image
Is applied with heat and pressure by the fixing device 8, and the image is fixed on the paper P. The transfer residual toner remaining on the photoconductor 1 is removed from the photoconductor 1 by the cleaner 3.

Next, the non-magnetic one-component developing device will be described. As the developing roller 200, a roller having a diameter of 12 mm is used in which a rubber layer having a predetermined resistance value is formed on a metal shaft having a diameter of 6 mm. The hardness of rubber is 28 degrees
By setting it to 50 degrees (JIS-A; the same applies hereinafter), it is possible to obtain a stable developing nip without permanent distortion. Also, the resistance value of the rubber material is 10 ⁴ Ω · c
By setting m to ^{10 10} Ω · cm, it is possible to obtain a clear image without bias leak. It should be noted that the surface of the roller is coated with urethane paint, which has good toner releasability.
It is applied in a thickness of about 0 to 150 μm, and prevents the toner from sticking without impairing the elasticity of the roller. The rubber hardness of the roller after applying the surface layer is 30 degrees to 55 degrees.
It is a degree. Further, in order not to impair the developing characteristics, the surface layer should have a resistance of about 10 ⁵ to 10 ¹⁰ Ω · cm. Furthermore, the charge control agent is dispersed in consideration of the triboelectric charging performance of the toner.

The layer forming member 201 is in contact with the developing roller 200 at a pressure of 300 g to 1500 g, and charges the toner while regulating the amount of the toner layer formed on the developing roller. The structure of the layer regulating member 201 is φ1
A layer similar to the surface layer of the developing roller is formed on the surface of the metal rod of 0 mm to secure the charging performance and the toner greasiness. Although the layer regulating member 201 is fixed in the embodiment, it may be rotated with a peripheral speed difference with respect to the developing roller. Further, in this embodiment, the layer regulating member 201 has the same potential as the developing roller 200, but a potential difference is provided to control the amount of toner formed on the developing roller,
It is also possible to charge the toner by injecting charges.

The toner supply roller 202 has a volume resistance of 10
⁵ to 10 ¹¹ Ω · cm hardness (ASKER-C) 20 to
35 degree firing roller (shaft φ6mm, roller diameter 12
mm) and supplies toner to the surface of the developing roller 200. In this embodiment, the toner supply roller 202
Is in contact with the developing roller 200 with a biting amount of 0.7 mm. While supplying toner, the toner on the developing roller is peeled off and charged at the same time.

As the toner, a toner having a negative charge polarity using a polyester resin as a binder is used. The toner particle size is 10.2 μm (deposited average particle size). When the above toner is used in the developing device configured as described above, the toner layer formed on the developing roller 200 has a charge amount of −8.2 μc / g and a layer formation amount of 0.73 mg.
Was / cm ² .

The transfer brush 6 has a volume resistance of 10 ⁵ to 10 ¹² Ω · cm and a brush diameter of ³ to 1 as shown in FIG.
The brush has a configuration of 0D and a density of 10,000 to 400,000 / inch and is sandwiched by sheet metals. The bias applied to the transfer brush 6 is +500 to + 2000v, which is opposite to the charging polarity of the toner. Further, the transfer brush 6 is configured so that it can be separated from the photoconductor 1 to prevent contamination.

The charging brush 4 is an L-shaped metal plate (thickness 1 to 1).
3mm aluminum), the specific resistance of the material is 10 ³ to 10 ¹¹ Ω ・
cm, fiber diameter 2D to 10D, brush flocking density 10000
It is configured to have brushes of up to 400000 pieces / inch. If the resistance of the brush is too low, a portion having a high surface potential is locally generated due to charge injection, the uniformity of density is impaired, and white streaks are generated in halftone. On the other hand, if the resistance is too high, partial charging is not performed, and black streaks occur in halftone. Table 1 below shows the relationship between the brush resistance and the image quality. In this case, the brush fiber diameter is 6D and the brush bristle density is 20000 fibers / inch.

Table 1 Brush resistance and halftone streaks (coverage 50%) Brush resistance (Ω · cm) White streaks Black streaks 10 ³ × ○ 10 ⁵ ○ ○ 10 ⁷ ○ ○ 10 ⁹ ○ ○ 10 ¹¹ ○ ○ 10 ¹² ○ ○ 10 ¹³ △ ×

From Table 1 above, it can be seen that good images were obtained at 10 ⁵ to 10 ¹² Ω · cm. The relationship between the brush fiber diameter and the generation of streaks in halftone is shown in Table 2 below. In this case, the brush resistance is 10 ⁶ Ω · c
m, and the brush flocking density is 20000 lines / inch.

Table 2 Brush fiber diameter and halftone streak (50% coverage) Brush fiber diameter (D) Halftone streak 1 × Brush breakage occurred 2 ○ 4 ○ 6 ○ 8 ○ 10 ×

From Table 2 above, it can be seen that when the fiber diameter is 10 D or more, the image streaks in the halftone become thicker and more conspicuous. As for the image quality, the smaller the brush diameter is, the better. However, if the brush diameter is 2D or less, the brush fibers are broken and broken, and they penetrate into the developing device, causing an image defect. Table 3 below shows the relationship between the brush flocking density and the background fog. In this case, the brush fiber diameter is 6D and the brush resistance is 10 ⁶ Ω · cm.

Table 3 Brush flocking density and background fogging Brush flocking density (thousands / inch) Ground fogging 5 × 8 × 10 ○ 50 ○ 100 ○ 200 ○ 400 ○ 500 × Unmanufacturable

As shown in Table 3 above, 10,000 lines / i
If the number is equal to or less than nch, the portion where the brush does not come into contact with the photoconductor 1 becomes defective in charging and fogging occurs. On the other hand, 400
It is difficult to realize a brush density of 000 brushes / inch or more from the viewpoint of manufacturing.

Disturbance of the bristle at the upstream and downstream ends of the brush in the direction of rotation of the photosensitive member causes a local increase in charge due to abnormal discharge, resulting in white streaks in halftone. It is preferable to provide a mylar guide so that the hair does not protrude. However, if the length of the bristles of the brush is too long, the bristles tend to stick out even if a guide is provided, so the bristles should have a length of 7 mm or less.

In this embodiment, a bias of -1000V is applied to the charging brush member by a DC constant voltage power source to charge the photosensitive member. As the applied bias,
It is also possible to use AC / DC superimposed bias. When the contact charging as in this embodiment is used, the stability of charging in the initial use state becomes a problem. FIG. 4 shows changes in the charging potential when charging is performed with a completely new brush. From FIG. 4, especially in a hot and humid environment, the initial surface potential is extremely high, and it takes an average of 1 minute to stabilize. When printing is performed in such a high potential state, there arises a problem that the halftone density is low. Further, in such a state where the surface potential is high, a high potential portion due to charge injection partially exists, and this high potential portion causes white streaks in halftone.

However, if the potential is once stable, even if it is left in a humid environment again, the surface potential is slightly high at the time of starting, but an abnormally high potential like a new brush does not occur. Absent. Therefore, in the embodiment, when the process unit is mounted on the machine, it is determined whether or not the process unit is new. When it is determined that the process unit is new, the charging operation of the photoconductor by the charging brush is performed as the initialization operation. . Here, the initialization operation is performed for about 1 minute.

The initialization operation is an operation of applying a predetermined bias to the charging member while rotating at least the photosensitive member. In this embodiment, a normal bias of -200V is applied to the developing device, and the developing roller also rotates. FIG. 5 shows the sequence of the initialization operation when the machine power is turned on.

Next, a method for determining whether or not the currently installed process unit is new will be described. The process unit has a substrate that includes a memory in which the manufacturing members of the process unit are recorded. When the process unit is turned on while it is attached to the main body, or when the process unit is attached while the power is on, the main unit side Controller reads the manufacturing members of the process unit. The storage member on the main body side stores the manufacturing members of the process units that have been installed so far, and determines whether the unit is new by comparing it with the number of the installed process unit. If it is judged as new,
The initialization operation is performed for 1 minute, and if not, the normal warm-up operation is started.

In addition, as a method of judging whether or not the process unit is new, a part of the photoconductor of the new unit,
Alternatively, there is also a method in which the whole is covered with black paper and it is judged whether it is new by reading it with an optical sensor. The black paper at this time is automatically wound up and collected inside the process unit. In addition, the manufacturing number is displayed as a bar code at a predetermined position of the process unit, and this is read by the bar code reader on the main unit,
There is also a way to determine if the process unit is new.

In this embodiment, the instability of the initial surface potential of the new brush is attempted to be eliminated by performing the initializing operation for a certain period of time. In the fixed type charging brush as in the present embodiment, as shown in FIG.
Regarding the time Ts until the potential is stabilized, there are few differences among brushes, and a uniform initialization time often causes no problem. However, when a rotating type charging brush is used, the difference in individual brushes poses a problem.

Next, as another embodiment, as shown in FIG. 7, an example in which the fixed brush 4 of the above-mentioned embodiment is replaced with a rotating brush 4 will be described. Other than changing the charging brush,
The structure is exactly the same as that of the embodiment shown in FIG.
First, the rotating brush will be described. The proper resistance value of the brush fiber, the flock density, and the thickness of the fiber are the same as those of the fixed type shown in FIG. In the case of the example shown in FIG. 7, the resistance value is 1
A brush having a brush density of 0 ⁸ Ω · cm, a flocking density of 100,000 / inch, and a fiber thickness of 6D is used. Further, as shown in FIG. 8, the rotary type brush is formed by spirally winding a band-shaped fiber around a base shaft (φ6 mm), so that the seam portion of the winding margin has a substantially low bristle density. If you print with the molded brush as it is,
In a halftone image or the like, diagonal density unevenness as shown in FIG. 9 occurs.

Therefore, in the example shown in FIG. 7, FIG.
As shown in FIG. 10 (b), the straight hair-shaped brush is rotated in a cylinder through which steam is passed for a predetermined time, so that a brush with slanted bristles as shown in FIG. 10 (c) is used. There is. In this way, by obliquely bristling, it is possible to make the portion of the seam having a low brush density inconspicuous. Here, a straight bristling brush once molded to φ14 mm is obliquely bristled to have a diameter of φ12 mm.

The rotation speed of the rotary brush is 1.5 to 3 times the movement speed (process speed) of the photoconductor in the case of the with rotation and 1 to 3 times in the case of the against rotation. As a result, it is possible to obtain a good image without a halftone streak and the winding trace.

The rotating brush described above also has a problem that the initial surface potential of a new brush becomes high. In the embodiment shown in FIG. 1, the time for performing the initializing operation is an average stabilizing time, but the rotating brush has a large difference in the individual solids depending on the time until it stabilizes.
This method is difficult.

FIG. 6 shows two rotary brushes and two fixed brushes.
The result of having measured the initial surface potential of 0 is shown. The fixed brushes (under high temperature and high humidity conditions) had a very small difference in potential fluctuation due to the fixed difference, and all the brushes had stable charging potentials after aging for 1 minute. However, with some rotating brushes, some brushes stabilize the potential in about 1 minute, while
Some require about a minute. If the initialization time is set to 1.5 minutes, most brushes will stabilize to a potential at which there is almost no problem, but depending on the object, it may be stable from a potential that is 15 minutes.
Something as high as 0V will come out. In such cases,
When considering aging for a certain period of time in all units as shown in FIG. 1, some units may not be stable in 1 minute, and image defects may occur. However, all brushes are stable for 3 minutes. Is too long from the user's point of view.

Therefore, in the example using the rotating brush shown in FIG. 7, it was considered to perform the initialization operation in consideration of the individual difference due to this brush. FIG. 11 shows the relationship between the inflow current from the power source to the brush and the surface potential of the photoconductor. Figure 1
It can be seen from 1 that the two have a substantially proportional relationship. Therefore, the surface potential of the photoconductor can be known by detecting the current flowing into the brush by the detection circuit as shown in FIG. Therefore, in the process of stabilizing the surface potential during the initializing operation, it was considered to terminate the initializing operation when the surface potential becomes lower than a certain potential.

FIG. 13 shows the relationship between the photoreceptor surface potential and the halftone density at a printing rate of 50% when the developing bias is -200V. If the absolute value of the photoconductor potential becomes smaller than -550V, the halftone density difference from the standard surface potential of -500V becomes 0.1 or less, and there is no problem in image quality. From FIG. 11, the current value I when the surface potential is −500 V is −8 μm.
m, and the current value I at −550V is 8.8 μA. Therefore, the current value is 8.8μ during the initialization operation.
If it becomes A or less, the initialization operation is ended. Figure 1
FIG. 4 shows a flowchart of the initialization operation in the example using the rotary charging brush.

It should be noted that, as shown in FIG. 15, the brush used once does not show a remarkable increase in surface potential even when left in a hot and humid environment again. However, since a slight increase can be seen, it is desirable to perform the aging operation each time the power is turned on when the brush charging is used in a device such as a color printer that requires high image quality. in this way,
By aging until the current value to the charging brush falls below a specified value, good printing can be performed without unnecessary initialization and without being affected by changes in image density due to initial surface potential fluctuations. I can do it.

Next, it was considered that high-definition printing is performed using a small particle size toner. It is known that when printing is performed using a toner particle size of 6.2 μm (accumulation average particle size), resolution, halftone density, and the like are improved. But,
Reducing the toner particle size causes some problems. FIG. 16 shows the relationship between the photoreceptor surface potential and the amount of toner adhered to the non-image area (in short, the amount of fog toner) when the developing bias is set to -200V. In the non-image area, fogging is suppressed by the electric field due to the difference between the developing bias and the photosensitive member surface potential. However, fogging is likely to occur even if this potential difference is too large.
This tendency is due to the contact one-component development as described above, and
This is remarkable when a small particle size toner is used.

Toner adhesion amount to the non-image area is 0.01 m
When it exceeds g / cm ² , problems such as an increase in toner consumption amount and blistering of the cleaning blade occur. As described above, when the new charging brush is used, the surface potential is high during the initialization operation. At this time, the surface potential may exceed −700 v, and the toner adhesion amount to the non-image area exceeds 0.01 mg / cm ² .

Therefore, at this time, the developing bias is set to -200.
When V is changed to −300 V, as shown in FIG. 16, the toner adhesion amount in the non-image area can be 0.01 mg / cm ² or less. When the initializing operation is completed and the normal printing operation is performed, the surface potential is set to about -500V, so the developing bias may be set to -200V. By controlling the developing bias in this way, it is possible to prevent excessive toner consumption and curling of the cleaning blade during the initialization operation of the new brush.

In the above description, the toner adhesion to the non-image area is prevented by controlling the developing bias. However, during the initialization operation, the adhesion of the toner can be prevented by stopping the rotation of the developing device. it can. Further, the method of detecting the charging current and controlling the developing bias is also effective in the normal print mode. When toner adheres to the brush, the surface potential is likely to rise in a humid environment.
Then, as described above, excessive toner adheres to the non-image area, which increases the toner consumption amount and lowers the halftone density. Therefore, it was considered to detect the charging current I and control the developing bias according to the current value.

When the surface potential fluctuates from -500V to -700V, the developing bias is not changed and -2
The development bias is set to −20 when the voltage remains at 00V and I
The amount of toner adhered to the non-image area and the halftone (coverage50 when changing from 0V to -300V)
%) Concentration variation is shown in Table 4 below.

Table 4 Surface potential Development bias -200 V Development bias control Halftone toner Non-image area toner Halftone toner Non-image area toner Concentration Adhesion amount (mg / cm ² ) Concentration Adhesion amount (mg / cm 2 ² ) -500V 0.72 0.02 0.72 0.02 -600V 0.58 0.035 0.70 0.02-700V 0.51 0.012 0.69 0.03

From Table 4 above, by controlling the developing bias, the fog on the drum was kept at 0.01 mg / cm ² at all times.
It will be understood that the density variation of the halftone can be set to 0.1 or less.

Next, a method for preventing an increase in surface potential of a new brush by devising a brush manufacturing process will be described. When a new brush is used, the phenomenon in which the surface potential is initially high and gradually decreases and becomes stable is considered to be because oil and the like that adhere to the brush during the brush manufacturing process adhere to the photoconductor. Therefore, in order to prevent the above phenomenon by removing the component in the brush manufacturing process, the following (a) to (c) are considered.
The three brushes of

(A) After finishing the slanting step as shown in FIG. 10, the brush is energized by an apparatus as shown in FIG. The treatment is performed in the final step after the steps such as brush bristling and drying are completed. First, the metal cylinder 3
Insert the brush roller 300 inside 02, and
While rotating at a speed of rpm, electricity was applied between the brush shaft and the metal cylindrical body 302 to perform electricity treatment. The energizing current and the energizing time were changed to energize the brush 300, and the initial surface potential of the brush 300 and the surface potential after 5 minutes were measured. The result is shown in FIG.

In the figure, Is represents the amount of current per unit area of the contact surface of the brush. In the device shown in FIG. 17, when the amount of current detected by the ammeter 303 is I (μA), the width of the brush is L (cm), and the radius of the brush is R (cm), Is is represented by the following formula. You can Is = I / 2πRL (μA / cm ² )

From FIG. 18, by setting the processing conditions so that Is × T> 150, the increase of the initial surface potential can be set to 30 V or less. The above is brush
As for La, even with fixed type brushes,
Similarly, by setting the processing conditions so that Is × T> 150, it is possible to suppress the increase in the initial surface potential.

(B) After the slanting step as shown in FIG. 10 is completed, the brush is charged by the device as shown in FIG. That is, in the final process of brush manufacturing,
The brush 300 was brought into contact with the discharge target tube 310, a bias was applied, and discharge was performed. The discharge target tube 310 is formed by coating a resin layer having a thickness of 20 μm on the surface of an aluminum tube, and is rotating at a peripheral speed of about 20 to 100 mm / sec. The brush 300 rotates in the direction of against the discharge target tube 310 at a speed of about 1 to 3 times the peripheral speed of the discharge target tube 310. In the figure, 311 is an apparatus for removing the substance adhering to the discharge target tube 310 from the brush 300.

In the example shown in FIG. 19, two sets are set in one discharged tube 310, one side is applied with a negative bias and the other side is applied with a positive bias. By doing so, it is not necessary to discharge the discharge target tube by a corona discharger, etc., and the processing apparatus shown in FIG. 19 can be made inexpensive and can be made safe. Further, when the two bias polarities are switched (reversed) and the reprocessing is performed, a better result is obtained.

FIG. 20 shows the discharge current is (i / i
FIG. 5 is a characteristic diagram showing L) and an increase in initial surface potential when the treatment is performed while changing the discharge time. Note that is is
It is a current value per unit length in the brush longitudinal direction. Unlike the energization process, the discharge is not performed on the entire surface of the contact nip, so the value per unit area of the contact nip is meaningless.

From FIG. 20, it can be seen that by satisfying is × T> 10, it is possible to suppress the initial potential sj king to 50 V or less. Note that, in the example shown in FIG.
However, it is also applicable to a fixed type brush, and even if the applied bias at the time of discharge processing is AC, is × T
Good results are obtained by satisfying> 10.

(C) As shown in FIG. 21, the energizing process is performed at the same time when the slanting process is performed. FIG. 21 shows FIG.
In the bristling step shown in FIG. 0, a bias is applied between the brush shaft and the outer cylinder to perform the energization process while bristling.

FIG. 22 shows initial potential fluctuations of the photoconductors of the brushes processed by the methods (a) to (c) described above and the normal brush. From FIG. 22, (a)-
All the treatments of (c) were effective, and particularly in regard to (b) which was discharged by charging, a remarkable effect was shown on the initial potential stability. Therefore, it is understood that charging (discharging) is more effective than just energizing.

[0064]

As described above, according to the present invention,
When the power of the device is turned on, when the charging device is replaced, etc., the aging operation is performed for a predetermined period of time, the image forming operation is performed after the charging current from the charging device reaches a predetermined value, or the charging current value The development bias is changed in accordance with the above, so that it is possible to prevent halftone density fluctuations, increase in toner consumption, etc. due to instability of the initial potential of contact charging, especially charging using a brush. It is possible to form an image. Further, in the manufacturing process of the charging member, it is possible to obtain a charging member having a stable initial charging potential by performing a charging process by energizing or discharging.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall outline of a printer using a fixed charging brush according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a transfer brush.

FIG. 3 is a diagram showing prevention of halftone lines by Mylar support.

FIG. 4 is a characteristic diagram showing a change in initial surface potential of a new fixed brush.

FIG. 5 is a diagram showing an initialization operation of the fixed charging brush according to the embodiment of the present invention.

FIG. 6 is a characteristic diagram showing a difference in initial surface potential fluctuation between a fixed brush and a rotating brush.

FIG. 7 is a diagram showing an overall outline of a printer using a rotary charging brush according to another embodiment of the present invention.

FIG. 8 is a diagram showing a method of molding a rotary charging brush.

FIG. 9 is a diagram showing a halftone winding mark of a rotary charging brush.

FIG. 10 is a diagram illustrating a step of slanting a rotary charging brush.

FIG. 11 is a characteristic diagram showing the relationship between charging current and surface potential.

FIG. 12 is a diagram showing a charging potential detection circuit.

FIG. 13 is a characteristic diagram showing the relationship between surface potential and halftone density.

FIG. 14 is a diagram showing an initializing operation of a rotary charging brush according to another embodiment of the present invention.

FIG. 15 is a characteristic diagram showing a difference in fluctuation of surface potential between a new brush and a used brush.

FIG. 16 is a characteristic diagram showing a relationship between a surface potential and a toner adhesion amount (non-image area fog) on a non-image portion.

FIG. 17 is a diagram showing a brush energization processing device.

FIG. 18 is a characteristic diagram showing the relationship between the energization processing time and the rise of the initial surface potential.

FIG. 19 is a diagram showing a brush charging device.

FIG. 20 is a characteristic diagram showing a relationship between charging processing time and an increase in initial surface potential.

FIG. 21 is a diagram showing a method for conducting electricity while slanting.

FIG. 22 is a characteristic diagram showing the relationship between the aging time and the surface potential of a brush treated by various treatment methods.

[Explanation of Codes] 1 ... Photosensitive member 2 ... Developing device 3 ... Cleaner 4 ... Charging brush 5 ... Exposure means 6 ... Transfer brush 7 ... Paper cassette 8 ... Fixing device 201 ... Developing roller 201 ... Layer forming member 201 ... Toner supply roller 300 ... Brush roller 301 ... Power source 302 ... Cylindrical body 303 ... Ammeter 310 ... Discharge tube 311 ... Blade

Claims (5)

[Claims] 1. A contact charging means for charging the surface of a rotatable image carrier, an electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier, and developing the electrostatic latent image. A developing unit for forming a developer image; and a unit for rotating the image carrier for a predetermined time during non-image formation and for charging the surface of the image carrier by the contact charging unit. A characteristic image forming apparatus. 2. A contact charging means for charging the surface of a rotatable image carrier, an electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier, and developing the electrostatic latent image. A developing means for forming a developer image and aging for performing an aging operation of rotating the image carrier for a predetermined time during non-image formation and charging the surface of the image carrier by the contact charging means. And a unit including the contact charging unit or the unit including the contact charging unit, the contact charging unit or the unit being mounted, and the contact charging unit or the unit being mounted. Is detected as a new one, and when the contact charging means or the unit mounted by the detecting means is new, the aging means causes an error.
An image forming apparatus, further comprising: a means for performing a cleaning operation. 3. A contact charging means for charging the surface of a rotatable image carrier, an electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier, and developing the electrostatic latent image. A developing means for forming a developer image and an aging operation for rotating the image carrier for a predetermined time during non-image formation and for charging the surface of the image carrier by the contact charging means. A charging means, a charging current detecting means for detecting a charging current for charging the surface of the image carrier during the aging operation by the contact charging means, and a current value detected by the charging current detecting means within a predetermined range. And a means for shifting from the aging operation to the image forming operation. 4. A contact charging means for charging the surface of a rotatable image carrier, an electrostatic latent image forming means for forming an electrostatic latent image on the charged image carrier, and developing the electrostatic latent image. Developing means for forming a developer image, voltage applying means for supplying a developing bias voltage to the developing means, the image carrier is rotated for a predetermined time during non-image formation, and the contact charging means is used to An aging means for charging the surface of the image carrier and an aging operation; and a charging current detecting means for detecting a charging current for charging the surface of the image carrier by the contact charging means during the aging operation. An image forming apparatus comprising: a means for changing a developing bias applied to the developing means in accordance with a current value detected by the charging current detecting means. 5. A method of manufacturing a contact charging member, comprising the step of removing impurities adhering to the brush-like member by subjecting the brush-like member to an electrification treatment by energization or a discharge.