JPH0683162A - Electrifier, image forming device and process unit capable being attached/detached to/from it - Google Patents

Abstract

PURPOSE:To obtain a stable image without causing a failure in power supply with long-term use by providing a first voltage supplying means for an electrifying member electrifying a body to be electrified while being rotated and a second voltage supplying means for which a resistor higher than that of the first voltage supplying means by one digit or more is interposed from a power source to the electrifying member. CONSTITUTION:The first voltage supplying means 41 for the electrifying member 2 provided in contact with the body to be electrified 1 and electrifying in while being rotated and the second voltage supplying means 42 for which the resistor 42a higher than that of the first voltage supplying means 41 by one digit or more is interposed from the power source 10 to the electrifying member 2 are provided. Thus, most of current normally flows from the first power feeding means 41, so that the second power feeding means 42 hardly has a deterioration caused by the flowing of the current. When the first power feeding means 41 has a very small defect, a spark discharge is not generated therefrom, but the current flows via the second power feeding means 42. Therefore, the deterioration caused by the spark discharge can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact type charging device for charging a surface of an object to be charged (including static elimination processing) by bringing a charging member into contact with an object to be charged such as a photoconductor, and an image provided with the same. The present invention relates to a forming apparatus and a process unit that can be attached to and detached from the image forming apparatus.

[0002]

2. Description of the Related Art For example, in an image forming apparatus such as an electrophotographic apparatus (copier, laser beam printer, etc.) and electrostatic recording apparatus, the surface of an image bearing member such as a photoconductor or a dielectric is charged. A corona discharge device (corona charger) has been widely used as a device for processing.

The corona discharge device is effective as a means for uniformly charging the surface of an object to be charged such as an image carrier to a predetermined potential. However, it requires a voltage power supply, the charging efficiency is poor,
There are problems that the structure is large and complicated, the cost is high, a relatively large amount of undesired ozone is generated by corona discharge, and the discharge wire is contaminated or cut.

In such a corona discharge device, the contact charging means for contacting a charging member to which a voltage has been applied to the body to be charged to charge the surface of the body to be charged can lower the power supply voltage.
Since the structure is simple, there is no cutting of wires, and even if ozone generation is observed, the amount is extremely small, so for example, in an image forming apparatus, an image carrier such as a photoconductor or a dielectric, As another means for charging the surface of the body to be charged, which is an alternative to the corona discharge device, research on its practical use is underway (Japanese Patent Application Laid-Open No. 57-178267 / 56-104351).
・ 58-40566 ・ 58-139156 ・ 58-15
0975 publication).

6A and 6B show an example of a contact charging device using a rotating roller body (hereinafter referred to as a charging roller) as a charging member. 6A is a side view, and FIG. 6B is a partially cutaway front view.

Reference numeral 81 denotes a member to be charged, which is, for example, a rotary drum type photoconductor (hereinafter referred to as a photoconductor drum) of an electrophotographic apparatus.
And The photosensitive drum is rotationally driven in the clockwise direction indicated by the arrow at a predetermined process speed (peripheral speed).

The cored bar 82 is a charging roller, and is composed of a conductive cored bar 82a which is a base material and an elastic layer 82b which is integrally formed on the outer periphery of the cored bar and is made of conductive rubber having a low volume resistivity.
And a high resistance surface layer (high resistance layer) 82c formed on the outer circumference of the roller portion. That is, the cover layer of the base material includes the elastic layer 82b and the surface layer 82c.

Both ends of the roller 82a are rotatably held by bearings 83 so that the longitudinal direction of the roller is substantially parallel to the generatrix direction of the photosensitive drum 81 and brought into contact with the surface of the photosensitive drum. The charging roller 82 is brought into contact with the photosensitive drum 81 with a predetermined pressing force by urging the pressing springs 84 so that they can move toward the photosensitive drum 81.

Reference numeral 85 denotes a power source for applying a bias voltage to the charging roller 82. The power source 85 causes the charging roller 82 to be charged to the charging roller 82 via a conductive electrode 86 having a spring property such as stainless steel. DC voltage V of, for example, about 1 to 2 KV from the end surface of the conductive cored bar 82a.
_DC or superposed voltage V _DC + V of DC voltage and AC voltage V _AC
AC bias voltage is applied.

As a result, the peripheral surface of the photosensitive drum 81 which is rotationally driven is contact-charged with a predetermined polarity and potential (conventional example 1).

Further, an electrophotographic printer which is a conventional image forming apparatus uses a laser as a light source for image exposure, a laser beam printer which raster scans the laser to write an image signal, an LED printer by blinking a light emitting diode array, and a back surface. A liquid crystal printer or the like which has a light source and writes an image signal by opening and closing a liquid crystal shutter array is known.

These write an image in the horizontal direction (main scanning) while scanning light in one row (or two or more rows) at right angles to the movement of the electrophotographic photosensitive member which receives the light, and vertically move by moving the electrophotographic photosensitive member. Write the image in the direction (sub-scan).

In order to express a halftone or a gray scale with such a printer, a sub-number of pixel blocks are formed in the main scanning direction and the sub scanning direction, and the gradation is represented by the black area in the pixel. For example, as shown in FIG. 15, when a matrix in which numbers 1 to 16 are applied to a 4 × 4 pixel block is formed and the block density is 3, 1,
It is generally used to make a few pixels black.

The method of assembling the matrix includes a spiral type as shown in FIG. 15, a halftone type, a concentrated type and a Bayer type.

On the other hand, for charging the surface of the electrophotographic photosensitive member, corona charging is used and contact charging with almost no generation of ozone is used. In contact charging, a roller or brush extending in the scanning direction is used as a contact. In addition to a DC electric field, it is often used for the contactor to superimpose AC, which is excellent in uniformity of charging and contamination of the contactor (conventional example 2).

Further, in the contact charging device in the image forming apparatus, a conductive member to which a voltage is applied is brought into contact with the surface of the image carrier, and charges are directly transferred (injected) to the surface of the image carrier to make the surface of the image carrier predetermined. It is charged to the electric potential of, compared to the corona charging device that has been widely used as a charging device.
The applied voltage required to obtain a predetermined potential on the surface of the image carrier is lowered, the amount of ozone generated during the charging process is extremely small, and a filter for removing this is unnecessary. As a result, the exhaust system of the apparatus has the advantages that it can be simplified, maintenance-free, and that the configuration is simple.

Therefore, for example, an electrophotographic apparatus (copier,
In an image forming apparatus such as a laser beam printer) and an electrostatic recording device, as a device for charging the surface of an image bearing member such as a photoconductor or a dielectric, it has attracted attention as an alternative to the corona charging device and has been put into practical use. There is.

The applicant of the present invention relates to this contact charging device
For uniform charging, an oscillating voltage obtained by superposing an AC voltage on a DC voltage is applied to a conductive member, and the conductive member is brought into contact with the surface of the image carrier to carry out charging (Japanese Patent Laid-Open No. Sho 61-206). 63-149669 gazette etc.).

FIG. 25 shows an embodiment thereof. In FIG. 25, 251 is a photosensitive drum as an image bearing member,
It is rotationally driven in the direction of arrow B at a predetermined peripheral speed (process speed).

Reference numeral 252 is a charging roller as a conductive member, which comprises a conductive cored bar 252a and a conductive elastic layer 252b formed on the outer peripheral surface thereof. This charging roller 2
52 is applied to both end portions in the longitudinal direction of the conductive cored bar 252a and is pressed by a not-shown pressing spring to cause the photosensitive drum 25 to move.
It is pressed against one surface with a predetermined pressing force, and is driven to rotate as the photosensitive drum 251 rotates.

Further, reference numeral 253 is a high-voltage power source for the charging roller 252, whereby a contact leaf spring 254 which is brought into contact with the conductive core metal 252a of the charging roller 252,
A DC voltage V _DC, superimposed oscillating voltage an AC voltage V _AC having a voltage V _PP between two or more times the peak of the charge starting voltage of the photosensitive drum 251 surface is supplied, only the DC voltage (V _DC +
V _AC ) is applied to the charging roller 252, and the surface of the photosensitive drum 251 that is rotationally driven is uniformly charged to a predetermined potential.

The conductive member is not limited to the roller type as described above, but may be a blade type, pad type, belt type, web type, brush type or the like.

The contact charging method for charging the surface of the image bearing member by applying the oscillating voltage obtained by superimposing the AC voltage on the DC voltage to the conductive member in this manner is hereinafter referred to as AC contact charging method (conventional example 3).

Further, the laser printer in the conventional image forming apparatus is constructed as shown in FIG. 33, and FIG. 34 shows an example of the roller type contact charging device 301.

An electrophotographic photosensitive member 302 (hereinafter referred to as a photosensitive drum) as an image bearing member, which is generally a rotary drum type.
The periphery of is uniformly charged to a predetermined polarity potential by a charging device 301, and the surface of the charged photosensitive drum is laser scanner 308 as image exposure means, and the laser scanner 308 as image exposure means outputs time-series electric digital pixel signals of target image information. The laser beam modulated and output according to the above is scanned and exposed (raster scan) in the generatrix direction of the photosensitive drum 2 through the reflection mirror 7 to form an electrostatic latent image, and the latent image developing device is formed. The powder image visualized by 309 and visualized thereby is synchronously transferred by the transfer device 310 onto the transfer material P, which has been previously conveyed, and is fixed by the fixing device 330 to output an image-formed product. It is a thing.

The developer not transferred at the time of transfer is collected by the cleaner 311.

Conventionally, as means for uniformly charging the surface of an image bearing member such as a photosensitive drum of an image forming apparatus, there are known ones using corona discharge and contact charging. The latter contact charging is performed by bringing a charging member such as a roller type, a blade type, a rod type, or a brush type into contact with a rotating photosensitive drum to perform charging, and is caused by ozone generation or corona discharge unevenness as compared with corona charging. It has an advantage that uneven charging does not occur. In particular, the roller type charging member (hereinafter, referred to as charging roller) if the is, for example, such a structure shown in FIG. 34, 10 ⁴ to 1 of the EPDM or the like is formed on the cored bar 3
A conductive rubber layer 314 of 0 ⁵ Ωcm is provided, a medium resistance layer 313 of hydrin rubber or the like of about 10 ⁷ to 10 ⁹ Ωcm is provided on the outside thereof, and an N-methoxymethyl nylon nylon-based material 10 is provided on the outside thereof. ^{7 ~10 10 Ωcm}
The blocking layer 312 of 1. is provided as a surface layer. Also, the hardness at this time is 50 ° by ASKER-C measurement.
It is generally about 70 °.

When the charging roller 301 is used, it is generally rotated at the same speed as the surface movement of the photosensitive drum 302 which is an image carrier.

However, in the case of the reflective contact charging, the surface shape of the charging member appears as minute charging unevenness, and in the case of using the charging roller, the eccentricity or distortion of the charging roller causes a partial charging failure, resulting in an image failure. There was a problem such as affecting.

As a means for solving the former problem of uneven charging, it has been proposed to adjust the resistance value of the charging member to an optimum value and apply a bias voltage containing an AC component to the charging member ( JP-A-63-149669 and Japanese Patent Application No. 62-23033). Further, as a means for solving the latter problem of poor charging, it is known that a contact angle between the photosensitive drum 302 and the charging roller is provided with an intersecting angle so that the charging roller is uniformly contacted with the entire area of the photosensitive drum. (See JP-A-63-208880).

FIG. 35 shows a sequence of a conventional example of applying a charging bias containing this AC component.

When the main motor is rotated and the rotation is stabilized, a bias in which a DC component from the DC power source 382 and an AC voltage from the AC power source 381 are superimposed is applied to the charging roller 301. The DC voltage at this time is the photosensitive drum 30.
The voltage is almost equal to the voltage for charging to 2, and the AC voltage is applied at a voltage that is at least twice the charging start voltage value. The charging bias (AC + DC) is applied with the same bias until the end of the post-rotation after the image output is completed. Figure 3
In the sequence of No. 5, for the sake of convenience, a conventional example of a reversal development method using a negative-polarity photosensitive drum and a negative-polarity toner is shown (conventional example 4).

[0033]

In the prior art example 1, since the electrode 86 and the cored bar 82a are both metal, the performance as an electrode is guaranteed by controlling the pressing force (deformation amount) of the spring electrode 86. It will be.

However, as a result of a more detailed study by the inventors of the present invention, the power feeding by the above-described method exhibits sufficient performance in an apparatus having a relatively short initial life and a long life, but if the equipment is durable for a long period of time, a power failure will occur. Something has happened to happen.

As a result of investigating the cause, this phenomenon shows that the contact resistance between the electrode 86 and the cored bar 82a is as low as almost 0Ω at the initial stage of durability, and there is no problem in the power feeding performance, but a high voltage is applied while sliding. When passing an electric current, there may be a case where an extreme spark discharge occurs due to the presence of small dust particles or subtle vibrations. It is considered that by repeating such a phenomenon, the electrode contact portion is carbonized or oxidized and the contact resistance gradually increases, and the voltage applied to the charging roller drops.

Even when there is no spark discharge, the contact resistance increases due to the flow of current although the time speed is considerably slower than that during spark discharge.

This means that no voltage is applied, that is,
This is supported by the fact that the contact resistance remains almost unchanged when only sliding rotation is performed without passing an electric current.

The first object of the present invention is to solve the above-mentioned problems, and a predetermined voltage is applied to the charging member for a long period of time without deterioration of the voltage supplying means to the charging member. An object is to provide an image forming apparatus.

Further, in the conventional example 2, in the contact charging in which AC is superposed, a cycle mark is generated due to the AC ripple, so that the ripple interval should be at least 0.2 mm or less, preferably 0.15 mm or less. For example, if the moving speed of the photoconductor is 50 mm, 250 to 33
It becomes 0H _Z or more frequencies. In this state, even if a ripple of the cycle mark occurs on the electrostatic latent image, the cycle mark cannot be visually recognized because the responsiveness of development cannot be fully coped with if the resolution of the eyes is not so good.

However, if halftone reproduction is performed in this state, the pattern of the pixel block and the cycle mark generated on the electrostatic latent image may interfere with each other to cause moire. For example, in the spiral pattern as shown in FIG.
By the way, as shown in FIG. 16, a black line of 1 dot and 3 dots
It is equivalent to continuing the white line (1dot3space). FIG. 16 is a quarter of FIG. 15 for clarity.
Has been reduced to. Therefore, the repeating pattern of black lines is
In case of 300 dpi, 25.4 ÷ 300 × (1 + 3) =
It has a periodicity of 0.3387.

If the moving speed of the photoconductor is 50 mm, 50 ÷
0.3387 = 148H _Z near the 296H _Z of multiples thereof
Moire occurs in the vicinity.

From the experimental results of the applicant, the occurrence of moire is centered at the time when the repeating width of the image pattern coincides with the width of the cycle mark, and within ± 10% of the center,
It occurs twice as much. It is almost unrecognizable at 3 times.

From this, in the spiral pattern of the 4 × 4 pixel matrix, 1 dot 3 space, 2 dot
It is necessary to determine the AC frequency so that moire does not occur in 2 space and 3 dot 1 space.
The larger the pixel matrix, the more combinations there are, so it is necessary to escape it.

In order to prevent moire, the frequency of AC should be raised. However, in this case, the vibration of the contact due to AC produces a sound called charging noise. Charging noise 1KH _Z
It is unfavorable because the sound gradually becomes louder up to the rank, and becomes louder when it is higher than that, but the sound becomes uncomfortable.

If the frequency is increased, the toner is likely to be fused to the surface of the electrophotographic photosensitive member.

Therefore, it is necessary to keep the frequency as low as possible.

A second object of the present invention is to solve the above-mentioned problems, and an image forming apparatus which does not cause moire even at a low charging frequency for preventing the generation of charging noise and performs good halftone reproduction. To provide.

The AC contact charging method as in the conventional example 3 is effective as a means for uniformly charging the surface of the image bearing member, but has the following problems.

(1) Charging Sound An electric field is generated between the image carrier and the conductive member that is brought into contact with the image carrier by applying a voltage, and an electric force is generated. A
When an oscillating voltage is used as the applied voltage as in the C-contact charging method, the electric force of the oscillating voltage changes depending on the voltage change of the AC voltage component, causing vibration on the image bearing member, resulting in “charging noise”. See the generation of noise called. This charging sound is relatively offensive to the ears and is perceived as device noise.

(2) Fusing of toner To the contact portion between the photosensitive drum as the image bearing member and the charging roller as the conductive member, cleaning (not shown) is provided upstream of the charging roller in the rotation direction of the photosensitive drum. If an extremely small amount of toner that could not be completely removed from the surface of the photosensitive drum enters by the device, the mechanical and electrical force of the above vibration will rub them firmly against the surface of the photosensitive drum. The toner becomes a nucleus and gradually grows into a large spotted toner fusion. This toner fusion appears on the image as white spots on the black background or black spots on the white background, resulting in what is called an image defect.

A third object of the present invention is to solve the above-mentioned problems, and except during the image forming process, only a DC voltage is applied to the charging member to reduce the charging noise and to reduce the image. Another object of the present invention is to provide an image forming apparatus capable of preventing the fusion of the toner on the surface of the carrier.

As in the prior art example 4, a contact type charging roller to which an alternating voltage is applied vibrates microscopically on the charging roller 301 and the photosensitive drum 302, and a charging sound is generated. It is also clear that the fusion phenomenon as shown in FIG. 36 is accelerated. That is, to improve the fusion phenomenon in the charging device to which the alternating voltage is applied is an important subject to be examined from the viewpoint of improving the image quality.

Further, in the contact type charging roller to which an alternating voltage is applied, the cycle of the latent image due to the image exposure of the laser and the synchronization of the latent image potential on the photosensitive drum corresponding to the charging frequency interfere with each other, and those skilled in the art Is known to generate moire fringes. Although the countermeasure effect can be expected by increasing the charging frequency to eliminate this problem, the above-mentioned fusion occurs remarkably, and it was impossible to increase the frequency in reality.

With respect to the bias applied to the charging roller up to the present, the known technique is to apply a bias having a DC voltage alone or an alternating voltage superimposed in common to the image portion and the non-image portion. No application of different voltages is found in the non-image area.

A fourth object of the present invention is to solve the above problems and to provide an image forming apparatus which suppresses the generation of moire fringes and prevents the toner from being fused to the charging member. .

[0056]

In order to achieve the first object, a charging device according to the present invention is provided in contact with an object to be charged and rotates while rotating. A first voltage supply means for charging a charging member for charging a body to be charged, and a second voltage supply means for interposing a resistor higher than the first voltage supply means by one digit or more between the power source and the charging member. The image forming apparatus according to the present invention is provided with an image carrier and the image carrier in contact with the image carrier.
A first voltage supply unit for charging the image carrier while rotating and a second resistor having a resistor higher than the first voltage supply unit by one digit or more are provided between the power source and the charging unit. A process unit detachable from the image forming apparatus according to the present invention is provided with an image carrier, the image carrier, and the image carrier and the image carrier in contact with each other. While having a charging member for charging the image bearing member, a first supply means for supplying a voltage to the charging member, and a resistor higher than the first supply means by one digit or more are provided between the power source and the charging member. It is characterized by having an intervening second voltage supply means.

The operation is as follows. That is, by providing the first power feeding means and the second power feeding means in which the resistor between the power source by the first power feeding means and the charging member is higher than the resistance by one digit or more, the second power feeding means is provided in most cases. Since the current flows from the first power supply means, the second power supply means is hardly deteriorated by the current flow. Then, when a very small defect occurs in the first power supply means, spark discharge does not occur from that, and a current flows through the second power supply means. Therefore, deterioration due to spark discharge is prevented.

Further, even if the deterioration rate is slow but the resistance rises due to the flow of current, most of the power is usually supplied by the first power supply means. Therefore, the second power supply means is completely damaged. Absent. If the resistance of the first power feeding means gradually increases as the durability is increased in such a state (the resistance is partially increased), the proportion of power feeding from the second power feeding means increases. Therefore, even if the resistance of the first power feeding means increases, the first power feeding means and the second power feeding means may alternately receive their roles. Since the relationship with the power feeding means is only reversed, the life of the power feeding section is dramatically extended compared to the conventional case.

In order to achieve the second object, the image forming apparatus according to the present invention, as in claim 5, performs uniform charging on the surface of the electrophotographic photosensitive member by contact charging, and a blinking signal of light. In an image forming apparatus that forms an electrostatic latent image by imagewise exposing, develops with toner, transfers and fixes it, and obtains a printed image, the contact charging involves contacting portions extending in the main scanning direction of imagewise exposure. It has a direct current electric field and a repetitive oscillating electric field is superposed and applied between the contact portion and the electrophotographic photosensitive member to perform charging, and the pixel growth during halftone recording first grows in the sub-scanning direction. It is characterized in that it grows in the main scanning direction.

By the above means, during image formation, ozone is not generated, moire does not occur even at a low charging frequency, and halftone reproduction which is advantageous for charging noise and fusion is performed.

In order to achieve the third object, in the image forming apparatus according to the present invention, as in claim 6, a conductive member is brought into contact with the surface of the image carrier and a voltage is applied to the conductive member. By doing so, in an image forming apparatus equipped with a contact charging device for charging the surface of the image bearing member to a predetermined potential,
The voltage applied to the conductive member is an oscillating voltage obtained by superimposing an AC voltage on a DC voltage during the image forming step, and is only a DC voltage except during the image forming step.

By the means described above, at least during the image forming process, that is, during the pre-rotating process of the image carrier after the main switch of the apparatus is turned on, during the paper interval during continuous paper passage, and after the image forming process is completed. During the post-rotation process of the carrier, etc., the generation of the charging noise is suppressed, the device noise is minimized as a whole, and the voltage applied to the conductive member is adjusted as described above except during the image forming process. By using only the DC voltage, the vibration of the image carrier and the charging roller is suppressed, the chance that the charging roller strongly presses the toner against the surface of the photosensitive drum is reduced, and the toner fusion is suppressed.

In order to achieve the fourth object, the image forming apparatus according to the present invention has a charging area having a distance area in which the distance from the surface of the body to be charged increases as in claim 9. Image formation in which a member to be charged is charged by a member, and a voltage value equal to or higher than a charging start voltage value for the member to be charged is applied between the surface to be charged and the distance region of the charging member, and in particular, an oscillating electric field is applied to an image portion. In the device, in the non-image part and the image part,
The bias values applied to the distance regions are different values, and the maximum voltage of the non-image portion is lower than that of the image portion.

By the above means, it is possible to improve fusion and further increase the charging frequency for eliminating moire fringes.

[0065]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment according to claims 1 to 4 of the present invention.
6 to 6 will be described.

FIG. 1 is a schematic configuration of an example of an image forming apparatus using the contact type charging device according to the present invention as a primary charging means of an electrophotographic photosensitive drum (hereinafter referred to as a photosensitive drum) as an image carrier. Is shown. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process.

The photoconductor drum 1 is a photoconductor layer 1b (thickness, for example, 20 μm) made of an organic photoconductor layer (OPC) formed on the outer peripheral surface of a drum base body 1a made of a conductive material such as aluminum and grounded.
m) with a diameter of 30 mm, and a predetermined process speed (peripheral speed), for example 50, in the clockwise direction indicated by the arrow.
It is rotationally driven at mm / sec. Selenium, amorphous silicon, ZnO, or the like can be used as the photoreceptor layer.

Reference numeral 2 denotes a charging roller as a contact charging member, which is a conductive core metal 2a made of iron or the like as a base material (core material).
EPDM, which is an elastic layer integrally formed on the outer periphery of the
(Ternary copolymer of ethylene propylene diene) A conductive rubber roller portion 2b and a resistance layer 2c mainly formed of epichlorohydrin rubber formed on the outer periphery thereof.

The core metal 2a of the charging roller 2 has a power source 10
Thus, an oscillating voltage, which is a superimposed voltage of the negative DC voltage and the AC voltage, is applied. At this time, on the surface of the rotary photosensitive drum 1 that has been negatively charged by the charging roller 2, at a constant print density Ddpi corresponding to the time series electric digital pixel signal of the target image information output from the laser scanner 12. By scanning exposure with the image-modulated laser beam 5, the potential of the exposed portion is attenuated and an electrostatic latent image is formed on the surface of the photosensitive drum 1. To the latent image surface, the negatively charged toner is supplied from the developing sleeve 4 of the developing device 6 to reversely develop the latent image.

On the other hand, the transfer material P is fed from a paper feeding section (not shown) through the guide 7 to the contact nip portion (transfer section) between the photosensitive drum 1 and the transfer roller 8 as a transfer member.
The toner image on the surface of the photosensitive drum 1 is transferred to the transfer material P side by the transfer bias having a polarity opposite to the charging polarity of the toner applied from the power source 10 to the transfer roller 8 while being fed in time with the toner image on the surface. Are sequentially transferred (transcribed) to.

The transfer material P that has passed through the transfer portion is the photosensitive drum 1
It is separated from the surface and introduced into a fixing unit (not shown) to undergo image fixing, and is output as an image formed product (print).

After the transfer material is separated, the surface of the photosensitive drum 1 is cleaned by a cleaning device 9 to remove adhering contaminants such as untransferred toner, and is repeatedly used for image formation.

Reference numeral 11 is a control unit (CPU) for automatically setting the bias applying power source 10 for the charging roller 2 and the transfer roller 8 to a predetermined application timing and a predetermined potential.

The charging roller 2, the developing device 6, the cleaning device 9, and the photosensitive drum 1 serving as an image carrier are supported by the process unit 13. The process unit 13 is attachable to and detachable from a laser beam printer which is an image forming apparatus.
Is slid along the guide 14, that is, moved in the direction perpendicular to the paper surface of FIG. However, the process unit 13 may include at least the charging roller 4 and the photosensitive drum 1.

As shown in FIG. 2, the charging roller 2 is rotatably supported by bearings at both ends of a core metal 1a so that the longitudinal direction of the roller is substantially parallel to the generatrix direction of the photosensitive drum 1. The charging roller 2 is brought into contact with the surface of the photosensitive drum 1, and the bearings 3 on both ends of the roller are urged by the pressure springs 4 so as to be movable toward the photosensitive drum. There is. In this example, the spring constant of the pressure spring 4 is 0.08 kg / mm on one side. Also,
The applied pressure is 1 kg as a total pressure with 500 g of spring on one side. If the total pressure exceeds 1.5 kg, the roller 2
Since the friction of the drum 1 and the drum 1 becomes severe, 1.5 kg or less is preferable. In the case of this example, the charging roller 2 is driven to rotate as the photosensitive drum 1 is rotationally driven.

A bias power source 10 is provided on the charging roller 2.
From the first voltage supply means 41 having a predetermined bias voltage having a spring property such as stainless steel and the same material configuration as the first voltage supply means, but with the second voltage supply means 42 via the resistor 42a. The peripheral surface of the photosensitive drum 1 which is rotationally driven by being applied by is charged with a predetermined polarity and potential. In the case of this example, it is not charged. Charging roller 2
Oscillating voltage is a superposed voltage sinusoidal alternating voltage of summer 1400V _pp ~2000V _pp between the DC voltage -600V and the peak from a bias power source 10 is applied to. Here, if the peak-to-peak voltage of the oscillating voltage is less than twice the charging start voltage value of the photoconductor drum 1 that is the member to be charged, spot-like charging unevenness occurs on the photoconductor drum 1, so that uniform charging is performed. It is desirable that the charging start voltage value is twice or more. This charging start voltage is defined as follows.

That is, when only the direct current voltage is applied to the contact charging member with respect to the charged body having a potential of 0 and gradually increased, the photosensitive drum which is the charged body corresponding to the applied DC voltage is applied. Try to write a graph of surface potential. At this time,
DC voltage is taken every 100V, but 100V is the first point when the surface potential appears when the surface potential is 0.
Take 10 points for each. From these 10 points, the minimum 2 in statistics
A straight line is drawn by multiplication, and the value of the applied DC voltage when the surface potential is 0 on this straight line is the charging start voltage.

When the photosensitive drum 1 having the organic photoconductive layer of this embodiment was used as the member to be charged, the charging start transfer voltage value was 560V.

Next, the charging device will be described in detail.

The contact resistance between the first voltage supply means and the core of the charging roller is approximately 0Ω. The contact resistance at the contact portion between the second voltage supply means and the core of the charging roller is approximately 0Ω.
However, the resistor 42a is interposed between the power source 10 and the contact portion. This resistance value is suitably in the range of 10Ω to 500 kΩ, and the resistance of 10 kΩ was used in the first embodiment. When a voltage is applied in this state, most of the current flows from the first voltage supply means 41 side and 1/2 from the second voltage supply means side.
Only about 10,000 flows.

<Comparative Example> FIG. 5 shows a comparative example. In FIG. 5, the same members as those in FIG. 2 are designated by the same reference numerals, and the configuration thereof is substantially the same as that of the first embodiment. However, in this comparative example, the voltage supply means is the same as that of the first embodiment. Only one voltage supply means was used.

At this time, the contact resistance between the voltage supply means and the core of the charging roller is approximately 0Ω.

Image evaluation and durability evaluation (20,000 sheets) were carried out in the image forming apparatus described in the section of Examples using the respective charging devices according to the above Examples and Comparative Examples.
The results are shown in Table 1.

[0084]

[Table 1]

As is clear from the above results, in the example, the resistance value reached through the second voltage supply means even after the endurance of 20000 sheets, and it was very stable as compared with the comparative example. Recognize.

FIG. 3 shows another embodiment of the present invention, in which the first voltage supply means 41 is the same as in the first embodiment.

The second voltage supply means brings the polyacetal 43 in which carbon is dispersed into pressure contact with the core metal 2a of the charging roller 2. This polyacetal 43 controls the resistance value to 10 ² to 10 ³ Ω by dispersing carbon.

With the above arrangement, the charging roller 2 is pressed against the second voltage supply means 43 by the force applied in the axial direction by the first voltage supply means 41.

By doing so, the position of the charging roller 2 is accurately determined in the axial direction, and since there is no resistance, the productivity is good and the cost is reduced.

When the same evaluation as the above was carried out using the above apparatus, the same effect as that of the above example was confirmed by the initial and durability tests.

FIG. 4 shows still another embodiment of the present invention,
From the power supply 10 through the conductive pressure spring 51, carbon is dispersed in the polyacetal, and the first means for supplying power from the bearing 52 whose resistance is controlled to 0 to 10 ² Ω and the conductive means on the opposite side in the axial direction. Second means for supplying electric power from the bearing 53 whose resistance is controlled to 10 ³ to 10 ⁵ by dispersing carbon in polyacetal via the pressure spring 51.

With the above configuration, a bearing and an electrode can be used in common, productivity and cost are excellent, and a high-performance device having the first and second power feeding means intended by the present invention is realized. Was done.

The above charging device can also be applied to a transfer charging device which is a device for contact-charging the back surface of the transfer material P.

Next, an embodiment according to claim 5 of the present invention will be described with reference to FIG.
16 to 16 will be described.

FIG. 7 is a block diagram of an electrophotographic printer as an image forming apparatus of the present invention.

Reference numeral 101 denotes an electrophotographic photosensitive member, in which a photosensitive material such as OPC, amorphous Se or amorphous Si is formed on a cylinder-shaped or belt-shaped substrate such as aluminum or nickel. Since it is often cylindrical, it is called a photosensitive drum. The charging roller 102 uniformly charges the photosensitive drum 101. Then, the laser scanner 103 laser scans the image signal to expose it. The laser scanner 103 scans the blinking of the semiconductor laser with a polygon scanner, and forms an image on the photosensitive drum by an optical system. This creates an electrostatic latent image. The formed electrostatic latent image is developed by the developing device 104. Development is jumping development, two-component development, FE
ED development or the like is used, and when recording, image exposure in which a laser is turned on to eliminate the electric charge of the latent image and reversal development in which toner is attached to the less charged electric charge are often used in combination.

The developed image is transferred to a transfer material.
The transfer material is stored in the cassette 105 and is fed one by one by the paper feed roller 106. When a print signal is sent from the host, paper is fed by the paper feed roller 106, and the timing roller 107 causes the transfer roller 8 to transfer the toner image onto the transfer material in synchronization with the image signal. The transfer roller 108 is an electrically conductive elastic body having a low hardness, and is electrostatically transferred by a bias electric field in a nip portion formed by the photosensitive drum 1 and the transfer roller 108.

The transfer material on which the image is transferred is the fixing device 109.
The paper is fixed on the paper and is sent by the paper ejection roller 110, and the paper ejection tray 1
It is discharged to 11. On the other hand, the toner remaining after the transfer is cleaned by the cleaner 112 by the blade.

FIG. 8 shows a contact charging device.

Reference numeral 101 is an electrophotographic photosensitive member. A charging roller 102 includes a core metal 121, an elastic layer 122, and a surface layer 1.
It consists of 23.

The core bar 121 is made of iron, aluminum, stainless steel,
And so on. The elastic layer 122 is made by adding carbon or a metal oxide such as TiO ₂ or ZnO to a solid or foamed solid elastic body such as urethane, silicon rubber or EPDM to have a volume resistance of 10 ¹⁰ to 10 ¹³ Ωcm. is there.

The surface layer 123 is a synthetic resin film in which nylon resin such as resin, polyethylene, polyester, fluororesin, polypropylene or the like is made conductive. It is desirable that the resistance value be equal to or higher than the resistance of the inner elastic body. As a result, even if there are pinholes on the surface of the electrophotographic photosensitive member, the electric current is not concentrated and does not flow.

Electrophotographic photosensitive member 101 and charging roller 102
Between them, the oscillating electric field (A
C) is applied, and the charging of the surface of the electrophotographic photosensitive member converges to a voltage substantially equal to the DC voltage. The oscillating electric field is a rectangular wave, a triangular wave, a pulse wave, a sine wave, etc., and has a frequency of 10
0~1000H _Z is used.

In the present invention, halftone reproduction is performed by growing pixels in the sub-scanning direction first and then in the main scanning direction as shown in FIG. Therefore, as shown in FIG. 10, the relevance of pixels in the main scanning direction disappears, and the relevance in the sub scanning direction becomes stronger. FIG. 10 is reduced to a quarter of FIG. 9 for clarity. Therefore, 1 dot3space,
The charging frequency may be determined in consideration of the basic 1-dot repeating pattern without considering 2dot2space and 3dot1space.

In the case where the pixel matrix is 8 × 8, similarly, the charging frequency may be determined in consideration of the basic repeating pattern of 1 dot, so that moire can be avoided without considering the size of the pixel block.

FIG. 11 shows another embodiment of the present invention. The elastic blade 113 is used as the contact charging device. The elastic blade is an elastic body such as urethane rubber or silicon rubber and has a volume resistance of 10 ¹⁰ to 10 ¹³ Ωcm.
Like the roller charging, AC and DC are superposed on the blade 113. The configuration of the printer itself is the same as that of the above embodiment. To reproduce halftone, a pixel matrix that grows first in the sub-scanning direction and then grows in the main-scanning direction is used, as in the above embodiment. This eliminates the need to avoid moire in consideration of the combination of pixel matrices, and by using a blade, charging can be carried out at a low cost, with almost no generation of ozone, little charging noise, and no problem of fusion.

Another embodiment of the present invention will be described.

FIG. 12 shows a halftone pattern of another embodiment. In this embodiment, 1 × 2 pixels are set as one block, and one block is divided into 10 equal parts. That is, one pixel is divided into five equal parts in the main scanning direction. Such a process can be performed by a time modulation method in which the light emission time corresponding to each density signal is recorded in a table and light is emitted only for that time, a pulse width modulation method (PWM), or the like.

In the laser beam printer, such processing can be performed because the laser spot moves in the main scanning direction by raster scanning.

According to this, the halftone can be represented by the thickness of the line in the sub-scanning direction as shown in FIG.
Moire can be avoided by determining the charging frequency in consideration of the dot repeating pattern. FIG. 13 has been reduced to a quarter of FIG. 12 for clarity.

The present embodiment is effective even for a system such as an LED printer or a liquid crystal printer in which one pixel cannot be subdivided or a laser beam printer in which resolution is poor and the pixel cannot be subdivided. In this case, which is a characteristic of reproducing an electrophotographic image, one pixel is not subdivided and is expressed as an intermediate density as shown in FIG.

In this embodiment, halftones can be reproduced without enlarging the pixels and the pattern in the sub-scanning direction is emphasized. Therefore, light and shade appear in the sub-scanning direction, such as pitch unevenness and uneven rotation of the electrophotographic photosensitive member. The feature is that unevenness is less noticeable.

Next, an embodiment according to claims 6 to 8 of the present invention will be described with reference to FIGS.

FIG. 17 is a diagram showing another embodiment of the image forming apparatus according to the present invention. The image forming apparatus shown in this embodiment is a laser beam printer by an electrophotographic process using a roller type contact charging device as a charging device for an image bearing member.

In FIG. 17, reference numeral 201 denotes a photosensitive drum as an image bearing member, which comprises a substrate 201a made of aluminum having a thickness of 1 mm and an organic photosensitive layer 201b formed on the outer peripheral surface of the substrate 201a. Is 30m
At m, it is rotationally driven in the direction of arrow A at a predetermined peripheral speed V _P (process speed) of 50 mm / sec.

Reference numeral 202 denotes a charging roller as a contact charging member, which is composed of a conductive cored bar 202a made of SUS and a conductive elastic layer 202b made of urethane rubber containing carbon formed on the outer peripheral surface thereof. Outer diameter is 12m
m, and both end portions in the longitudinal direction of the conductive cored bar 202a are pressed against the surface of the photosensitive drum 201 by spring members (not shown) and are driven to rotate.

A predetermined voltage is applied to the charging roller 202 by a high voltage power source 203 through a contact leaf spring 204, so that the surface of the photosensitive drum 201 is charged to a predetermined potential, for example, -650V.

Reference numeral 205 denotes a laser beam scanner, which outputs a laser beam 205a which is image-modulated at a constant print density in response to a time-series electric digital pixel signal of a target image input from a host device (not shown). The surface of the photosensitive drum 201 that has been charged as described above is subjected to main scanning exposure with the laser beam 205a output from the laser beam scanner 205 controlled by the controller, so that the surface of the photosensitive drum 201 corresponding to the target image information is statically exposed. A latent image is formed.

Next, this electrostatic latent image is developed by the developing device 206 with the negatively charged toner, and the developed image is transferred onto the transfer material 208 which is introduced into the transfer device 207 at a predetermined timing from a paper feeding unit (not shown). Will be transcribed.

The transfer material 208 that has passed through the transfer device 207 is separated from the surface of the photosensitive drum 201 and is conveyed to a fixing device (not shown). The surface of the photosensitive drum 201 after the image transfer is cleaned by the cleaning device 209 by removing adhered contaminants such as transfer residual toner, and is repeatedly used for image formation.

Now, the voltage applied to the charging roller according to the present invention will be described in detail.

In the conventional image forming apparatus, the transfer material may or may not pass between the photosensitive drum and the transfer device while the main motor is driven and the photosensitive drum as the image carrier is rotationally driven. However, the charging roller always has a DC voltage of, for example, -650V and an AC voltage of, for example, 2000V.
_PP, oscillating voltage is applied by superimposing the 500H _Z.
In other words, after turning on the main switch, during the pre-rotation process to stabilize the potential on the surface of the photosensitive drum, during the paper interval during continuous paper feeding, toner attached on the surface of the photosensitive drum after image formation, etc. During the post-rotation process for removing the adhered substances, the oscillating voltage obtained by superimposing the AC voltage on the DC voltage is always applied to the charging roller. This state is shown in FIG.
It will be specifically described with reference to the timing chart shown in FIG.
The timing chart of this example shows an example of two consecutive printouts.

According to this, while the main motor is driven and the photosensitive drum is rotationally driven, the oscillating voltage in which the AC voltage is superimposed on the DC voltage is always applied to the charging roller, and during this period, the oscillating voltage is always applied. An offensive charging sound is generated, and an extremely small amount of toner that causes toner fusion is struck on the surface of the photosensitive drum.

Therefore, in order to minimize the charging noise and suppress the occurrence of toner fusion, the voltage applied to the charging roller is set to the DC voltage −6 during the image forming process.
To 50 V, and an AC voltage 2000V _PP, oscillating voltage obtained by superimposing 500H _Z, except in time of image formation process, by only a DC voltage -650 V, may do it by minimizing the vibration of the photosensitive drum.

However, a new problem arises here. That is, when the voltage applied to the charging roller except during the image forming step is only the DC voltage of −650V, the surface of the photosensitive drum is charged only to about −100V, and due to the uneven charging, the surface of the photosensitive drum is charged. Toner adheres. The transfer material does not pass between the photosensitive drum and the transfer device while the photosensitive drum is rotationally driven except during the image forming process. And the transfer function is deteriorated, and back stain occurs at the time of image output. Such a problem is more serious in a transfer device including a contact transfer member such as a transfer roller. For this reason, it is necessary to charge the surface of the photosensitive drum within a range in which the transfer device is not contaminated even while the photosensitive drum is rotationally driven except during the image forming process.

Therefore, FIG. 19 shows the experimental results regarding the applied voltage and the charging potential on the surface of the photosensitive drum when only the DC voltage is applied to the charging roller. According to this, when the DC voltage applied to the charging roller is −550V or less, the surface of the photosensitive drum is not charged, and in order to charge the surface of the photosensitive drum to approximately −650V, the DC voltage is applied to the charging roller. A voltage of -1200V must be applied. At this time, the surface of the photosensitive drum is charged to about -650V,
Since the AC voltage is not superposed, slight uneven charging occurs, but it does not lead to contamination of the transfer device.

[0127] Therefore, in this embodiment, the voltage applied to the charging roller, at the time of image forming process, an AC voltage 2000V _PP into a DC voltage -650 V, and the vibration voltage obtained by superimposing 500H _Z, except during image formation process In
Only DC voltage -1200V was used.

Here, experimental results regarding charging noise and toner fusion will be shown.

First, regarding the charging sound, under the above conditions, the image forming apparatus is installed in an anechoic room with a background noise of 30 dB or less, and when the apparatus is operated by a noise meter at a distance of 1 m from the front of the image forming apparatus. The sound pressure was measured to be 45 dB during the pre-rotation process, the paper interval, and the post-rotation process.
It was 57 dB in the image forming step. On the other hand, as in the conventional image forming apparatus, while the photosensitive drum is rotationally driven, the AC voltage is always superposed on the DC voltage to the charging roller regardless of the image forming process and other than the image forming process. When the oscillating voltage was applied, a sound pressure of 57 dB was always observed.

According to this result, in the image forming apparatus according to the present invention, the sound pressure can be reduced by 12 dB in the pre-rotation step, the sheet interval, and the post-rotation step as compared with the conventional image forming apparatus. It has been done.

Next, regarding toner fusion, a paper passing durability test of the image forming apparatus was conducted under the above conditions. As a result, almost no toner fusion was found on the surface of the photosensitive drum even after 6000 sheets had passed. It was not confirmed, and there was no effect on the image. On the other hand, as in the conventional image forming apparatus, while the photosensitive drum is rotationally driven, the AC voltage is always superposed on the DC voltage to the charging roller regardless of the image forming process and other than the image forming process. When the oscillating voltage was applied, a small amount of toner was fused on the surface of the photosensitive drum after about 3000 sheets had passed, and after 4000 sheets had passed, the adverse effect appeared on the image.

From the above results, according to the configuration of the present invention,
It is possible to minimize the charging noise and prevent toner fusion.

FIG. 20 shows an example of a switching timing chart of the voltage applied to the charging roller according to the present invention. The timing chart of this example shows an example of two consecutive printouts. First, when the main switch of the image forming apparatus is turned on, the pre-rotation step starts, and the photosensitive drum starts to rotate. Then voltage is applied to the charging roller,
The charging of the surface of the photosensitive drum is started. The applied voltage at this time is only DC voltage -1200V. After that, the developing bias and the transfer bias are applied to the developing device and the transfer device, respectively, and the image forming process is started. After the pre-rotation step,
The laser emits light in response to the image signal, and an electrostatic latent image is formed on the surface of the photosensitive drum. In the image forming apparatus shown in this embodiment, the photosensitive drum rotates from the charging device to the laser irradiation position. It takes about 0.12 seconds.
Therefore, the charging roller enters the image forming process about 0.12 seconds before the image signal, and before that, it is necessary to switch the voltage applied to the charging roller to the oscillating voltage in which the AC voltage is superimposed on the DC voltage. is there. Therefore, in this embodiment, the voltage applied to the charging roller is switched 0.22 seconds before the image signal. After that, the voltage applied to the charging roller may be switched to only the DC voltage again in synchronization with the completion of the image forming process of the charging roller. This timing is, when the length of the transfer material in the transport direction is Lmm,
This is after a lapse of L / _VP seconds from the time when the charging roller enters the image forming process. In the present embodiment, it was set to L / V _P +0.2 seconds after the charging roller entered the image forming process.

Another embodiment of the present invention will be described below. The basic structure of the photosensitive drum as the image carrier and the charging roller as the contact charging device, and the switching of the voltage applied to the charging roller. The timing is the same as that shown in the above embodiment.

In the embodiment according to FIG. 18, the surface of the photosensitive drum is charged by keeping the DC voltage applied to the charging roller constant except during the image forming step. However, in this embodiment, the photosensitive drum surface is charged at any time. It is characterized in that the film thickness of the organic photosensitive layer is detected by a film thickness detecting means, and the DC voltage applied to the charging roller is varied and controlled based on the detection.

Here, the experimental results according to the present embodiment will be shown.

FIG. 21 shows the relationship between the DC voltage applied to the charging roller and the current.

According to this, there is a proportional relationship between the DC voltage applied to the charging roller and the current, and the inclination and the intercept with respect to the voltage axis, that is, the charging start voltage of the surface of the photosensitive drum is It can be seen that it depends on the film thickness of the organic photosensitive layer. That is, a DC voltage, for example, -10
00V and -1500V are applied, the charging start voltage is calculated by detecting the current value at this time, and a DC voltage obtained by adding a predetermined photosensitive drum surface potential -650V to this value is applied to the image forming apparatus. Even when the organic photosensitive layer of the photosensitive drum is worn out for a long time, the surface potential of the photosensitive drum can be always charged to a predetermined potential of −650 V except during the image forming process.
It is possible to prevent contamination of the transfer device as described above.

FIG. 22 shows the configuration of the image forming apparatus according to the present invention, and FIG. 23 shows a timing chart for switching the voltage applied to the charging roller. First, when the main switch of the image forming apparatus is turned on, the pre-rotation process starts, and the photosensitive drum 2
01 starts rotating.

At the same time, a DC voltage of -1000V is applied to the charging roller 202 by the high voltage power source 203 for 0.2 seconds, and the current value I ₁ at this time is detected by the current detection circuit 210. Then, the charging roller 20 is driven by the high voltage power source 203.
A direct current voltage of -1500 V is applied to No. 2 for 0.2 seconds, and the current value I ₂ at this time is detected by the current detection circuit 210. The current values I ₁ and I ₂ detected in this way are input to the arithmetic circuit 211, and immediately the photosensitive drum 2 at this time is input.
The charging start voltage V _{TH of} 01 is calculated. This result is fed back to the high voltage power supply 203, and this value is -650V.
Is output DC voltage V _a obtained by adding the photosensitive drum 201 surface other than the image forming process is charged to a predetermined potential -650 V.

This series of detection and control is preferably performed during the pre-rotation step. The subsequent timing chart is the same as that shown in the above-mentioned embodiment, and the description thereof is omitted.

Another embodiment according to the present invention will be described below. The basic structure of a photosensitive drum as an image carrier and a charging roller as a contact charging device, and a voltage applied to the charging roller will be described. The switching timing is the same as that shown in the embodiment according to FIG.

In the above-described embodiment, the surface of the photosensitive drum is charged by setting the DC voltage applied to the charging roller during the image forming process higher than the DC voltage applied to the charging roller during the image forming process. However, in the present embodiment, the DC voltage applied to the charging roller has the same value during the image forming process in which the AC voltage is superposed and during the image forming process in which the AC voltage is not superposed, and instead, the image forming process is performed. Other than the time, at least the DC voltage of the developing bias applied to the developing device is set lower than the DC voltage applied to the charging roller.

That is, during the image forming process, a DC voltage of −650 V and an AC voltage of 200 are applied to the charging roller.
0V _PP, but charging the photosensitive drum surface to a predetermined potential -650V by applying an oscillating voltage obtained by superposing an 500H _Z, except in time of image formation process, for applying only a DC voltage -650V to the charging roller Moreover, the surface of the photosensitive drum is charged only to about -100V. In such a state, when a developing bias including at least a DC voltage, for example, −450 V is applied to the developing device as in the conventional image forming apparatus, the toner adheres to the surface of the photosensitive drum as described above. This will contaminate the transfer device.

Therefore, in this embodiment, the DC voltage component contained in the developing bias is lower than the surface potential of the photosensitive drum, for example, −, except during the image forming step in which only the DC voltage is applied to the charging roller. It is set to 50V.

FIG. 24 shows an example of a switching timing chart of the voltage applied to the charging roller and the developing bias applied to the developing device according to the present invention. The timing chart of this example shows an example of two consecutive printouts. First, when the main switch of the image forming apparatus is turned on, the pre-rotation step starts, and the photosensitive drum starts to rotate. Subsequently, a voltage is applied to the charging roller to start charging the surface of the photosensitive drum. The applied voltage at this time is only a DC voltage of -650V. After that, the developing bias and the transfer bias are applied to the developing device and the transfer device, respectively. Before the image forming process, at least the DC voltage of the voltage applied to the developing device is set to −50V. After the pre-rotation step, the laser emits an image signal to form an electrostatic latent image on the surface of the photosensitive drum, and the developing device develops the toner. However, in the image forming device shown in this embodiment, It takes about 0.42 seconds for the photosensitive drum to rotate from the laser irradiation position to the developing device. Therefore, the developing device enters the image forming process for about 0.42 seconds from the image signal, and the DC voltage applied to the developing device before this is set to the set value −4 during the image forming process.
It is necessary to switch to 50V. Therefore, in this embodiment, the voltage applied to the developing device is switched 0.32 seconds after the image signal. After that, the voltage applied to the developing device may be switched again to the set value −50 V other than during the image forming process in synchronization with the end of the image forming process of the developing device. This timing is after L / V _P seconds or more has elapsed from the time when the developing device entered the image forming step, when the length of the transfer material in the transport direction was L mm. In the present embodiment, it was set to L / V _P +0.2 seconds after the developing device entered the image forming step.

When an oscillating voltage obtained by superimposing an AC voltage on a DC voltage is used as the developing bias applied to the developing device, the DC voltage applied to the developing device is not applied during the image forming process according to this embodiment. The alternating voltage superimposed on this may be turned off in synchronization with the switching of the value.

Next, an embodiment according to claims 9 to 16 of the present invention will be described with reference to FIGS.

Another embodiment of the present invention will be described with reference to FIGS.
33 and 3 in this embodiment.
Members having the same functions as those of the conventional example shown in FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted for simplification.

FIGS. 26 and 27 show another embodiment of the present invention, and FIG. 26 is a drawing which best shows the features of the present invention and is a schematic view of the image forming apparatus of this embodiment. In the figure, 305a is a high-voltage power supply that generates a DC voltage, 305b
Is a high-voltage power supply that generates a voltage obtained by superimposing an AC voltage on a DC voltage. In each of the power supplies, the DC voltage is a constant voltage power supply, and the AC power supply used for 305b is a constant current power supply.

Further, 304 is the above-mentioned 305a and 305b.
Is a control device for switching-controlling the high-voltage power supply of 305 a, 30
It is a mechanism that can control 5b.

Here, the DC power supplies 305a and 305b can output with independent voltage values.

FIG. 27 shows the main sequence of the image forming apparatus in this embodiment. It is characteristic that the charging bias is divided into two as compared with the conventional example shown in FIG. Here, the charging (a) in the figure corresponds to the DC high-voltage power supply 305a in FIG. 26, and the charging (b) in FIG.
AC high-voltage power supply 305b on which the DC voltage in 6 is superimposed
The sequence is equivalent to.

The DC high-voltage power supply 305a and the DC superimposing AC high-voltage power supply 305b are controlled by the control device 304 shown in FIG. 26 as in the sequence charging (a) and charging (b) shown in FIG. That is, high voltage application of only direct current is applied during the pre-rotation and the space between sheets, and in the image area, an alternating voltage to which direct current is applied is applied. Next, the effect of this example will be described based on a comparative example.

The main items of the experimental example in this example are as follows.

<Experimental Example Items> Process speed = 47.1 mm / s (drum diameter 30 m
m) Paper interval = 50.0 mm Pre-rotation / paper interval DC voltage = -1270V Image area DC voltage = -720V Image area AC current = 500μA (V _PP = 1 at this time)
600 V) / sine wave Charging frequency (image area) = 500 Hz _Z paper passing size A4 = 297 mm <Comparative example 1> Process speed = 47.1 mm / s (drum diameter 30 m
m) Paper interval = 50.0 mm Pre-rotation / paper interval / image area = AC + DC control DC voltage = −720V AC current = 500 μA (V _PP = 1 at this time)
600 V) / Sine wave AC frequency = 500 Hz _Z paper size A4 = 297 mm <Comparative example 2> Process speed = 47.1 mm / s (drum diameter 30 m
m) Paper interval = 50.0 mm Pre-rotation, paper interval, image area = DC control DC voltage = -1270 V Paper size A4 = 297 mm Note that the toner used here is a one-component magnetic toner and has a negative polarity and reverse development. A laser beam printer using the system was used.

The developing method used is a jumping phenomenon, and V _PP = 1600 V V _fr = 1800 H _{Z VDC} = −50
It is 0V.

Further, in the present embodiment, the control is changed between the sheet interval and the image area as shown in the sequence of FIG. 27, but at the developing position, both are substantially equal, dark potential V _D = -70.
I was able to control it to 0V. Here, the bright potential V _L = −150V.

In this example, the following items were compared with the comparative example.

1. Image roughness (characters, fine lines, density uniformity) 2.35 ° C., 90% RH (high temperature / high humidity) toner drum fusion fusion Here, with respect to 2 here, continuous durability up to 4000 sheets under the above environment The results are shown in Table 2 on the next page.

[0161]

[Table 2]

As is clear from Table 2, this embodiment is The image roughness is equivalent to that when an AC + DC bias is continuously applied to the charging roller. Regarding 2.35 ° C. and 90% RH toner fusing, it is closer to the case where the DC bias is continuously applied to the charging roller, and is considerably improved as compared with the case where the AC + DC bias is continuously applied. I understand. Where Δ in Table 2
The level is a level where practically no problem occurs.

It is obvious to those skilled in the art that this fusion phenomenon occurs remarkably only under a high temperature and high humidity environment, and that a lower image ratio tends to occur.

Regarding the paper-passing mode, the larger the amount of heat radiated onto the drum (mainly from the fixing device), the more noticeable it is. Therefore, in the image forming apparatus having the structure as shown in FIG. 28, for example. In some cases, the one-sheet intermittent sheet feeding mode is more remarkable than the continuous mode. It is considered that the above facts depend on the amount of heat received by the drum between sheets and how much the vibration when the AC + DC bias is applied to the charging roller is received by the drum.

Table 3 shows the image forming apparatus having the structure as shown in FIG. 28, in which the effects of the present embodiment are examined with respect to the above-mentioned examples.

[0166]

[Table 3]

Another embodiment of this embodiment is shown in FIGS.
9 will be described. In this embodiment, a bias is applied to the charging roller 301 in the sequence shown in FIG. 29 by using the charging bias printing device shown in FIG.

That is, in the process of pre-rotation and shifting from the sheet interval to the image area, the output of the DC voltage power supply 305a in FIG. 26 is gradually decreased, and the output of the DC + AC voltage high voltage power supply 305b is correspondingly increased. It has a feature. Here, the process speed, the charging frequency, and the maximum value of each high-voltage power source are the same as those in the above embodiment.

The transition process of the high voltage output, which is a feature of this embodiment, is 10 msec to 1 sec.

In this way, the image area starts after the output of the DC + AC high voltage power supply 305b rises, and image exposure is performed.

By gradually switching the high pressure in this way,
Microscopically, no abrupt change in latent image potential occurs due to switching switching, and switching memory does not occur in the image area. (The memory here is a memory on the drum that occurs after one round of the switching drum.) Similarly, the effect of this embodiment is established even in the process of shifting from the image area to the space between sheets. The other effects are the same as those in the above-mentioned embodiment.

Yet another embodiment of the present invention will be described. In this embodiment, the image forming apparatus shown in FIG. 28 is performed in the sequence shown in FIG.

The feature of the present embodiment is that a bias of AC + DC is applied to the charging roller for a fixed time during the pre-rotation or the paper interval, and the DC voltage is applied after the elapse of the fixed time until the time corresponding to the pre-rotation or the paper interval. Is applied to the charging roller.

The certain period of time referred to here is, for example, a period of time corresponding to one round of a cylindrical photosensitive drum, or a period of time corresponding to one round of a transfer roller when a transfer roller (not shown) is used.

The former example is effective in completely erasing the memory on the characteristic of the photosensitive drum, and the latter case is effective in completely erasing the influence of the memory of the transfer roller between the sheets. is there.

3 for this example and the comparative example which is a conventional example
Comparison was carried out at 5 ° C. and 90% RH. Details of each example are as follows.

Experimental Example (1) Process speed: 47.1 mm / s (2) Mode: 3 sheets / min (3) Paper size: A4 (= 297 mm) (4) Paper interval: DC after AC + DC charging charging AC + DC charging: 2 seconds _{· V PP / V fr: 1200V} / 500H Z (i AC
= 375μA) / sine wave · V _DC: -700V _DC charge: about 11 seconds · V _DC: -1270V (5) image area: AC + DC charging AC bias: 1600V / 500H _Z (i _AC
= 500 μA) / Sine wave DC bias: −700 V (Comparative example) (1) Process speed: 47.1 mm / s (2) Mode: 3 sheets / min (3) Paper size: A4 (= 297 mm) (4) inter-sheet-image areas both: AC + DC charging _{V PP / V fr: 1600V /} 500H Z (i AC = 5
00 μA) / sine wave _VDC : −700 V Under the above conditions, image development was performed under the same developing conditions as in the above-mentioned Examples, and evaluation was performed. The results are shown in Table 4.

[0178]

[Table 4]

Here, in order to make the phenomenon noticeable, the image memory was evaluated under a higher bias than the normal transfer condition. The environment in which the image memory was evaluated was 10 ° C 10
% RH.

In this embodiment, AC + D is applied to the charging roller between the sheets.
When C was applied, the AC bias value was made lower than the AC bias value in the image area. However, it is not limited to the value of this embodiment, and the above-mentioned effect is recognized. AC bias value of

Further, in the present embodiment, the time for applying the inter-sheet bias value between the sheets is the time corresponding to one round of the drum, but it is not limited to this.

Another embodiment of the present invention will be described. A schematic view of the image forming apparatus used in this embodiment is shown in FIG. Reference numeral 350 is a high-voltage power supply for applying a bias to the charging roller 301, and 351 therein is an AC voltage generating portion, of a type whose output and frequency can be changed by a control CPU of an image forming apparatus (not shown). Again 352
Is a direct current high voltage generating portion, and similarly the output can be arbitrarily changed by the control CPU of the image forming apparatus. FIG. 3 shows a control sequence relating to the present embodiment of FIG.
It is 2.

The feature of this embodiment is that the charging frequency in FIG. 32 is changed between the paper interval and the image area.

Particularly effective in this embodiment is a medium-speed high-resolution printer. This is because the latent image due to image exposure and the moire interference due to the charging frequency occur as the resolution becomes higher at a higher speed, and the charging frequency is raised to eliminate this.

For this reason, the above-mentioned drum fusion occurs remarkably, and both the moire and the drum fusion are practically satisfied.

The present invention has been made in view of this situation, and takes the sequence of FIG. 32 as an example. The effects will be described below in comparison with the present example and the comparative example.

[0187] (common conditions) process speed: between 94.2mm / s · paper: 100mm (= 1.06 seconds) Resolution: 600DPI <Experimental Example> (1) paper between the conditions charging frequency: 500H _Z / sine wave Charging i _AC : 500 μA (= 1600 V _PP ) Charging _VDC : = −700 V (2) Image area condition Charging frequency: 1000 Hz _Z charging i _AC : 1000 μA (= 1600 V _PP ) Charging _VDC : = −700 V <Comparative example 1> inter-sheet-image areas common charging frequency: 500H _Z / sine wave charging _{i AC: 500μA (= 1600V PP} ) charging V _DC: = - 700V <Comparative example 2> inter-sheet-image areas common charging frequency: 1000H _Z / sine wave Charge i _AC : 1000 μA (= 1600 V _PP ) Charge _VDC : = −700 V For each of the above examples, moire fringes occurred, 35 ° C., 90% RH
Table 5 shows the results of the evaluation of the drum fusion of the toner in the above.

[0188]

[Table 5]

That is, as shown in the present embodiment, by changing the charging frequency between the paper and the image area as in the present invention, the toner fusing on the drum is performed without degrading the performance of the image area related to moire. It is possible to reduce the occurrence of.

In the above embodiments, the charging roller is used as an example of the contact type charging device, but a brush type or blade type charging device may be used.

As the bias power supply for applying to the charging device, the constant voltage type was used for the DC voltage and the constant current type was used for the AC voltage in the embodiments, but the present invention is not limited to this. it is obvious. Further, it goes without saying that a transfer device such as a transfer roller type or a transfer belt type can be used without depending on the developing device and the polarity of the toner.

[0192]

As described above, according to the first to fourth aspects of the invention, the first voltage applied to the charging member which is provided in contact with the charged body and charges the charged body while rotating. By having the second voltage supply means in which the supply means and the resistor higher than the first voltage supply means by one digit or more are interposed between the power source and the charging member, there is no power supply failure due to long-term durability. Therefore, a stable image can be obtained.

According to the fifth aspect of the invention, the surface of the electrophotographic photosensitive member is uniformly charged by contact charging, and an electrostatic latent image is created by imagewise exposing a flashing signal of light to develop it with toner. In an image forming apparatus for transferring, fixing, and obtaining a printed image, the contact charging has a contact portion extending in the main scanning direction of image exposure, and a repetitive vibration is generated in a DC electric field between the contact portion and the electrophotographic photosensitive member. The electric field is charged by superimposing and applying an electric field. The growth of pixels at the time of halftone recording is such that ozone grows first in the sub-scanning direction and then in the main-scanning direction. In addition, moire does not occur even at a low charging frequency, and halftone reproduction that is advantageous for charging noise and fusion can be performed.

According to the sixth to eighth aspects of the invention, the voltage applied to the charging roller is changed during the image forming step.
With an oscillating voltage obtained by superimposing an AC voltage on a DC voltage, and except during the image forming step, by using only the DC voltage, at least during the image forming step, that is, after the main switch of the apparatus is turned on, During the pre-rotation step, during the interval between continuous sheets, during the post-rotation step of the image carrier after the image forming step, etc., the above-mentioned charging noise is suppressed and the device noise is minimized as a whole. It becomes possible. Further, except during the image forming step, by applying only the DC voltage to the conductive member as described above, the vibration of the image carrier and the charging roller is suppressed, and the charging roller firmly fixes the toner to the surface of the photosensitive drum. It is possible to reduce the chances of pressing against the toner, and it is possible to suppress the occurrence of toner fusion.

According to the ninth to sixteenth aspects of the invention, the charging member is charged by the charging member having the distance region in which the distance from the surface of the charging target increases, and the charging start voltage for the charging target voltage is increased. In the image forming apparatus in which a voltage value equal to or higher than the above value is applied between the surface to be charged and the distance area of the charging member, and in particular, an oscillating electric field is applied to the image area, the non-image area and the image area are applied to the area. By having a charging device characterized in that the bias value to be different,
1. Improvement of toner drum fusion under high temperature and high humidity environment, 2. Moire when the charging frequency is increased and the latitude of toner fusing on the drum are improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a front view of an embodiment of the image forming apparatus of the present invention.

FIG. 3 is a front view of another embodiment of the image forming apparatus of the invention.

FIG. 4 is a front view of another embodiment of the image forming apparatus of the present invention.

FIG. 5 is a front view showing a comparative example of the image forming apparatus.

FIG. 6 is a diagram showing a conventional example of an image forming apparatus.

FIG. 7 is a diagram showing another embodiment of the image forming apparatus of the invention.

FIG. 8 is a diagram of a contact charging device section in another embodiment of the image forming apparatus of the invention.

FIG. 9 is a diagram showing an example of pixel growth in the image forming apparatus.

FIG. 10 is a diagram showing an example of a halftone pattern of the present invention.

FIG. 11 is a diagram showing another embodiment of the image forming apparatus of the invention.

FIG. 12 is a diagram showing an example of another halftone pattern of the present invention.

13 is a diagram showing reproduction of the halftone pattern of FIG.

FIG. 14 is a diagram showing another example of reproduction of the halftone pattern of FIG. 11.

FIG. 15 is a diagram showing an example of still another halftone pattern of the present invention.

FIG. 16 is a diagram showing reproduction of yet another halftone pattern of the present invention.

FIG. 17 is a diagram showing another embodiment of the image forming apparatus according to the present invention.

FIG. 18 is an example of a conventional timing chart according to the present invention.

FIG. 19 is a diagram showing a charging potential on the surface of the photosensitive drum when a DC voltage is applied.

FIG. 20 is a diagram showing an example of a timing chart according to the invention.

FIG. 21 is a diagram showing a relationship between a DC voltage applied to the charging roller and a current.

FIG. 22 is a diagram showing still another embodiment of the image forming apparatus according to the present invention.

FIG. 23 is a diagram showing another embodiment of the timing chart according to the present invention.

FIG. 24 is a view showing still another embodiment of the timing chart according to the present invention.

FIG. 25 is a diagram showing an example of a conventional image forming apparatus according to the present invention.

FIG. 26 is a schematic view of another embodiment of the image forming apparatus according to the present invention.

FIG. 27 is a sequence explanatory diagram of another embodiment of the image forming apparatus according to the present invention.

FIG. 28 is a schematic view of a main body of another embodiment of the other embodiment of the image forming apparatus according to the present invention.

FIG. 29 is a sequence explanatory view of another embodiment of the image forming apparatus according to the present invention.

FIG. 30 is a sequence diagram of another embodiment of the image forming apparatus according to the present invention.

FIG. 31 is a schematic view of a main body of still another embodiment of the image forming apparatus according to the present invention.

FIG. 32 is a sequence explanatory diagram of still another embodiment of the image forming apparatus according to the present invention.

FIG. 33 is a schematic view of a main body of a conventional example of an image forming apparatus.

FIG. 34 is an explanatory diagram of a conventional charging roller of an image forming apparatus.

FIG. 35 is a sequence explanatory diagram of a conventional example of the image forming apparatus.

FIG. 36 is an explanatory diagram of toner fusion in a conventional example of the image forming apparatus.

[Explanation of symbols]

1 ... Drum 2 ... Charging roller 41, 52 ... 1st voltage supply means 42, 43, 53 ...
Second voltage supply means 42a ... Resistor 101 ... Electrophotographic photosensitive member 102 ... Charging roller 103 ... Laser scanner 104 ... Developing device 108 ... Transfer roller 109 ... Fixing device 112 ... Cleaner 113 ... Charging blade 201, 251 ... Photosensitive drum 202, 252 ... Charging roller 203, 253 ... High-voltage power supply 204, 254 ... Contact plate spring 205 ... Laser beam scanner 206 ... Developing device 207 ... Transfer device 208 ... Transfer material 209 ... Cleaning device 210 ... Current detection circuit 211 ... Arithmetic circuit 301 ... Charging Roller 302 ... Photosensitive drum 304 ... High voltage power supply switching control device 305a ... Constant voltage DC high voltage power supply 305b ... Constant current AC high voltage power supply 308 ... Exposure device 309 ... Developing device 310 ... Transfer device 311 ... Cleaning device 330 ... Fixing device

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Koichi Hiroshima 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tatsuichi Tsukada 3-30-2 Shimomaruko, Ota-ku, Tokyo No. Canon Inc. (72) Inventor Katsuhiko Nishimura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Toshio Miyamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. In the company

Claims (16)

[Claims] 1. A means for supplying voltage to a charging member, which is provided in contact with a body to be charged and charges the body to be charged while rotating, comprising: first voltage supply means from a power source to the charging member; A charging device comprising: a second voltage supply means in which a resistor, which is higher than the one voltage supply means by one digit or more, is interposed between a power source and a charging member. 2. A voltage supplying means for an image carrier and a charging member which is provided in contact with the image carrier and charges the image carrier while rotating. 2. The image forming apparatus according to claim 1, further comprising: a voltage supply unit and a second voltage supply unit in which a resistor higher than the first voltage supply unit by one digit or more is interposed between the power source and the charging member. 3. The image forming apparatus according to claim 2, further comprising a detachable process unit including the image carrier and the charging member. 4. A process unit detachable from an image forming apparatus, wherein a voltage is supplied to an image carrier and a charging member which is provided in contact with the image carrier and charges the image carrier while rotating the image carrier. A first voltage supply means from the power supply to the charging member, and a second voltage supply in which a resistor higher than the first voltage supply means by one digit or more is interposed between the power supply and the charging member. A process unit comprising means. 5. An electrophotographic photosensitive member surface is uniformly charged by contact charging, and an electrostatic latent image is created by imagewise exposing a flashing signal of light, developed with toner, transferred, fixed, and printed image. In the image forming apparatus, the contact charging has a contact portion extending in the main scanning direction of image exposure, and charging is performed by repeatedly applying an oscillating electric field to a DC electric field between the contact portion and the electrophotographic photosensitive member. The pixel growth at the time of halftone recording first grows in the sub-scanning direction.
An image forming apparatus characterized in that it grows in the main scanning direction. 6. An image forming apparatus comprising a contact charging device for charging a surface of an image carrier with a conductive member and applying a voltage to the conductive member to charge the surface of the image carrier to a predetermined potential. An image forming apparatus characterized in that the voltage applied to the conductive member is an oscillating voltage obtained by superimposing an AC voltage on a DC voltage during an image forming step, and is only a DC voltage except during an image forming step. . 7. The image forming apparatus according to claim 6, wherein the DC voltage applied to the conductive member except during the image forming step is set higher than the DC voltage applied to the conductive member during the image forming step. . 8. The image forming apparatus according to claim 7, wherein the DC voltage applied to the conductive member except during the image forming step is variably controlled according to the charging start voltage of the surface of the image carrier. 9. A charged member is charged by a charging member having a distance region in which the distance to the surface of the charged body increases, and a voltage value equal to or higher than a charging start voltage value for the charged body In an image forming apparatus that applies a voltage between the charging member and the distance area, and particularly applies an oscillating electric field to the image area, the bias value applied to the distance area is different between the non-image area and the image area. The image forming apparatus is characterized in that the maximum voltage of the non-image area is lower than that of the image area. 10. The image forming apparatus according to claim 9, wherein the voltage is at least one of a DC voltage and an AC voltage. 11. The image according to claim 9, wherein the voltage applied to the distance area in the non-image area is a DC voltage, and the voltage applied to the distance area in the image area is a DC voltage and an alternating voltage. Forming equipment. 12. The voltage applied to the distance region in the non-image part is an alternating voltage or an alternating voltage superposed with a DC voltage for a certain period of time, and the voltage value is changed after the certain period of time. 10. The image forming apparatus according to claim 9, wherein the voltage applied to the distance area in the image portion is an alternating voltage on which a DC voltage is superimposed. 13. A charged member is charged by a charging member having a distance region in which the distance from the surface of the member to be charged increases, and a voltage value equal to or higher than a charging start voltage value for the member to be charged is set to the surface to be charged. In an image forming apparatus that applies an electric field between the charging member and the distance area, and particularly applies an oscillating electric field to the image area, in the non-image area, the frequency of the oscillating electric field applied to the charging apparatus and to the apparatus in the image area. The image forming apparatus is characterized in that the frequencies of the oscillating electric field are set differently. 14. The image forming apparatus according to claim 9, wherein the charging member is a contact type charging member. 15. The image forming apparatus according to claim 9, wherein the charging member has a roller shape. 16. The image forming apparatus according to claim 9, wherein the charging member has a brush shape or a pad shape.