JPH0815952A - Image-forming device - Google Patents

Abstract

PURPOSE:To provide an image-forming device which removes memory effect on an image carrier by means of electrification (auxiliary electrification), obtains an image free of an irregularity, etc., suppreses the generation of discharge products such as O3 and Nox, and prevents exposure and deterioration of the image carrier, environmental pollution. etc. CONSTITUTION:The photoreceptive drum 4 is subjected to the auxiliary electrification by an auxiliary electrifire 15 and is destaticized by being subjected to entire exposure by means of a destaticizing lamp 25, thereby removing a memory effective area from the photo-sensitive drum 4, and then it is subjected to a primary electrification by means of a first electrifier 6 and the following process. In this case, the auxiliary electrification current is controlled based on image formation conditions, for example the resistance value of a transfer material. By this control a required amount of the auxiliary electrification current is reduced, and the removal of the memory effective area of the photosensitive drum 4 and the uniform primary electrification of the photoreceptive drum 4 can be achieved and the suppression of the generation of a discharge product, such as O3, can also be achieved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an electrophotographic type, electrostatic recording type image forming apparatus, etc., but is not particularly limited to a multicolor electrophotographic apparatus having a plurality of developing devices. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus which can be suitably embodied in various color copying machines such as a copying apparatus, a recording apparatus that constitutes an output unit of a facsimile or a computer, a color printer, and the like. Although a multicolor electrophotographic copying apparatus will be described in the present specification, the image forming apparatus of the present invention is not limited to this as described above.

[0002]

2. Description of the Related Art Conventionally, various multicolor electrophotographic copying apparatuses have been proposed. FIG. 16 shows an example of a multicolor electrophotographic copying machine equipped with a developing device which is a typical so-called rotary developing device.

As shown in FIG. 16, a multicolor electrophotographic copying apparatus has an image bearing member rotatably supported in the direction of an arrow, that is, a photosensitive drum 1, and an image forming means on its outer peripheral portion. Will be placed. Although any image forming means can be adopted, in this example, a primary charger 106 that uniformly charges the surface of the photosensitive drum 104 and an optical image obtained by color-separating a color image or an optical image corresponding to the color image are formed. An exposure unit 107, such as a laser beam exposure device, which irradiates the photosensitive drum 104 to form an electrostatic latent image of an image on the photosensitive drum 104.
And a rotary developing device 109 for developing the electrostatic latent image on the photosensitive drum 104 to visualize it as a toner image.

The rotary type developing device 109 has four units in which a yellow developing agent, a magenta developing agent, a cyan developing agent and a black developing agent are specially stored around a substantially cylindrical casing 104a which is rotatably supported. Developing device 109Y, 10
It holds 9M, 109C and 109K. In the rotary developing device 109, when the housing 104a rotates, a developing device that stores a developer of a color corresponding to the electrostatic latent image formed on the photosensitive drum 104 is placed at a developing position facing the outer peripheral surface of the photosensitive drum 104. The electrostatic latent image on the photosensitive drum 104 is conveyed by the developer to be visualized as a toner image by the developer of that color, and this is repeated for other colors, and full color development for four colors is possible. ing.

The toner image formed on the photosensitive drum 104 is transferred onto the transfer material P carried by the transfer device 105A. In this example, the transfer device 105A is a drum type including a transfer drum 105 that is rotatably supported. As will be understood with reference to FIG. 17, the transfer drum 105 includes a pair of cylinders arranged at both ends. 105
A transfer material carrying sheet 501 is stretched as a transfer material carrying member on the outer peripheral surfaces of the air spaces a and 105a. A transfer material gripper 105c that holds the transfer material P fed from a sheet feeding device (not shown) is provided in a non-tensioned portion of the transfer material carrying sheet 501 on the outer peripheral surface of the transfer drum 105.
A charging device 105b that constitutes a transfer unit is provided in 05. Further, inside and outside the transfer drum 105, as shown in FIG. 16, an inner charge eliminating charger 105d and an outer charge eliminating charger 105e constituting a charge eliminating means are disposed.

The transfer material carrying sheet 501 is usually provided with
Films such as polyethylene terephthalate resin and polyvinylidene fluoride resin are used.

The process of forming a full-color image by the multicolor electrophotographic copying apparatus having the above-mentioned structure will be briefly described as follows.

First, the primary charger 106 and the exposure means 10
By operating 7, a blue color-separated electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 104, and this electrostatic latent image is developed with a yellow developer by the developing device 109Y of the rotary developing device 109. It On the other hand, the transfer material P fed to the transfer device 105A is transferred to the gripper 105 on the transfer drum 105.
It is gripped by c and comes into contact with the toner image formed on the photosensitive drum 104 as the transfer drum 105 rotates. This toner image is transferred onto the transfer material P by the operation of the transfer charger 105b, and at the same time, the transfer material P is transferred onto the transfer material carrying sheet 501.
Adsorbed and retained by.

By repeating the above-described image forming and transferring operations for each color of magenta, cyan and black, an image in which the toner images of four colors are superposed and transferred onto the transfer material P can be obtained. The transfer material P on which the toner images of four colors have been transferred is the inner charging device 105d and the outer charging device 10.
After the charge is removed by 5e, it is separated from the transfer drum 105 by the separation claw 108a, the image is then fixed by the heat fixing roller 126, and then discharged to the outside of the copying machine.

On the other hand, the toner remaining on the photosensitive drum 104 is removed by the cleaner 113 and is again subjected to the image forming process.

[0011]

However, although the multicolor electrophotographic copying apparatus having the above-mentioned structure operates extremely favorably, according to the studies and experiments by the present inventors, in the transfer step, particularly the transfer of the transfer drum 105, Material carrying sheet 501
Using polyvinylidene fluoride resin film etc. as
It has been found that problems arise when using transfer paper as the transfer material P, and especially when the humidity is high.

FIG. 17 is an explanatory diagram showing the state of electric charges at the end of the transfer material P, particularly Pa at the end of the transfer material P in the transfer portion of the transfer device 105A. The transfer material P was transferred onto the transfer drum 105 and a toner image of one color was transferred, but the transfer material P is still wound around the transfer drum 105 without being separated, and a toner image of another color is transferred. In order to do so, it is rotated together with the transfer drum 105. The polarity of the transfer voltage supplied to the transfer charger 105b is, for example, when the latent image is formed with a negative charge and the toner of the developer of each developing device is negatively charged to reversely develop the latent image. Is set to plus.

According to the research and experiment conducted by the present inventor, when a polyvinylidene fluoride resin film is used as the transfer material carrying sheet 501 and a transfer paper is used as the transfer material P, the volume resistance of the polyvinylidene fluoride resin film is 1
0 ¹³ [Omega] cm, (at high humidity) volume resistivity 10 ⁹ [Omega] cm of the transfer sheet to 10 ¹² [Omega] cm for a (low humidity state), the positive charge from the transfer charger 105b transfer material carrying sheet 5
It was found that the positive charges were injected into the transfer material P via 01 and accumulated in the surface area of the transfer material P.

Further, the inventor has found that the positive charges accumulated in the surface area of the transfer material P generate a high electric field between the surface of the photosensitive drum 104 and the transfer material P, as shown in FIG. When the photosensitive drum 104 is separated from the photosensitive drum 104, peeling discharge occurs, and the negative charge in the air generated thereby is attracted by the positive charge of the transfer material P and moves onto the transfer material P, but the positive charge in the air is a negative charge. Photosensitive drum 104
It has been found that it moves upward and damages the photosensitive drum 104, that is, causes a memory effect.

The memory effect is that the amount of primary charge on the photosensitive drum 104 by the primary charger 106 is set to the photosensitive drum 10.
The width of the photosensitive drum 104 is reduced to the width in the axial direction of No. 4, and as a result, uniform charging of the photosensitive drum 104 is impossible, causing a remarkable image defect.

The memory effect as described above mainly occurs in response to the operation of the transfer charger 105b, but as shown in FIG. 18, especially at the end portion Pa of the transfer material P, the positive charge is generated. Was more likely to be accumulated, and as a result, the memory effect was generated more strongly, causing strong streak-shaped image unevenness along the axial direction of the photosensitive drum 104.

In order to reduce the above memory effect,
A separate charging device (not shown) is provided at the subsequent stage of the transfer charging device 105b, and this charging device causes the photosensitive drum 10 after the transfer process
The memory effect area of No. 4 is decharged, or precharging to the same polarity as the primary charging is performed so that the memory effect area can be sufficiently reduced by destaticizing exposure and primary charging of the photosensitive drum 104. A sufficient effect cannot be obtained only by removing the charge, and the effect of reducing the memory effect area was recognized when the toner is charged to the same polarity as the primary charge, but the toner remaining on the photosensitive drum 104 is also charged. Therefore, there is a problem that cleaning failure occurs.

When the photosensitive drum 104 is precharged to the same polarity, it is necessary to charge the photosensitive drum 104 to a remarkably high potential in order to sufficiently reduce the memory effect on the end portion Pa of the transfer material P. At times, problems such as occurrence of image defects due to dielectric breakdown of the photosensitive drum 104 may occur. Further, there arises a problem that an extra space is required.

That is, conventionally, the memory effect generated on the photosensitive drum 104 due to the transfer operation being performed by the contact between the photosensitive drum 104 and the transfer material P is generated rather than the memory effect generated in the area relative to the transfer material end portion Pa. There has been no effective means for reducing the problems, including a strong memory effect, without causing problems such as cleaning failure and dielectric breakdown of the photosensitive drum 104, and without using an extra space.

An object of the present invention is to provide an image forming apparatus which eliminates the problem of image unevenness due to the memory effect by removing the memory effect generated on the image bearing member by electrification without causing defective cleaning. .

Another object of the present invention is to suppress the generation of discharge products such as O ₃ and Nox at the time of removing the memory effect by electrification, thereby exposing and degrading the image carrier by the discharge products. An object of the present invention is to provide an image forming apparatus that prevents environmental pollution and the like caused by discharge products.

[0022]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, according to the present invention, the first charging is performed on the image carrier by the auxiliary charging device and the entire surface is exposed, and the first charging is performed by the primary charging device.
The second charging having the same polarity as that of the above is uniformly charged on the image carrier to a desired potential, and then the image carrier is exposed in accordance with an image pattern to form an electrostatic latent image. In the image forming apparatus, which develops the electrostatic latent image with a developer to visualize it as a toner image, the first charging condition is controlled based on the image forming condition.

According to the present invention, the auxiliary charger comprises a charger without a grid, and the first charging condition is the total discharge current of the charger. The auxiliary charger is a charger with a grid, and the first charging condition is the grid bias potential of the charger. Further, the image forming condition is any one of the electric resistance value of the transfer material, the environment of thickness and humidity of the transfer material, or the number of image formed sheets.

[0024]

【Example】

First Embodiment FIG. 1 is a schematic configuration diagram showing an embodiment of the image forming apparatus of the present invention. The image forming apparatus of this embodiment is applied to a multicolor electrophotographic copying machine having four image units I to IV.

In the present multicolor electrophotographic copying machine, each of the image forming units I to IV has photosensitive drums 4a to 4d, around which primary chargers 6a to 6d with a grid and a developing device 9 are provided.
a to 9d, transfer chargers 10a to 10d, cleaner 13a
13d are arranged, and an endless transfer material carrying belt 41 is arranged as a conveying means below the photosensitive drums 4a to 4d so as to penetrate the image forming units I to IV. Transfer material P to transfer charger 10a-1
0d is arranged so as to be in contact with the photosensitive drums 4a to 4d of the image forming units I to IV and to be conveyed.

Further, in order to charge the photosensitive drums 4a to 4d and to expose the entire surface at the same time, auxiliary chargers 15a to 15d are provided.
And static elimination lamps 25a to 25d (see FIG. 3) are provided at the same position on the surface of the photosensitive drums 4a to 4d so as to be vertically stacked.

In this embodiment, the diameter of each of the photosensitive drums 4a to 4d is set to 60 mm, and the photosensitive drums 4a to 4d are set to rotate at 135 mm / sec in the arrow direction. The surface of the photosensitive drums 4a to 4d is -300V to -900V by the primary chargers 6a to 6d.
Are charged to the surface, and the surface potential thereof is sensors 14a to 14d.
(See FIG. 3), and the proper photosensitive drum 4a is monitored.
A surface potential of ~ 4d is calculated. A laser beam exposure device was used as the exposure means 2.

The developing devices 9a to 9d for the respective colors have negatively charged toners of the respective colors, and the toners are carried on the respective developing sleeves and conveyed to the developing areas in the vicinity of the photosensitive drums 4a to 4d. The voltage (developing bias) applied to each developing sleeve and the photosensitive drums 4a-4
By a developing electric field formed by the surface potential of d, the toner is attached to the electrostatic latent images on the photosensitive drums 4a to 4d by reversal development and visualized as a toner image.

After the residual toner on the surface of each of the photosensitive drums 4a to 4d is removed by the cleaners 13a to 13d, the auxiliary chargers 15a to 15d are used to remove the residual toner.
a to 4d are charged with the same polarity as that of the electrostatic latent image formed thereon, that is, are negatively charged, and at the same time, are uniformly exposed by the charge eliminating lamp, and both the memory effect area and the normal area have the surface potential. The charge is removed to about 0V. Thereafter, by operating the primary chargers 6a to 6d and the laser beam exposure device 2 of the image exposure means, color-separated electrostatic latent images corresponding to the image exposure patterns are formed on the photosensitive drums 4a to 4d, and the developing device 9a. .About.9d, the electrostatic latent images are developed into visible images developed by yellow, magenta, cyan, and black toners, respectively, and these visible images are changed by the transfer chargers 10a to 10d. Carrying belt 3
1 is sequentially transferred onto the transfer material P carried on the transfer material P.
A full color is formed on top.

In this embodiment, a blade-shaped contact type transfer charger was used, but the optimum transfer current is determined by the environment. In this embodiment, it is set to 18 μA when the temperature is 25 ° C. and the humidity is 5%. .

FIG. 2 is a diagram showing a transition of the surface potential when the electrostatic latent image forming area of the photosensitive drum having the memory effect area is subjected to the primary charging as in the conventional case. Figure 2
As is clear from the figure, the potential (about +100 to + 700V) in the memory effect area of the photosensitive drum remains as it is after the photosensitive drum is neutralized by the static elimination exposure, and the surface potential of the photosensitive drum is reduced to -700V by performing the primary charging. Even when charged, the potential of the memory effect region is -300V to -65.
It is 0V. Therefore, the potential of the memory effect area
A developing electric field corresponding to a potential difference (shown by a dotted line in the drawing) which is a difference between 300V to -650V and a developing bias voltage -550V is formed, that is, even in a non-image area where an electrostatic latent image is not originally formed, a memory effect is caused. An electrostatic latent image has been formed, and this is developed to form an unnecessary toner image. As a result, this unnecessary toner image is transferred onto the transfer material P, and image unevenness occurs.

Alternatively, since the memory effect area is formed in the image area where the electrostatic latent image is formed, even if the electrostatic latent image is formed in the image area, the electrostatic latent image has no memory effect. The potential becomes lower than the potential of the electrostatic latent image in the normal image area, and the electrostatic latent image in the memory effect area is deeply developed, resulting in image unevenness.

That is, since the memory effect area of the photosensitive drum is charged with a potential having a polarity opposite to that of the electrostatic latent image formed on the photosensitive drum, that is, positive polarity in this example, the static elimination lamp 9 is used. The following primary charging step is performed without being discharged by the discharging exposure by. Therefore, in order to charge the memory area to a desired potential, more charge is applied to the normal area that has been neutralized, and as a result, the memory effect area is normally charged even after the primary charge. That is, the electric potential becomes lower than that of the region charged to.

Particularly in the memory effect region of the portion corresponding to the edge of the transfer material P, the memory effect is remarkable, so that the surface potential difference from the normal region after primary charging also remains, resulting in a large image density difference. Will appear as.

Therefore, in the present invention, in order to solve the above-mentioned problems, the entire surface of the photosensitive drum is exposed simultaneously with charging. Therefore, in this embodiment, FIG.
As shown in FIG. 3, which shows a schematic configuration of the latent image forming portion of the image forming apparatus, the auxiliary charger 15 and the charge eliminating lamp 25 are provided at the same position on the surface of the photosensitive drum so as to be vertically overlapped with each other. Image defects due to the memory effect can be sufficiently reduced.

A specific description will be given below with reference to FIG. FIG. 4 shows changes in surface potential when the present invention is applied to a photosensitive drum having a memory effect area.

In this embodiment, after the residual toner on the surface of the photosensitive drum 4 is removed by the cleaner 13, the photosensitive drum 4 has the same polarity as the electrostatic latent image formed on the photosensitive drum 4, that is, the photosensitive drum assists the negative polarity. It is charged by the charger 15 (first charging), and at the same time, the static elimination lamp 25 uniformly exposes the entire surface of the photosensitive drum. In this case, if only the charging by the auxiliary charging device 15 is performed and the exposure by the discharge lamp 25 is not performed, the memory effect area and the normal area of the photosensitive drum 4 are
As shown in FIG. 4, each is about 0V to -700V.
And about -800V to -850V.

On the other hand, as described above, the static elimination lamp 25
Is operated simultaneously with the auxiliary charger 15 and sufficient exposure is performed at the same time as charging, the charge charged by the auxiliary charger 15 is immediately conducted through the photoconductive layer due to the photoconductivity of the photosensitive drum 4, and is attenuated. As a result, the normal area of the photosensitive drum 4 is
The auxiliary charger 15 does not charge the battery to a remarkably high potential, and the charge is removed to almost 0 V. In the memory effect area of the photosensitive drum 4, the opposite polarity charge (positive charge) is removed and the memory effect disappears. Almost 0 as in the normal area
The charge is removed to V. After that, the photosensitive drum 4 becomes the primary charger 6
Is charged (second charging), that is, the surface is charged to a surface potential of −700V by the primary charging.

The developing bias voltage for forming the developing electric field is set to -550V. The difference between the charging potential of the photosensitive drum of -700V and the developing bias voltage of -550V, 150V, is the fog removal voltage. Due to the electric field formed by this potential difference, the toner of the developing device is not always attracted to the developing sleeve of the developing device and does not adhere to the photosensitive drum 4, and therefore the fog does not occur in the white portion of the image.

On the other hand, since the portion of the photosensitive drum 4 corresponding to the image pattern is irradiated with the laser beam with the intensity corresponding to the image density, the potential of the portion exposed by the laser beam is sufficiently lowered, and FIG. As shown, the developing bias voltage becomes -350V, which is lower than -550V, and the toner on the developing sleeve causes the toner on the developing drum to develop due to the developing electric field formed by the developing bias voltage and the surface potential of the exposed portion of the photosensitive drum. 4 and a toner image is formed on the photosensitive drum 4.

As described above, according to this embodiment, prior to the primary charging of the photosensitive drum 4, the memory effect area of the photosensitive drum 4 has the same polarity as that of the electrostatic latent image formed on the photosensitive drum 4, that is, Since the auxiliary charging device 15 charges the photosensitive drum 4 (first charging) so as to have a negative polarity, and at the same time, the photosensitive drum 4 is discharged by the discharging lamp 25, so that the photosensitive drum 4 is charged before the primary charging. It is possible to remove the memory effect region and to eliminate the charge to a substantially uniform potential without charging the normal region not subjected to the memory effect to a remarkably high potential. Therefore, the subsequent secondary charging, ie, the primary charging, the image exposure, and the developing process are normally performed, a toner image is formed in the memory effect area as in the conventional case, and the toner image is transferred to the transfer material P. Disturbance did not occur.

However, as compared with the case where only the conventional primary charging (second charging) is performed, various problems may occur due to the auxiliary charging of the first charging.

That is, problems such as exposure and deterioration of the photosensitive drum due to discharge products such as O ₃ and Nox generated by performing auxiliary charging, environmental pollution due to discharge products, and increase in power consumption are compounded. In particular, a large amount of current flows through the photosensitive drum due to the entire surface exposure that is performed at the same time as the auxiliary charging, and the change in the light attenuation characteristics is significantly accelerated, such as an increase in the residual potential that increases as the photosensitive drum is used. There is a problem that the deterioration of image quality becomes remarkable.

More specifically, according to experiments and research conducted by the present inventors, the disturbance of the potential due to the memory effect that occurs on the photosensitive drum after the transfer causes the transfer charging condition when the toner image is transferred by the transfer charger 10. It has been found that, for example, the transfer current value significantly changes. For example, FIG. 5 shows the relationship between the transfer current value and the surface potential of the photosensitive drum in the memory effect region. From this figure, the potential disturbance due to the memory effect occurring on the photosensitive drum depends on the transfer current value. It is understood that the sizes are different. That is, it can be seen that the surface potential of the photosensitive drum in the memory effect area increases (becomes stronger) depending on the transfer current value.

On the other hand, the optimum conditions of the transfer charger 10 are the surrounding environmental conditions, the type of the transfer material P, the state of the electrostatic latent image on the photosensitive drum, the state of the toner in the developing device 9, or the photosensitive drum 4.
It changes depending on the state of the photoconductor. Therefore, in order to obtain a high quality image, the transfer charging condition is changed according to the image forming condition. Particularly in an image forming apparatus capable of forming a full-color image, the optimum transfer charging condition is different for each color toner. For example, when standard paper is used as the transfer material P in a normal temperature and normal humidity environment, the transfer current value is, for example, 1 Color is +2
00μA, + 250μA for second color, + 300μ for third color
The A and fourth colors are changed to +350 μA. In a low humidity environment, the transfer current value is, for example, +300 μ for the first color.
A: + 350μA for second color, + 400μA for third color, 4
The color is changed to +500 μA.

FIG. 6 shows the charging current (auxiliary charging current) of the auxiliary charger 15 required to eliminate the charge in the memory effect area.
Is shown as a relationship with the surface potential of the memory effect region. As can be seen from FIG. 6, the stronger the memory effect region is, that is, the higher the positive polarity of the surface potential of the memory effect region is opposite to the normal charging polarity and the higher the memory effect region is. The charging current of the auxiliary charger 15 required for removing the electric charge also increases.

Therefore, if the charging condition of the auxiliary charger 15 is not controlled and is fixed, a problem occurs. For example, in order to eliminate the maximum memory effect that occurs when the transfer condition of the fourth color transfer current value is +500 μA under a low humidity environment, the charging current value (auxiliary charging current value) of the auxiliary charger 15 is set to −400 μA. Must be set to, but with the auxiliary charging current value fixed,
When a transfer condition of a color transfer current value of +200 μA is used, most of the auxiliary charging current passes through the photoconductive layer of the photosensitive drum without contributing to static elimination of the memory effect. Will increase the energization deterioration of the photosensitive drum.

Therefore, when removing the charging memory effect by the auxiliary charging, it is necessary to control the auxiliary charging current according to the degree of the charging memory. However, the charging memory effect varies depending on the electric resistance of the transfer material under the same environment and the same transfer condition. That is, it was found that the memory effect tends to be large when the resistance of the transfer material is low, and the memory effect tends to be small when the resistance of the transfer material is high.

Therefore, in this embodiment, when the memory effect is removed by the auxiliary charging, the resistance of the transfer material is measured and the charging condition of the auxiliary charging is controlled based on the resistance value. As a result, it is possible to suppress the generation of discharge products such as O ₃ and Nox to the minimum, and to reduce the exposure and deterioration of the image carrier due to the discharge products and the pollution of the environment due to the discharge products. It was Hereinafter, a specific description will be given.

The transfer current of the contact transfer charger 10 is set to 18 μA.
When it is kept constant, the positive surface potential generated on the photosensitive drum 4 after transfer decreases as the volume resistance value of the transfer material increases, as shown in FIG. When the charging condition of the auxiliary charger 15 is fixed, the setting value is set to a value that can be removed when the memory effect is strongest. Therefore, when the memory effect is small, the surplus current accelerates the change of the photosensitive drum. .

In this embodiment, when the transfer material has a low resistance, the memory potential is +800 V, so that the discharge current of the auxiliary charger requires only −400 μA to −480 μA. However, if the transfer material has a high resistance, the memory potential is +200.
The discharge current of the auxiliary charger is −200 μA
It can be set to −250 μA.

As described above, by detecting the resistance of the transfer material, it becomes possible to perform control to minimize deterioration of the photosensitive drum and increase of discharge products due to auxiliary charging. The resistance of the transfer material varies greatly depending on the environment and the standing state even if the transfer material is of the same type. In particular, a transfer material that has been left in an environment of high temperature and high humidity has a large memory effect because of its low resistance value.

The resistance detecting method will be described below by taking sheet paper as an example of the transfer material. FIG. 8 shows the resistance detection device used in this embodiment.

As shown in FIG. 8, the resistance detecting device has a pair of electrode plates 32 made of a metal fixed electrode plate 32a and a movable electrode plate 32b. The fixed electrode plate 32a is fixed in the sheet conveying path, and is grounded at its lower surface. The movable electrode plate 32b is arranged so as to face the fixed electrode plate 32a, and moves up and down toward the fixed electrode plate 32a, and is connected to the switch 33 on the upper surface thereof. The switch 33 is for connecting the movable electrode plate 32a to the resistance measuring circuit 34 or the capacitance measuring circuit 35, and is switchably connected to the resistance measuring circuit 34 and the capacitance measuring circuit 35.

The resistance measuring circuit 35 has a function of measuring the resistance value of the sheet paper 100 which is the transfer material sandwiched between the pair of electrode plates 32 and outputting a signal R indicating the resistance value to the arithmetic circuit 36. . The capacitance measuring circuit 35 is for measuring an electrostatic capacitance value in a state where the sheet 100 is sandwiched by the pair of electrode plates 32 and outputting a signal C indicating the electrostatic capacitance value to the arithmetic circuit 36. is there.

The arithmetic circuit 36 receives the signal R from the resistance measuring circuit 34, estimates the dielectric constant of the transfer material, that is, the paper 100 based on the resistance value indicated by the signal R, and calculates the dielectric constant and the capacitance. The control circuit 37 controls the thickness of the paper 100 based on the capacitance value indicated by the signal C input from the measurement circuit 35.
The control circuit 37 includes an electromagnetic solenoid 3 in addition to the arithmetic circuit 36.
9 is a circuit for controlling the switch 9 and the switch 33.
have.

The detector 38 is disposed above the left end of the fixed electrode plate 32a, and the paper 100 conveyed in the direction of the arrow.
Detect the tip of the. The control circuit 37 controls the electromagnetic force of the solenoid 39 based on the detection signal.
That is, the control circuit 37 controls the direction of the current flowing through the solenoid 39, and the solenoid 39 moves the movable electrode plate 32b in the direction of the fixed electrode plate 32a by its electromagnetic force. Subsequently, the control circuit 37 switches the switch 33 from the resistance measuring circuit 34 to the capacitance measuring circuit 35, moves the connection state of the movable electrode plate 32b from the resistance measuring circuit 34 to the capacitance measuring circuit 35, and switches information of the switch 33. A signal indicating the presence / absence information of the paper 100 is output to the arithmetic circuit 36.

Therefore, when the sheet 100 is conveyed in the direction of the arrow and its leading end reaches under the detector 38, a detection signal is sent from the detector 38 to the control circuit 37. The control circuit 37, to which the detection signal is input, causes the solenoid 39
Is controlled to move the movable electrode plate 32b to the fixed electrode plate 32a side, whereby the paper 100 is sandwiched on the fixed electrode plate 32a and stopped. At the same time as this operation,
The resistance value of the paper 100 is measured by the resistance measuring circuit 34, the signal R indicating the resistance value is output to the arithmetic circuit 36, and the resistance value is calculated as a numerical value.

In this example, the total discharge current of the auxiliary charger 15 was controlled in three stages based on the resistance value of the transfer material measured as described above. Specifically, when the resistance of the transfer material is 1.0 × 10 ¹³ Ω or more, the total discharge current Isub of the auxiliary charger is −200 μA, and the resistance of the transfer material is 1.0 × 10.
^{When 10 to} 1.0 × 10 ¹³ Ω, Isub is -300 μ
A, when the resistance of the transfer material is 1.0 × 10 ¹⁰ Ω or less, Is
ub was set to −400 μA.

As described above, in the present embodiment, the memory effect generated on the photosensitive drum due to the peeling discharge caused by the accumulation of the charges on the surface of the transfer material, particularly the accumulation of the charges on the end portions of the transfer material is sensitized. The drums 4a to 4d are charged (first charging) by the auxiliary chargers 15a to 15d so as to have the same polarity as the electrostatic latent image, that is, the negative polarity, and at the same time, the photosensitive drums 4a to 4d are charged with the static elimination lamps 25a to. Two
Since the charge-exposing exposure is performed by 5d, the memory effect area of the photosensitive drums 4a to 4d is removed before the primary charging, and the normal area which is not subjected to the memory effect is charged to a remarkably high potential to cause dielectric breakdown or the like. It is possible to eliminate the charge to a substantially uniform potential without causing it. Therefore, the subsequent steps of primary charging, image exposure, and development are performed normally,
A high-quality image that reliably prevents image distortion and image unevenness due to the memory effect area without developing the memory effect area on the photosensitive drum and transferring it to the transfer material as in the past. I was able to get

In this embodiment, further, at that time, the resistance value of the transfer material is measured, and the auxiliary chargers 15a to 15d are measured based on the measured resistance value.
Since the total discharge current of O ₃ and NOx is controlled
It has become possible to minimize the generation of discharge products such as the above, and to reduce the exposure and deterioration of the photosensitive drum due to the discharge products and environmental pollution.

In the above description, the fuse lamp array 66 as shown in FIG. 11 is used as the discharge lamp 25 for exposing the photosensitive drum 4 to the entire surface to remove the charge. However, the fuse LED lamp array 66 as shown in FIG. 12 is exposed. Means can also be used.

Although the four-drum type full-color image forming apparatus has been described, the same effect can be obtained with a one-drum type full-color image forming apparatus or a monochrome image forming apparatus.

Example 2 The apparatus configuration of this example is the same as that of Example 1 except for the auxiliary charger. That is, the auxiliary charger 15 used in Example 1
Was a corotron type charger without a grid, which was configured to include a charging wire 42a connected to a high voltage power source 42a, as shown in FIG. On the other hand, the auxiliary charger 15 used in this embodiment is a scorotron type charger having a grid 42c as shown in FIG. According to this charger, the amount of discharge emitted from the charging line 42a due to the application of the high voltage from the high voltage power source 42a is determined by the grid 42 from the grid bias power source 42d.
It can be controlled by applying a control voltage to c.

In the present embodiment, the total discharge current of the auxiliary charging device 15 is controlled based on the resistance value of the transfer material in the first embodiment, whereas the total charging current of the auxiliary charging device 15 is controlled based on the resistance value of the transfer material. The feature is that the grid bias potential is controlled. The other structure of this embodiment is basically the same as that of the first embodiment. Hereinafter, description will be made with reference to FIGS. 1 and 3 described above as necessary.

In the case where the resistance value of the transfer material is not measured to control the total discharge current of the auxiliary charger 15 as in the first embodiment, that is, in the conventional case, for example, the auxiliary charger 15 is discharged. When the total discharge current was constant at -450 μA, the grid bias potential had to be -700 V to -800 V, and therefore the photosensitive drum 4 had to be constantly charged to a high potential. As a result, the photosensitive drum may be deteriorated by energization and the life of the drum may be shortened.

In this embodiment, the resistance value of the transfer material was measured, and the grid bias potential (Vgrid) of the auxiliary charger 15 was controlled in multiple stages based on the resistance value. Specifically, as shown in Table 1, it was controlled in 5 stages.

[0068]

[Table 1]

Also in this embodiment, as in the case of the first embodiment, the auxiliary charging devices 15a to 15d are connected to the photosensitive drums 4a to 4d.
Auxiliary charging by the photosensitive drums 4a ...
Since 4d is subjected to static elimination exposure by the static elimination lamps 25a to 25d, the memory effect area of the photosensitive drums 4a to 4d is removed before the primary charging, and the normal area not subjected to the memory effect is not charged to a significantly high potential, The charge can be removed to a substantially uniform potential. Then, the subsequent steps of primary charging, image exposure, and development are normally performed, and a high-quality image in which image distortion and image unevenness due to the memory effect region are surely prevented can be obtained.

Further, in this embodiment, the resistance value of the transfer material is measured, and the grid bias potentials of the auxiliary chargers 15a to 15d are controlled based on the measured resistance value, so that the deterioration of energization of the photosensitive drums 4a to 4d is reduced. It became possible to do. Specifically, when the grid bias potential of the auxiliary charger is not controlled, each color has an average of about 24,000.
Although the photosensitive drum replacement life was reached by repeating the image forming process 0 times, the average of about 36,0 in the present embodiment.
It has become possible to significantly extend the replacement life up to 00 times. In addition, due to the rectifying function of the grid, image defects (unevenness) caused by unevenness of deterioration of the photosensitive drum due to excess current,
Or, the unevenness of erasing the memory against uneven discharge is reduced,
The uniformity in the longitudinal direction of the photosensitive drum is also improved.

Although the four-drum type full-color image forming apparatus has been described above, the same effect can be obtained with a one-drum type full-color image forming apparatus or a monochrome image forming apparatus. Further, although the corona charger has been described in this embodiment, the same effect can be obtained also with the contact type charger.

Embodiment 3 The present embodiment is characterized in that the thickness of the transfer material is detected and the charging condition of the auxiliary charger is controlled based on this.
Other configurations of this embodiment are basically the same as those of the first embodiment.

When the transfer material is separated from the photosensitive drum, a peeling discharge occurs, and the memory effect increases as the transfer material becomes thicker, as shown in FIG. 9, when the volume resistivity is constant. Until now, the total discharge current of the auxiliary charging device was kept constant at -400 μA when the transfer material thickness was not detected. However, if a constant value of −400 μA is constantly maintained during image formation, discharge products such as 0 ₃ , NOx, etc. are generated, which causes problems such as adhesion and deterioration of discharge products on the photosensitive drum and environmental pollution.

Therefore, in this embodiment, as described above,
The charging condition of the auxiliary charger was controlled by detecting the thickness of the transfer material. As a result, the total discharge current of the auxiliary charger can be minimized.

As shown in FIG. 10, the transfer material thickness detecting device includes a registration roller 19 supported axially and a spring 2 from above.
1 and a registration roller 20 which is pressed against the registration roller 19 and is movable up and down. This 2
When transfer materials having different basis weights pass between the two registration rollers 19 and 20, the position of the registration roller 20 changes,
The change is transmitted to the potentiometer 23 by the clutch 22 and the thickness of the transfer material is detected. The total discharge current (Isub) of the auxiliary charger is controlled according to the detected thickness of the transfer material.

Specifically, the transfer material has a thickness of 0.085 m.
When m or less, the total discharge current of the auxiliary charger is Isub -2
00 μA, when the thickness is 0.085 to 0.120 mm I
When sub is -300 μA and thickness is 0.12 mm or more, Is
The ub could be -400 μA.

As described above, also in this embodiment, since the memory effect generated on the photosensitive drum is subjected to the static elimination exposure at the same time as the auxiliary charging as in the first embodiment,
It is possible to obtain a high-quality image in which image distortion and image unevenness due to the memory effect area are prevented.

Further, since the thickness of the transfer material is detected and the total discharge current of the auxiliary charger is controlled based on the detected thickness, O ₃ , NO
It has become possible to suppress the generation of discharge products such as x to the minimum and reduce the exposure and deterioration of the photosensitive drum due to the discharge products and environmental pollution.

In the above, the control is performed in three steps depending on the thickness of the transfer material, but it is also possible to perform stepless control.
Further, the same effect can be obtained by controlling the grid bias potential of the scorotron type charger. Further, the same effect can be obtained by using a contact type charger.

Although the four-drum system full-color image forming apparatus has been described, the same effect can be obtained also in the one-drum system full-color image forming apparatus or the monochrome image forming apparatus.

Example 4 In this example, resistance value detection of the transfer material similar to that in Example 1,
The thickness of the transfer material can be detected in the same manner as in the third embodiment. The other structure of this embodiment is basically the same as that of the first embodiment.

In Examples 1 to 3, the total discharge current of the auxiliary charger or the grid bias potential was controlled by the resistance value or the thickness of the transfer material to reduce the deterioration of the photosensitive drum and the environmental pollution.

From the results of the experiments so far, even if the memory effect occurs, the image defect may not occur,
It has been found that it is not always necessary to operate the auxiliary charger for image formation. That is, it has been found that there is a combination of the resistance value and the thickness of the transfer material which does not require the auxiliary charging. However, as in Examples 1-3,
By measuring only one of the resistance value and the thickness of the transfer material, it is not possible to find out whether or not the condition that does not require the operation of the auxiliary charger is satisfied.

Therefore, in this embodiment, the resistance and thickness of the transfer material are measured, and the auxiliary charger is controlled based on the measured resistance and thickness. And by the measurement, it became possible to eliminate unnecessary operation of the auxiliary charger.

Specifically, when the transfer material is a paper sheet, the transfer material has a thickness of 0.085 mm or less and a resistance value of 1.
It is the case of 0 × 10 ¹¹ Ω or more. Under these conditions, the auxiliary charger did not have to be operated, and no image defect occurred.

In this embodiment, as described above, the discharge product can be reduced by controlling the auxiliary charger based on the resistance value and the thickness of the transfer material.

By making the same as this embodiment, the same effect can be obtained not only in the 4-drum type full-color image forming apparatus but also in the 1-drum type full-color image forming apparatus or the monochrome image forming apparatus. Same as before. Similarly, it is possible to control the grid bias potential of a scorotron type charger, or to use a contact type charger.

Example 5 In this example, in addition to the control of the auxiliary charger based on the transfer material resistance value and the thickness of Example 4, the auxiliary charger was controlled based on the environmental data of temperature and humidity. The other structure of this embodiment is basically the same as that of the fourth embodiment.

In the image forming apparatus of the present embodiment, the environment temperature and humidity can be measured by the environment sensor installed in the apparatus. In image forming apparatuses, especially full-color image forming apparatuses, it is important to keep the maximum density of an image constant. However, the charge amount of the developing toner fluctuates according to changes in the environment, and it is difficult to keep the maximum density constant at a constant developing contrast potential.

Therefore, the maximum density is kept constant by controlling the development contrast potential according to changes in temperature and humidity. That is, when the temperature is low and the humidity is low, the charging potential of the photosensitive drum is high in order to increase the development contrast potential, and conversely, when the temperature is high and the humidity is high, the charging potential of the photosensitive drum is low in order to reduce the development contrast potential.

From the results of the experiments so far, it was found that the memory effect that occurs when the transfer material is peeled from the photosensitive drum is small when the charging potential of the photosensitive drum is high and is large when the charging potential is low. . Therefore, by performing the control based on the environmental data, the fourth embodiment
It was possible to more effectively exhibit the same effect as.

Example 6 From the results of the experiments so far, the memory effect generated when the transfer material is peeled from the photosensitive drum does not change significantly even if the image forming process is repeated, but the memory effect region of the auxiliary charger is It was found that the removal efficiency changes with repeated image formation. It was also found that the efficiency may be higher or lower depending on the type of photosensitive drum used.

In this example, an OPC having a surface protective layer was used.
The photosensitive drum of the photoconductor was used. With this photosensitive drum,
By repeating the image formation, the efficiency of removing the memory effect due to auxiliary charging is lowered, so that the memory effect may not be completely removed.

Therefore, in this embodiment, the auxiliary charger is controlled based on the number of times the image forming process is repeated.
This makes it possible to more effectively control the auxiliary charging.

Specifically, every time the image formation is repeated about 1000 times on average, the total discharge current control system for auxiliary charging is -5.
The setting value was changed by adding 0 μA each and -100 V each in the grid bias control system. As a result, almost the same effect as the initial stage was obtained.

As described above, by controlling the auxiliary charger based on the number of times image formation is repeated, it is possible to more effectively remove the memory effect from the initial use of the photosensitive drum to the replacement life. became.

In this embodiment, the case where the memory effect removal efficiency is lowered by the repeated image formation is described. However, when the efficiency is increased, the total discharge current of the auxiliary charger can be reduced and the discharge product Since it is possible to minimize the occurrence and the effect of deterioration due to energization is reduced from the beginning, it is possible to further extend the life of the photosensitive drum.

[0098]

As described above, in the image forming apparatus of the present invention, the memory effect generated on the photosensitive drum by the charge accumulation on the surface of the transfer material, especially the peeling discharge caused by the charge accumulation at the edge of the transfer material. In contrast, the photosensitive drum is first charged and simultaneously exposed to the entire surface.
The second charging having the same polarity as that of No. 1 charges the photosensitive drum uniformly to a desired potential, and then exposes the photosensitive drum according to the image forming pattern to form an electrostatic latent image. Since the latent image is developed with a developer and visualized as a toner image, the memory effect area on the photosensitive drum is not developed and transferred onto the transfer material as in the conventional case, and the photosensitive drum is prevented. It is possible to obtain a high-quality image in which image distortion and image unevenness due to the memory effect region are surely prevented without causing any adverse effects such as dielectric breakdown.

Further, in the present invention, the total discharge current or the grid bias potential of the auxiliary charger is determined based on the resistance of the transfer material and / or the thickness of the transfer material, and further based on the environmental conditions and the number of times the image forming process is repeated. I controlled it, so 0
₃ , the generation of discharge products such as N0x can be minimized, and the deterioration of the photosensitive drum due to the adhesion of discharge products can be minimized, and the effect of the auxiliary charger is extended to the life of the photosensitive drum. It became possible to obtain.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a transition of a surface potential of a photosensitive drum having a memory effect area in a conventional image forming apparatus.

FIG. 3 is a schematic configuration diagram illustrating a latent image forming unit of the image forming apparatus according to the first exemplary embodiment.

FIG. 4 is a diagram showing a transition of a surface potential of a photosensitive drum having a memory effect area.

FIG. 5 is a diagram showing a relationship between a transfer current value and a surface potential of a photosensitive drum having a memory effect area.

FIG. 6 is a diagram showing a relationship between a surface potential of a memory effect region and a necessary charging current of an auxiliary charger.

FIG. 7 is a diagram showing a relationship between a memory resistance and a volume resistance of a transfer material.

FIG. 8 is a schematic diagram of a transfer material resistance detection device used in Examples 1 and 2.

FIG. 9 is a diagram showing a relationship of memory potential with respect to the thickness of a transfer material.

FIG. 10 is a perspective view of a transfer material thickness detection device used in Example 3;

FIG. 11 is a cross-sectional view showing a fuse lamp array as a static elimination lamp that can be used in the present invention.

FIG. 12 is a cross-sectional view showing an LED lamp array as a static elimination lamp that can be used in the present invention.

FIG. 13 is a cross-sectional view showing a scorotron type charger as an auxiliary charger used in the present invention.

FIG. 14 is a sectional view showing a corotron type charger as an auxiliary charger used in the present invention.

FIG. 15 is a schematic configuration diagram showing an example of a conventional image forming apparatus.

16 is a perspective view showing a transfer drum of a transfer device used in the image forming apparatus of FIG.

FIG. 17 is an explanatory diagram showing a state of charges at an end portion of a transfer material in a transfer portion of the transfer device of FIG.

FIG. 18 is an explanatory diagram showing peeling discharge at the end of the transfer material.

[Explanation of symbols]

 4, 4a to 4d Photosensitive drum 6, 6a to 6d Primary charging device 9, 9a to 9d Developing device 10, 10a to 10d Transfer charging device 13, 13a to 13d Cleaner 15, 15a to 15d Auxiliary charging device 25, 25a to 25d lamp

Claims (7)

[Claims] 1. A first charging device for an image carrier by an auxiliary charger.
And the entire surface is exposed, and the primary charging device performs the second charging having the same polarity as the first charging, thereby uniformly charging the image carrier to a desired potential, and then the image. In the image forming apparatus, the carrier is exposed to light corresponding to an image pattern to form an electrostatic latent image, and the electrostatic latent image is developed with a developer and visualized as a toner image. An image forming apparatus, which is controlled based on a forming condition. 2. The image forming apparatus according to claim 1, wherein the auxiliary charger is a charger without a grid, and the first charging condition is a total discharge current of the charger. 3. The image forming apparatus according to claim 1, wherein the auxiliary charger is a charger with a grid, and the first charging condition is a grid bias potential of the charger. 4. The image forming apparatus according to claim 2, wherein the image forming condition is an electric resistance value of a transfer material. 5. The image forming apparatus according to claim 2, wherein the image forming condition is the thickness of the transfer material. 6. The image forming apparatus according to claim 2, wherein the image forming condition is a temperature and humidity environment. 7. The image forming apparatus according to claim 2, wherein the image forming condition is the number of images to be formed.