JPH05257347A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a chargeless image forming device which can form a sharp toner image without causing the ground soiliing on the surface of a photosensitive body and efficiently transfer it to a transfer material by means of electrical transfer. CONSTITUTION:In the chargeless image forming device, insulated toner is used as the toner of developer and a bias voltage applied to a developing roller 3 is an AC voltage in which its polarity becomes the same as that of the electrification of the toner of a developer layer on a developing roller 3 during image exposure, in synchronism with a repitition of image exposure along a line on the inside surface of the photosensitive body by the use of an image exposure means 2, and becomes opposite to that in a period between the image exposure and the subsequent image exposure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chargeless image forming apparatus. More specifically, the image exposure means repeats image exposure on a surface of a rotating photoconductor along a line substantially perpendicular to the direction of rotation of the photoconductor. The present invention relates to an image forming apparatus for forming a toner image by making a developer layer on a developing roller, to which a developing means is applied a bias voltage, face an outer surface of a photoconductor at the line position.

[0002]

2. Description of the Related Art Conventionally, as a chargeless image forming apparatus, one using a conductive toner has been known. This has a problem that electrical transfer is difficult.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and an electric transfer is performed by forming a clear toner image on the surface of a photoconductor using an insulating toner without scumming. It is an object of the present invention to provide a chargeless image forming apparatus capable of efficiently transferring to a transfer material.

[0004]

In the chargeless image forming apparatus of the present invention, an insulating toner is used as the toner of the developer, and a bias voltage applied to the developing roller while the developing unit forms a toner image is applied. In synchronism with the repetition of image exposure by the image exposure means, an alternating voltage having the same polarity as the charging of the toner during the image exposure and having the opposite polarity to the charging of the toner between the image exposures is characterized. And
This feature achieves the above objective.

[0005]

That is, in the chargeless image forming apparatus of the present invention, since the bias voltage of the developing roller has the opposite polarity to the charging of the toner between the image exposure along a line and the next image exposure, Toner contacting the outer surface of the photoconductor in the non-exposed area where the charge was not transferred to the photosensitive layer during image exposure is pulled toward the developing roller, and the photoconductor in the exposed area where the charge has been transferred The toner adhering to the outer surface stays in the same place, and as a result, a clear toner image with almost no background stain can be formed.Because the toner is an insulating toner, the toner image can be efficiently transferred by electrical transfer. It can be transferred to a transfer material.

[0006]

The present invention will be described below with reference to the illustrated examples.

FIG. 1 is a schematic structural sectional view showing an example of an image forming apparatus of the present invention, FIG. 2 is a partially enlarged view, FIG. 3 is a partial sectional view of a photoconductor, and FIG. 4 is a block diagram of a main part of a control circuit. FIG. 5 is a timing chart of writing by image exposure and bias voltage of the developing roller.

In FIG. 1, reference numeral 1 denotes a transparent electrode layer 1a formed on a transparent substrate as shown in FIG. 3, a charge generation layer 1b on the transparent electrode layer 1a side, and a hole charge transport layer 1 as an intermediate layer.
c, a photoconductor drum 2 having a structure in which photoconductor layers each having a surface charge generating layer 1d are laminated and rotating in the direction of the arrow 2 is a light emitting element array 2a such as an LED or EL and a rod lens array. A converging optical transmitter 2b,
The image exposing means 3 which is provided stationary inside the photoconductor drum 1 and repeats the image exposure along the line substantially perpendicular to the rotation direction on the inner surface of the photoconductor drum 1 is made of a non-magnetic conductive material such as aluminum. , A developing roller provided with a magnet body 4 in which N and S magnetic poles are circumferentially arranged.

The developing roller 3 attracts the two-component developer of the insulating toner and the magnetic carrier or the one-component developer of the insulating magnetic toner to the surface by the magnetic force of the magnet body 4, and the developing roller 3 or the magnet body 4 or both. The developer is conveyed in the direction of the rotation arrow of the developing roller 3 by the rotation of the developing roller 3 and the developer layer formed on the surface of the developing roller 3 is exposed on the outer surface of the photoconductor drum 1 at the position where the image light is incident. Contact.

The relationship between the position of the line where the image exposure means 2 repeats the image exposure on the photosensitive drum 1 and the position where the developing roller 3 contacts the developer layer is as shown in FIG.
Center O ₃ of the developing roller 3 to the center O ₁ of the photoconductor drum 1, or the line connecting the developing roller 3 to the point closest to the photoconductor when the photoconductor is a belt. When the angle θ formed by the line connecting O ₃ to the line position where the image exposure means 2 repeats the image exposure is within the range of −10 ° ≦ θ ≦ 10 °, the image exposure line position is closer to the photosensitive member of the developing roller 3. It is preferably upstream from the approaching position. Thereby, the movement of charges in the photoconductor layer for forming an electrostatic image on the photosensitive drum 1 can be ensured by the incidence of image light and the strong electric field due to the bias voltage of the developing roller 3. When θ is out of the above range, the electric field strength at the position of the image exposure line becomes weak and the electrostatic image formation becomes insufficient.

As shown in FIG. 5, the developing roller 3 is selectively turned on based on the image data of the light emitting element array 2a by the control circuit shown in FIG. In synchronization with the repetition of image exposure along the line that is the scanning direction, a positive constant voltage with the same polarity as the toner charging is written during writing, and the entire surface is turned off from the end of writing the line to the writing of the next line. Is applied as a bias voltage, which is a rectangular wave AC voltage having a negative constant voltage having a polarity opposite to that of toner charging. As a result, the toner adheres only to the portion corresponding to the exposed portion of the image exposure along the line on the outer surface of the photosensitive drum 1 and does not adhere to the portion other than the non-exposed portion including the writing. A toner image with almost no background stain is formed.

In the control circuit of FIG. 4, the CPU controls the drive motor of the photosensitive drum 1 based on the reference clock pulse from the clock pulse generation circuit, and the image data memory in which the image data is stored. Transfer of image data corresponding to the scanning line to the image exposure means and latching,
The image exposure timing control of the image exposure means and the bias power supply for applying the rectangular wave AC bias voltage which changes at the times T ₁ and T ₂ in synchronization with the image exposure timing to the developing roller 3 as shown in FIG. 5 are performed. It is a thing. The portion surrounded by the dotted line frame of the control circuit in FIG. 4 is further added when the image exposure means is a laser optical system. Also, FIG.
In the above example, the linear velocity of the photoconductor having a thickness of 25 μm was set to 40 mm / sec. However, a photosensitive member having a layer thickness of 10 to 50 μm can be used, and the linear velocity of the photosensitive member can be selected within a range of 10 to 300 mm / sec. Even in such a range, a toner image with almost no background stain can be formed.

In the illustrated example, the photoconductor is the OPC photoconductor having the layer structure shown in FIG. 3, but there are the following two mechanisms for forming an electrostatic image and a toner image on the photoconductor. In this case, the charge transfer layer 1C was a hole transfer type.

The first mechanism is to use the charge generation layer 1b on the transparent electrode layer 1a side as shown in the schematic view of the image forming portion in FIG. In this case, the bias voltage of the developing roller 3 becomes negative during image exposure along the line, and positive charges are injected into the exposed portion of the photoconductor, that is, the image light of the charge generation layer 1b is generated in the incident portion. The holes are attracted and trapped on the surface of the photoconductor, and a negatively charged toner is used as the insulating toner to adhere to the surface of the photoconductor where the holes are trapped. Then, the bias voltage of the developing roller 3 becomes positive from the image exposure along the line to the next image exposure,
The toner adhering to the surface of the photoconductor in which holes are not trapped is pulled toward the developing roller 3 side, whereby a toner image without fog is formed on the surface of the photoconductor. Such a positive / negative inversion of the bias voltage is performed by the rectangular wave generating circuit 25, and this inversion also functions to vibrate the developer layer to accelerate the toner image forming operation described above.

The reason why the charge generation layer 1d on the surface of the photoconductor is provided is that the positive charge remaining on the surface after the toner image is transferred and the surface is cleaned is erased by uniform exposure. When the charge generation layer 1d is uniformly exposed from the inner surface side or the outer surface side of the photoconductor, charges are generated and the trapped positive charges are released. That is, the uniform exposure means for removing charge may be provided on the inner surface side or the outer surface side of the photoconductor.

The second mechanism is the use of the charge generation layer 1d, which is the surface layer of the photoreceptor, as shown in the schematic view of the image forming portion in FIG. In this case, during image exposure along the line, the bias voltage of the developing roller 3 becomes positive and negative charges are injected into the exposed portion of the photoconductor, that is, the image light of the charge generation layer 1d is generated in the incident portion. The holes escape to the transparent electrode layer 1a side to trap the negative charges on the surface of the photoconductor, and the positively charged toner is used as the insulating toner to adhere to the surface of the photoconductor where the negative charges are trapped. Then, the bias voltage of the developing roller 3 becomes negative between the image exposures along the line and the next image exposure, and the toner adhering to the surface of the photosensitive member where the negative charges are not trapped is developed by the developing roller 3. Three
Sided, thereby forming a fog-free toner image on the surface of the photoreceptor.

The reason why the charge generation layer 1b on the transparent electrode layer 1a side is provided is that the negative charges remaining on the surface after transfer and cleaning are erased by uniform exposure. Charge generation layer 1b
Is uniformly exposed from the inner or outer surface of the photoreceptor,
The positive charges generated in the charge generation layer 1b neutralize the negative charges trapped on the surface.

The charge generation layers 1b and 1d are set to have photosensitivity and light transmissivity so as to act on one of the image exposure light and the uniform exposure light for neutralization.

Unlike the example of FIG. 3, when the photoconductor layer of the photoreceptor is a single-layered inorganic or organic photoreceptor having ambipolar charge mobility, development during imagewise exposure along the line is performed. Both positive and negative bias voltages of the roller 3 and therefore positive and negative charges of the insulating toner are used. However, since a large amount of image light is absorbed on the side of the photoconductor substrate, the first mechanism described above is used. It is preferable to use the same operation as.

The photoconductor layer of the photoconductor is the conventional OPC.
As described above, in the case where the charge generation layer is provided on one side of the charge transfer layer, the charges tend not to disappear even if the charge is removed by uniform exposure.

Since the developer is a two-component developer and the magnetic carrier is also insulating, the electric field strength can be increased by controlling the charging of the toner and increasing the positive and negative voltages of the bias voltage of the developing roller 3. Further, it is preferable that the magnetic carrier is spherical in terms of improving the stirring property of the toner and the carrier and the transporting property of the developer, and making the aggregation of the toner and the toner and the carrier less likely to occur. Then, the spherical magnetic carrier has an average particle size of 30.
It is preferably in the range of ˜80 μ.

If the average particle size of the magnetic carrier is too small, the magnetic carrier is likely to adhere to the surface of the photoconductor and fogging is likely to occur. On the other hand, if it is too large, the ears of the magnetic brush in the developer layer become rough, the toner density of the ears becomes low, and the toner image becomes rough, or the density becomes low.

The preferable magnetic carrier as described above is iron, which is the same as in a conventional magnetic carrier as a magnetic material.
Metals such as chromium, nickel and cobalt, or their compounds and alloys such as ferric tetroxide, γ-ferric oxide,
Spherical particles of ferromagnetic materials such as chromium dioxide and ferrite, or the surface of these magnetic particles are styrene resin, vinyl resin, ethylene resin, rosin modified resin, acrylic resin, polyamide resin, epoxy resin ，
Particles obtained by spherical coating with a resin such as polyester resin or by making spherical particles of resin containing magnetic fine particles dispersed therein are subjected to particle size selection by a conventionally known average particle size selection means. Obtained by

In addition to the above-described effect, forming the carrier into a spherical shape by using a resin or the like as described above causes the non-sphericalized carrier to be magnetized and adsorbed in the longitudinal direction of the carrier to attach the toner to the photosensitive member. It is easy to give directionality when it is peeled off or when it is peeled from the photoconductor, and because there is an edge part, the electric field is concentrated at the edge part and breakdown easily occurs, which disturbs the image formed on the photoconductor. There is also an effect that the drawback of performing is eliminated, a high bias voltage can be applied, and a clear toner image without disturbance can be formed.

In addition to the spherical carrier having the above-mentioned effects, the carrier has a resistivity of 10 ⁸ Ωcm or more, especially 10 ⁸ Ωcm or more.
It is preferable that insulating magnetic particles are formed so as to have a resistance of ¹³ Ωcm or more. The resistivity after tapping putting particles in a container having a sectional area of 0.50 cm ^2, a load of 1 kg / cm ² on packed particles, between the load and a bottom electrode
It is a value obtained by reading the current value when a voltage that generates an electric field of 1000 V / cm is applied. If this resistivity is low, charges are injected into the carrier when a bias voltage is applied to the developing roller 3. As a result, the carrier easily adheres to the surface of the photoconductor, or the breakdown of the bias voltage easily occurs.

In summary, the magnetic carrier is spherical so that the ratio of the major axis to the minor axis is at least 3 times or less, and there are no protrusions such as needles and edges, and the resistivity is high. Is 10 ⁸
It is a proper condition that it is Ωcm or more, preferably 10 ¹³ Ωcm or more. For such magnetic carrier, spherical magnetic particles having high resistance or resin-coated carrier, magnetic particles are selected to be as spherical as possible, and a resin coating treatment is applied to the magnetic particles. The carrier (2) is manufactured by using magnetic fine particles as much as possible and subjecting the dispersed resin particles to a spheroidizing treatment, or obtaining the dispersed resin particles by a spray drying method.

Next, the toner will be described. Generally, when the average particle size of the toner particles becomes small, the charge amount qualitatively decreases in proportion to the square of the particle size, and the adhesion force such as the van der Waals force is relatively increased. Becomes large, the toner becomes difficult to separate from the carrier, the density of the toner image formed on the photoconductor surface becomes insufficient, and fogging easily occurs. When the bias voltage of the developing roller is a DC voltage and the average particle size of the toner particles is 10 μm or less, the above-mentioned problem appears.

However, in the chargeless image forming apparatus according to the present invention, since the bias voltage of the developing roller 3 is a rectangular wave AC voltage, the toner adhering to the developer layer is electrically applied to the developer layer to cause vibration. Away from the surface of the photoconductor, the toner adhered to the non-image portion of the surface of the photoconductor is easily moved to the developing roller 3 side, and a clear toner image without fog is formed on the surface of the photoconductor. Therefore,
A toner having an average particle size of several μm can be used without any problem.

Even when a one-component insulating developer such as a one-component non-magnetic toner or a one-component magnetic toner is used, the above-described effect due to the bias voltage being an AC voltage can be obtained in substantially the same manner. That is, due to the vibration of the toner, a sufficient amount of toner adheres to the image portion of the photosensitive surface, the toner of the non-image portion is removed, and as a result, a clear toner image without fog is formed.

As the two-component developer, a developer in which the above-mentioned spherical carrier and toner are mixed in the same proportion as in the conventional two-component developer is preferably used.
In addition, if necessary, a fluidizing agent for improving the flow slippage of the particles, a cleaning agent useful for cleaning the surface of the photoreceptor, and the like are mixed. As the fluidizing agent, colloidal silica, titanium oxide or a nonionic surface active agent can be used, and as the cleaning agent, a fatty acid metal salt, an organic group-substituted silicon or a surface active agent such as fluorine can be used.

In FIG. 1, this shows the case where a one-component magnetic toner is used, and 5 is a developer supply member such as a sponge roller for supplying the developer in the developer chamber 6 to the surface of the developing roller 3. Reference numeral 7 is a layer thickness regulating member such as a rubber plate for regulating the layer thickness of the developer layer conveyed by the developing roller 3, and 8 is a shaft 8a, a side plate 8b and a bottom plate 8c. It is rocked so as to move slowly in the direction of the developer supply member 5 and fast in the opposite direction by the means, thereby moving the developer in the developer chamber 6 to the developer supply member 5 side. The members 9 and 10 can be attached to the bottom plate 8c of the swinging feed member 8 if necessary in order to prevent the developer from entering between the swinging feed member 8 and the rear wall or the bottom wall of the developer chamber 6. It is a flexible sheet.

The developer supplying member 5 and the elastic layer thickness regulating member 7 made of a rubber plate also frictionally charge the toner with the developing roller 3. However, in place of the swinging feed member 8, a rotary stirring blade is used to triboelectrically charge the toner and the developing roller 3 for the developer.
Alternatively, the developer supplying member 5 may be omitted. A doctor blade may be used as the layer thickness regulating member 7. The gap between the photoconductor and the developing roller 3 is 30 to 500 μ.

When a one-component non-magnetic developer is used, a developer layer is formed on the developing roller 3 as a thin layer of one or two toner particles, and a toner image is sufficiently formed under the condition of being brought into contact with the photoreceptor surface. can do. In that case, the photoconductor and the developing roller 3
Has a toner layer thickness in the range of 5 to 50 μm, and under such conditions, a strong developing electric field can be formed in the toner layer, whereby the charge in the photoconductor layer during image exposure can be reduced. The movement is effectively performed, and a good toner image can be obtained.

When a two-component developer is used, the thickness of the developer layer formed on the developing roller 3 needs to be such that a layer in which toner uniformly exists is formed. The gap between the roller 3 and the photosensitive drum 1 is 50-1000μ
m is preferred. If this gap is too narrower than 50 μm, the presence of toner in the developer layer becomes non-uniform, making it difficult to form a toner image of sufficient density,
The developer layer is clogged in the gap. Also, the gap is 1000μ
When m is greatly exceeded, the counter electrode effect is lowered and the electrostatic image and the toner image are insufficiently formed, and the toner image without fog is not formed.

The bias voltage of the developing roller 3 shown in FIG. 5 will be further described below.

The bias voltage applied to the developing roller 3 is
In order to prevent fogging of the developer, it is preferable that the average voltage has a DC component of 20 to 200 V having a polarity opposite to that of the toner charge. On the other hand, during the image exposure along the line, it is preferable to effectively move the charge of the photoconductor layer by the voltage V ₁ having the same polarity as the charging of the toner, and this voltage is maintained until the transfer of the charge is completed. It is necessary. Since it is preferable to satisfy this condition, the charge transfer voltage V ₁ is an absolute value | V with respect to the fog prevention voltage V ₂ .
It is preferable that ₁ | ≧ | V ₂ |.

However, under this condition, the developing roller 3
The average DC component of the bias voltage has the same polarity as that of the toner charge and increases its value, and fogging is likely to occur in the entire image. _{That, | V 1 | <| V} 2 | duration T ₂ of the duration T ₁ and V ₂ of if V ₁ was but no problem as _{T 1 = T 2, | V} 1 | ≧ | V 2 If |, T ₁ <
It must be T ₂ . That is, V ₁ , V ₂ , T ₁ , T ₂
It is preferable that the result of the setting is that the average voltage has a DC component having a polarity opposite to that of the toner charge.

Also important is the difference t between the end of image exposure along the line and the time at which the bias voltage switches from V ₁ to V ₂ . It must be longer than the time required for the last charge generated in the photoconductor layer by imagewise exposure to move. In particular, since the charge transfer speed is low in the OPC photosensitive member, it is necessary to set this time t sufficiently. That is, the relationship between the exposure time Texp and the duration T ₁ is T ₁ −Te
It is desirable that xp = t> 0.

[0039] Consequently, the frequency of the image exposure namely write and bias voltage, preferred considering the charge transfer speed of the photosensitive member is about 10Hz～5KH _Z, particularly preferred is 10Hz~3KH _Z. On the other hand, the bias voltage is also used for development, and induces development pitch unevenness at low frequencies. So, from both of these, the frequency is 100Hz ~
5KH _Z becomes no preferred range practical problem, particularly preferably in the range of 100Hz~3KH _Z. Since the writing and the developing bias voltage are synchronized, the recording speed for forming a clear and even toner image is restricted by this frequency.

The bias voltage V applied to the developing roller 3
₁ is 200 to 2000 V, which has the same polarity as the toner charge, especially
The range of 300 to 1000 V is preferable, and the range of V ₂ is 50 to 1500 V, which is the opposite polarity to the charging of the toner, and particularly 50 to 700 V.

In FIG. 1, 11 is a feed roller for feeding the transfer material of the paper feed cassette, 12 is a pair of conveying rollers for nipping the transfer material fed by the feed roller 11, and feeding it.
Reference numeral 13 denotes a pair of timing rollers for nipping and transferring the transfer material at the timing when the toner image formed on the photoconductor drum 1 is transferred to the transfer material, and 14 denotes the photoconductor drum for the transfer material sent by the timing roller 13. 1 is a transfer roller that is pressed against 1 to transfer the toner image on the feed photosensitive drum 1 to a transfer material. A transfer bias voltage having a polarity opposite to that of the charging of the toner during transfer is applied to the transfer roller 14 by a power source (not shown).

In the chargeless image forming apparatus of the present invention,
Since the toner is an insulating toner, the transfer efficiency of the toner image onto the transfer material can be remarkably enhanced by the bias voltage applied to the transfer roller 14. Further, as the transfer means, a corona discharge electrode may be used instead of the transfer roller.

Reference numeral 15 is the photosensitive drum 1 without being transferred to the transfer material.
To make it easier to scrape the toner remaining on the upper side with the scraper blade 16 on the downstream side, lightly touch the outer surface of the photoconductor drum 1 to shift the position where the residual toner adheres, or to further charge the toner and the surface of the photoconductor to the ground. A flexible sheet 17 to be released is a scraper blade 17 that includes a position where the scraper blade 16 is in contact with the outer surface of the photosensitive drum 1 or evenly exposes the inner surface on the upstream side of the position to eliminate the charge of the photosensitive drum 1. LE that makes it easier to scrape toner with 16
It is a static elimination exposure means including a D array, an EL and the like.

By providing the charge eliminating exposure means 17 and the scraper blade 16 and the flexible sheet 15, it is possible to form a toner image with further less background stain. However, since the transfer efficiency can be increased as described above, not only the flexible sheet 15 but also the scraper blade 16 and the charge removing exposure means 17 may be provided as necessary. Scraper blade
When 16 is omitted, the developing roller 3 also has a cleaning function. It should be noted that if the charge eliminating exposure unit 17 is omitted, electric charges may remain on a part of the photoconductor, which may adversely affect the formed image.

The toner scraped off the photosensitive drum 1 by the scraper blade 16 drops onto the developing roller 3 or the developer supplying member 5, and the developing roller 3 causes the developing roller 3 to approach the photosensitive drum 1 in a developing area. Carried by the developer supply member 5 or returned to the developer chamber 6 for reuse. Reference numeral 18 denotes a partial partition wall made of a flexible sheet that allows the developer, which is conveyed by the developing roller 3 and is returned to the developer chamber 6, to pass therethrough and prevents the developer from jumping out of the developer chamber 6.

Reference numeral 19 is a scraper blade for removing the toner, paper powder, etc. adhering to the transfer roller 14 and dropping it into the collecting container 20, and 21 is a tip end which is substantially in contact with the outer surfaces of the photosensitive drum 1 outside the image forming area. As described above, the transfer material guide is provided on the main body frame 30 of the image forming apparatus or the image forming unit frame 31 described later to prevent the transfer material from being wrapped around the photosensitive drum 1.
It goes without saying that the transfer material guide is also provided so as to form a transfer material transfer path to prevent the transfer material from being wound around the transfer roller or the like.

The transfer material on which the toner image has been transferred has the toner image fixed by the heat roller fixing device 22, and the discharge roller 23
Is discharged to the outside of the main body frame 30.

In the image forming apparatus of FIG. 1, a developing device including a photosensitive drum 1 having an image exposing means 2 therein, a cleaning means thereof, a developing roller 3 and a means for forming a developer layer on the developing roller 3 is a main frame. The image forming unit frame 31 is integrally and detachably attached to the image forming unit frame 31, and the image forming unit frame 31 is taken out by opening the door 30a provided on the top plate of the main body frame 30 and from the upper side. It is dropped into the forming device and mounted.

Reference numeral 31a is a lid for the developer supply port to the developer chamber 6,
Reference numeral 31b is a slide-type protective cover that covers and protects the outside of the exposed portion of the photosensitive drum 1 when the image forming unit frame 31 is taken out from the main body frame 30.

The present invention is not limited to the above-described example, and the image exposure means may omit the rod lens array and perform image exposure by directly bringing the LED or EL array close to the inner surface of the photoconductor. Further, the image forming unit frame 31 may be taken out to the rear wall side of the body frame 30, that is, the side opposite to the fixing device 22, or of course, the photoconductor drum 1 or the developing device may be directly attached to the body frame 30. Good. As already mentioned,
A photoconductor belt may be used instead of the photoconductor drum 1.

When a photoconductor belt is used, a laser beam modulated on the image exposure means 2 based on image data is scanned by a polarizing means such as a rotary polygon mirror to make image light incident on the inner surface of the photoconductor belt. It is easy to use a laser optical system. Also in the case of this laser scanning, the bias voltage applied to the developing roller 3 is applied during the time Texp during which the laser beam image-exposes a line corresponding to the image portion on one surface of the rotary polygon mirror and during the subsequent time t. Is a constant voltage having the same polarity as the toner charging during the total time T ₁ of the toner, and then the toner is charged during the time T ₂ until the image exposure of the line corresponding to the image portion on the next surface of the rotary polygon mirror. A rectangular wave AC voltage having a constant voltage of opposite polarity is used. As a result, a clear toner image without background stain can be formed.

In this case, the control circuit of FIG. 4 also includes a circuit surrounded by a dotted frame, and the CPU controls the rotation speed of the rotary polygon mirror rotation motor by using the clock pulse from the clock pulse generation circuit, and the index sensor. The timings T ₁ and T ₂ of image exposure and bias voltage are controlled based on the information obtained by detecting the rotational phase of the rotary polygon mirror.

[0053]

According to the chargeless image forming apparatus of the present invention, a clear toner image with almost no background stain can be formed on the surface of the photoconductor and can be efficiently transferred to the transfer material by electric transfer. ..

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a configuration showing an example of an image forming apparatus of the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a partial cross-sectional view of a photoconductor.

FIG. 4 is a block diagram of a main part of a control circuit.

FIG. 5 is a timing chart of incidence of image light and bias voltage of the developing roller.

FIG. 6 is a schematic diagram of an image forming unit.

FIG. 7 is a schematic diagram of an image forming unit.

[Explanation of symbols]

 1 photoconductor drum 2 image exposure means 3 developing roller 6 developer chamber 13 timing roller 14 transfer roller 22 fixing device 30 body frame

Claims (3)

[Claims] 1. A developer on a developing roller to which a bias voltage is applied by a developing means, wherein the image exposing means repeats image exposure along a line substantially perpendicular to the rotating direction of the photosensitive body on the surface of the rotating photosensitive body. In an image forming apparatus that forms a toner image by facing a layer to the outer surface of the photoconductor at the line position, an insulating toner is used as the toner of the developer, and a bias voltage applied to the developing roller is set to a value that repeats the image exposure. An image forming apparatus is characterized in that an AC voltage having the same polarity as the charging of the toner during the image exposure and having the opposite polarity to the charging of the toner between the image exposure and the next image exposure is synchronized. .. 2. The photoconductor is configured by providing a charge generation layer on an inner surface side transparent conductive layer, a charge transport layer thereon, and an outer surface side charge generation layer thereon, 2. The image forming apparatus according to claim 1, further comprising: a discharging exposure unit that inputs light for discharging to a photosensitive member until it reaches the line position on the downstream side. 3. The image forming apparatus according to claim 1, wherein the AC voltage applied to the developing roller is a rectangular wave.