JPH0419776A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of phenomena such as irregularities in an image and defective transfer by supplying a bias voltage for a bias impressing member from the bias power source of a contact charging member and changing impressed voltage on the bias impressing member in accordance with the load change of the contact charging member. CONSTITUTION:By making the outputs of bias means 13 and 12A for impressing on the contact charging member 1 to be a bias supplying source for impressing the bias on the bias impressing member of a destaticizing needle 7 which is disposed on the way of a transfer material carrying path, a bias value which is impressed on the destaticizing needle 7 can be properly changed in accordance with the load change of the contact charging member 1 with reference to the change in a peripheral environment. Thus, the occurrence of the phenomena such as the irregularities in the image and the defective transfer caused on the electrical interference between the transfer material P and the bias impressing member 7 which is arranged opposite to the transfer material P on the way of the transfer material P traveling path can be prevented irrespective of the environmental change; even under the environment of low humidity, or under the environment of high humidity.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an image forming process (electrophotographic process, electrostatic recording dielectric, etc.) that includes a step of charging the surface of an image carrier (electrophotographic photoreceptor, electrostatic recording dielectric, etc.). A transferable image (unfixed toner image) corresponding to the desired image information is formed using an electronic recording process, etc.
The present invention relates to an image forming apparatus that forms an image by transferring the transferable image onto a transfer material using a transfer means.

More specifically, the present invention relates to an image forming apparatus that uses a contact charging device as a charging processing means for an image carrier, which charges a surface of the image carrier by bringing a charging member to which a voltage is applied into contact with the image carrier.

(Prior Art) In the image forming apparatus as described above, a corona discharge device has conventionally been widely used as a device for charging a charged object such as an image carrier or a transfer material.

A corona discharge device is effective as a means for uniformly charging the surface of an object to be charged, such as an image carrier, to a predetermined potential. but,
It requires a high-voltage power supply and has the problem of generating undesirable ozone due to corona discharge.

In contrast to such a corona discharge device, a contact charging device, which charges the surface of the charged object by bringing the charging member to which a voltage is applied as described above into contact with the surface of the charged object, can reduce the voltage of the power source and eliminate ozone. Because of its advantages such as low generation amount, it can be used, for example, in image forming apparatuses to charge the surface of image carriers such as photoreceptors and dielectrics, transfer materials, and other charged objects instead of corona discharge devices. It has attracted attention as a means and device, and research on its practical application is progressing.

For example, the present applicant first proposed (Patent Application No. 62-51492
No. FI2-230334, etc.), in a contact charging device, an oscillating electric field ( By forming an alternating electric field (an electric field (voltage) whose voltage value changes periodically with time) between the charging member and the charged object, and by using a charging member with a high resistance layer on the surface layer, Uniform charging of the charged object It is possible to prevent leakage due to pinholes, scratches, etc. on the surface of the charged object such as a photoreceptor.

The contact charging member can be in the form of a roller, belt, web, plate, pad, or various other forms, and is often constructed of an elastic body having medium to high resistance. A medium to high resistance is generally used because it is advantageous to prevent leakage with the charged object and to perform uniform charging, and a resistance of about 105 Ω・cm to 10 IO Ω・cm is used. is often used.

FIG. 9 shows a schematic configuration of an example of an image forming apparatus using contact charging means as the charging means for the image carrier and the transfer means.

Reference numeral 3 denotes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as drum) as an image carrier, which is rotated clockwise as indicated by an arrow at a predetermined circumferential speed (process speed).

1 is a rotating roller-like member (hereinafter referred to as a charging roller) as a contact charging member that is brought into contact with the drum 3 with a predetermined pressing force;
Ac) Bias + Direct current (DC) An AC power source and a DC power source are used as bias power sources to apply bias, and the circumferential surface of the rotating tram 3 is uniformly charged to a predetermined polarity and potential by the charging roller 1 to which this voltage is applied. It is processed.

The surface of the drum 3, which has been uniformly charged by the charging roller 1, is then subjected to exposure means (laser, scanning exposure means, etc.) (not shown).
By receiving exposure 6 of target image information by a slit exposure means for an original image, an electrostatic latent image corresponding to the target image information is formed on the peripheral surface. The latent image is then developed (regular development or reversal development) by the developing device 4 and visualized as a transferable toner image.

On the other hand, a nip portion (
A transfer material P is fed to the transfer section) at appropriate timing synchronized with the rotation of the tram 3, and the toner image on the drum 3 surface is sequentially transferred onto the surface of the transfer material P.

A voltage of opposite polarity to the toner is applied to the transfer roller 2 by a bias power supply 14, and when the back side of the feeding transfer material P is charged by the transfer roller 2, the toner image on the drum 3 side is formed by the charging electric field. or transfer to the second side of the transfer material.

The transfer material P that has passed through the transfer section is separated from the three surfaces of the drum,
The toner image is guided by the transport kite 8 and the fixing guide 11 and introduced into the nip between the heat fixing roller 9 and the pressure roller 10, where the toner image is fixed.

After the transfer material has been separated, the surface of the drum 1 is cleaned by a cleaning device 5 to remove residual toner and other drum surface residue after transfer, and is then turned over and used for image formation.

Reference numeral 7 denotes a charge eliminating needle for eliminating charges on the back surface of the transfer material P that has passed through the transfer section. Reference numeral 15 denotes a bias power supply that applies voltage to the static eliminating needle 7.

(Problems to be Solved by the Invention) In the image forming apparatus as described above, the resistance of the transfer material P (transfer paper) introduced into the apparatus tends to change considerably when environmental conditions change.

For example, if the transfer material P is exposed to high temperature and high humidity of about 35°C and 85% RH, the resistance will be 1/10 of that under normal environment]
/1000.

Therefore, if the environmental conditions change, it is easy to see the occurrence of transfer failure problems caused by the transfer current of the transfer means 2 flowing through the transfer material P into surrounding members.

In other words, the bias applied to the transfer roller 2 flows into surrounding members such as the static eliminating needle 7, causing a transfer failure.

In particular, since a bias having a polarity opposite to the transfer bias is generally applied from the power supply 15 to the charge eliminating needle 7 in order to eliminate charges on the back side of the transfer material P, the current of the transfer means 2 tends to flow therein.

In order to prevent this, if the bias value of the static elimination needle 7 is lowered, the excess backside charge of the transfer material P will be abnormally discharged to the conveyance guide 8 during double-sided printing or in a low humidity environment, causing image distortion. So I don't like it.

In this way, in the conventional device, due to changes in the environment, the transfer roller 2 and surrounding members, especially members such as the static elimination needle 7 to which a bias of opposite polarity is applied to the transfer bias (transfer material in the travel path of the transfer material) It has been difficult to make optimal settings because interference occurs via the transfer material P (bias application member disposed facing the bias application member) and the transfer material P, resulting in poor transfer and image disturbance.

The present invention relates to this type of image forming apparatus, and is capable of producing high-quality image-formed products without image defects caused by the above-mentioned image disturbance phenomenon or transfer failure phenomenon regardless of environmental changes, that is, under low humidity environments or high humidity environments. (Means for solving the problem) The present invention forms a transferable image on the surface of an image carrier by an image forming process including a step of charging the surface of the image carrier. The transferable image is transferred to a transfer material fed to an image carrier by a transfer means to form an image, and a bias applying member is disposed facing the transfer material in the travel path of the transfer material. In the image forming apparatus, the charging means for the surface of the image carrier is in contact with the surface of the image carrier;
A contact charging member to which a voltage is applied from a bias power supply, and the bias voltage to the bias application member is supplied from the bias power supply of the contact charging member, and the voltage applied to the bias application member is adjusted according to load fluctuations of the contact charging member. The image forming apparatus is characterized in that the image forming apparatus also changes the image forming apparatus.

Specifically, the bias applying member mentioned above is a static eliminating means for eliminating the static charge on the transfer material, and at least one side of a pair of heat fixing rollers that fixes the transferable image of the transfer material that has undergone image transfer on the surface of the transfer material. This is Laura Nato.

(Function) In other words, by using the output of the bias means that applies to the contact charging member as a bias supply source for applying bias to bias application members such as static elimination needles and fixing rollers placed in the transfer material conveyance path, In response to changes in the environment, it is possible to appropriately change the bias value applied to the static elimination needle, fixing roller, etc. as the load on the contact charging member changes. A high-quality image-formed product free of image defects due to image disturbance phenomena or transfer failure phenomena caused by electrical interference between a transfer material and a bias application member disposed opposite to the transfer material in the travel path of the transfer material. It is possible to always output stably.

(Example) <Example 1> (Figs. 1 to 4) Fig. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. Components and portions common to those of the image forming apparatus shown in FIG. 9 are given the same reference numerals and will not be described again.

The tram 3 as an image carrier is an OPC photoreceptor.

The charging roller 1 as a contact charging member has a second layer structure.
As shown in the cross-sectional model diagram in the figure, a conductive rubber layer 18 of 104 to 105 Ω·CI made of EPDM or the like is arranged on the core bar 19, and on top of that is a conductive rubber layer 18 of 107 to 109 Ω·cm made of hydrin rubber or the like.
A medium resistance layer 17 is provided on the outer peripheral surface of the layer 17, and a 107 to 1010 Ω·Cl layer made of a nylon material such as Trezin is provided on the outer peripheral surface.
A blocking layer 16 of l1 is provided, and the hardness is As.
An angle of about 50° to 70° was used in the ker-C measurement.

This charging roller 1 is powered by a constant voltage DC power source 13.
A superimposed bias of 0v direct current (D'C) bias and alternating current (AC) bias is applied, and this DC+ACC1
The three surfaces of the drum are uniformly and stably charged to -700V by the ass.

The bias voltage applied to the charging roller 1 is generated by the DC power supply 13 and the AC type #12A, or the DC power supply 13 has a constant voltage, whereas the AC power supply 12A performs constant current (effective value) control.

This is because the charging roller 1 causes a large load fluctuation depending on the environmental conditions, so the AC bias is optimized in accordance with this.

As an example, when constant current control is performed using a sine wave bias with an effective value of 700μA, RMS, at room temperature and humidity (23℃
, 50%RH) environment, an AC voltage of 1800Vpp is applied, whereas in a low temperature/low humidity environment (15℃, 10%RH)
The environment is 2200Vpp, high temperature and high humidity (35℃, 85%
In the RH) environment, an AC voltage of 1200 Vpp (7) is applied. This prevents pinholes due to poor charging in a low humidity environment or leakage discharge in a high humidity environment.The tram 3, which has been uniformly charged by the charging roller to 1700cm, is subjected to laser beam scanning exposure 6 in this example. As a result, an electrostatic latent image opposite to the target image information is formed, and this latent image is reversely developed in this example by the developing device 4 (developed by the laser beam exposure section). A sine wave bias of 1200 Vpp-1400 Hz from an AC power source 17 and a DC bias of about 15 oov from a DC power source 18 are applied to the developing sleeve 20 of the developing device 4 in a superimposed manner.

The transfer roller 2 is made of EPDM with a resistance value of 107 to 109 Ω・C [O1 hardness (Asker -C) of about 20° to 40°].
A rubber roller is used, and a positive bias of opposite polarity to the toner is applied to this transfer roller 2 by a bias power supply 14, and the applied bias value is +1°5 V to 4 KV.
The degree is appropriate.

By this transfer roller 2, the toner image on the side of the drum 3 is sequentially transferred onto the surface of the transfer material P fed to the transfer section between the tram 3 and the transfer roller 2.

The transfer material P that has passed through the transfer section is separated from the surface of the drum 3 and is conveyed along a conveyance guide 8 to a pair of fixing rollers 9 and 10. At this time, in order to prevent the charge on the back surface of the transfer material P from discharging to surrounding members and disturbing the unfixed toner image transferred from the drum side on the surface of the transfer material, the excess back charge is removed by the charge removal needle 7. Ru.

The static elimination needle 7 has a needle height u=3 mm as shown in Fig. 3.
- A serrated member made of stainless steel plate with a spacing d = 1.5 mm and a thickness of 0.2 t was used.

The static eliminating needle 7 is a bias applying member disposed facing the transfer material in the traveling path of the transfer material P.
The power supply 12A is rectified by a rectifier circuit 15A (FIG. 1) to apply a negative DC bias having a polarity opposite to that of the transfer bias.

FIG. 4 shows a specific circuit example of the rectifier circuit 15A. C1~
C4 is a capacitor, and D1 to D4 are tie autos. The bias value is -2 in normal environment due to variable resistor R1.
Adjustments were made so that the voltage was 8 V. With this configuration, the bias value applied to the static eliminating needle 7 can be changed almost ideally according to environmental changes as described below.

(1) In a low temperature/low humidity (15° C., 10% RH) environment, the resistance of the charging roller 1 increases, and the output of the AC bias power supply 12A becomes 2200 Vpp culm.

At this time, the output of the rectifier circuit 15A rises to about -3.4 KV, and the charge on the back surface of the transfer material P is strongly removed.

As a result, it is possible to prevent the toner image from being disturbed in the conveying section 8, which is particularly likely to occur under low humidity conditions. Also transfer the transfer material P to the drum 3.
It can also promote the effect of separation from

(2) In a high temperature and high humidity environment (35° C., 85% RH), the resistance of the charging roller 1 decreases, and the output of the AC bias power supply 12A becomes approximately 1200 Vpp.

At this time, the output of the rectifier circuit 15A drops to about -1.87V. Generally, in a high humidity environment, the resistance of the transfer material P is low, so there is almost no disturbance of the toner image in the conveying section 8. 7 and other surrounding members, and as mentioned above, the surface potential of the transfer roller 2 drops, resulting in poor transfer. However, in this embodiment, as the resistance of the charging roller 1 decreases, the bias applied to the charge removal needle 7 also decreases, so that the transfer bias can be prevented from leaking to the charge removal needle 7, and transfer failures do not occur.

<Embodiment 2> (Figure 5) In this embodiment, a negative bias is applied to the pair of fixing rollers in order to prevent the negative toner on the transfer material conveyed from the transfer section to the pair of fixing rollers from being offset to the heat fixing roller. In this case, as shown in FIG. 5, the AC power source 12A of the charging roller 1 is connected to the heat fixing roller 9, which serves as a bias applying member, and is disposed facing the transfer material in the travel path of the transfer material, through a rectifier circuit 15A. Nekatoner T is a rectified toner to which a negative bias with a repulsion relationship is applied.

Generally, when a bias is applied to the fixing roller 9, when the transfer material P absorbs moisture and becomes low in resistance under high temperature and high humidity conditions, the positive bias of the transfer roller 2 tends to flow into the fixing roller 9, resulting in poor transfer.

However, as in this embodiment, by converting the alternating current bias of the charging roller 1 into a constant current, rectifying it, and using it as the fixing roller bias, it is possible to counter environmental changes in the same manner as described in the first embodiment. It is possible to optimize the fusing bias.

Specifically, the resistor R1 in FIG. 3 is adjusted, and the rectifier circuit 15A is
The output was adjusted to -1.5KV under normal conditions. As a result, (1) In a low temperature/low humidity (15°C, 10% RH) environment, the resistance of the charging roller 1 increases, and the AC bias power supply 12A (
7) The EB power is about 2200Vpp, and the rectifier circuit 15
The output of A increases to about -1,83KV. The electrostatic offset of NEKA toner T to the fixing roller 9 generally tends to worsen in a low humidity environment, or at this time the fixing roller bias also increases, so that the offset prevention effect is improved.

(2) In a high temperature/high humidity (35° C., 85% RH) environment, the resistance of the charging roller 1 decreases, and the output of the AC bias power supply 12A becomes approximately 1200 Vpp.

At this time, the output of the rectifier circuit 15A drops to about -1, OKV. Therefore, it is possible to prevent the transfer bias from leaking to the fixing roller 9 via the transfer material P, and on the other hand,
Since offset is less likely to occur under high humidity conditions, a sufficient fixing bias can be supplied from the standpoint of offset resistance.

<Embodiment 3> (Figs. 6 and 7) This embodiment uses the fixing roller pair 9 and 1 in the above-mentioned Embodiment 2.
0 pressure roller 10, the AC power supply 12A of the charging roller 1 is rectified by a second rectifier circuit 15B (FIG. 6) provided separately from the rectifier circuit 15A for the fixing roller 9, and a positive bias is applied. It was designed to do so. The bias value is set to +1.5KV under normal circumstances.

The second rectifier circuit 15B is connected to the tie motor D1 as shown in FIG.
The direction of ~D4 is set to have an opposite relationship to that of the first rectifier circuit 15A.

With this configuration, the NEKA toner T is transferred to the fixing roller 9.
The offset prevention effect can be further improved by repelling the transfer material P and attracting it to the transfer material P using the bias of the pressure roller 10. Moreover, since both the fixing roller bias and the pressure roller bias decrease under high humidity, both rollers 9 and
10 and leakage to surrounding members via the transfer material P can be prevented.

<Embodiment 4> (FIG. 8) This embodiment is an example in which the output of the rectifier circuit 15A is supplied to the static elimination needle 7 and the fixing roller 9 at divided pressures.

Adjust the bias values so that the neutralizing needle bias is -2.8 KV and the fixing roller bias is -1.5 V under normal circumstances. Therefore, voltage dividing resistor R3 = 390M
Ω, R4=450MΩ.

By setting R3 and R4 large in this way, R3 can also serve as a current control resistor, preventing draughts when the fixing roller 9 shorts with surrounding members, and suppressing transfer bias leakage under high humidity. The effect can be improved.

For the same purpose, also for the static elimination needle 7. R5=200MΩ is included.

With this configuration, it is possible to appropriately apply the neutralizing needle bias and the fixing roller bias under any environment with a simple configuration consisting of only the rectifier circuit 15A and the voltage dividing resistor.

Incidentally, in the above embodiments, an example was explained in which a roller charging method was used as the transfer means, but a similar transfer defect problem also exists in a transfer method using corona charging, and the present invention is also effective against this problem. It acts on

In addition, although the embodiment has been described in which AC and DC voltages are superimposed as biases applied to the contact charging member 1, the present invention can be applied in the same way by performing constant current control even in a system where only DC voltage is applied. It is possible to implement it.

(Effects of the Invention) As described above, according to the image forming apparatus of the present invention, regardless of environmental changes, the transfer material and the transfer material in the travel path of the transfer material can be used even in a low humidity environment or a high humidity environment. It is now possible to always stably output high-quality image-formed products without image defects caused by image disturbance phenomena or transfer failure phenomena caused by electrical interference with the bias application member disposed opposite to the A goal is well achieved.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of the device of the first embodiment. FIG. 2 is a cross-sectional model diagram showing the layer structure of the charging roller. FIG. 3 is a front view of a portion of the static eliminating needle member. Figure 4 is a rectifier circuit diagram. FIG. 5 is a schematic configuration diagram of the device of the second embodiment. FIG. 6 is a schematic configuration diagram of the device of the third embodiment. FIG. 7 is a second rectifier circuit diagram. FIG. 8 is a schematic configuration diagram of the device of the fourth embodiment. FIG. 9 is a schematic configuration diagram of an example of a conventional device. 1 is a charging roller as a contact charging member, 2 is a transfer roller,
3 is an electrophotographic photosensitive drum as an image carrier, 7 is a static eliminating needle, 9 and 10 are a pair of fixing rollers, 12 and 12A are AC power supplies, 13 is a DC power supply, and 15A and 15B are first and second rectifier circuits. . Kaya map

Claims (3)

[Claims] (1) A transferable image is formed on the surface of an image carrier by an image forming process including a step of charging the surface of the image carrier, and the transferable image is transferred by a transfer means to a transfer material fed to the image carrier. In an image forming apparatus that performs image formation and has a bias applying member disposed in a travel path of the transfer material facing the transfer material, the charging means on the surface of the image carrier is in contact with the surface of the image carrier,
A contact charging member to which a voltage is applied from a bias power source, and the bias voltage to the bias applying member is supplied from the bias power source of the contact charging member, and the voltage applied to the bias applying member is adjusted according to load fluctuations of the contact charging member. An image forming apparatus characterized in that the image forming apparatus changes. (2) The image forming apparatus according to claim 1, wherein the bias applying member is a charge eliminating means for eliminating charges on the transfer material. (3) The image forming apparatus according to claim 1, wherein the bias applying member is a roller on at least one side of a pair of heat fixing rollers that fixes the transferable image of the transfer material that has undergone image transfer onto the surface of the transfer material. .