JPH04281486A - Transfer device for image forming device - Google Patents

Abstract

PURPOSE:To prevent a transfer current from being increased and to execute the excellent transfer even when transfer is executed on a transfer paper which is humidified under a high humid environment and whose resistance value is lowered by obtaining such constitution that an electrode member on which a bias is impressed is provided near a transfer member and the current is made to flow to the electrode member from the transfer member under the state of the high humid environment. CONSTITUTION:A toner image formed and carried on the surface of an electrophotographic photosensitive drum 1 is transferred on the transfer paper which is made to abut on the drum 1 and passed through the drum 1 and a transfer roller 5 on which the bias is impressed. Then, the bias impressed on the roller 5 when the paper is passed and the transfer is executed is controlled to a constant voltage by impressing the bias of the constant current on the roller 5 abutting on the dark potential part of the drum 1 when the paper is not passed and deciding the transfer voltage when the paper is passed and the transfer is executed based on the voltage generated at that time. Besides, an electrode plate 21 on which the bias voltage is impressed is arranged at a position near the roller 5 where the current from the roller 5 is made to flow in when the bias of the constant current is impressed on the roller 5 when the paper is not passed under the high humid environment.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus. More specifically, a transferable image is formed and carried on the surface of an image carrier such as an electrophotographic photoreceptor or an electrostatic recording dielectric material by an image forming process that includes a step of charging the image carrier surface to a predetermined dark potential (primary charging). The present invention relates to a transfer device of an image forming apparatus that transfers the transferable image to a transfer material passed between the image carrier and a transfer member that is brought into contact with the image carrier and applied with a bias.

0002

2. Description of the Related Art FIG. 9 is a schematic diagram of an example of an image forming apparatus using a transfer roller as a transfer member, and this example is a printer or a copying machine using an electrophotographic process.

Reference numeral 1 denotes a rotating drum-type electrophotographic photosensitive member (hereinafter abbreviated as drum) as an image carrier. Electrophotographic process equipment such as a primary charger 2, an image exposure device 3, a developing device 4, a transfer roller 5 as a transfer member, and a cleaning device 6 are arranged around the drum 1.

14 is a paper feed tray, 15 is a transfer material (hereinafter referred to as paper) stacked on the tray, and 13 is a transfer material that separates the stacked paper into individual sheets by working with a separating claw (not shown) or the like. This is a paper feed roller that feeds and conveys paper into the device, and the paper 15 that is fed into the device.
is conveyed to the abutment nip portion (transfer portion) N between the drum 1 and the transfer roller 5 via the guide 12a → registration roller pair 10 and 11 → transfer guides 8 and 9. Then, the paper that has passed through the transfer section N is discharged to the paper discharge tray 16 via the guide 12b and the fixing device 7. 17 is the exterior of the device.

The image forming apparatus of this embodiment is of a reversal development type, and the drum 1 is charged with a negative charge, and the charge (triboelectric charge) of the toner as a developer is also charged with a negative charge.

The drum 1 is rotated clockwise as indicated by an arrow at a predetermined circumferential speed (process speed), and the surface of the rotating drum is charged with a predetermined dark potential VD by a primary charger 2.
Then, image exposure is performed by an exposure device 3 such as a laser scanner, and the exposed portion of the drum 1 has a small absolute value of the potential VD, becomes a bright potential VL, and an electrostatic latent image is formed. Ru.

[0007] This latent image is reversely developed as a toner image by a developing device 4. In the developing device 4 of this embodiment, a thin layer of negatively charged toner is coated on a rotatably mounted sleeve 4a, and the sleeve 4a has a dark potential VD of the drum 1 which is smaller than the bright potential VL. A large voltage is applied, and the toner on the sleeve 4a is transferred only to the bright potential VL portion of the drum 1, and the latent image is visualized.

The toner image formed on the drum 1 is transferred from a paper feed tray 14 to a paper feed roller 13, a conveyance guide 12a, a pair of upper and lower registration rollers 10 and 11, and a pair of upper and lower transfer guides 8.
- The image is transferred onto the paper 15 fed and conveyed to the transfer unit N via the transfer roller 5 by the transfer roller 5 to which a positive bias is applied. The paper 15 to which the toner image has been transferred is separated from the drum 1 and introduced into the fixing device 7 by the guide 12b, where the toner image is heated and fixed on the paper surface, and then discharged to the paper discharge tray 16.

On the other hand, the toner remaining on the drum 1 without being transferred is collected by the cleaning device 6 and removed from the drum 1.
is cleaned and used repeatedly for imaging.

The transfer roller 5 is made up of a core metal 5a and an elastic layer 5b formed concentrically with the core metal into a roller shape by molding or the like, and is applied parallel to the drum 1 with a predetermined contact pressure. The drum 1 is brought into contact with the drum 1 and rotates in the forward direction at approximately the same circumferential speed as the drum 1.

In the transfer roller 5 of this example, the core metal 5a has an outer diameter φ.
8.0, the outer diameter of the elastic layer 5b is 20.0 mm, and the roller length is 2.
It is 2cm. The elastic layer 5b has a resistance value adjusted by adding and dispersing carbon and zinc oxide into a foamed EPDM rubber material, and the resistance value is approximately 2.5×10 3 Ωcm and the rubber hardness is 3.
0° (Asuka C). The width of the nip N formed between the drum 1 and the transfer roller 5 when they are brought into contact with the drum 1 with a total pressure of 1.5 kg is approximately 2.5 mm, and the width between the nip N and the transfer roller core 5a is approximately 2.5 mm. The resistance of is 2×108 Ω.

When transferring using the transfer roller 5 as described above, the bias applied to the transfer roller 5 is 2.
．． Approximately 8KV is appropriate. However, it is difficult to control the resistance value of such a transfer roller 5 during manufacture, and the resistance value varies slightly during manufacture. Further, the resistance value varies depending on the environment, especially the amount of moisture in the atmosphere. Due to this resistance value variation, the appropriate bias applied to the transfer roller 5 during transfer also changes.

As an effective bias control means for the transfer roller 5 which undergoes such changes, the present applicant has previously proposed a control method as disclosed in Japanese Patent Application No. 1983-276106.

[0014] This control method uses, for example, a dark potential of -700V.
The transfer roller 5 is brought into contact with the drum 1 on which the paper is placed, and a constant current bias is applied to the transfer roller 5. Based on the voltage generated at this time, the voltage is applied to the transfer roller 5 during transfer (when paper passes). This control method is used to determine the bias (hereinafter, this control method will be referred to as the ATVC method). The current value of the constant current bias applied to the transfer roller 5 may be determined as necessary, but it is determined that the current value of the constant current bias applied to the transfer roller 5 is
It is sufficient if the current is about 20 μA, and in this case, 20 μA is used in particular.

FIG. 10 shows the relationship between the bias applied to the transfer roller 5 and the current in this case. FIG. 10 is a diagram (VI characteristic diagram) showing the relationship between the bias voltage V applied to the transfer roller 5 and the current I in a normal environment (20° C., 60% RH), and ID in the diagram is a non-paper-passing diagram. The transfer roller current with respect to the transfer roller voltage at the time, IP is the transfer roller current at the time of paper passing. When the transfer roller current ID when the paper is not passing is 20 μA, the voltage V is 2.8 KV, and the transfer roller current IP when the paper is passing is 7 μA. If this transfer roller current is 7 μA or more, transfer failures due to insufficient current will not occur.

FIGS. 11(a) and 11(b) show equivalent circuits of the transfer device when paper is not passing and when paper is passing, respectively, and R1 is the resistance of the drum 1 (the resistance of the VD potential of the photoreceptor of the drum). ), R5
is the resistance between the core metal 5a of the transfer roller 5 and the nip portion N formed by the transfer roller 5 and the drum 1 (resistance of the rubber material of the transfer roller).

R15 is the resistance of the paper 15 that is the transfer material, V is the power supply voltage that supplies power to the transfer roller 5, 20 is the ground, and ID
is the current when a constant current bias is applied to determine the transfer voltage when paper is not passing, and is 20 μA here, and IP is the current during transfer, which is 7 μA.

Here, the resistance R1 is 2×10 7 Ω,
Resistor R5 is approximately 1.2×108 when V=2.8KV
Ω, and resistance R15=2.6×10 8 Ω. First, as shown in FIG. 11(a), the current ID=20μ when paper is not passing.
When a constant current bias of A is applied to the transfer roller 5 and the voltage is held, the paper 15 acts as a resistor R15 as shown in (b) during paper passing, and the current IP becomes 7 μA.

[0019]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional apparatus, although it is possible to control the voltage according to changes in the resistance value of the transfer roller 5 due to the environment using the AVTC method, it is difficult to cope with changes in the resistance value R15 of the transfer material, especially the paper 15. Since the voltage is not controlled, there is a problem in that a voltage higher than necessary is applied in a high humidity environment.

For example, if a transfer roller 5 with a resistance value of 2×10 8 Ω (resistance measurement voltage 2 KV) is used in an environment of high temperature and high humidity of 32° C. and 85%, the paper 15 that has been left in this environment for a long period of time and has sufficiently absorbed moisture is transferred. FIG. 12 shows the VI characteristics when transferring. IH is the VI characteristic when transferring to moisture-absorbing paper. When the paper 15 absorbs moisture, the resistance of the paper decreases, so the voltage required to obtain a transfer current of 7 μA may be about 2 KV, but in this case, a current of 10 μA or more flows during paper passing. This is equivalent to the resistance R15 becoming smaller in the equivalent circuit shown in FIG. 11(b).

[0021] In this way, in a high-humidity environment, the voltage is increased more than necessary, which increases the burden on the high-voltage power supply. Also,
Since a large current is passed through the drum 1 as an image carrier, electrical deterioration of the drum 1 is caused quickly. Moreover, since the drum potential is lowered by the transfer current, the margin for background fog (paper traces) that occurs is also disadvantageously reduced.

The present invention similarly uses the ATVC method to control the voltage applied to the transfer member, but it is possible to perform image transfer without the above-mentioned problems even if the transfer material absorbs moisture and its resistance decreases. An object of the present invention is to provide a transfer device for an image forming apparatus.

[0023]

[Means for Solving the Problems] The present invention forms and carries a transferable image on the surface of an image carrier by an image forming process that includes a step of charging the surface of the image carrier to a predetermined dark potential, and the transferable image is , the image is transferred to a transfer material that passes between the image carrier and a transfer member that is in contact with the image carrier and a bias is applied, and the bias application to the transfer member at the time of paper passing transfer is changed to a non-paper passing transfer member. An image forming apparatus that controls a constant voltage by applying a constant current bias to a transfer member that is in contact with the dark potential portion of the image carrier surface, and determining the transfer voltage during paper transfer based on the voltage generated at that time. In this transfer device, a bias voltage (including 0 V) is applied to a position near the transfer member such that a current flows from the transfer member when a constant current bias is applied to the transfer member when paper is not passing in a high humidity environment. This is a transfer device of an image forming apparatus characterized by disposing an electrode member to which an applied voltage is applied.

[0024]

[Operation] In other words, in a high humidity environment, current flows from the transfer member to the electrode member close to the transfer member, which lowers the voltage during transfer, and when ATVC control is performed, the hold voltage is lowered and the voltage is lowered than necessary. This eliminates the need to increase the transfer current, making it possible to transfer images even on paper whose resistance has decreased due to moisture absorption in a high-humidity environment, without passing an excessive current, reducing the load on the high-voltage power supply. This makes it possible to slow down the progress of deterioration of the carrier.

[0025]

[Example] <First Example> (Figs. 1 to 3) Fig. 1 is a schematic diagram of the main parts of the apparatus of the first example, and 19 is a transfer member brought into contact with the drum 1 as an image carrier. transfer roller 5
21 is an electrode plate disposed close to the transfer roller 5; 22 is a power source that applies a bias voltage to the electrode plate 21; The outer diameter of the transfer roller 5 is 20 mm, the length is 22 cm, the opposing area between the transfer roller 5 and the electrode plate 21 is 20 cm 2 , and the electrode plate 21 is held with a gap of 2 mm from the transfer roller 5. Electrode plate 2
1 facing the transfer roller 5, the voltage V of the power supply 22
22 may be arbitrarily set by experiment or the like. In this embodiment, in order to promote current leakage from the transfer roller 5 to the electrode plate 21, a sharp protrusion 21a is formed on the surface of the electrode plate 21 facing the transfer roller. It doesn't really need to be.

It should be noted that the image forming apparatus is constructed by disposing necessary image forming process equipment around the drum 1 and at necessary parts as shown in FIG. 9, but these are omitted in FIG.

In this embodiment, the high humidity environment is 32° C. and 85%, and the resistance of the transfer roller 5 is 2.0×10 8 when the potential of the drum 1 is VD-700V and a bias voltage of 2KV is applied.
Let it be Ω. Here, in order to apply a bias voltage to the transfer roller 5, a constant current bias (20 μA) is applied from the power supply 19 to the core bar 5a of the transfer roller 5 when the paper is not passing. There is a plate 21, to which a bias voltage of approximately -2 KV of polarity opposite to that of the bias power source 19 of the transfer roller 5 is applied from a power source 22. This state is shown in an equivalent circuit as shown in FIG.

In FIG. 2, R21 is the resistance between the core metal 5a of the transfer roller 5 and the electrode plate 21, and
This includes the resistance of the rubber material and the space gap between the transfer roller 5 and the electrode plate 21. V22 is the bias voltage of the power supply 22, ID is the current flowing from the transfer roller 5 to the drum 1,
Ia is a current flowing from the transfer roller 5 to the electrode plate 21.

In a normal environment (20° C., 60%), the resistance R21 is very large and the current Ia is close to 0, but in a high humidity environment, the resistance R21 becomes small and the current Ia becomes large. come. FIG. 3 shows the VI characteristics when paper is passed and when paper is not passed in this high humidity environment. ID+Ia is V-I when a bias voltage is applied to the electrode plate 21 when paper is not passed.
As a characteristic, the voltage at which 20 μA flows through the transfer roller 5 at this time is held. In this case, it is 2KV.

On the other hand, the V-I characteristic of the voltage and the current flowing from the transfer roller 5 to the drum 1 when the moisture-absorbing paper is passed is as shown by IH, and the bias voltage applied to the transfer roller 5 is 2K.
The current at V is 7 μA, and no excessive current flows.

Furthermore, in a normal environment, the resistance R21 is very large and the current Ia is almost 0, so no voltage drop occurs during transfer, and if the humidity becomes high, the transfer roller will change depending on the humidity. The voltage applied to 5 can be lowered.

<Second Embodiment> (FIGS. 4 to 7) The electrode member close to the transfer member does not need to be provided with a dedicated electrode member, and a functional part inside the image forming apparatus can also be used as the electrode member. It is also possible to perform the same control as in the case where the electrode plate 21 in the first embodiment is provided by causing the current from the transfer roller 5 to flow therein.

FIG. 4 shows an example of this, in which the static eliminating needle is also used as an electrode member. That is, 24 is the transfer roller 5
A static elimination needle provided near (for example, a proximity distance of 1 mm)
25 is an insulating member covering the static eliminating needle 24, and 26 is a power source that applies a bias voltage to the static eliminating needle 25.

The static eliminating needle 24 is originally used for cleaning paper 1 in a low humidity environment.
In order to improve the instability of paper conveyance caused by electrification in step 5,
Since it is provided for the purpose of neutralizing the paper 15, a bias of polarity opposite to the transfer bias is generally applied (including 0 V). In this embodiment, the static eliminating needle 25 is also used as an electrode member through which a current flows from the transfer roller 5 at high temperatures, and a voltage of -2.5 KV is applied to the static eliminating needle 24 from the power source 26.

Generally, the static eliminating needle 24 is covered with an insulating member 25 except for its tip, and is configured such that current flows only from the portion of the distal end of the static eliminating needle that faces the paper 15. In order to actively flow current from the transfer roller 5 to the static elimination needle 24 in a humid environment, the portion of the insulating member facing the transfer roller 5 is largely cut out as indicated by a two-dot chain line 25a.

FIG. 5 shows an equivalent circuit of the apparatus of this embodiment when paper is not passing, where R24 is the resistance between the static elimination needle 24 and the core bar 5a of the transfer roller 5, and V26 is the voltage of the static elimination needle bias power supply 26. , Ib is a current flowing from the core metal 5a of the transfer roller 5 to the static elimination needle 24. This current Ib is approximately 0 in a low humidity environment or a normal environment, but increases in a high humidity environment.

Therefore, when a constant current control of 20 μA is performed in a high humidity environment of 32° C. and 85%, the V-I characteristic as shown in FIG. 6 is obtained. ID is the current flowing through drum 1, I
D+Ib is the sum of the currents flowing from the core metal 5a of the transfer roller 5 to the drum 1 and the static elimination needle 24, and the sum of this current ID+
When Ib=20μ, the bias voltage applied to the transfer roller 5 is 2KV.

FIG. 7 shows an equivalent circuit when paper is passed, and R
15 is the resistance of the paper 15 at the nip between the drum 1 and the transfer roller 5, IH is the current flowing through the nip, R15' is the resistance of the paper 15 between the transfer roller 5 and the static elimination needle 24, and Ic is the resistance between the transfer roller 5 and the static elimination This is the current flowing through the needle 24. In this way, the current during paper passing can be divided into one that flows to the drum 1 via the paper 15 and one that flows through the static eliminating needle 24 through the air. The VI characteristic in this case is shown in FIG. 6. paper 1
The current IH flowing to the drum 1 via the transfer roller 5 is 7 μA when a bias voltage of 2 KV is applied to the transfer roller 5, but the current from the transfer roller 5 is IH (7 μA) + Ib (8 μA) + I
c (4 μA), so the current is 19 μA.

As described above, the static eliminating needle 24 is also used as a proximal electrode for the transfer roller 5, and while stabilizing the paper conveyance in a low humidity environment, it also serves as a proximal electrode for the paper 15 in a high humidity environment.
The current flowing to the drum 1 through the drum 1 can be reduced.

Third Embodiment (FIG. 8) In this embodiment, a pair of upper and lower rollers guide the paper 15 from the pair of registration rollers 10 and 11 to the pressure nip (transfer section) N between the drum 1 and the transfer roller 5. The lower transfer guide 8 of one of the transfer guides 8 and 9 is used as a proximal electrode member for the transfer roller 5. The lower transfer guide 8 has its leading end close to the transfer roller 5 in order to guide the paper 15, which is the transfer material, close to the nip N between the drum 1 and the transfer roller 5. In this embodiment, the tip of the lower transfer guide 8 is bent downward along the arc of the transfer roller 5 in order to increase the area facing the transfer roller 5, but this shape is not the same as shown in the figure. It is not limited to the shape.

In this embodiment, the lower transfer guide 8 is grounded, but it goes without saying that a bias having a polarity different from the transfer bias may be applied. Also, the lower transfer guide 8 is the paper 15
The tip is disposed as close to the transfer roller 5 as possible so that the transfer roller 5 can be smoothly conveyed and a current can flow from the transfer roller 5 in a high humidity environment. Here, lower transfer guide 8
The distance between the transfer roller 5 and the transfer roller 5 is 0.5 mm.

With the above configuration, the lower transfer guide 8 is also used as a proximal electrode for the transfer roller 5, and the current flowing to the drum 1 through the paper 15 can be reduced in a high humidity environment.

[0043]

As described above, according to the present invention, a constant current bias is applied to the transfer member when paper is not passing, and the voltage applied to the transfer member during transfer (when paper is passing) is applied based on the voltage generated at this time. In the transfer device that determines the voltage, an electrode member to which a bias is applied is provided near the transfer member, and a current flows from the transfer member into this electrode member in a high humidity environment. However, even when transferring to a transfer material with a reduced resistance value, the voltage at the time of transfer is lowered, making it possible to transfer without excessive current flowing, reducing the load on the voltage power supply, and reducing the image bearing capacity of the photoreceptor, etc. It has the effect of slowing down the progression of body deterioration.

[Brief explanation of the drawing]

[Figure 1] Schematic diagram of the first embodiment device

[Figure 2]
Equivalent circuit diagram

[Figure 3] VI characteristic diagram in high humidity environment

[Figure 4
] Schematic diagram of the second embodiment device

[Figure 5] Equivalent circuit diagram when paper is not passing

[Figure 6] VI characteristic diagram in high humidity environment

[Figure 7] Equivalent circuit diagram when passing paper

[Figure 8] Schematic diagram of the third embodiment device

[Figure 9]
Schematic diagram of an example of an image forming apparatus

[Figure 10] VI characteristic diagram in normal environment

[Figure 11] (a) and (b)
are equivalent circuit diagrams when paper is not passing and when paper is passing, respectively.

[Figure 12] VI characteristic diagram when transferring to moisture absorbing paper

[Explanation of symbols]

1 Drum (image carrier) 5 Transfer roller (transfer member) 8 Lower transfer guide (also serves as electrode member) 15 Paper (transfer material) 21 Electrode plate (electrode member) 24 Static elimination needle (also serves as electrode member)

Claims (1)

[Claims] 1. A transferable image is formed and carried on the surface of an image carrier by an image forming process that includes a step of charging the surface of the image carrier to a predetermined dark potential, and the transferable image is transferred between the image carrier and the image. The image is transferred to the transfer material passed between the transfer member that is brought into contact with the carrier and a bias is applied, and the bias applied to the transfer member during the paper transfer is applied to the dark potential portion of the image carrier surface when the paper is not passed. In a transfer device of an image forming apparatus, a constant current bias is applied to the transfer member in contact with the transfer member, and the transfer voltage during paper transfer is determined based on the voltage generated at that time to control the constant voltage. An electrode member to which a bias voltage is applied is arranged at a position near the transfer member such that a current flows from the transfer member when a constant current bias is applied to the transfer member when paper is not passing through the transfer member. Transfer device of image forming device.