JP3229410B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided with a discharger provided so as to face an image carrier.

[0002]

2. Description of the Related Art In an image forming apparatus using, for example, a drum-shaped or belt-shaped photoconductor as an image carrier, various dischargers (chargers) are used. For example, when transferring a toner image on a photoconductor to a recording medium such as transfer paper, corona discharge is performed by a discharger facing the photoconductor, and the toner image is transferred to the recording medium. Further, after the transfer, a corona discharge is performed by a discharger for separation to separate the recording medium moving while being in contact with the photoconductor from the photoconductor.

[0003] In this type of image forming apparatus, a transfer discharger and a separation discharger are sometimes integrated, but such an integrated transfer / separation discharger or a single discharger is used. The transfer discharger is provided with a sheet-like recording medium guide member for appropriately guiding the recording medium before transfer to the transfer section. That is, such a recording medium guide member is provided at the entrance side of the discharger.

Heretofore, as a recording medium guide member of this type, a sheet having a large volume resistivity and being easily triboelectrically charged, such as a synthetic resin sheet (eg, a polyester sheet), has been used. When such a resin sheet is charged due to mutual rubbing with the recording medium, or when the discharge charge from the discharger stays on the resin sheet via the recording medium, the resin sheet floats around the resin sheet. This makes it easier for the remaining toner to adhere to the resin sheet. Further, in an image forming apparatus in which toner adheres between image forming areas on a photoreceptor, the toner is attracted to the resin sheet side, and easily adheres to the resin sheet.

When the toner adheres to the resin sheet, the toner adhered to the resin sheet adheres to the back surface of the recording medium when the next recording medium passes through the portion of the resin sheet. The toner adhered to the recording medium in this manner is fixed in a later fixing step, and thus appears as so-called back contamination by the toner.
In particular, when an image is formed on both sides of a recording medium, or when a transparent or translucent transfer paper is used as the recording medium, the stain on the back of the recording medium becomes noticeable.

In order to solve such problems, for example, a technique in which a resin sheet is made conductive as disclosed in Japanese Patent Application Laid-Open No. 58-10767 has been proposed. When a conductive material is used, the electrical resistivity of the recording medium decreases in a high-humidity environment, so that the discharge charges during transfer and separation are transferred to the shield case of the discharger via a conductive resin sheet. Flows to the side,
Transfer or separation failure may occur. From this point, it is advantageous to use a recording medium guide member having a large volume resistivity as the recording medium guide member.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned conventional drawbacks and to suppress the occurrence of back stains on a recording medium.
An object of the present invention is to provide an image forming apparatus that can always obtain a high-quality image regardless of environmental conditions.

[0008]

In order to achieve the above object, the present invention comprises a discharger provided so as to face an image carrier and a material having a volume resistivity of 10 ¹⁰ Ω · cm or less, A recording medium guide member for guiding a recording medium between the discharger and the image carrier, and a material having a volume resistivity greater than 10 ¹⁰ Ωcm, and the recording medium guide member and a shield case of the discharger; A support member interposed between the recording medium guide member and a static eliminator for neutralizing the guide member while the recording medium guide member is in a grounded state. The recording medium guide member is wound around a plurality of rollers to perform recording. An image forming apparatus is proposed which is formed as an endless belt which is stopped when guiding a medium, and wherein the charge removing means is made of a charge removing member which is in contact with the endless belt and is grounded.

At this time, it is desirable to provide a switch circuit for cutting off the grounding state of the recording medium guide member when the recording medium passes between the image carrier and the discharger.

Similarly, the present invention provides a discharger provided so as to face an image carrier and a material having a volume resistivity greater than 10 ¹⁰ Ω · cm. A recording medium guide member for guiding the recording medium to the recording medium guide member; and a charge removing means for removing charges remaining on the surface of the recording medium guide member from the side in contact with the recording medium. Is wrapped around multiple rollers,
An image forming apparatus is provided, wherein the image forming apparatus is formed as an endless belt that is stopped when guiding a recording medium, and wherein the static elimination unit includes a static elimination member that is in contact with the endless belt and is grounded.

When the number of recording media passing between the discharger and the image carrier is counted to a predetermined number,
It is desirable to provide a driving unit for driving the endless belt to rotate.

Further, it is also advantageous to provide a cleaning member which abuts on the endless belt and cleans a surface of the endless belt which is in contact with the recording medium by rotation of the belt.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a transfer / separation device and its periphery of an image forming apparatus. In this figure, reference numeral 1 is
1 shows a drum-shaped photoconductor, which is a configuration example of an image carrier. A transfer / separation discharger 2 is provided below the photoconductor 1 so as to face the photoconductor. The transfer / separation discharger 2 includes a shield case 3, a transfer wire 4 extended without electrically contacting the shield case 3,
Similarly, it mainly includes a separation wire 5 and the like that are stretched without electrically contacting the case 3.

A transfer paper 6, which is an example of a recording medium, is fed toward a pair of registration rollers 7 from a paper supply unit (not shown). The transfer paper 6 is sent to a transfer section 8 between the photoreceptor 1 and the transfer wire 4.

On the photoreceptor 1, well-known charging, exposure,
A toner image is formed by sequentially performing development and the like. The toner image is transferred to the transfer paper 6 by corona discharge from a transfer wire 4 to which a voltage is applied by a high-voltage power supply (not shown). Transcribed above. After this transfer, the transfer paper 6 moving in contact with the photoreceptor 1 by corona discharge from the separation wire 5 (corona discharge in which an AC component is superimposed on a DC component) is transferred to the photoreceptor 1.
Separated from At the time of this separation, a peeling nail (not shown) may be used in some cases. After being separated from the photoreceptor 1, the transfer paper 6 is sent to the fixing roller pair 13, where the toner image transferred onto the transfer paper 6 is fixed.

Now, with respect to the transfer section 8, the side on which the transfer paper 6 enters is referred to as an "entrance side" and the exit side is referred to as an "exit side". A medium guide member 9 is provided.

In this embodiment, the recording medium guide member 9 is fixedly attached to the shield case 3 via a rigid support member 11. The guide member 1 is also provided on the exit side.
0 is provided, which is fixedly attached directly to the shield case 3.

The recording medium guide member 9 on the entrance side has a function of reliably guiding the transfer paper 6 to the transfer section 8 between the discharger 2 and the photoconductor 1, and the exit guide member 10 guides the transfer paper. This achieves a function of preventing the shield case 3 from being put inside.

In the present embodiment, the recording medium guide member 9 on the entrance side (hereinafter simply referred to as “entrance guide member”) 9
It is made of a material having a volume resistivity of ¹⁰ Ω · cm or less, for example, about 10 ⁶ Ω · cm. That is, in this example, the entrance guide member 9 is made of a material having a relatively low volume resistivity or a conductive material.

Here, when the corona discharge is performed by the transfer wire 4, the electric charge released from the transfer wire 4 is transmitted to the surface of the entrance guide member 9 along the transfer paper 6. At this time, since the entrance guide member 9 is made of a material having a low volume resistivity as described above, the electric resistivity of the transfer paper 6 is reduced particularly under high humidity, and the discharge charges are reduced.
And transfer failure of the toner image and separation failure of the transfer paper 6 may occur.

Therefore, in the present embodiment, the support member 1 provided between the entrance guide member 9 and the shield case 3 of the discharger 2 is provided.
1 is made of a material having a volume resistivity of more than 10 ¹⁰ Ω · cm, particularly an insulator having a volume resistivity of 10 ¹² Ω · cm or more, or a material that can be regarded as an insulator. The entrance guide member 9 is fixed to the shield case 3. As a result, the discharge charge does not fall from the entrance guide member 9 to the ground through the metal shield case 3, and in any environment, a failure that causes a transfer failure of the toner image or a separation failure of the transfer paper 6 is prevented. It is possible to do.

On the other hand, after the transfer paper 6 has passed through the transfer section 8,
When the charge remains on the entrance guide member 9 and the degree of the residual becomes significant, the toner floating around the entrance guide member 9 or the toner of the pattern image for controlling the toner density formed on the photoreceptor 1, etc. Is electrostatically attracted toward the entrance guide member 9. If such toner adheres to the entrance guide member 9, it adheres to the back surface of the transfer paper 6, causing a back stain.

Therefore, in the present embodiment, there is provided a static elimination means for setting the entrance guide member 9 to a grounded state and eliminating static electricity from the guide member 9. That is, the entrance guide member 9 is grounded via the ground wire 14. When such a configuration is adopted, the charge of the entrance guide member 9 escapes to the ground side, so that floating toner and the like are less likely to be electrostatically attracted toward the entrance guide member 9. As a result, it is possible to prevent the back stain of the transfer paper.

Here, the entrance guide member 9 may be kept in the ground state at all times. In this case, when the toner image on the photoreceptor 1 is transferred to the transfer paper 6, or when the transfer paper 6
When the photoconductor 1 is separated from the photoreceptor 1, the discharge charge from the discharger 2 may fall to the ground through the entrance guide member 9 having a low volume resistivity and the ground wire 14, and transfer and separation failure may occur.

Therefore, in this embodiment, as shown in FIG.
4, a transfer circuit 6 is provided between the photosensitive member 1 and the discharger 2, that is, when the transfer of the toner image and the separation of the transfer paper 6 are performed. As shown in (1), the switch 16 of the switch circuit 15 is opened and turned off, and the ground state of the entrance guide member 9 is cut off. This can prevent the above-described problem from occurring.

As the switch circuit, a mechanical switch such as a relay or other appropriate switching element may be used.

In FIG. 1, what is indicated by reference numeral 18 is a jam detection sensor including a photo sensor and the like. The sensor 18 detects the transfer paper 6. If the transfer paper does not reach the transfer section 8 after a predetermined time, the operation of the image forming apparatus is stopped assuming that the transfer paper has jammed. It has become. The sensor 18 is for detecting a jam, but in this example, such a sensor 18 is used.
Is used to control the on / off of the switch 16.
Of course, it is also possible to provide a dedicated sensor for the switch 16 and control the on / off thereof by this.

When the leading end of the transfer paper 6 reaches the position of the sensor 18, the output level of the transfer paper 6 becomes low as shown in the timing chart of FIG. That is, the leading end of the transfer paper is detected by the sensor 18. After the detection, when a predetermined time elapses, the switch 16 that has been on is turned off. The a-second is the time required from when the leading end of the transfer paper reaches the position of the sensor 18 to when the transfer paper reaches the transfer / separation discharger 2. a is the sensor 18 and the transfer / separation discharger 2
X (cm), and the transfer speed of the transfer paper is v
(Cm / sec) is calculated by dividing the distance x by the speed v.

In FIG. 2, b (second) is a value obtained by dividing the length L (cm) of the transfer paper 6 by the transfer paper transport speed v. The time it takes for the transfer paper to pass. In any case, if the trailing edge of the transfer paper is detected by the sensor 18 after the leading edge of the transfer paper is detected, the output level of the sensor 18 changes from low to high. Then, when a second has elapsed, the switch 16 is turned on. The time for turning off the switch 16 may be set slightly longer than that shown in FIG. These switching controls are performed by the CPU 12 (FIG. 1).

After all, the switch 16 is connected to the transfer paper 6
Is turned off while passing through the discharger 2 (during transfer and separation), and while the transfer paper is not passing through the discharger 2 (during transfer and separation). It is turned on, and during this time, the entrance guide member 9 is discharged. Such ON / OFF timing naturally depends on the length of the transfer sheet (length in the feed direction).

When the discharger for transferring the toner image and the discharger for separating the transfer paper are separated, when the transfer paper passes through the discharger for transferring the toner image, that is, the transfer is performed. , The switch 16 may be controlled to be turned off.

As described above, the entrance guide member 9 is supported by the shield case 3 via the insulating support member 11,
In addition, the ground wire 14 is connected to the entrance guide member 9, the switch 16 provided in the ground wire 14 is opened only while the transfer paper 6 passes through the discharger 2, and the switch 16 is closed for other intervals. By doing so, even in a high humidity environment, it is possible to suppress the occurrence of back contamination of the transfer paper while making it difficult to cause transfer failure and separation failure.

Next, in FIG. 3, the transfer wire 4 and the separation wire 5 of the discharger 2 provided so as to face the photoreceptor (FIG. 1) are made of insulating material provided at both ends of the shield case 3. And is insulated from the shield case 3. This point is shown in FIG.
There is no difference from the discharger 2 shown in FIG. In the embodiment shown in FIG. 3, the entrance guide member 19 attached to such a transfer / separation discharge device 2 is formed as an endless belt wound around a plurality of rollers 19a and 19b. When the belt-shaped entrance guide member 19 guides the transfer paper 6 and guides the transfer paper 6 between the photoconductor (FIG. 1) and the discharger 2, the belt-shaped entrance guide member 19 is held in a stopped state so as to guide the transfer paper 6 without trouble. At the time of static elimination, which will be described later, the motor is driven to rotate by the drive motor 23 for a certain period of time.

Here, in this embodiment, the entrance guide member 19 is made of a synthetic resin sheet. That is, the guide member 19
Is made of a material having a volume resistivity of more than 10 ¹⁰ Ω · cm, particularly a material having a volume resistivity of 10 ¹² Ω · cm or more. This is in the category of insulating materials.

Since the entrance guide member 19 is such an insulator, it is not necessary to support the guide member 19 on the shield case 3 via an insulating support member as shown in FIG. As the number of sheets passed increases due to rubbing with the paper 6 and discharge for transferring the toner image, the surface potential of the entrance guide member 19 gradually increases as shown in FIG. Then, at a certain surface potential, floating toner and the like adhere to the entrance guide member 19.

Therefore, also in this embodiment, a charge removing means for removing the electric charges remaining on this surface of the entrance guide member 19 from the side in contact with the transfer paper 6 is provided, and the embodiment shown in FIG. In this embodiment, the static elimination means is constituted by a static elimination member composed of a static elimination brush 24 that is in contact with the above-mentioned surface of the entrance guide member 19 formed as an endless belt, that is, the ground surface. When the entrance guide member 19 is not guiding the transfer paper 6, the motor 23 is operated to rotate the entrance guide member 19 made of an endless belt in the direction of the arrow.
4, the entrance guide member 19 is neutralized. Accordingly, it is possible to prevent the toner from adhering to the entrance guide member, and hence the toner from adhering to the transfer paper 6.

By the way, the transfer paper 6 is moved to the entrance guide member 19.
May be carried out by rotating the entrance guide member 19 as described above, but with such a configuration, it takes a certain time to execute the charge eliminating operation. A relatively large interval must be provided between the transfer papers 6 that are conveyed in a regular manner, and a time for the static elimination operation must be secured.
As a result, the number of images formed per time decreases, and the copy speed decreases.

Therefore, in this embodiment, when the number of transfer papers 6 passing between the discharger 2 and the photosensitive member is counted to a predetermined number, the motor 23 constituting the driving means is operated and the endless belt is driven. The entrance guide member 19 having the above configuration is configured to be rotationally driven to execute the charge removing operation. For example, the surface potential of the limit at which toner does not adhere to the entrance guide member 19 is measured in advance, and if the number of passed sheets corresponding to this is grasped, the motor 23 is operated every time the number of sheets is reached. Thus, the entrance guide member 19 is driven to rotate, and the charge removal operation of the entrance guide member 19 can be performed by the charge removal brush 24. By doing so, the interval between transfer sheets can be reduced, and a decrease in copy speed can be prevented.

Here, suppose that the limit of the number of sheets that does not allow toner to adhere to the entrance guide member 19 is 50, and when the number of sheets is counted by a counter (not shown), the motor 23 rotates. Starting, while the motor 23 rotates for a certain period of time, the electric charge retained in the entrance guide member 19 is released to the grounding side via the discharging brush 24. Here, assuming that the width of the transfer paper 6 is W, the entrance guide member 1 has a length obtained by adding a margin to the width W.
9 may be rotated, and the fixed time is the time required to rotate the entrance guide member 19 by this length. The number of passed sheets can be counted using, for example, a jam detection sensor 18 composed of a reflective photosensor for detecting a transfer sheet jam at the position of the registration roller pair 7.

By the way, the toner adhering to the entrance guide member 19 may be merely mechanically adhering without relying on the action of sucking the electric charge on the surface. For example, photoconductor 1
(FIG. 1) Alternatively, if toner falls from a developing device (not shown) placed above the transfer / separation discharge device 2, such toner adheres even if no charge is placed on the entrance guide member 19. I do. Also in this case, arrowheads, transfer paper back stains, and the like are generated.

Therefore, in the embodiment shown in FIG. 3, the transfer paper 6 of the entrance guide member 19 formed as an endless belt is provided.
And a cleaning member for cleaning the surface in contact with the cleaning member. That is, as shown in FIG.
A cleaning member formed as a cleaning pad 25 is in contact with the surface of 9, and at the same time as the above-described static elimination,
The surface of the entrance guide member 19 is cleaned by the cleaning pad 25, and the toner adhered to the surface is removed from the surface. Of the number of sheets passed before the electrostatic charge of the toner is started due to the charge on the surface of the entrance guide member 19 and the number of sheets to which toner adheres due to dropping of toner, etc. It is more efficient if the above-described static elimination and cleaning are performed simultaneously each time the number of sheets is counted. In any case, the cleaning member performs the cleaning operation every time the number of passed sheets is counted to the predetermined number.

By the way, the transfer paper 6 may be jammed near the transfer section 8 (FIG. 1). When such a jam occurs, the transfer paper having the jam is removed. At this time, the toner adhered to the photoconductor 1 and the transfer paper 6 adheres to the entrance guide member 19 and accumulates. It will be easier.

After the removal of the transfer sheet having the jam, the toner adhered to the entrance guide member 19 can be removed by the above-described cleaning member. For example, when a jam is detected by the sensor 18 or the transfer paper does not reach the fixing entrance sensor 26 (FIG. 1) at a predetermined timing (when a jam occurs in front of the fixing unit), After removing the transfer paper, the motor 23
Is rotated for a certain period of time, and cleaning is performed by the cleaning pad 25 at the same time as static elimination. After the transfer sheet is removed, the count data is cleared.

FIG. 5 is an example of a flowchart of a main routine corresponding to the above-described embodiment. The opening / closing door is an opening / closing door of the image forming apparatus located on the operator side. Will open it. The cleaner operation is defined as the motor 2 in FIG.
3 rotates and the cleaning pad 25 causes the entrance guide member 1
9 cleaning.

FIG. 6 is an example of a flowchart relating to the opening / closing door opening check. FIG.
It is an example of a flowchart relating to a remaining sheet check and the like.
FIG. 8 shows an example of a flowchart relating to the cleaner operation request processing, and FIG. 9 shows an example of a flowchart relating to the cleaner operation. The copy counter for the cleaner operation in FIG. 8 is incremented when, for example, the fixing entrance sensor is turned on, and the counter value is stored in the nonvolatile memory.

As shown in FIG. 3, the recording medium guide member is formed as an endless belt wound around a plurality of rollers and stopped when guiding the recording medium. However, the configuration of the static elimination member that is in contact with the endless belt and is in a grounded state is such that the recording medium guide member has a resistance of 10 ¹⁰ Ω ·
cm, and a supporting member having a volume resistivity of more than 10 ¹⁰ Ω · cm is interposed between the guide member and the shield case of the discharger, and the recording medium guide member is grounded. And an image forming apparatus having a switch circuit for shutting off a ground state of the recording medium guide member when the recording medium passes between the image carrier and the discharger. Applicable.

It is also apparent that the present invention can be applied to an image forming apparatus in which the transfer discharger is separated from the separation discharger.

[0049]

According to the first aspect of the present invention, since the recording medium guide member is discharged, the toner is less likely to be electrostatically attracted to the recording medium guide member, and the occurrence of back contamination of the recording medium is suppressed. be able to. Further, although the volume resistivity of the recording medium guide member is set to be relatively low, discharge charges do not flow to the shield case side, and transfer failures and the like hardly occur even if there is a change in humidity.

According to the configuration of the second aspect, problems such as transfer failure can be more reliably prevented.

According to the third aspect of the present invention, since the recording medium guide member is discharged, the toner is less likely to be electrostatically attracted to the recording medium guide member, and the occurrence of back contamination on the recording medium can be suppressed. .

According to the configuration of the fourth aspect, it is possible to prevent the back stain on the recording medium without reducing the number of images formed per unit time.

According to the fifth aspect of the invention, even if toner adheres to the recording medium guide member by an action other than electrostatic attraction, the toner can be removed by cleaning, and the toner caused by the adhered toner can be removed. It is possible to prevent back contamination of the recording medium.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram around a transfer / separation device section of an image forming apparatus.

FIG. 2 is a timing chart at the time of turning on / off a static elimination switch of an entrance guide member.

FIG. 3 is a configuration perspective view of a periphery of an entrance guide member of another example.

FIG. 4 is a diagram showing a correlation characteristic between the number of passed sheets and the surface potential of an entrance guide member.

FIG. 5 is an overall schematic diagram of a flowchart corresponding to the other embodiment.

FIG. 6 is a flowchart related to an open / close door open check.

FIG. 7 is a flowchart relating to closing of an opening / closing door, checking for remaining paper, and the like.

FIG. 8 is a flowchart related to a cleaner operation request process.

FIG. 9 is a flowchart relating to a cleaner operation.

[Explanation of symbols]

 2 Discharger 3 Shield case 11 Support member 19 Recording medium guide member 19a Roller 19b Roller

Claims (5)

(57) [Claims] 1. A discharger provided to face an image carrier and a material having a volume resistivity of 10 ¹⁰ Ω · cm or less, and a recording medium is guided between the discharger and the image carrier. A recording medium guide member, a support member made of a material having a volume resistivity greater than 10 ¹⁰ Ω · cm, and provided between the recording medium guide member and a shield case of the discharger; The recording medium guide member is wound around a plurality of rollers, and is formed as an endless belt that is stopped when guiding the recording medium. The image forming apparatus includes a static elimination member that is in contact with the endless belt and is grounded. 2. The image forming apparatus according to claim 1, further comprising a switch circuit for shutting off a ground state of the recording medium guide member when the recording medium passes between the image carrier and the discharger. 3. A discharger provided to face the image carrier and a material having a volume resistivity greater than 10 ¹⁰ Ω · cm, wherein a recording medium is provided between the discharger and the image carrier. A recording medium guide member for guiding, and a charge removing unit for removing charges remaining on the surface of the recording medium guide member from the surface in contact with the recording medium, wherein the recording medium guide member includes a plurality of recording medium guide members. Formed as an endless belt that is wrapped around rollers and stopped when guiding the recording medium,
The image forming apparatus according to claim 1, wherein the static eliminator includes a static elimination member that is in contact with the endless belt and is grounded. 4. A driving means for rotating the endless belt when the number of recording media passing between the discharger and the image carrier is counted to a predetermined number. The image forming apparatus according to any one of the above. 5. The image forming apparatus according to claim 1, further comprising a cleaning member that abuts on the endless belt and cleans a surface of the endless belt on a side in contact with a recording medium by rotation of the belt. apparatus.