JPH09329975A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an excellent image being free from the image defect by effectively destaticizing the electric charge on a recording medium after transferring even under the super low humidity environment with an excellent destaticizing capacity, and preventing disturbance of the unfixed toner image from being caused. SOLUTION: This device is provided with the image carrier carrying while transporting the toner image formed corresponding to the image information, and transferring means (2 to 5) making the toner image being carried on the image carrier directly or through an intermediate recording medium 1 (paper sheet) P. On the downstream side vicinity of the transfer area Q with respect to the transporting direction of the paper sheet P, the conductive guide roll 6 is disposed while held in contact with a rear surface of the paper sheet P on which the toner image Y is transferred and rotated at the same peripheral speed as its transporting speed. It is preferable to provide plural insulated projections on a conductive body periphery in the shaft direction, in order to form a specific space gap between the conductive body periphery on the guide roll 6 and the paper sheet P rear surface transported in the downstream direction of the transfer area Q.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to an image forming apparatus using an electrophotographic system such as a printer, a facsimile, and a composite device of these. More specifically, an image forming apparatus configured to apply a transfer electric field to a toner image formed on an image carrier or an intermediate transfer member to transfer the toner image to a recording medium such as paper to obtain a reproduced image. Regarding

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic system uniformly rotates a surface of an image carrier (photosensitive drum) having a photosensitive layer made of an inorganic or organic photoconductive material while rotating the surface of the image carrier. After being charged, image information is image-processed to form an electrostatic latent image, and then the electrostatic latent image is developed with charged toner to obtain a visualized toner image. Then, this toner image is transferred to a transfer material such as paper directly or through an intermediate transfer body to obtain a required reproduced image. As a color image forming apparatus, there is a system in which toner images of respective colors formed on an image carrier are directly transferred onto a transfer material in a multiple transfer manner. However, this method has a problem that the quality of the color image formed on the transfer material is deteriorated due to many factors such as the thickness and surface characteristics of the transfer material, and the transfer characteristics of the transfer material with respect to the image carrier. On the other hand, there is a system in which toner images of respective colors formed on an image carrier are temporarily transferred to an intermediate transfer member in a multiple transfer manner and then collectively transferred to a transfer material (see JP-A-62-206567). According to this method, the toner images of the respective color components are always multi-transferred to the same intermediate transfer member, and the synthetic toner images thus multi-transferred are collectively transferred to the transfer material, so that the above problems can be eliminated. . In addition, it is possible to effectively prevent the occurrence of image disturbance and color shift during multiple transfer, and it is possible to use a wide variety of transfer materials.

Corona transfer method and roller transfer method have been conventionally known as transfer methods of toner images in various image forming apparatuses. In the latter roller transfer method, a transfer roll is arranged in pressure contact with a transfer portion of an image carrier or a secondary transfer portion when a secondary transfer member is used. Then, a strong electric field is applied from the back surface of the transfer material while passing the transfer material between the transfer roll to which a voltage having a polarity opposite to that of the toner is applied and the image carrier or the intermediate transfer body, and the toner image is electrostatically charged. A reproduced image is formed by transferring and transferring the toner to a transfer material. In such a roller transfer method, compared with the corona transfer method, a transfer material can be pressed against an image carrier or a backup roller facing a transfer roll to reliably hold a toner image. Therefore, it is difficult to cause transfer deviation at the transfer site, and the transfer bias can be set to a relatively low pressure and low capacity.
There are many advantages such as high transfer efficiency, a small device size, and a very small amount of ozone.

A conventional color image forming apparatus employing the roller transfer system will be described with reference to FIG. In the figure, a charging device 02, a developing device 03, a primary transfer device 04, a cleaning device 05 and the like are sequentially arranged on the peripheral surface of the photoconductor drum 01 along the rotation direction thereof. Photoconductor drum 01
An intermediate transfer belt 06 that moves in the direction of the arrow while being in contact with the surface of the drum 01 is supported between the transfer rollers 07a, 07b, 07c and the backup roller 08 between the transfer roller 04 and the transfer device 04 that is disposed opposite to the transfer roller 04. . A transfer roll 09 and a cleaner 010 are arranged to face the backup roller 08 and the conveyance roller 07a via a belt 06, respectively. A peeling claw 011 is arranged between the transfer roll 09 and the cleaner 010. Further, a paper feed tray 012, a pickup roller 013, a feed roller 014, and a guide guide 015 are sequentially arranged on the upstream side of the transfer material conveying path in the secondary transfer portion where the backup roller 08 and the transfer roll 09 face each other.
A transfer material receiver 016, a transport belt 017, and a fixing device 018 are sequentially arranged on the downstream side of the transport path. The backup roller 08 is formed by covering a metal shaft with an elastic roll layer such as rubber or sponge. Also a backup roller
The transfer roll 09, which is pressed against 08, is also made of rubber on the metal shaft.
It is formed by coating a conductive elastic layer such as sponge.

In the image forming apparatus shown in FIG. 6, electrostatic latent images corresponding to each color of blue, green and red are formed in the exposure area between the charging device 02 and the developing device 03. The electrostatic latent image on the photoconductor drum 01 is a toner image of each color (B, Y, M, C) with the black B, yellow Y, magenta M, and cyan C developers stored in the developing device 04. It is formed. The toner images of the respective colors are transferred onto the intermediate transfer belt 06 by the primary transfer device 04 for each rotation of the photoconductor drum 01, and a combined toner image of four colors is formed. During this time,
Since the backup roller 08 stretches and supports the intermediate transfer belt 06, the transfer belt 06 moves in the direction of the arrow along with the rotation of the driving conveyance roller 07a, and the backup roller 08 also rotates following. In the secondary transfer section, the transfer roll 09 is
While forming a nip, the backup roller 08 is pressed and rotates at the same peripheral speed as the intermediate transfer belt 06. When the transfer material S is passed through the transfer nip, the toner images on the transfer belt 06 are collectively transferred to the transfer material S. The transfer material S on which the unfixed toner image is transferred is separated from the transfer belt 06,
After falling on the transfer material receiver 016, fix it with the conveyor belt 017.
Transported to 018. In the fixing device 018, the unfixed toner image is fixed and a full color image is formed.

There is also known an image forming apparatus in which a roller transfer system is applied to a secondary transfer portion for transferring a toner image on the intermediate transfer member onto a transfer material by replacing the belt forming the intermediate transfer member with a drum. In this image forming apparatus, the portion where the transfer roll is arranged facing the intermediate transfer drum serves as the secondary transfer portion. As described above, this intermediate transfer body method also passes the transfer material between the transfer roll and the intermediate transfer drum,
A strong electric field is applied from the back surface of the transfer material to electrostatically transfer the toner image to the transfer material. In order to obtain good transfer efficiency in the secondary transfer portion, it is ideal to control the amount of charge applied to the back surface of the transfer material, and constant current control is considered suitable. However, in the above-mentioned contact transfer method using a transfer roll, the impedance between the photosensitive drum or the intermediate transfer member and the transfer roll greatly differs depending on the presence or absence of the transfer material. Especially when using a small-width transfer material such as a postcard, a large amount of current flows in the area where the transfer roll is in direct contact with the photoconductor drum or the intermediate transfer material, resulting in transfer failure due to insufficient charging of the transfer material. There is a problem of doing. Therefore, in the contact transfer method, charging control is generally performed by constant voltage control.

In such a secondary transfer section of the intermediate transfer member type, the transfer material after applying the strong electric field from the back side of the transfer material to transfer the toner image is substantially non-conductive. , Is strongly charged by the action of the electric field. Compared to the non-contact transfer method using corona discharge, the contact transfer method such as a transfer roll requires a lower applied voltage, but its charging property depends on the resistance value of the transfer material. Below, it will be charged to a strong electric potential. By the way, when the transfer material is separated from the intermediate transfer body in a state of being charged to a high electric potential and is conveyed to the fixing section, if it comes very close to a conductive material portion such as a transfer material receiver or a conveyance guide arranged on the conveyance path, A local discharge may occur and the charge may move rapidly. Along with this abrupt movement of charges, the unfixed toner image transferred to the surface of the transfer material is disturbed, and image defects such as toner scattering and tailing are likely to occur. In such a phenomenon, the higher the resistance value of the transfer material is, and the higher the gradation is, that is, the larger the amount of toner on the image is, the stronger the electric charge is, so that the image defect is more likely to occur. When paper is used as the transfer material, its volume resistivity fluctuates greatly depending on the water content.Therefore, in a low humidity environment where the volume resistivity of the paper is extremely high, toner image distortion and image defects occur remarkably. To do. In particular, when an image original having a high image density is copied onto a sheet sufficiently conditioned to the environment under an extremely low humidity environment of a temperature of 20 ° C. and a relative humidity of 10%, a drastic toner image called toner explosion may occur. Distortion occurs, and the entire surface of the image is contaminated with toner, so that a copy having a high degree of image defects can be obtained.

In order to deal with this problem, for example, in Japanese Unexamined Patent Publication No. 1-2696969, a needle electrode having an apex and supported by an insulating support member is provided in the vicinity of the downstream of the transfer roll to remove the charge on the back surface of the transfer paper. As a result, an image forming apparatus is disclosed in which an image defect due to toner image disorder is prevented and the peeling property of transfer paper is improved. In addition, JP-A-2-21
In Japanese Patent No. 3879, a peeling plate made of a plate-shaped grounded conductor is arranged along the axial direction of the transfer roller near the transfer roller on the paper discharge side of the transfer unit, and the paper charged by the transfer roller is used as the paper. Discloses a paper peeling device in an electrophotographic device in which a peeling plate in which electric charges are induced in opposite polarities is attracted to prevent peeling defects of paper. Further, in Japanese Patent Laid-Open No. 7-36287,
A thin layer static eliminator provided with an insulating member so that its end is exposed on the conductive member is arranged in the vicinity of the downstream of the transfer unit,
An image forming apparatus and an electronic device for the same, in which an image defect is prevented by discharging in a gap between the transfer material and a transfer material formed when the transfer material passes near the insulating member to eliminate the charge of the transfer material. A photographic method is disclosed.

[0009]

In general, abrupt movement of electric charges causes toner to scatter, and therefore, in each of the image forming apparatuses described in the above publications, the transfer material and a conductor such as a needle electrode are both provided. It is configured to discharge slowly in the formed void to remove the charge. However, these image forming apparatuses have the following problems. Even if a conductor is arranged in the vicinity of the downstream side of the transfer part to discharge slowly in the gap, the surface area of the conductor part facing the back surface of the transfer material is dwarfed, so that it has sufficient static elimination capability. Is hard to say. That is, a predetermined effect can be expected in the case of an image disturbance such that toner of a character image is scattered, or in the case of a small-sized sheet as a transfer material and an extremely low transport speed. However, in the ultra-low humidity environment as described above,
The charge of the transfer material that induces toner explosion cannot be sufficiently removed during the transfer material is conveyed, so that the disturbance of the toner image cannot be completely prevented and the image defect is prevented. It is not possible.

In order to remedy the drawbacks of the image forming apparatus described in the above publication, a bias voltage having a polarity opposite to that of the toner is applied instead of grounding the charge elimination needle to neutralize the charge on the paper. Things have been proposed. Therefore, the present inventor conducted a copy test under the following conditions to investigate the occurrence of image defects. Under ultra-low humidity environment with temperature of 20 ° C and relative humidity of 10%, DC voltage -1kV and frequency 1kHz
Of the alternating voltage of 14 kV is 0.1
An original having an image density of 60% was copied onto a sheet left in the above environment for 10 hours while applying a 1.5 mm stainless steel static elimination needle and keeping the clearance between the static elimination needle and the back surface of the sheet at 1.5 mm. As a result, severe disturbance of the toner image was suppressed, but each time the paper discharged from the transfer site fell on the insulating paper receiving plate, the impact caused the residual charge to discharge to the surrounding conductive parts, resulting in a positive flame. Disturbances occurred at several places. In the copying test under the ultra-low humidity environment, the charge remained on the paper even after the charge was removed, and the image defect could not be prevented yet. Also,
A power supply circuit or the like for applying the superimposed voltage to the charge elimination needle is required, and the number of parts of the charge eliminating member increases, and the overall structure of the image forming apparatus becomes complicated and large, resulting in high cost.

As described above, none of the conventional techniques can essentially solve the problem of image defects due to the disturbance of the toner image. Therefore, the present invention is intended to solve the above-mentioned problems, and has a high static elimination ability, and effectively eliminates the electrostatic charges of the recording medium after transfer even in an ultra-low humidity environment. Another object of the present invention is to provide at low cost an image forming apparatus capable of preventing an unfixed toner image from being disturbed and forming a good image without image defects.

[0012]

Means for Solving the Problems The present inventor has made earnest studies to effectively eliminate the electric charges applied to the recording medium after transfer, and found that a rotatable roll was used as the electricity eliminating member. , The discharge area between the recording medium discharged from the transfer area and the conductor is formed to be wide, and the speed difference between the peripheral speed of the roll and the conveying speed of the recording medium is eliminated to prevent the rapid movement of charges. By doing so, the inventors have found that the above problems can be solved, and have completed the present invention. That is, the image forming apparatus of the present invention, an image carrier for carrying and carrying the toner image formed according to the image information,
A transfer unit that electrostatically transfers the toner image carried on the image carrier to the recording medium, either directly or via an intermediate transfer member, and the toner image is provided in the vicinity of the downstream side of the transfer region in the recording medium conveyance direction. A conductive guide roll is provided which is in contact with the back surface of the recording medium on which is transferred and rotates in the conveying direction of the recording medium at the same peripheral speed as the conveying speed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the image forming apparatus of the present invention, even if the toner image carried on the image carrier is directly transferred to the recording medium, or after the toner image is once transferred to the intermediate transfer member, It may be transferred to a recording medium. Hereinafter, the present invention will be described in detail mainly with respect to the latter intermediate transfer body method with reference to the drawings. FIG. 1 is a schematic configuration diagram of a secondary transfer area in the image forming apparatus of the present invention. In the figure,
A backup roll 3 is arranged at a position facing the transfer roll 2 with the belt-shaped intermediate transfer body 1 carrying the unfixed toner image X primarily transferred. The intermediate transfer body 1 is supported by the backup roll 3. The transfer roll 2 is connected to a power supply 4, and a transfer voltage is applied from the transfer roll 2 to the backup roll 3. Backup roll 3
An earth roll 5 is pressed against the earth roll 5, and the earth roll 5 is grounded. The transfer means in the present invention is composed of these constituent elements (2 to 5). Further, for example, in the transport direction of a recording medium such as a sheet of paper P (hereinafter, represented by the sheet of paper P), rotatable conductive material is provided in the vicinity of the downstream side of the transfer area Q where the transfer roll 2 and the intermediate transfer body 1 are in pressure contact with each other. A guide roll 6 is provided. The guide roll 6 contacts the back surface of the paper P on which the unfixed toner image Y has been transferred,
The paper P is guided in the carrying direction while rotating at the same peripheral speed as the carrying speed. Further, a cleaning blade 7 is in contact with the transfer roll 2 to clean the toner and the like adhering to the surface of the transfer roll 2.

The belt-shaped intermediate transfer member 1 is formed by mixing various resins or rubber materials with an appropriate amount of a conductive agent such as carbon black to have a thickness of, for example, 0.05 to 0.15 mm. Its volume resistivity is adjusted in the range of 10 ⁶ to 10 ¹⁶ Ωcm. Examples of various resins include acrylic resin, polyvinyl chloride, polyester, polycarbonate, and polyimide. The transfer roll 2 constituting the transfer electrode is separated from the intermediate transfer body 1 while the toner image carried on the image carrier is primarily transferred onto the intermediate transfer body 1, and is carried by the intermediate transfer body 1. When the toner image X is secondarily transferred onto the sheet P, the intermediate transfer body 1 is pressed against the backup roll 3 by pressing. The transfer roll 2 is
The outer diameter is usually in the range of 15 to 35 mm. Its volume resistivity is in the range of 10 ⁴ to 10 ⁸ Ωcm, and its hardness is 2 in Asker C.
Each is preferably in the range of 0 to 45 °. The layer structure of the transfer roll 2 is not particularly limited,
For example, as an example of a two-layer structure, the conductive elastic layer 2b fixed to the outer peripheral surface of the cored bar 2a is covered with the conductive layer 2c.
A conductive agent such as carbon black is dispersed in these layers 2b and 2c in order to adjust the resistance.

In the transfer roll, the core metal functions as an electrode and a supporting member of the transfer roll, and is made of, for example, aluminum, iron, copper alloy, stainless steel (SUS).
It is composed of a conductive material such as. The outer diameter of the core is usually 10
It is in the range of up to 20 mm. As the rubber material of the elastic layer,
Examples thereof include silicone rubber, urethane rubber, EPDM and the like, or foams thereof. The conductive layer has a function of adjusting the conductivity, hardness and smoothness of the transfer roll to provide an appropriate transfer electric field. Further, it has an effect of alleviating the impact at the time of pressure contact with the intermediate transfer member and ensuring good cleaning performance when removing the toner adhering to the surface of the transfer roll with the cleaning blade. As the material of this conductive layer,
Fluorine-based resin, polyurethane, silicone rubber, resin, etc. may be mentioned.

The backup roll forming the counter electrode may have a single-layer structure or a multi-layer structure. In the case of a single-layer structure, it is composed of an insulating rubber roll such as EPDM, silicone rubber, urethane rubber or the like, to which an appropriate amount of a conductive agent is mixed. For example, in the case of a two-layer structure, the surface of the rubber roll layer 3b fixed to the outer peripheral surface of the core metal 3a similar to the core metal 2a is covered with a semiconductive film layer 3c having a film thickness of 10 to 200 μm. A conductive agent such as carbon black is dispersed in these layers 3b and 3c in order to adjust the resistance. The outer diameter of the backup roll 3 is in the range of 15 to 35 mm, which is the same diameter as the transfer roll 2. The earth roll 5 is pressed against the surface of the backup roll 3 at a distance of 20 to 40 mm in the circumferential direction from the contact position with the intermediate transfer body 1. The earth roll 5 is grounded so as to release the charges provided for the transfer. This earth roll 5
Has an outer diameter usually in the range of 10 to 15 mm.
It is made of an electrically conductive material such as US or aluminum. A voltage having a polarity opposite to the charging polarity of the toner is applied to the transfer voltage, and is usually in the range of 1 to 5 kV (absolute value).
Then, in the transfer area, the toner image is transferred from the intermediate transfer member to the sheet passing through the pressure contact portion by the action of the electric field generated when the transfer voltage is applied. The transfer voltage may be applied by either constant voltage control or constant current control, but constant voltage control is desirable.

In the present invention, in the conductive guide roll 6 disposed near the downstream side of the transfer area Q, as shown in FIG. 2, a cylindrical conductor 6b is fixed to a shaft body 6a. The conductor 6b is not particularly limited as long as it is a material having good electrical conductivity and a volume resistivity of 10 ⁵ Ωcm or less, and is made of, for example, aluminum, iron, copper alloy, SUS or the like. On the outer peripheral surface of the conductor 6b, a plurality of sheets are provided at intervals in the axial direction so that the sheet P immediately after transfer is in direct contact with the surface of the conductor 6b or is not so close that the charged charges on the sheet P are suddenly discharged. It is preferable to form the protrusion 6c. It should be noted that when the amount of electric charge on the paper P is small, it is not always necessary to form the protrusion 6c. The protrusion 6c is preferably made of a material having a volume resistivity of 10 ¹⁴ Ωcm or more.
The material is not particularly limited as long as it is an electrically insulating material, and is made of, for example, resin such as acrylonitrile-butadiene-styrene resin (ABS resin), polycarbonate, nylon, or various rubbers. Further, the outer surface of the protrusion 6c is finished into a smooth curved surface by, for example, polishing so as to smoothly contact the back surface of the paper P on which the unfixed toner image Y is transferred.

FIG. 2 shows an annular rib which is continuous in the circumferential direction as the projection 6c, but the shape of the projection 6c may be arbitrary, for example, it may be discontinuous in the circumferential direction. Alternatively, the protrusions 6c may be formed on the entire outer peripheral surface of the conductor 6b at predetermined intervals or randomly. When forming the protrusions 6c, it is desirable that the discharge area of the paper P be as large as possible without the paper P coming into contact with or remarkably approaching the outer peripheral surface of the conductor 6b. Further, a porous insulating layer can be formed instead of the protrusion 6c. For example, regarding the dimension of the protrusion 6c illustrated in FIG. 2, the height h is 0.5 to 3 mm.
The range is preferably 1.0 to 2.0 mm. The width w and the spacing (pitch) d may be arbitrary,
As an example, the width w is 1 to 3 mm and the interval d is 10 to 30.
A dimension of mm can be exemplified. The outer diameter of the guide roll 6 is usually in the range of 10 to 15 mm.

The guide roll 6 is grounded so as to remove the electric charge on the paper P. As a method of removing this electric charge, a voltage having a polarity opposite to the electric charge of the paper P may be applied to the guide roll 6 instead of grounding. The guide roll 6 constituting the transfer device is unitized together with the transfer roll 2 and is rotationally driven by the same drive system. for that reason,
The guide roll 6 also performs the contact / separation operation at the same time as the transfer roll 2 contacts / separates. Further, when the transfer roll 2 is pressed against the backup roll 3, the guide roll is connected to a rotation drive system (not shown) of the backup roll 3 so that the intermediate roll 1 and the transfer roll 2 rotate at the same peripheral speed. The rotation speed of 6 is set.

In the present invention, a plurality of guide rolls 6 may be arranged along the conveyance direction of the paper P so that the electrostatic charges on the paper P immediately after transfer are discharged more slowly. FIG.
3 shows an example in which three guide rolls 6A, 6B and 6C are arranged. When arranging a plurality of guide rolls, the conductivity of the entire roll may be set higher as each roll is arranged on the downstream side in the transport direction of the paper P, that is, as the distance from the transfer roll 2 increases. desirable. More specifically, the conductors 6b shown in FIG. 2 are made of different materials, and the guide rolls 6A, 6B,
A method of sequentially setting the volume resistivity of 6C lower by 0.5 to 1.5 digits can be mentioned. For example, the upstream guide roll 6A
When the volume resistivity of the guide rolls is set to 10 ⁵ Ωcm, the guide rolls 6B and 6C on the downstream side have a volume resistivity of 10 ⁴ Ωcm, 1 respectively.
It is set to 0 ³ Ωcm. Further, as a method of increasing the conductivity of the entire roll as it is arranged on the downstream side, there is a method of sequentially decreasing the height h of the protrusion 6c shown in FIG. As an example, when the height h of the upstream guide roll 6A is 2.0 mm, the height h of the guide rolls 6B and 6C is
Are set to 1.5 mm and 1.0 mm, respectively. In addition,
It goes without saying that it is not always necessary to reduce the above-mentioned volume resistivity and height at equal intervals.

The operation of the present invention is as follows. An unfixed toner image is formed on the image carrier (19: see FIG. 4) according to the image information by a conventional method, and the unfixed toner image carried on the image carrier (19) is conveyed to the transfer area (Q). To be done. Transfer area
In (Q), the toner image is electrostatically transferred onto the paper P by the transfer means (2 to 5) or through the intermediate transfer body 1. In the latter case of the intermediate transfer member method, the toner image is temporarily transferred from the image carrier (19) onto the intermediate transfer member 1, and then the toner image X carried on the intermediate transfer member 1 is secondarily transferred onto the paper P. It will be transcribed.

According to the image forming apparatus of the first aspect of the present invention, the rear surface of the paper P on which the toner image Y is transferred is brought into contact with the vicinity of the downstream side of the transfer area (Q) in the transport direction of the paper P,
A conductive guide roll 6 that rotates at the same peripheral speed as the conveyance speed of the paper P is provided. Therefore, if the guide roll 6 is grounded, for example, when the leading edge of the paper P discharged from the transfer area (Q) approaches the guide roll 6, a charge having a polarity opposite to the charge of the paper P is induced in the guide roll 6. The leading edge of the paper P is electrostatically attracted to the guide roll 6 side, and the image carrier
(19) or reliably separated from the intermediate transfer member 1. Further, since the paper P is conveyed at the same conveyance speed as the peripheral speed of the guide roll 6, there is no speed difference between the paper P and the guide roll 6, and the paper P is smoothly conveyed to the downstream side of the transfer area (Q). can do. Therefore, there is no impact when the paper P comes into contact with the guide roll 6, so that the paper P applied during transfer is
There is no possibility that the electrified electric charges of the above will move and be discharged abruptly. Further, unlike the conventional static elimination method in which the discharge area of the paper P depends exclusively on the thickness of the tip of the conductive plate-like member, the curvature surface of the guide roll 6 can form a large discharge area. As described above, according to the first aspect of the invention, the charge removing capability of the guide roll 6 is high, and the charge of the paper P applied at the time of transfer can be effectively removed. Therefore, even if a conductive member such as a sheet conveying member is arranged on the downstream side of the transfer area (Q), the unfixed toner image Y on the sheet P will not be disturbed, and there will be no image defects and good images will be obtained. It is possible to form an image. Moreover, since the guide roll 6 is composed of relatively simplified components and structure, the transfer device can be manufactured at low cost.

According to the image forming apparatus of the second aspect, a plurality of guide rolls (6) are provided along the conveyance path of the paper P,
The conductivity of each roll (6A, 6B, 6C) is different. Therefore, for example, by increasing the conductivity of each of the guide rolls (6A, 6B, 6C) as the distance from the transfer roll 2 increases, it is possible to more slowly remove the electrostatic charge on the paper P. According to the image forming apparatus of claim 3, the outer peripheral surface of the conductor 6b of the guide roll and the transfer area (Q)
A constant space is formed between the sheet P and the back surface of the sheet P conveyed in the downstream direction. Therefore, since the charged paper P and the outer peripheral surface of the conductor 6b face each other for a relatively long time through the gap without directly contacting each other, not only can the charge removing capability of the guide roll 6 be sufficiently ensured, but also the paper P The electric charge will not be discharged violently. Therefore, even if the image density of the original document is high in an ultra-low humidity environment, there is no occurrence of toner explosion in which the unfixed toner image Y on the paper P is suddenly disturbed.

An image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to the third aspect.
In order to form the above-mentioned constant gap in the invention, a plurality of insulating protrusions 6c are provided on the peripheral surface of the conductor 6b in the axial direction. Therefore, the same operation as that of the third aspect of the invention is surely achieved. According to the image forming apparatus of the fifth aspect, a plurality of guide rolls (6) are provided along the conveyance path of the paper P, and the heights of the insulating protrusions 6c of the rolls (6A, 6B, 6C) are different from each other. . Therefore, for example, as the distance from the transfer roll 2 increases, the heights of the protrusions 6c of the respective guide rolls (6A, 6B, 6C) are sequentially lowered, so that the same effects as those of the second and third inventions can be reliably achieved.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings, but the present invention is not limited to the following embodiments. Embodiment 1 (Image Forming Apparatus) FIG. 4 is an overall view of a digital color copying machine provided with an intermediate transfer member as an image forming apparatus of the present invention. In FIG. 4, a document illumination lamp 12 that moves along the lower surface of a document (not shown) placed on the platen 11
The light emitted from the document and reflected by the document is converged on the CCD of the image reading unit via the moving mirror unit 13, the lens 14, and the fixed mirror 15. The CCD converts the original image into an electric signal for each color by using a large number of photoelectric conversion elements and filters of three colors of red (R), green (G) and blue (B). This electric signal is input to the image processing circuit 16, and the image processing circuit 16 has an image memory that converts the original image reading signal input for each color into a digital signal and stores the digital signal.

The optical writing control device 17 reads out the image data of the image processing circuit 16 at a predetermined timing and outputs it to the light beam writing device 18. Light beam writing device 18
Writes an electrostatic latent image corresponding to each of the above colors on the image carrier 19 composed of a photosensitive drum that rotates in the direction of arrow A. Around the image carrier 19, a charging charger 20 for uniformly charging the surface of the image carrier 19, a developing unit 21 for developing the electrostatic latent image written on the image carrier 19 into a toner image of each color, and a developing unit 21 for each color. A cleaner unit 22 having the intermediate transfer member 1 to which a toner image is transferred, a charge eliminator and a cleaning blade.
Is arranged. The developing unit 21 is black (K),
The electrostatic latent image is developed with the toners of the respective colors, and the electrostatic latent image is visualized by each of the developing devices having the toners of the respective colors of yellow (Y), magenta (M), and cyan (C). Intermediate transfer member 1
Is stretched around the backup roll 3 and the belt transport rolls 23, 24, 25 against which the earth roll 5 is pressed, and moves in the tangential direction while contacting the surface of the image carrier 19. In this embodiment, among the rolls (3, 23 to 25) that stretch the intermediate transfer member 1, the transport roll 23 is used as a driving roll and the other rolls (3, 23 to 25) are moved so that the intermediate transfer member 1 moves in the arrow B direction. 3, 24, 25) are configured as driven rolls. In order to prevent the intermediate transfer body 1 from bending,
The shaft of the belt transport roll 25 is biased in the direction C by a spring (not shown).

On the back surface side of the intermediate transfer body 1, a transfer corotron 26 for transferring the toner image of each color is arranged at the primary transfer portion where the image carrier 19 and the surface of the intermediate transfer body 1 are in contact with each other. On the other hand, the transfer roll 2 and the belt cleaner 27 are respectively arranged on the surface side of the intermediate transfer body 1 which holds the unfixed toner image, facing the backup roll 3 and the belt transport roll 23. A portion where the transfer roll 2 and the backup roll 3 face each other serves as a secondary transfer region. The conductive guide roll 6 is arranged in the vicinity of the downstream side of the secondary transfer area in the conveyance direction of the paper P.
A cleaning blade 7 made of urethane rubber is always in contact with the surface of the transfer roll 2 to remove foreign matter such as toner particles and paper powder attached at the time of secondary transfer.

An extractable paper feed tray 28 is provided at the bottom of the main body of the image forming apparatus U1, and a pickup roller 29 is arranged above it. On the downstream side of the pickup roller 29, a pair of feed rolls 30 for preventing double feeding of the paper P, a paper transport roll 31, a guide member 32 for guiding the paper P, and a registration roll 33 are sequentially arranged. On the downstream side of the secondary transfer area, in addition to the guide roll 6 that conveys the sheet P carrying the secondary-transferred toner image, the sheet receiving member 34 and the unfixed toner image on the sheet P are fixed. A fixing device 35 is arranged. further,
A pair of ejection rolls 36 for ejecting the paper P on which the fixed image is formed and a paper ejection tray 37 on which the ejected paper P is placed are arranged.

(Operation of Image Forming Apparatus) The surface of the image carrier 19 rotating in the direction of arrow A is uniformly charged by the charging charger 20. This uniformly charged image carrier 1
An electrostatic latent image 9 is written by the light beam writing device 18. The electrostatic latent image on the image carrier 19 is developed by the developing unit 21 into an unfixed toner image. In the formation of this toner image, the toner image of the first color is first formed, and thereafter, every time the image carrier 19 rotates for a predetermined time, the toner images of the second color to the fourth color are formed. In this embodiment, K, Y,
M and C color toner images are sequentially formed. The surface of the image carrier 19 is cleaned by the blade of the cleaner unit 22 after the toner image is transferred to the intermediate transfer body 1. Here, the optical writing control device 17 first reads out the digital signal of K color of the first color and outputs it to the light beam writing device 18. This writing device 1
Reference numeral 8 writes an electrostatic latent image corresponding to K color on the surface of the image carrier 19. The electrostatic latent image corresponding to the K color is developed into a visualized toner image of the K color by the developing device K in the developing unit 21, and is moved to the primary transfer portion. In the primary transfer portion, a transfer corotron 26 arranged on the back surface side of the intermediate transfer member 1 applies an electric field having a polarity opposite to the charging polarity of the toner image to the toner image of K color reaching the primary transfer portion. While being electrostatically adsorbed on the intermediate transfer body 1, the primary transfer is performed by the movement of the intermediate transfer body 1 in the arrow B direction.

The intermediate transfer body 1 moves at the same peripheral velocity as the image carrier 19 while adsorbing and carrying the K toner image. When the transfer of the K toner image of the first color is completed, the output of the optical writing control device 17 outputs the Y color of the second color until the transfer start position of the K toner image on the intermediate transfer body 1 reaches the primary transfer portion.
Writing of the electrostatic latent image of color is started. When the transfer start position of the intermediate transfer body 1 carrying the K toner image reaches the primary transfer portion, the transfer corotron 26 transfers the Y toner image of the second color. Then, the transfer of the M toner image and the C toner image is performed in the same manner as the transfer of the Y toner image. In this way, a multiple toner image superimposed on each color is formed on the intermediate transfer body 1. The transfer roll 2, the guide roll 6 and the belt cleaner 27 arranged on the surface side of the intermediate transfer body 1 are separated from the intermediate transfer body 1 until the toner images of the respective colors are primarily transferred onto the intermediate transfer body 1. It is held in the retracted position.

On the other hand, the paper P stored in the paper feed tray 28
Are picked up by the pickup roller 29 one by one at a predetermined timing, and are fed by a pair of feed rolls 30 and a sheet conveying roll 31.
It is stopped once at 3. The paper P is secondarily transferred from the registration roll 33 in synchronization with the multi-toner image of each color (K, Y, M, C) transferred onto the intermediate transfer body 1 thereafter to the secondary transfer area. Transported to the area. In the secondary transfer area, the transfer roll 2 is in pressure contact with the backup roll 3 via the intermediate transfer body 1. Then, the conveyed paper P passes through the secondary transfer area by the pressure contact conveyance between the rolls 2 and 3 and the movement of the intermediate transfer body 1. At this time, a transfer voltage having a polarity opposite to the charging polarity of the toner image is applied from a power source (not shown) to the transfer roll 2, and electrostatic attraction by the generated transfer electric field causes the toner that is adsorbed and carried on the intermediate transfer body 1. The image is secondarily transferred from the intermediate transfer body 1 to the paper P. When the transfer roll 2 is pressed against the backup roll 3, foreign matter such as toner particles attached to the surface of the transfer roll 2 is removed by the cleaning blade 7.

The transfer of the full-color image has been described above. However, in the case of forming a single-color image, when the toner image of, for example, K color that is primarily transferred on the intermediate transfer body 1 moves to the secondary transfer area, it is immediately transferred. The toner image is transferred to the paper P. When forming images of a plurality of colors, desired hues may be selected and the toner images may be transferred to the paper P when the multicolor toner images superimposed on those colors move to the secondary transfer area. . In the case of the transfer of the multicolor image, the toner images of the respective colors are accurately matched without shifting at the primary transfer portion.
As described above, the rotation of the image carrier 19 and the movement of the intermediate transfer body 1 are synchronized. As described above, the sheet P on which the toner image is transferred in the desired hue is in contact with the guide roll 6 whose rear surface is driven to rotate, and the sheet receiving member 34.
And is conveyed to the fixing device 35. Then, in the fixing device 35, after fixing the unfixed toner image and fixing it to the permanent image, the paper P is discharged to the paper discharge tray 37 by the pair of paper discharge rolls 36. When the secondary transfer is completed, the surface of the intermediate transfer body 1 is cleaned by the belt cleaner 27 provided on the downstream side of the secondary transfer area,
Prepare for the next transfer.

(Details of Secondary Transfer Member) The specific structure of the secondary transfer member in the image forming apparatus shown in FIG. 4 is as follows. The belt-shaped intermediate transfer member (1) has a thickness of 0.
A 1 mm polyimide film was used. Transfer roll (2)
As the roll, a roll having a length of 300 mm and an outer diameter of 25 mm in which a conductive elastic layer (2b) and a conductive layer (2c) having a thickness of 15 μm were coated on a SUS core metal (2a) having an outer diameter of 15 mm was used. . The elastic layer (2b) is made of foamed silicone rubber in which carbon black is dispersed, and the conductive layer (2c) is made of fluororesin in which carbon black is dispersed. The volume resistivity of the transfer roll (2) was 10 ⁶ Ωcm, and its hardness was 30 ° in Asker C. As the backup roll (3), a conductive urethane rubber layer (3b) molded to a thickness of 5 mm was coated with a film layer (3c) having a thickness of 100 μm on a SUS core metal (3a) having an outer diameter of 15 mm. Outer diameter 25mm
Rolls were used. The film layer (3c) was made of a fluororesin in which carbon black was dispersed, and the surface resistivity of the backup roll (3) was 10 ⁹ Ω / □. Power supply
From (4), a DC voltage of +1.5 kV is applied to the transfer roll (2), and this transfer voltage is controlled to a constant voltage. A SUS metal roll having an outer diameter of 12 mm was used as the earth roll (5).

A roll as shown in FIG. 2A was used as the guide roll (6). That is, a cylindrical SUS conductor (6b) is fixed to the shaft body (6a), and a plurality of rib-shaped ABS resin protrusions (6c) are formed on the outer peripheral surface of the conductor (6b) in the axial direction. It is provided in. The protrusion (6c) is set to have a height of 1.5 mm, a width of 2 mm and an interval of 20 mm, and its outer surface is subjected to smooth curved surface processing.
The outer diameter of the guide roll (6) is 15 mm. The shaft body (6a) of the guide roll is parallel to and parallel to the core metal (2a) of the transfer roll (2) and is grounded. The guide roll (6) and the transfer roll (2) are separated from each other so that the shortest distance between the protrusion (6c) and each outer peripheral surface of the conductive layer (2c) is 5 mm.

(Operation of Secondary Transfer Member) As described above,
When the paper P passes through the secondary transfer area, the toner image adsorbed and carried on the intermediate transfer body 1 is secondarily transferred from the intermediate transfer body 1 to the paper P. When the front end of the paper P discharged from the transfer area approaches the guide roll 6, the guide roll 6 is grounded, so that a charge having a polarity opposite to the charge of the paper P is induced in the guide roll 6. Therefore, the leading edge of the paper P is electrostatically attracted to the guide roll 6 side and is reliably separated without being attracted to the intermediate transfer body 1. As the paper P is further discharged, the back surface of the paper P comes into contact with the insulating protrusion 6c of the guide roll 6 and is conveyed while receiving the pressure contact conveyance force between the transfer roll 2 and the backup roll 3 and the rotational force of the guide roll 6. . During this time, the guide roll 6 rotates at the same peripheral speed as the conveyance speed of the paper P. Moreover, since the plurality of insulating protrusions 6c are provided on the peripheral surface of the conductor 6b in the axial direction, the paper P
A constant gap is formed between the back surface of the and the peripheral surface of the conductor 6b by the height of the protrusion 6c. Therefore, there is no speed difference between the paper P and the guide roll 6, the paper P can be smoothly transported to the downstream side of the transfer area, and there is no impact when the paper P contacts the guide roll 6, There is no possibility that the charged electric charge of the paper P applied during the secondary transfer moves and is not discharged abruptly. Moreover, since the discharge area of the paper P can be widened by utilizing the curved surface of the conductor 6b, the paper P is opposed to the peripheral surface of the conductor 6b for a relatively long time through a certain gap, so that the paper P is further improved. The electricity is slowly removed.

When the leading edge of the paper P separates from the guide roll 6, the paper P is placed on the paper receiving member 34 and the paper P is fixed on the fixing device 3.
5 is transported. Since the charge on the entire area of the paper P is effectively eliminated, the unfixed toner image on the paper P is not disturbed,
The fixing device 35 can form a good fixed image without image defects. By the way, under an ultra-low humidity environment of a temperature of 20 ° C. and a relative humidity of 10%, a DC voltage of 1.5 kV is applied to the transfer roll 2 by constant voltage control, and a paper left at the above environment for 10 hours has an image density of 60%. When copying the original, the obtained image shows no disturbance of the toner image,
Image defects could be prevented.

Embodiment 2 The image forming apparatus of this embodiment is different from the image forming apparatus of Embodiment 1 in that three guide rolls (6A, 6B, 6C) as shown in FIG. 3 are used. To do. These guide rolls are the same as those in Example 1 except for the following points. As the guide rolls are arranged on the downstream side in the transport direction of the paper P, the heights of the protrusions 6c are sequentially decreased, and the conductivity of the entire roll is increased. The height of the protrusions 6c on the upstream first guide roll 6A is 2.0 mm, and the heights of the protrusions 6c on the second guide roll 6B and the third guide roll 6C are 1.5 mm and 1. It is 0 mm. Further, each guide roll is grounded by a common wiring. Therefore, even when the charge amount of the paper P applied at the time of the secondary transfer is large, there is no sudden discharge to move the charges.
As compared with the guide roll 6 of the first embodiment, the charge can be removed more slowly.

Embodiment 3 FIG. 5 shows another image forming apparatus (printer) according to the present invention.
FIG. The image forming apparatus U2 of this embodiment is different from the image forming apparatus U1 shown in FIG. 4 mainly in that the toner image carried on the image carrier is directly transferred onto the paper P. In the image forming apparatus U2, there is arranged an image carrier 51 in which an organic photosensitive layer is coated on an aluminum cylindrical base material. The image carrier 51 is rotatable in the direction of the arrow, and a charger 52 for uniformly charging the surface of the image carrier 51 is arranged on the surface of the image carrier 51. On the surface of the image carrier 51 charged by the charger 52, an electrostatic latent image is written by the laser writing device 53 on the downstream side in the rotation direction. The laser writing device 53 includes a semiconductor laser oscillator 54 serving as a laser light source, and a collimator lens 5 that collects a laser beam L from the oscillator 54 and collimates it.
5. A polygon mirror 56 that deflects the laser beam L from the collimator lens 55 in the scanning direction, a convex lens 57 that forms an image of the deflected laser beam L onto the image carrier 51, and a surface tilt of the polygon mirror 56 is corrected. It is composed of a cylindrical mirror 58 and the like.

Further, around the image carrier 51, a developing device 59 and a developing device 59 are provided, which are provided with a developing roll 59b provided with a layer regulating member 59a in order from the laser writing area along the rotation direction thereof. A transfer roll 60 for transferring the toner image formed on the image carrier 51 to the paper P, a cleaner 61 having a cleaning blade 61a for removing residual toner on the image carrier 51, and the image carrier 51.
A static eliminator 62 for removing the upper residual charge is arranged. A paper feed tray 6 is provided at the bottom of the image forming apparatus U2 main body.
3 is provided, similar to the image forming apparatus U1 of the first embodiment,
The pickup roller 6 is sequentially provided on the downstream side in the transport direction of the paper P.
4, a pair of feed rolls 65, a pair of paper transport rolls 66, a guide member 67, and a pair of registration rolls 68 are arranged. Further, a guide roll 6, a sheet receiving member 69, a fixing device 70, a pair of discharge rolls 71 and a discharge tray 72 are sequentially arranged on the downstream side of the transfer area.

(Operation of image forming apparatus) After the surface of the image carrier 51 is uniformly charged by the charger 52, the laser beam L is irradiated in accordance with the image signal from the laser writing device 53 to carry the image carrier. An electrostatic latent image is formed on the surface of the body 51. The electrostatic latent image is then visualized with toner by the developing device 59, and a toner image is formed on the image carrier 51. On the other hand, the paper P stored in the paper feed tray 63 is conveyed to the transfer area at the same timing as the writing operation of the laser writing device 53. In the transfer area, the toner image on the image carrier 51 is transferred to the paper P. The paper P on which the unfixed toner image is transferred has a guide roller 6 whose rear surface is driven to rotate.
While being in contact with, the sheet is placed on the sheet receiving member 69 and conveyed to the fixing device 70. In the fixing device 70, the unfixed toner image is fixed and fixed to a permanent image. After the transfer, the toner remaining on the surface of the image carrier 51 is removed by the blade 61.
It is mechanically scraped by a, and the static eliminator 62 removes the residual charges on the image carrier 51, and one image forming cycle is completed.

(Transfer Device) The transfer device 73 of this embodiment is
The transfer roll 60 for pressing the paper P against the image carrier 51 is provided, and is configured as follows. Both end portions 60a, 60a of the transfer roll 60 are rotatably supported by a roll support arm 74. The support arm 74 is swingably supported around a swing shaft 75 supported by a frame (not shown) of the image forming apparatus U2. Transfer roll 6
The 0 surface is pressed toward the image carrier 51 side by a predetermined pressure by a tension spring 76 provided between the roll support arm 74 and the frame of the image forming apparatus U2. The transfer roll 60 has a length of 3 in which a conductive elastic layer and a conductive layer having a film thickness of 15 μm are coated on a SUS core metal having an outer diameter of 15 mm.
A roll having a diameter of 25 mm and an outer diameter of 28 mm was used. The elastic layer is made of foamed silicone rubber in which carbon black is dispersed, and the conductive layer is made of fluororesin in which carbon black is dispersed. The transfer roll volume resistivity is 10 ⁶ Ωc.
m 2 and its hardness was 30 ° in Asker C. The transfer voltage is controlled to a constant voltage, and a DC voltage of +1.5 kV is applied to the transfer roll 60. Further, the guide roll 6 having the same structure as that of the first embodiment is used, and the arrangement relationship with the transfer roll 60 is also the same as that of the first embodiment. The transfer device 73 of the present embodiment transfers the toner image directly onto the paper P, and the configurations of the transfer roll 60 and the guide roll 6 and the arrangement relationship between them are basically the same as those in the first embodiment. Therefore, the present embodiment has the same operation as that of the above-described first embodiment, and thus the description of the operation is omitted.

(Modifications) The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the claims. It is possible. For example, in each of the embodiments, the example of the photoconductor drum was given as the image bearing member, but it is needless to say that the invention can be applied to a belt-shaped photoconductor. It is possible to use an intermediate transfer drum instead of the belt-shaped intermediate transfer member as the intermediate transfer member. Further, even if the transfer roll is converted into a corona transfer device as the transfer means, the same operation corresponding to each embodiment is achieved.

[0043]

According to the image forming apparatus of the present invention, the recording medium discharged from the transfer area is electrostatically attracted to the guide roll side and is reliably separated from the image carrier or the intermediate transfer body. Further, there is no impact when the recording medium comes into contact with the guide roll, and the electric charge of the recording medium does not suddenly discharge. Further, even if the conductive member is arranged near the downstream side of the transfer area, the unfixed toner image on the recording medium is not disturbed. As described above, the guide roll of the present invention has a high static elimination ability and can effectively eliminate the electric charges of the recording medium applied at the time of transfer, so that a good image without image defects can be formed. . Moreover, since the guide roll has a small number of parts and a simple structure, it is possible to realize an inexpensive transfer device. Claim 4
According to the image forming apparatus of the invention, since a certain gap is formed between the conductive peripheral surface of the guide roll and the back surface of the recording medium via the insulating protrusion, the charge of the recording medium can be discharged more slowly. There is no fear that toner explosion will occur even in an ultra-low humidity environment.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a secondary transfer area in an image forming apparatus of the present invention.

FIG. 2 is an explanatory view of a guide roll of the present invention shown as an example, FIG. 2A is a front view thereof, and FIG. 2B is FIG. 2A.
FIG.

FIG. 3 is a schematic configuration diagram of a secondary transfer area in which another guide roll of the present invention is arranged.

FIG. 4 is an overall view of an image forming apparatus shown as one embodiment of the present invention.

FIG. 5 is an overall view of an image forming apparatus shown as another embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a conventional image forming apparatus.

[Explanation of symbols]

U1, U2 ... Image forming apparatus, P ... Paper (recording medium), Q ...
Transfer area, 1 ... Intermediate transfer body, 2, 60 ... Transfer roll (transfer means), 6 ... Guide roll, 6b ... Conductor, 6c ... Insulating projections, 19, 51 ... Image carrier.

Claims (5)

[Claims] 1. An image carrier for carrying and carrying a toner image formed according to image information, and a toner image carried on the image carrier, either directly or through an intermediate transfer member, are electrostatically recorded on a recording medium. A transfer means for transferring the recording medium to the recording medium, contacting the back surface of the recording medium on which the toner image has been transferred, in the vicinity of the downstream side of the transfer area in the conveying direction of the recording medium, and moving in the conveying direction of the recording medium at the same speed as the conveying speed. An image forming apparatus comprising a conductive guide roll that rotates at a speed. 2. The image forming apparatus according to claim 1, wherein a plurality of guide rolls are provided along a conveyance path of the recording medium, and the conductivity of each guide roll is different. 3. The image forming apparatus according to claim 1, wherein a constant gap is formed between the peripheral surface of the conductor of the guide roll and the back surface of the recording medium conveyed in the downstream direction of the transfer area. 4. The image forming apparatus according to claim 3, wherein a plurality of insulating protrusions are axially provided on the peripheral surface of the conductor. 5. The image forming apparatus according to claim 4, wherein a plurality of the guide rolls are provided along the conveyance path of the recording medium, and the height of the insulating protrusion is different for each guide roll.