JPH0980926A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device using an intermediate transfer body capable of obtaining a high-quality image without transfer omission. SOLUTION: This device has a latent image carrier on which a latent image in accordance with an image signal is formed, an intermediate transfer body 2 primarily transferring the toner image formed on the latent image carrier and carrying it, a secondary transfer roll 4 for secondarily transferring the toner image on a recording medium 11 by abutting on the toner image carrying surface of the transfer body 2 through the recording medium 11, and a backup roll 5 abutting on the back surface of the toner image carrying surface of the transfer body 2 at a position opposed to the roll 4; and is provided with a flatness correcting member 7 all over the area in the width direction of the back surface of the transfer body 2 on the upstream side of the roll 4 and near the upstream of the tacking position of the recording medium 11 to the transfer body 2.

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 such as a copying machine or a laser printer having an intermediate transfer member,
In particular, the present invention relates to an image forming apparatus of a system in which an unfixed toner image formed on a latent image carrier is transferred to a recording medium via the intermediate transfer member.

[0002]

2. Description of the Related Art As a transfer method in a color image forming apparatus such as an electrophotographic copying machine, a method of directly transferring a toner image formed on a latent image carrier such as a photosensitive drum to a recording medium, and a latent image carrier A method in which the toner image formed above is temporarily transferred onto a drum-shaped or belt-shaped intermediate transfer member and then the toner image on the intermediate transfer member is secondarily transferred onto a recording medium again to obtain a copied image. It has been known.

In particular, in an image forming apparatus using the above-mentioned intermediate transfer member, multiple transfer defects and color resists are caused by many factors such as the holding state and thickness of the recording medium or its "strain", that is, bendability, or its surface property. It is known to have the effect of suppressing the occurrence of deviation of the ratio. FIG. 11 is a schematic diagram illustrating a schematic structure of an electronic copying machine as an example of an image forming apparatus using an intermediate transfer member, in which 30 is a document scanning unit, 31 is a document mounting table,
32, 33 and 34 are mirrors, 35 is an imaging lens, 36 is a photoelectric converter such as CCD, 40 is a laser scanning writing unit,
41 is a laser, 42 is an image forming optical system, 43 is a scanning optical system, 44 is a mirror, 50 is an image processing unit, 60 is an image forming control unit, and 70 is an image forming unit.

The image forming section 70 stabilizes the running of the latent image carrier (here, a certain photosensitive drum) 1, the intermediate transfer body (here, the driving roll 2a, the driven roll 2b, the tension roll 2c, and the intermediate transfer body). Walk correction roll 2
d, a foil-shaped endless belt made of a semiconductive material stretched around the backup roll 5, a primary transfer device (here, a conductive roll) 3, a secondary transfer roll (a so-called bias roll) 4, A backup roll 5, a tray 15 for accommodating the recording medium 11, a pickup roll 16 for taking out one recording medium (paper or the like) 11, a taken-out recording medium 11 at a predetermined timing, and an intermediate transfer body 2 and a secondary transfer roller 4. A registration roll 17 which is fed between the intermediate transfer member 2 and the intermediate transfer member cleaner 12 for removing the residual toner on the intermediate transfer member 2 after the secondary transfer, and a recording medium transfer belt which transfers the recording medium 11 on which the toner is transferred to the fixing device 19. 18 and a discharge tray 20 for discharging the fixed storage medium.

Around the latent image carrier 1, a charger (here, corotron) 13 for uniformly charging the surface of the latent image carrier 1 with electric charges of a predetermined polarity, and the surface of the charger 13 are provided. A latent image carrier cleaner 24 for removing the residual toner, a charge eliminating lamp 25 for neutralizing the charges on the surface thereof, and the like are provided. In the figure, an original placed on the original placing table 31 is scanned by an optical system including mirrors 32, 33, 34 and an image forming lens 35 forming the original scanning unit 30, and an image signal is generated by a photoelectric converter 36 such as a CCD. Read as. The illumination light source is not shown.

The image signal of the read document is subjected to required processing in the image processing section 50 and given to the laser 41. The laser 41 emits laser light modulated by the processed image signal. The emitted laser light is scanned on the latent image carrier 1 by the imaging optical system 42, the scanning optical system 43, and the mirror 44.

The surface of the latent image carrier 1 is uniformly charged by a charger 13, and the surface of the latent image carrier 1 is scanned with a laser beam modulated with an image signal to cause the latent image carrier to be scanned. An electrostatic latent image corresponding to the original image is formed on the surface of 1. This electrostatic latent image is developed by the rotation of the latent image carrier 1 to the developing device 14
To reach the installation position and toner development is performed. The latent image carrier 1 carrying the toner image further rotates to reach the primary transfer portion where the primary transfer device 3 is arranged, and the toner image is primarily transferred to the intermediate transfer member 2.

The toner image primarily transferred to the intermediate transfer member 2 reaches the secondary transfer portion where the secondary transfer roll 4 is arranged by the movement of the intermediate transfer member 2. In accordance with the toner developing operation, the intermediate transfer body 2 moves at substantially the same speed as the peripheral speed of the latent image carrier 1, and the primary transfer device 3 is at a position where the latent image carrier 1 and the intermediate transfer body 2 come into contact with each other. Is primarily transferred to the intermediate transfer body 2 by a transfer electric field having a polarity opposite to the charging polarity of the toner applied to the intermediate transfer member 2.

In the case of a color copying machine, from the formation of the latent image to the primary transfer of the toner image, the required color (generally,
Black: BK, Yellow: Y, Magenta: M, Sian:
The color toner image in which the multicolor toners are superposed is formed on the intermediate transfer member 2 by repeating the procedure of C). That is, in the color image forming apparatus, the developing device 14 generally includes the Bk developing device 14a, the yellow developing device 14b, and the magenta developing device 14.
c, a four-color developing device of a cyan developing device 14d,
The developing devices 14a to 14d for the respective colors are selectively positioned at the developing portions so that the latent images of the respective colors formed on the latent image carrier 1 can be sequentially developed.

The toner image of the first color that has been transferred to the latent image carrier 1 is transferred onto the intermediate transfer belt 2 at the position of the primary transfer device 3. After the toner transfer, the latent image carrier 1 is cleaned by a latent image carrier cleaner 24 to remove residual toner and the charge is neutralized by a discharge lamp 25, and then a latent image corresponding to the second color is formed. Is done. The electrostatic latent image of the second color is also developed in the same manner, and the toner image thereof is transferred onto the toner image of the first color transferred onto the intermediate transfer body 2 in an overlapping manner.

Thereafter, the third and fourth colors are similarly multi-transferred to the intermediate transfer body 2, and as a result, a color toner image in which unfixed plural color toners are superposed is formed on the intermediate transfer body 2. It At this time, the secondary transfer roll 4 and the intermediate transfer member cleaner 12 are retracted from the intermediate transfer member 2 until the transfer of the final toner image is completed.

Then, when the intermediate transfer body 2 on which all the necessary toner images have been primarily transferred reaches the position of the secondary transfer roll 4, it is taken out from the tray 15 by the pickup roll 16 and is timed by the registration roll 16. The recording medium 11 sent out is fed between the intermediate transfer body 2 and the secondary transfer roll 4. When the recording medium 11 is nipped and conveyed by the secondary transfer roll 4, the intermediate transfer member 2 and the backup roll 5, the charging polarity of the toner image applied between the secondary transfer roll 4 and the intermediate transfer member 2 The toner image on the intermediate transfer member 2 is secondarily transferred to the recording medium 11 by the transfer electric field formed by the transfer voltage of the opposite polarity.

The secondary transfer roll 4 is made of a conductive material, and a predetermined transfer voltage is applied from a transfer power source (not shown). For example, the contact roll 6 arranged to rotate in contact with the backup roll 4 is connected to the ground,
A power supply for applying a bias voltage having a polarity opposite to that of the toner is connected to the secondary transfer roll 5. The recording medium 11 on which the toner image is secondarily transferred is separated from the intermediate transfer body 2 by a separation claw (not shown), and is sent to the fixing device 19 by the conveyor belt 18. Fixing device 1
Reference numeral 9 denotes a recording medium 11 when passing between a pair of fixing rolls.
Is heated / pressurized to fix the toner image, and the discharge tray 2
It is discharged to 0.

After the secondary transfer, the intermediate transfer body 2 is cleaned by the intermediate transfer body cleaner 12 to remove the residual toner.
Prepare for the next image forming operation. The above-described operation of the image forming unit 70 is controlled by the image forming process control unit 60.
In the color image forming apparatus using the intermediate transfer body 2 as described above, since the composite toner image (superimposed image of the toner images of the respective colors) that has already been multi-transferred is transferred onto the recording medium 11, it is directly transferred from the latent image carrier. This has an advantage that it is possible to effectively prevent the positional deviation between the toner images and the occurrence of the image disturbance in the method of sequentially transferring the toner images of the respective colors to the recording medium.

Conventionally, as this type of image forming apparatus, those described in JP-B-49-209 and JP-A-62-206567 are known.

[0016]

However, when the above-mentioned conventional method is used, there are the following problems. That is, in the case where an endless belt-shaped so-called intermediate transfer body belt is used as the intermediate transfer body, undulations and wrinkles (hereinafter referred to as undulations) are generated on the surface of the belt as the intermediate transfer body runs. Occurs, and the flatness is reduced.

FIG. 12 is an explanatory view of an example of the undulations or the like that occur on the intermediate transfer belt, and particularly shows the belt portion hung between the walk correction roll 2d and the backup roll 5 in FIG. Both ends indicate the positions of the walk correction roll 2d and the backup roll 5. As shown in the figure, when an intermediate transfer belt of this kind is stretched between rolls and run, a large undulation or the like occurs in the central portion.

A so-called tacking position at which the leading edge of the recording medium carried in abuts is set near the center of the intermediate transfer belt, and if the intermediate transfer belt has undulations as shown in FIG. It does not completely adhere to the surface of the intermediate transfer belt, and enters the secondary transfer portion where the secondary transfer roll is arranged with a gap between the two. When the recording medium enters the secondary transfer portion without being in close contact with the intermediate transfer belt, the electric field formed between the secondary transfer roller and the counter roller is generated in this gap at the secondary transfer portion or the area immediately before it. As a result, electric discharge occurs between the recording medium and the intermediate transfer belt. There is a problem that the toner image is disturbed by this discharge, or the charge polarity of the toner on the intermediate transfer belt is changed due to the attachment of charges generated by the discharge, and so-called transfer omission occurs. Particularly, the latter transfer omission occurs remarkably when an insulating transfer material such as OHP is used, and remarkably deteriorates the image quality.

FIG. 13 is a schematic view for explaining the positional relationship between the intermediate transfer belt and the recording medium at the secondary transfer portion when there is a gap between the secondary transfer roll and the recording medium, and FIG. 14 shows the intermediate transfer belt. FIG. 6 is a schematic diagram illustrating a change in toner charge due to discharge that occurs between recording media. As shown in FIG. 13, when the recording medium 11 enters between the secondary transfer roll 4 and the backup roll 5 together with the intermediate transfer belt 2, the toner T carried on the surface of the intermediate transfer belt 2 becomes two. An electrostatic force is applied by the transfer electric field E formed between the next transfer roll 4 and the backup roll 5, and the recording medium 1
1 and is transferred.

However, as shown in FIG. 14, when the recording medium 11 enters between the intermediate transfer belt 2 and the recording medium 11, a discharge due to the transfer electric field E occurs between the recording medium 11 and the intermediate transfer belt 2. The + ions generated by this discharge adhere to the toner T on the intermediate transfer belt 2 to reduce the charge amount or reverse the polarity, or the negative ions reduce the intensity of the transfer electric field E. As a result, the image quality is deteriorated due to the above-mentioned transfer omission.

In order to avoid this problem, for example, Japanese Patent Application Laid-Open No. 4-188176 proposes that the contact area between the recording medium and the intermediate transfer belt is increased by utilizing the "strain" of the storage medium. ing. However, even if the contact area between the recording medium and the intermediate transfer belt is increased, undulation occurs because the flatness of the intermediate transfer belt itself is not perfect and the belt is called a tension line due to lateral stress applied to the intermediate transfer belt. Due to wrinkles and the like, the transfer material and the intermediate transfer belt could not be brought into close contact with each other.

When an overhead projector recording medium (OHP), which is harder than paper, is used, the above-mentioned voids have a high probability of occurrence. The present invention
The purpose of this intermediate transfer is to solve the above-mentioned problems of the prior art, and the purpose thereof is not only general transfer paper but also an insulating transfer material such as OHP to obtain a high-quality image without transfer defects. An object is to provide an image forming apparatus using a body.

[0023]

In order to achieve the above object, the invention according to claim 1 provides a latent image carrier 1 that forms a latent image according to an image signal, and the latent image carrier 1. To intermediately transfer the formed toner image to the intermediate transfer body 2 for primary transfer, and to contact the toner carrying surface of the intermediate transfer body 2 via the recording medium 11 to secondarily transfer the toner image to the recording medium 11. Of the secondary transfer roll 4 and a backup roll 5 that is in contact with the back surface of the toner carrying surface of the intermediate transfer body 2 at a position facing the secondary transfer roll 4. A flatness correcting member 7 is provided on the upstream side of the transfer roll 4 and near the tacking position of the recording medium 11 onto the intermediate transfer body 2 over the entire width direction of the back surface of the intermediate transfer body 2. And

The present invention can be applied to the intermediate transfer body 2 which is either an endless belt having a plurality of rolls or a drum shape which is held by a basket-like base in a circular manner.
Further, as the flatness correction member 7, a flexible baffle plate or an elastic roll which is in sliding contact with the width of the intermediate transfer member is used.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION In the above-described structure of the present invention, after the surface of the latent image carrier 1 is uniformly charged, a latent image corresponding to the image signal is formed by optical writing according to the image signal. , Carry this. The toner image formed on the latent image carrier 1 is electrostatically primary-transferred at the primary transfer portion to the intermediate transfer member 2 and carries it.

The secondary transfer roll 4 comes into contact with the toner carrying surface of the intermediate transfer member 2 via the recording medium 11 to secondarily transfer the toner image onto the recording medium 11. The backup roll 5 is in contact with the back surface of the toner carrying surface of the intermediate transfer body 2 at a position facing the secondary transfer roll 4, and the recording medium 11 is placed between the secondary transfer roll 4 and the intermediate transfer body 2. The toner image carried on the intermediate transfer body 2 by being sandwiched is secondarily transferred onto the recording medium 11.

The flatness correcting member 7 arranged upstream of the secondary transfer roll transfer roll 4 and in the vicinity of the upstream of the tacking position of the recording medium 11 onto the intermediate transfer body 2 includes the flatness correcting member 7 of the intermediate transfer body 2. The entire surface of the back surface in the width direction is pressed, the flat surface of the intermediate transfer body 2 is flattened, the recording medium 11 is brought into close contact with the corrected intermediate transfer body 2, and in this state, it is sent to the secondary transfer portion.

When an endless belt having a plurality of rolls is used as the intermediate transfer member 2, the endless belt (intermediate transfer member belt) is hung on a driving roll, a walk correction roll, a tension roll and a backup roll. After being passed around and conveyed, the flatness straightening member 7 is arranged on the upstream side of the backup roll 5 and on the back side of the toner carrying surface in the vicinity of the upstream of the tacking position of the recording medium 11 onto the intermediate transfer belt for recording. At the position where the medium is tacked on the intermediate transfer belt, uniform tension in the width direction is applied to the intermediate transfer belt so that the surface of the intermediate transfer belt is flat.

Similarly, when the intermediate transfer member is formed in a drum shape, the flatness correcting member 7 is also used as the backup roll 5.
Recording medium 11 on the upstream side of the intermediate transfer drum
Is arranged on the back side of the toner carrying surface in the vicinity of the upstream of the tacking position of the intermediate transfer drum so that the width direction surface of the intermediate transfer drum is flat at the position where the recording medium is tacked to the intermediate transfer drum. Gives uniform tension in the width direction.

When a flexible baffle plate is used as the flatness correcting member, the leading edge of the baffle plate slides over the entire widthwise direction of the intermediate transfer belt or the drum, and the downstream side of the sliding contact portion. The toner carrying surface of the intermediate transfer belt or intermediate transfer drum is made to be a uniform flat surface. Similarly, when an elastic roll is used instead of the flexible baffle plate as the flatness correcting member, the elastic roll is pressed and slidably contacted across the width direction of the intermediate transfer belt or the intermediate transfer drum, and downstream of the slidable contact portion. The toner carrying surface of the intermediate transfer belt or the intermediate transfer drum in 1 is made to be a uniform flat surface.

With such a structure, in the image forming apparatus according to the present invention, the flatness correction member provided on the back surface of the intermediate transfer member causes the undulation due to the unevenness of the flatness of the intermediate transfer member itself. Since the tension line (wrinkle) due to the lateral stress applied in the width direction of the intermediate transfer member is corrected, the recording medium can be closely attached to the intermediate transfer member, and between the two that enter the secondary transfer portion. Voids can be prevented from occurring.

Therefore, the transfer electric field formed between the secondary transfer roller and the backup roll does not cause discharge between the recording medium and the intermediate transfer member at the secondary transfer portion or the area immediately before the secondary transfer portion. It is possible to obtain a high-quality image without disturbing the toner image carried on the intermediate transfer member or causing transfer failure.

[0033]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating the configuration of an embodiment of the image forming apparatus according to the present invention, and FIG.
The same reference numeral corresponds to the same portion, and 7 is a flatness correcting member. In the figure, reference numeral 1 denotes a photosensitive drum as a latent image carrier, which rotates in the direction indicated by an arrow in the figure. On the surface of the photoconductor drum 1, a charging roll 1 which is a charger is provided.
3, laser scanning writing unit 40, black, yellow,
Magenta and cyan color toner developing devices 14a to 14
A color developing device having d, a charging roll 3, a drum cleaner 24, and a discharge lamp 25 are attached, and a monochrome or multicolor toner image is formed by a well-known electrophotographic process.

The intermediate transfer belt 2 as an intermediate transfer member is arranged so as to contact the surface of the photosensitive drum 1 at the primary transfer portion where the charging roll 3 is arranged, and the driving roll 2a, the driven roll 2b, and the tension roll. 2 c, a walk correction roll 2 d for stabilizing the running of the intermediate transfer belt 2, and a backup roll 5 are stretched around and conveyed.

The backup roll 5 installed at the secondary transfer portion forms an insulating rubber layer such as Si (silicon) or EPDM having a thickness of 2 to 5 mm on a metal cored bar. A semiconductive tube is coated on the top, and a contact roll 6 is arranged so as to contact the semiconductive tube. The toner image transferred from the photosensitive drum 1 to the intermediate transfer belt 2 by the action of the primary transfer roll 3 advances to the secondary transfer portion by the rotation of the intermediate transfer belt 2,
The pick-up roll receives the action of a transfer electric field formed by a current flowing from the contact roll 6 to which a bias having the same polarity as that of the toner is applied via the semi-conductive tube of the backup roll 6 to the grounded secondary transfer roller 4. 16
Is taken out from the tray 15 and transferred by the registration roller 17 to the recording medium 11 sent to the secondary transfer portion at a predetermined timing.

The recording medium 11 on which the toner image is transferred is sent to the fixing device 19 by the recording medium conveying belt 18, and is pressed / heated by a pair of rolls constituting the fixing device to fix the toner on the recording medium 11. Is fixed. In this embodiment, a flexible baffle plate is used as the flatness correcting member 7 of the intermediate transfer belt 2 provided on the back surface of the intermediate transfer belt 108. The material for this baffle plate has a thickness of 100.
.About.300 μm PET (polyethylene terephthalate), PVdF (polyvinylidene fluoride), PC (polycarbonate), PI (polyimide), etc. were used.

Further, although the insulating baffle material is used in this embodiment, the resistance (that is, the volume resistivity is 10 ⁹ Ωcm) at which no current flows from the region of the secondary transfer portion to the flexible baffle plate 7. When the intermediate transfer belt 2 having the above) is used, it is also possible to use a conductive or semi-conductive material by mixing a resistance control agent such as CB (carbon black) into the material of the baffle plate. .

FIG. 2 is a schematic view of an essential part for explaining the operation of the flexible baffle plate which is the flatness correcting member of the intermediate transfer belt used in this embodiment, and the same reference numerals as those in FIG. 1 correspond to the same parts. , 7a is a flexible baffle plate, and 7b is a tension spring. The flexible baffle plate 7a is a thin plate having a substantially rectangular shape extending over the entire width direction of the intermediate transfer belt 2, and one end edge (leading edge) having good linearity along the longitudinal direction is formed on the intermediate transfer body. By bringing the other end of the fulcrum V into contact with the belt 2 and pulling the other end with the tension spring 7b, the one end is pressed against the intermediate transfer belt 2, and is slidably contacted as the intermediate transfer belt 2 circulates. Apply tension.

The urging load by the tension spring 7b is 200 gf.
~ 1000 gf, preferably 400-600 gf. In this range, the larger the load is, the higher the effect of preventing discharge discharge is obtained. However, in the baffle plate using the above-mentioned material, when a load larger than 1000 gf is applied, the flexible baffle plate 7a is plastically deformed or the intermediate Transfer belt 2
It causes problems such as abrasion. Therefore, if the baffle plate is made of a material that resists such compositional deformation and wear, it can be used with a large load.

The tip edge of the flexible baffle plate 7a is separated from the secondary transfer portion (nip position) of the secondary transfer roll 4 and the backup roll 5 which face each other by D ₁ along the intermediate transfer belt D ₁ = 20. ~ 80 mm, preferably 40-60
It is in contact with the intermediate transfer belt 2 at a point P ₁ located upstream of mm. On the other hand, the recording medium 11 from the recording medium conveying roll 8
Is enters to tacking the intermediate transfer belt 2 at about 15mm around P ₂ at a distance D ₂ on the upstream side along the intermediate transfer belt 2 from the nip position.

The material of the intermediate transfer belt 2 used in the above image forming apparatus is PI, PVdF, PET or PC mixed with a resistance control agent such as CB and having a volume resistivity of 10 ⁷ to 10 ¹⁴ Ωc.
However, when the volume resistivity is lower than 10 ⁸ Ωcm, the charge applied to the back surface of the intermediate transfer belt 2 at the primary transfer portion spreads out of the transfer nip position through the resistance of the intermediate transfer belt 2. For this reason, the toner is transferred from the photoconductor drum 1 to the intermediate transfer belt 2 before the photoconductor drum 1 and the intermediate transfer belt 2 come into contact with each other, so that the toner is largely scattered and a good image cannot be obtained.

Further, when the volume resistivity is higher than 10 ¹² Ωcm, the intermediate transfer belt 2 is charged and a charge eliminating device is required, so that the volume resistivity is preferably 10 ⁸ to 10 ¹² Ωcm. Further, the thickness of the intermediate transfer belt 2 is 5
If the thickness is 0 μm or less, the mechanical strength is insufficient and the belt may be broken or torn. Therefore, the thickness needs to be thicker than 50 μm.

The volume resistivity of the above-mentioned intermediate transfer belt was measured by "Hi-Resta" (trade name) manufactured by Mitsubishi Yuka. The electrode used for the measurement was an HR probe (high resistance probe) manufactured by the same company, and the volume resistivity when a voltage of 100 V was applied for 30 seconds was used. The environment of the measurement location was maintained at a temperature of 22 to 25 ° C. and a humidity of 50 to 60% RH, and the intermediate transfer belt to be measured was allowed to stand in this environment for 4 hours or more before the measurement.

FIG. 3 is a plan view illustrating a more specific structural example of the flatness correcting member using the flexible baffle plate in the present embodiment, and FIG. 4 is a side view of the main part for explaining the operation. In FIG. 3, the flexible baffle plate 7a is fixed to a shaft 7d attached to a pair of machine frames 9 across the width of the intermediate transfer belt 2 in a length corresponding to at least the entire width of the intermediate transfer belt 2. ing.

A baffle base 7c is fixed to the shaft 7d, and tension springs 7b are attached to brackets 10 fixed to the machine frame 9 at both ends of the baffle base 7c. As shown in FIG. 4, the baffle plate 7a is urged in the direction of the arrow B by the tensile force of the tension spring 7b in the direction of the arrow A with the shaft 7d as a fulcrum, and the leading edge slidably contacting the intermediate transfer belt 2 is the intermediate portion. By pressing the transfer belt 2, the flatness of the surface of the intermediate transfer belt 2 downstream of the portion in sliding contact with the baffle plate 7a is corrected and the close contact with the recording medium is ensured.

FIG. 5 is an explanatory view of the effect of improving the flatness of the intermediate transfer belt by the flatness correcting member using the flexible baffle plate of this embodiment, and the waviness and the like generated in the intermediate transfer belt is reduced. It is an explanatory view of an example of that, and both ends show the positions of the walk correction roll 2d and the backup roll 5 shown in FIG. As shown in the figure, a flexible baffle 7 for correcting the undulations of the intermediate transfer belt 2
a always follows the displacement of the intermediate transfer belt 2 and never separates. Therefore, even when the intermediate transfer belt 2 is driven and the intermediate transfer belt is vibrated or the tension of the belt is changed, substantially flat planarity is ensured.

FIG. 6 shows the discharge with respect to the distance from the nip position of the secondary transfer portion to the sliding contact of the flexible baffle plate and the intermediate transfer belt when OHP is used as the recording medium in the image forming apparatus according to the present embodiment. FIG. 7 is an explanatory diagram of the relationship between dropout occurrence voltages, where the horizontal axis represents the distance from the nip position of the secondary transfer portion to the flexible contact of the baffle plate and the sliding contact of the intermediate transfer belt, and the vertical axis represents the discharge occurrence voltage .

In this embodiment, 1 from the nip of the secondary transfer portion (the point where the secondary transfer roll and the backup roll face each other).
A recording medium conveying path (paper chute) is arranged at a position of 5 mm so that the recording medium 11 fed to the secondary transfer portion by the registration roller 16 comes into contact (tacking) with the intermediate transfer belt 2. In the figure, when the transfer voltage is 3500V or lower, the transfer rate of the secondary transfer roll is deteriorated and a transfer failure occurs. Therefore, it is necessary to set the transfer voltage to 3500V or higher. It is necessary that the distance from the nip position of the secondary transfer portion to the sliding contact point of the flexible baffle plate and the intermediate transfer belt at a voltage above this voltage is about 8 mm or more. Also, 15m
When m is exceeded, the discharge omission occurrence voltage exceeds 4500 V, and above that, the voltage value is substantially the same. Based on this, in this embodiment, it is set to 15 mm.

FIG. 7 is an explanatory view of the relationship between the discharge loss generation voltage and the load of the flexible baffle plate when OHP is used as the recording medium in the image forming apparatus according to this embodiment.
The horizontal axis represents the load applied to the flexible baffle plate from the nip position of the secondary transfer portion, and the vertical axis represents the discharge omission generation voltage. In the figure, the transfer voltage 35 that does not cause deterioration of the secondary transfer rate
The load of the baffle plate is 200 to 10 in the range exceeding 00V.
Although it is 00 gf, in consideration of the strength of the baffle plate and the secondary transfer roll and the like, and when the discharge omission occurrence voltage is 4000 V or more, it is practically sufficient.
It was set to 600 gf.

According to the embodiments described above, it is possible to provide an image forming apparatus using an intermediate transfer member which can obtain a high-quality image without transfer defects. Next, another embodiment of the present invention will be described. FIG. 8 is a schematic view of an essential part for explaining the action of the elastic roll which is the flatness correcting member of the intermediate transfer belt used in this embodiment. The same reference numerals as those in FIG. 1 correspond to the same parts, and 7e is an elastic roll, 7f is a pressing spring.

The intermediate transfer belt 2 is pressed by the pressing spring 7f.
The load applied to the elastic roll 7e that is urged toward 200 gf to 3000 gf, preferably 400 to 200 gf
0 gf. The elastic roll 7e is separated from the secondary transfer portion (nip position) of the secondary transfer roll 4 and the backup roll 5 facing each other by D ₁ along the intermediate transfer belt 2 by D _1.
= 20 to 80 mm, preferably 40 to 60 mm, and is pressed against the intermediate transfer belt 2 at a point P ₁ located upstream.

On the other hand, the recording medium 11 from the recording medium conveying roll 8 is separated from the nip position along the intermediate transfer belt 2 upstream by D _{2 at a} distance of about 15 mm and at a position P ₂ near the toner carrying surface of the intermediate transfer belt 2 ( Enter to tackle the surface). The elastic roll 7e is a pressing spring 7f.
Is pressed against the back surface of the intermediate transfer belt 2 to apply tension over the entire width of the intermediate transfer belt 2 to correct the flatness of the surface of the intermediate transfer belt downstream of the intermediate transfer belt 2 to ensure the adhesion with the recording medium 11. To do.

FIG. 9 is a plan view illustrating a more specific structural example of the flatness correcting member using the elastic roll according to the present embodiment, and FIG. 10 is a side view of a main part for explaining the operation. In FIG. 9, the elastic roll 7e has a length corresponding to at least the entire width of the intermediate transfer belt 2 and a pair of arms 7g fixed to shafts 7h attached to a pair of machine frames 9 across the width of the intermediate transfer belt 2 in the width direction. Is swingably supported on the intermediate transfer belt 2 at its free end.

At the elastic roll mounting end (free end) of the arm 7g, the bracket 1 fixed to the pair of machine frames 9 is attached.
A push-down spring 7f attached to 0'is provided, and the push-down spring 7f uniformly presses the elastic roll 7e over the entire width of the intermediate transfer belt 2 in the lateral direction. That is,
As shown in FIG. 10, the push-down spring 7f pushes down the arm 7g in the arrow A direction, so that the arm 7g moves in the arrow B direction.
The elastic roll 7e applies tension to the intermediate transfer belt 2 as a result.

As a result, the flatness of the surface of the intermediate transfer belt downstream of the pressing point of the elastic roll is corrected, and the close contact with the recording medium 11 is guaranteed. In this embodiment, the elastic roll 7e is used as a correction member for the undulations of the intermediate transfer belt 2. The elastic roller 7e is formed by coating a metallic core metal with a rubber elastic material such as Si (silicon) or EPDM having a thickness of 2 to 5 mm, and the hardness of the elastic material layer is "SRIS ASKER C". 30 to 6 in hardness
It is 0 °, preferably 30-40 °.

As described above, in this embodiment, since the elastic roller 7e is used as a correction member for the waviness of the intermediate transfer belt 2, a larger load than that using the flexible baffle plate 7a of the above embodiment. There is no plastic deformation even when applied. Further, since the elastic roll 7e is driven by the movement of the intermediate transfer belt 2, the intermediate transfer belt 2 is not worn and a larger load than that using the flexible baffle 7a can be applied. A higher effect of preventing discharge omission can be obtained.

The flatness correcting member of the intermediate transfer belt according to the present invention is not limited to the structure of each of the embodiments described above, and other modified examples may be adopted as long as the structure has the same function as these. You can also Similarly, when applied to a drum-shaped intermediate transfer member, by installing the above-mentioned flatness correction member inside the intermediate transfer drum,
Similar effects can be obtained.

In the description of FIG. 1, the bias voltage having the same polarity as that of the toner is applied to the contact roll 6, but the present invention is not limited to this. The same can be applied to an image forming apparatus configured to apply a bias having a polarity opposite to that of the toner to the next transfer roll 4.

[0059]

As described above, in the image forming apparatus according to the present invention, the correction member, that is, the flatness, of the undulation of the intermediate transfer member, which is provided on the back surface of the intermediate transfer member, that is, the surface opposite to the toner carrying surface, is provided. The straightening member can correct the waviness of the intermediate transfer member itself and the tension line caused by the uneven tension applied to the intermediate transfer member, so that the recording medium and the intermediate transfer member are brought into close contact with each other to prevent a gap from being formed between them. You can

Therefore, even if the electric field formed between the secondary transfer roller and the backup roll is received in the secondary transfer portion or the area immediately before the secondary transfer portion, no discharge occurs between the recording medium and the intermediate transfer member. Even when an insulating recording medium such as OHP is used, a high-quality image without disturbance of the toner image and transfer omission can be obtained. Further, since the flexible baffle as the flatness correcting member of the intermediate transfer body adopted in the embodiment does not always follow the displacement of the intermediate transfer body and separates, the intermediate baffle at the time of driving the intermediate transfer body. Even if the vibration of the transfer member or the tension of the intermediate transfer member fluctuates, the intermediate transfer member flatness correcting member and the intermediate transfer member are not separated from each other.

Further, since the elastic roll as the flatness correcting member for the intermediate transfer member employed in the other embodiment is driven by the movement of the intermediate transfer member, it does not wear due to friction with the intermediate transfer member. The undulations of the transfer body can be effectively corrected.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating the configuration of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic view of a main part for explaining the action of a flexible baffle plate which is a flatness correcting member of an intermediate transfer belt used in one embodiment of an image forming apparatus according to the present invention.

FIG. 3 is a plan view illustrating a more specific structural example of the flatness correcting member using the flexible baffle plate in the embodiment of the image forming apparatus according to the present invention.

FIG. 4 is a side view of the main parts for explaining the operation of the flexible baffle plate in the embodiment of the image forming apparatus according to the present invention.

FIG. 5 is an explanatory diagram of an effect of improving the flatness of the intermediate transfer belt by the flatness correcting member using the flexible baffle plate of the embodiment of the image forming apparatus according to the present invention.

FIG. 6 is from the nip position of the secondary transfer portion to the sliding contact between the flexible baffle plate and the intermediate transfer belt when OHP is used as a recording medium in the image forming apparatus according to the first embodiment of the image forming apparatus of the present invention. FIG. 5 is an explanatory diagram of a relationship of a discharge omission generation voltage with respect to the distance.

FIG. 7 is an explanatory diagram of a relationship between discharge loss occurrence voltage and load of a flexible baffle plate when an OHP is used as a recording medium in an image forming apparatus according to an embodiment of the image forming apparatus according to the present invention.

FIG. 8 is a schematic view of a principal part for explaining the action of an elastic roll which is a flatness correcting member of an intermediate transfer belt used in an embodiment of the image forming apparatus according to the present invention.

FIG. 9 is a plan view illustrating a more specific structural example of the flatness correcting member using the elastic roll in the embodiment of the image forming apparatus according to the present invention.

FIG. 10 is a side view of the main parts for explaining the operation of one embodiment of the image forming apparatus according to the present invention.

FIG. 11 is a schematic diagram illustrating a schematic structure of an electronic copying machine as an example of an image forming apparatus using an intermediate transfer member.

FIG. 12 is an explanatory diagram of an example of undulations and the like that occur on the intermediate transfer belt.

FIG. 13 is a schematic diagram illustrating the positional relationship between the intermediate transfer belt and the recording medium at the secondary transfer portion when there is a gap between the secondary transfer roll and the recording medium.

FIG. 14 is a schematic diagram for explaining a change in toner charge due to electric discharge generated between the intermediate transfer belt and the recording medium.

[Explanation of symbols]

1 ...- Latent image carrier (photosensitive drum), 2 ...- Intermediate transfer member (intermediate transfer belt), 2a ...- Drive roll, 2b ... Tension roll, 2d ... Walk correction roll, 5 ...
Backup roll, 3 ... Primary transfer device (conductive roll), 4 ... Secondary transfer roll (bias roll), 5 ... Backup roll, 6 ... Contact roll, 7 ... ..Flatness correction members, 7a ...
・ Flexible baffle plate, 7b ... Extension spring, 7c
.... Baffle base, 7d ... Shaft, 7e
.... Elastic roll, 7f .... Push-down spring, 7g
・ ・ ・ ・ Arm, 7h ・ ・ ・ ・ Shaft, 8 ・ ・ ・ Recording medium transport roll, 9 ・ ・ ・ ・ Machine frame 10, 10, ...
・ Bracket, 11 ・ ・ ・ ・ Recording medium, 14 ・ ・ ・ ・ Developing device, 15 ・ ・ ・ ・ Recording medium tray, 16 ・ ・ ・ ・ Pickup roll, 17 ・ ・ ・ ・ Register roll, 18 ・ ・
..Recording medium conveying belt, 19 ... Fixing device, 20.
... Discharge tray, 30 ... Document scanning unit, 31 ...
..Document placing table, 32, 33, 34 ... Mirrors, 3
5 ...- Imaging lens, 36 ... Photoelectric converter such as CCD, 40 ... Laser scanning writing section, 41 ...
-Laser, 42 ...- Imaging optical system, 43 ...- Scanning optical system, 44 ...- Mirror, 50 ...- Image processing unit, 60 ... Image forming control unit, 70 ...・ ・ ・ Imaging department.

Claims (1)

[Claims] 1. A latent image carrier that forms a latent image according to an image signal, an intermediate transfer member that primarily transfers and carries the toner image formed on the latent image carrier, and the toner of the intermediate transfer member. A secondary transfer roll for abutting the bearing surface through a recording medium to transfer the toner image to the recording medium, and a toner transfer surface of the intermediate transfer member at a position facing the secondary transfer roll. An image forming apparatus having a back-up roll in contact with the back surface, wherein the back surface of the intermediate transfer member is provided on the upstream side of the secondary transfer roll and near the tacking position of the recording medium onto the intermediate transfer member. An image forming apparatus comprising a flatness correction member that presses the entire width direction.