JP3249746B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a transfer process, such as an electrostatic copying machine or a printer, and more particularly to an image forming apparatus suitable for a multiple transfer process.

[0002]

2. Description of the Related Art Conventionally, in a color image forming apparatus using an electrophotographic system or an electrostatic recording system, a multi-transfer system in which a visible image of each color is sequentially transferred to a recording material carried on a recording material carrier. Is widely used.

Among them, a general color image forming apparatus having many advantages such as high-speed recording performance can be easily realized, and various types of recording requirements can be realized by a linear transport path, is taken as an example. The technology and problems of the conventional color image forming apparatus will be described. The color image forming apparatus shown in FIG. 4 will be described as an example.

The copying machine has four image forming units P in the apparatus.
a, Pb, Pc and Pd are arranged side by side, and in these image forming sections, toner images of different colors are formed through processes of latent image, development and transfer.

The image forming units Pa, Pb, Pc and Pd are:
Each of the photosensitive drums 101a, 101b, 101c, and 101d includes a dedicated image carrier, in this example, electrophotographic photosensitive drums 101a, 101b, 101c, and 101d, and a process device that causes the photosensitive drums to create an image forming process. Each color toner image is formed thereon. A recording material carrier (transfer belt) 108 is provided adjacent to each of the photosensitive drums 101a to 101d.
The toner images of each color formed on 1d are superimposed and transferred onto the recording material 6 carried and conveyed on the transfer belt 108 by a transfer member described later. The recording material 6 onto which the toner images of each color have been transferred is then separated from the transfer belt 108 and conveyed to a fixing device (not shown). The fixing device melts and mixes the toner image by heating and pressing to fix the toner image on the recording material.
The image is discharged outside the apparatus as a recorded image.

In the image forming units Pa, Pb, Pc and Pd, the transfer charging means is in contact with the contact type transfer charging members 104a, 104a which make contact with the back side of the transfer belt 108 to perform the transfer.
04b, 104c and 104d.

By the way, in order to increase the speed and the image quality, the direction of movement of the transfer belt 108 is changed as shown in FIG.
Push-up members 411a to 411d for deforming and pressing the transfer belt 108 are provided up to a portion of the photosensitive drum corresponding to a region substantially covering the range where the transfer electric field of each transfer charging member 104a to 104d substantially extends on the upstream side, and It has been proposed to support a recording material and a transfer belt and to stabilize a pre-transfer discharge in a transfer process.

The above-mentioned upstream push-up members 411a to 411
When the toner image d is not installed, when the toner images on the photosensitive drums 101a to 101d are sequentially and multiplex-transferred onto the recording material carried on the transfer belt 108 in each image forming unit, immediately before the transfer, that is, the transfer is performed. There is a space near the upstream side of the contact point between the belt 108 and the photosensitive drums 101a to 101d, and even in this small space, the transfer electric field acts, and the toner on the photosensitive drum Among them, some toners whose mirroring power is smaller than other toners fly early, or the polarity of toners whose mirroring power is larger than other toners is reversed, so that not only is it not transferred to the recording material. And image defects such as toner scattering and transfer omission, such as hindering the transfer of other toner adjacent to the reversal toner for transfer, that is, image defects due to pre-transfer discharge. Flip and had. However, according to the configuration of the transfer section as described above, the upstream push-up members 411a to 411a-4
11d, the transfer belt 108 is pushed up by the photosensitive drum 1 on the upstream side of the contact point.
01a to 101d, so that this was prevented.

Further, the upstream push-up members 411a-411
When the recording material carrier 411d is not installed, the conveyance speed, the thickness of the recording material,
The carry-in path (paper path) into the transfer area fluctuates due to the size and the like, and is unstable. Therefore, the gap width (gap interval) between the photosensitive drum and the transfer belt 108 before transfer is set.
Is also in an unstable state. Then, even when outside the discharge area, the discharge occurred when the gap width was reduced. However, according to the configuration of the transfer unit as described above, the transfer belt 108 and the recording material by the upstream push-up members 411a to 411d were used. The paper path can be stabilized by the support of
This was prevented.

[0010]

However, in the conventional color image forming apparatus shown in FIG. 5, the demand for a recording material in recent years has increased, and the suction and conveyance of a thicker paper or a paper with a stronger stiffness than the conventional paper is required. The upstream push-up member 411a-
When a force for pushing 411d downward is applied, and the recording material is curled, the force tends to further increase. Therefore, each of the transfer charging members 104a-104
On the upstream side to which the transfer electric field d is applied, there is again a space having a distance proportional to the downward pushing force, which may cause image deterioration due to abnormal discharge.

This is because the upstream push-up members 411a to 411a
1d can be suppressed by increasing the pressing force. On the other hand, if there is an excessive pressing force in the transfer nip portion, the toner is agglomerated, and the mirror force of the toner and the image carrier is increased. This leads to reduced efficiency. In particular, this is remarkable in the center of a thin line or the like. In order to suppress this, conversely, light pressure transfer has been proposed.

Further, the upstream push-up members 411a-411
Due to the excessive pressing force of d, there is a disadvantage that the scraping or setting of the upstream push-up member is promoted, and the durability life for the push-up effect of the transfer belt is shortened.

In addition, in an image forming apparatus having no upstream push-up member, a transfer charging member presses a transfer belt at a transfer nip, thereby bringing the transfer belt into close contact with the photosensitive drum. However, similarly to the upstream push-up member, when the recording material is suctioned and conveyed, such as thicker paper or strongly stiff paper, which has recently increased in demand, a force for pushing down the transfer charging member is applied, and the transfer electric field generated by the transfer charging member is increased. The transfer nip that gives the transfer belt to the transfer belt may be shifted to the downstream side.

This phenomenon is more remarkable in an image forming apparatus in which the area where the photosensitive drum and the transfer belt are in close contact with each other is widened by the upstream push-up member, and the position of the transfer nip and the position where the transfer belt is in close contact with the photosensitive drum. But,
In some cases, they did not match.

Therefore, a minute space is formed between the transfer nip position on the transfer belt and the photosensitive drum, which may cause a drop due to an abnormal discharge similar to the discharge before transfer and scattering of toner dots.

An object of the present invention is to solve the above-mentioned problems and to provide separate upstream lifting members corresponding to the thickness of the recording material and the degree of the stiffness.
An object of the present invention is to provide an image forming apparatus that suppresses discharge before transfer.

Another object of the present invention is to provide an image forming apparatus capable of achieving both good conveyance stability of a recording material and excellent transferability.

Further objects and features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.

[0019]

The above object is achieved by an image forming apparatus according to the present invention. In summary, an image forming apparatus according to the present invention includes an image carrier on which a visible image is formed, a recording material carrier for carrying a recording material on its surface and transporting the recording material to a transfer position, and the recording material at the transfer position. A transfer charging member that contacts the back surface of the carrier and transfers a visible image from the image carrier to the recording material carried on the recording material carrier; and a moving direction from the transfer charging member on the back surface side of the recording material carrier. A pressing position that is provided upstream and protrudes the recording material carrier with respect to a tangent line of the image carrier at a position where the transfer charging member presses the image carrier via the recording material carrier. In the image forming apparatus including the first pressing unit, a second pressing unit that presses the recording material carrier from the back surface is provided between the transfer charging member and the first pressing unit. Features.

Alternatively, the image forming apparatus according to the present invention comprises:
An image carrier on which a visible image is formed, a recording material carrier supported by a plurality of support rollers in a belt shape for carrying the recording material on the surface and transporting the recording material to a transfer position, and the recording material carrier at the transfer position A transfer charging member that contacts a back surface of the image carrier and transfers a visible image from the image carrier to a recording material carried on the recording material carrier; and the transfer charging member moves the image carrier through the recording material carrier. And a line connecting a recording material carrier support position by the support roller on the recording material carrier moving direction upstream side from the transfer position.
An image forming apparatus comprising: a first pressing unit having a pressing position for pressing the recording material carrier from the back surface thereof, wherein the recording material is disposed between the transfer charging member and the first pressing unit. A second pressing means for pressing the carrier from the back surface is provided.

In the present invention, the transfer charging member is in a plate shape, and an angle formed by the transfer charging member and the recording material carrier on an upstream side in the moving direction of the recording material carrier is an acute angle.

The first pressing means and the second pressing means include plate-like first and second pressing members.

The distance between the position at which the transfer charging member contacts the recording material carrier and the position at which the pressing member presses the recording material carrier is 10 to 30 mm. The distance between the second pressing member and the position is preferably 10 mm or less.

Further, the distance between the tangent line and the position where the pressing member presses the recording material carrier is preferably 0.5 to 5 mm.

That is, in the region where the transfer electric field is formed by the transfer charging member, the image carrier and the recording material carrier are brought into contact in the most upstream region in the moving direction of the recording material carrier. It is preferable that the pressing member is disposed at the end.

At least one of the pressing member and the second pressing member has an acute angle with respect to the recording material carrier, the angle on the upstream side in the direction of movement of the recording material carrier. When the recording material passes through the transfer position, the amount of deformation of the second pressing unit is larger than the amount of deformation of the transfer charging member, and smaller than the amount of deformation of the pressing unit.

Further, a toner image of a plurality of colors can be superimposedly transferred onto the recording material carried on the recording material carrier.
Further, a plurality of the image carriers and the transfer charging members are provided, and a plurality of images can be superimposedly transferred from the plurality of image carriers to the recording material carried on the recording material carrier.

At this time, the line connecting the transfer positions of the plurality of image carriers is substantially linear.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) An embodiment of the image forming apparatus of the present invention will be described below with reference to the drawings.

FIG. 3 is a side view showing an example of the image forming apparatus of the present invention.

A copying machine as an image forming apparatus shown in FIG. 1 includes first, second, third and fourth image forming units Pa, Pb, P
c and Pd are provided side by side, and toner images of different colors are formed through the processes of latent image, development, and transfer.

In brief, the image forming units Pa, Pb,
Pc and Pd are dedicated image carriers, in this example, the electrophotographic photosensitive drums 1a, 1b, 1c and 1d
, And a toner image of each color is formed on each of the photosensitive drums 1a, 1b, 1c, and 1d. Each photosensitive drum 1a-1
d, a recording material carrier (transfer belt) 8 is installed, and the toner images of each color formed on the photosensitive drums 1a to 1d are transferred onto the recording material 6 carried on the transfer belt 8 and conveyed. Transcribed. The recording material 6 to which the toner images of each color have been transferred is
After the toner image is fixed by heat and pressure in the fixing unit 32, the toner image is discharged outside the apparatus as a recording image.

The above configuration will be described in more detail. Exposure lamps 21a, 21b, 21c and 21 are provided on the outer periphery of the photosensitive drums 1a, 1b, 1c and 1d, respectively.
d, drum chargers 2a, 2b, 2c and 2d, potential sensors 13a, 13b, 13c and 13d, developing device 3
a, 3b, 3c and 3d, a contact-type transfer charging member 4a,
4b, 4c and 4d, and cleaners 5a, 5b and 5
c and 5d are provided, and in the upper part of the device,
A light source device (not shown) and a polygon mirror 17 are provided.

The laser light emitted from the light source device is scanned by rotating the polygon mirror 17 by rotating the polygon mirror 17, the light beam of the scanning light is deflected by the reflection mirror, and is scanned by the fθ lens on the generatrix of the photosensitive drums 1a, 1b, 1c and 1d. To the photosensitive drums 1a, 1b, 1c and 1d
A latent image corresponding to the image signal is formed thereon.

The developing devices 3a, 3b, 3c and 3d include:
A predetermined amount of toner of cyan, magenta, yellow, and black is filled as a developer by a supply device (not shown). Developing units 3a, 3b, 3c and 3d
Develops the latent images on the photosensitive drums 1a, 1b, 1c and 1d, respectively, and visualizes them as a cyan toner image, a magenta toner image, a yellow toner image and a black toner image.

The recording material 6 is accommodated in a recording material cassette C,
From there, it is supplied onto the transfer belt 8 via a plurality of transport rollers and registration rollers 13, and is sequentially transported by the transfer belt 8 to a transfer section facing the photosensitive drums 1 a, 1 b, 1 c and 1 d.

The transfer belt 8 is made of a dielectric resin sheet such as a polyethylene terephthalate resin sheet (PET sheet), a polyvinylidene fluoride resin sheet, or a polyurethane resin sheet, and its both ends are overlapped and joined. , Endless or seamless (seamless) belts.

In this embodiment, as the transfer belt 8, P
An ET sheet seamless belt having a thickness of 100 μm was used.

When the transfer belt 8 rotates, the recording material 6 is sent out from the registration roller 13 to the transfer belt 8, and
The recording material 6 is transported toward the transfer section of the first image forming section Pa. At the same time, the image writing signal is turned ON, and an image is formed on the photosensitive drum 1a of the first image forming unit Pa at a certain timing based on the signal. Then, the transfer charging member 4a applies an electric field or electric charge at the lower transfer portion of the photosensitive drum 1a, so that the first color toner image formed on the photosensitive drum 1a is transferred onto the recording material 6. By this transfer, the recording material 6 is firmly held on the transfer belt 8 by electrostatic attraction, and is conveyed to the second image forming portion Pb and thereafter.

In the same manner, image formation and transfer in the second image forming section Pb to the fourth image forming section Pd are performed. Next, the recording material P to which the four color toner images have been transferred is discharged at the end of the transfer belt 8 at the end of the transfer belt 8 by removing the charge by the separation charger 12 at the downstream portion in the transport direction of the transfer belt 8 and attenuating the electrostatic attraction force. break away. The detached recording material 6 is fixed to the fixing device 32.
Transported to

The fixing device 32 includes a fixing roller 51, a pressure roller 52, heat-resistant cleaning members 54 and 55 for cleaning the respective rollers, roller heaters 56 and 57 installed in the rollers 51 and 52, and a fixing device. The roller 51 includes an application roller 50 that applies a release agent oil such as dimethyl silicone oil to the roller 51, an oil reservoir 53, and a thermistor 58 that detects the temperature of the surface of the pressure roller 52 and controls the fixing temperature. By fixing the recording material 6 to which the four color toner images have been transferred, the toner images are mixed and fixed to the recording material 6 to form a full-color copy image.

The photosensitive drums 1a, 1b, 1 after the transfer is completed
c and 1d are the respective cleaners 5a, 5b, 5c
And 5d to clean the toner remaining after transfer,
It is removed and subsequently ready for the formation of the next latent image.
The toner attached on the surface of the transfer belt 8 is
The surface of the belt is removed by a discharging roller 21 and a counter electrode 22 on the back side of the belt.
Then, the cleaning web (non-woven fabric) 19 abutting on the surface of the belt 8 wipes off the charge.

FIG. 1 shows a schematic configuration diagram of the transfer section in the present embodiment. In the present embodiment, this transfer unit is configured as each of the first to fourth image forming units Pa to Pd shown in FIG.

As shown in FIG. 1, the transfer section is provided with a contact-type charging member 4 supported by a fixed section of the apparatus main body.
And a plate-shaped conductive base (conductive blade) 42 provided thereon. The plate-shaped conductive substrate, that is, the conductive blade 42 is formed in a plate shape having a thickness direction in a plane parallel to the moving direction of the transfer belt 8, and moves the transfer belt 8 toward the photosensitive drum 1. It extends obliquely from the upstream side to the downstream side in the direction, and contacts (or approaches) the photosensitive drum 1 via the transfer belt 8. The mechanical contact point of the transfer charging member 4 with the transfer belt is called "transfer nip". The contact point of the transfer charging member with the transfer belt is configured to face the photosensitive drum.

In the present invention, as the material of the conductive blade 42, a material having a JIS A hardness of 50 ° obtained by adding carbon black to epichlorohydrin rubber was used.

On the upstream side of the transfer charging member 4, a first push-up member 45 is installed in the apparatus main body similarly to the transfer member, and the first upstream push-up member 45 is provided on the transfer belt 8 similarly to the conductive blade 42. It is formed in a plate shape having a thickness direction in a plane parallel to the moving direction. The first upstream push-up member 45 extends obliquely from the upstream side to the downstream side in the direction of movement toward the transfer belt 8, and at the time of transfer, comes into contact with the mechanical contact point of the conductive blade 42 with the transfer belt 8. On the other hand, on the upstream side, the transfer belt 8 is pushed up in the direction of the photosensitive drum 1 and pressed and deformed, and the transfer belt 8 is
To be in close contact with.

The contact of the transfer belt 8 with the photosensitive drum 1 by the first upstream push-up member 45 corresponds to the portion of the photosensitive drum 1 corresponding to the point where the transfer electric field upstream of the contact point of the conductive blade 42 stops working. Position 1
The installation position of the upstream push-up member 45 is set. In the present embodiment, a first upstream push-up member 45 is provided at an end of the area upstream of the contact point to which the transfer electric field is applied, and the first upstream push-up member 45 is connected to the photosensitive drum 1 via the transfer belt 8.
The transfer belt 8 was brought into contact with the photosensitive drum 1 so as to satisfy the above-mentioned contact conditions.

A dotted line m is a tangent line of the photosensitive drum 1 in the transfer nip of the transfer charging member 4 and connects the transfer nip of the transfer charging member 4 and a position where the transfer belt 8 starts to be supported by the roller 10. Line. The pressing position of the transfer belt 8 by the first upstream push-up member 45 is determined by the line m
It is provided so as to protrude more.

The distance between the transfer nip of the transfer charging member 4 and the position at which the first upstream push-up member 45 presses the transfer belt 8 is preferably 5 to 30 mm. Is preferably 0.5 to 5 mm, preferably 1 to 1.5 mm above the dotted line m.

In this embodiment, the first upstream push-up member 45 has a thickness of 200 to 600 μm, preferably 450 to 550 μm, and more preferably about 500 μm.
Using an ET film, a distance of about 15 mm upstream from the transfer nip of the transfer charging member 4 and 1.5 mm from the dotted line m
It was pressed at the upper position.

The pressure at which the first upstream push-up member 45 presses the transfer belt 8 is preferably smaller than the pressure at which the transfer charging member 4 presses the transfer belt 8. That is, when a thick recording material or a strong stiff recording material is conveyed by the transfer belt 8, the transfer charging member 4,
It is preferable that the first upstream push-up member 45 is easy to move so that vibration does not occur in the first upstream push-up member 45. When the recording material passes through the transfer position, the deformation amount of the second upstream push-up member is larger than the deformation amount of the transfer charging member 4 and smaller than the deformation amount of the first upstream push-up member 45.

The angle θ ₁ on the upstream side of the angle formed between the transfer belt 8 and the first upstream push-up member 45 is preferably an acute angle.

In the present embodiment, the first upstream push-up member 45 that has pressed and deformed the transfer belt 8 is brought into contact with the photosensitive drum 1 via the transfer belt 8. It is not always necessary to make contact.

That is, the first upstream push-up member 45 is installed outside the end of the conductive blade 42 where the transfer electric field is applied in the upstream area of the contact point, and the first upstream push-up member 45 pushes up the transfer belt 8. The transfer belt 8 is brought into contact with the portion of the photosensitive drum 1 corresponding to the point at which the transfer electric field stops acting on the upstream side of the contact point, and the first upstream push-up member 45 itself transfers the photosensitive drum 1 via the transfer belt 8. , The transfer belt 8 may be firmly supported so that there is no vertical vibration accompanying the rotation.

One of the features of the present embodiment is that the first
A second upstream push-up member 46 is provided between the upstream push-up member 45 and the transfer nip of the transfer charging member 4.

The second upstream push-up member 46 is similar to the conductive blade 42 and the first upstream push-up member 45.
The transfer belt 8 is formed in a plate shape having a thickness direction in a plane parallel to the moving direction of the transfer belt 8. Second upstream lifting member 4
6 extends obliquely from the upstream side to the downstream side in the moving direction toward the transfer belt 8, and transfers the transfer belt 8 to the transfer nip of the conductive blade 42 near the upstream side of the photosensitive drum 1 at the time of transfer. The transfer belt 8 is brought into contact with the photosensitive drum 1 so as to be in close contact therewith.

The distance between the transfer nip of the transfer charging member 4 and the position where the second upstream push-up member 46 presses the transfer belt 8 is preferably 10 mm or less.

In the present embodiment, the second upstream push-up member 46 has a thickness of 60 to 120 μm, preferably 65 to 120 μm.
The transfer belt 8 was pressed at a distance of about 3 mm upstream from the transfer nip of the transfer charging member 4 using a PET film of about 100 μm, more preferably about 70 μm. Further, among the angles formed by the transfer belt 8 and the second upstream push-up member 45, the upstream angle θ ₂ is preferably an acute angle.

In the above embodiment, each push-up member has been described as an example of PET, but the present invention is not limited to this, and it is a matter of course that another resin having the same function can be adopted.

With the above construction, as the recording material, thin paper or weakly stiff paper is operated by the action of the first upstream push-up member 45, and thick paper or strong stiff paper is caused by the action of the second upstream push-up member 46. , Transfer belt 8 and photosensitive drum 1
And is transferred after being in close contact with the photosensitive drum. For this reason, in the present invention, the occurrence of transfer discharge due to the minute gap between the transfer belt 8 and the photosensitive drum 3 on the upstream side of the transfer nip of the transfer charging member 4 can be suppressed in the present invention.

That is, when a thin paper or a paper with a weak stiffness is transferred as a recording material, the resistance of the paper itself is small, and abnormal discharge of the minute gap caused by the action of the transfer electric field of the transfer charging member 4 is directly received. The transfer belt 8 is brought into contact with the photosensitive drum 1 by the first upstream push-up member 45 so that the transfer belt 8 can reach a position corresponding to the point where the transfer electric field of the transfer charging member 4 stops working. By setting the first upstream push-up member 45 and bringing the transfer belt 8 and the photosensitive drum 1 into close contact, abnormal discharge could be prevented.

As a result, the transfer path (paper path) into the transfer area fluctuates, so that the transfer belt 8 and the photosensitive drum 1
It was also possible to prevent the minute gap distance from becoming unstable, and to solve the problem of abnormal discharge.

In the case where thick paper or strong paper is transferred as a recording material, a force for pushing down the first upstream push-up member 45 is applied to the first upstream lifting member 45 due to the strength of the transfer. The minute gap between the photosensitive drum 8 and the photosensitive drum 1 is created again, and the distance is widened.

However, due to the thickness and strain of the recording material, the carry-in path (paper path) into the transfer area fluctuates very little.
It is considered that abnormal discharge is unlikely to occur due to this, and furthermore, in general, since thick paper has a somewhat high resistance value of paper itself, abnormal discharge of minute voids caused by the action of the transfer electric field of the transfer charging member 4 is unlikely to occur. Was.

However, when the toner image is transferred from the photosensitive drum 1 to the recording material, although there is no clearly visible discharge pattern transfer omission, the toner scatters in units of dots, resulting in a defective overall image. turn into.
In order to prevent this, the second upstream push-up member 46 is
The above problem could be suppressed by pushing up the transfer belt 8 near the upstream side of the transfer nip of the transfer charging member 4 and bringing the transfer belt 8 into close contact with the photosensitive drum 1.

In the present invention, an experiment was carried out to examine the effect of preventing the presence of the first upstream push-up member 45 and the second upstream push-up member 46 against image defects and discharge before transfer.

The first upstream push-up member 45 has a thickness of 50
Using a 0 μm PET film, the transfer belt 8 is pressed at a position about 15 mm upstream from the transfer nip of the transfer charging member 4 and about 1.5 mm above the dotted line m in FIG.

The second upstream lifting member 46 has a thickness of 70 mm.
Using a μm PET film, the transfer belt 8 is pressed at a distance of about 3 mm upstream from the transfer nip of the transfer charging member 4. The free lengths of the first and second upstream push-up members were 30 mm and 35 mm, respectively.

The experiment was carried out in a case where only the first upstream push-up member 45 was provided, a case where only the second upstream push-up member 46 was provided, a case where both were provided, and a case where both were not provided. Transfer the halftone image while shaking the grammage, and the missing image due to the discharge before transfer,
The difference in the situation in which toner dots were scattered was compared between the above countermeasures. Table 1 shows the results. To the transfer charging member 4, a constant current of a high current value of 30 μA was applied assuming that double-sided image formation was performed in a low humidity environment.

As shown in Table 1, when only the first upstream push-up member 45 is provided, the gap between the transfer belt 8 and the photosensitive drum 1 is reduced to a region where the transfer electric field by the transfer charging member 4 is hardly reached. The recording material has a basis weight of 6
In the case of 4 to 105 g / m ² , a missing image due to abnormal discharge,
It was confirmed that the toner dots had an effect of preventing scattering.

However, when the basis weight of the recording material was 200 g / m ² , the first upstream push-up member 45 was pushed down due to its strength, and the effect of preventing image defects was lost. .

When only the second upstream push-up member is provided, the area for eliminating the gap is very small, so that the effect of preventing image defects due to the pre-transfer discharge is small. However, as described above, the basis weight of the recording material is 200 g.
/ M ² , the resistance value of the paper itself is also combined to prevent image defects due to discharge before transfer.

When both the first and second upstream push-up members 45 and 46 according to the present invention are installed, even if the recording material has a basis weight of 64 to 200 g / m ² , sufficient image defects due to pre-transfer discharge can be obtained. The effect of preventing is obtained.

[0074]

[Table 1]

(Embodiment 2) In this example, the first upstream push-up member and the second upstream push-up member are pressurized integrally. FIG. 2 shows the transfer charging section of this embodiment.

The first upstream push-up member 455 has a thickness of 5 mm.
With a 00 μm PET film, the free length is 30 mm, and at a distance about 15 mm upstream from the transfer nip of the transfer charging member 4,
At a position protruding about 1.5 mm from the dotted line m, the transfer belt 8
Is pressed. On the other hand, the first upstream push-up member 455
Second upstream push-up member 4 integrated at the support portion
66 is a 70 μm thick PET film having a free length of 3
When the transfer belt 8 was set at 5 mm, the transfer belt 8 could be pressed at a position at a distance of about 3 mm from the transfer nip of the transfer charging member 4 as in the first embodiment.

As in the case of the first embodiment, of course, not only the thickness of the recording material and the strength of the stiffness, but also a missing image due to a discharge before transfer and scattering of toner dots could be suppressed.

(Embodiment 3) Another example of a transfer section that can be used in the apparatus of FIG. 3 will be described. Although the first and second upstream push-up members in the first and second embodiments are always in the pressed state, they need not always be in the pressed state.

As the recording apparatus of the electrophotographic system, a release agent such as silicone oil is widely and generally used at the time of fixing. However, when the release agent adheres to the transfer belt, it gradually transfers to the photosensitive drum, and the toner adheres. This causes image stains.

The reason why the release agent adheres to the transfer belt is that the release agent adhered to the first transfer image surface during the double-sided image output, at the time of the second-side transfer, or during the conveyance of the recording material. Transfer to the surface of the transfer belt upon contact with the transfer belt. For this reason, when the position of the recording material carried on the transfer belt on the first surface and the second surface is different on the transfer belt, when the recording material having different paper sizes is continuously recorded, the place where the paper is carried on the transfer belt is obtained. In various cases, such as when the toner is insufficient, the release agent on the transfer belt may transfer onto the photosensitive drum.

Therefore, in this example, the first and second embodiments are used.
When the transfer is not performed, that is, when the transfer electric field is not applied, the first and second upstream push-up members 45 and 46 are moved downward together with the transfer charging member 4 to thereby exert the pressing force. Is released from the transfer belt 8. Thereby, the transfer of the release agent described above could be prevented. Further, the first and second upstream push-up members 4
It also has an effect on scraping and setting of 5, 46, leading to a longer life.

(Embodiment 4) In Embodiment 3, the pressing force from the transfer belt is released from the first and second upstream lifting members together with the transfer charging member.
It is not necessarily limited to this. According to the present invention, a linear paper transport path is used as one of the features of an image forming apparatus in which a transfer belt is arranged and a plurality of image carriers are provided as in the color image forming apparatus shown in FIG. This is for a recording material that is thicker than the conventional one and has a strong stiffness.

That is, as described in the first embodiment, when the first upstream push-up member is provided in addition to the transfer charging member, a temporary curvature conveyance path particularly occurs. Therefore, when a recording material having a thickness greater than that of the prior art and a strong stiffness is conveyed, a force is exerted to push down the first upstream push-up member, but in this case, the transfer is performed by the effect of the second upstream push-up member. Predischarge is suppressed.

Therefore, when the transfer charging member and the first and second upstream push-up members are pressurized integrally, a force for pushing down the first upstream push-up member is applied by the recording material having strong stiffness. From the pressing position on the transfer belt,
Even if the distance to the dotted line m becomes smaller, other members,
That is, it is necessary to install the transfer charging member and the second upstream push-up member in a configuration that does not affect the transfer charging member and the second upstream lifting member.

When the transfer charging member is pushed down,
During transfer, if the transfer nip position of the transfer charging member shifts to the downstream side, or if the transfer charging member separates from the photosensitive drum, a minute space is created between the transfer nip on the transfer belt and the photosensitive drum. In addition, an abnormal discharge similar to the pre-transfer discharge occurs, and a transfer electric field cannot be sufficiently formed, resulting in an image defect.

Further, when the second upstream push-up member is pushed down, when the thick paper or the recording material having a strong strain is transferred,
The pre-transfer discharge cannot be suppressed, causing a missing image or scattering of toner dots.

Therefore, in this embodiment, the above-mentioned problem is solved by providing a structure in which the first and second upstream push-up members and the transfer charging member can be independently pressurized, and high image quality can be obtained even with various recording materials. Thus, it is possible to realize an image forming apparatus that achieves stable transportability. In addition, the first and second upstream push-up members and the transfer charging means each have a means for independently biasing, so that the effect of the present invention can be more suitably obtained. For example, the means for independently biasing is a spring member, and the first and second upstream push-up members are made of an elastic body, and the first and second upstream push-up members and the transfer charging member are When the spring is pressed by one spring member at the same time, the first and second springs are less than the pressing force of the spring member.
When the elastic force of the upstream push-up member is lower, the spring member presses independently. For example, a PET film having a thickness of 500 μm and a free length of 30 mm is used for the first upstream push-up member, and a PET film having a thickness of 70 μm and a free length of 35 mm is used for the second upstream push-up member. When pressure is applied, the amount of deformation is absorbed by the deflection of the PET film, and the above effects can be obtained.

In particular, when thick paper or strongly stiff paper is used as the recording material, when the recording material passes through the transfer position, the amount of deformation of the first and second upstream pressing members is determined by the amount of deformation of the transfer charging member. It is better to make it larger.

(Embodiment 5) In Embodiments 1 to 4, the case where the present invention is applied to a color image forming apparatus having a plurality of developing units has been described. However, the present invention is limited to a color image forming apparatus. It is not something to be done.

For example, in a monochrome type image forming apparatus having one photosensitive drum and one developing device and a belt-shaped recording material carrier disposed in contact with the photosensitive drum, the contact type transfer charging member is used. It will be easily understood that the present invention can be applied to the provided transfer unit.

[0091]

As described above, according to the present invention,
With respect to the moving direction of the recording material carrier, by providing the second pushing member between the transfer charging member and the first pushing member provided on the upstream side, the recording material is thick, Even if the paper is strong, even if the paper is thin and stiff, the pre-transfer discharge can be suppressed, and the occurrence of image defects such as transfer omission due to abnormal discharge can be prevented. Scattering in units can also be prevented.

According to another aspect of the present invention, the transfer charging member is brought into contact with the photosensitive drum via the transfer belt without forming a gap, whereby abnormalities occurring in the gap between the transfer charging member and the photosensitive drum are achieved. It is also possible to prevent image defects such as transfer omission due to electric discharge, and scattering of toner in dot units.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a transfer unit of an image forming apparatus according to the present invention.

FIG. 2 is a cross-sectional view illustrating another example of a transfer unit of the image forming apparatus according to the present invention.

FIG. 3 is a side view illustrating an example of the image forming apparatus according to the present invention.

FIG. 4 is a cross-sectional view illustrating an example of a transfer unit of a conventional image forming apparatus.

FIG. 5 is a cross-sectional view illustrating another example of the transfer unit of the conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 primary charger 3 developing device 4 transfer charging member 5 cleaning device 6 recording material 8 transfer belt 41 electrode 42 conductive blade 45 first upstream lifting member 46 second upstream lifting member

Claims (25)

(57) [Claims] An image carrier on which a visible image is formed; a recording material carrier for carrying a recording material on a surface thereof and transporting the recording material to a transfer position;
A transfer charging member that contacts a back surface of the recording material carrier at the transfer position and transfers a visible image from the image carrier to a recording material carried on the recording material carrier; and a back surface of the recording material carrier. The recording material carrier is provided at a position upstream of the transfer charging member in the moving direction on the side, and the tangential line of the image carrier at a position where the transfer charging member presses the image carrier via the recording material carrier. An image forming apparatus comprising: a first pressing unit having a pressing position in which the first charging unit projects from the transfer charging member.
An image forming apparatus comprising: a second pressing unit that presses the recording material carrier from a back surface. 2. The image forming apparatus according to claim 1, wherein the first pressing unit and the second pressing unit include plate-shaped first and second pressing members, respectively. 3. The image forming apparatus according to claim 1, wherein the transfer charging member has a plate shape. 4. The image forming apparatus according to claim 3, wherein an angle between the transfer charging member and the recording material carrier on the upstream side in the recording material carrier moving direction is an acute angle. 5. The transfer charging member and the first and second transfer charging members.
5. The image forming apparatus according to claim 1, wherein at least one of the upstream push-up means is movable to a position apart from the recording material carrier. 6. When a recording material passes through the transfer position,
The image forming apparatus according to claim 1, wherein a deformation amount of the second pressing unit is larger than a deformation amount of the transfer charging member and smaller than a deformation amount of the first pressing unit. 7. A distance between a position at which the transfer charging member contacts the recording material carrier and a position at which the first pressing means presses the recording material carrier is 10 to 30 mm. The image forming apparatus according to claim 1, wherein a distance between the position of the second pressing unit and the position of the second pressing unit is 10 mm or less. 8. The image forming apparatus according to claim 1, wherein a distance between the tangent and a position at which the first pressing unit presses the recording material carrier is 0.5 to 5 mm. 9. The image carrier and the recording material carrier may be in contact with the most upstream region in the moving direction of the recording material carrier in a region where a transfer electric field is formed by the transfer charging member. The image forming apparatus according to claim 1, wherein the first pressing unit is disposed on the image forming apparatus. 10. The method according to claim 1, wherein at least one of said first pressing means and said second pressing means has an acute angle with respect to the recording material carrier in a direction upstream of the moving direction of the recording material carrier. 3. The image forming apparatus according to claim 1, wherein: 11. The image carrier and the transfer charging member are provided in a plurality, and a plurality of images are superimposedly transferred from the plurality of image carriers to a recording material carried on the recording material carrier. The image forming apparatus as described in the above. 12. The image forming apparatus according to claim 10, wherein a line connecting the transfer positions of the plurality of image carriers is substantially linear. 13. An image carrier on which a visible image is formed, a recording material carrier supported by a plurality of support rollers in a belt shape for carrying a recording material on the surface and conveying the recording material to a transfer position; A transfer charging member that contacts a back surface of the recording material carrier and transfers a visible image from the image carrier to a recording material carried on the recording material carrier; and the transfer charging member is disposed via the recording material carrier. The recording material carrier with respect to a line connecting a position where the image carrier is pressed with the support roller and a position where the recording medium carrier is supported by the support roller upstream of the transfer position in the recording material carrier moving direction. And an image forming apparatus comprising: a first pressing unit having a pressing position for pressing the transfer charging member from the back surface thereof.
An image forming apparatus provided with second pressing means for pressing the recording material carrier from the back surface between the pressing means and the pressing means. 14. The first pressing means and the second pressing means each include a plate-shaped pressing member.
The image forming apparatus as described in the above. 15. The image forming apparatus according to claim 13, wherein the transfer charging member has a plate shape. 16. The image forming apparatus according to claim 15, wherein an angle between the transfer charging member and the recording material carrier on the upstream side in the recording material carrier moving direction is an acute angle. 17. The image forming apparatus according to claim 1, wherein at least one of the transfer charging member and the first and second upstream push-up means is movable to a position away from the recording material carrier.
15. The image forming apparatus according to 3 or 14. 18. The deformation amount of the second pressing means when the recording material passes through the transfer position is larger than the deformation amount of the transfer charging member and smaller than the deformation amount of the pressing means. The image forming apparatus as described in the above. 19. The distance between a position where the transfer charging member contacts the recording material carrier and a position where the pressing member presses the recording material carrier is 10 to 30 mm, and the position of the transfer charging member is The image forming apparatus according to claim 13, wherein a distance between the first pressing member and the position of the second pressing member is 10 mm or less. 20. The image forming apparatus according to claim 13, wherein a distance between the tangent and a position at which the pressing member presses the recording material carrier is 0.5 to 5 mm. 21. The image carrier and the recording material carrier are brought into contact with each other in the most upstream region in the moving direction of the recording material carrier in a region where a transfer electric field is formed by the transfer charging member. The image forming apparatus according to claim 13, wherein the first pressing unit is disposed on the image forming apparatus. 22. At least one of the first pressing member and the second pressing member has an acute angle at an upstream side in the moving direction of the recording material carrier among angles formed by the recording material carrier. The image forming apparatus according to claim 13 or 14, wherein: 23. The image forming apparatus according to claim 13, wherein a plurality of color toner images are superimposedly transferred onto the recording material carried on the image carrier. 24. The image carrier and the transfer charging member are provided in a plurality, and a plurality of images are superimposedly transferred from the plurality of image carriers to a recording material carried on the recording material carrier. The image forming apparatus as described in the above. 25. The image forming apparatus according to claim 22, wherein a line connecting the transfer positions of the plurality of image carriers is substantially linear.