JPH0695519A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device capable of preventing splashing of a toner and polluting of the back of a transfer material at a non-paper feed portion during transfer process. CONSTITUTION:In an image forming device, wherein a toner image is formed on a photoereceptor drum 2 and a transfer material is passed through the pressure contact portion (transfer portion) between the photoreceptor drum 2 and a transfer roller 1 abutting to and rotated by the drum 2 and a transfer bias of reversed polarity with respect to a toner is applied to the transfer roller 1 and the toner image on the photoreceptor drum 2 is transferred onto the transfer material by the action of an electric field formed by the bias, a number of small suction holes 3 of diameter 1mm or less are provided in the surface of the transfer roller 1 and a device for sucking air inwards from the surface of the transfer material 1 through the suction holes 3 is provided. The toner remaining on the transfer roller 1 is sucked into the transfer roller 1 via the suction holes 3 and removed from the transfer roller 1, so that splashing of the toner and polluting of the back of the transfer material can be prevented during transfer process.

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 utilizing an electrostatic transfer process such as an electrostatic copying machine and an electrostatic printer.

[0002]

2. Description of the Related Art A toner image is formed on a running image carrier by toner charged to a predetermined potential, and a contact type transfer member such as a transfer roller that runs in synchronization with the image carrier is pressed against the image carrier. The transfer nip portion of both of them as a transfer portion, a transfer material such as paper is passed through the transfer portion, and a transfer bias having a polarity opposite to that of the toner is applied to the transfer member. An image forming apparatus configured to transfer a toner image on an image carrier to a transfer material has already been proposed.

The transfer means used in such an image forming apparatus can hold the transfer material more reliably than the transfer means using a well-known corona discharger, so that the transfer deviation occurs in the transfer portion. Since it is difficult and the transfer bias is relatively low, the apparatus can be made compact and compact, and there are various advantages such as generation of ozone.

However, in such a transfer means, for example, when the document width is wider than the transfer material width, or when a thick document such as a book is printed, the portion outside the width of the transfer material is developed, The toner in that portion adheres to the transfer roller, and this toner may scatter to contaminate each portion in the vicinity of the transfer roller or to cause back stain on the subsequent transfer material.

In order to avoid the above situation, JP-A-51-9
As disclosed in Japanese Patent No. 840, it is proposed to apply a bias for cleaning, which has the same polarity as the toner, to the transfer member in a non-sheet-holding manner to return the toner attached to the transfer member to the image carrier. .

Another method is to scrape off the adhered toner by bringing a blade, brush, felt or the like into contact with the surface of the transfer roller.

[0007]

However, since toner adheres to minute recesses on the surface of the transfer roller and the toner has a van der Waals force that resists the force of the electric field, the toner layer is completely removed from the surface of the transfer roller. It turns out that it is impossible to peel off. In practical use, there is an initial level at which the backside of the transfer material does not stain even if the toner remains on the surface of the transfer roller without being peeled to some extent.

However, the toner gradually accumulates due to long-term use and the time comes to stain the back surface of the transfer material again. In that case, the toner is often already fixed, and the toner is further fixed. Not only can it be peeled off easily, but problems such as uneven transfer occur.

Further, in the case of the cleaning bias, since it works after the transfer bias is applied, many layers of toner are coated on the surface of the transfer roller in the non-sheet passing portion during the transfer process, and the transfer roller is rotated in that state to form an image. Since contact and separation are repeated with respect to the carrier, there is a problem in that toner scatters, and the scattered toner collects on the transfer guide and the transport member and stains the transfer material passing therethrough.

Therefore, an object of the first and second inventions is to provide an image forming apparatus capable of preventing the toner scattering and the back stain of the transfer material at the non-sheet passing portion during the transfer process. is there.

By the way, in an image forming apparatus which employs a contact transfer system for a transfer section, a transfer roller 101 is provided in the apparatus main body 100 in pressure contact with a photosensitive drum 102, as shown in FIG. And the photosensitive drum 1
When 02 is rotated in the direction of the arrow (clockwise) in the drawing, the transfer roller 101 is rotated in the direction of the arrow (counterclockwise), the transfer material P is sandwiched between the contact portions (transfer portion) of the two, and the photosensitive drum 10
The toner image on 2 is transferred to the transfer material P.

The structure around the transfer roller 101 will be described with reference to FIGS. 30 and 31.

FIG. 30 shows how the toner T1 is transferred to the transfer material P. The transfer material P is sandwiched between the photosensitive drum 102 and the transfer roller 101, and the toner T1 on the photosensitive drum 102 is transferred onto the transfer material P at the nip portion (transfer portion) N. That is, at the time of transfer, a voltage having a polarity opposite to that of the toner T1 is applied to the transfer roller 101, the toner T1 is attracted to the transfer material P side, and is transferred onto the transfer material P as T2.

FIG. 31 shows a transfer process and a transfer process (transfer material P1.
And between the transfer material P2). Transfer roller 1
Since 01 is always in pressure contact with the photosensitive drum 102,
The residual toner T1 on the photosensitive drum 102 is transferred to the transfer roller 10
Adhere on 1. Therefore, if the transfer roller 101 is rotated as it is, the residual toner T4 on the transfer roller 101 adheres to the back surface of the transfer material P2 to be transferred next, and the back surface of the transfer material P2 becomes dirty.

Therefore, a voltage having the opposite polarity to that during transfer is applied to the transfer roller 101 between the transfer material P1 and the transfer material P2 (hereinafter, referred to as "between transfer materials") to transfer the toner T4 to the photosensitive drum 102 side. The operation is called back (hereinafter, this operation is referred to as "cleaning of the transfer roller") to prevent the back surface of the transfer material P2 from being soiled.

However, in the above-mentioned conventional image forming apparatus, the transfer roller 101 is in contact with the photosensitive drum 102 and rotates when the transfer roller 101 is not being transferred.

That is, as shown in FIG. 31, the transfer roller 101 performs cleaning between transfer materials. However, if the speed of the transfer material P becomes faster, the space L1 between the transfer materials becomes shorter, and this transfer material P1 becomes shorter. When the interval L1 becomes shorter than the circumference of the transfer roller 101, the transfer is performed while the toner T4 remains on the transfer roller 101, and the back surface of the transfer material P is soiled.

In order to solve the above problem, there is a method of using a transfer roller having a small diameter. According to this method, the number of rotations of the transfer roller becomes faster as the diameter of the transfer roller becomes smaller. The total contact distance of the roller with the photosensitive drum also becomes long, the durability thereof deteriorates, and there arises a problem that the transfer roller is frequently replaced.

Therefore, an object of the third invention is to provide an image forming apparatus capable of preventing toner from adhering to the back surface of a transfer material.

By the way, a contact charging device has been proposed as a device for charging an object to be charged, in place of the conventional corona charging device. This contact charging device presses a charging member against an object to be charged and applies a voltage (a DC voltage or a superimposed voltage of a DC voltage and an AC voltage) to the charging member so that the surface of the object to be charged has a predetermined polarity. And to be charged to a potential.

The contact charging device has a merit that a lower applied voltage can be used and a smaller amount of ozone is generated than the corona charging device, but the AC superposed voltage in the contact charging device is reduced. In the step of applying and charging, the toner is apt to be fused to the member to be charged due to long-term durability, resulting in an increase in size of the power supply and a cost increase.

In view of the above problems, the charging process in which a constant DC voltage is applied is superior, but in this process, the charging ability is inferior to that of the AC superposed voltage, and therefore the surface of the charging member becomes dirty ( Poor charging occurs due to adhesion of foreign matter such as toner), resulting in defective images.

Therefore, the object of the fourth aspect of the present invention is to prevent the charging failure due to the dirt on the surface of the charging member, the fusion of the toner to the member to be charged, etc., and the stable charging for a long period of time. An object of the present invention is to provide an image forming apparatus capable of performing the same.

By the way, FIG. 32 shows an example of a conventional contact charging device. In this example, the charging roller 14 is used as the charging member.
0, a transfer roller 101 is used as a transfer member, and the charging roller 140 is rotatably supported by bearing members (not shown) at both ends of a cored bar 140c, and is arranged in parallel with the photosensitive drum 102 which is a member to be charged. Then, the photosensitive drum 102 is pressed by the pressing means (not shown), and is rotated by the rotation of the photosensitive drum 102.

When the photosensitive drum 102 is rotationally driven, the charging roller 140 to which the bias voltage is applied charges the outer peripheral surface of the photosensitive drum 102 to a predetermined polarity and potential. After charging, the photosensitive drum 102
Image exposure is performed on the surface according to the image content, and an electrostatic latent image is formed on the photosensitive drum 102.

The electrostatic latent image is visualized as a toner image by toner, and when a bias voltage is applied to the transfer roller 101, the toner image on the photosensitive drum 102 is transferred onto the transfer material P, and the toner image is transferred. Transfer material P that received the transfer
Is conveyed to a fixing device (not shown), where the toner image is fixed, and then discharged to the outside of the machine. The toner remaining on the photosensitive drum 102 after the transfer is cleaned by the cleaning device 1.
The cleaning blade 143a of 43 removes the charge and initializes it in preparation for the next image exposure.

However, as described above, the transfer roller 101
When the transfer processing of the photosensitive drum 102 is performed using a transfer member such as the transfer member 101, the transfer material P is not conveyed or the toner is transferred to the surface of the transfer roller 101 because the transfer roller 101, which is the transfer member, is in contact with the photosensitive drum 102. There was a problem that paper dust and the like adhere. When toner, paper powder, or the like adheres to the surface of the transfer roller 101, the resistance value varies on the surface of the transfer roller 101, and a good image cannot be obtained thereafter.

Therefore, conventionally, a method has been adopted in which a bias having a polarity opposite to that of the transfer bias is applied to the transfer member during the non-image forming period to return the toner and the like adhering to the transfer member to the photosensitive drum.

However, according to the above method, it is not possible to remove even paper dust adhering to the surface of the transfer member or foreign matter that does not depend on the charge, such as non-polar toner, so that the life of the transfer member can be extended. It was a hindrance.

Therefore, the object of the fifth aspect of the present invention is to reliably remove foreign matter such as paper powder and non-polar toner adhering to the surface of the transfer member, which does not depend on the charge, so that a good image can be obtained for a long period of time. An object of the present invention is to provide an image forming apparatus capable of obtaining the following.

[0031]

[Means for Solving the Problems] In order to achieve the above object,
According to a first aspect of the present invention, a toner image is formed on a traveling image carrier by a charged toner, and a contact type transfer member that travels in synchronization with the image carrier is brought into pressure contact with the image carrier so that both pressure contact nip portions serve as transfer portions. A structure in which the transfer material is passed through the transfer portion, a transfer bias having a polarity opposite to that of the toner is applied to the transfer member, and the toner image on the image carrier side is transferred to the transfer material by the action of an electric field formed by the transfer bias. In the image forming apparatus described above, a large number of minute suction holes having a diameter of 1 mm or less are provided on the surface of the transfer member, and a device for sucking air inward from the surface of the transfer member through the suction holes is provided.

According to a second aspect of the invention, a toner image is formed on the running image carrier by a charged toner, and a contact type transfer member that runs in synchronization with the image carrier is pressed against the image carrier to form a pressure contact nip portion between them. As a transfer portion, the transfer material is passed through the transfer portion, and a transfer bias having a polarity opposite to that of the toner is applied to the transfer member, and the toner image on the image carrier side is transferred to the transfer material by the action of the electric field formed by the transfer bias. In the image forming apparatus configured as described above, an air suction device is provided near the surface of the transfer member.

A third aspect of the present invention is an image forming apparatus comprising a contact transfer device for sandwiching a transfer material between a contact transfer member to which a voltage is applied and a non-charged member to transfer a plurality of the contact transfer members. It is characterized in that it is held on a movable holding plate, and the contact transfer member is replaced every time the transfer process to the transfer material is completed.

In a fourth aspect of the present invention, an image is provided with a contact charging device for charging the image bearing member by bringing the charging member into contact with the image bearing member and applying a DC constant voltage to the charging member to energize the image bearing member. The forming apparatus is characterized in that a cleaning mechanism for applying an AC voltage to the charging member is provided in order to clean and remove foreign matter such as toner attached to the charging member.

A fifth aspect of the present invention is an image forming apparatus comprising a contact charging device for performing transfer by sandwiching a transfer material between a transfer member to which a voltage is applied and a member to be charged, wherein the transfer member is separated from the member to be charged. A cleaning member that comes into contact with the transfer member when separated is provided.

[0036]

According to the first aspect of the present invention, the toner remaining on the surface of the transfer member is sucked into the transfer member through the suction holes to remove the toner remaining on the surface of the transfer member, and to remove the toner remaining in the transfer process. It is possible to prevent the toner from scattering at the sheet passing portion and the backside of the transfer material from being soiled.

According to the second aspect of the invention, the toner remaining on the surface of the transfer member is sucked and removed by the air suction device.
It is possible to prevent the toner from scattering at the non-sheet passing portion and the backside of the transfer material during the transfer process.

According to the third aspect of the invention, since the plurality of contact transfer members are replaced every time the transfer process to the transfer material is completed, the adhesion of the toner to the back surface of the transfer material can be prevented.

According to the fourth aspect of the invention, since foreign matter such as toner adhering to the charging member is cleaned and removed by the cleaning mechanism, poor charging due to dirt on the surface of the charging member and fusion of toner to the member to be charged. And the like can be prevented, and stable charging can be performed for a long period of time.

According to the fifth aspect of the invention, not only the toner on the transfer member, but also foreign matter that does not depend on the charge, such as paper dust and non-polar toner, is reliably removed by the cleaning member.
A good image can be obtained over a long period of time.

[0041]

【Example】

[First Invention] An embodiment of the first invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 1 is a block diagram of a transfer portion of an image forming apparatus according to the first embodiment of the present invention, in which a transfer roller is mounted on a cylindrical photosensitive drum 2 rotating in the direction of arrow X in the drawing. 1 is abutted to form a transfer portion.

When the toner image previously formed on the surface of the photosensitive drum 2 arrives at the transfer portion, a transfer material (not shown) is supplied to the transfer portion at the same timing as the toner image, and the transfer material is transferred together with the transfer material. A transfer bias is applied to the roller 1, and an electric field formed by the transfer bias acts on the photosensitive drum 2
The toner image on the side is transferred to the transfer material.

Specifically, the photosensitive drum 2 is composed of an OPC photosensitive member having a diameter of 40 mm which is negatively charged, and the transfer roller 1 is made of carbon black dispersed foam EPDM (volume resistance: 10 ⁶ Ωcm) on a core metal having a diameter of 7 mm. It is formed by forming a base layer and has a diameter of 16 mm.

The process speed is 70 mm / sec, and the length of the transfer roller 1 (length of the transfer material in the width direction) is 220 mm.
Then, the toner was a one-component magnetic positive toner. During transfer, the transfer roller 1 applies a transfer bias of negative polarity.

FIG. 2 is a detailed perspective view of the inside of the transfer roller 1, and FIG. 3 is a sectional view of the inside of the transfer roller 1.

The transfer roller 1 is manufactured as follows. That is, a pipe-shaped core metal 4 formed by forming a plurality of holes 5
Then, EPDM (tube-shaped) in which carbon black is dispersed is added and foamed to obtain a foamed rubber 6, and the foamed rubber 6 is press-fitted into a core metal 4 to bond them together (adhering is still better). After that, the outer peripheral portion of the foamed rubber 6 is polished to set the outer diameter dimension of the transfer roller 1 to a predetermined value, and a surface of the transfer roller 1 (foamed rubber 6) is mechanically cut to a diameter of 1 mm or less with a tool such as a drill. Innumerable minute suction holes 3 are formed. If the open-cell type rubber is used, it is not necessary to form the suction hole 3 by cutting.

Using this transfer roller 1, an arrow Y in FIG.
If the air is constantly blown in the direction, the toner on the surface of the transfer roller 1 is sucked into the core metal 4 through the holes 3 and 5, and the toner is scattered at the non-sheet passing portion during the transfer process and the back side of the transfer material. Prevents dirt.

<Second Embodiment> Depending on the copying machine, the sheet passing position has a center reference shown in FIG. 4A and a front (back side) reference shown in FIG. 4B.

Therefore, as described above, the transfer roller 1 becomes dirty due to the document width being wider than the transfer material width. However, in the cases of FIGS. 4A and 4B, the transfer roller 1 is obviously dirty. Position 7 (diagonal position) is different.

Therefore, when the present invention is applied, FIG.
In the case shown in (b), it is desirable to form a large number of suction holes 3 (see FIGS. 2 and 3) intensively in the shaded portion 7 and to draw air from the direction of the arrow Y ₂ as shown in FIG. 4 (a). In the case shown, many suction holes 3 are formed intensively in the shaded portion 7,
A good effect can be obtained by drawing air from the directions of the arrows Y ₁ and Y ₂ .

If a proper number of suction holes 3 are formed in the paper passing portion 8, the transfer material can be easily peeled from the photosensitive drum 2.

<Third Embodiment> As described above, if the surface of the transfer roller 1 is too dirty to be removed by toner and the toner cannot be completely removed by suction, a cleaning bias is also used when the paper is not passed. On the contrary, it is effective to use a method in which air is blown from the inside of the transfer roller 1 to the outside in the suction hole 3 to transfer the toner to the surface of the photosensitive drum 2.

FIG. 5 shows the operation of the transfer roller 1 when the paper is not passed. That is, the flow of air is switched from the inside of the transfer roller 1 to the outside, and the bias of the power supply 1'is switched from the polarity opposite to that of the toner at the time of paper passage to the same polarity. FIG. 6 shows the sequence.

The cleaning bias method is not limited to the above. [Second Invention] An embodiment of the second invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 7 is a block diagram of a transfer portion of an image forming apparatus according to a first embodiment of the present invention, in which a transfer roller is provided on a cylindrical photosensitive drum 2 rotating in the direction of arrow X in the drawing. When the toner image previously formed on the surface of the photosensitive drum 2 arrives at the transfer portion, the transfer material is supplied to the transfer portion at the same timing, and the transfer material is transferred together with the transfer image. A transfer bias is applied to the roller 1, and an electric field formed by the transfer bias causes the toner image on the photosensitive drum 2 side to be transferred to the transfer material.

Specifically, the photosensitive drum 2 is composed of an OPC photosensitive member having a diameter of 40 mm which is negatively charged, and the transfer roller 1 is made of carbon black dispersed foam EPDM (volume resistance: 10 ⁶ Ωcm) on a core metal having a diameter of 7 mm. It is formed by forming a base layer and has a diameter of 16 mm.

The process speed is 70 mm / sec, and the length of the transfer roller 1 (length in the width direction of the transfer material) is 300 mm.
Therefore, a one-component magnetic positive toner is used as the toner. Then, at the time of transfer, a transfer bias V _T having a negative polarity is applied to the transfer roller 1.

In FIG. 7, 9 is an insulating duct formed of resin or the like, the inside of which is constantly sucked by air in the Y direction, and the toner T on the non-sheet passing portion of the photosensitive drum 2 is The toner is sucked into the insulating duct 9, and thereby, the scattering of the toner T and the back stain of the transfer material at the non-sheet passing portion in the transfer process are prevented.

A thin nozzle 9'shown in FIG. 8 may be used in place of the insulating duct 9, but when the amount of toner adhering to the surface of the transfer roller 1 is excessively large (A3 horizontal length of about 4).
When the toner at the time of 2cm partial solid black is all transferred to the surface of the transfer roller 1 with a diameter of 16 mm, to become the amount of about 1 g / cm ^2), the toner T 'is scattered on the transfer roller 1, charge removal for separation The needle 10, the transfer guide 11, and the conveying member 12 are contaminated, and as a result, the transfer material passing therethrough is contaminated and the performance of the charge elimination needle 10 is deteriorated. Therefore, the configuration shown in FIG. 7 is more effective.

<Second Embodiment> In this embodiment, FIG.
As shown in FIG. 10, the air suction duct 9 ″ is extended to a position where the transfer material P passes, and according to this, on the axis of the transfer roller 1 as shown in FIGS. Even when the paper passing portion 8 and the non-paper passing portion (hatched portion) 7 occur in the paper passing portion 8, the toner T on the photosensitive drum 2 is transferred onto the transfer material P at the paper passing portion 8 and at the same time the transfer material P is Since the duct 3 ″ is covered as shown in FIG. 9 (a), the wind speed in the non-sheet passing portion 7 is increased, and unnecessary toner T on the photosensitive drum 2 is removed as shown in FIG. 9 (b). After transferring to the transfer roller 1 as T _2, it is forcibly sucked and removed in the Y direction.

<Third Embodiment> As shown in FIG. 11A, the toner T remaining on the transfer roller 1 is sprayed and adhered to the photosensitive drum 2 when the paper is not passed, and the toner T is applied to a photosensitive member cleaner (not shown). It is also possible to recover.

At this time, as shown in FIG. 11B, a more effective result can be obtained by combining with the cleaning bias V _C disclosed in the above-mentioned Japanese Patent Laid-Open No. 51-9840.

<Fourth Embodiment> The toner once attached to the transfer roller 1 may be attached fairly strongly. In such a case, as shown in FIGS. The clean bias V _C to be applied at the time of paper is appropriately switched between positive and negative, an alternating electric field is generated, and the wind direction of the air suction device is alternately changed to blowing and suction to cause turbulence in the duct 9 shown in FIG. When the toner T is easily peeled off from the transfer roller 1 and an appropriate cleaning bias V _C is applied to the transfer roller 1, the toner transfer electric field generated between the transfer roller 1 and the photosensitive drum 2 causes the toner T to be transferred to the photosensitive drum 2.
Can be more easily transferred. [Third Invention] An embodiment of the third invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 16 is a sectional view of an image forming apparatus according to the first embodiment of the present invention, and FIGS. 17 to 19 are enlarged detailed views of the vicinity of a transfer portion of the image forming apparatus.

In the figure, 100 is a main body of the apparatus, 50 is a process cartridge, 2 is a photosensitive drum, 1A and 1B are transfer rollers, and these transfer rollers 1A and 1B are in pressure contact with the photosensitive drum 2 and are counterclockwise. Follow the rotation.

Reference numeral 16 is a holding plate that holds the transfer rollers 1A and 1B, and the holding plate 16 is rotatably attached by a shaft 17. The holding plate 16 is adapted to rotate at the timing when the toner T is transferred onto the transfer material P by the motor 19 shown in FIG.

Reference numeral 18 denotes a cleaning roller. When the cleaning roller 18 comes into contact with the transfer rollers 1A and 1B, a voltage having a polarity opposite to that of the toner T is applied to suck the toner T adhering to the surfaces of the transfer rollers 1A and 1B. Clean it.
Then, the toner T adhering to the surface of the cleaning roller 18 is scraped off by the scraping member 21 and collected in the toner pool 22 shown in FIG.

Reference numeral 10 is a charge elimination needle, which weakens the electrostatic attraction force between the transfer material P and the photosensitive drum 2 to facilitate the separation of the transfer material P. Reference numeral 23 is a conveyor belt for conveying the transfer material P to a fixing device (not shown).

Now, the switching mechanism for the transfer rollers 1A and 1B will be described.

As shown in FIG. 17, two U-shaped grooves are formed in the holding plate 16, and the spring 2 is formed in the grooves.
Bearings 26 and 27 urged by 4, 25 are slidably fitted.

The transfer rollers 1A and 1B are rotatably supported by the bearings 26 and 27, and the transfer rollers 1A and 1B contact the photosensitive drum 2 or the cleaning roller 18 at a predetermined pressure. It is like this. It should be noted that the U-shaped groove does not come off the retainers 16a and 16b.
Is provided, and the bearing 2 is driven by the pressure of the springs 24 and 25.
It is designed so that 6 and 27 do not pop out.

A pulley 28 is integrally provided on the holding plate 16, and the pulley 28 and the pulley 2 of the motor 19 are integrated.
An endless belt 30 is wound between 9 and the power of the motor 19 is transmitted to the holding plate 16 via the pulley 29, the belt 30 and the pulley 28 so that the holding plate 16 is rotated. There is.

The motor 19 has a predetermined position (see FIG. 1).
The holding plate 16 is rotated counterclockwise between the transfer materials where the transfer rollers 1A and 1B are located at the position shown in FIG. 7 and the position where the transfer rollers 1A and 1B are exchanged). This situation is shown in Figure 1.
9 shows.

Next, the cleaning process between the transfer materials of the image forming apparatus according to this embodiment will be described with reference to FIGS. 18 and 19.

FIG. 18 shows a state in which the toner T is transferred to the transfer paper P by applying a voltage having a polarity opposite to that of the toner T to the transfer roller 11A. Here, the transfer roller 1A is in pressure contact with the photosensitive drum 2 and is rotating counterclockwise.

FIG. 19 shows a state between transfer steps on the transfer sheet P (between the transfer sheet P1 and the transfer material P2). During this time, the transfer rollers 1A and 1B are replaced. That is, when the holding plate 16 is rotated counterclockwise by the motor 19 as described above, one transfer roller 1A moves to the B position and the other transfer roller 1B moves to the A position. Immediately thereafter, the transfer roller 1B starts the transfer process, and the transfer roller 1A starts the cleaning process by the cleaning roller 18. This operation is performed between the transfer paper P1 and the transfer paper P2.

Thus, if the transfer rollers 1A and 1B are exchanged for each transfer to the transfer material P, the transfer roller 1A that is always cleaned even if the distance between the transfer materials is insufficient.
Since (1B) and the toner T are in contact with each other, it is possible to prevent the toner T from adhering to the back surface of the transfer material P.

Further, since the two transfer rollers 1A and 1B are used, the life of the transfer rollers 1A and 1B is doubled as compared with the case of one conventional transfer roller. Therefore, the period of regular maintenance of the transfer rollers 1A and 1B is extended, and a great merit that the service cost is reduced can be obtained.

In this embodiment, two transfer rollers 1A,
Although 1B is used, it goes without saying that the number of transfer rollers may be increased according to the image forming process speed and the transfer material.

<Second Embodiment> In the first embodiment, the transfer roller is replaced every time the transfer process is completed, but the replacement interval may be changed depending on the width (paper size) of the transfer material.

FIG. 20 shows the positional relationship between the photosensitive drum 2 and the transfer material in the width direction.

Here, in the present embodiment, assuming that the maximum document size of the image forming apparatus is A3 size, the range of toner adhesion on the photosensitive drum 2 is the A3 width portion in FIG. At this time, a transfer material (for example, B4
Size, A4 size, B5 size)
0, the range of L2 (for B4 size), L3 (for A4 size), and L4 (for B5 size) of the transfer roller 1 is during the transfer process (the process of attracting toner to the transfer material side), the photosensitive drum 2 Since the toner is in direct contact with the transfer roller 1, a large amount of toner adheres to the transfer roller 1 and is easily stained.

In particular, as shown in FIG. 21, the document thick plate 33
If you make a copy with the document open, the original P3
Toner is entirely attached (solid black) on the surface of the photosensitive drum 2 corresponding to the shaded portion 32 other than the position where the transfer roller 1 is contaminated. This state is shown in FIG.

As shown in FIG. 22, since the toner on both ends 2a of the photosensitive drum 2 is transferred to the both ends 1a of the transfer roller 1, the toner adheres to the back side of the P1 _a part of the transfer material P1 after the transfer and becomes dirty. Will end up.

In order to prevent this, in this embodiment, the size of the transfer material is detected in advance, and the replacement interval of the transfer rollers 1 (1A, 1B) is changed according to the size. For example, A3 size is for every 5 transfer materials, B4 size is for every 3 transfer materials, A4 size is for every 2 transfer materials, B5
By changing the size of each transfer material 1 (that is, every time) between the transfer rollers 1A and 1B as shown in FIG. 19, backside smearing of the transfer material can be prevented.

As a method of detecting the size of the transfer material,
For example, there are a method of detecting from the paper feed cassette, a method of detecting the size of the transfer material by a member that guides the width of the transfer material in the manual feed portion, and the like.

<Third Embodiment> As a third embodiment,
When the original pressing plate 33 is opened for copying as shown in FIG. 21, for the same reason as above, the transfer roller may be replaced every time, regardless of the size of the transfer material, as in the first embodiment.

<Fourth Embodiment> Further, as a fourth embodiment,
There is a method of changing the number of times the transfer roller is replaced depending on the number of continuous copies of the transfer material. For example, up to 10 continuous sheets may be replaced every 2 sheets, and 10 or more consecutive sheets may be replaced every transfer process. This number may be changed according to the size of the transfer material in combination with the second embodiment.

As described above, by changing the replacement intervals of the transfer rollers according to various patterns, it is possible to prevent the backside of the transfer material from being soiled. [Fourth Invention] An embodiment of the fourth invention will be described below with reference to the accompanying drawings.

The contact charging device provided in the image forming apparatus according to the present invention has a constant DC voltage applied to the charging member in order to prevent fusion of the toner to the member to be charged due to long-term durability and to obtain a good image. It is a device for charging only the charged body by applying only the charging member, and is provided with a cleaning mechanism for applying an AC voltage when cleaning dirt adhering to the charging member.

When an AC voltage is applied to the charging member by the cleaning mechanism, the charging member vibrates subtly in accordance with the frequency of the applied bias, and the vibration causes the dirt on the surface of the charging member to fly to the member to be charged. The removed dirt is cleaned by the cleaning mechanism of the image forming apparatus.

By the way, ideally, the cleaning timing of the cleaning mechanism for applying an alternating current to the charging member to clean it is preferably to remove the dirt on the charging member at every copy. In a low-speed machine having a short durability life, there is no problem of toner fusion to the member to be charged due to the AC voltage applied to the charging member. Therefore, even if an AC voltage is applied and cleaning is performed before each copy at each copy, no serious problem occurs.

However, in a high-speed machine having a long durability life, an image defect due to toner fusion due to the application of an AC voltage as described above occurs, and therefore an AC voltage is applied every time copying is performed. There is a big problem in cleaning by cleaning.

Further, in the sequence in which the alternating voltage is applied for each specific number of sheets, the cleaning mechanism may be inserted during copying.
Due to cleaning, the potential of the member to be charged rises slightly, causing a problem that the image density changes during copying.

Therefore, the cleaning time by the cleaning mechanism is
Limited during warm-up after the main power of the image forming device is turned on,
Further, the fixing temperature of the fixing device when the main power of the image forming apparatus is turned on is limited to a predetermined value or less, and the so-called “morning one” (one in the morning) operation of the cleaning mechanism is most effective.
FIG. 23 shows a cleaning sequence of AC voltage application for cleaning the charging member in "morning first". Although the cleaning of the charging member is almost satisfactory at the above cleaning time, even in the above case, for example,
When copying 8,000 to 10,000 sheets a day, cleaning of the charging member by applying an AC voltage may not be able to keep up due to the use of toner or the like that easily adheres to the charging member.

That is, the cleaning sequence may be changed at any time depending on the shape and material of the charging member, the method of contacting the member to be charged (photosensitive member), the scale and specifications of the image forming apparatus, and the prescription of toner.
For example, it may be determined once every 100 times, once every 500 times, or the like, and the time of the AC voltage applied to the charging member may be similarly determined. In that case, it must be taken into consideration that even if cleaning is performed with the number of copies, there is no great influence on the potential of the member to be charged (photoconductor) and therefore there is almost no change in image density. In other words, the number of copies that does not require charging due to dirt on the surface of the charging member without cleaning the charging member changes depending on the prescription of toner or the like, and thus the number of copies that become defective in charging also changes.

Also, depending on the scale of the image forming apparatus, the durable life,
The number of copies per day is expected, and the cleaning sequence may be determined in consideration of this.

FIG. 24 shows a cleaning sequence in which an AC voltage for cleaning the charging member is applied every time copying is performed.

By the way, the frequency K of the applied AC voltage is
(Hz) is preferably as small as possible in order to prevent fusing of toner to an object to be charged and an unpleasant charging sound generated when an AC voltage is applied. When D (mm / sec) is set, the range expressed by the following equation is desirable.

[0101]

[Formula 1] (D / 5) (mm / sec) <K (H _Z ) <
(4D) (mm / sec) Incidentally, when K is D / 10 or less, the cleaning ability is poor, and conversely, a fused image having D / 3 or more, and an unpleasant charging sound is likely to be generated at the time of application, which is preferable. Absent.

The AC voltage M is preferably as small as possible for the above reason, and preferably,

[0103]

## EQU2 ## The range of 200V _PP <M <3KV _PP is desirable.

When the AC voltage M is 200 V _PP or less, the cleaning ability is poor, and when it is 4 KV _PP or more, the fused image, the charging sound generated at the time of application, and the like become large. In addition, the withstand voltage of the charging member is greatly affected, which is not preferable.

By doing the above, it is possible to prevent the image density change during copying by cleaning at the above-mentioned time, and to apply an AC voltage to the charging member frequently in the medium and high speed machine. It is possible to prevent the occurrence of image defects due to the fusion of the toner on the member to be charged due to long-term durability.

Specific examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 Using EPDM having carbon black dispersed therein as a conductive layer, resin resin (EF-30T, manufactured by Teikoku Kagaku Co., Ltd.), which is a polyamide resin, was coated with tin oxide so as to have a resistance value of 10 ⁸ Ω. It was dispersed, a coating layer was formed by a dipping method, and it was heated and dried at 150 ° C. for 30 minutes to prepare a conductive roll as a charging member.

The charging member is attached to the portion of the primary charger of the image forming apparatus and adjusted, and the speed of the charged body (photoreceptor) is set to 2
It was adjusted to 00 (mm / sec), the cleaning time was set to "morning one", and the durability test was performed in two environments at 300 sheets / day and 5,000 sheets and 40,000 sheets.

The results were evaluated according to the following evaluation items.

AC voltage by the cleaning mechanism is -1.5K
The V _PP was set to 600 Hz, and this AC voltage was applied for the time required for the conductive roller, which is a charging member, to make three turns. As the toner, the one used in NP-2020 manufactured by Canon Inc. was used.

1) This image forming apparatus is operated at an air temperature of 25.5 ° C.
Durability of 40,000 sheets was carried out in an environment with a humidity of 5%, and image evaluation was visually conducted according to the following evaluations.

⊚: Good image, no problem ◯: Minor poor charging image generation (practical use possible) Δ: Partial charging failure image generation (practical lower limit) ×: Poor charging image formation (not practical use) 2) This image formation The device was subjected to durability of 40,000 sheets under an environment of an air temperature of 32.0 ° C. and a humidity of 90%, and image evaluation was visually performed according to the following evaluations.

⊚: Image is good, no problem. ◯: Minor fusion image is generated (practical use). Δ: Partial fusion image is generated (practical lower limit). X: Fusion image is generated on the entire surface of the image (impractical use). It shows in Table 1.

<Example 2> The same evaluations as in Example 1 were carried out except that the durability was set at 5000 sheets / 1 day.

The results are shown in Table 1.

<Example 3> The same evaluation as in Example 1 was carried out except that the cleaning time was once / ten sheets.

The results are shown in Table 1.

<Embodiment 4> The speed of the member to be charged (photoreceptor) is set to 4
The evaluation was performed in the same manner as in Example 1 except that the cleaning voltage was set to 00 (mm / sec), the frequency of the AC voltage applied for cleaning was set to 300 Hz, and the sheet was durable at 1000 sheets per day.

The results are shown in Table 1.

<Example 5> The same evaluation as in Example 4 was carried out except that the durability was set at 5000 sheets / day.

The results are shown in Table 1.

<Example 6> The same evaluation as in Example 4 was carried out except that the cleaning time was once per 20 sheets.

The results are shown in Table 1.

<Embodiment 7> The speed of the body to be charged (photoconductor) is set to 2
4 (mm / sec), the frequency of the AC voltage applied for cleaning was 40 Hz, and the same evaluation as in Example 1 was carried out except that 50 sheets / day were durable.

The results are shown in Table 1.

<Example 8> The same evaluations as in Example 7 were carried out except that the durability was set at 2000 sheets / 1 day.

The results are shown in Table 1.

<Example 9> The same evaluation as in Example 9 was performed except that the cleaning time was once / 25 sheets.

The results are shown in Table 1.

Example 10 The same evaluation as in Example 1 was carried out except that the frequency of the alternating voltage applied for cleaning was 3 KHz.

The results are shown in Table 1.

<Example 11> The same evaluation as in Example 1 was conducted except that the frequency of the AC voltage applied for cleaning was 50 Hz.

The results are shown in Table 1.

[0134]

[Table 1] [Fifth Invention] An embodiment of the fifth invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 25 is a schematic view of the essential parts of an image forming apparatus according to the first embodiment of the present invention.

Reference numeral 2 is a photosensitive drum as a member to be charged,
The photosensitive drum 2 is a conductive base layer 2 made of aluminum.
b and a photoconductive layer 2a formed on the outer peripheral surface of the drum type electrophotographic photosensitive member as a basic constituent layer, which has a predetermined peripheral speed in the arrow direction (clockwise direction) around the support shaft 2d. Is driven to rotate.

Reference numeral 40 denotes a charging roller which is in contact with the surface of the photosensitive drum 2 and uniformly performs a primary charging process on the surface of the photosensitive drum 2 to a predetermined polarity and potential. The charging roller 40 includes a central core metal 40c, a conductive layer 40b formed on the outer periphery thereof, made further the resistance layer 40a formed on the outer peripheral _1, 40a ₂ Prefecture, both end portions (not shown) of the core metal 40c Is rotatably supported by the bearing member. Then, the charging roller 40
Are arranged in parallel with the photosensitive drum 2, are pressed against the surface of the photosensitive drum 2 with a predetermined pressing force by a pressing means (not shown), and are driven to rotate as the photosensitive drum 2 is rotationally driven.

When a predetermined DC bias is applied to the core metal 40c of the charging roller 40 from the power source 41, the peripheral surface of the photosensitive drum 2 is contact-charged to have a predetermined polarity and potential.

The surface of the photosensitive drum 2 that has been uniformly charged by the charging roller 40 as described above is then exposed by the exposing means with the target image information (laser beam scanning exposure, slit exposure of the original image, etc., in the present embodiment, the original document). By subjecting the image to slit exposure), an electrostatic latent image corresponding to the target image information is formed on the peripheral surface thereof. Then, the electrostatic latent image is sequentially visualized as a toner image by the developing device 42.

The toner image is conveyed from the sheet feeding means (not shown) by the transfer roller 1 in synchronism with the rotation of the photosensitive drum 2 and is conveyed to the transfer portion between the photosensitive drum 2 and the transfer roller 1 at an appropriate timing. The images are sequentially transferred onto the surface of the transfer material P. The transfer roller 1 according to this embodiment transfers the toner image on the surface of the transfer material P to the surface of the transfer material P by charging the transfer material P from the back side with a polarity opposite to that of the toner.

The transfer material P to which the toner image has been transferred is separated from the surface of the photosensitive drum 2 and conveyed to a fixing means (not shown) to be fixed with the toner image and output as an image-formed product. Alternatively, when the image is formed on the back surface, it is re-transported to the transfer section.

After the image transfer, the surface of the photosensitive drum 2 is cleaned by the cleaning means 43 to remove adhering contaminants such as toner remaining on the surface of the transfer drum, and the surface of the photosensitive drum 2 is further neutralized by the neutralization exposure device 45 to be repeatedly used for image formation. To be done.

FIG. 26 is an operation sequence diagram of the image forming apparatus shown in FIG.

This example shows the case of a two-sheet continuous printer.

Based on the printer start signal, the rotation drive of the photosensitive drum 2 of the device which has been in the standby state until then is started, and the pre-rotation period is started.

The transfer roller 1 in the above pre-rotation period
For a predetermined time (transfer roller 1
Is applied for about 1 to 2 times), an application bias having a polarity opposite to that at the time of transfer is applied, a developer such as toner is returned onto the photosensitive drum 2, and the transfer roller 1 is cleaned.

The cleaning of the transfer roller 1 is similarly performed by the method until the above-mentioned cleaning is completed, the image formation of the first sheet is completed, and the image formation of the second sheet is performed.

When the image formation of the final print is completed, the photosensitive drum 2 enters the post-rotation period. At this time as well, the same processing as that for cleaning the transfer roller 1 is performed.

The transfer roller 1 has a resistance value of 10 ⁷ to 1
A single-foam or continuous-foam EPD with a resistance of about 0 ¹⁰ Ω
M, SBR, BR etc. roller diameter 20mm, length 300m
What was processed to about m was used.

In this structure, when image formation is carried out, from the time when about 30,000 sheets are formed,
Adhesion of paper powder, non-polar toner, and the like became conspicuous, and when an image was further formed, a transfer failure such as transfer unevenness occurred, and a good image could not be obtained in some cases.

Therefore, in this embodiment, instead of applying a cleaning bias when cleaning the transfer roller 1, the transfer roller 1 is separated from the photosensitive drum 1, and the transfer roller 1 is made of a cleaning brush 46 made of exene.
When the rubbing cleaning is performed by bringing the transfer roller 1 into contact with the transfer roller 1 and rotating the transfer roller 1, a good transfer image, that is, an image can be obtained without causing transfer defects such as transfer unevenness even after 30,000 sheets of image formation. Therefore, the life of the transfer roller 1 can be extended.

<Second Embodiment> FIG. 27 is a schematic configuration diagram of a main portion of an image forming apparatus according to the second embodiment of the present invention, and FIG. 28 is an operation sequence diagram of the image forming apparatus.

In this embodiment, a conductive brush is used as the material of the cleaning brush 46, and a bias having a polarity opposite to that of the toner is applied to the cleaning brush 46 while the transfer roller 1 is contacting and slidingly rotating. By doing so, the releasability of the toner on the surface of the transfer roller 1 is improved, and when cleaning is performed, a good image can be obtained without causing uneven transfer even if the number of image formations exceeds 150,000. I was able to.

Further, in the first embodiment, the transfer roller 1
Cleaning was performed only for the time required for two rotations of the transfer roller 1, but in the present embodiment, cleaning is performed only for the time required for the transfer roller 1 to make one rotation, and a cleaning performance equal to or higher than that of the first embodiment is exhibited. Therefore, not only the life of the transfer roller 1 can be extended, but also the cleaning time can be shortened, and sufficient cleaning can be performed even in a high-speed machine having a high image forming speed.

<Third Embodiment> The surface of the transfer roller 1 is coated with a film thickness of about 10 μm (the resistance value of the transfer roller 1 is almost the same) by using polyurethane or the like, so that toner, paper powder, and After improving the releasability of stains such as non-polar toner and performing image formation and cleaning with the cleaning brush 46, even if the number of image formations exceeds 150,000, transfer unevenness does not occur and it is good. I was able to get a good image.

Further, as in the second embodiment, the transfer roller 1
Sufficient cleaning properties could be obtained with the cleaning time for rotation.

[0157]

As is apparent from the above description, according to the first aspect of the present invention, the toner remaining on the surface of the transfer member is sucked into the transfer member through the suction holes to remove the toner remaining on the surface of the transfer member. It is possible to prevent the toner from being scattered and the back surface of the transfer material from being soiled during the transfer process.

According to the second aspect of the invention, the toner remaining on the surface of the transfer member is sucked and removed by the air suction device, so it is possible to prevent the toner from scattering and the back stain of the transfer material during the transfer process.

According to the third aspect of the invention, since the plurality of contact transfer members are replaced every time the transfer process onto the transfer material is completed, the adhesion of the toner to the back surface of the transfer material can be prevented.

According to the fourth aspect of the invention, since foreign matter such as toner adhering to the transfer member is cleaned and removed by the cleaning mechanism, poor charging due to dirt on the surface of the charging member or fusion of the toner to the body to be charged. And the like can be prevented, and stable charging can be performed for a long period of time.

According to the fifth aspect of the invention, not only the toner on the transfer member but also the foreign matter which does not depend on the electric charge, such as paper dust and non-polar toner, is reliably removed by the cleaning member.
A good image can be obtained over a long period of time.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a transfer unit of an image forming apparatus according to a first embodiment of the first invention.

FIG. 2 is a perspective view of the inside of a transfer roller as seen obliquely.

FIG. 3 is a sectional view of the inside of a transfer roller.

FIGS. 4A and 4B are diagrams showing sheet passing positions (center reference and front reference) with respect to the transfer roller according to the second embodiment of the first invention.

FIG. 5 is a configuration diagram of a transfer unit of an image forming apparatus according to a third embodiment of the first invention.

6 (a) and 6 (b) are sequence diagrams showing switching of bias, air blowing, and suction when paper is passed and when paper is not passed.

FIG. 7 is a configuration diagram of a transfer unit of the image forming apparatus according to the first embodiment of the second invention.

FIG. 8 is a configuration diagram of a transfer unit of an image forming apparatus showing a modification of the first embodiment of the second invention.

9A and 9B are configuration diagrams of a transfer unit of an image forming apparatus according to a second embodiment of the second invention.

10A and 10B are diagrams showing sheet passing positions (center reference and front reference) with respect to the transfer roller.

11A and 11B are configuration diagrams of a transfer unit of an image forming apparatus according to a third embodiment of the second invention.

FIG. 12 is a configuration diagram of a transfer unit of an image forming apparatus according to a fourth embodiment of the second invention.

13 (a) and 13 (b) are sequence diagrams showing switching of bias, air blowing, and suction during paper passing and non-paper passing.

14 (a) and 14 (b) are sequence diagrams showing switching between bias, air blowing, and suction during paper passing and non-paper passing.

15 (a) and 15 (b) are sequence diagrams showing switching of bias, air blowing, and suction during paper passing and non-paper passing.

FIG. 16 is a sectional view of the image forming apparatus according to the first embodiment of the third invention.

FIG. 17 is an enlarged cross-sectional view of the vicinity of a transfer portion of the image forming apparatus according to the first embodiment of the third invention.

FIG. 18 is an enlarged sectional view of the vicinity of a transfer portion of the image forming apparatus according to the first embodiment of the third invention.

FIG. 19 is an enlarged cross-sectional view of the vicinity of the transfer portion of the image forming apparatus according to the first embodiment of the third invention.

FIG. 20 is a diagram showing a positional relationship in the width direction between a photosensitive drum and a transfer material showing a second embodiment of the third invention.

FIG. 21 is a perspective view showing a state in which a document pressure plate is opened and copying is performed.

FIG. 22 is a perspective view showing how the transfer roller is soiled.

FIG. 23 is a cleaning sequence diagram of AC voltage application for cleaning the charging member according to the fourth aspect of the invention.

FIG. 24 is a cleaning sequence diagram of AC voltage application for cleaning the charging member according to the fourth aspect of the invention.

FIG. 25 is a schematic configuration diagram of a main part of an image forming apparatus according to a first embodiment of the fifth invention.

FIG. 26 is an operation sequence diagram of the image forming apparatus according to the first embodiment of the fifth invention.

FIG. 27 is a schematic configuration diagram of a main part of an image forming apparatus according to a second embodiment of the fifth invention.

FIG. 28 is an operation sequence diagram of the image forming apparatus according to the second embodiment of the fifth invention.

FIG. 29 is a sectional view of a conventional image forming apparatus.

FIG. 30 is an enlarged cross-sectional view of a transfer section of a conventional image forming apparatus.

FIG. 31 is an enlarged cross-sectional view of a transfer section of a conventional image forming apparatus.

FIG. 32 is a schematic configuration diagram of a main part of a conventional image forming apparatus.

FIG. 33 is an operation sequence diagram of a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transfer roller (transfer member) 1A, 1B Transfer roller (transfer member) 2 Photosensitive drum (charged body) 3 Suction hole 16 Holding plate 46 Cleaning brush (cleaning member) P Transfer material

Front page continued (72) Inventor Takao Honda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takeo Yamamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (17)

[Claims] 1. A toner image formed of charged toner is formed on a running image carrier, and a contact type transfer member that runs in synchronization with the image carrier is pressed against the image carrier to form a pressure contact nip portion between them. A structure in which the transfer material is passed through the transfer portion, a transfer bias having a polarity opposite to that of the toner is applied to the transfer member, and the toner image on the image carrier side is transferred to the transfer material by the action of an electric field formed by the transfer bias. In the image forming apparatus described above, an infinite number of minute suction holes having a diameter of 1 mm or less are provided on the surface of the transfer member, and a device for sucking air inward from the surface of the transfer member through the suction holes is provided. apparatus. 2. The image forming apparatus according to claim 1, wherein the suction force on the surface of the transfer member is partially changed. 3. A non-sheet passing sheet having no transfer material in the transfer portion, particularly, air is blown from the inside of the transfer roller to the outside through the suction hole, and at the same time, the transfer member has the same polarity as the toner or a polarity opposite to that of the toner. The image forming apparatus according to claim 1, wherein the bias is applied alternately. 4. A toner image formed of charged toner is formed on a running image carrier, and a contact type transfer member that runs in synchronization with the image carrier is brought into pressure contact with the image carrier to form a pressure contact nip portion between them as a transfer portion. A structure in which the transfer material is passed through the transfer portion, a transfer bias having a polarity opposite to that of the toner is applied to the transfer member, and the toner image on the image carrier side is transferred to the transfer material by the action of an electric field formed by the transfer bias. In the image forming apparatus described above, an air suction device is provided near the surface of the transfer member. 5. The image forming apparatus according to claim 4, wherein more than half of the transfer member is covered with the air suction device. 6. The image forming apparatus according to claim 4, wherein the air suction device performs a suction operation when a sheet is passed, and blows out or alternately performs a blowing operation and a suction operation when the sheet is not passed. 7. The image forming apparatus according to claim 4, wherein a cleaning bias for peeling off the toner from the transfer member and transferring the toner to the image carrier is applied to the transfer member when the paper is not passed. 8. An image forming apparatus comprising a contact transfer device for sandwiching a transfer material between a contact transfer member to which a voltage is applied and a member to be charged and transferring the plurality of contact transfer members. An image forming apparatus, which is held on a holding plate, and the contact transfer member is replaced every time the transfer process onto the transfer material is completed. 9. The image forming apparatus according to claim 8, wherein the replacement interval of the contact transfer member after the step of transferring to the transfer material is changed according to the transfer material. 10. The image forming apparatus according to claim 8, wherein the contact transfer member is replaced every time the transfer process to the transfer material is completed, when the image forming is performed by opening the original pressure plate. 11. The image forming apparatus according to claim 8, wherein the replacement interval of the contact transfer member after the completion of the transfer step onto the transfer material is changed in accordance with the number of image formations of the transfer material. 12. An image forming apparatus comprising a contact charging device for charging an image carrier by bringing the charging member into contact with the image carrier and applying a constant DC voltage to the charging member to energize the image carrier. An image forming apparatus comprising a cleaning mechanism for applying an AC voltage to the charging member in order to clean and remove foreign matter such as toner adhered to the charging member. 13. The operation of the cleaning mechanism is limited to a case where a warm-up operation is performed after the main power is turned on, and a temperature detected by the fixing device when the main power is turned on is equal to or lower than a predetermined value. The image forming apparatus according to claim 12, which is characterized in that. 14. An image forming apparatus comprising a contact transfer device for performing transfer by sandwiching a transfer material between a transfer member to which a voltage is applied and a member to be charged, when the transfer member is separated from the member to be charged. An image forming apparatus characterized in that a cleaning member that comes into contact with the transfer member is provided on the image forming apparatus. 15. The image forming apparatus according to claim 14, wherein the transfer member is a transfer roller formed of a cylindrical roll. 16. The image forming apparatus according to claim 15, wherein the transfer roller has a coat layer formed on a surface thereof. 17. The image forming apparatus according to claim 14, wherein the cleaning member is a conductive brush.