JP2899186B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an image forming apparatus, and more particularly to a method for forming a toner image on an image carrier formed by an electrophotographic system or an electrostatic recording system.
The present invention relates to an image forming apparatus that obtains an image by transferring an image onto a recording material supported on a recording material support. Such image forming apparatuses include black-and-white, mono-color or full-color electrophotographic copying machines, printers, and various other recording devices.

[0002]

2. Description of the Related Art In a color image forming apparatus, a toner image on a photosensitive drum as an image carrier is transferred to a recording material supported on a transfer drum as a recording material support, and then released to prevent offset. It is known that toner is fixed on a recording material by a fixing unit to which an agent is applied.

When the fixing means coated with a release agent is used, the toner is once transferred onto the surface of the recording material,
After the image is fixed by the fixing unit, the toner is transferred again to the back surface of the same recording material, and if the double-sided image is formed by fixing, the following inconvenience has been found by experiments of the present inventors. .

[0004]

That is, after the first image forming operation is completed and the first heating and fixing of the surface of the recording material is performed, oil as a release agent adheres to the toner and the recording material. When the recording material is re-fed for double-sided copying, the toner surface that has been fixed for the first time (that is, the surface to which oil has adhered) faces the transfer drum surface side.
Therefore, when the recording material is wound around the transfer drum, the oil adhering to the toner or the recording material is transferred onto the recording material carrying sheet, and then the recording drum is separated from the transfer drum. The oil on the transfer drum is transferred to the photosensitive drum by the rotation of.

[0005] When the oil is transferred to the photosensitive drum in this manner, the toner cannot be cleaned because the oil cannot be sufficiently cleaned even by the cleaning device on the photosensitive drum. However, since the toner adheres to the image, there is a problem in that, in a subsequent copy, a dirty image to which the excess toner adheres is finally obtained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which prevents image deterioration due to transfer of a release agent attached to a recording material during fixing to an image carrier via a recording material support. .

Another object of the present invention is to provide an image forming apparatus capable of forming a good image on both sides of a recording material.

[0008]

The above objects are achieved by the present invention. According to the present invention, an image carrier for supporting a toner image, a recording material support for supporting a recording material, and a toner image on the image carrier are transferred to a recording material supported by the recording material support. An image forming apparatus comprising: a pressing unit that presses the recording material support toward the image carrier; and a fixing unit that is coated with a release agent and fixes a toner image on the recording material to the recording material. The first fixing of the recording material by the fixing means.
After fixing the toner image on the surface, the second side of the recording material supported on the recording material support from the image carrier is opposite to the first surface.
The toner image can be transferred to the surface, and after the image transfer of the recording material to the second surface is completed, the pressing operation by the pressing means is released, and the recording material support is separated from the image carrier. It is a feature.

[0009]

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

FIG. 6 shows a multicolor electrophotographic copying apparatus having a developing device called a so-called rotary developing device as an image forming device.

Referring briefly to FIG. 6, the multicolor electrophotographic copying apparatus is provided with an image carrier, that is, a photosensitive drum 3, which is rotatably supported in a rotatable manner and rotates in the direction of the arrow. Forming means is arranged. The image forming means may be any means. In this embodiment, a primary charger 4 for uniformly charging the photosensitive drum 3 and a color-separated light image or a light image corresponding thereto are irradiated on the photosensitive drum 3. An exposure unit 8 such as a laser beam exposure device for forming an electrostatic latent image on the photosensitive drum 3 and a rotary developing device 1 for turning the electrostatic latent image on the photosensitive drum 3 into a visible image are provided.

The rotary developing device 1 includes a magenta color developer,
Four developing devices 1M, 1M each storing a developer of four colors of a cyan developer, a yellow developer, and a black developer, respectively.
C, 1Y, 1Bk and these four developing units 1M, 1C,
1Y, 1Bk, and a substantially cylindrical housing that is rotatably supported. The rotary developing device 1
Is configured to transport a desired developing device to a position facing the outer peripheral surface of the photosensitive drum 3 by rotation of a housing, and develop an electrostatic latent image on the photosensitive drum, thereby enabling full-color development for four colors. .

The visible image on the photosensitive drum 3, ie, the toner image, is transferred to a transfer material P carried and transported by a transfer device 9. In the present embodiment, the transfer device 9 is a transfer drum rotatably supported on a shaft. The transfer drum 9 includes cylinders 9a and 9b disposed at both ends and the transfer drum 9 as can be understood from FIG. A connecting portion 9c for connecting the cylinders 9a and 9b is provided, and a recording material holding member 93 for holding the recording material is stretched over the opening area of the outer peripheral surface of the cylinders 9a and 9b. As the recording material holding member 93, a film-like dielectric sheet such as polyethylene terephthalate or polyvinylidene fluoride resin film is usually used. or,
The connecting portion 9c has a recording material P fed from a paper feeding device.
And a recording material gripper 7 for holding the recording material. Further, inside and outside the transfer drum 9, a transfer discharger 10, an inner discharger 13 and outer dischargers 11 and 14, which constitute a discharging unit, are disposed.

Further, in order to increase the transfer efficiency and obtain a clear transfer image, as shown in FIG. 8, the transfer discharger 10 is provided on the upstream side when viewed from the rotation direction of the transfer drum 9. A pressing member as pressing means for pressing the dielectric sheet 93 toward the photosensitive drum, that is, the elastic sheet 18, which is supported by the support member on the upstream side of the sheet, extends in the downstream direction, contacts the dielectric sheet 93, and presses the dielectric sheet 93 toward the photosensitive drum. Is provided to improve the transferability.

The process of forming a full-color image by the multicolor electrophotographic copying machine having the above-described configuration will be briefly described as follows.

The photosensitive drum 3 is uniformly charged by the primary charger 4 and irradiated with a light image E corresponding to image information by the exposure means 8, so that an electrostatic latent image is formed on the photosensitive drum 3. The electrostatic latent image is visualized by forming a toner image on the photosensitive drum 3 with a toner having an average particle diameter of 8 μm using a resin as a base material by the rotary developing device 1.

On the other hand, the recording material P is sent to the transfer drum 9 by the registration roller 6 in synchronization with the image, the leading end of the recording material P is gripped by the gripper 7 and the like.
Is transported in the direction of the arrow in the figure.

Next, a corona discharge having a polarity opposite to that of the toner is received by the transfer discharger 10 from the back surface of the recording material supporting member of the transfer drum 9, that is, the back surface of the dielectric sheet 93, in the area where the photosensitive drum 3 contacts. 3 is transferred onto the recording material P.

After the transfer of the recording material P is performed a required number of times, and the transfer process is completed, the transfer belt 16 peeled off from the transfer drum 9 by the action of the separation claw 15 while being subjected to charge removal by the discharge devices 11, 13, and 14 for charge removal. To the fixing device 17. After being fixed by heat in the fixing unit 17, the sheet is discharged outside the apparatus.

On the other hand, the photosensitive drum 3 is subjected to the image forming process again after the residual toner on the surface is cleaned by the cleaning device 12.

Further, the surface of the dielectric sheet of the transfer drum 9 is also cleaned by the operation of the cleaning device 5 composed of a fur brush and the cleaning auxiliary means 8 after the transfer process is completed and the rear end of the recording material has passed from the transfer position. After that, it is again subjected to the image forming process.

At this time, the fixing operation speed of the fixing device 17 is 90 mm / sec, which is lower than the main body process speed of 160 mm / sec. This is because a sufficient amount of heating must be applied to the toner when the unfixed image on which two to four layers of toner are loaded is melted and mixed, as described later, so that the fixing is performed at a speed lower than the main body speed. As a result, the amount of heat applied to the toner is increased.

As described above, since a multicolor toner forms two to four layers in a color image, the electrophotographic apparatus for forming a color image uses the black and white toner in the following two points. It has different features from the device.

The first characteristic relates to the toner used.

This toner has a melting property when heated,
Since good color mixing is required, a sharp melt toner having a low softening point and a low melt viscosity is used. By using such a sharp melt toner, the color reproduction range of a copy can be widened and a color copy faithful to a multi-color or full-color image of a document can be obtained.

Such a sharp melt toner includes, for example, a binder resin such as a polyester resin or a styrene-acryl ester resin, a colorant (a dye, a sublimable dye),
It is manufactured by melt-kneading, pulverizing, and classifying a toner-forming material such as a charge control agent. If necessary, an external addition step of adding various external additives (for example, hydrophobic colloidal silica) to the toner may be added. As such a color toner, a toner using a polyester resin as the binder resin is particularly preferable in consideration of the fixing property and the sharp melt property. Examples of the sharp-melt polyester resin include a polymer compound having an ester bond in the main chain of a molecule synthesized from a diol compound and a dicarboxylic acid.

In particular, the following equation

[0028]

[Outside 1] (Wherein R is an ethylene or propylene group, x, y
Is a positive integer of 1 or more, and the average value of x + y is 2 to 10. A) a bisphenol derivative or a substituted product thereof as a diol component, and a carboxylic acid component comprising a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof (for example, fumaric acid, maleic acid, maleic anhydride, Phthalic acid, terephthalic acid,
A polyester resin obtained by co-condensation polymerization with at least trimellitic acid and pyromellitic acid) is more preferable because it has sharp melting characteristics.

The softening point of the polyester resin is 75 to 15
0 ° C, preferably 80 to 120 ° C.

FIG. 9 shows an example of the softening characteristics of a sharp melt toner containing the polyester resin as a binder resin. The measurement conditions are as follows.

Using a flow tester CFT-500A type (manufactured by Shimadzu Corporation), a die (nozzle) diameter of 0.2 m
m, a thickness of 1.0 mm, a 20 kg extrusion load, an initial set temperature of 70 ° C., a preheating time of 300 seconds, and a constant temperature rise at a rate of 6 ° C./min. A curve (hereinafter referred to as a softening S-shaped curve) was obtained. The toner used as the sample is a fine powder precisely weighed from 1 to 3 g, and the cross-sectional area of the plunger is 1.0 cm ² . Softening S
The character curve becomes a curve as shown in FIG. As the temperature rises at a constant speed, the toner is gradually heated and starts to flow (plunger descent A → B). When the temperature is further increased, the toner in the molten state flows out greatly (B → C → D), the plunger descent stops, and the process ends (D → E).

The height H of the S-shaped curve indicates the total amount of outflow, and H /
The temperature T0 corresponding to the C point 2 indicates the softening point of the toner.

Whether or not the toner and the binder resin have sharp meltability can be determined by measuring the apparent melt viscosity of the toner or the binder resin.

The toner or binder resin having such a sharp melt property is defined as a temperature when the apparent melt viscosity shows 10 ³ poises is T1, and a temperature when the apparent melt viscosity shows 5 × 10 ² poises is T2. T1 = 90 to 150 ° C. | △ T | = | T1−T2 | = 5 to 20 ° C.

The sharp-melt resin having these temperature-melt viscosity characteristics is characterized in that the viscosity is sharply reduced by heating. Such a decrease in viscosity causes appropriate mixing between the uppermost toner layer and the lowermost toner layer, and furthermore, the transparency of the toner layer itself is sharply increased, and good color reduction mixing is caused.

Such a sharp-melting color toner also has a property of having a high affinity and being easily offset to the fixing roller.

Therefore, in the fixing device of the image forming apparatus using the above color toner, it is necessary to exhibit high releasability over a long period of time. Hereinafter, the fixing device 17 which is a second feature of the electrophotographic apparatus for forming a color image will be described with reference to FIG.

In FIG. 10, a fixing roller 29 as a fixing means has an HTV (high temperature vulcanization type) silicone rubber layer 32 on an aluminum cored bar 31 and an RTV (room temperature vulcanization type) on the outside thereof.
With a silicone rubber layer 33, thickness 3 mm, diameter 40 m
m.

On the other hand, a pressing roller 30 as a pressing means is provided with an HTV having a thickness of 1 mm on an aluminum core 34 and an RTV silicone rubber layer 35 on the surface thereof.
It has become.

The fixing roller 29 is provided with a halogen heater 36 which is a heating means, and the pressure roller 30 is also provided with a heater 37 in a metal core for heating from both sides. Thermistor 38 in contact with pressure roller 30
And the controller 39 controls the halogen heaters 36 and 37 based on the detected temperature, so that the temperature of the fixing roller 29 and the temperature of the pressure roller 30 are both kept constant at about 170 ° C. Is controlled. The fixing roller 29 and the pressing roller 30 are pressed by a pressing mechanism (not shown) with a total pressure of about 40 kg.

In FIG. 10, O is an oil application device as a release agent application means, C is a cleaning device, and C1 is a cleaning blade for removing oil and dirt from the pressure roller. The oil applicator O is a dimethyl silicone oil 41 (KF9630 manufactured by Shin-Etsu Chemical Co., Ltd.) in an oil pan 40.
0 cs) is passed through the oil pumping roller 42 and the oil application roller 43, and the oil application amount is regulated by the oil application amount adjusting blade 44 so that the oil is applied onto the fixing roller 29.
In the apparatus shown in FIG. 10, a coating amount of 0.08 g / A4 is applied by a measuring method described later.

The amount of silicone oil applied by the oil application device O is determined as follows.

First, the weight of 50 sheets of A4 size blank paper is
1 g, without transferring the image onto the blank paper and without applying silicone oil to the rubber layer of the fixing roller.
Blank paper 50 after passing between the fixing roller and the pressure roller
Let the weight of the sheet be B (g). Next, similarly, the weight of another 50 sheets of A4 size paper is set to A2 (g), and the image is not transferred onto this white paper. However, silicone oil is applied to the rubber layer of the fixing roller, and the fixing is performed. The weight of 50 blank sheets after passing between the roller and the pressure roller is defined as C (g). When the above A1, B, A2, and C are used, the coating amount X (g) of the silicone oil per sheet of A4 size white paper is used.
Is obtained by the following equation.

X = (C + A1-B-A2) / 50 On the other hand, the cleaning device C cleans the non-woven fabric web 46 made of Nomex (trade name) by pressing it against the fixing roller 29 with the pressing roller 45. Further, the web 46 is appropriately wound by a winding device (not shown) so that toner or the like does not accumulate on the contact portion.

This apparatus once transfers the toner onto the recording material,
After the image is fixed by the fixing device, the same recording material is again fed to the color image forming electrophotographic apparatus, and the toner image surface of the recording material on which the image is formed is held on the surface of the transfer drum. By transferring and fixing the toner image on the opposite side again, a double-sided image can be formed.

When a double-sided image is formed, a recording material is placed on a tray T as shown in FIG. 6, after the transfer and fixing, the recording material is discharged, and then the recording material on the side opposite to the image forming surface of the recording material is discharged. The recording material is again placed on the tray T so that an image is formed on the surface, transferred, fixed, and discharged.

Next, with reference to FIG. 1, the pressing member 18 in the transfer device and the driving means for moving the pressing member 18 toward and away from the transfer drum will be specifically described.

As described above, at the transfer position where the photosensitive drum 3 and the transfer drum 9 are close to each other, the dielectric material made of polyvinylidene fluoride resin (PVdF) or the like, which is a recording material support, is within the discharge width of the transfer charger 10. An elastic pressing member 18 is provided extending from the introduction side of the sheet 93 toward the downstream side in the movement direction (forward direction with respect to the movement direction of the transfer drum). The pressing member 18 is a pressing sheet made of, for example, a synthetic resin film such as polyethylene, polypropylene, polyester, polyethylene terephthalate, etc., and is disposed over the entire area of the transfer section. The volume resistivity of these resin films is 10 ¹⁴ Ω · cm or more. In this example, a polyethylene terephthalate resin was used.

The pressing sheet 18 presses the dielectric sheet 93 by its own elastic force, and the leading end of the pressing sheet 18 on the dielectric sheet side is at the position where the transfer material P has come into contact with the photosensitive drum. Or a position where contact is started, or a position as close as possible to such a position.

If the dielectric sheet 93 is simply pressed, the backup member 18 is moved from the opposite side of the dielectric sheet 93 to the upstream side in the moving direction (counter direction with respect to the transfer drum moving direction). May be provided,
In such a configuration, the effect of suppressing the image scattering caused by the start of the transfer before the photosensitive drum and the recording material come into contact with each other cannot be obtained, and therefore, as shown in the present embodiment, the pressing member 18 It is preferable to provide the sheet 93 from the introduction side to the downstream side in the movement direction.

In this embodiment, a driving means for moving the pressing member 18 into and out of contact is further provided.

The driving means includes three link members 181, 182, and 183 for supporting the pressing member 18 and the link member 1.
A cam 185 for moving the motor 83 around the shaft 183a, a motor 186 for rotating the cam 185, and a bracket 2
4 and a tension spring 184 which is a resilient means for exerting an elastic force in a direction in which the pressing member 18 is separated from the recording material support 93 by being stretched between the link member 181 and the link member 181. The motor 186 includes a main body controller (not shown).
Is driven asynchronously with the rotation of the transfer drum 9.

In such a configuration, the primary charging, exposure, development, transfer charging, and the contact / separation operation of the pressing member by driving the motor 186 with reference to the rotation of the transfer drum 9 when forming an image are described below. This will be described with reference to FIG.

FIG. 2 is an example of a timing chart when the size of the recording material P on the transfer drum 9 is, for example, A4 size paper.

In order to form a magenta (M) image of the first color, corona discharge is performed by the primary charger 4 to uniformly charge the surface of the photosensitive drum 3. And according to the image information,
The laser beam is irradiated, and a latent image of the M image is formed on the photosensitive drum 3.

At the developing position, the magenta developing device 1M, which has been moved in advance, is on standby, and starts developing driving.
The M image is visualized. The developing drive is a developer carrying member that carries and conveys the developer in the developing device toward the photosensitive drum, that is,
In anticipation of the time t at which the developing sleeve rises to a certain rotational speed,
Driving is started earlier by the time t than the leading end of the image at the developing position.

At the transfer position, the transfer charger 10 is activated almost at the same time as the recording material reaches the transfer position in accordance with the movement timing of the recording material held on the transfer drum 9 and the movement of the connecting member 9c of the transfer drum 9. Activates and performs transfer charging.
On the other hand, the pressing member 18 is pressed against the dielectric sheet 93 slightly before or almost at the same time as the transfer charging. As a result, the dielectric sheet 93 is pressed against the photosensitive drum 3, and in this state, the transfer drum rotates substantially once, and the M image is transferred to the recording material. The transfer charger operates when the recording material is at the transfer position.

When the pressing member 18 is pressed against the dielectric sheet 93, as shown in FIG.
Since a latent image is being formed by performing exposure on the photosensitive drum 3, if the vibration generated during pressing is large, the latent image is greatly affected, and image defects such as pitch unevenness occur. Therefore, it is preferable to combine the motor and the cam, as shown in the present embodiment, to make the pressing sheet 18 smoothly contact the dielectric sheet 93 so as to minimize vibration. When using a pressure contact mechanism using a tension spring and a solenoid to simplify the mechanism,
The recording material is carried on the transfer drum from above the connecting member by a gripper provided on the connecting member 9c, or
From above, it is preferable that the pressing member is carried on the transfer drum using electrostatic force of a suction corona discharger or the like, and the pressing member is brought into contact with the connecting member 9c at the timing of contact. Further, it is preferable that a buffer member such as a sponge is provided on the pressing member 18 side of the connecting member 9c so as to minimize vibration when the pressing member 18 contacts the transfer drum.

Then, during the second rotation of the same transfer drum, the rotary developing device 1 rotates, and moves the cyan developing device 1C to the developing position in preparation for developing the cyan (C) image. Thereafter, when the transfer drum enters the third rotation, the above process is repeated to transfer the C image to the recording material.

By repeating the above steps for a yellow image and a black image, a superimposed transfer image of four colors is obtained on a recording material carried on a transfer drum. At the same time that a series of transfer steps for four colors is completed and the rear end of the recording material is separated from the transfer position, the pressing member 18 is moved by the above-described mechanism.
Are in a standby state apart from the dielectric sheet 93. In this standby state, the pressing member 18 does not come into contact with the dielectric sheet 93, and no pressing force acts on the dielectric sheet 93. In this state, the dielectric sheet 93 and the photosensitive drum 3 maintain a gap of about 100 μm. It is configured as follows.

Almost simultaneously with the start of the transfer of the fourth color black image, the charge removal charger 11 of the dielectric sheet 93,
13 is operated, and the dielectric sheet 93 is neutralized at the sixth and seventh rotations of the transfer drum.

When two-sided copying is performed in a conventional color image forming apparatus, the oil adhering to the surface of the recording material is transferred to the dielectric sheet at the time of fixing, and during the rotation of the transfer drum where the transfer of the toner image is completed, the so-called rear multi During rotation, or during rotation just before starting to form an image on the back surface of the recording material, during so-called pre-multi-rotation, the dielectric sheet to which the oil has adhered is directly pressed and adhered to the photosensitive drum by the pressing member. The oil on the body sheet was re-transferred to the photosensitive drum, causing image defects. However, with the configuration in which the dielectric sheet and the drum are separated from each other as described above, when the dielectric sheet directly contacts the photosensitive drum during the subsequent multiple rotations or during the previous multiple rotations, the pressing member is pressed. In the standby state, the dielectric sheet is prevented from contacting the photosensitive drum as much as possible, so that it is possible to prevent a defective image caused by oil adhering to the photosensitive drum, which has conventionally occurred.

In this embodiment, the contact and separation of the pressing member 18 are performed at the timing as shown in FIG.
As shown in FIG. 3, a more preferable result can be obtained by performing contact / separation in synchronization with the transfer charging so that the surface of the dielectric sheet where the recording material does not exist on the surface is prevented from contacting the photosensitive drum at all. It goes without saying that you can get it. However, in this case, the number of times of contact and separation increases, and as described above, image defects such as pitch unevenness may occur due to the influence on the latent image due to the vibration at the time of press contact. At the time of contact, it is preferable that the motor is driven at a low speed just before the contact, for example, so that vibration at the time of contact is minimized.

Further, in this embodiment, the transfer means is constituted by a transfer charger capable of forming a transfer electric field by corona discharge and a pressing member. However, the transfer means is provided through the electrode 20 as shown in FIGS. A brush 19 made of a fiber spring having a volume resistivity of 10 ⁰ to 10 ⁸ Ω · cm configured to be capable of applying a voltage or a blade 19 having an equivalent resistivity.
May be used, or a voltage may be applied through the electrode 22.
Also for a system using a rubber roller 21 having the same resistivity, the same effect as that of the above-described embodiment can be obtained by providing a contact / separation mechanism and causing the contact / separation.

Next, another embodiment for separating the recording material carrying member from the photosensitive drum will be described.

In this embodiment, as can be better understood with reference to FIG. 11, in the image forming apparatus shown in the above-mentioned embodiment, the entire transfer drum 9 can be brought into contact with and separated from the photosensitive drum 3.

As shown in FIG. 11, the pressing means for bringing the transfer drum 9 into and out of contact with the photosensitive drum 3 (pressing / separating) includes a fixed shaft 190 and a support member fixed to the central shaft of the transfer drum 9. 187 and the supporting member 187
It comprises a cam 188 that moves around zero and a motor 189 that drives the cam 188 to rotate.

In such a configuration, the primary charging, exposure, development, transfer charging, and the contact / separation operation of the transfer drum by driving the motor 189 with reference to the rotation of the transfer drum 9 during image formation will be described. This will be described with reference to FIG.

FIG. 12 is an example of a timing chart when the size of the recording material P on the transfer drum 9 is, for example, A4 size paper.

In order to form a magenta (M) image of the first color, corona discharge is performed by the primary charger 4 to uniformly charge the surface of the photosensitive drum 3. And according to the image information,
The laser beam is irradiated, and a latent image of the M image is formed on the photosensitive drum 3.

At the developing position, the magenta developing device 1M, which has been moved in advance, is on standby, and starts developing driving.
The M image is visualized. The developing drive is a developer carrying member that carries and conveys the developer in the developing device toward the photosensitive drum, that is,
In anticipation of the time t at which the developing sleeve rises to a certain rotational speed,
Driving is started earlier by the time t than the leading end of the image at the developing position.

At the transfer position, the transfer charger 10 is activated almost at the same time as the recording material reaches the transfer position in accordance with the movement timing of the recording material held on the transfer drum 9 and the movement of the connecting member 9c of the transfer drum 9. Activates and performs transfer charging.
On the other hand, prior to or almost at the same time as the transfer charging, the transfer drum 9 or the photosensitive drum 3 is pressed against the transfer drum 9. In this state, the transfer drum rotates substantially once, and the M image is transferred to the recording material. The transfer charger operates when the recording material is at the transfer position. Then, at the second rotation of the same transfer drum, the rotary developing device 1 rotates, and moves the cyan developing device 1C to the developing position in preparation for developing the cyan (C) image. Thereafter, when the transfer drum enters the third rotation, the above process is repeated to transfer the C image to the recording material.

By carrying out the above steps similarly for the yellow image and the black image, a transfer image of four colors can be obtained. Almost at the same time when the transfer charging for four colors is completed and the rear end of the recording material is separated from the transfer position, the transfer drum 9 is separated from the photosensitive drum 3 and is in a standby state. In this standby state, the transfer drum 9 does not come into contact with the photosensitive drum 3, and a gap of approximately 100 μm is maintained between the two.

By adopting such a structure, the recording material-carrying sheet to which the oil adheres is minimized from coming into direct contact with the photosensitive drum as in the case of the above-described embodiment. The image defect caused by the adhesion of the image can be prevented.

In the above-described embodiment, the oil of the recording material adheres to the transfer drum when an image is formed on the back surface of the recording material. Therefore, at least after this, the photosensitive drum and the transfer drum are separated from each other. It is desirable to prevent transfer of oil from the photosensitive drum to the photosensitive drum. That is, it is desirable that the recording material supporting member of the transfer drum and the photosensitive drum be separated by post-rotation after at least image formation on the back surface of the recording material is completed. According to the sequences of FIGS. 2 and 3, it is desirable that the separation be performed after the transfer of the fourth color is completed and at least the rear end of the recording material has passed the transfer position. After this, if the oil adhering to the transfer drum is cleaned by the cleaning member during the rotation, the transfer drum and the photosensitive drum may be in contact with each other because the transfer drum has a considerably small amount of oil in the pre-rotation during the next image formation. .

The present invention is also applicable to the four
It can also be embodied in a multicolor electrophotographic copying machine having one image forming unit I to IV.

In this embodiment, each of the image forming units I to IV
Has photosensitive drums 3a to 3d, around which primary charging devices 4a to 4d, exposure means 8a to 8d, developing devices 1a to 1d,
Transfer chargers 10a to 10d, static eliminators 11a to 11d
And 13a to 13d, and cleaners 12a to 12d, and an endless belt-shaped conveying means 23 is disposed below the photosensitive drum so as to penetrate each image forming unit.

On the other hand, pressing members 18a to 18d are provided as urging means for urging the endless belt-shaped conveying means 23 toward the respective photosensitive drums within the respective discharge widths of the transfer dischargers 10a to 10d. Further, contact / separation mechanisms 180a to 180d for pressing and separating the pressing member to and from the transporting means 23
Is provided.

In this embodiment, at the same time as the recording material passes through the transfer position at each image forming station, the transfer charging starts and the pressing member is pressed almost simultaneously with the leading end of the recording material reaching the transfer position. The transfer is stopped, and the transfer charge is stopped and the pressing member is separated almost at the same time as the recording material finishes passing through each transfer position. When the pressing member is separated, the photosensitive drum and the transfer belt are separated.

With this configuration, in this embodiment, as in the above-described embodiment, after double-sided copying, oil adhering to the surface of the belt-shaped conveying means is re-adhered to the photosensitive drum, and image defects occur. That can be prevented.

In this embodiment, as can be better understood with reference to FIG. 14, in the image forming apparatus shown in the previous embodiment, instead of separating the photosensitive drum and the conveying belt by separating the pressing member, the recording material is conveyed. The entire belt unit is configured to be able to contact and separate from the photosensitive drums 3a to 3d.

As a pressing means for aligning (pressing / separating) the entire conveying belt unit as a recording material support unit to and from the photosensitive drums 3a to 3d, as shown in FIG. Is a fixed axis,
It comprises a support member 261 fixed to another transport belt support roller 26, a cam 262 for moving the support member 261 up and down, and a motor 263 for rotating the cam 262.

In such a configuration, at the same time as or just before the recording material is fed from the paper supply unit to the transfer position of the first station and reaches the transfer position of the first station, the transfer belt unit performs the above-described transfer. The belt driving means contacts the photosensitive drums 3a to 3d. And
Transfer charging is performed, and a magenta image is transferred. Further, the transfer is successively performed on the recording material at the respective image forming stations, and the transport belt unit is separated from the photosensitive drum by the operation of the transport belt driving means almost at the same time as the recording material passes the fourth station. did.

With this configuration, in this embodiment, as in the previous embodiment, after double-sided copying, oil adhering to the surface of the belt-shaped conveyance means is re-adhered to the photosensitive drum, causing image defects. That can be prevented.

In the embodiments shown in FIGS. 13 and 14, the oil of the recording material adheres to the conveyance belt when an image is formed on the back surface of the recording material. It is desirable to separate oil from the conveyor belt to the photosensitive drum by separating them from each other. That is, it is desirable that the conveying belt and the photosensitive drum be separated by post-rotation after at least image formation on the back surface of the recording material is completed. If the oil adhering to the conveyance belt is cleaned during the subsequent rotation, the conveyance belt is almost free of oil in the pre-rotation at the time of the next image formation, so that the conveyance belt may contact the photosensitive drum.

FIG. 15 shows another embodiment of the present invention. The present inventors continued their research experiments, and as a result, FIG.
As shown in FIG. 2, a member 28 such as a sensor for detecting the position of the transfer material supported on the transfer drum 9 is provided near the transfer drum 9, and the pressing member 18 is provided based on a signal from the position detection member 28. It has been found that a further effect can be obtained by making the structure contact and separate from the dielectric sheet 93. This will be described in detail below.

As can be understood from FIG. 15, according to the present embodiment, the transfer drum 9 is constructed by concentrically disposing cylindrical members 9a and 9b and connecting them together by a connecting member 9c. Is provided between the guide plate 27 which is a part of the recording material transport system and the transfer position.

The recording material supplied to the transfer drum 9 after passing through the guide plate 27 is attracted to the dielectric sheet 93 by electrostatic means (not shown). The sucked recording material moves in accordance with the movement of the transfer drum 9, and when the leading end of the recording material passes through the transfer position detecting member 28, the leading end position of the recording material is taken into the storage device on the main body side. The recording material continues to move, and when the trailing end passes through the recording material position detecting member 28, the trailing end position is again taken into the storage device on the main body side.

When the leading end and the trailing end position of the recording material taken into these storage devices and the distance from the recording material position detecting member 28 to the transfer position are calculated, when the leading end of the recording material reaches the transfer position, When the pressing member 18 is brought into contact with the dielectric sheet 93 and the rear end of the transfer material passes through the transfer position, the pressing member 18 is immediately separated from the transfer member, and is in a standby state.

With this configuration, even if the recording material is of any size and the position of the recording material is slightly shifted on the recording material support, the occurrence of image defects is prevented as in the above-described embodiment. It is possible to do.

[0091]

As described above, according to the present invention,
An image carrier for supporting the toner image, a recording material support for supporting the recording material, and an image carrier for transferring the toner image on the image carrier to the recording material supported by the recording material support. In an image forming apparatus comprising: a pressing unit that presses toward a carrier; and a fixing unit that is coated with a release agent and fixes a toner image on the recording material to the recording material. After the toner image is fixed, the toner image can be transferred from the image carrier to the second surface of the recording material supported on the recording material support opposite to the first surface, and can be transferred to the second surface of the recording material. After the completion of the image transfer, the pressing operation by the pressing means is released, and the recording material support is separated from the image carrier, so that the image defect due to the release agent adhered to the recording material support being transferred to the image carrier. Can be prevented from occurring.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an urging mechanism of a pressing member of an image forming apparatus according to the present invention.

FIG. 2 is an operation sequence of the image forming apparatus of the present invention.

FIG. 3 is an operation sequence of the image forming apparatus of the present invention.

FIG. 4 is a sectional view of a modification of the pressing member of the image forming apparatus of the present invention.

FIG. 5 is a sectional view of a modification of the pressing member of the image forming apparatus of the present invention.

FIG. 6 is a sectional view showing an embodiment of the image forming apparatus of the present invention.

FIG. 7 is a perspective view of a transfer device.

FIG. 8 is an enlarged sectional view near a transfer portion.

FIG. 9 is a graph showing softening characteristics of a sharp melt toner used in the present apparatus.

FIG. 10 is a cross-sectional view of a fixing device used in the present apparatus.

FIG. 11 is a sectional view of a main part showing a release mechanism of a recording material carrier of the image forming apparatus of the present invention.

FIG. 12 is an operation sequence in the apparatus of FIG. 11;

FIG. 13 is a sectional view showing another embodiment of the image forming apparatus of the present invention.

FIG. 14 is a sectional view showing another embodiment of the image forming apparatus of the present invention.

FIG. 15 is a sectional view of a main part showing another embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

3, 3a, 3b, 3c, 3d Photosensitive drum 9 Transfer device (transfer drum) 93 Dielectric sheet 10 Corona discharger for transfer 18 Pressing member 19 Brush for transfer charging 21 Roller for transfer charging 23 Recording material transport belt 28 Recording material Position detecting member 29, 30 Toler for fixing 181 to 186, 180a to 180b Pressing member driving unit 187 to 190 Transfer drum contact / separation driving unit 261 to 263 Recording material transport belt driving unit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G03G 15/16 G03G 15/00 106

Claims (9)

(57) [Claims] An image carrier for supporting a toner image; a recording material support for supporting a recording material; and a method of transferring a toner image on the image carrier to a recording material supported by the recording material support. An image forming apparatus comprising: a pressing unit that presses the recording material support toward the image carrier; and a fixing unit that is coated with a release agent and fixes a toner image on the recording material to the recording material. After fixing the toner image on the first surface of the recording material by the fixing means, a toner image is formed on the second surface of the recording material supported on the recording material support from the image carrier on the side opposite to the first surface. The image forming apparatus is capable of transferring, and after the transfer of the image of the recording material to the second surface is completed, the pressing operation by the pressing means is released, and the recording material support is separated from the image carrier. apparatus. 2. The image forming apparatus according to claim 1, wherein the pressing unit is provided on a side opposite to the image carrier via the recording material support. 3. The image forming apparatus according to claim 1, wherein the pressing unit electrostatically transfers the toner image on the image carrier to a recording material supported on the recording material support. apparatus. 4. The image forming apparatus according to claim 1, further comprising a recording material support unit provided with the recording material support, wherein the pressing unit presses the recording material support unit toward the image carrier. Image forming device. 5. A detecting means for detecting a position of a rear end of the recording material supported by the recording material support, and a timing for canceling a pressing operation of the pressing means in accordance with a detection result by the detecting means. The image forming apparatus according to claim 1, further comprising a control unit. 6. A multi-color toner image is formed on a recording material by repeating a step of transferring a toner image on the image carrier to a recording material supported on the recording material support. The image forming apparatus according to claim 1. 7. The transfer of the toner image of the first color onto the second surface of the recording material after the transfer of the toner image of the first color to the start of transfer of the toner image of the second color following the first color. 7. The image forming apparatus according to claim 6, wherein the pressing operation by the pressing unit is released while the recording material support is separated from the image carrier. 8. The recording material supporter by the pressing means from the time when the transfer of the first color toner image to the second surface of the recording material is started to the time when the transfer of the final color toner image is completed. Is pressed by the image carrier, after the end of the transfer of the final color toner image, the pressing operation by the pressing means is released,
7. The image forming apparatus according to claim 6, wherein the recording material support is separated from the image carrier. 9. The image forming apparatus according to claim 6, wherein a plurality of the image carriers are provided to carry the toner images of the plurality of colors, respectively.