JPH09237004A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the potentials of fixing rotary bodies to proper ones and to prevent the scattering of unfixed images by switching the fixing rotary bodies to electrifiable states, at the time of carrying a transfer material to which the unfixed images are transferred to the fixing rotary bodies. SOLUTION: An electrical connection controller (a) for the fixing rotary bodies is provided and a fixing roller 51 and a pressure roller 52 as the fixing rotary bodies are electrically connected. In other words, setting is attained to make both rollers grounded states, when a switch (a) is on the side of (e) and floated states, when the switch (a) is on the side of (f). Control is attained to lay the switch (a) on the side of (f), when the transfer material P is supplied and on the side of (e) except this time. Thus, when unfixed toner (t) is infiltrated into a nip, the fixing roller 51 and the pressure roller 52 are increased to the proper potentials, because the rollers are in the floated states, so that the potential difference between the rollers 51 and 52 and a toner image is eliminated and the scattering of toner is prevented as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine of an electrophotographic system or an electrostatic recording system, a laser beam printer or the like, and more particularly to a transfer material carrying a visible image formed on an image carrier. The present invention relates to an image forming apparatus which obtains an output image by transferring a transfer material carried on a body.

[0002]

2. Description of the Related Art An example of a conventional electrophotographic color image forming apparatus will be described with reference to FIG. The color image forming apparatus shown in FIG. 4 has a digital color image reader section in its upper part and a digital color image printer section in its lower part.

First, in the reader section, the reflected light image from the original 30 obtained by placing the original 30 on the original glass 31 and exposing and scanning with the exposure lamp 32 is collected on the full color sensor 34 by the lens 33. Illuminate to obtain a color separated image signal. This color-separated image signal is amplified by an amplifier circuit (not shown), processed by a video processing unit (not shown), and sent to the printer section.

Next, in the printer section, the photosensitive drum 1, which is an image carrier, is a large-diameter photosensitive drum having a diameter of 180 mm and is rotatably supported in the direction of the arrow in the figure. Around the photosensitive drum 1, a pre-exposure lamp 11 for initializing the surface of the photosensitive drum 1, a charger 2 such as a corona charger for uniformly charging the surface of the photosensitive drum 1, a photosensitive drum 1 Image exposure means 3 for forming an electrostatic latent image according to image information thereon, a potential sensor 12 for detecting the potential of the surface of the photosensitive drum 1, and an electrostatic latent image formed on the photosensitive drum 1 into a visible image A fixedly arranged developing device including four developing devices 4C, 4M, 4Y and 4K accommodating developers (toners) of different colors to be developed, a light detecting means 13 for detecting the amount of toner on the photosensitive drum 1, and a transfer. A transfer device 5 including a transfer drum 5a as a material carrier, a cleaner 6 for removing a developer remaining on the photosensitive drum 1, and the like are provided.

The image exposure means 3 is a polygon mirror 3
a, a lens 3b, a mirror 3c, and the like. The polygon mirror 3a reflects the laser light E from the laser output section, which is modulated by the color image signal of each color separated from the reader section, and is reflected by the lens 3b and the mirror. The image is projected onto the surface of the photosensitive drum 1 through 3c to form an electrostatic latent image corresponding to the color image signal of each color.

At the time of image formation in the printer section, the photosensitive drum 1 is rotated in the direction of the arrow at a speed of 133 mm / sec. First, the surface of the photosensitive drum 1 is neutralized and initialized by the pre-exposure lamp 11, and then charged. The photoconductor drum 1 is uniformly charged by the device 2, and the surface of the photoconductor drum 1 is sequentially irradiated with the laser light E corresponding to the image signals of the respective colors separated by the image exposure unit 3 in a predetermined color order. Form an electrostatic latent image.

Next, a predetermined developing device is operated in the order of predetermined development of cyan (C), magenta (M), yellow (Y), and black (K) to develop a latent image on the photosensitive drum 1. Are developed to sequentially form toner images based on resin on the photosensitive drum 1. Here, each developing device 4 of the developing device
C, 4M, 4Y, 4K are eccentric cams 24C, 24M, 2
By the operations of 4Y and 24K, a predetermined developing unit alternatively approaches the photosensitive drum 1 according to the color of the formed latent image, and
It is configured to perform a developing operation.

On the other hand, the transfer material P such as paper fed from the transfer material cassette 7a, 7b, or 7c (may be manually fed) by a conveying system such as a pick up roller, a paper feed guide, and a paper feed roller is It is wound around the transfer device 5 in synchronization with a predetermined timing. The transfer device 5 includes a transfer drum 5a having a diameter of 180 mm as a transfer material carrier, a transfer charger 5b for transferring the toner image on the photosensitive drum 1 to the transfer material, and a transfer material adsorbed on the transfer drum 5a. It has an adsorbing corona charger 5c, which is an adsorbing and charging means, and an adsorbing (contacting) roller 5g as an opposite pole, an inner corona charger 5d, and an outer corona charger 5e, and is driven to rotate. A transfer material carrying sheet 5f made of a dielectric sheet such as a polycarbonate film is integrally stretched in a cylindrical shape as a transfer material carrying means in a peripheral opening area of the transfer drum 5a pivotally supported on the transfer drum 5a.

In the transfer device configured as described above, the transfer drum 5a is rotated in the direction of the arrow in the figure in synchronization with the photosensitive drum 1, and the cyan toner image developed by the cyan developing device 4C is charged for transfer at the transfer portion. The transfer material is transferred to the transfer material carried by the transfer material carrying sheet 5f by the device 5b.
The transfer drum 5b continues to rotate and is ready for transfer of the next color (magenta) image. In such a transfer device, two transfer materials of A4 size or the like and one transfer material of A3 size or the like are carried, and thus image formation on the two transfer materials is performed by continuously transmitting the same image signal. This is performed by continuously forming a toner image on the photosensitive drum 1 and performing transfer.

On the other hand, after the transfer of the toner image, the photoconductor drum 1 is cleaned by the cleaner 6 to remove the adhering substances such as residual toner, and is uniformly charged again by the charger 2, and the next magenta image signal is generated. The image exposure as described above is performed by the modulated laser light. The magenta latent image is developed by the magenta developing device 4M to form a magenta toner image, and the magenta toner image is transferred to the transfer material carrying sheet 5f by the transfer charger 5b at the transfer portion.
The magenta toner image is transferred onto the cyan toner image by being transferred onto the transfer material carried thereon. The transfer drum 5b continues to rotate and is ready for transfer of an image of the next color (for example, yellow).

Subsequently, the above-described process is performed for yellow and black image formation and transfer, and when the superimposing transfer of the toner images of four colors is completed, the transfer material performs AC corona discharge. The charge is removed by 5h, then separated from the transfer drum 5a by the action of the separation push-up roller 8b and the separation claw 8a, sent to the heat roller fixing device 9 by the conveying means, fixed in a batch, and discharged onto the external tray 10. .

In addition, since powder is scattered and adhered on the transfer material carrying sheet 5f of the transfer drum 5a and oil on the transfer material is adhered, the fur brush 14 and the transfer material are prevented in order to prevent them. Cleaning is performed using a backup brush 15 facing the fur brush 14 via the carrying sheet 5f, and a backup brush 17 facing the oil removing roller 16 via the oil removing roller 16 and the transfer material carrying sheet 5f. There is. Such cleaning is performed before or after image formation, and at any time when a jam (paper jam) occurs.

Next, as shown in detail in FIG. 5, the heat roller fixing device 9 rotates the fixing roller 51, which is rotatably provided as a fixing rotating member, and presses against the fixing roller 51. The pressure roller 52, a release agent applying device 53 as a release agent supplying and applying means, and a roller cleaning device 54 are provided. Heaters 56 and 57 such as halogen lamps are provided inside the fixing roller 51 and the pressure roller 52.
Are arranged respectively. Further, the thermistors 58 and 59 are disposed so as to be in contact with the fixing roller 51 and the pressure roller 52, respectively, and by controlling the voltage to the heaters 56 and 57 via the temperature adjusting circuit,
The surface temperature of the fixing roller 51 and the pressure roller 52 is set to 17
Adjustments are made to maintain it at 0 ° C.

Further, a cleaning device 54 and a release agent applying device 53 are attached to the fixing roller 51. The cleaning device 54 cleans the toner offset on the fixing roller 51 and the release agent. A silicone oil or the like as a release agent is applied to the fixing roller 51 by the application device 53, so that separation of the transfer material P from the fixing roller 51 is facilitated and toner offset is prevented.

The cleaning device 54 includes a cleaning web 54a made of a band-shaped heat-resistant nonwoven fabric, and a pressing roller 5 for pressing the cleaning web 54a against the fixing roller 51.
4b, an unwinding roller 54c that unwinds a new cleaning web 54a, and a winding roller 54b that gradually winds the cleaning web 54a having a reduced cleaning ability due to the adhesion of toner and the like. In order to prevent the offset toner from adhering to the thermistor 58 and causing a detection failure to the thermistor 58,
The cleaning device 54 is provided upstream of the thermistor 58 in the rotation direction of the fixing roller 51.

The release agent applying device 53 includes an oil tank 53a having a release agent such as silicone oil, pumping rollers 53b and 53c for pumping oil as a release agent from the oil tank 53a, and pumping rollers 53b and 53.
a coating roller 53d for applying the oil from the fixing roller 51 to the fixing roller 51, and a blade 53e for controlling the amount of oil applied from the coating roller 53d. In order to achieve this, the release agent applying device 53 is disposed downstream of the thermistor 58 in the rotation direction of the fixing roller 51. The application roller 53d is a rotatable roller in which sponge rubber is coated with silicone rubber, and is in contact with the fixing roller 51 as necessary, and applies oil to the fixing roller 51.

The fixing roller 51 is made of an aluminum core 12
2 HTV silicone rubber (high temperature vulcanized silicone rubber)
The layer 123 is coated, and the LTV silicone rubber (low temperature vulcanized silicone rubber) layer 124 is laminated thereon to a thickness of about 200 μm. The pressure roller 52 is formed by coating the aluminum core metal 126 with the HTV silicone rubber layer 127. I am using one.

In the fixing device having such a structure, when the transfer material P such as paper is conveyed, the fixing roller 51 and the pressure roller 52 rotate at a constant speed, and in the case of general paper, the same 133 mm as the main body. When the transfer material P passes through between the fixing roller 51 and the pressure roller 52, the surface of the fixing roller 51 is coated with silicone oil as a release agent. The unfixed toner image on the surface of the transfer material is melted and fixed by being pressed and heated by pressure and temperature, and a full color image is formed on the transfer material P. The transfer material P on which the image has been fixed is separated from the pressure roller 52 by the lower separation claw 68 and discharged out of the apparatus.

As described above, since the fixing roller 51 and the pressure roller 52 continue to rotate while being in pressure contact with each other, when the operation is continued for a long time, the core metal or the entire roller is charged due to rotational friction, which sometimes causes spark discharge. May occur and a malfunction due to this discharge may occur during the image forming operation.

Therefore, conventionally, both or one of the fixing roller 51 and the pressure roller 52 is constructed such that the core metal portion is always electrically grounded.

[0021]

However, in the conventional image forming apparatus, when the unfixed toner image enters the pressure contact portion (hereinafter referred to as a nip portion) between the fixing roller 51 and the pressure roller 52, In some cases, the toner was scattered just before this nip portion. Although the cause of this is not clear, the potential of the entire roller is low because the core metal is grounded as described above, and the force of moving the charged toner to the roller side acts immediately before the nip and may scatter. It is estimated that there is.

Therefore, in order to avoid this phenomenon, it is possible to always leave the roller in a floating state, but in this method, the potential of the roller rises due to friction charging for a long time, and a discharge leak occurs. There was an occasion. Also,
If the roller is excessively charged, a large difference is again generated between the potential of the roller and the charge (potential) of the toner, which may cause scattering.

Such a toner scattering phenomenon may be remarkable in the case of the color image forming apparatus as in the above-mentioned conventional example. That is, in the case of a color image forming apparatus, since the unfixed toner image is formed on the transfer material as a plurality of layers of 3 to 4 layers, the repulsive force due to the same charging has already occurred in the toner layer, and When such a difference from the roller potential occurs, scattering may easily occur.

Since a sharp melt (low melting point) toner is used as the color toner because color mixing is required, silicone oil is used in the rubber layer of the fixing roller or the like in order to improve the releasability of the toner. When silicone rubber is used, the silicone rubber is likely to be charged, so that electric charges are likely to be accumulated particularly when the silicone rubber is floated, and discharge leakage is likely to occur.

Further, when the fixing roller and the pressure roller are provided with rubber layers as in the conventional example, the rubbing force at the nip portion is large, and the adhesion is high as the surface property, so that the roller itself is high. The toner may be easily charged, and in this case, it is not preferable to always keep the roller in a floating state because scattering of the toner due to the potential difference of the toner is likely to occur and leak discharge of the roller is likely to occur.

When the fixing roller and the like are always grounded as described above, in the image forming apparatus in which the transfer material is present at the fixing nip and the transfer portion at the same time in the image forming operation, the transfer material is transferred. There were cases where defects were generated.

For example, in the case of A4R paper, A3 paper, or the like, which has a long length in the traveling direction, even if the leading end of the transfer material enters the fixing nip, the trailing end may exist in the transfer portion. At this time, the transfer current or electric charge that is performing the transfer flows to the fixing roller or the like through the transfer material. When the fixing roller or the like is grounded, a transfer current or charge may eventually flow to the ground, resulting in a transfer failure.

This phenomenon is likely to occur when a transfer material having a low resistance value is used, or even when the same transfer material is used, the resistance value of the transfer material decreases at high humidity.

Further, in particular, the transfer device is composed of a transfer brush, a transfer roller, a transfer blade, etc., and the transfer device is brought into contact with the inside of the transfer material carrying sheet and directly injects an electric charge or an electric current to perform the transfer. In such a case, because of the contact, the transfer charge or the current easily flows to the transfer material as described above, and the phenomenon of the transfer being omitted may be particularly likely to occur.

Further, in the same manner as the transfer current and the inflow of the charge, the inflow of the charge occurs due to the separation and charge removal also in the separation charger, and the image is similarly scattered.

Therefore, it is an object of the present invention to provide an image forming apparatus capable of preventing the image from scattering at the fixing portion and preventing the discharge leak of the fixing rotary member such as the fixing roller. .

Another object of the present invention is to provide an image forming apparatus capable of preventing the transfer charge and the transfer current from flowing out from the transfer device.

A further object of the present invention is to provide an image forming apparatus capable of preventing the outflow of charges from the separating charger.

[0034]

According to the first invention of the present application, the above object is achieved by means for forming an unfixed image, a transfer device for transferring the unfixed image to a transfer material, and a transfer device. In an image forming apparatus provided with a fixing rotator for fixing an unfixed image to a transfer material, the fixing rotator can be electrically switched to a grounded state or a chargeable state during an image forming operation. Achieved by

Further, according to the second invention of the present application,
The above object can be achieved by the unfixed image being a color image having a plurality of layers in the first invention.

Further, according to the third invention of the present application, the above object can be achieved by the contact transfer device in the first invention.

According to the fourth aspect of the present invention,
The above object is achieved in the above-mentioned first invention, in which the fixing rotator has an elastic layer made of silicone rubber.

Further, according to the fifth invention of the present application, the above object is achieved by the silicone rubber containing the conductive filler in the fourth invention.

According to the sixth invention of the present application,
The above object can be achieved in the first aspect of the present invention, in which the chargeable state is an electrically floating state.

Further, according to the seventh invention of the present application, the above object is achieved in the first invention, wherein the chargeable state is a state in which a high voltage is electrically applied.

According to the eighth invention of the present application,
The above-mentioned object is an image forming apparatus including a unit for forming an unfixed image, a transfer device for transferring the unfixed image to a transfer material, and a fixing rotator for fixing the transferred unfixed image on the transfer material. When the separation charger is not operated, the fixing rotator is electrically grounded, and when the separation charger is operated, the fixing rotator is electrically chargeable. A characteristic image forming apparatus.

That is, in the first aspect of the present invention, when the transfer material having the unfixed image transferred thereon is conveyed to the fixing rotator, the fixing rotator is switched to the chargeable state. The rotating body for fixing rises to an appropriate potential, the potential difference from the unfixed image disappears, and the scattering of the unfixed image does not occur. In addition, when the transfer material is not conveyed to the fixing rotator, the fixing rotator is electrically grounded to prevent an excessive increase in potential and prevent leakage discharge.

Further, in the second invention of the present application, since the unfixed image of the first invention is composed of a plurality of layers as a color image, a repulsive force due to the same charging occurs in the plurality of layers. Therefore, scattering easily occurs, but as in the first aspect of the invention, by switching the fixing rotator to the charged state, the fixing rotator rises to an appropriate potential, and an unfixed image is formed. The potential difference disappears and the unfixed image does not scatter. Therefore, a good color image is formed.

Further, in the third invention of the present application, since the transfer device of the first invention is a contact type transfer device, when the fixing rotator is electrically grounded, the transfer is performed. Although a charge or transfer current easily flows to the fixing rotator to cause a transfer failure, such a transfer failure is prevented by making the fixing rotator chargeable at the time of transfer as in the first aspect of the invention. .

Further, in the fourth invention of the present application, since the fixing rotator of the first invention has the elastic layer made of silicone rubber, it is easily charged and the fixing rotator is floated. At this time, electric charge is particularly likely to be accumulated and discharge leakage is likely to occur. However, as in the first aspect of the invention, the fixing rotator is made chargeable only during the fixing operation, and in other cases, the fixing rotator is used. By electrically grounding the body, excessive charging of the elastic layer made of silicone rubber is suppressed. Therefore, it is possible to obtain good releasability from the low melting point toner while suppressing the scattering of unfixed images and the transfer failure.

Further, in the fifth invention of the present application, since the silicone rubber of the fourth invention contains a conductive filler, generally, the insulating silicone rubber should have a low resistance. It makes it easy to control the electric potential of the roller and prevents extreme charge-up at the time of float.
When grounded, the potential and electric field decay faster, and leak discharge is reliably prevented.

Further, in the sixth invention of the present application, since the chargeable state of the first invention is an electrically floating state, scattering of an unfixed image and transfer failure are caused by a simple structure. prevent.

Further, in the seventh invention of the present application, the chargeable state of the first invention is a state in which a high voltage is electrically applied, and therefore the unfixed image is more reliably scattered and scattered. Prevent transfer failure.

In the eighth aspect of the present invention, when the separation charger is not operated, the fixing rotator is electrically grounded to prevent the occurrence of leak discharge, and the separation charger is operated. At this time, the fixing rotator is electrically charged so that the electric charge from the separating charger does not flow to the fixing rotator, thereby preventing the image from scattering.

[0050]

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

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIG. The image forming apparatus of the present embodiment is common to the conventional image forming apparatus shown in FIGS. 4 and 5 except for the points described in detail below, and the common portions will be denoted by the same reference numerals and will not be described. Omit it.

In this embodiment, as shown in FIG. 1, an electrical connection control device (hereinafter referred to as a switch) a for the fixing rotary member is provided, and as shown in FIG. The fixing roller 51 and the pressure roller 52 as
Electrical connection is made. In other words, if the switch a is in the e direction, both rollers will be grounded,
The float state is set in the f direction.

Then, control is performed so that the switch a is tilted in the f direction while the transfer material P is being supplied, and is tilted in the e direction at other times. This control may be automatically performed in accordance with the image forming operation timing by a conventionally known remote switch, for example.

As described above, when the unfixed toner t enters the nip, the fixing roller 51 and the pressure roller 52 are in a floating state, so that the potential rises to an appropriate level and the potential difference from the toner image is increased. No longer occurs, and toner scattering does not occur. Moreover, no leak discharge occurred. This is because the time during which the float state is controlled is short and the potential state remains at an appropriate level.

When the transfer material P is not supplied,
By fixing the fixing roller 51 and the pressure roller 52 to the grounded state, an excessive increase in potential was eliminated, leak discharge and the like were not generated, and malfunction of the image forming apparatus was eliminated.

As the material of the silicone rubber of the fixing roller 51 of this embodiment, a material which is charged to the negative side as a result of frictional charging with the pressure roller 52 is selected. This is because the toner has a negative polarity in this embodiment.

As described above, in order to charge the surface layer of the fixing roller to the negative side, the material of the fixing roller may be appropriately selected in combination with the material of the pressure roller within a conventionally known range.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

This embodiment is different from the first embodiment in that the control shown in the first embodiment is applied to an image forming apparatus using a contact type transfer apparatus as a transfer apparatus in the image forming apparatus. is there.

In this embodiment, particularly as shown in FIG.
A transfer brush 80 was used as a contact type transfer device. In FIG. 2, 5f is a transfer material carrying sheet, 81 is a transfer brush made of rayon, 82 is a backup member for preventing the settling of the transfer brush 81 made of resin, 83 is an electric field regulating sheet for regulating an electric field, and 84 is a transfer brush 81. It is a high voltage power supply that applies a high voltage to.

In such an image forming apparatus, by performing the control of the first embodiment, in addition to the effects of the first embodiment, the transfer current and the transfer charge do not flow into the fixing device, and in any case. However, there are no cases where transfer defects occur.

(Third Embodiment) Next, a third embodiment of the present invention will be described. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the conventional image forming apparatus, the separating charger 5h does not always operate when the transfer material is separated, but the operating state changes depending on the external environment. That is, the discharge is performed only when the humidity is low and peeling discharge is likely to occur, and the discharge is not performed when the humidity is high and the same phenomenon is unlikely to occur. As a guide, the boundary has a humidity of about 50%.

Therefore, in this embodiment, the grounding state and the floating state of the fixing rotator are controlled in accordance with the operation of the separating charger 5h.

That is, in the environment in which the separating charger 5h operates, the transfer material P is floated when passing through the nip, and in the environment in which the separating charger 5h does not operate, the earthing state is controlled. .

As described above, in this embodiment, in addition to the effects of the first embodiment, when the separation charger operates, the charge from the separation charger does not flow to the fixing rotator, and the image The problems such as splattering have disappeared.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the present embodiment, 20 parts of the conductive filler is mixed in the LTV silicone rubber 124 on the surface layer of the fixing roller 51 to provide low resistance due to the insulating property which is a characteristic of general silicone rubber.

When the operation of the first to third embodiments is carried out using such a roller, the potential control of the roller becomes more preferable, and the extreme roll charge-up at the time of float can be prevented. , When it is dropped to the ground, the potential and electric field decay faster, and the effect is greater.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described with reference to FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, as shown in FIG. 3, a high voltage power source 85 capable of applying a high voltage to the core metal of the fixing rotator is provided in the first embodiment, and a drive circuit (not shown) is provided. The switching of the application was performed by).

That is, when the high voltage power supply 85 is turned on, a high voltage is applied to the roller and the high voltage power supply 85 is turned off.
When in the state, the core has a circuit configuration in which the core falls to the ground. In this embodiment, since the toner has a negative polarity, a negative high voltage was applied.

In such a structure, when the core metal is floated in the first to fourth embodiments, the high voltage power supply 85 must be turned on and grounded in this embodiment. When there is a high voltage power 85
Was controlled to be turned off.

With the above structure, the same effects as those of the first to fourth embodiments can be obtained.

In each of the above-described embodiments, the case where the transfer brush is used as the transfer device has been described, but the same effect can be obtained when other contact type transfer devices such as blades and rollers are used.

As an example of the method for grounding the fixing rotary member, a core metal is used. However, such a method may be performed by contacting and rubbing a conventionally known carbon rubbing contact with the core metal. A method can be adopted, or a method in which a brush or the like on the surface of the roller is brought into contact with the surface to ground the roller can be adopted.

Further, the surface rubber material was made conductive by the carbon filler, but other known materials such as iron oxide may be used.

Further, the timing at which the fixing rotator is charged, that is, in the so-called float state, or when the high voltage is applied, is set to the timing when the nip passage or the separation charger is turned on. Instead, it is preferable to control ON / OFF with a margin in the front / rear direction.

Further, although the chargeable state and the grounding are performed simultaneously with the upper and lower rollers, the upper side may be controlled especially in the case of one-sided copying.

The high voltage application level to the fixing rotary member depends on the image forming apparatus used. That is, the final potential of the toner on the transfer material depends on the apparatus depending on the transfer conditions and the like. Therefore, the output value to be appropriately applied is determined by each device, but preferably regardless of polarity,
The range of 1 kV to 10 kV is preferable.

[0081]

As described above, the first embodiment according to the present application is described.
According to the invention, when the transfer material on which the unfixed image is transferred is conveyed to the fixing rotator, the fixing rotator is switched to the chargeable state, so that the fixing rotator has an appropriate potential. It is possible to raise the temperature and prevent the unfixed image from scattering.
If the transfer material is not conveyed to the fixing rotator,
By electrically setting the fixing rotator to the grounded state, an excessive increase in potential is eliminated, and the occurrence of leak discharge can be prevented.

According to the second invention of the present application,
Since the unfixed image of the first invention is composed of a plurality of layers as color images, the repulsive force due to the same charging is generated in the plurality of layers, so that scattering easily occurs,
As in the first aspect of the present invention, by switching the fixing rotator to the charged state, the fixing rotator can be raised to an appropriate potential, and it is possible to prevent scattering of unfixed images and to form a good color image. Can be done.

Further, according to the third invention of the present application, since the transfer device of the first invention is a contact type transfer device, when the fixing rotator is electrically grounded, Although transfer charge or transfer current easily flows to the fixing rotator to cause transfer failure, the transfer deficiency is prevented by making the fixing rotator chargeable during transfer as in the first aspect of the invention. be able to.

According to the fourth invention of the present application,
Since the fixing rotator according to the first aspect of the invention has the elastic layer made of silicone rubber, it is easily charged, and when the fixing rotator is floated, electric charge is particularly likely to accumulate and discharge leak is likely to occur. As in the first aspect of the invention, the fixing rotator is made of a silicone rubber by setting the fixing rotator to a chargeable state only during the fixing operation, and otherwise making the fixing rotator electrically grounded. It is possible to obtain an excellent releasability for a toner having a low melting point while suppressing excessive charging of the elastic layer, suppressing scattering of unfixed images and transfer failure.

Further, according to the fifth invention of the present application, since the silicone rubber of the fourth invention contains a conductive filler, generally, the insulating silicone rubber is made to have a low resistance. Therefore, it is possible to easily control the potential of the roller, prevent an extreme charge-up at the time of float, and accelerate the decay of the potential and the electric field in the grounded state, so that the leak discharge can be surely prevented.

According to the sixth invention of the present application,
Since the chargeable state of the first aspect of the invention is an electrically floating state, it is possible to prevent scattering of unfixed images and transfer defects with a simple configuration.

Further, according to the seventh invention of the present application, since the chargeable state of the first invention is a state in which a high voltage is electrically applied, the unfixed image is more reliably scattered. In addition, transfer failure can be prevented.

According to the eighth invention of the present application,
When the separation charger is not operated, the fixing rotator is electrically grounded to prevent leak discharge.When the separation charger is operated, the fixing rotator is electrically chargeable. By doing so, the charge from the separation charger does not flow to the fixing rotator, and it is possible to prevent the image from scattering.

[Brief description of drawings]

FIG. 1 is a diagram showing a fixing device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a transfer brush according to a second embodiment of the present invention.

FIG. 3 illustrates a fixing device according to a fifth exemplary embodiment of the present invention.

FIG. 4 is a diagram showing a color image forming apparatus in a conventional example.

FIG. 5 is a diagram showing a fixing device in a conventional example.

[Explanation of symbols]

 5 Transfer Device 51 Fixing Roller (Rotating Body for Fixing) 52 Pressure Roller (Rotating Body for Fixing) 5h Separation Charger 80 Transfer Brush (Contact Type Transfer Device) 122, 123, 127 Silicone Rubber Layer (Elastic Layer) P Transfer Material t Unfixed toner (unfixed image)

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Jiro Ishizuka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. An image forming apparatus comprising: a unit for forming an unfixed image; a transfer device for transferring the unfixed image to a transfer material; and a fixing rotator for fixing the transferred unfixed image on the transfer material. In the image forming apparatus, the fixing rotator can be electrically switched to a grounded state or a chargeable state during an image forming operation. 2. The image forming apparatus according to claim 1, wherein the unfixed image is a color image including a plurality of layers. 3. The image forming apparatus according to claim 1, wherein the transfer device is a contact type transfer device. 4. The image forming apparatus according to claim 1, wherein the fixing rotator has an elastic layer made of silicone rubber. 5. The image forming apparatus according to claim 4, wherein the silicone rubber contains a conductive filler. 6. The image forming apparatus according to claim 1, wherein the chargeable state is an electrically floating state. 7. The image forming apparatus according to claim 1, wherein the chargeable state is a state in which a high voltage is electrically applied. 8. An image forming apparatus comprising: a unit for forming an unfixed image, a transfer device for transferring the unfixed image to a transfer material, and a fixing rotator for fixing the transferred unfixed image on the transfer material. In the apparatus, the fixing rotator is electrically grounded when the separation charger is not operated, and the fixing rotator is electrically chargeable when the separation charger is operated. An image forming apparatus characterized by.