JP2000214698A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a uniform and stable transfer by preventing generation of a memory on a photoreceptor drum and cleaning failure, making greater the possible size of recording material to be utilized and controlling transfer current according to the difference in resistance value of a transfer belt and the size of the transfer material. SOLUTION: In this image forming device, a transfer blade unit is constituted from a transfer blade 24, pushing up members 25 that is divided into 3 parts (251, 252, 253), and solenoids 26 (261, 262, 263) making the pushing up members 25 operate. The width size of the recording material is detected, only the part corresponding to that width is pushed up and appropriate transfer current is applied.

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, a facsimile, and a printer for obtaining a hard copy by forming an image on a recording material using an electrophotographic method.

[0002]

2. Description of the Related Art Conventionally, a plurality of image forming units are provided, each of which forms a toner image of a different color, and the toner images are sequentially superimposed on the same recording material and transferred to form a color image. Various image forming apparatuses have been proposed.

Under such circumstances, an electrophotographic color image forming apparatus using an endless recording material conveying means has been used for high-speed recording.

An example of the above color image forming apparatus will be described with reference to FIG. In the image forming apparatus, first, second, third, and fourth image forming units Pa, Pb, Pc, and Pd are arranged side by side, and toner images of different colors are latent images, developed, and transferred. Formed.

Each of the image forming units Pa to Pd includes a dedicated image carrier, in this example, an electrophotographic photosensitive drum (hereinafter, simply referred to as "photosensitive drum") 3a, 3b, 3c, 3d. To 3d, a toner image of each color is formed. A recording material conveying means (hereinafter, referred to as a “transfer belt”) 130 is provided adjacent to each of the photosensitive drums 3a to 3d, and is transferred onto a recording material P carried and conveyed on the photosensitive drums 3a to 3d. Further, the recording material P on which the toner images of the respective colors have been transferred is heated and pressed to fix the toner images in the fixing unit 9, and then discharged out of the apparatus as a recorded image.

Exposure lamps 111a, 111b, and 111 are provided on the outer circumference of the photosensitive drums 3a, 3b, 3c, and 3d, respectively.
c, 111d, drum chargers 2a, 2b, 2c, 2d,
Potential sensors 113a, 113b, 113c, 113d,
Developing devices 1a, 1b, 1c, 1d, transfer chargers 24a, 24b, 24c, 24d as charge supply means, and cleaners 4a, 4b, 4c, 4d are provided, and a light source device (not shown) is provided above the device. And polygon mirror 11
7 are installed.

Laser light emitted from the light source device is scanned by rotating the polygon mirror 117, the light beam of the scanning light is deflected by the reflection mirror, and is condensed on the generatrix of the photosensitive drums 3a to 3d by the fθ lens. By performing the exposure, a latent image corresponding to the image signal is formed on the photosensitive drums 3a to 3d.

The developing devices 1a to 1d are filled with a predetermined amount of cyan, magenta, yellow and black toners, respectively, as a developer by a supply device (not shown). The developing devices 1a to 1d are respectively provided with the photosensitive drums 3a to 3d.
The latent image on d is developed and visualized as a cyan toner image, a magenta toner image, a yellow toner image, and a black toner image.

The recording material P is accommodated in a recording material cassette 10, is supplied to the transfer belt 130 through a plurality of transport rollers 11 and registration rollers 12, and faces the photosensitive drums 3a to 3d by the transport by the transfer belt 130. It is sequentially sent to the transfer unit.

The transfer belt 130 is made of a dielectric resin sheet such as a polyethylene terephthalate resin (PET resin), a polyvinylidene fluoride resin sheet, or a polyurethane resin sheet. A shaped or seamless (seamless) belt is used, and is stretched around the driving roller 13 and the driven rollers 14 and 15.

When the transfer belt 130 is rotated by the driving roller 13 and is confirmed to be at a predetermined position, the recording material P is transferred from the registration roller 12 to the transfer belt 13.
0, and the recording material P is conveyed toward the transfer unit of the first image forming unit Pa. At the same time, the image write signal is turned on, and the first
An image is formed on the photosensitive drum 3a of the image forming unit Pa. Then, the transfer charger 24a applies an electric field or electric charge at the lower transfer section of the photosensitive drum 3a, so that the first color toner image formed on the photosensitive drum 3a is transferred onto the recording material P.

As the transfer charger 24, a contact charger using a transfer charging member such as a blade, a roller, or a brush is used.
With a contact charger, ozone-less, resistant to temperature and humidity environmental fluctuations,
There are advantages such as high image quality. In addition, static elimination needles 7a to 7d may be provided for stabilizing transferability. Static elimination needles 7a to 7
Although d is not in contact with the transfer belt 130, it plays a role of discharging and releasing part of the transfer current. With this configuration, it is possible to prevent discharge due to uneven charging after the photosensitive drum and the recording paper are separated.

Image formation and transfer in the second to fourth image forming units Pb to Pd are performed in the same manner as in the first image forming unit Pa. Next, the recording material P to which the four color toner images have been transferred is separated from the end of the transfer belt 130 by removing the charge by the separation charger 32 and attenuating the electrostatic attraction force in the downstream portion of the transfer belt 130 in the transport direction. .

Particularly, in a low-humidity environment, the recording material dries and the electrical resistance increases, so that the electrostatic attraction force with the transfer belt 130 increases, and the effect of the separation charger 32 increases. Usually, the separation charger 32 charges the recording material P in a state where the toner image is not fixed, so that a non-contact charger is used.

Recording material P detached from transfer belt 130
Is transferred to the fixing device 9 by the transport unit 62 through the separation guide 64.
Transported to The separation guide 64 stabilizes the leading end behavior of the recording material P.

The fixing device 9 includes a fixing roller 51 and a pressure roller 52, heat-resistant cleaning members 54 and 55 for cleaning the rollers 51 and 52,
52, heaters 56 and 57 installed in 52, an application roller 50 for applying a release agent oil such as dimethyl silicone oil to the fixing roller 51, an oil reservoir 53 thereof,
A thermistor 58 for controlling the fixing temperature for detecting the temperature of the surface of the pressure roller 52.

The recording material P to which the four color toner images have been transferred is
By the fixing, the color mixture of the toner image and the fixation to the recording material P are performed to form a full-color copy image, which is discharged to the discharge tray 63.

The photosensitive drums 3a to 3d after the transfer are completed.
The transfer residual toner is cleaned and removed by each of the cleaners 4a to 4d, and is prepared for the formation of the next latent image.

The toner and other foreign matters remaining on the transfer belt 130 are transferred to the surface of the transfer belt 130 by the cleaning blade 20 and the cleaning web (nonwoven fabric) 19.
To make contact and wipe off.

In the cleaner section, the charge removing roller 2 is provided.
The charges on the transfer belt 130 remaining after the recording material is separated by steps 1 and 22 are eliminated. Therefore, the static elimination roller 21,
22 is grounded.

A structure in which a high voltage of about 2 to 4 kV is applied to the charge removing roller 21 to not only remove the charge from the transfer belt 130 but also charge it to the opposite potential so that the potential of the transfer belt at the end of transfer is reduced. There is also.

The transfer belt 130 used in the image forming apparatus having the above-described structure is a dielectric sheet such as a PET sheet, a polyvinylidene fluoride sheet, or a polyurethane sheet as described above, and has a volume resistance of 10 or more.
Those having ¹³ to 10 ¹⁸ Ωcm are generally used.

It is known that the transfer charging means stabilizes an image when the current contributing at the time of transfer is made constant at an appropriate current.

That is, the volume resistivity is about 10 ⁷ depending on the type (thickness, material, etc.) of the recording material and the conditions of moisture absorption.
It changes to 〜１０10 ¹⁴ Ωcm. Generally, constant current control is performed so that a current necessary for transfer can be obtained even when the resistance value of the recording material changes.

FIG. 6 shows the values of the appropriate transfer current depending on the paper size and the resistivity of the transfer belt (（10 ¹³ Ωcm, 1710 ¹⁷ Ω).
cm), and when A3 size is set as a reference value, when transferred to A4 vertical size paper,
It can be seen that a larger transfer current is required when the transfer current is set large and the transfer is performed on postcard-size paper than when the transfer is performed on A4-size paper. When the transfer current is smaller than the appropriate value, there is a problem that the transfer current is insufficient and transfer failure occurs, and the toner image is easily disturbed when the recording material is separated from the transfer belt. When it is high, there is a problem that the toner is reversely charged at the time of transfer and white spots occur.

Therefore, in view of such conventional problems, it has been proposed to change the transfer current according to the size of the recording material.

[0027]

However, when the control for changing the transfer current according to the size of the recording material is performed as described above, an appropriate transfer current as high as 50 to 70 μA, such as a postcard size, is used. If the value is set, a new problem arises that a memory is generated on the photosensitive drum because an overcurrent flows to the photosensitive drum in the non-sheet passing portion. Further, there is a problem that the amount of toner that causes transfer failure increases, and cleaning failure of the photosensitive drum occurs.

Accordingly, a main object of the present invention is to provide an image forming apparatus using a contact type transfer system which can prevent generation of a memory on an image carrier and defective cleaning.

Another object of the present invention is to make it possible to increase the size of a usable recording material, to control the transfer current according to the difference in the resistance value of the recording material conveying means and the size of the recording material, and to achieve uniform and stable operation. It is an object of the present invention to provide an image forming apparatus using a contact-type transfer system capable of obtaining an improved transfer.

[0030]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier on which an image is formed, a recording material transport unit formed of a dielectric material and capable of contacting the outer peripheral surface of the image carrier, and a charge supply unit for contacting the recording material transport unit to supply a charge; An abutting unit for bringing the charge supply unit into contact with the recording material conveyance unit, wherein the charge supply unit is arranged in a direction orthogonal to a moving direction of the recording material conveyance unit. The image forming apparatus is characterized in that the length of the charge supply unit that contacts the recording material conveyance unit can be changed.

According to one aspect of the present invention, the length of the charge supply unit contacting the recording material transporting unit is changed by partially operating the divided contacting unit. According to the aspect, the charge supply unit is made of an elastic body, and the length of contact with the recording material conveyance unit changes by being deformed.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings. In the following description of the embodiments, the present invention will be described as being embodied in the color image forming apparatus shown in FIG. Therefore, description of the overall configuration and functions of the color image forming apparatus will be omitted. The same members as those described above are denoted by the same reference numerals.

Embodiment 1 A first embodiment of the present invention will be described with reference to FIGS.

The transfer blade unit 124 of the present embodiment
Each of a, 124b, 124c, and 124d includes a transfer blade 24 as a charge supply unit and a push-up member 25 as a contact unit. Since the transfer blade units 124a to 124b have the same structure,
In the following description, the transfer blade unit 124 will be described by omitting the suffix alphabet of each component.

The transfer blade 24 is made of a plate-shaped conductive rubber and has a resistivity of 10 ⁵ to 10 ⁷ Ωcm. Hardness is JIS
-A 40-60 ° is desirable. Push-up member (contact means) 2
Reference numeral 5 denotes a resin made of resin having a thickness of 0.4 to 1 mm.
Are brought into contact with the photosensitive drums 3 respectively.

In the present embodiment, the central portion W1 = 251 is set to 150 m with respect to the thrust width W = 310 mm.
m, and both ends 252 and 253 are represented by W2 = W3 = 80.
mm and divided into three parts.
62 and 263 are operated independently.

More specifically, the lifting member 251,
252, 253 are supported by the support members 271, 272, 273, and the respective support members 271, 272, 27
3 is connected to solenoids 261, 262, 263 by arm members 281, 282, 283, respectively.

In this configuration, the recording material width is 150 mm
If less than the above, the solenoid 261 is operated from the position shown by the dotted line to the position shown by the solid line to push up only the central portion 251 of the lifting member 25. At this time, the transfer blade 2
4 is bent, and only the central portion 251 is
Abuts on the photosensitive drum 3 through both ends 252, 2
53 does not abut.

On the other hand, when the recording material width is 150 mm or more, the solenoids 262 and 263 are further operated from the position shown by the dotted line to the position shown by the solid line, and both ends 252 and 263 are operated.
It operates so as to push up the whole to which 53 has been added. At this time, the central portion 251 and both ends 252 and 253 contact the photosensitive drum 3 via the transfer belt 130.

As described above, although the optimum value of the amount of charge applied to the transfer belt 130 differs depending on the size of the recording material, by detecting the size width of the transfer paper, only the portion corresponding to the width is pushed up. Control to apply the optimum transfer current. That is, in the case of this embodiment, the electric charge is supplied to the conductive portion of the entire width in the case of A3 transfer paper, but the electric charge is supplied using only the central portion 251 of the push-up member 25 in the case of A5 size or less.

As described above, in this embodiment, electric charges are applied to a part of the transfer belt 130 corresponding to the size of the recording material, so that the efficiency of supplying electric charges to the recording material can be increased. When a method in which the lifting member 25 is not divided into a plurality is used, for example, the resistivity is 10
^In the case of the transfer belt 130 of ¹³ Ωcm, the transfer current in the A3 size is about 12 μA, and about 60 μA is necessary for the postcard. This is because the charge flowing into the belt portion outside the width of the recording material must also be taken into consideration.If the transfer current value increases in this way, an overcurrent flows through the photosensitive drum in the non-sheet passing portion. There is a problem that a memory is generated on the photosensitive drum. In addition, there is a problem that the amount of reverse charge of the toner increases and cleaning failure of the photosensitive drum occurs.

However, by adopting a configuration in which the lifting member 25 is divided as in the image forming apparatus of the present embodiment, the effective width of the transfer blade 24 is changed, and the extra width flowing into the transfer belt 130 outside the size width is changed. Since the charge can be suppressed and the charge can be supplied only to the recording material, only the charge required for the transfer is sufficient as the charge supplied from the electrode.

In this embodiment, the lifting member is divided into three parts. However, the present invention is not limited to this. The lifting member may be further divided into five parts or seven parts.

Further, the contact charging means is not limited to the blade,
Similar effects were obtained even when a conductive brush was used.

Embodiment 2 Next, a second embodiment of the present invention will be described with reference to FIGS. In this embodiment, transfer rollers 224a, 224b, 224c, 224d are used instead of the transfer blades 124a, 124b, 124c, 124d of the first embodiment.
Is used. Other configurations and basic operations are the same as those shown in the conventional example.

FIG. 4 shows a transfer roller 224 which is a feature of this embodiment. As shown in FIG.
Reference numeral 241 denotes a columnar shape having a width W1 = 100 mm and both ends 2
242b and 2243 are tapered.

The transfer belt 1 of the transfer roller 224
The abutment nip is changed by changing the abutment pressure of the abutment 30 by appropriate means. This changes the effective width of the transfer charge. For example, if the amount of entry is 5 mm, 300
mm nip and 14 mm when the amount of approach is 1 mm
0 mm.

In accordance with the detected paper size, the amount of transfer roller 224 is controlled so as to obtain an optimum charging width as described above.

Even in such a configuration, since charges are given to a portion corresponding to the size of the recording material, the charges supplied to the recording material can be increased, and extra charges flowing into the transfer belt outside the size width can be removed. Thus, it is possible to supply charges only to the recording material.

[0050]

As is apparent from the above description, according to the image forming apparatus of the present invention, the length of contact of the charge supply means with the recording material conveyance means can be changed, so that the image formation on the image carrier can be performed. The occurrence of memory and cleaning failure can be prevented, so that the size of the usable recording material can be increased, and the transfer current can be controlled in accordance with the difference in the resistance value of the recording material conveying means and the size of the recording material, and the uniformity can be obtained. Stable transfer can be obtained, and good images can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a perspective view illustrating a transfer blade unit according to the first embodiment.

FIG. 3 is a schematic configuration diagram illustrating an image forming apparatus according to a second embodiment of the present invention.

FIG. 4 is a perspective view illustrating a transfer roller according to a second embodiment.

FIG. 5 is a schematic configuration diagram illustrating an example of a conventional image forming apparatus.

FIG. 6 is a graph showing an appropriate transfer current value depending on a paper size with respect to a resistivity of a transfer belt.

[Explanation of symbols]

 Reference Signs List 3 photosensitive drum (image carrier) 24 transfer blade (charge supply means) 25 push-up member (contact means) 130 transfer belt (recording material transport means) 224 transfer roller (charge supply means)

Claims (3)

[Claims] 1. An image carrier on which an image is formed, a recording material transporting unit formed of a dielectric material and capable of contacting an outer peripheral surface of the image carrier, and supplying a charge by contacting the recording material transporting unit. An image having a charge supply unit and an abutting unit for bringing the charge supply unit into contact with the recording material conveyance unit, wherein the charge supply unit is arranged in a direction orthogonal to a moving direction of the recording material conveyance unit. The image forming apparatus according to claim 1, wherein a length of the charge supply unit in contact with the recording material conveying unit is changeable. 2. The image forming apparatus according to claim 1, wherein a length of the charge supply unit contacting the recording material conveying unit is changed by partially operating the divided contact unit. 3. The image forming apparatus according to claim 1, wherein the charge supply unit is made of an elastic material, and a length of the charge supply unit that contacts the recording material conveyance unit is changed by being deformed.