JP2985486B2 - Transfer device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic recording system, such as a copying machine, a printer, and a facsimile, and more particularly to a transfer device.

[0002]

2. Description of the Related Art In recent years, personal use of image forming apparatuses using an electrophotographic recording system, particularly printers and facsimile machines, has been progressing with the miniaturization of terminal equipment and the development of telephone communication networks. The transfer device, which is one of the sub-processes of the electrophotographic recording method, greatly affects the image quality.Developing an image forming device for personal use, there is almost no generation of ozone, and it is easy to reduce the size of the machine. Items, etc. are required.

As a transfer device suitable for the above-described image forming apparatus, there is a bias roller transfer device. This method uses a small amount of transfer current and generates almost no ozone due to discharge, does not require a high-voltage power supply as compared with the conventionally used corona transfer method, and transfers a recording medium while pressing it onto an image carrier. There are advantages such as obtaining a quality image. Hereinafter, an example of the above-described conventional bias roller transfer device will be described with reference to the drawings.

FIG. 6 is a sectional view of a transfer roller installed in a bias roller transfer device. The transfer roller 10 is manufactured by dispersing a conductive filler 10a in an insulating elastomer material 10b so that the volume resistance becomes a predetermined value and fixing the conductive filler 10a to a rotating shaft 10c. When such a filler-dispersed material is used, the volume resistance of the transfer roller 1 depends on the structure of the conductive filler 10a dispersed therein. It has the advantage of not fluctuating.

FIG. 7 shows the configuration of an image forming apparatus provided with a bias roller transfer device. In FIG.
Reference numeral 2 denotes an image carrier having a photoconductive film 2b formed on a conductive base material 2a, reference numeral 11 denotes a main charger, reference numeral 12 denotes an exposure device, and reference numeral 13 denotes a developing device provided with a developing roller 13a. Reference numeral 10 denotes a transfer roller having the above configuration, 5 denotes a power supply for applying a voltage to the transfer roller 10, and 3 denotes a transfer material. 14 is a fixing device, and 7
Is a cleaning member.

The operation of the image forming apparatus configured as described above will be described below.

First, after the surface of the image carrier 2 is uniformly negatively charged by the main charger 11, image exposure is performed by the exposure device 12, so that the surface potential of the image carrier at the exposure portion is reduced.
An electrostatic latent image is formed. When the electrostatic latent image reaches the developing site where the developing device 13 is disposed, a negative voltage is applied to the developing roller 13a to supply negatively charged toner to the surface of the image carrier 2, so that the toner adheres to the exposed portion. Thus, a toner image is formed.

When the toner image formed on the image carrier 2 reaches the transfer portion where the transfer roller 10 is disposed, a positive charge is supplied from the transfer roller 10 to the back surface of the transfer material 3 by the voltage applied from the power supply 5. . By the action of the electric field formed by the positive charges, electrostatic attraction acts on the toner image toward the transfer roller 10, and the toner image is transferred to the surface of the transfer material 3.

The toner image transferred to the surface of the transfer material 3 is conveyed to a fixing device 14 and fixed on the surface of the transfer material 3. Further, the toner remaining on the surface of the image carrier 2 is
And the surface of the image carrier 2 moves to the next image forming step.

[0010]

However, the above-described conventional configuration has a problem that the control of the voltage or current applied to the transfer roller becomes complicated. The reason is described below.

One of the factors that complicate the voltage or current control is a phenomenon called a transfer memory that occurs remarkably in a low-temperature and low-humidity environment. Transfer memory is Paschen
This is a phenomenon in which the image carrier drum is positively charged by the transfer roller when paper is not passed due to the air discharge phenomenon based on the curve. Therefore, the negative charging of the image carrier by the main charger is not sufficiently performed,
Since the development is performed in a state where the surface potential of the image carrier in the non-image area is lowered, the background fog is easily generated. Therefore, a high-quality image cannot be obtained in a low-temperature and low-humidity environment, and when the applied voltage is reduced in a low-temperature and low-humidity environment in order to prevent a transfer memory, transfer efficiency is reduced.

As a means for preventing the transfer memory, a method of reducing the amount of dispersed conductive filler and increasing the volume resistance of the transfer roller to make it difficult to generate air discharge is considered. However, when the resistance of the transfer roller is increased, the amount of electric charge supplied to the back surface of the transfer material is reduced in a normal temperature, normal humidity, and a high temperature and high humidity environment. In this case, a void electric field cannot be formed, and the transfer efficiency is lowered.

Therefore, it is necessary to take measures for preventing the transfer memory by controlling the voltage or the current. That is, a method of applying a voltage lower than that at the time of transfer or a voltage of the opposite polarity to the transfer roller during non-sheet passing (for example, Japanese Patent Application Laid-Open No. 2-264278).
JP, JP-A-2-264279, JP-A-2-3
However, voltage control as described above must be performed even during continuous paper feeding, and complicated applied voltage control must be performed.

The second reason is cleaning of the transfer roller. In the case of insufficient cleaning of the surface of the image carrier or transfer with a small paper size such as a postcard or business card, in the roller transfer method in which the image carrier drum is always in contact, the toner on the surface of the image carrier is transferred to the transfer roller. To the side of the transfer material, which causes the back surface of the transfer material to be stained. Therefore, it is necessary to clean the transfer roller by some method. However, when a transfer roller cleaning mechanism having a scraper, a felt, a web, and a toner scraping means and a waste toner box is provided, the configuration of the transfer device becomes large, and thus it is not suitable for downsizing the image forming apparatus.

Accordingly, in the configuration without the transfer roller cleaning mechanism as shown in FIG. 4, a voltage having the same polarity as the charged toner is applied during non-transfer, and the toner adhering to the transfer roller is transferred to the image carrier side. Then, there is a method of cleaning the transfer roller (see, for example,
No. 247781), which also has a problem that the applied voltage control is complicated.

In view of the above problems, the present invention provides a transfer device which does not require complicated applied voltage or current control and which does not cause fog by a transfer memory even in a low-temperature and low-humidity environment, and which can obtain a high-quality image. Things.

[0017]

In order to solve the above-mentioned problems, a transfer device according to the present invention includes a transfer unit that comes into contact with an image carrier that carries a toner image, and the transfer unit is provided with a hydrophilic side chain. conductivity and is characterized in Rukoto which have a elastomer that will be imparted by sexual functional group attached water molecules.

Further, the transfer means is constituted by a member made of a conductive urethane elastomer.

[0019]

[0020]

[0021]

According to the present invention, the transfer means comprises a hydrophilic side chain.
Conductivity is imparted by the attachment of water molecules to functional groups
Because it has an elastomer , even when the humidity changes,
The amount of charge supplied to the back surface of the transfer material or the surface of the image carrier is adjusted by the moisture-sensitive action of the conductive elastomer. Accordingly, in a low-temperature and low-humidity environment, discharge from the transfer unit to the surface of the image carrier is suppressed, so that a transfer memory can be prevented.

[0022]

[0023] Namely, the present invention is the configuration described above, without using a complex voltage or current control for generating prevent the transfer memory can be obtained a high-quality image.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A transfer apparatus according to one embodiment of the present invention will be described below.
This will be described with reference to the drawings.

FIG. 1 shows an embodiment of an image forming apparatus provided with the transfer device of the present invention. Reference numeral 1 denotes a transfer unit, and a conductive elastomer 1a having a hydrophilic functional group in a side chain is fixed to a rotating shaft 1b. In the conventional filler-dispersed transfer means, the structure of the conductive filler dispersed in the insulating elastomer is used as the conductive path. However, the conductive elastomer 1a has water molecules attached to the hydrophilic functional group in the side chain. It becomes a conductive path. Therefore, when the amount of water molecules attached increases, the volume resistance of the conductive elastomer 1a decreases, and when the amount of water molecules attached decreases, the resistance of the conductive elastomer 1a increases. This means that the volume resistance of the conductive elastomer 1a changes depending on the external humidity. That is, the volume resistance of the conductive elastomer 1a increases at high humidity and decreases at low humidity.

By utilizing the moisture-sensitive action of the above-mentioned conductive elastomer 1a for the transfer means, it is possible to prevent a transfer memory which is remarkably generated in a low-temperature and low-humidity environment. Because at low humidity, the volume resistance of the transfer means increases,
This is because even if a transfer voltage is applied during non-sheet passing, the amount of charge supplied to the surface of the transfer unit is reduced, and discharge from the transfer unit to the image carrier is suppressed. Further, in a normal temperature, normal humidity, high temperature and high humidity environment, the transfer means absorbs moisture and has a low volume resistance, so that a high quality image can be obtained without reducing the amount of charge supplied to the back surface of the transfer material.

Reference numeral 11 denotes a main charger, which has a roller shape in the figure, but may use a corona charger, a fur brush or the like. Reference numeral 2 denotes an image carrier in which a photoconductive film 2b is formed on a weakly magnetic and conductive base material 2a such as aluminum or a polymer material coated with a conductive layer. The photoconductive film 2b includes selenium, an organic photoconductor, amorphous silicon, and the like. However, the organic photoconductor is advantageous because it is easy to manufacture and inexpensive. The image carrier 2 is in contact with the transfer means 1 via the transfer material 3 at least at the time of transfer to form a nip portion, and the nip portion is a transfer portion. Reference numeral 4 denotes a magnetic toner. Reference numeral 5 denotes a voltage power supply applied to the transfer unit 1. Reference numeral 6 denotes a magnet which moves to 6a during non-transfer. Although the magnet 6 at the time of transfer is shown at a position facing the developing device 13 in FIG. 1, it may be placed at any position as long as the toner image formed on the image carrier 2 is not deteriorated. There is no problem in a region where toner does not exist on the body 2, that is, a region from downstream of the cleaning member 7 to upstream of the developing device 13. Further, even when the cleaning member 7 has deteriorated and cleaning failure has occurred, the residual toner on the image carrier 2 after transfer is arranged at the contact portion between the cleaning member 7 and the image carrier 2 so as not to transfer to the charged portion. Is also good.

The operation of the transfer device configured as described above will be described below with reference to FIGS.

The operation at the time of transfer will be described with reference to FIG. As soon as the toner image formed by the magnetic toner 4 formed on the image carrier 2 reaches the transfer site, the transfer member 3 is transported to the transfer site. At the same time, a constant voltage is applied to the transfer unit 1 by the power supply 5 to form an electric field at the transfer site by the electric charge supplied from the transfer unit 1 to the back surface of the transfer material 3, and the electric field is transferred to the toner image by the action of the electric field. An electrostatic attractive force acts in the direction of the unit 1 to transfer from the image carrier 1 to the surface of the transfer material 4. The magnetic toner 4 remaining on the surface of the image carrier 2 is removed by the cleaning member 7.

Next, the operation during non-transfer will be described with reference to FIG. The magnetic toner 4 adheres to the surface of the transfer unit 1 due to poor cleaning of the surface of the image carrier or a change in the size of the transfer material 3. At the time of non-transfer, the magnet 6 is moved to the position 6a facing the transfer unit 1 via the image carrier 2, and the voltage applied to the transfer unit 1 is set to 0V. For this reason, the magnetic toner 4 on the transfer unit 3 receives a magnetic force toward the image carrier 2 by the action of the magnetic field formed by the magnet 6 a and is transferred to the surface of the image carrier 2, thereby cleaning the transfer unit 1. . The magnetic toner 4 transferred to the surface of the image carrier 2 is removed by the cleaning member 7.

FIG. 3 is an operation diagram at the time of non-transfer when the electromagnet is used as the second embodiment. An electromagnet 8 in which a coil 8b is wound around a ferromagnetic material 8a such as iron or nickel.
Is disposed at a position facing the transfer unit 1 via the image carrier 2. The other peripheral configuration is the same as that of FIG. At the time of non-transfer, a magnetic field is formed by applying a voltage to the coil
To the image carrier 1 side. According to this configuration, without moving the magnet 6 as shown in FIGS.
The transfer unit 1 can be cleaned only by applying a voltage to the electromagnet 8.

Hereinafter, the results using a transfer roller made of a material having a moisture-sensing effect will be shown in Examples, and the results using a transfer roller made of a filler-dispersed material will be shown in Comparative Examples.

Example 1 A transfer roller in which a foam of a conductive urethane elastomer was fixed on a rotary shaft of φ6 mm with dimensions of 16.7 mm in length and 216 mm in length was prepared.
Was incorporated in the image forming apparatus having the configuration shown in FIG. The hardness of the transfer roller is preferably 45 ° (JIS A) or less, and more preferably 35 ° or less. If it is more than the above range, the nip width with the image carrier becomes short, and the running stability of the transfer material is impaired. The pressing force of the transfer roller against the image carrier is 5
00 to 1500 gr is good, and preferably 700 to 100 gr.
0 gr is good. In the low-hardness foam as described above, since the deflection in the circumferential direction of the transfer roller occurs about 0.1 to 0.3 mm, if the pressing force is smaller than the above range, the uneven pressing force in the circumferential direction of the transfer roller occurs. 1. Uniform transfer cannot be performed on one sheet of paper. If the pressing force is above the above range, the adhesive force of the toner to the transfer roller side becomes strong, and it becomes difficult to clean the transfer roller. Here, a transfer roller having a hardness of 31 ° was used, and the pressing force against the image carrier was set to 1000 gr.

High temperature and high humidity (33 ° C./85% RH), normal temperature and normal humidity (20 ° C./50% RH), low temperature and low humidity (7 ° C./20% RH)
In the three environments H), a halftone was output on plain paper at a process speed of 24 mm / sec. Trek 610C was used as a high voltage power supply, and a transfer voltage was applied to the transfer roller from the start of the process operation to the stop thereof. The transfer current flowing at that time was output from the monitor output of the high-voltage power supply to the pen recorder. The output halftone image was measured for image density using a densitometer (MACBETH RD914), and a range in which transfer efficiency was sufficiently high was obtained. Further, a halftone image was observed with a loupe, and a range without toner scattering or transfer memory was obtained. An image within the above-mentioned range was determined as a high quality image.

FIG. 4 shows the VI characteristics measured under the above conditions. The shaded area in the figure is an area where the transfer efficiency is sufficiently high and a high quality image without toner scattering or transfer memory is obtained. As is apparent from this figure, the resistance of the transfer roller was increased in a low-temperature and low-humidity environment, and a high-quality image free of transfer memory was obtained. Further, from this figure, it was found that the high-quality image area spreads in the horizontal direction, and that a high-quality image can be obtained by applying a constant current under each environment. Then, when a constant current of about 1.7 μA was applied under each environment, it was confirmed that a high quality image could be obtained under any environment. Therefore, the power supply 5 shown in FIG.
May be a constant current power supply. Rather, the constant current power supply can be set to a fixed amount of current regardless of the environment, so that voltage adjustment when the environment changes does not need to be performed.

(Comparative Example) A transfer roller was prepared by dispersing carbon black in EPDM foamed rubber on a rotating shaft and fixed on the rotating shaft, and the same experiment as in the above example was performed.
Other than the material of the transfer roller, the settings are the same as above.

FIG. 5 shows the VI characteristics at this time. As is apparent from this figure, although the change in volume resistance of the transfer roller due to the environment is small, fog due to the transfer memory occurred in a low-temperature and low-humidity environment, and a high-quality image was not obtained.

In the embodiment, the transfer means is a sponge roller, but may be a solid one. Although the transfer means has a roller shape, the transfer means may be a belt shape or a member covering the roller with a belt. Although the toner is a magnetic toner, a non-magnetic toner may of course be used in the case where cleaning of the transfer unit using a magnetic force is not performed.

[0039]

As is evident from the foregoing description, the present invention is by there use a transfer means having a <br/> elastomer conductivity Ru is imparted by adhesion of moisture child hydrophilic functional group in the side chain, without complicated applied voltage or current control for the transfer memory prevention, pear quality images of the environment-dependent resistance.

[Brief description of the drawings]

FIG. 1 is a side view of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a side view of the image forming apparatus for explaining operation during non-transfer in the embodiment.

FIG. 3 is a side view of an image forming apparatus for explaining an operation according to a second embodiment of the present invention;

FIG. 4 is a graph showing VI characteristics of a transfer roller according to the embodiment of the present invention.

FIG. 5 is a graph showing VI characteristics of a transfer roller in a comparative example of the present invention.

FIG. 6 is a cross-sectional view of a known transfer roller.

FIG. 7 is a side view of a known image forming apparatus.

[Explanation of symbols]

 15 Power supply for main charger 16 Power supply for developing roller

Claims (2)

(57) [Claims] An image bearing member that carries a toner image is provided with a transfer unit, and the transfer unit includes a hydrophilic functional group in a side chain.
Transfer apparatus according to claim Rukoto which have a gill <br/> Sutoma the conductivity Ru is imparted by the water molecules adhere to. 2. A transfer means transfer apparatus according to claim 1, wherein the is composed of members made of a conductive urethane elastomer.