JPH07129000A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an excellent image preventing the irregular transferring by grounding a conductive member and a fixing means through the same resistive element or constant voltage element. CONSTITUTION:In the transfer system that the image receiving paper 10 is nipped between the contact type transferring roller 5 and the photoreceptor 1 while supplying the constant current, the leakage current flows through the image receiving paper 10 to the contact-nip part from the charging guide 7 for guiding the image receiving paper 10 or the fixing unit 9. Particularly under the circumstances of high temperature/high humidity, the resistance of the image receiving paper 10 is reduced, therefore, the phenomena become more conspicuous. In order to evade the above, the charging guide 7 and the fixing unit 9 are grounded through the resistance, however, if the resistance differs, the transfer potential is affected and the irregular transferring in the image is caused. Hence, the excellent image can be obtained by using the same grounding resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a facsimile,
The present invention relates to a printer, and particularly to an image forming apparatus.

[0002]

2. Description of the Related Art In recent years, image forming apparatuses have been shifting from the purpose of office use to personal use, and have been downsized.
There is a demand for a technology that realizes maintenance-free operation. Small printers intended for personal use are expected to be placed in a corner of a desk or used in a general household, and may meet conditions such as maintenance and low ozone emissions. It becomes a point of popularization.

A printing process of an electrophotographic copying machine or printer will be described. First, the photoreceptor is charged to form an image. As a charging method, a corona discharger which has been widely used in the past is used, and in recent years, a photoreceptor is applied by a contact-type charging method in which a conductive roller is directly pressed against the photoreceptor in order to reduce ozone generated. Charge the surface uniformly. After the photoconductor is charged, in the case of a copying machine, the copy original is irradiated with light and the reflected light is irradiated onto the photoconductor through a lens system. Alternatively, in the case of a printer, an image signal is sent to a light emitting diode or a laser diode as an exposure light source to form a latent image on the photoconductor by turning the light ON-OFF. When a latent image (high or low surface potential) is formed on the photosensitive member, the photosensitive member is pre-charged with colored toner (5 μm to 15 μm in diameter).
It is visualized by (μm position). The toner adheres to the surface of the photoconductor according to the level of the surface potential of the photoconductor, and is electrically transferred to the copy sheet. That is, the toner is charged positively or negatively in advance, and a charge having a polarity opposite to the polarity of the toner is applied from the back surface of the copy sheet and is electrically attracted. Up to now, a corona discharger has been widely used as the charge applying method as in the charging method, but in recent years, a transfer device using a conductive roller has been put into practical use in order to reduce ozone generation.

FIG. 2 is a schematic view showing the arrangement of a toner image transfer device disclosed in Japanese Patent Laid-Open No. 2-226282.
In FIG. 2, reference numeral 20 is a transfer roller made of foamed or solid rubber and adjusted to have a volume resistance value of 10 ⁸ to 10 ¹³ Ωcm, 21 is a power supply for applying voltage to the transfer roller, and 22 is a photoconductor. Reference numeral 23 is an image receiving paper (copying paper), 24 is a conductive guide for guiding the image receiving paper to the contact portion between the transfer roller 20 and the photoconductor 22, and 25 is a resistor. The operation of the transfer device configured as described above will be described.

An image is formed on the surface of the photoconductor 22 by the toner described above. Now, it is assumed that the photoconductor 22 has a negative polarity and the toner has a positive polarity. Transfer roller 20
Is in contact with the photoconductor 22 with a predetermined pressing force. Image receiving paper 23
Is supplied to the contact point (nip) between the photoconductor 22 and the transfer roller 20, and is pressed against the photoconductor 22 by the transfer roller 20 to come into contact with the toner. Since a negative voltage opposite to the polarity of the toner is applied to the transfer roller 20 from the power supply device 21, the toner is transferred to the image receiving paper 23. Since the transfer roller 20 is in contact with the image receiving paper 23, the voltage applied from the power source 21 is 1.0 kV to 5.0 kV. Conductive guide 24
Is provided to prevent the toner from flying due to an electric field acting on the image receiving paper before reaching the transfer nip, resulting in an image with a lot of scattering. However, the guide 24
Is grounded via the resistor 25 to prevent inadvertent leakage of current and ensure transfer performance. The image receiving paper 23 to which the toner image is transferred passes through the contact point between the photoconductor 20 and the transfer roller 22 and is conveyed to a fixing unit (not shown).

[0006]

The above-mentioned transfer method has the following problems.

Generally, a developing method installed in a printer or the like uses a reversal developing method in which a photosensitive member is charged, then imagewise exposed, and toner is attached to the exposed portion. In this developing system, since the polarities of the photosensitive member and the toner are the same, an electric field opposite to the toner polarity is applied when the image is transferred onto the image receiving paper. When the transfer electric field acts, the electric field spreads from the image area (toner adhesion) on the photoconductor to the non-image area, resulting in the scattering of the toner. In order to avoid this, a method of increasing the resistance of the transfer roller and increasing the applied voltage is adopted (the horizontal electric field that acts from the image area to the non-image area on the photoconductor is transferred from the photoconductor by the strong electric field). However, the method of applying a constant voltage to the transfer roller cannot completely eliminate the tendency of the electric field to concentrate on the image area, especially the image area, on the photoconductor. Toner scattering does not stop.

[0008]

In order to solve the above problems, the present invention is an image forming apparatus characterized by the following constitution.

The present invention is as follows: 1. A developing unit that forms a developed image on the electrostatic latent image carrier. 2. A conductive electrode for sandwiching the image receiving paper between the electrostatic latent image carrier and the electrostatic latent image carrier. 3. Power supply means for applying a constant current to the conductive electrode, 4. A conductive member for guiding the image receiving paper to the conductive electrode, And a fixing unit composed of at least one conductive electrode for fixing the developed image transferred on the image receiving paper, wherein the conductive member and the fixing unit are provided with the same resistance element or constant voltage element. The image forming apparatus is characterized by being grounded.

Further, in the image forming apparatus, the conductive electrodes are roller-shaped. Or, 1. 1. A developing unit that forms a developed image on the electrostatic latent image carrier. 2. A conductive electrode for sandwiching the image receiving paper between the electrostatic latent image carrier and the electrostatic latent image carrier. 3. Power supply means for applying a constant current to the conductive electrode, 4. A conductive member for guiding the image receiving paper to the conductive electrode, A fixing unit composed of at least one conductive electrode for fixing the developed image transferred on the image receiving paper, wherein the conductive member and the fixing unit have the same resistance or constant voltage element of 200 MΩ or more. The image forming apparatus is characterized in that it is grounded through the image forming apparatus.

Further, in the image forming apparatus, the conductive electrode has a roller shape.

[0012]

As described above, when a developed image obtained by reversal development, which is often used in printers, is transferred to an image receiving paper, a high image quality can be obtained because transfer can be performed by applying a relatively low voltage, so that the contact type A transfer roller is used. There are roughly two methods of applying a voltage to the transfer roller.
One is a constant voltage application method and the other is a constant current application method. The latter constant current application method is superior in that the image is less scattered. The reason for this will be described with reference to the drawings. Figure 3
Is a diagram schematically showing the relationship between the electric potential on the photoconductor and the electric potential at the time of transfer, and the one-dot chain line in the center indicates the 0 V level. Above the center line is plus (voltage applied during transfer), and below is minus (surface potential on the photoconductor). In FIG. 3, the left side shows the case where a constant voltage is applied to the transfer roller, and the right side shows the case where a constant current is applied. When a constant voltage is applied, a constant voltage is applied to the transfer roller, so that a strong electric field is formed between the non-image area of the photoconductor and the toner in the image area also moves due to this electric field. On the other hand, when a constant current is applied, the photoconductor and toner (actually the image receiving paper is also included) are considered as impedance components, so the impedance component of the photoconductor and toner is larger than the photoconductor alone. When a constant current is passed, the voltage becomes higher when toner is present. Therefore, the electric field formed between the transfer roller and the photoconductor becomes larger when toner is present, and the toner is less likely to be scattered to the non-image portion. For the above reason, the toner scattering is smaller when the constant current is applied. However, in the case of applying a constant current, if the resistance of the image receiving paper decreases in a high temperature and high humidity environment, the electric charge escapes through the image receiving paper and the necessary transfer voltage is not applied. In particular, when the environment is 33 ° C. and 80% RH or more, the resistance of the image receiving paper is considerably lowered, and the electric charge leaks from the grounded conductive guide for guiding the image receiving paper or the fixing device having the conductive roller grounded. Therefore, the guide and fuser are grounded via a resistance element or constant voltage element in order to avoid an appropriate charge leak under low temperature and low humidity environment and unnecessary charge leak under high temperature and high humidity environment. To do. In FIG. 4, plain paper (65 g / cm ² ) as an image receiving paper is left in an environment of 33 ° C. and 80% RH for about 2 days, and a voltage applied to the transfer roller when a constant current of about 2 μA is applied to the surface is shown. It is the result measured by the electrometer. The horizontal axis represents the voltage generated during transfer, and conductive guides and fixing devices are used. (A) is a voltage generated during transfer when the guide and the fixing device are grounded via 200 MΩ, and (B) is a transfer voltage when the guide is floated and the fixing device is grounded via a 200 MΩ resistor. This is the voltage generated. The vertical axis represents time, and the image receiving paper passes within the broken line (arrow). The figure shows the state when two sheets have passed. (A) shows a substantially constant voltage of about 350 V while passing through the image receiving paper, while in (B), about 700 V at the portion a and about 250 V at the portion b, the transfer voltage with passage of the image receiving paper. Change. Even in the actual image, the transfer voltage was too high in the portion (a) of (B) to lower the transfer efficiency, and uneven density appeared in a and b. In the case of (B), a is before the image receiving paper comes into contact with the guide and enters the fixing device, and b is immediately after entering the fixing device. In this case, since the guide is a float, there is no portion where the current leaks through the image receiving paper, but when the guide enters the fixing device, the current is leaked through the conductive roller.
Therefore, the transfer voltage is high at a before entering the fixing device and is low at b after entering the fixing device. In order to avoid this, the guide and the fixing device may be grounded via the same resistance element as in a. In particular, it is effective when the distance from the transfer position to the fixing position is shorter than the length of the image receiving paper. When the current leaking from the guide and the fixing device was measured,
A current of about 0.8-1.0 μA leaks through these components. If the guide and the fixing device are grounded via a resistance of 100 MΩ, the leak current reaches about 1.5 μA and an appropriate transfer voltage cannot be obtained. Therefore, the ground resistance is preferably 200 MΩ or more.

[0013]

1 is a block diagram showing the arrangement of an image forming apparatus according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a photoconductor as an electrostatic latent image carrier, which uses a phthalocyanine-based pigment dispersed in a resin as a charge generation layer on a conductive base material, and is formed on the charge generation layer. As the charge transport layer, an organic photoconductor was used in which hydrazone was mixed with resin so that the thickness of the photoconductive layer was 20 μm. Two
Is a corona discharge device for charging the photoconductor 1, 3 is an exposure device for performing image exposure on the photoconductor, and 4 is a developing device for visualizing a latent image after exposure. It is composed of a fixed magnetic field generating magnet 4a included in the photoconductor 1 for adhering the toner which is a magnetic developer to the toner, and a conductive member for applying a voltage to collect excess toner other than the image portion. The developing electrode 4b includes a power supply device 4c capable of applying a voltage and a holding electric field to the developing electrode 4b. Alternating current (AC) and direct current (DC) are singly or superposed on the developing electrode 4b, and are applied by the power supply device 4c. Reference numeral 5 denotes a transfer roller set so as to come into contact with the photoconductor 1. The transfer roller 5 is an elastic roller in which a conductive rubber is provided around a shaft made of a conductive member. The pressing force applied to the photoconductor 1 is 0 to 2000 g, preferably 50 per transfer roller 5 (about 216 mm).
It is 0 to 1000 g. This is to transfer the transfer roller 5 to the photosensitive member 1.
It was measured from the product of the spring coefficient and the amount of contraction of the spring for pressing against. The nip width with the photoreceptor is about 0.5 mm to 5 mm. The rubber hardness of the transfer roller 5 is 80 degrees or less by the measuring method of Asker C, and preferably 30 to 60 degrees. Reference numeral 7 denotes a plunge guide made of a conductive member for introducing the image receiving paper to the transfer roller 5, which is grounded via a resistance of 100 MΩ or more. Reference numeral 8 is a conveyance guide made of a resin member, 9 is a fixing device, which is composed of a heat roller 9a in which a conductive paint in which conductive powder is dispersed in fluorine or silcon resin is applied on a conductive pipe material, and a silicone rubber. It is composed of a pressure backup roller 9b. A halogen lamp can be arranged in the heat roller 9a for heating. Further, the bearing of the heat roller 9a is made of a conductive material, and is electrically connected to the casing of the fixing device 9, and the casing is grounded via a resistance of 100 MΩ or more. In this embodiment, the distance between the contact nip between the photoconductor 1 and the transfer roller 5 and the tip of the thrust guide is about 5 m.
The distance between the nip and the contact nip between the heat roller 9a and the pressure roller 9b of the fixing device 9 is about 90 mm. The resistance value inserted between the rush guide 7 and the ground is 200
MΩ, and the resistance inserted between the fixing device 9 and the ground is 20
It was 0 MΩ. Reference numeral 10 is an image receiving paper, 11 is a cleaning device for cleaning the toner remaining on the surface of the photosensitive member 1 after transfer, and 12 is toner. 13 is a transfer roller 5
It is a voltage generating power supply for applying a voltage to the. Regarding the specific dimensions of each member, a negatively charged organic photoreceptor having an outer diameter of the photoreceptor 1 of 30 mm, a conductive base material of aluminum and a thickness of 1 mm was used. The transfer roller 5 has a foamed conductive urethane elastomer around a shaft having a diameter of 6 mm and a resistance value of 10 ⁷ Ω.
(An electrode is provided on the shaft and the surface, and 500 V is applied to both of them). The outer diameter of the entire transfer roller 5 is 18.7.
mm, the hardness was 65 degrees for Asker C. The transfer roller 5 was brought into contact with the photoconductor 1 by pressing the shaft of the transfer roller 5 with a metal spring. The pressing force was about 1000 g.
The toner 12 has an average particle size of about 12 μm, is magnetically insulating, and is negatively charged.

The operation will be described using the apparatus described above. The surface of the photoconductor 1 is negatively charged by using the corona discharge device 2.
After charging, the developing device 4 visualizes the latent image formed by the surface charges of the photoconductor 1 by the exposure device 3. For visualization, the toner 12 as a magnetic developer is attached to the surface of the photoconductor 1 by the magnet 4a contained inside the base material of the photoconductor 1. When the reversal developing method in which a developing bias similar to the surface potential of the photoconductor 1 is applied to the collection roller 4b by the power supply device 4c, the photoconductor surface potential of the portion exposed by the exposure device 3 becomes low, and the negative electrode Toner 12 that is electrically charged adheres,
The toner 12 in the non-image area where the surface potential of the photoconductor is high is collected by the collecting roller 19b. At the same time that the photoconductor 1 reaches the contact position of the transfer roller 5, the image receiving paper 10 is supplied to the contact portion between the photoconductor 1 and the transfer roller 5. A constant current having a polarity opposite to that of the toner 12 is applied to the transfer roller 5, and the toner 12 is transferred to the image receiving paper 10 by electrostatic force. In this embodiment, about 2 μ
A constant current of A was used. The voltage generated at this time is as described above (FIG. 4). The image receiving paper 10 is separated from the photoconductor 1, passes through the conveyance guide 8, the fixing device 9, and the toner 12
Is fixed on the image receiving paper 10. After the transfer process, the toner 12 remaining on the photoconductor 1 without being transferred is cleaned by the cleaning device 1.
In 1, the waste toner box is collected.

[0016]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, the conductive means for sandwiching the image receiving paper between the developing means for forming a developed image on the electrostatic latent image carrier and the electrostatic latent image carrier. An electrode, a power supply means for applying a constant current to the conductive electrode, a conductive member for guiding the image receiving paper to the conductive electrode, and at least for fixing the developed image transferred on the image receiving paper. An image forming apparatus comprising: a fixing unit composed of one conductive electrode, wherein the conductive member and the fixing unit are grounded via the same resistance element or constant voltage element.

Further, in the image forming apparatus, the conductive electrodes are roller-shaped. Alternatively, developing means for forming a developed image on the electrostatic latent image carrier, a conductive electrode for sandwiching the image receiving paper between the electrostatic latent image carrier and a constant current applied to the conductive electrode. A power source unit for guiding the image receiving sheet to the conductive electrode, and a fixing unit including at least one conductive electrode for fixing the developed image transferred on the image receiving sheet. In the image forming apparatus, the conductive member and the fixing unit are grounded via the same resistance of 200 MΩ or more or a constant voltage element.

Further, by using the image forming apparatus in which the conductive electrodes are roller-shaped, it is possible to obtain a good image without transfer defects.

As described above, in the system in which the image receiving paper is sandwiched between the contact type transfer roller and the photoconductor and the transfer is performed by applying a constant current, the current is received from the guide or fixing device for guiding the image receiving paper to the contact nip. Leaks through the paper. Especially high temperature
In a high-humidity environment, the phenomenon is remarkable because the image receiving paper has a low resistance. In order to avoid this, the guide and the fixing device are grounded via a resistor, but if this resistance is different, the transfer potential is affected and transfer unevenness in the image occurs. Therefore, a good image can be obtained by using the same ground resistance.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram for explaining a conventional transfer roller method.

FIG. 3 is a diagram schematically showing a surface potential of a photosensitive member and a voltage applied at the time of transfer for explaining that toner scattering is less when a constant current is applied than when a constant voltage is applied.

FIG. 4 is a diagram when a voltage applied to a transfer when a constant current is applied is measured by changing a ground resistance of a guide and a fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Corona discharge device 3 Exposure device 4 Developing device 4a Magnetic field generating magnet 4b Developing electrode 4c Power supply device 5 Transfer roller 7 Push-in guide 9 Fixing device 9a Heat roller 9b Pressure roller

Claims (4)

[Claims] 1. A developing means for forming a developed image on an electrostatic latent image carrier, a conductive electrode for sandwiching an image receiving paper between the electrostatic latent image carrier and the conductive electrode. A fixing device including a power supply unit for applying a constant current, a conductive member for guiding the image receiving paper to the conductive electrode, and at least one conductive electrode for fixing the developed image transferred on the image receiving paper. Means, the conductive member and the fixing means are the same resistance element, or
An image forming apparatus, which is grounded via a constant voltage element. 2. The image forming apparatus according to claim 1, wherein the conductive electrode has a roller shape. 3. A developing means for forming a developed image on an electrostatic latent image carrier, a conductive electrode for sandwiching an image receiving paper between the electrostatic latent image carrier and the conductive electrode. A fixing device including a power supply unit for applying a constant current, a conductive member for guiding the image receiving paper to the conductive electrode, and at least one conductive electrode for fixing the developed image transferred on the image receiving paper. An image forming apparatus, wherein the conductive member and the fixing unit are grounded via the same resistance of 200 MΩ or more or a constant voltage element. 4. The image forming apparatus according to claim 3, wherein the conductive electrode is roller-shaped.