JP2001075372A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize stable printing quality for a long time by using plural transfer rollers and making transfer voltage applied to a nip part between a downstream side transfer roller and an image carrier lower than the transfer voltage of an upstream side transfer roller. SOLUTION: The transfer rollers 100 and 101 are installed to press-contact with a photoreceptor drum 1. The pressing pressure of the rollers 100 and 101 is set to appropriate pressure which does not cause image deterioration such as transfer omission. Paper 9 being transfer material passes through the nip formed by the rollers 100 and 101 and the drum 1, and a toner image on the drum 1 is transferred to the paper 9. Transfer bias voltage is applied to the rollers 100 and 101 by external power sources 102 and 103, respectively, and the rollers 100 and 101 give an effect by electrostatic attractive force in addition to pressure transfer. A bias voltage value in such a case is set to <=1000 V as an absolute value. In such a case, toner scattering amount around a dot is reduced by setting the transfer voltage value for the roller 101 smaller than that for the roller 100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic printing apparatus utilizing an electrophotographic system, such as a copying machine and a printer.
In particular, the present invention relates to an image forming apparatus such as a line printer that performs high-speed printing and uses a roller transfer unit in a transfer unit.

[0002]

2. Description of the Related Art The electrophotographic system is one of the most well-known printing systems used in copying machines and printers. In particular, in the line printer market, as the amount of information to be processed increases, higher-speed printing capability is desired. Further, in recent years, there has been a great demand for image image printing due to the attention of POD, and as a result, a high quality and high definition print image has been desired.

The printing quality in electrostatic printing depends on all printing processes (charging, exposure, development, erasing, cleaning and transfer means, fixing means, etc. of an image carrier). The problem of image quality deterioration in a transfer unit for transferring to a transfer material (paper) is important, and many countermeasures have been taken conventionally.

As transfer means for realizing high quality print image quality, a contact-type transfer means such as a transfer roller disposed in contact with the transferable toner image formed on the surface of the running image carrier is provided. A roller transfer unit configured to supply a transfer material such as paper to the transfer unit at the same time as being conveyed to the transfer unit provided, and apply a transfer bias to the transfer roller to transfer a toner image to the transfer material; Is well known in the art. In the roller transfer method, the transfer material is in thick contact with the toner image,
Since the charge is injected directly from the contact portion, it is an effective transfer means in printing on various types of paper, double-sided printing, and color printing using a plurality of toner layers. However, in high-speed printing at a printing speed of 150 ppm or more, since the time required to pass through the transfer nip region is short, charge injection becomes insufficient, and it becomes difficult to secure transfer efficiency. In order to secure sufficient transfer efficiency, it is common to take measures such as increasing the transfer current, increasing the roller load, or increasing the transfer nip width by increasing the diameter of the roller. A problem of non-uniformity in volume resistance occurs, and an increase in roller load and a reduction in hardness of the roller shorten the life of the transfer roller. Further, even if the transfer efficiency can be secured by increasing the transfer current, the transferred toner image is disturbed by a sudden potential difference generated between the sheet and the transfer roll when the sheet leaves the transfer nip,
As a result, the print quality deteriorates.

Therefore, in order to realize high-speed printing, the above-described line printer generally employs a corona transfer method in which electric charges are applied to the back surface of a transfer material at high speed. In this corona transfer method, a charge having a polarity opposite to that of the toner is generated by corona discharge, and the charge is supplied to the surface of the transfer material opposite to the toner adhering surface, so that the toner image on the image carrier is transferred by the electrostatic attraction. Transfer and adsorb to the material. Since the corona transfer method can charge the transfer material at high speed, it is a very effective means for high-speed printing as described above. However, the change in the thickness of the transfer material, the change in the dielectric constant of the transfer material due to the environment (humidity), and the like. There is a problem that the transfer efficiency is greatly affected by the thickness of the transferred toner image. Further, in a double-sided printing printer that performs printing on the back side after printing on one side (front side), the transfer efficiency becomes uneven when printing on the back side due to the thermal deformation of the transfer material due to the fixing process during the front side printing and the effect of the printed toner image. Problems arise. As a measure against these problems, a method of measuring the dielectric constant of the transfer material immediately before the transfer process and controlling the transfer current is used. However, in order to realize high-quality color double-sided printing with a high-speed line printer, a transfer method capable of obtaining more stable transfer efficiency has been desired.

[0006]

SUMMARY OF THE INVENTION The present invention uses a roller transfer method as a transfer means in a high-speed electrostatic printing process to provide stable printing against changes in transfer material characteristics and double-sided printing and color printing. The goal is to achieve quality for a long time.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to use a plurality of transfer rollers for a transfer means, and to apply a transfer voltage applied to a nip between a downstream transfer roller and an image carrier to an upstream transfer roller. This can be realized by making the size smaller than that of the roller. By employing a plurality of transfer rollers in this way, it is not necessary to increase the diameter of the rollers and reduce the hardness of the rollers, and it is possible to secure the transfer nip width with sufficient transfer efficiency at a relatively low cost. Becomes

The volume resistance of each transfer roller is 10 ⁴ Ωcm
To 10 ⁹ [Omega] cm is improved, performs transfer by applying a following transfer voltage 1500V to the transfer roller. If the volume resistivity is smaller than 10 ⁴ Ωcm, the transferability depends too much on the characteristics (dielectric constant) of the paper as the transfer material, and problems such as transfer unevenness are likely to occur. On the other hand, if the volume resistance is larger than 10 ⁹ Ωcm, it is difficult to secure a sufficient transfer current value below the withstand voltage of the photoreceptor serving as the image carrier, resulting in a decrease in transfer efficiency. Here, usually, the material of the image carrier used in the electrophotographic electrostatic printing device is a Se-based photoconductor, a-
If the transfer voltage is higher than 1500 V, the photoconductor may be dielectrically damaged.

The material of the elastic resistance member of the transfer roller is any one of conductive polyurethane rubber, conductive silicon rubber, EPDM, and conductive polyimide, and the proper rubber hardness is 20 to 60 degrees in Asker hardness, and The thickness of the elastic resistance member is preferably 20 mm to 100 mm. If the rubber hardness is less than 20 degrees, the amount of wear of the roller due to friction with the transfer material becomes significant. On the other hand, when the rubber hardness is greater than 60 degrees, it is difficult to secure the transfer nip width because the amount of deformation of the roller due to pressing is small. Further, when the thickness of the elastic resistance member is smaller than 20 mm, it is difficult to secure the transfer nip width because the amount of deformation of the roller by pressing is small, and when the thickness of the elastic resistance member is 100 mm, the volume resistance of the material is reduced. It is difficult to ensure the uniformity of

Further, by setting the applied current value of the transfer roll provided downstream of the transfer material in the transfer direction to be smaller than the transfer current value applied to the transfer roll provided upstream of the transfer material in the transfer direction, Efficient transfer can be performed without causing image quality deterioration. When the voltage applied to the transfer roller on the most downstream side is large, the toner is easily scattered due to a sharp potential gradient when the transfer material separates from the transfer nip portion, and the transferred image is disturbed.

By using the technical means as described above, it is possible to secure both transfer efficiency and high-quality images in a high-speed printing process. In particular, the present invention is effective in a high-speed printing process at a printing speed of 100 mm / s or more.

In the above technical means, as long as the image carrier bears a toner image, not only the photoreceptor but also a toner image used in color printing or the like is primarily transferred and held. It also contains an intermediate transfer member. The image forming apparatus to which the present invention can be applied can be replaced with an electrophotographic method, an electrostatic recording method, a charged ink method, or the like as long as a visible image is formed using a charging material such as toner. is there.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. (Embodiment 1) FIG. 1 is an example of a schematic view of an image forming apparatus according to the present invention. Reference numeral 1 denotes a photosensitive drum serving as an image carrier, and a charger 2, an exposure device 3,
Developing machine 4, Transfer unit 5, AC electricity removal 6, Erase lamp 7
In addition, a process device such as a cleaning device 8 for forming an image is provided. The photosensitive drum 1 has an arrow A
After the surface is charged with electrostatic charge by the charger 2 according to the rotation in the direction, the image pattern to be printed by the exposure device 3 is written on the photosensitive drum, so that the image is A pattern is formed as an electrostatic latent image (in this embodiment, an image pattern having a resolution of 600 dpi was prepared using an Ar laser having a wavelength of 488 nm as an exposure apparatus). The electrostatic latent image is developed by the developing device 4, visualized as a toner image, and then transferred by the transfer device 5 to paper 9 as a transfer material.
The sheet 9 to which the toner image has been transferred is conveyed by the sheet conveying retractors 10 and 11 with the unfixed toner image attached thereto, and the toner image on the sheet 9 is fixed as a permanent image by a fixing device (not shown). Here, the tension for transporting the paper 9 is given by a tension roller and a paper transport retractor 11 provided downstream of the fixing device.
Since a tension of about 200 gF or more is applied to the sheet 9, the sheet 9 between the transfer rollers is wound around the photosensitive member 1 without slack.

The untransferred toner remaining on the photosensitive drum 1 without being transferred by the transfer device 5 is discharged by an AC discharger 6, and then cleaned by a cleaning device 8 (in this embodiment, the cleaning device 8). Is removed from the photosensitive drum 1 by using a fur brush made of nylon. Further, the photosensitive drum 1 is exposed by an erase lamp 7 to remove its surface charge, and prepare for charging for the next image formation.

FIG. 2 is a sectional view showing the structure of the transfer unit 5 used in the embodiment of the present invention. In this embodiment, two transfer rollers are used, and the transfer rollers 100 and 101 have a thickness of 500 μm.
It is coated with FA (Perfluoroalkoxy Copolymer), and the base material of the surface coating member is an elastic resistance member made of a conductive polyurethane rubber having a resistance value adjusted by dispersing carbon, and has a volume resistance value of about 10 ⁶ Ωcm. It is.
The transfer rollers 100 and 101 are placed in pressure contact with the photosensitive drum 1 as shown in FIG. Transfer rollers 100, 101
Is set to an appropriate pressure (generally 180 g / cm ² or less) that does not cause image deterioration such as transfer omission. The paper 8 as a transfer material passes between the nips formed by the transfer rollers 100 and 101 and the photosensitive drum 1, and transfers the toner image on the photosensitive drum 1 to the paper 9. Further, transfer bias voltages are applied to the transfer rollers 100 and 101 from the external power supplies 102 and 103, respectively, so that an effect by electrostatic attraction is provided in addition to the pressure transfer. The absolute value of the bias voltage at this time is 1000 in consideration of the dielectric strength of the photosensitive drum 1.
V or less. In this embodiment, a transfer voltage of 1000 V was applied to the transfer roller 100 and a transfer voltage of 500 V was applied to the transfer roller 101, and a printing experiment was performed at a printing speed of 800 mm / sec. As a result, there was no toner scattering during transfer, and a high-quality printing result was obtained. Obtained.

Table 1 shows the results of the transfer voltage applied to the transfer rollers 100 and 101, the transfer efficiency, and the print quality.

[0017]

[Table 1]

Here, the print quality was evaluated based on the degree of toner scattering around dots in halftone dot printing. From this result, the transfer voltage value V
By reducing the transfer voltage value V ₁₀₁ of the transfer roller 101 from _100, it is possible to reduce toner scattering amount of surrounding dots. (Embodiment 2) FIG. 3 shows another embodiment of the present invention. In this embodiment, the transfer was performed using three transfer rollers at a printing speed of 1500 mm / sec. Transfer rollers 104, 105, 10
The configuration of No. 6 is the same as that of the first embodiment, and its volume resistance is about 10 ⁶ Ωcm. Transfer rollers 104, 105, 106
As shown in FIG. 3, the photoconductive drum 1 is placed in pressure contact with the photosensitive drum 1, and transfer bias voltages are applied by external power supplies 107, 108, and 109, respectively.

Table 2 shows the results of the voltage value applied to each transfer roller, the transfer efficiency, and the toner scattering state.

[0020]

[Table 2]

From this result, it can be seen that the most downstream transfer roller 106
In a transfer voltage value V ₁₀₆ can be smaller than the transfer voltage value V ₁₀₅ of the preceding stage of the transfer roller 105, reducing toner scattering amount of peripheral dots, it can be seen that high-quality printing results.

[0022]

As described above, in the electrostatic printing apparatus of the present invention and the roller transfer means used for the same, the current applied to the plurality of transfer rolls is inclined from the upstream side to the downstream side of the transfer material. It can prevent toner scattering in the transfer area,
Good transferability is always ensured, and a high-quality image free from image defects can be easily obtained. Further, by increasing the number of transfer rolls, the width of the transfer nip can be easily widened, and it is possible to easily cope with higher-speed printing.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an electrostatic recording device.

FIG. 2 is a schematic diagram illustrating a transfer device and a transfer roller according to an embodiment of the present invention.

FIG. 3 is a schematic view illustrating a transfer device and a transfer roller according to another embodiment of the present invention.

[Explanation of symbols]

1: photoreceptor drum, 2: corona charger, 3: exposure unit
4: developing machine, 5: transfer unit, 6: AC neutralizer, 7: erase lamp, 8: cleaning device, 9: paper, 10: paper transport retractor, 11: paper transport retractor, 10
0: transfer roller 1, 101: transfer roller 2, 102: high-voltage power supply for transfer roller 1, 103: high-voltage power supply for transfer roller 2, 104: transfer roller 1, 105: transfer roller 2, 1
06: transfer roller 3, 107: high-voltage power supply for transfer roller 1, 108: high-voltage power supply for transfer roller 2, 109: high-voltage power supply for transfer roller 3.

Claims (4)

[Claims] 1. An image forming apparatus comprising: an image carrier; an image forming unit for forming an image on the image carrier; and a transfer unit for transferring an image formed on the image carrier to a transfer material. The transfer voltage applied to the nip portion between the transfer roller provided on the most downstream side in the transport direction of the transfer material and the image carrier is applied to the transfer roller provided on the upstream side using a plurality of transfer rollers. An image forming apparatus characterized in that the transfer voltage is lower than the transfer voltage to be applied. 2. The volume resistance value of a plurality of transfer rollers is 10 ⁴
2. The image forming apparatus according to claim 1, wherein the transfer voltage is in a range from Ωcm to 10 ⁹ Ωcm, and an absolute value of a transfer voltage applied to the transfer roller is 1500 V or less. 3. The transfer roller has a rubber hardness of Asker hardness of 20 to 60 degrees and a diameter of the roller of 2 to 60 degrees.
2. The image forming apparatus according to claim 1, wherein the distance is from 0 mm to 100 mm. 4. Use of continuous paper as a transfer material, and a printing speed of 1
The image forming apparatus according to claim 1, wherein the image forming speed is equal to or higher than 00 mm / s.