JP2001335208A - Electrostatic printing device - Google Patents

Abstract

(57) Abstract: An object of the present invention is to provide an electrostatic recording apparatus for performing high-speed printing, in which even when continuous paper is used as a transfer material, toner scattering in a transfer process portion is small, and high-quality printing is performed stably for a long time. Provided is an electrostatic recording device capable of obtaining image quality without increasing costs. SOLUTION: In an electrostatic printing apparatus having a transfer mechanism for transferring a toner image formed on an image carrier to a transfer material, the transfer material is moved independently of the transfer area by upstream and downstream of a transfer area. Performed by the device. The transfer material moving between these paper transport devices is given an appropriate slack, and at least the transfer material in the transfer nip portion is driven by the toner image carrier, so that the transfer material and the image carrier are moved. A transfer mechanism and an electrostatic printing apparatus using the transfer mechanism, wherein the speed difference between the transfer mechanism and the transfer mechanism is almost zero.

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 such as a copying machine and a laser printer.

[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. In recent years, there has been a lot of demand for image image printing due to the attention of POD (print on demand), and as a result, a high quality and high definition printing image quality has been desired.

[0003] The printing image quality in electrostatic printing depends on each printing process (charging, exposure, development, erasing, cleaning and transfer mechanism, fixing mechanism, etc. of the image carrier), and particularly, the formed toner image is transferred. It is important to take measures against image quality deterioration in the transfer mechanism for transferring to a material. One possible cause of the deterioration of the image quality in the transfer mechanism is a slip between the support and the transfer material in the transfer unit due to a difference in the moving speed of the image carrier and the transfer material. The image forming toner is scattered due to physical friction between the image carrier and the transfer material caused by the slip, and as a result, the halftone gradation and the sharpness of the line image are reduced.

[0004] As a measure for reducing the speed difference between the transfer material and the support, a method of aligning the phase of the speed fluctuation between the image carrier and the transfer material (Japanese Patent Application Laid-Open No. Hei 10-78734), and the method of adjusting the registration roller in accordance with the paper transport speed. Method for correcting driving speed (Japanese Patent Laid-Open No. 7-261485)
And the like.

[0005] These countermeasures are effective in printers and copiers using cut paper as the transfer material. This is because cut paper has a relatively short size in the transport direction and the paper end in the transfer section is free, so if the paper transport speed is controlled at the edge of the paper, the paper is then attracted to the photosensitive drum and transported. Therefore, slipping at the transfer portion is unlikely to occur.

On the other hand, in an electrostatic printing apparatus that uses continuous paper as a transfer material, slippage is likely to occur because tension is applied to the paper at the transfer section for transport. In this continuous paper printing, control such as equalizing the paper transport speed and the rotation speed of the photosensitive drum is performed. However, continuous paper (especially when used at high speed and used in a large-sized printer) has a long transport direction size. The paper expands and contracts due to the tension during transport,
Precise control of the paper transport speed becomes difficult. For this reason, in a continuous paper printer, toner scattering due to a transfer portion slip is more likely to occur than in a cut paper printer, which is a major factor in lowering print quality.

As a countermeasure for this, there is a method in which the movement of the image carrier is made to follow the transfer material. However, this method imposes a heavy load on the transfer material and makes it difficult to employ it in a high-speed printing machine.

On the other hand, 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 transfer efficiency is greatly affected by the use of various types of transfer materials, changes in the dielectric constant of the transfer materials due to changes in the printing environment (such as humidity), and the thickness of the toner image to be transferred. There is. Also, in a duplex printer that prints on the back side after printing on one side (front side),
Due to the thermal deformation of the transfer material due to the fixing process during front side printing and the effect of the printed toner image, there is also a problem that the transfer efficiency becomes uneven during back side printing. As a countermeasure, a method of measuring a transfer material dielectric constant just before a transfer process and controlling a transfer current is used. However, in order to realize high-quality color double-sided printing with a high-speed line printer, a transfer method that can obtain more stable transfer efficiency has been desired.

As transfer means for realizing high quality printing quality, a transfer type toner image formed on the surface of a running image carrier is contact-type transfer means such as a transfer roller disposed in contact with the image carrier. A roller transfer mechanism configured to supply a transfer material such as paper to the transfer mechanism at the same time as transferring the toner image to the transfer material by applying a transfer bias to the transfer roller while conveying the transfer material to the transfer mechanism having Are known. The roller transfer method presses the transfer material against the toner image and injects electric charge directly from the contact area, so it is an effective transfer means for printing on various papers, double-sided printing, and color printing consisting of multiple toner layers. It is.

However, in a line printer which requires low cost and high speed printing, continuous paper is frequently used as printing paper. When the continuous paper is used as the transfer material as described above, it is difficult to make the moving speeds of the transfer material, the transfer roller, and the image carrier equal, and the transfer speed between the transfer material, the transfer roller, and the image carrier at the transfer nip portion is difficult. Slip occurs and the image quality of the transferred image tends to be reduced.

FIG. 4 shows a schematic diagram of a general electrostatic printing apparatus as a specific example of the prior art.

Here, reference numeral 1 denotes a photosensitive drum which is an image carrier, and a charger 2, an exposure device 3,
Developing machine 4, Transfer unit 5, AC neutralizer 6, Erase lamp 7
Further, a process device for forming an image such as a cleaning device 8 is provided, and continuous paper is used as a transfer material. As the photosensitive drum 1 rotates in the direction of arrow A, an electrostatic charge is applied to the surface by the charger 2, and then an image pattern to be printed by the exposure device 3 is written on the photosensitive drum 1. On 1, the image pattern is formed as an electrostatic latent image. The electrostatic latent image is developed by a developing device 4, visualized as a toner image, and then transferred by a transfer device 5 to a sheet 9 as a transfer material. The paper 9 is a paper transport pulley 20
The sheet is conveyed by the sheet tractors 16 and 17, and is guided to the transfer nip formed by the photosensitive drum 1 and the transfer unit 5 by the carry-in sheet guide 10. After the toner image has been transferred, the unloaded paper guide 11 is kept attached with the unfixed toner image.
The toner image on the sheet 9 is fixed as a permanent image by a fixing device 18 using a heat roll. Further, a paper buffer 19 is provided between the paper tractor 17 and the fixing device 18, and the fixing device 18 and the paper tractor 17 are provided.
To absorb the difference in the paper transport speed between the two. Also,
The untransferred toner remaining on the photosensitive drum 1 without being transferred by the transfer device 5 is removed from the photosensitive drum 1 by the cleaning device 8 after being discharged by the AC discharger 6. Further, the photosensitive drum 1 is exposed by an erase lamp 7 to remove its surface charge, and is ready for the next image formation.

Here, the transport speed of the paper 9 in the transfer area depends on the paper transport pulley 20 and the paper tractor 1.
6 and 17, the speed is controlled at the same speed as the photosensitive drum 1. However, actually, the backlash by the paper buffer 19 affects the transport state (transport speed) of the paper 9 between the paper tractors 16 and 17, and the In some cases, the transport speed of the paper 9 and the speed of the photosensitive drum 1 are different. As a result, a slip occurs between the sheet 9 and the photosensitive drum 1 at the transfer nip portion, and the image quality such as toner scattering is reduced.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-speed electrostatic printing process using continuous paper as a transfer material, to prevent a decrease in image quality at a transfer portion and to achieve stable printing quality without increasing costs. It is to be realized for a long time.

[0016]

The above object can be attained by making the speed difference between the transfer material transport speed and the image carrier speed in the transfer area substantially zero. The presence of this speed difference means that a slip occurs between the image carrier and the transfer material in the transfer nip, and the slip scatters the transfer toner image, thereby lowering the gradation and sharpness of the image.

A specific means for making the speed difference substantially zero is that the image carrier and the transfer material are moved by independent drive devices, respectively, and a transfer nip portion formed by the transfer means and the image carrier. Only in the transfer area), the movement of the transfer material is made to follow the image carrier. More specifically, the transfer of the transfer material is performed by a transport device independently provided upstream and downstream of the transfer area, and the average movement speed is set to be substantially equal to the average movement speed of the image carrier. Here, the transfer material that moves between the two transfer devices (particularly near the transfer area) is given an appropriate slack, and at least the transfer material in the transfer nip portion is driven by the image carrier. By doing so, the speed difference between the transfer material and the image carrier is reduced to almost zero.

Further, by providing transfer material guide means for guiding the transfer material into or out of the transfer region portion upstream and downstream of the transfer region, the transfer material can be more stably driven by the image carrier. Can be done. The transfer material guide means disposed upstream and downstream of the transfer area acts to wind the transfer body around the image carrier. As a result, the contact area between the transfer material and the image carrier increases, and the slip between the transfer material and the image carrier can be reduced. If there is no transfer material guide means, or if the transfer material is not sufficiently wound around the image carrier by the guide, slippage occurs between the transfer material and the image carrier, and toner scattering during transfer is likely to occur. Become. The effect of winding the transfer material around the image carrier by the transfer material guide is particularly effective during high-speed printing and large-format printing.

Further, a buffer means for absorbing a difference between the transport speed of the transfer material transport device provided upstream and downstream of the transfer area and the rotation speed of the image carrier is provided between the transfer material transport device for loading and the transfer section. , And between the unloading transfer material transfer device and the transfer section, the transfer material can be stably transferred. If the buffer means is not installed, the difference between the moving speed of the transfer material and the rotation speed of the image carrier is accumulated, and as a result,
Excessive loosening or tearing of the transfer material is likely to occur.

Further, the present invention is more effective when a roller transfer system in which charges are directly injected from a transfer nip to a transfer material to transfer a toner image is employed in a high-speed printing process. In the roller transfer method, since the transfer roller presses the transfer material against the image carrier, the slip of the transfer material at the transfer nip portion is small,
Further, since charge injection contributing to transfer can be performed directly from the transfer roll, it is suitable for transfer such as color printing with a large toner layer thickness. However, in line printers that frequently use continuous paper as the transfer material, slip at the transfer nip is inevitably caused by the difference in the moving speed between the transfer material and the image carrier, and the image quality degradation is larger than that of corona transfer. . Here, by using the transfer mechanism of the present invention, even if a slight moving speed difference occurs between the transfer material and the image carrier, the transfer material guide and the buffer mechanism installed upstream and downstream of the transfer nip portion. In the transfer nip portion, the transfer material moves following the image carrier, so that the difference in travel speed between the image carrier and the transfer material can be made substantially zero. as a result,
Even when continuous paper is used as the transfer material, high-definition transfer characteristics, which is a feature of the roller transfer method, can be realized.

By using the above technical means, it is possible to realize both transfer efficiency and high quality image 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 a transfer material, as long as a toner image is transferred, not only printing paper but also an intermediate image for primarily transferring and holding a toner image used in color printing or the like. It also contains a transcript. The electrostatic printing apparatus to which the present invention can be applied can be replaced with an electrophotographic method, an electrostatic recording method, a charged ink method, and the like as long as a visible image is formed using a charging material such as toner. It is.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

(Embodiment 1) FIG. 1 is an example of a schematic view of an electrostatic printing apparatus according to the present invention.

Reference numeral 1 denotes a photosensitive drum, which is an image carrier. Around the photosensitive drum 1, a charger 2, an exposure device 3, a developing device 4, a transfer device 5, an AC neutralizer 6, an erase lamp 7, and a cleaning device 8 And other process equipment for forming an image. As the photosensitive drum 1 rotates in the direction of arrow A, an electrostatic charge is applied to the surface by the charger 2, and then an image pattern to be printed by the exposure device 3 is written on the photosensitive drum 1. The image pattern is formed as an electrostatic latent image on 1 (in the present embodiment, an imager having a resolution of 600 dpi was prepared using an exposure apparatus using an Ar laser having a wavelength of 488 nm). The electrostatic latent image is developed by a developing device 4, visualized as a toner image, and then transferred by a transfer device 5 to a sheet 9 as a transfer material. The paper 9 is conveyed by the paper carry-in devices 12 and 13, and is guided by the carry-in paper guide 10 to a transfer nip formed by the photosensitive drum 1 and the transfer device 5. After the toner image is transferred, the unfixed toner image is conveyed by the carry-out paper guide 11 while being adhered, and the toner image on the paper 9 is fixed as a permanent image by a fixing device (not shown). A paper buffer 1 is provided between the paper loading devices 12 and 13 and the loading / unloading paper guides 10 and 11.
4 and 15 are provided to adjust the slack of the sheet upstream and downstream of the transfer nip portion.

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 uses a fur brush made of nylon). Further, the photosensitive drum 1 is exposed by an erase lamp 7 to remove its surface charge, and is ready for the next image formation.

In this embodiment, the transfer material has a thickness of 80 μm (55 k
g paper), using continuous paper with a width of 15 inches, and a printing speed of 32.5
Inches / second. The moving speed of the photosensitive drum 1 and the paper 9 measured by a Doppler speedometer (measurement positions B,
C) is 825.5 ± 8.0 mm / sec for photosensitive drum 1 and 82 for paper 9
5.5 ± 20.0 mm / sec.

FIG. 2 is a sectional view of the transfer mechanism used in the first embodiment of the present invention. In this embodiment, roller transfer is used for transfer. The transfer roller 100 is made of PFA (Pe
rfluoroalkoxy copolymer), and the base material of the surface coating member is an elastic resistance member having a configuration of conductive polyurethane rubber in which the resistance value is adjusted by dispersing carbon, and its volume resistance value is about 10 ⁶ Ωcm. . The transfer roller 100 is placed in pressure contact with the photosensitive drum 1 as shown in FIG. The pressing pressure of the transfer roller 100 is an appropriate pressure (generally 180 g / cm ²⁾ that does not cause image deterioration such as transfer omission.
Below). The paper 9 as a transfer material passes between the nip formed by the transfer roller 100 and the photosensitive drum 1, and transfers the toner image on the photosensitive drum 1 to the paper 9. The transfer bias voltage is applied to the transfer roller 100 from the external power supply 101, and the transfer roller 100 provides an effect by electrostatic attraction in addition to the pressure transfer. At this time, the absolute value of the bias voltage value is set to 1000 V or less in consideration of the dielectric strength of the photosensitive drum 1. In this embodiment, the transfer roller 100
The transfer was performed at room temperature and normal humidity (24 ° C., 50%) by applying a transfer voltage of V.

The paper guides 10 and 11 are made of stainless steel sheet metal and are grounded. The paper guides 10 and 11 are arranged so as to wind the paper 9 around the photosensitive drum 1 as shown in FIG. In this embodiment, the width of the paper 9 wound around the photosensitive drum 1 by the paper guides 10 and 11 is set to 70 mm. Further, a paper buffer 14 arranged between the paper guide 10 and the paper carry-in device 12 and a paper buffer 15 arranged between the paper guide 11 and the paper carry-out device 13 cause upstream and downstream of the transfer nip portion. The paper 9 was prevented from loosening and hypertension. The reaction force and the pressing pressure of the paper buffers 14 and 15 were set to 100 g and 300 g, respectively.

A printing test of 100,000 pages was performed under the above conditions. The print quality was evaluated by visual evaluation of toner scattering around dots in gray scale printing of halftone dots. Further, the ream weight: 70 kg paper, 90 kg paper, 1
A similar test was performed using 35 kg printing paper. As a result, no slippage between the paper 9 and the photosensitive drum 1 at the transfer nip portion was observed in all the used papers, and a high-quality transferred image with little toner scattering was obtained.

Example 2 In the printing process of Example 1, a corona transfer was used as a transfer device, and the same printing test as in Example 1 was performed. FIG. 3 is an enlarged sectional view of the transfer mechanism used in this embodiment. A transfer current of 1.0 mA was applied to the corona transfer device 102 by the high voltage power supply 103. Also, paper guide 1
The winding width of the paper 9 around the photosensitive drum 1 by 0 and 11 is 1
It was set to 00 mm. In corona transfer, the paper 9 is attracted to the photosensitive drum 1 only by electrostatic attraction. Therefore, in order to make the paper 9 follow the photosensitive drum 1 completely, it is necessary to increase the winding width as compared with the roller transfer. Printing conditions other than the transfer device were the same as in Example 1, and a printing evaluation test using several types of printing paper was performed in the same manner as in Example 1.

As a result, no slip was observed between the sheet 9 and the photosensitive drum 1 in the transfer nip portion in all the sheets used. A high quality transfer image with little toner scattering was obtained.

The present invention can obtain a high-quality transferred image in any of the embodiments, but is particularly suitable for color printing which requires precision such as accurate superposition of multicolor toner images. It is valid.

[0034]

As described above, in the transfer mechanism and the electrostatic printing apparatus according to the present invention, the paper guides 10, 11 for guiding the transfer material into and out of the transfer nip area.
And a paper buffer 14, 1 for adjusting the tension of the transfer material.
5, the continuous paper that is the transfer material is driven by the image carrier in the transfer nip area, so that the toner scatters in the transfer area due to the slip between the transfer material and the image carrier in the transfer nip. Prevention, always ensuring good transferability,
A high-quality image free from image defects can be easily obtained.

Further, according to the present invention, it is easy to employ the roller transfer method in a high-speed printing process.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an electrostatic printing apparatus used in an embodiment of the present invention.

FIG. 2 shows a cross-sectional structure of the transfer device used in the first embodiment.

FIG. 3 illustrates a cross-sectional structure of a transfer device used in a second embodiment.

FIG. 4 is a diagram illustrating a configuration of a general electrostatic printing apparatus using continuous paper.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 2 ... Corona charger, 3 ... Exposure part, 4 ...
Developing machine, 5: transfer unit, 6: AC neutralizer, 7: erase lamp, 8: cleaning device, 9: paper, 10: paper guide, 11: paper guide, 12: paper transport device, 13 ...
Paper transport device, 14, 15: paper buffer, 18: fixing device, 20: paper transport pulley, 100: transfer roller,
101: High voltage power supply for transfer roller, 102: Corona transfer device, 103: High voltage power supply for corona transfer.

Claims (4)

[Claims] An image forming means for forming an image on the toner image carrier; a transfer means for transferring a toner image formed on the toner image carrier to a transfer material; In the electrostatic printing apparatus using continuous paper as the transfer device, a paper loading device is provided on the upstream side with respect to the transfer material transport direction of the transfer unit and a paper discharge device is provided on the downstream side, and a transfer area formed by the transfer unit and the toner image carrier is provided. Wherein the guide member is provided between the paper carrying-in device and the paper carrying-out device so that the movement of the transfer material is driven by the toner image carrier. 2. The paper feeding device according to claim 1, wherein said guide means includes a carry-in paper guide means between the paper carry-in device and the transfer means, and a carry-out paper guide means between the transfer means and the paper carry-out device. Electrostatic printing device. 3. The electrostatic printing apparatus according to claim 2, wherein a paper buffer is provided between the carry-in paper guide means and the paper carry-in device, and between the carry-out paper guide means and the paper carry-out device. 4. The electrostatic printing apparatus according to claim 1, wherein a roller transfer is used as the transfer unit.