JP4237902B2 - Electrostatic recording device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic recording apparatus using an electrophotographic method, and in particular, in an electrostatic recording apparatus using a roll transfer method for transferring a toner image from an image carrier to a transfer material, corresponding to sheets of different widths. The present invention relates to an electrostatic recording apparatus that can be used.
[0002]
[Prior art]
Compared with the non-contact type corona transfer method, the roll transfer method can hold the transfer material (paper) reliably at the transfer position where the transfer roll is pressed against the image carrier, and transfer bias is less likely to occur. Can be set at a relatively low voltage and low capacity, so that there are advantages such as good transfer efficiency, miniaturization of the apparatus, and a small amount of ozone generated. Further, since there is a pressure effect, there is an effect that the transfer material can be transferred from the leading edge to the leading edge. Further, in a color printer, it is also effective when a plurality of toners are stacked. In the configuration of an electrostatic recording apparatus using a roll transfer system, a photosensitive member (drum or sheet) or an intermediate transfer member is used as an image carrier, and cut paper or continuous paper is used as a transfer material, and plastic is used. There are sheets.
[0003]
With the spread of electrostatic recording devices such as copiers and printers, there is a need to print on different paper sizes such as A4, A3, B4 for cut paper and 12, 15, 18 inch width for continuous paper. It came out. In particular, in high-speed machines, continuous paper is used because of the high-speed conveyance of paper, and after passing through the fixing machine, it can be output in the form of cut paper by the post-processing machine. In fact, it is in the direction of speeding up. FIG. 4A shows the configuration of an electrostatic recording apparatus using the transfer roll 7. Here, a case where the photosensitive drum is for positive charging such as SeTe or As ₂ Se ₃ will be described as an example. An electrostatic latent image is formed by irradiating the photosensitive drum 1 having a positive charge on the surface by the charger 2 with a light pattern by the exposure unit 3. The electrostatic latent image portion is reversely developed by the developing device 4 to form a toner image with positively charged toner. The paper 6 passes through the pressure nip (transfer site) between both the photosensitive drum 1 and the transfer roll 7. In the transfer roll, an elastic body 9 such as rubber is formed on the outer periphery of the metal roll 8, and a film 10 having releasability from toner such as fluororesin is formed on the outer periphery thereof. Usually, the material of the elastic body 9 and the coating film 10 having releasability has a volume resistivity of 10 ⁶ to 10 ⁹ Ω · cm. The toner image 5 on the photosensitive drum is transferred to the paper 6 by applying a DC voltage (−Vt) having a polarity opposite to the toner charging polarity (plus charging) to the transfer roll 7 by the bias power source 12. The sheet 6 is fixed by a fixing device (not shown). Reference numeral 19 denotes a cleaning mechanism for the transfer roll 7. When the photosensitive drum is negatively charged OPC, the same can be explained by reversing the polarity in the above description.
[0004]
[Problems to be solved by the invention]
Unlike the corona transfer method, the roll transfer method is a method in which a sheet is passed through the pressure nip portion between the transfer roll 7 and the photosensitive drum 1. Since the length of the transfer roll is a length that supports the maximum width of the transferable paper, when using a paper having a width smaller than this, as shown in FIG. The transfer roll surface and the photosensitive drum surface are in direct contact. For this reason, the following problems occur.
(1) In a region where the transfer roll is in direct contact with the photosensitive drum surface, the transfer roll surface to which a negative voltage is applied floats in fog toner on the drum surface (a dark potential at an unexposed portion where no image is formed) or in the apparatus. Paper dust (which tends to be positively charged) 23 adheres easily, the transfer roll becomes more dirty, and the burden on the cleaning mechanism 19 increases.
(2) Unlike the corona transfer method, the roller transfer method does not apply a charge to the back surface of the paper 6. Therefore, as shown in FIG. 4C, after passing through the transfer portion, the transferred toner 5a and the paper Since there is no adhesion due to electrostatic force, a part of the toner image 5a (plus charge) becomes scattered toner from the sheet during sheet running and adheres electrostatically to the negative polarity transfer roll surface. This toner is designated as 15a. Cleaning of the toner 15a is not easy, and the toner 15a cannot be removed by the cleaning mechanism 19 together with the fog toner shown in (1) or the paper dust floating in the apparatus. (Rotation in the direction opposite to the rotation direction) is increased, the rotation of the transfer roll 7 that is originally rotated by following the photosensitive drum 1 is stopped, causing a transfer deviation or the surface of the transfer roll. There arises a problem of promoting wear of the release layer 10.
(3) Furthermore, when a high-speed machine is used, the time required to pass through the transfer area nip is shortened. Therefore, it is necessary to apply a large current to the transfer area nip, and the volume of the elastic body layer and the release layer of the transfer roll. It is necessary to reduce the resistivity to 10 ⁶ to 10 ⁷ Ω · cm. When the development method is regular development, the charging polarity of the photosensitive drum and the polarity of the bias potential of the transfer roll are the same, so there is no problem even if the transfer roll surface and the photosensitive drum surface are in direct contact with each other in the non-paper area. In the case of reversal development, in the area that is in direct contact with the photosensitive drum, negative charges directly flow from the transfer roll to the positively charged photosensitive drum surface, and the positive charge of the photosensitive drum surface potential (unexposed portion; dark potential) and medium charge. Summing and reducing the surface potential of this region. When there are many negative charges, the negative charges remaining without being neutralized remain until the next process, and as a result, the remaining negative charges and a part of the positive charges supplied by the charger 2 are neutralized and dark portions are obtained. Becomes lower than the dark part potential of the paper region, and the memory becomes a memory and the difference in surface potential remains. For this reason, when the amount of fog toner increases, or when this area is developed by changing to a wide paper, the image density in this area increases. In particular, at the time of halftone image printing, image deterioration that halftone expression cannot be performed in an area in contact with the transfer roll occurs.
[0005]
As a method for preventing this, Japanese Patent Laid-Open No. 2-53091 is provided with a plurality of transfer rolls, a plurality of transfer rolls are combined according to the width of the paper, and a transfer voltage is applied to them to transfer only to the paper portion. Although a method of applying a voltage has been proposed, there is a problem in that transfer omission occurs in a gap between transfer rollers.
[0006]
[Means for Solving the Problems]
The present invention provides an electrostatic recording apparatus for transferring a toner image on an image carrier onto a transfer material by supplying a transfer material to a nip portion where a transfer roll is pressed against the image carrier at a transfer site. The toner development is a reversal development method, and a means for imparting electric charge is provided downstream of the transfer portion when viewed from the transfer direction of the transfer material, and the charge is applied when the transfer material passes through the transfer portion. The means for applying is characterized in that the charge having the polarity opposite to the polarity of the charged charge of the toner is applied so as to flow into both the front surface of the transfer roll and the back surface of the transfer material on which the toner is not transferred. Further, the means for applying the charge is a corona charger or a conductive brush.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The means 1 will be described with reference to FIG. A corona charger 11 is provided facing the transfer roll 7 to apply a negative charge to the surface of the transfer roll. FIG. 1A shows a region where the transfer material shown in FIG. 4B is present. The transfer roll is in contact with the transfer material. Powder adheres. However, a negative charge is applied to reduce the charge amount of the paper, and the adhesion force to the transfer roll 7 is reduced, and the transfer roll cleaner (not shown) facilitates cleaning. On the other hand, since the surface of the transfer material 6 is positively charged, if the charging polarity of the paper powder is made negative by the corona charger 11, the paper powder can be attached to the back surface of the transfer material 6 and discharged. The transfer roll surface can be prevented from being soiled without using a cleaner. FIG. 1B corresponds to the region without the transfer material in FIG. The positively charged toner 15a scattered from the transfer material 6 and attached to the surface of the transfer roll receives a negative charge from the corona charger 11 and becomes a negatively charged toner 15b. When the transfer roll 7 rotates and comes into contact with the photosensitive drum 1, a suction force acts between the photosensitive drum potential (dark potential) and adheres to the surface of the photosensitive drum.
[0008]
This is designated as toner 15c. The toner is cleaned and removed by the photosensitive drum cleaner 13.
[0009]
The means 2 will be described with reference to FIG. The charger 11 applies a negative charge having a polarity opposite to that of the charged charge (plus) of the toner 5 a transferred to the back surface of the transfer material 6. As a result, the adhesion force of the toner 5a to the transfer material is increased, so that the scattering during the running of the paper is reduced, the image quality is deteriorated, and the area without the transfer material on the transfer roll surface shown in FIG. Can be reduced. Note that the corona charger 11 shown in FIG. 2 has a structure in which charges flow into both the transfer material and the transfer roll.
[0010]
The means 3 will be described with reference to FIG. The electrodes of the conventional transfer roll have a common rotation axis as shown in 8 of FIG. 4B, whereas the paper of width size A as shown in FIG. 3C. The electrode 19a (common to the rotating shaft 8) has an electrode structure in which the electrode 19b corresponds to a transfer material having a width size B, and the electrode 19c corresponds to a sheet having a width size C. Reference numerals 20a and 20b are insulating layers. With this electrode structure, by selecting an electrode corresponding to the width size of the transfer material and applying a voltage, the transfer voltage -Vt is applied directly to the area of the transfer roll surface that directly contacts the photosensitive drum. Never happen.
[0011]
FIG. 1 shows an embodiment of the present invention. The photosensitive drum 1 is SeTe, As ₂ Se ₃ or an OPC photosensitive member for positive charging. A positive charge is given by the charger 2, and an electrostatic latent image is formed by irradiating a light pattern by an exposure unit 3 such as a laser optical system or LED, and a positively charged toner 5 is formed on the drum by reversal development. The transfer roll 7 forms a foamed polyurethane rubber layer 9 having a volume resistivity of 10 ⁸ Ω · cm and a thickness of 20 mm on the surface of a metal roll 8 having a diameter of 10 mm, and has a volume resistivity of 10 ⁸ Ω · cm, A polyurethane-based coating layer 10 with improved release properties is formed by mixing a fluororesin having a thickness of 100 μm, and the length is 20 inches. The bias power supply 12 applies -1200V. −5 kV is applied to the corona wire of the corona charger 11. In this embodiment, a case where a transfer material having a width of 12 inches is used is shown. As shown in FIG. 1A, the toner image 5a on the photosensitive drum is transferred to the paper 6 by a transfer roll. Although a negative charge is imparted on the transfer roll 7, it does not affect the transfer characteristics because it has the same polarity as the bias power source. As shown in FIG. 1B, a little less than 8 inches in the longitudinal direction of the transfer roll is in direct contact with the photosensitive drum 1. The toner 15a (charge amount: 15 μC / g) scattered from the paper and adhering to the surface of the transfer roll 7 becomes 15b whose polarity is inverted to minus by the inflow current from the corona charger 11 (power supply not shown). The drum adheres to the photosensitive drum 1 (toner 15c) by the unexposed potential (+ 500V to 900) of the drum, and is cleaned by the cleaner 13. In this way, the toner adhering to the surface of the transfer roll 7 in the area (including both ends) in direct contact with the photosensitive drum is cleaned, so the burden on the transfer roll cleaner (not shown) is reduced. For this reason, there is a possibility of eliminating the transfer roll cleaner as shown in FIG.
[0012]
Another embodiment of the present invention will be described with reference to FIG. In FIG. 2A, an opening of a corona charger 11 (power supply is not shown) is arranged to face the photosensitive drum through the paper so that a corona charge (minus) is also applied to the back surface of the paper 6. The configuration was As a result, the adhesion force of the toner 5 (plus charge) to the paper 6 is increased, the transport speed of the paper 6 is increased, or even if the transport direction is changed from the horizontal direction to the vertical direction in FIG. It was found that scattering can be reduced. Reference numeral 17 denotes a transfer roll cleaner.
[0013]
In FIG. 2B, the corona charger 11 is mounted at a different angle so that a corona charge (minus) is applied not only to the transfer roll surface but also to the back surface of the paper 6. As a result, it has been found that the scattering of the toner 5 from the paper 6 can be reduced and the cleaning property of the transfer roll can be improved.
[0014]
Although FIG. 2B shows a case where the transfer roll cleaner is not used, there is no problem in using it.
[0015]
Another embodiment of the present invention will be described with reference to FIG. The transfer roll used here is a transfer roll used in a high-speed machine having a printing speed of 100 ppm or more, and has an external appearance of electrode terminals 8, 20a, and 20b for applying a voltage as shown in FIG. The structure is shown in FIG. One feature is that it has a plurality of electrodes corresponding to sheets of different widths (size A, size B, size C). A metal roll 8 serving as a rotating shaft is a center electrode (full size: size A compatible), an insulating film layer 21a such as polyimide or polyester is provided around the metal roll 8, and a metal tape such as aluminum or copper is wound around the outside. The electrode layer 20a is provided, the insulating film layer 21b is provided on the outer side, and the electrode layer 20b is provided on the outer side. Strictly speaking, the length of the electrode is increased by L1 (this time about 10 mm) on both sides of the width of the paper. This is because the disturbance of the transfer electric field due to the electric field concentration at the electrode edge portion does not affect the nip portion of the paper. Further, an insulation distance L2 (about 15 mm) is taken between adjacent electrodes. In order to improve reliability, the insulating treatment 22 may be performed in the vicinity of the edge portion of the electrode where the electric field is concentrated. A foamed polyurethane rubber layer 9 having a volume resistivity of 10 ⁶ Ω · cm and a thickness of 40 mm is formed outside the electrode structure, and a fluorine resin having a volume resistivity of 10 ⁶ Ω · cm and a thickness of 100 μm is mixed thereon. In this way, the polyurethane-based coating layer 10 with improved releasability is formed. Since the time required for the sheet to pass through the transfer portion is short, the transfer current is increased, so that the volume resistivity of the elastic layer is 1 to 2 orders of magnitude smaller than that of the transfer roll of the above-described embodiment, and transfer with the photosensitive drum 1 is performed. In order to expand the pressure nip portion (transfer site) between both of the rolls 7, the elastic layer thickness is increased. FIG. 3A shows the configuration of an electrostatic recording apparatus using the transfer roll of the present invention. Since the transfer roll 7 rotates, lead wires are connected by slip rings from the three electrode terminals, while transfer voltages −Vt and −Vs are connected to the terminal changeover switch 18 from the bias power source 12. Vs is a voltage smaller than Vt so as not to contribute to the transfer.
[0016]
Reference numeral 19 denotes a voltage switching circuit, which detects the width of the paper and performs switch switching control.
(A) For size A: -Vt is applied to all of the electrodes 8, 20a, and 20b.
(B) Size B: -Vs is applied to the electrode 8, and -Vt is applied to the electrodes 20a and 20b.
(C) For size C: -Vs is applied to electrodes 8 and 20a, and -Vt is applied to 20b.
[0017]
In this example, -Vt was set to -1200V, and -Vs was set to -600V. The reason why −Vs was not set to 0 V is to avoid an increase in electric field applied to the insulating layer and to improve reliability. A transfer voltage is applied to the transfer roll portion corresponding to the width of the paper, and only a sufficiently low voltage is applied to the area in direct contact with the photosensitive drum in the non-paper area, causing current to flow into the photosensitive drum. There is no problem of memory generation.
[0018]
In the electrostatic recording apparatus of Example 3, the corona charger 11 shown in Example 2 is disposed. As a result, it is possible to realize a transfer roll system for a high-speed machine that can cope with transfer materials having various widths and does not require a cleaner.
[0019]
FIG. 5 is a diagram showing another embodiment, and the difference from FIG.
Instead of the corona charger, a conductive brush 24 is used, which is suitable for applying a charge to a narrow area between the paper 6 and the transfer roll. Reference numeral 25 denotes a power source applied to the conductive brush 24.
[0020]
【The invention's effect】
(1) Cleanability of paper dust and scattered toner adhering to the transfer roll surface is improved. Specifically, the paper dust adheres to the back surface of the paper 6 and is discharged, and the scattered toner adheres to the photosensitive drum surface and can be cleaned and removed by a photosensitive drum cleaner. For this reason, an electrostatic recording apparatus with a small amount of printing does not require a cleaning device for the transfer roll, and it is desirable to provide a cleaning device when the amount of printing is large, but the burden on the cleaning device is reduced. There is an effect that can be done.
(2) The toner image transferred from the photosensitive drum to the transfer material can be prevented from scattering from the transfer material during transportation, and contamination in the apparatus and contamination on the transfer roll can be greatly reduced.
(3) Transfer materials having different widths can be used, and even when the transfer material is narrower than the width of the transfer roll, high-quality image transfer is possible and the transfer roll region is in direct contact with the photosensitive drum. Since only a low voltage is applied, it is possible to prevent the occurrence of memory on the photosensitive drum.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an embodiment of the present invention.
FIG. 2 is a schematic diagram for explaining another embodiment of the present invention.
FIG. 3 is a schematic view showing another embodiment of the present invention.
FIG. 4 is a schematic diagram illustrating a problem of the present invention.
FIG. 5 is a schematic view showing another embodiment of the present invention.
[Explanation of symbols]
1: photosensitive drum, 4: developing machine, 3: toner, 6: paper, 7: transfer roll, 8: metal roll, 9: elastic layer, 10: releasable coating layer, 11: corona charger, 12: Bias power supply for transfer roll, 13: photosensitive drum cleaner, 14: corona charge applied to transfer roll surface, 15: toner attached to transfer roll surface, 16: corona charge applied to back surface of paper, 17: Transfer roll cleaner, 18: terminal changeover switch, 20: electrode, 21: insulating layer, 23: fog toner on the photosensitive drum and paper dust floating in the apparatus.

Claims (2)

In an electrostatic recording apparatus for transferring a toner image on an image carrier to a transfer material by supplying a transfer material to a nip portion where a transfer roll is pressed against the image carrier at a transfer site.
When the toner development on the image carrier is a reversal development method, and a means for applying an electric charge is provided on the downstream side of the transfer portion as viewed from the transport direction of the transfer material, and the transfer material passes through the transfer portion. The charge applying means applies a charge having a polarity opposite to the polarity of the charged charge of the toner so as to flow into both the transfer roll surface and the back surface of the transfer material on which the toner is not transferred. An electrostatic recording apparatus characterized by the above.   2. The electrostatic recording apparatus according to claim 1, wherein the means for applying the charge is a corona charger or a conductive brush.

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