JP2006119505A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer system which does not require improvement of the surface of a photoreceptor or heating of the photoreceptor by minimizing production of ozone which causes an out-of-focus image and image deletion. <P>SOLUTION: On transferring by using a corona charger, a transfer region is irradiated with laser light at a time of applying a transfer bias so that a linear gas discharge by laser-induced discharge and coincident with the laser optical path is obtained, which extremely narrows the discharge region. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a transfer unit used in an image forming apparatus such as a copying machine, a printer, and a fax machine that forms an image using an electrophotographic system.

  Conventionally, as a transfer means for transferring a toner image on an image carrier onto a transfer material such as paper by applying a high voltage, one using a corona charger or a roller member has been known. Used in photographic image forming apparatuses.

  Of these, corona chargers (corotrons, scorotrons) whose main components are wire electrodes (for example, metal wires such as tungsten wires plated with gold of 50 to 100 μmφ) and shield plates are charged in a non-contact manner. There is little damage to the carrier, and when used as a transfer member, there are merits of uniform charging regardless of the transfer material and high durability performance. Further, since the pressure applied between the image carrier and the transfer means can be reduced as compared with the contact type transfer means, the developer on the image carrier is agglomerated under pressure in the transfer process due to the pressure, and particularly characters. “Transfer dropout” is difficult to occur in which only the edge portion is transferred without transferring the central portion of the line of the image.

  However, since the current due to the voltage application hardly flows through the shield plate surrounding the wire electrode rather than the wire electrode, there is a problem that the energy consumption efficiency is poor and a considerably large amount of ozone (O3) is generated. The generated ozone oxidizes nitrogen in the air to generate nitrogen oxides (NOx) and the like. Further, the generated nitrogen oxides react with moisture in the air to generate nitric acid and the like. Then, corona discharge products such as nitrogen oxides and nitric acid adhere to and deposit on the image carrier and peripheral devices, thereby fouling their surfaces. Such a corona discharge product has a high hygroscopic property, and the surface of the image carrier that has adsorbed the corona discharge product has a low resistance due to the absorption of the adsorbed corona discharge product so that the charge holding ability can be substantially fully or partially. And may cause image defects called image blurring or image flow (a state where the surface charge of the image carrier leaks in the plane direction and the electrostatic charge latent image pattern is broken or not formed). .

  Further, the corona discharge product adhering to the inner surface of the shield plate of the corona charger volatilizes and liberates not only during the operation of the electrophotographic apparatus but also during the rest of the apparatus such as at night. The volatilized and liberated product adheres to the surface of the image carrier corresponding to the discharge opening of the shield plate of the corona charger and further absorbs moisture. For this reason, the resistance of the surface of the image carrier may be lowered. In addition, image blur and image flow are likely to occur in the area corresponding to the shield plate opening during the pause of the apparatus in the first copy that is output first when the apparatus is restarted after the apparatus is paused, or the subsequent several copies. In particular, when the image bearing member is an a-Si type photosensitive member, there may be a problem of image blur and image flow due to the corona discharge product.

  That is, in the case of an a-Si type photoconductor, the surface hardness is extremely higher than that of other photoconductors, so that the surface of the photoconductor is not excessively scraped in the cleaning process or the like, and adhering substances are removed together with the surface of the photoconductor. The corona discharge product adhering to the surface of the photoreceptor tends to remain indefinitely. The following two methods are known as methods for preventing the above-described image blur and image flow phenomenon.

  One of them is that a heater for heating the electrophotographic photosensitive member is built in or a hot air blower is used to blow warm air to the electrophotographic photosensitive member to heat the surface of the photosensitive member. This is a method of reducing humidity. Specifically, Patent Document 1 discloses an image forming process such as charging, exposure, development, and transfer while maintaining the temperature in the vicinity of the photoreceptor surface at 30 to 40 ° C. in order to improve the image quality of the a-Si photoreceptor. By performing the above, there is disclosed a technique for preventing a decrease in surface resistance due to moisture adsorption on the surface of the photosensitive member and an image flow that occurs accompanying the decrease.

  Another method is to improve the water repellency of the surface of the electrophotographic photosensitive member, thereby making it difficult for the corona discharge products to adhere from the beginning, thereby preventing image flow. Specifically, Patent Document 2 discloses an aC surface layer whose surface is plasma-treated with a gas containing fluorine. Patent Document 3 discloses a surface layer made of an amorphous material containing carbon and halogen atoms.

  When a corona charger is used, corona ions are also supplied to the area before and after the transfer material enters the transfer area, and an electric field is formed in the gap between the image carrier and the transfer material. When a strong electric field is formed in the gap before entering the transfer region, a phenomenon called image scattering, that is, so-called scattering, occurs when the toner on the image carrier flies toward the transfer material. Further, even when a strong electric field is formed in the gap after passing through the transfer region, the toner image once transferred onto the transfer material may be disturbed by the influence of the electric field and may be scattered. On the other hand, Patent Documents 4 and 5 describe a discharge regulating plate provided on the upstream side of the transfer material of the corona charger, and Patent Documents 6 to 9 include an insulating member on the upstream side of the transfer material of the corona charger. Patent Document 10 describes a discharge restriction plate provided on the downstream side of the transfer material of the corona charger to reduce the electric field strength in the area before and after entering the transfer area. ing.

  The transfer belt type transfer means is for realizing transfer of the transfer material, transfer of the toner image to the transfer material, and separation / transport of the transfer material after transfer from the image carrier. The material can be transported and has the advantage of being compatible with a wide variety of transfer materials from thin paper to thick paper.

  However, there is a burr or the like at the end of the paper that is the transfer material, and when this burr is large at the front end of the paper and is directed toward the transfer belt, if a transfer current is applied from the front end of the paper, An adsorptive force is generated between the paper and the image carrier, and the adsorptivity to the transfer belt at the leading edge of the paper is impaired. For this reason, the leading edge of the paper floats up, and an image defect occurs due to a transfer defect, and especially on a transfer material having a small rigidity such as recycled paper, thin paper, and coated paper, so-called paper stiffness, the paper is wound around the image carrier. In some cases, the transportation itself could be damaged. On the other hand, the separability from the image carrier can be improved by reducing the transfer electric field at the leading end of the transfer material or slightly delaying the timing of applying the transfer bias from the leading end.

  However, since the transferability at the front end of the transfer material is lowered, this portion is usually a blank. Reducing the transfer bias at the leading edge of the paper and delaying the application of the transfer bias can be achieved relatively easily with the contact-type transfer bias application means, but with the non-contact-type transfer means with a wide discharge area. It was very difficult.

JP-A-60-95551 JP-A-61-289354 US Pat. No. 4,559,289 Japanese Utility Model Publication No. 60-189057 JP-A-1-191178 Japanese Utility Model Publication No. 63-124261 Japanese Utility Model Publication No. 63-124262 Japanese Utility Model Publication No. 63-124263 Japanese Utility Model Publication No. 63-155157 Japanese Utility Model Publication No. 63-138571

  However, the above-described method of heating the photosensitive member against the image blur and image flow caused by ozone increases the power consumption due to the power required for heating, and increases the temperature of the developing device adjacent to the photosensitive member by heating the photosensitive member. In some cases, this causes a problem that the developer is hardened and the toner is more likely to be filmed on the surface of the photosensitive member. For this reason, it is desired to provide a transfer system that does not require improvement of the surface of the photoreceptor and heating of the photoreceptor by minimizing the generation of ozone, which is the cause of image blur and image flow.

  In addition, it is a non-contact transfer means that provides the advantages of uniform charging, high durability performance, and low transfer loss, regardless of the transfer material, while reducing the electric field strength in the areas before and after the transfer area. Also, it is desired to provide a transfer method that can achieve high image quality without occurrence of scattering.

  Furthermore, as a transfer bias applying means for the transfer belt, the timing of the discharge of the corona charger is a non-contact transfer bias applying means that can reduce the occurrence of the hollowing out phenomenon with little damage to the transfer belt and the image carrier. Transfer bias application means that can accurately identify the location where charge is applied and transfer belt transfer bias that can improve the separation of the transfer material from the image carrier by not applying electrification to the transfer material tip The provision of means is also desired.

  The present invention is an image forming apparatus characterized by the following configuration.

  Laser induction for inducing discharge by irradiating laser light in an image forming apparatus having a corona charger that discharges by applying a voltage to a stretched wire electrode and an image carrier on which a toner image is formed It is characterized by inducing a discharge from the corona charger to a predetermined place by discharging. The laser light irradiation breaks down the gas in the optical path and facilitates discharge, so that the laser light path and the discharge path coincide with each other, and discharge other than from the corona wire to the image carrier, such as flowing through the shield plate, occurs. Therefore, the energy consumption efficiency is improved, the generation of ozone can be reduced, and image blur and image flow due to ozone can be prevented.

  Further, the laser light serves as a trigger for discharging the corona charger. Since the discharge from the corona charger is a laser-induced discharge, the laser beam path and the discharge path coincide, and the laser beam is the trigger for the discharge of the corona charger, so the laser irradiation and discharge are synchronized. The place where the laser is irradiated coincides with the place where the charge is applied by the discharge of the corona charger, and the place where the charge is applied can be specified accurately. Furthermore, since laser induced discharge is performed only when the laser beam passes in the vicinity of the wire, no discharge other than in the direction of the image carrier is generated, and only a very narrow region is discharged. Occurrence can be minimized.

  Further, the corona charger is a transfer charger for transferring a toner image formed on the image carrier onto a transfer material. As a result, since the discharge is possible only in a very narrow region even though it is a non-contact transfer means, it is possible to achieve high image quality without occurrence of scattering.

  Furthermore, the corona charger is a transfer-type transfer bias applying means having a transfer belt that carries a transfer material and conveys it to a transfer nip portion. As a result, the transfer belt can be used to provide stable transfer material transport and support a wide variety of transfer materials from thin paper to thick paper, and the transfer bias application means must be non-contact. As a result, damage to the transfer belt is minimized, and high durability of the transfer belt can be realized. In addition, since it is non-contact, the occurrence of transfer dropout can be reduced. Furthermore, because it is a non-contact transfer bias application means, it is possible to narrow the discharge area for laser-induced discharge and accurately control the discharge timing, so use a transfer material with no burr and rigidity. Even when the transfer bias is applied, the transfer bias application timing is slightly delayed from the front end portion, whereby the separation property of the transfer material from the photosensitive drum can be improved and the reliability of the apparatus can be improved. Furthermore, since generation of ozone can be reduced, deterioration of the transfer belt due to ozone can be reduced, and high durability of the transfer belt can be realized.

  According to the present invention, in the corona charger of the image forming apparatus, by passing the laser light through the optical path connecting the vicinity of the corona wire and the image carrier, the laser optical path and the discharge path by the corona charger coincide with each other. Therefore, it is possible to minimize the discharge that is not necessary for image formation, and it is possible to prevent the occurrence of image blur and image flow caused by generation of ozone and corona discharge products.

  Furthermore, laser induced discharge makes it possible to narrow the discharge area of the corona charger by matching the laser light path with the discharge path of the corona charger, thereby preventing image deterioration due to transfer scattering occurring before and after the transfer area. be able to.

  Furthermore, by using laser light as a trigger for the discharge of the corona charger, the discharge timing of the corona charger and the place where charge is applied can be specified accurately. Especially when a transfer belt is used, charge is applied to the tip of the transfer material. By not performing the above, it is possible to improve the separation from the image carrier and to obtain a stable transfer material transportability.

<Embodiment 1>
Embodiment 1 of the present invention will be described with reference to FIG.

  The overall configuration and function of the image forming apparatus according to the present embodiment will be described.

  The image forming apparatus includes a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is provided with a photoconductive layer on a cylindrical conductive substrate. Generally, the photoconductive layer includes an organic photoconductor (OPC), an amorphous silicon photoconductor (a-Si), Se, or the like. A photosensitive material is used. The photosensitive drum 1 is pivotally supported by the image forming apparatus main body so as to be rotatable in the direction of the arrow in the figure.

  The surface of the photosensitive drum 1 is uniformly charged by the scorotron charger 2 while being rotated. The uniformly charged photosensitive drum 1 is exposed by a laser beam driven by a signal proportional to the image density of the document from the laser scanner unit 10, and an electrostatic latent image corresponding to the document is formed on the surface of the photosensitive drum 1. Is done.

  The laser scanner unit 10 includes an illumination lamp 13 that optically scans a document 12 placed on a document table glass 11. The reflected light of the image information from the document 12 optically scanned by the illumination lamp 13 is guided to the mirrors 15a, 15b and 15c and imaged on the photoelectric conversion element (CCD) 14 through a lens (not shown). The photoelectric conversion element 14 converts the image information on the reflected light into an analog image electrical signal, and the A / D converter 16 converts the image signal into a digital image electrical signal proportional to the image density.

  This digital image signal is sent to the laser driver 17, and the laser driver 17 drives the laser 18 according to the image signal to generate laser light modulated according to the image density.

  The image laser light scans the photosensitive drum 1 via the polygon mirror 19 and forms an electrostatic latent image as described above. The electrostatic latent image on the photosensitive drum 1 is developed by the developing device 3 and visualized as a toner image (developer image).

  In the present embodiment, the developing device 3 employs a method of reversing and developing the electrostatic latent image on the photosensitive drum 1 by a magnetic jumping development method. In general, in the jumping development method, a toner is held in a thin layer on a developing sleeve 3 a as a developer carrying member that rotates with a magnetic field generating means inside the developing device 3, and the toner layer faces the photosensitive drum 1. The developing unit is placed in non-contact with the photosensitive drum 1, and an AC bias superimposed with an AC bias or a DC voltage is applied to the developing sleeve 3 a between the photosensitive drum 1 and the toner is caused to fly to the photosensitive drum 1, and the photosensitive drum 1 1 develops the electrostatic latent image on 1.

  If non-magnetic toner is used, a non-magnetic jumping development system is used, and if magnetic toner is used, a magnetic jumping development system is used.

  The magnetic jumping development method used in the present embodiment has a magnet (not shown) inside the developing sleeve 3a, and the magnetic toner adhered on the developing sleeve 3a by the magnet is regulated by the magnetic blade 3b to develop the developing sleeve. A thin layer of toner is formed on 3a, and uniform development faithful to the latent image is possible.

  In this embodiment, an amorphous silicon photosensitive drum having an outer diameter of 80 mm is used as the photosensitive drum 1, and the latent image has a dark portion potential Vd = 400 to 450V and a bright portion potential Vl = 10 to 50V. The process speed of this image forming apparatus was set to 300 mm / second.

  The developing sleeve 3a of the developing device 3 is a non-magnetic SUS sleeve having an outer diameter of 25 mm, and has a surface coated with a resin coat. The distance between the magnetic blade 3b and the developing sleeve 3a is 300 to 400 μm, and the magnetic toner layer on the developing sleeve 3a regulated by the magnetic blade 3b has a layer thickness of about 100 μm and a toner amount of 1 mg / cm 2. The magnetic toner used was a positive toner having an average particle diameter of 6 μm, and the amount of the internally added magnetic powder was 90 parts with respect to the resin part 100.

  The interval (SD interval) between the developing sleeve 3a and the photosensitive drum 1 is 200 μm. During development, the frequency is 2 kHz as the developing bias between the bias power source 7 and the developing sleeve 3a to the photosensitive drum, and the peak-to-peak voltage is 1 kVpp. A square wave bias was applied.

  A transfer material is conveyed from a paper feed cassette to a transfer device 100 described later by a paper feed mechanism (not shown), and a toner image on the photosensitive drum is transferred by the transfer device 100 and then sent to the fixing device 5 where the toner image is transferred. It is fixed on the transfer material by the action of heat and pressure.

  After the transfer is completed, the transfer drum remaining on the surface of the photosensitive drum 1 is removed by the cleaning blade 6a of the cleaning unit 6 to prepare for the next image formation.

  The transfer corona charger 103 applies a high voltage to a corona wire made of a tungsten wire or the like having a diameter of about 50 to 100 μm, a grounded shield plate surrounding the wire, an insulating block surrounding the fixing portion fixing the wire end, and the wire. It is comprised from the electric power feeding part. A transfer bias applying unit is connected to the power supply unit and supplies negative charges having a polarity opposite to that of the toner to the back surface of the transfer material. In this embodiment, a bias of −5 kV is applied. The shield plate is provided with a discharge opening on the surface facing the photosensitive drum and a laser light incident opening on the opposite surface. A laser driver drives the laser 101 in accordance with the timing of applying the transfer bias to generate laser light. The laser beam passes through the polygon mirror 102 through the laser beam incident opening of the shield and a place very close to the corona wire, and scans the back surface of the transfer material. Since the gas optical breakdown occurs in the optical path through which the laser beam has passed and discharge is more likely to occur than in places other than the laser beam path, the discharge from the corona wire coincides with the laser beam path when the laser passes through. Discharge occurs only on the back surface of the transfer material.

  The toner image on the photosensitive drum 1 is subjected to a Coulomb force toward the transfer corona charger 103, and the toner image moves to the transfer material, and is electrically applied to the transfer material by the negative charge applied to the back of the transfer material. Be bound. In the present embodiment, the discharge that does not contribute to the transfer in the direction other than the back surface of the transfer material due to the laser induced discharge is very small, so that the energy consumption efficiency is improved and the generation of ozone can be reduced. Since the generation of ozone can be reduced, ozone deterioration such as photosensitive drums and cleaning blades can be reduced and the life of the apparatus can be extended, and nitrogen oxides (NOx) generated by the oxidation of nitrogen in the air by ozone. And the generation of corona discharge products such as nitric acid generated by the reaction of the generated nitrogen oxides with moisture in the air can be reduced. By adhering to and depositing on these devices, the surface of the photoconductor is soiled, and the resistance of the photoconductor is reduced by absorbing the adsorbed corona discharge products. It is possible to prevent the occurrence of a defective image called image blur and image flow (state in which the surface charge of the image carrier leaks in the surface direction and the electrostatic charge latent image pattern is broken or not formed).

<Embodiment 2>
In the transfer device of this embodiment, the position of the corona wire is adjusted so that no discharge occurs even when a bias is applied when laser induced discharge does not occur. Therefore, when the laser is not irradiated, no discharge occurs even if a transfer bias is applied to the corona wire. The transfer bias is applied until the transfer material passes completely from before entering the transfer area, but the laser light for laser induced discharge starts from the time when the leading edge of the transfer material enters the laser beam path and the trailing edge of the transfer material passes through the laser beam path. At timing, the laser driver drives the laser 101 to emit light.

  In this embodiment, the discharge from the corona charger is a laser induced discharge, the laser light path and the discharge path coincide with each other, and the laser light serves as a trigger for the discharge of the corona charger. It discharges only in the direction of the transfer material only when it is being applied. As a result, only the discharge necessary for the transfer occurs only when the transfer is necessary. Therefore, since it is possible to perform only the minimum necessary discharge, energy consumption efficiency and generation of ozone can be minimized.

  In addition, since discharge is possible only in a very narrow area toward the back surface of the transfer material, a strong electric field is formed in the gap before entering the transfer area, and the toner on the photosensitive drum flies toward the transfer material. However, since a strong electric field is formed in the gap after passing through the transfer region, and the toner image once transferred onto the transfer material is not disturbed by the influence of the electric field, high image quality without scattering can be achieved.

<Embodiment 3>
The transfer device according to the present embodiment will be described with reference to FIG. 3. An endless transfer belt 104 includes three rollers 105 and 106 arranged substantially in parallel with each other in a direction substantially perpendicular to the transfer material conveyance direction. 107 is suspended. The driving roller 107 is driven by a driving roller driving device (not shown), and the transfer belt is rotationally driven in the arrow direction at a predetermined speed.

  In the driving roller portion, the transfer belt 101 and the transfer material are separated by curvature separation. To improve the separation of thin paper, it is effective to reduce the curvature, but if the diameter is too small, problems such as bending occur, so it is effective to set it to φ12 to 20 mm. The driven roller 105 can be moved up and down so that the photosensitive drum and the belt can be contacted and separated. This is because when the image is formed, the transfer belt and the photosensitive drum can move downward to improve the jam handling property so that a transfer nip can be formed.

The transfer belt 101 has a volume resistivity of 1 × 10 ⁷ to 10 ¹⁰ Ωcm according to a resistance measurement method based on JISK6911, a surface resistivity on the belt front side of 10 ⁹ to 10 ¹² Ω, and a surface resistivity on the inner side of the belt of 10 ⁸ to 10 ⁸ . It is made of a medium-resistance conductive material having 10 ¹¹ Ω, and has a belt circumferential length of 380 mm and a belt longitudinal length of 310 mm. The cleaning backup roller 106 is provided with a fur brush 108 at a position facing the belt, and cleans the surface of the transfer belt by rotating in the counter direction with the transfer belt 101. A transfer corona charger 103 is disposed on the inner side of the transfer belt below the photosensitive drum 1 and is connected to a bias applying unit to supply negative charges having a polarity opposite to that of the toner to the back surface of the transfer material via the transfer belt. . In this embodiment, a bias of −6 kV is applied. The toner image on the photosensitive drum 1 is subjected to Coulomb force toward the transfer corona charger 103, and the toner image moves to the transfer material and is electrically restrained on the transfer material by the negative charge applied to the back side of the transfer material. Is done.
In the transfer apparatus of the present embodiment, the position of the corona wire is adjusted so as not to discharge even when a bias is applied when laser induced discharge does not occur. The transfer bias is applied until the transfer material passes completely from before entering the transfer area, but the laser light for laser-induced discharge starts from the time when the margin at the front end of the transfer material enters the laser beam extension line. The laser driver drives the laser 101 to emit light at a timing when the blank portion of the laser beam passes over the laser optical path extension line.

  In this embodiment, the discharge from the corona charger is a laser induced discharge, the laser light path and the discharge path coincide with each other, and the laser light serves as a trigger for the discharge of the corona charger. The place where the charge is applied by the discharge of the corona charger coincides. As a result, since the laser does not emit light at the leading edge of the transfer material, no discharge from the corona charger occurs and no charge is applied.After that, the laser emits light, and the corona charger starts discharging until the leading edge of the image. Then, electrification is applied to the transfer material, and the toner image on the photosensitive drum is transferred to the transfer material. Since no transfer bias is applied to the transfer material tip, even if the transfer material tip has a large burr and faces the transfer belt, an adsorption force is generated between the transfer material and the photosensitive drum, Transfer of the leading edge of the transfer material due to the loss of the adsorbability of the leading edge of the paper to the transfer belt, resulting in poor image quality due to poor transfer, especially the rigidity of recycled paper, thin paper, coated paper, etc., so-called paper stiffness It is possible to prevent the material from being wound around the photosensitive drum.

  Therefore, in the present embodiment, since it is a non-contact transfer bias applying means, the pressure applied between the image carrier and the transfer material can be reduced, so that not only the transfer void is difficult to occur, but also the transfer The belt system's original stable transfer material transfer, transfer of toner images to the transfer material, and separation / transfer of the transfer material after transfer are realized, and it can be used for various transfer materials from thin paper to thick paper. Obtainable. In addition, when a corona charger is installed in the transfer belt, ozone is likely to stay inside the belt, and the durability of the transfer belt may be significantly reduced due to ozone deterioration on the inner surface of the transfer belt. Met.

  However, in the present embodiment, since the generation of ozone can be minimized, no exhaust fan or duct is required, the ozone deterioration of the transfer belt can be prevented, and high durability of the transfer belt can be realized.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to Embodiment 1 of the present invention. It is a schematic block diagram which shows embodiment of the transfer apparatus which concerns on Embodiment 3 of this invention.

Explanation of symbols

101 Laser 102 Polygon mirror 103 Transfer corona charger 104 Transfer belt

Claims (4)

In an image forming apparatus having a corona charger that discharges by applying a voltage to a stretched wire electrode, and an image carrier on which a toner image is formed,
An image forming apparatus, wherein a discharge from a corona charger is guided to a predetermined place by laser induced discharge that induces discharge by irradiating a laser beam.   2. The image forming apparatus according to claim 1, wherein the laser beam is a trigger for discharging the corona charger.   3. The image forming apparatus according to claim 1, wherein the corona charger is a transfer charger for transferring a toner image formed on the image carrier to a transfer material.   The image forming apparatus according to claim 1, wherein the corona charger is a transfer-type transfer bias applying unit having a transfer belt that carries a transfer material and conveys the transfer material to a transfer nip portion.

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