JP2006350020A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of efficiently removing discharge products such as nitrogen oxide and ozone produced by a discharge means in the image forming apparatus. <P>SOLUTION: In the image forming apparatus having the discharge means 302 which performs processing for applying or eliminating charge to an object in image forming operation, the discharge means 302 has: a discharge part for image forming which performs the processing for applying or eliminating charge to the object by discharge in the image forming operation; a plasma discharge part which generates plasma discharge from a discharge electrode to a counter electrode 25 different from the object; and a photocatalyst 26 which is arranged so as to receive light by the plasma discharge, and is constituted so that power under a driving condition different between when it is for driving the discharge part for image forming and when it is for driving the plasma discharge part is switched and input. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile using an electrophotographic method or an electrostatic recording method. More specifically, the present invention relates to a charging process of an image carrier, and from an image carrier to a transferred material. The present invention relates to an image forming apparatus having means for removing a discharge product in an image transfer process to the head.

  For example, an electrophotographic image forming apparatus generally includes a cylindrical photosensitive drum having a photosensitive layer on the surface, and a corona charger is used as a primary charging means for charging the surface of the photosensitive drum. Yes. The corona charger is a so-called non-contact type charging means that applies a high voltage to a charging wire or an electrode in the air and gives positive or negative ions generated by the discharge at this time to the surface of the photosensitive drum. .

  The corona charger ionizes oxygen molecules in the atmosphere to generate unnecessary ozone, and also generates nitrogen oxides (NOx) and the like as discharge generation substances. This ozone weakens the electric field of the corona discharge and inhibits the surface of the photosensitive drum from reaching a desired potential, or deteriorates the performance of the photosensitive layer on the surface of the photosensitive drum, thereby inducing image defects. Nitrogen oxides adhere to the surface of the photoreceptor and reduce the surface resistance, which causes problems such as an image flow phenomenon.

  Therefore, conventionally, using a filter coated with activated carbon or a catalyst, it is adsorbed with activated carbon or decomposed with a catalyst to remove discharge products such as ozone and nitrogen oxides generated by the corona charger. It was broken. This filter is generally disposed so as to remove ozone with an ozone filter while discharging air containing ozone with an exhaust device such as a drive fan. For example, a technique for discharging ozone through a duct by driving a driving fan is disclosed (Patent Document 1). The duct is integrally formed with a duct guide that guides a recording material such as paper to a transfer site. Further, as a technique applied to an electrophotographic image forming unit, a technique is disclosed in which a duct is connected to a shield case of a corona charger so that ozone can be efficiently collected (Patent Document 2). .

  As ozone removing means other than the above-mentioned adsorption-type filters and catalyst-type filters, a technique is disclosed in which a heating element is provided in a charging device to thermally decompose ozone generated in the charging device (Patent Document 3).

Further, as a technique related to the removal of nitrogen oxides, a technique using a three-way catalyst (HC-CO reduction action) is generally known as an exhaust gas treatment related technique. Furthermore, assuming that the selective reduction action by ammonia (NH ₃ ) is used, ammonia gas is generated as necessary, and NOx in the exhaust gas discharged from the combustion equipment is removed by the catalytic reaction of this ammonia gas and NOx. A technique is disclosed (Patent Document 4).

  Activated carbon has been mainly used as the adsorption filter as described above. However, these adsorptive filters operate by incorporating molecules into the micropores on the surface, and thus have a limited ability to incorporate molecules. For this reason, it is necessary to periodically inspect and replace the filter. If the filter is not replaced, the adsorption capacity decreases. As a filter capable of improving such a point, a filter using titanium oxide, which is typically called a photocatalyst, is sometimes used.

This photocatalyst is a substance that absorbs light and becomes in a high energy state, and gives the reaction substance a chemical reaction. When titanium dioxide (TiO ₂ ), which is a photocatalytic substance, absorbs light, holes are formed in the valence band, and it reacts with electrons of neighboring substances. For example, these holes react with water and dissolved oxygen to generate OH radicals, which decompose harmful substances. Currently, it is used in various applications such as anti-fouling measures for building outer walls and window glass using properties such as hydrophilicity, which is another feature, such as air purifiers that utilize oxidative decomposition. Is planned.

  In particular, in the case of an electrophotographic image forming apparatus, nitrogen oxidation generated by discharge at the contact portion between the contact charging member and the target by adding or applying a photocatalytic substance to the surface layer of the contact charging member. Some products and ozone are decomposed by a photocatalytic substance (Patent Document 5).

  Further, regarding the removal of nitrogen oxides generated in the electrophotographic image forming apparatus, NOx generated by the discharge is decomposed by using a method in which creeping glow discharge devices are arranged in parallel on the same substrate of the discharge electrode for charging. A charging device is disclosed (Patent Document 6).

  As described above, ozone and nitrogen oxides generated in an image forming apparatus having an electrostatic copying process adversely affect an image with respect to high image quality. In addition, according to the announcement of “Air Quality Guidelines: Guidelines for Air Quality” by WHO, improvement of the air quality discharged from the image forming apparatus at a higher level is demanded. Also, an effective method for removing nitrogen oxides that cause image deterioration is desired due to the demand for higher image quality as described above.

  As described above, for example, in an electrophotographic image forming apparatus, removal of discharge products such as ozone and nitrogen oxides generated in an image forming unit which is the heart of the image forming device is an important issue. As conventional techniques for this, the above-described ones can be mentioned, but improvement is still required. For example, in the physical removal method using a filter disclosed in Patent Document 1 and Patent Document 2, performance deterioration due to aging of the filter is inevitable. Moreover, in the method of thermal decomposition of ozone disclosed in Patent Document 3, there is a concern about the influence of temperature on, for example, a developer. Further, in the method of adding or applying a photocatalytic substance to the surface layer of the contact charging member disclosed in Patent Document 5, appropriate conditions are considered in relation to the ability as a charging means and the ability to remove discharge products. Setting is difficult. The nitrogen oxide removal method disclosed in Patent Document 6 also requires a complicated structure in which creeping glow discharge devices are arranged in parallel on the same substrate as the discharge electrode for charging. Furthermore, in Patent Document 6, no consideration is given to the removal of ozone generated during discharge.

In the above description, the conventional problems have been described, particularly in relation to the primary charging means for charging the photosensitive drum. However, for example, in an image forming apparatus using an electrophotographic image forming process, other than the primary charging means. Discharge means for applying or removing a charge to a target by discharge is used. For example, post-charging means for discharging the charged toner image (toner) on the photosensitive drum, transfer charging means for transferring the toner image on the photosensitive drum to the recording material, and discharging the recording material onto which the toner image has been transferred There is a separation charging means for separating from the surface of the photosensitive drum. Since discharge products such as nitrogen oxides and ozone are generated from these discharge means, in particular, non-contact discharge means for applying or removing charges in a non-contact manner to a target such as a corona charger, the same problem occurs. There is.
JP-A-4-67184 JP 2003-307915 A Japanese Patent Laid-Open No. 05-281829 Japanese Patent Laid-Open No. 11-165042 JP 2000-356931 A JP 09-114191 A

  An object of the present invention is to provide an image forming apparatus capable of efficiently removing discharge products such as nitrogen oxides and ozone generated by discharge means in the image forming apparatus.

  One of the more detailed objects of the present invention is to prevent nitrogen oxides and ozone generated by the discharge means in the image forming apparatus with a simple configuration without worrying about the replacement timing of replacement parts such as filters. Another object of the present invention is to provide an image forming apparatus that can be removed over a long period of time.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus having discharge means for applying or removing charge to an object in an image forming operation, wherein the discharge means applies charge to the object by discharging in the image forming operation. Alternatively, an image-forming discharge portion that performs a removal process, a plasma discharge portion that generates a plasma discharge from the discharge electrode with respect to a counter electrode that is different from the target, and a photocatalyst that is arranged to receive the light of the plasma discharge. The image forming apparatus is characterized in that electric power under different driving conditions is switched and input for driving the image forming discharge section and driving the plasma discharge section.

  According to the present invention, discharge products such as nitrogen oxide and ozone generated by the discharge means in the image forming apparatus can be efficiently removed. In addition, as one of the operational effects obtained by the present invention, nitrogen oxide, ozone, etc. generated by the discharge means in the image forming apparatus are concerned with the replacement timing of replacement parts such as a filter with a simple configuration. Without being able to be removed over a long period of time.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
[Image forming apparatus]
First, the overall configuration and operation of the image forming apparatus of this embodiment will be described with reference to FIG. FIG. 1 shows a schematic cross section of an image forming apparatus 1 of the present embodiment. The image forming apparatus 1 of this embodiment is a copying machine using an electrophotographic system.

  A folding device 400 and a finisher 500 are connected to the image forming apparatus 1 of the present embodiment. The image forming apparatus 1 includes an image reader 200 that reads a document image and an apparatus main body (printer) 300.

  A document feeder 100 is mounted on the image reader 200. The document feeder 100 feeds a desired number of documents set upward on the document tray one by one in order from the first page in the left direction in the figure. Then, the document is conveyed from the left to the right in the drawing on the platen glass 102 through the curved path, passed through the position where the document is read, and then discharged toward the external discharge tray. When the original passes through the sink reading position on the platen glass 102 from the left to the right in the figure, the image of the original is read by the scanner unit 104 held at a position corresponding to the sink reading position. This reading method is generally called document scanning. Specifically, when the original passes through the reading position, the reading surface (image recording surface) of the original is irradiated with the light of the lamp 103 of the scanner unit 104, and the reflected light from the original is reflected by the mirrors 105 and 106. , 107 to the lens 108. The light that has passed through the lens 108 forms an image on the imaging surface of the image sensor 109.

  By transporting the document so that it passes through the flow reading position from the left to the right in the figure, the document is read with the direction perpendicular to the document transport direction as the main scanning direction and the transport direction as the sub-scanning direction. A scan is performed. That is, when the document passes through the flow reading position, the document image is read in the sub-scanning direction while reading the document image by the image sensor 109 line by line in the main scanning direction, thereby reading the entire document image. .

  The optically read image is converted into image data by the image sensor 109 and output. The image data output from the image sensor 109 is subjected to predetermined processing in an image signal control unit (not shown), and then converted into a video signal to an exposure control unit 303b of an exposure apparatus (laser scanner) 303 provided in the printer 300. Entered.

It is also possible to read a document image by transporting the document onto the platen glass 102 by the document feeder 100 and stopping it at a predetermined position, and scanning the scanner unit 104 from left to right in the drawing in this state. . This reading method is generally called fixed document reading.
When reading a document without using the document feeder 100, first, the user lifts the document feeder 100 and places the document on the platen glass 102. Then, the scanner unit 104 is scanned from the left to the right in the figure to read the original image. Therefore, when reading a document without using the document feeder 100, a fixed document reading is performed.

  An exposure control unit 303b of a laser scanner 303 as an exposure unit provided in the printer 300 modulates and outputs a laser beam based on the input video signal. The laser light is irradiated onto a cylindrical electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 301 while being scanned by a polygon mirror 303a. An electrostatic image (latent image) corresponding to the scanned laser beam is formed on the photosensitive drum 301. Here, the exposure control unit 303b outputs a laser beam so that a correct image (an image that is not a mirror image) is formed at the time of document fixed reading. As will be described in detail later, prior to exposure by the laser scanner 303, the surface of the photosensitive drum 301 is charged substantially uniformly by a primary charger 302 as primary charging means. In this embodiment, the primary charger 302 is a corona charger that is a non-contact discharge means for processing an object in a non-contact manner.

  The electrostatic image on the photosensitive drum 301 is visualized as a developer image (toner image) by the toner of the developer supplied from the developing device 304 as a developing unit.

  Also, recording material P such as recording paper (sheet) is supplied from each cassette 309, 310, manual paper feed unit 311, or double-sided conveyance path 314 as a recording material supply unit at a timing synchronized with the start of laser beam irradiation. Is done. The recording material P is conveyed between the photosensitive drum 301 and a transfer charger 305 as a transfer unit. The toner image formed on the photosensitive drum 301 is transferred onto the supplied recording material P by a transfer bias voltage applied to the transfer charger 305. The recording material P to which the toner image has been transferred is separated from the photosensitive drum 301 by a separation bias voltage applied to a separation charger 306 disposed so as to be opposed to the photosensitive drum 301 integrally with the transfer charger 305. As will be described in detail later, in this embodiment, both the transfer charger 305 and the separation charger 306 are corona chargers that are non-contact discharge means for processing an object in a non-contact manner.

  Next, the recording material P is conveyed to the fixing unit 308. The fixing unit 308 fixes the toner image on the recording material P by heating and pressurizing the recording material P. The recording material P that has passed through the fixing unit 308 is discharged from the printer 300 to the outside, that is, the folding device 400 in this embodiment, via the flapper 312 and the discharge roller 315. The toner (transfer residual toner) remaining on the photosensitive drum 301 after the toner image is transferred to the recording material P is collected by the cleaning device 307.

  Here, when the recording material P is discharged in a state where the image forming surface faces downward (face down), the recording material P that has passed through the fixing unit 308 is once guided into the reverse path 313 by the switching operation of the flapper 312. . Then, after the trailing edge of the recording material P passes through the flapper 312, the recording material P is switched back and discharged from the printer 300 by the discharge roller 315. This form of paper discharge is called reverse paper discharge. This reverse discharge is performed in order from the first page, such as when an image read using the document feeder 100 is formed on a sheet, or when an image output from a computer is formed on a recording material P. This is performed at the time of forming, and the order of the recording materials P after the discharge becomes the correct page order.

  Further, when a hard recording material P such as an OHP sheet is fed from the manual paper feed unit 311 and an image is formed on the recording material P, the recording material P is not guided to the reverse path 313 but the recording material P is used. The sheet is discharged by the discharge roller 315 with the P image forming surface facing upward (face-up).

  Further, when the double-sided recording mode in which image formation is performed on both sides of the recording material P is set, the recording material P is guided to the reverse path 313 by the switching operation of the flapper 312, and then the recording material P is transferred to the double-sided conveyance path. Transport to 314. The recording material P guided to the duplex conveyance path 314 is fed again between the photosensitive drum 301 and the transfer charger 305 and separation charger 306 at the timing described above.

  The recording material P discharged from the printer 300 is sent to the folding device 400. The folding device 400 performs a process of folding a sheet into a Z shape. For example, when the paper is A3 size or B4 size and the folding process is designated, the folding device 400 performs the folding process of the recording material P. In other cases, the paper discharged from the printer 300 passes through the folding device 400 and is sent to the finisher 500. The finisher 500 is provided with an inserter 501 for feeding a special sheet (insert sheet) such as a cover sheet or a slip sheet to be inserted between the recording materials P on which images are formed. The finisher 500 performs post-processing such as bookbinding, binding, and punching. The recording material P that has been processed by the finisher 500 or simply passed through the finisher 500 is discharged onto discharge trays 502 and 503.

[Discharge means]
Incidentally, in the image forming apparatus 1, the entire surface of the photosensitive drum 301 is substantially uniformly charged by the primary charger 302 before the laser beam is irradiated to form an electrostatic image. Further, when the toner image that has been visualized by attaching toner to the electrostatic image is transferred to the recording material P, the recording material P is charged by the transfer charger 305. Further, after the toner image is transferred to the recording material P, when the recording material P is separated from the photosensitive drum 301, the recording material P is charged (discharged) by the separation charger 306.

  These primary charger 302, transfer charger 305, and separation charger 306 generate corona discharge between the target (photosensitive drum 301 and recording material P) around the photosensitive drum 301. Therefore, it is generally known that discharge products such as nitrogen oxide and ozone are generated around the photosensitive drum 301. As described above, when these products stay around the photosensitive drum 301, they cause damage to the photosensitive drum 301 and cause image deterioration such as image flow.

  Therefore, in the present embodiment, the image forming apparatus 1 having the discharge unit that applies or removes the charge to the target in the image forming operation is applied to or removed from the target by the discharge unit in the image forming operation. A photocatalyst containing an image-forming discharge part for processing, a plasma discharge part for generating a plasma discharge from the discharge electrode with respect to a counter electrode different from the above object, and a photocatalyst substance arranged to receive the light of the plasma discharge (Photocatalyst holding body), and the power for driving conditions different between the image forming discharge section and the plasma discharge section is switched on.

  The electric power input to the image forming discharge unit and the plasma discharge unit may be a DC voltage, an AC voltage, or a pulse voltage. In a preferred embodiment, plasma discharge is generated by pulse discharge because higher plasma discharge energy is obtained by pulse discharge. Further, the adjustment of the power input to the image forming discharge unit and the plasma discharge unit, that is, the setting of the driving conditions of the high voltage discharge unit can be performed by adjusting the applied voltage level and / or the oscillation frequency. . As a result, the driving conditions of the high-voltage discharge section can be made different between the specifications for image formation and the specifications intended for low-temperature plasma generation. The discharge means can be used as a means for applying or removing a charge to a target in an image forming operation, and can be used as a plasma reactor. In a preferred embodiment, the discharge means is utilized as a pulsed discharge plasma reactor. The discharge generated in the plasma discharge section may be a pulse discharge, a creeping discharge, a silent discharge, or the like, as long as it can generate a plasma discharge (low temperature plasma, atmospheric pressure plasma) at normal temperature and normal pressure. .

  In a preferred embodiment, power is input from a common power source for the image forming discharge section and the plasma discharge section. This is extremely advantageous in reducing the power supply cost. In this case, the high voltage generator serving as the power supply means supplies the power input from the power source to the image forming discharge unit and the plasma discharge unit, respectively, for the driving conditions for image formation (for processing discharge) and for plasma discharge. Means for switching between driving conditions is provided. Of course, it is also possible to input power from separate power sources to the image forming discharge section and the plasma discharge section. In another embodiment, power may be supplied from a common power source to at least the plasma discharge unit and at least one other element (powered supply element) in the apparatus. In a preferred embodiment, the discharge means is a primary charger 302, which is used as a pulsed discharge plasma reactor. In this case, switching means for changing the output voltage from the DC voltage output in the image forming operation to the pulse output is provided in the output stage of the power source.

In addition, by providing a photocatalyst containing a photocatalytic substance such as titanium dioxide (TiO ₂ ), the generation of active species by plasma discharge and the action of removing discharge products by activation of the photocatalyst by light of plasma discharge are utilized. can do. Usually, a photocatalyst is arrange | positioned between the discharge electrode and counter electrode of a plasma discharge part. Moreover, a photocatalyst can also be arrange | positioned on the counter electrode of a plasma discharge part. In a preferred embodiment, the photocatalyst includes a porous material having excellent adsorption performance such as silica gel and apatite in addition to the photocatalytic substance, and has an adsorption action.

  With the above-described configuration, it is possible to remove and decompose the discharge generation material such as nitrogen oxide and ozone generated by the discharge means in the image forming operation at the generation source. That is, according to the configuration as described above, the high-pressure discharge part that is a generation source of discharge generation substances such as nitrogen oxide and ozone generated during image formation is typically connected to the high-pressure discharge part. It can be used as a plasma reactor by changing the driving conditions of the voltage generator. And, by generating oxidation / reduction action by active species generation by plasma discharge and oxidation / decomposition action of photocatalyst by light of plasma discharge at the electrode part, the discharge product can be decomposed and removed at its source. It becomes possible. In addition, by using a photocatalyst having an adsorption action, ozone that has a slow reaction rate and nitrogen oxides that have not been decomposed by light of plasma discharge are once adsorbed, so that the emission amount is reduced and the plasma after the next time is reduced. It can be decomposed during discharge.

  Although described in more detail below, in order to avoid complexity, here, the primary charger 302 will be described in detail as an example of the discharging means according to the present invention. It will be easily understood that the same configuration can be applied to other discharge means such as the transfer charger 305 and the separation charger 306 in the image forming apparatus 1 of this embodiment. Hereinafter, as will be described in detail, in this embodiment, the function of the pulse discharge plasma reactor is combined with the primary charger. Therefore, hereinafter, for the sake of simplicity, the discharge means having the functions of both the primary charger and the pulse discharge type plasma reactor is simply referred to as “charger 20”.

  FIG. 2 shows a schematic cross section of the charger 20 and a high voltage generator 30 that inputs power to the charger 20. The charger 20 is disposed substantially parallel to the longitudinal direction with a predetermined gap with respect to the surface of the photosensitive drum 301. The charger 20 has a discharge wire (discharge electrode) 21 and a grid electrode 22 in a shield case 23. A high voltage generating power source (primary charging high voltage power source) 31 for a primary charger, which is a DC power source for applying a positive or negative DC voltage, is connected to a discharge wire 21 by a high voltage output intermittent switch 32 (described later). Connected through. In the present embodiment, the primary charging high-voltage power supply 31 and the high-voltage output intermittent switch 32 constitute a high voltage generation unit 30 as power supply means.

  The opening 23 c on the photosensitive drum 301 side of the shield case 23 is covered with the grid 22, but air can pass through the holes of the grid 22. Further, the side plate 23 b of the shield case 23 is partially formed of an electrical insulator 24. The grid 22 is connected to a grid bias power source (not shown).

  In the image forming operation, a high voltage is applied to the discharge wire 21 from the primary charging high-voltage power supply 31 and a high voltage is applied to the grid 22 from a grid bias power supply (not shown). As a result, the surface of the photosensitive drum 301 is substantially uniformly charged to a predetermined polarity and potential by corona ions generated by corona discharge. In the present embodiment, the discharge wire 21 constitutes an image forming discharge portion.

  In this embodiment, the charger 20 functioning as the primary charger 302 is a corona charger provided with a grid 22 to which a grid bias voltage is applied in order to suppress unevenness of the charging potential of the target, that is, a scorotron. It is assumed that However, the present invention is not limited to this, and a corotron without the grid 22 may be used.

  On the other hand, the charger 20 has a function of a pulse discharge plasma reactor in addition to the function of the primary charger as described above. In the present embodiment, the discharge wire 21 also serves as a discharge electrode of the plasma discharge portion. In this embodiment, the counter electrode 25 constituting the plasma discharge portion is provided inside the top plate 23a of the shield case 23. The counter electrode 25 may be integrally formed as a part or all of the top plate 23a of the shield case 23. As described above, the discharge wire 21 is connected to the primary charging high-voltage power supply 31, which is a DC power supply, via the high-voltage output intermittent switch 32 as a switching means. The counter electrode 25 is grounded via a high voltage output intermittent switch 32. When the charger 20 functions as a pulse discharge type plasma reactor, the output of the charging high-voltage power supply 31 is changed to a pulse output using the high-voltage output intermittent switch 32, so that the discharge wire 21 and the counter electrode 25 are placed between them. Apply high voltage pulse. Thereby, plasma discharge can be generated between the discharge wire 21 and the counter electrode 25. In this embodiment, the discharge wire 21 and the counter electrode 25 constitute a plasma discharge part. In the present embodiment, the plasma discharge part is provided at the opposite position separately from the image forming discharge part (that is, the charging treatment discharge part).

  As described above, according to this embodiment, the image forming charger (here, the primary charger for charging the photosensitive drum) and the pulse discharge plasma reactor for the purpose of generating low temperature plasma are integrated. Configured. In this embodiment, the discharge wire 21 is shared by the primary charger and the pulse discharge plasma reactor. This is extremely advantageous in reducing the apparatus cost and simplifying the configuration. Also, when the discharge wire 21 is shared by the primary charger and the pulse discharge plasma reactor, as shown in FIG. 2, the distance L2 from the discharge wire 21 to the counter electrode (plasma discharge electrode) 25 is an image. It is arranged so as to be shorter than the formation discharge distance (that is, the distance from the discharge wire 21 to the surface of the photosensitive drum 301 to be charged) L1.

The charger 20 is provided with a photocatalyst 26 containing a photocatalytic substance which is TiO ₂ in this embodiment. The photocatalyst 26 is disposed at a position where it can receive plasma discharge light. Typically, the photocatalyst 26 is disposed between a discharge wire (discharge electrode) 21 and a counter electrode 25 constituting a plasma discharge unit. In the example shown in FIG. 2, the photocatalyst 26 is disposed on the surface of the counter electrode 25. FIG. 3 shows the charger viewed from the direction of the top plate 23 a of the shield case 23. As shown in FIG. 3, a plurality of long photocatalysts 26 are arranged substantially parallel to the longitudinal direction of the charger 20. The photocatalysts 26 are arranged so as to be substantially parallel to the longitudinal direction of the discharge wire 21 and at a predetermined distance d1.

  In addition, if this photocatalyst (photocatalyst holding body) 26 is arrange | positioned on the electrode surface, it can be provided by apply | coating the photocatalyst coating material containing a photocatalyst substance. Further, as the photocatalyst 26, an electric insulator having a photocatalyst paint applied to the surface can be used in a desired shape. However, as the photocatalytic action, the larger the surface area, the higher the catalytic effect due to the increased probability of contact with the decomposition target substance. For this reason, in order to enhance the action of the photocatalyst, the photocatalyst 26 may be arranged or applied in a striped manner in the longitudinal direction of the charger 20 like the grid 22.

  The photocatalyst 26 preferably has an adsorption action. That is, the photocatalyst 26 preferably contains a photocatalytic substance and a highly adsorbable porous material. As will be described in detail later, for example, the photocatalyst 26 is formed of a composite material containing a photocatalytic substance and a porous material, or the surface of an electrical insulator contains a photocatalytic substance and a porous material. This can be achieved by using a material coated with a paint having an adsorption action. Furthermore, the photocatalyst 26 may be an electrode itself. In this case, the electrode (for example, the counter electrode 25) includes the function of the photocatalyst.

  In order to further utilize the photocatalytic action, it is possible to arrange the photocatalyst 26 as shown in FIGS. FIG. 4 is a schematic cross-sectional view of the charger 20, and FIG. 5 is a view of the charger 20 as viewed from the top plate 23 a direction of the shield case 23. That is, between the discharge wire 2 and the counter electrode 25, a plurality of plate materials (insulating plates) made of an electrical insulator having a photocatalyst paint applied on the surface are arranged in parallel as the photocatalyst 26. That is, the surfaces of the photocatalyst 26 made of a plurality of insulating plates are opposed to each other, and the photocatalyst 26 is also arranged in parallel to the longitudinal direction of the discharge wire 21. In this case, the counter electrode 25 is preferably a mesh structure. By using in-machine convection and by using a photocatalyst paint that has an adsorption action, it is more efficient to decompose nitrogen oxides by oxidation / reduction with photocatalysts and to absorb nitrogen oxides and ozone that cannot be decomposed. Can be performed automatically.

  The driving condition of the charger 20 as the primary charger for charging the surface potential of the photosensitive drum 301 to a predetermined value in the image forming operation is within a voltage range that can be output from the primary charging high-voltage power supply 31. The maximum is about DC10KV. As a result, the surface potential of the photosensitive drum 301 is controlled in the range of about several hundred V to 1 kV.

  On the other hand, the driving level of the charger 20 when used as a pulse discharge plasma reactor varies depending on the molecules to be decomposed / removed. In general, negative ions are generated by dissociation / electron attachment including excitation of molecules / atoms and generation of free radicals at 6 eV or less, and generation of positive ions requires about 5 to 25 eV. Here, the high voltage power supply output setting is set to 5 to 7 kV for NOx. Then, this voltage is intermittently applied during an ON period of about 1 μs, thereby sustaining the discharge at the pulse discharge electrode (plasma discharge part) for several seconds.

  In the image forming unit, in addition to the primary charger 302, a high-voltage power source is provided for each of the transfer charger 306, the developer 304, the separation charger 306, and the like. And according to the use, there are a high-voltage output form such as a direct-current output and an alternating-current output. Although the output level of the high voltage is different, it is mainly several hundreds to several kV, and in the case of AC output, the output frequency is about several hundreds to 2 kHz.

  FIG. 7 shows a schematic connection diagram of the high-voltage power supply in this embodiment. In the high voltage generation unit (high voltage power supply unit) 30, the drive conditions are set for image formation (for processing discharge) and for plasma discharge (for decomposition / removal of discharge products) according to a command from the controller unit 10 of the image forming apparatus 1. And can be switched. Information related to this command is stored in a memory 40 built in or connected to the controller 10. Further, the drive condition or information designating the drive condition is stored in the memory 40. At this time, the high-voltage power supply unit 30 also performs output connection switching as necessary. As will be described later, the high voltage power supply for primary charging is not used as the power supply for plasma discharge, and it is also possible to use a plasma reactor that is not a pulse discharge type. In this case, the power supply for plasma discharge is 1 A configuration different from the high voltage power supply for secondary charging can be used.

  As described above, the ionization / excitation of the target substance by plasma discharge and the decomposition of the target substance based on the generation of active species by the photocatalyst decompose and remove the discharge product as the target substance in each interaction. . The operation timing of the charger 20 (that is, the primary charger 302) as a pulse discharge plasma reactor can be arbitrarily set as long as the primary charger 302 is not involved in the image forming operation. For example, the operation timing of the plasma reactor is such that the surface potential control by the primary charger 302 is performed before the electrostatic image is formed on the photosensitive drum 301 in the process of the image forming operation (for example, copy production). Any setting can be made as long as it is performed and before the charging operation of the photosensitive drum 301 for forming the next electrostatic image.

  In the controller unit 10 of the image forming apparatus 1, the operation timing of each unit is controlled so that the entire image forming process is accurately executed by the installed software. Therefore, operation timing and output level control of a high-voltage power source used for charging, transfer, and development are also performed. Therefore, it is possible to easily switch the operation of these high-voltage power supplies as necessary and change the output level. As a result, the high-voltage power supply can be shared for various uses, including a high-voltage power supply for primary charging.

  Even if a high-voltage power source for plasma discharge is used for another purpose that is not for primary charging, it can be used for plasma discharge at an arbitrary timing as long as the high-voltage power source is not involved in the image forming operation. No problem.

  When the charger 20 is used as a pulse discharge type plasma reactor, the high voltage output intermittent switch 32 provided in the high voltage generator 30 may be either a mechanical switch or a semiconductor switch. In the case of a pulse discharge type plasma reactor, a rotary type mechanical switch having a simple configuration and a fast voltage rise at turn-on is used more often.

  With the above configuration, a discharge product generated by discharge under driving conditions for image formation, particularly when nitrogen oxide is the main target, higher plasma discharge energy (here, high voltage due to pulse discharge)・ Implementation of molecular ionization and excitation using repetitive energy of discharge in a short time). At the same time, the photocatalyst provided in the electrode portion or the like also causes a decomposition action using the discharge light. These interactions make it possible to reliably decompose and remove nitrogen oxides.

  In the above description, the function of the plasma reactor provided integrally with the charger 20 together with the function of the primary charger has been described as being achieved by the pulse discharge plasma reactor. However, the present invention is not limited to this. Is not to be done. Not only the pulse discharge type but also a plasma reactor such as a creeping discharge type may be used. Further, as described above, when the charger 20 functions as a plasma generator, it is possible to use another high voltage generating power source without using the primary charging high voltage power source 31.

  For example, FIG. 6 shows an example when the charger 20 is used as a creeping discharge plasma reactor. That is, the charger 20 shown in FIG. 6 has a discharge electrode 27 and a counter electrode 28 as a pair of opposing electrodes. A discharge element is configured in such a manner that an electric insulator (insulator) 29 is sandwiched between the discharge electrode 27 and the counter electrode 28 as a dielectric.

  In the illustrated example, the discharge electrode 27 forms part of the top plate 23 a of the shield case 23. The insulator 29 forms part of both side plates 23 b and 23 b of the shield case 23, and a part of the top plate 23 a of the shield case 23 is also formed of the insulator 29.

  The counter electrode 28 is arranged in the vicinity of the grid 22 and can be opened and closed in a direction substantially perpendicular to the longitudinal direction of the photosensitive drum 301 from both side plates 23b and 23b of the shield case 23. That is, first and second counter electrodes 28a and 28b are provided.

  In this case, an AC high voltage is applied between the discharge electrode 27 and the counter electrodes 28a and 28b with the counter electrode 28 closing the opening 23c on the photosensitive drum 301 side of the shield case 23. As a result, electric charges are uniformly generated on the surface of the insulator 29 which is a dielectric, and a discharge is generated between the counter electrodes 28a and 28b. That is, in this example, the discharge electrode 27, the counter electrodes 28a and 28b, and the insulator 29 constitute a plasma discharge portion. The configuration when the charger 20 functions as a primary charger is the same as the charger 20 shown in FIG.

In the charger 20 of FIG. 6, a photocatalyst paint is applied to the surface of the insulator 29 as a photocatalyst 26 containing a photocatalytic substance which is TiO _{2 in} this example. That is, the insulator 29 includes the function of the photocatalyst 26.

  The open / close counter electrodes 28a and 28b are opened during normal image forming operation and closed during plasma discharge. Thereby, nitrogen oxides can be decomposed by plasma discharge in a state where discharge products such as ozone and nitrogen oxides generated during image formation are confined.

  In addition, you may use what has the photocatalyst 26 on the surface as this open / close type counter electrode 28a, 28b. For example, the photocatalyst 26 having an adsorption action, which is a composite material containing the photocatalytic substance and the porous material as described above, can be used as the counter electrodes 28a and 28b. Further, the photocatalyst 26 may be disposed between the discharge electrode 27 (and the insulator 29) and the counter electrode in the same manner as the charger of FIG.

  The high voltage generator 30 that supplies power to the charger 20 shown in FIG. 6 has a power supply for image formation and a power supply for plasma generation separately. That is, the charger 20 shown in FIG. 6 has a function as a creeping discharge type plasma reactor having the above configuration. Accordingly, in order to apply an AC high voltage between the discharge electrode 27 and the counter electrodes 28a, 28b, for example, the output of an AC high voltage generating power source (developing high voltage power source, AC high voltage power source) for the developing device is several kV, frequency 2 kHz. It can be used as a degree. That is, as shown in FIG. 6, the discharge electrode 27 of the charger 20 is connected to the development high voltage power supply 33 via the high voltage output changeover switch 34. When the charger 20 functions as a plasma reactor, the output of the development high voltage power supply 33 is switched to the discharge electrode 27 side by a high voltage output changeover switch, and an alternating high voltage is applied between the discharge electrode 27 and the counter electrode 28. That is, in this example, the high voltage generator 30 is configured by the primary charging high-voltage power supply 31, the development high-voltage power supply 33, and the high-voltage output changeover switch 34. In the case of such a creeping discharge type plasma reactor, the high voltage output changeover switch 34 is either a mechanical switch or a semiconductor switch, similar to the high voltage output intermittent switch 32 in the case of the above-described pulse discharge type plasma reactor. May be used.

[photocatalyst]
Here, the photocatalyst will be described in more detail.

As shown in FIG. 8, when TiO ₂ is irradiated with light, electrons (e−) and holes (p +) are generated on the surface of TiO ₂ . The generated electrons and holes react with oxygen (O ₂ ), water (H ₂ O), etc. in the air, and radicals having an active oxidizing power such as OH radicals and HO ₂ radicals are generated on the surface of TiO ₂ . Due to the generated radicals, NOx (NO, NO ₂ ) becomes
Reaction 1: HO ₂ + NO → OH + NO ₂
Reaction 2: NO ₂ + OH → HNO ₃
Is oxidized into nitrogen dioxide (NO ₂ ) and further nitric acid (HNO ₃ ).

In addition, as described above, holes of semiconductor materials such as TiO ₂ are generated when irradiated with light. And the excitation electron in this semiconductor substance becomes a free electron, becomes a movable state, and has a reduction action. Thereby, the excited electrons generated in TiO _{2 and the} like can reduce and decompose ozone and NOx by the reducing action.

In this way, ozone generated by the discharge means through the image forming operation by using the generation of active species by plasma discharge, the oxidation action of photocatalyst such as TiO ₂ by the light of plasma discharge, and the accompanying reduction action, Discharge products such as nitrogen oxides can be removed and decomposed at the source.

As a photocatalytic substance for decomposing ozone and NOx, WO ₃ , ZnO, CdS and the like can be used in addition to the above TiO ₂ . TiO ₂ is preferable in terms of reaction efficiency. In addition, these photocatalytic substances may use the substances exemplified above alone, but those obtained by mixing two or more of these substances, or those obtained by mixing these substances with Pt, Pd, Rh, Nb, etc. May be used.

It also improves that photocatalytic substances such as TiO ₂ cannot float or adsorb a large amount of gas or organic matter or bacteria that are suspended in the atmosphere or dispersed in water. Therefore, a composite material combined with a multi-pore material can be used. For example, the photocatalytic substance can be combined with a porous material having excellent adsorption performance such as silica gel and apatite. As a result, the adsorbed material is decomposed and removed by a photocatalytic material such as TiO ₂ when exposed to light, so that the adsorbing capacity of the adsorbing material is regenerated each time and can be used semipermanently. Such a combination can be used, for example, in the form of an adsorbent photocatalyst paint containing a photocatalytic substance and an adsorbing porous material.

Note that even if nitrogen dioxide (NO ₂ ) or nitric acid (HNO ₃ ), which cannot be decomposed and adheres and precipitates on the catalyst surface, is solidified and generated, it can be easily recovered by providing a cleaning mechanism. For example, the movement of the cleaning member (elastic body, foamed elastic body, etc.) along the longitudinal direction of the charger 20 can be performed by rubbing the surface of the catalyst to remove the substance adhered to the catalyst surface. As described above, it is also effective to provide a cleaning function for periodically removing secondary products generated by the oxidation / reduction action in the discharge electrode portion, particularly nitric acid. Thereby, a nitrogen oxide can be efficiently removed semipermanently.

  In addition, in the process of action by the photocatalyst, ozone, which is one of the discharge products, is an active oxygen species, but the rate of contribution to the reaction is usually low because of its slow speed. However, by using a photocatalyst in the discharge product generation space, it is possible to obtain a function as an accelerator during the decomposition action in the catalyst portion. Further, as described above, when the photocatalyst has an adsorbing action, substances that could not contribute to the reaction are also captured by the pores in the adsorbing action portion. For this reason, there is also obtained an effect that the slow reaction of ozone or the decomposition of the substance trapped with the ozone is removed by the light of the plasma discharge at the next plasma discharge.

  As described above, according to the present embodiment, discharge generation such as ozone and nitrogen oxides generated in the discharge means for performing the corona discharge operation such as the primary charger, the transfer charger, the separation charger, etc. using the high voltage of each part. Objects can be disassembled and removed at the same location, and typically by switching the drive conditions of the same high voltage power source. Therefore, it is possible to suppress the occurrence of factors that hinder the deterioration of the photoreceptor and the high image quality such as image flow. That is, according to the present embodiment, discharge products such as nitrogen oxides and ozone generated by the discharge means in the image forming apparatus can be efficiently removed. An image forming apparatus that can remove nitrogen oxides, ozone, and the like generated by the discharge means in the image forming apparatus over a long period of time without worrying about the replacement time of replacement parts such as filters. Is to provide.

1 is a longitudinal side view of an example of an image forming apparatus to which the present invention can be applied. It is a schematic sectional block diagram of one Example of the charger used as a primary charger and a pulse discharge type plasma reactor according to the present invention. FIG. 3 is a top sectional view of the charger shown in FIG. 2. It is a general | schematic cross-section block diagram of the other Example of the charger used as a primary charger and a pulse discharge-type plasma reactor according to this invention. FIG. 5 is a top sectional view of the charger shown in FIG. 4. It is a schematic sectional block diagram of one Example of the charger used as the primary charger and creeping discharge type plasma reactor according to the present invention. FIG. 2 is a schematic control block diagram of an image forming unit according to the present invention. It is a schematic diagram for demonstrating the effect | action of a photocatalyst.

Explanation of symbols

21 Discharge wire (discharge electrode)
25 Counter electrode (Plasma discharge electrode (GND side))
26 Photocatalyst 27 Discharge electrode 28 Counter electrode 29 Insulator 301 Photosensitive drum 302 Primary charger (discharge means)
304 Developing device (developing means)
305 Transfer charger (discharge means)
306 Separating charger (discharge means)
201a Charging wire

Claims (14)

In an image forming apparatus having a discharge means for applying or removing charges to a target in an image forming operation,
The discharge means includes an image forming discharge unit that applies or removes a charge to the target by discharge in an image forming operation, and a plasma discharge unit that generates a plasma discharge from the discharge electrode to a counter electrode different from the target. And a photocatalyst disposed so as to be able to receive the light of the plasma discharge, and the electric power under different driving conditions is switched for driving the image forming discharge unit and driving the plasma discharge unit. An image forming apparatus characterized by being input.   The image forming apparatus according to claim 1, wherein the plasma discharge unit generates the plasma discharge by pulse discharge.   The power supply means for inputting power to the discharge means includes a common DC power supply for generating power input to the image forming discharge section and the plasma discharge section, and switching means for using the output of the DC power supply as a pulse output. The image forming apparatus according to claim 2, further comprising:   4. The image forming apparatus according to claim 1, wherein the image forming discharge section generates a discharge at a discharge electrode shared with the plasma discharge section.   The image forming apparatus according to claim 1, wherein the plasma discharge unit generates the plasma discharge by creeping discharge.   The power supply means for inputting power to the discharge means is a common AC power source that generates power to be input to the plasma discharge portion of the discharge means and at least one power supply element other than the discharge means in the apparatus main body. The image forming apparatus according to claim 5, further comprising: a switching unit that switches an input target of the output of the AC power supply.   The image according to claim 5 or 6, wherein the plasma discharge part has an electrical insulator between the discharge electrode and the counter electrode, and the photocatalyst is disposed on the electrical insulator. Forming equipment.   The image forming apparatus according to claim 1, wherein the photocatalyst is disposed on the counter electrode.   The image forming apparatus according to claim 1, wherein the photocatalyst is disposed between the discharge electrode and the counter electrode.   The image forming apparatus according to claim 1, wherein the photocatalyst includes a photocatalytic substance and a porous material.   The image forming apparatus according to claim 1, wherein a plurality of the photocatalysts extend substantially parallel to a longitudinal direction of the discharge electrode and are provided at a predetermined interval.   The photocatalyst is a plurality of plate materials in which an adsorptive photocatalyst paint containing a photocatalyst substance and a porous material is applied to the surface of a plate material made of an electrical insulator, and the surfaces of the plate materials forming a pair face each other, and 12. Each of the plate members is disposed between the discharge electrode and the counter electrode so as to be substantially parallel to the longitudinal direction of the discharge electrode. Image forming apparatus.   The image forming apparatus according to claim 12, wherein the counter electrode has a mesh structure.   The image forming apparatus according to claim 1, wherein the image forming discharge section generates corona discharge.

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