JP2007199264A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus equipped with a charging device having small nip width variations and stable charging property over a long period. <P>SOLUTION: In the image forming apparatus, a cleaning roll 22 is formed into the so-called "crown shape" which is made a little larger for the outside diameter at the lengthwise center part than at ends, and then the pressing force of the cleaning roll 22 to a charging roll 12 is made uniform along the length to correct a charging nip. The cleaning roll 22 of a crown shape, as shown in Fig. 5, energizes the charging roll 12 toward a photoreceptor drum 11 so as to obtain a pressing force distribution which is uniform along the length. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus using a contact charging method in which discharge is a charging principle.

  Conventionally, as a charging device for an image forming apparatus such as a copying machine or a printer adopting an electrophotographic method, a device using a corona discharge phenomenon such as a scorotron charger has been widely used, but a charging device using a corona discharge phenomenon is used. In this case, the generation of ozone and nitrogen oxides that have a negative effect on the human body and the global environment is a problem. In contrast, the contact charging method in which a conductive charging roll is brought into direct contact with the photosensitive member to charge the photosensitive member generates less ozone and nitrogen oxides and has good power supply efficiency. It has become.

  In such a contact charging type charging device, since the charging roll is always in contact with the photosensitive member, there is a problem that the surface of the charging roll is likely to be contaminated with foreign matter. The surface of the photoreceptor on which the image forming operation is repeatedly performed passes through a cleaning process for removing foreign matters such as residual toner after transfer on the downstream side of the transfer process, and then enters the charging process area. Even after passing, fine particles smaller than the toner, such as a part of the toner and the external additive of the toner, remain on the photosensitive member without being cleaned, and adhere to the surface of the charging roll. The foreign matter adhering to the surface of the charging roll causes unevenness in the surface resistance value of the charging roll, resulting in abnormal discharge or unstable discharge, which deteriorates charging uniformity.

  As a technique for improving such a problem, a cleaning method has been proposed in which a plate-like brush or sponge is brought into contact with the surface of the charging roll to scrape off the surface contamination of the charging roll. However, such a cleaning method has a drawback that foreign matter accumulates between the charging roll and the plate-like brush or sponge, and the cleaning performance is deteriorated due to clogging.

  For this reason, a cleaning method has been proposed in which a rotatable roll-shaped cleaning member is brought into contact with the surface of the charging roll and the surface contamination of the charging roll is cleaned by the rotation of the cleaning member (see, for example, Patent Document 1).

  However, when the cleaning member is always in contact, as described below, it is difficult to stably maintain the charging nip that is the contact portion between the photosensitive member and the charging roll and the cleaning nip that is the contact portion between the charging roll and the cleaning member. There is.

  That is, conventionally, when the charging roll is pressed against the photosensitive member, the contact pressure at the center in the length direction is lower than the pressure at the end due to the bending of the shaft, so the outer diameter at the center of the charging roll is made larger than the end. The charging nip is corrected by using a so-called crown shape.

  In this case, if the crown amount is too large, the pressure contact load at the end will become weak and the nip will become non-uniform if the elasticity of the charging roll pressing member decreases with time, etc. Thus, an appropriate crown amount, for example, 50 μm to 500 μm is set so that the nip becomes substantially uniform within the assumed load range.

  However, in the case of an image forming apparatus having a cleaning member, the charging roll receives a load from the cleaning member because the cleaning member is installed so as to contact or bite the charging roll.

  Therefore, even if it is set so that a uniform nip can be obtained with a certain biting amount or pressing load, if the biting amount changes due to mounting tolerance of the cleaning member, variation in outer diameter, or change in outer diameter over time, etc. There was a problem that a stable charging nip could not be formed.

In view of the above facts, the present invention provides an image forming apparatus including a charging device that achieves stable charging over a long period of time while preventing contamination such as toner, external additives, and foreign matters from adhering to the charger. The purpose is that.
JP-A-5-297690

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus provided with a charging device that prevents the charger from being contaminated and realizes a stable charging property over a long period of time.

  The image forming apparatus according to claim 1, wherein an image carrier that forms an image on a surface, a charging roll that is driven to rotate by the image carrier, a surface that contacts the surface of the charging roll, and cleans the charging roll. An image forming apparatus having a cleaning roll that presses against the image carrier, wherein the cleaning roll is a roll member having a shape in which the diameters of the central portion in the length direction and the end portions are different.

  In the invention having the above-described configuration, the pressure distribution between the charging roll and the photoconductor can be controlled by changing the diameter of the cleaning roll depending on the location.

  The image forming apparatus according to claim 2, wherein the pressure distribution of the cleaning roll to the charging roll is defined such that the nip width between the charging roll and the image carrier is substantially constant in the length direction. It is characterized by.

  In the invention with the above configuration, the pressure distribution between the charging roll and the photoconductor can be made constant by changing the diameter of the cleaning roll depending on the location.

  The image forming apparatus according to claim 3, wherein the cleaning roll and the charging roll are supported by a pair of bearing members so that an inter-axis distance is constant, and the cleaning roll and the charging roll are integrated with each other. It is characterized by being pressed against the image carrier.

  In the invention with the above configuration, a stable pressing force can be obtained by integrally supporting the cleaning roll and the charging roll.

  The image forming apparatus according to claim 4, wherein the cleaning roll is pressed against the charging roll with a substantially constant load, and the charging is performed with a substantially constant load smaller than the first pressing means. And a second pressing means for pressing the roll against the image carrier.

  In the invention with the above configuration, the charging roll can be uniformly pressed against the photoconductor by pressing the cleaning roll against the charging roll with a force stronger than the force pressing the charging roll against the photoconductor.

  The image forming apparatus according to claim 5, an image carrier that forms an image on a surface, a charging roll that rotates following the image carrier, a cleaning roll that contacts the charging roll and cleans the surface, and the cleaning A cleaning roll pressing member that contacts the surface of the roll and presses the charging roll and the cleaning roll against the image carrier drum, and the cleaning roll pressing member is thicker in the center in the length direction than both ends. It is a roll member having a crown shape.

  In the invention having the above-described configuration, the pressure distribution of the charging roll on the photosensitive member can be made uniform by pressing the crown-shaped cleaning roll having a thick center against the charging roll.

  Since the present invention has the above-described configuration, an image forming apparatus including a charging device that realizes a stable charging property over a long period with little variation in the nip width can be obtained.

<Basic configuration>
1 to 3 show a basic configuration of an image forming apparatus according to the present invention.

  FIG. 1 shows an example of a drum type four-color image forming apparatus according to the present invention.

  Reference numeral 11 denotes a photosensitive drum, which rotates at a speed of 165 mm / sec in a direction indicated by an arrow in the drawing. A charger 12, an exposure device 13, black toner and color toner developing devices 14a to 14d, an intermediate belt 15, a photoconductor cleaner 16, and a static elimination lamp 17 are attached to the surface of the photoconductor drum 11 in order from the upstream side. A black and white or color toner image is formed by a known electrophotographic process.

  Reference numeral 50 denotes an intermediate belt 15 disposed so as to contact the surface of the photosensitive drum 11 at the primary transfer position, and rotates at substantially the same speed as the photosensitive drum 11. The toner image transferred to the intermediate belt 15 by the action of the primary transfer unit 51 proceeds to the secondary transfer unit 50, and a secondary transfer roll 52 to which a bias having a polarity opposite to that of the toner is applied, and a secondary transfer opposing roll 53. Is transferred to the transfer material 19 fed to the secondary transfer position by the feed roll 81 and the resist roll 82.

  The transfer material 19 to which the toner image has been transferred is sent to the fixing device 20 by the conveying belt 83 and fixed. At the same time, the toner remaining on the intermediate belt 15 is collected by the intermediate cleaner 54 and is transferred to the next image. Ready for formation.

  On the other hand, the toner remaining on the photoconductive drum 11 is conveyed to the photoconductive cleaner 16 and is disturbed by the cleaning brush 61 to reduce the adhesive force with the photoconductive member, and then mechanically scraped by the sliding of the cleaning blade 62. The surface is removed from the surface of the photosensitive drum 11 by receiving the removal force.

  In addition to the above example, a so-called tandem image forming apparatus in which developing devices are arranged in a straight line may be used.

  That is, as shown in FIG. 2, the number of colors necessary for image formation is arranged below the photosensitive drum, and the charger 12 and the exposure device 13 are arranged on the surface of the photosensitive drum 11 in order from the upstream side of the rotation. The toner developing device 14, the photoconductor cleaner 16, and the charge eliminating lamp (not shown) are attached, and a black and white or color toner image is formed by a well-known electrophotographic process as in FIG. .

  The intermediate belt 15 disposed so as to contact the surface of the photosensitive drum 1 rotates at substantially the same speed as the photosensitive drum 11, and the toner images formed on the surface of the photosensitive drum 11 are sequentially transferred to the intermediate belt 15. Transfer on top.

  A photosensitive drum 11, a charger 12, an exposure device 13, a toner developing device 14, a photoconductor cleaner 16, and a charge eliminating lamp (not shown) are arranged side by side by the number of color toners along the conveyance path of the intermediate belt 15. That is, in the case of a four-color image forming apparatus, four sets of the above devices are arranged.

  The toner image transferred to the intermediate belt 15 proceeds to the secondary transfer unit 50, and the action of an electric field formed by the secondary transfer roll 52 and the secondary transfer counter roll 53 to which a bias having a polarity opposite to that of the toner is applied. Then, the image is transferred to the transfer material 19 sent to the secondary transfer position by the feed roll 81 and the resist roll 82.

  The transfer material 19 onto which the toner image has been transferred is sent to the fixing device 20 for fixing, and the toner remaining on the intermediate belt 15 is collected by the intermediate cleaner 54 and ready for the next image formation. It is done. On the other hand, the toner remaining on the photoreceptor drum 11 is carried to the photoreceptor cleaner 16 and removed from the surface of the photoreceptor drum 11.

  Alternatively, a monochrome image forming apparatus that forms a monochrome image instead of the color image forming apparatus may be used.

  That is, as shown in FIG. 3, a charger 12, an exposure device 13, a toner developing device 14, a photoconductor cleaner 16, and a static elimination lamp (not shown) are attached to the surface of the photoconductive drum 11 in this order from the upstream side. A black and white or color toner image is formed by a known electrophotographic process, similar to the tandem color image forming apparatus of FIG.

The monochrome image forming apparatus 10c is provided with a photoreceptor drum 11, a charger 12, an exposure device 13, a toner developing device 14, a photoreceptor cleaner 16, and a charge-removing lamp (not shown), and a monochrome image is formed on the photoreceptor 11 with one color toner. The toner image transferred to the intermediate belt 5 proceeds to the secondary transfer unit 50 and is formed by the secondary transfer roll 52 to which a bias having a polarity opposite to that of the toner is applied and the secondary transfer counter roll 53. Under the action of the electric field, the image is transferred to the transfer material 19 sent to the secondary transfer position by the feed roll 81.

The transfer material 19 onto which the toner image has been transferred is sent to a fixing device 20 for fixing, and the toner remaining on the photosensitive drum 11 is carried to the photosensitive drum cleaner 16 and removed from the surface of the photosensitive drum 11. The
<Charger / Cleaning roll>
Next, a charger according to the present invention and a cleaning roll for cleaning the charger will be described.

  FIG. 4A shows a cross section of the charger according to the present invention.

  The charger 12 is arranged in contact with the surface of the photoconductor 11 and applies a DC voltage or an AC voltage to the DC voltage to charge the surface of the photoconductor.

  In addition, the shape is a roll shape in which a resistive elastic layer is provided around the core material, and the resistive elastic layer can be divided from the outside in the order of the resistive layer and the elastic layer that supports them. is there. Furthermore, a protective layer can be provided on the outside of the resistance layer as necessary to impart durability and contamination resistance of the charger.

  That is, in this invention, as shown to Fig.4 (a), it is set as the structure which provides the electroconductive elastic layer 12b and the resistance layer 12c around the core material 12a, and covers the outer periphery with the protective layer 12d. Hereinafter, the case where the conductive elastic layer 12b, the resistance layer 12c, and the protective layer 12d are provided on the core member 12a will be described in more detail.

  The core material 12a is made of a conductive material, and generally iron, copper, brass, stainless steel, aluminum, nickel or the like is used. Also, a material other than metal can be used as long as it has conductivity and appropriate rigidity. For example, a resin molded product in which conductive particles are dispersed, ceramics, or the like can be used. In addition to the roll shape, a hollow pipe shape can also be used.

  The material of the conductive elastic layer 12b has conductivity or semiconductivity, and is generally a resin material or rubber material in which conductive particles or semiconducting particles are dispersed. Polyester resin, acrylic resin, melamine resin, epoxy resin, urethane resin, silicon resin, urea resin, polyamide resin, etc. are used as the resin material, and ethylene-propylene rubber, polybutadiene, natural rubber are used as the rubber material. Polyisobutylene, chloroprene rubber, silicon rubber, urethane rubber, epichlorohydrin rubber, fluorosilicone rubber, ethylene oxide rubber, or a foamed material obtained by foaming them is used.

  Conductive particles or semiconductive particles include metals such as carbon black, zinc, aluminum, copper, iron, nickel, chromium, titanium, ZnO-Al2O3, SnO2-Sb2O3, In2O3-SnO2, ZnO-TiO2, MgO-Al2O3, Metal oxides such as FeO-TiO2, TiO2, SnO2, Sb2O3, In2O3, ZnO, MgO, and ionic compounds such as quaternary ammonium salts can be used. These materials can be used alone or in combination of two or more. May be used. Furthermore, you may mix 1 type, or 2 or more types of organic fillers, such as inorganic fillers, such as a talc, an alumina, and a silica, and the fine powder of a fluororesin or a silicon rubber, as needed.

  The material of the resistance layer 12c and the protective layer 12d is one in which conductive particles or semiconductive particles are dispersed in a binder resin to control the resistance. The resistivity is 10 ^ 3 to 10 ^ 14 Ωcm, preferably 10 ^ 5-10 ^ 12 Ωcm, more preferably 10 ^ 7-10 ^ 12 Ωcm. The film thickness is 0.01 to 1000 μm, preferably 0.1 to 500 μm, and more preferably 0.5 to 100 μm. As binder resin, acrylic resin, cellulose resin, polyamide resin, methoxymethylated nylon, ethoxymethylated nylon, polyurethane resin, polycarbonate resin, polyester resin, polyethylene resin, polyvinyl resin, polyarylate resin, polythiophene resin, PFA, FEP, Polyolefin resin such as PET, styrene butadiene resin, melamine resin, epoxy resin, urethane resin, silicon resin, urea resin, etc. are used.

  As the conductive particles or the semiconductive particles, one or more of ionic compounds such as carbon black, metal, metal oxide, and quaternary ammonium salt exhibiting ionic conductivity, which are the same as those of the elastic layer, may be used. Mixed. If necessary, antioxidants such as hindered phenols and hindered amines, inorganic fillers such as clay, kaolin, talc, silica and alumina, organic fillers such as fine powder of fluororesin and silicon resin, silicone oil, etc. 1 type (s) or 2 or more types, such as a lubricant, can be added. Further, a surfactant, a charge control agent and the like are added as necessary.

  As a means for forming these layers, a blade coating method, a Meyer bar coating method, a spray coating method, a dip coating method, a bead coating method, an air knife coating method, a curtain coating method, or the like can be used.

  Next, the cleaning roll will be described.

  4B and 4C show the structure of the cleaning roll 22 according to the present invention.

  The cleaning roll 22 is formed of a core material 22 a and a porous elastic layer 22 b formed on the peripheral surface of the core material 22 a, and is disposed in contact with the charging roll 12 disposed in contact with the photosensitive drum 11.

  As the material of the core material 22a, a material that supports the porous elastic layer 22b and has a rigidity capable of maintaining a contact state with an appropriate pressure contact force to the charging roll 12 is used. Generally, iron, copper, In addition to metals such as brass, stainless steel, aluminum, and nickel, resin molded products, ceramics, and the like in which conductive particles are dispersed, and those in which an inorganic filler is dispersed can be used. In addition to the roll shape, a hollow pipe shape can also be used.

  The porous elastic layer 22b is a roll-like sponge formed with a predetermined cell density. For example, ether-based urethane foam, polyethylene foam, polyolefin foam, melamine foam, micropolymer, or the like can be used.

  Taking a polyurethane foam as an example, the production method will be briefly described. It is produced using a polyol, isocyanate, water, a catalyst (amine catalyst, metal catalyst, etc.) and a foam stabilizer (surfactant). Additives such as are used. When these raw materials are mixed and stirred, a chemical reaction occurs, and a urethane resin foam can be obtained.

  The cleaning roll 22 used in the present invention will be described below. As the cleaning roll 22 used in the present invention, as shown in FIG. 4B, a roll made of polyurethane foam covered with a porous elastic layer 22b is used around a metallic core material 22a.

  As a material used for the metal core material 22a, SUS303 stainless steel alloy with a diameter of 6 mm was used. The polyurethane foam has a thickness of 2 mm, a cell density of 40-50 pieces / 25 mm, and the hardness is adjusted so that the load required to push a disk-shaped member of Φ50 by 0.5 mm is about 80-150 g. Ether-based polyurethane was used.

  Moreover, as shown in FIG.4 (c), the outer diameter of the cleaning roll 22 used in the Example of this invention has changed regarding the longitudinal direction of the axis | shaft. That is, the cleaning roll 22 is formed in a crown shape whose central portion (intermediate portion, intermediate portion) is thicker than both end portions. In other words, the cleaning roll 22 is formed in a crown shape that increases in diameter as it goes from both end portions to the central portion.

More specifically, the outer diameter of the central portion of the cleaning roll 22 is larger by d1 than the outer diameter of both ends. When the outer diameter of both ends of the cleaning roll is D1, the outer diameter of the central portion is D1 + d1. That is, d1 here is a crown amount.
<Uniform pressing force of charging roll>
Next, the pressing force equalization between the charging roll and the photosensitive drum according to the present invention will be described.

  Conventionally, when the charging roll 12 rotates while pressing the photosensitive drum 11 as shown in FIG. 5 (a), the contact pressure at the center in the length direction is lower than the pressure at the end due to the deflection of the shaft. A configuration is considered in which the charging nip is corrected by forming a so-called crown shape in which the outer diameter of the central portion in the longitudinal direction of the roll 12 is larger than that of the end portion.

  As described above, when the crown amount is increased too much, when the elasticity of the pressing member that presses the charging roll 12 against the photosensitive drum 11 decreases with time, the pressure contact load at the end becomes weak and the nip becomes uneven. Therefore, an appropriate crown amount, for example, 50 μm to 500 μm is set so that the nip is substantially uniform within the assumed load range in accordance with the rubber hardness of the charging roll.

  However, in the case of the image forming apparatus having the cleaning roll 22, the charging roll 12 receives a load from the cleaning roll 22 because the cleaning member is installed so as to contact or bite the charging roll. That is, as shown in FIG. 5B, the cleaning roll 22 presses the charging roll 12, but this pressing force is also caused by the contact pressure at the center in the length direction due to the bending of the shaft as described above. Will not be uniform. Therefore, there is a problem that a uniform charging nip cannot be formed.

  Therefore, in the present invention, as shown in FIG. 5C, the cleaning roll 22 is also formed into a so-called crown shape in which the outer diameter of the central portion in the longitudinal direction is larger than that of the end portion. Is made uniform in the longitudinal direction to correct the charging nip.

In other words, as shown in FIG. 5D, the structure in which the charging roll 12 is urged toward the photosensitive drum 11 by the crown-shaped cleaning roll 22 enables a uniform pressure distribution in the longitudinal direction. This will be described below using mathematical formulas.
<Balance of pressing force>
FIG. 6 shows a balance of forces applied to the photosensitive drum, the charging roll, and the cleaning roll according to the first embodiment of the present invention.

  As shown in FIGS. 6 and 10, the charging roll 12 and the cleaning roll 22 are supported by a bearing 32 and are pressed toward the photosensitive drum 11 by a spring member 34 with a force f.

  In this example, the charging roll 12 and the cleaning roll 22 are attached to a bearing portion (through hole) provided in the bearing 32 and are regulated so that the distance between the axes is constant. A spring member 34 is attached to a part of the bearing 32 as a pressing member, and the charging roll 12 and the cleaning roll 22 are integrally biased to the photosensitive drum 11.

  The load of the spring member 34 is adjusted so that the charging roll 12 contacts the photoreceptor drum 11 with an appropriate pressure contact force, and is selected so that, for example, a load of 250 gf to 600 gf can be applied per side.

  Here, first, the force that the bearing 32 pushes the charging roll 12 is Fb, the force that pushes the cleaning roll 22 is Fc, the gravity that works on the charging roll 12 is Mg, the gravity that works on the cleaning roll 22 is mg, and the charging roll 12 is the photosensitive drum. 11 is Nb, and the charging roll 12 pushes the cleaning roll 22 (reaction received from the cleaning roll 22) is Nc.

At this time, the force acting on the charging roll 12 is 2Fb + Nc = Nb + Mg
And 2Fc = Nc + mg for the cleaning roll 22
The bearing 32, the charging roll 12, and the cleaning roll 22 are 2F = Nb + Mg + mg = Nb + (M + m) g
Therefore, the balance of the above three forces is 2Fb = Nb−Nc + Mg
= (2F- (M + m) g)-(2Fc-mg) + Mg
= 2F- (M + m) g-2Fc + (M + m) g
It becomes. As a result, Fb = F−Fc
It can be seen that it is.

  That is, when the loads applied to the bearings 32 and 36 of the charging roll 12 and the cleaning roll 22 are obtained from these three balance equations, the nip load between the cleaning roll 22 and the charging roll 12 remains in the bearing hole of the cleaning roll 12 as it is. On the other hand, it can be seen that only the difference between the nip load between the photosensitive drum 11 and the charging roll 12 and the nip load between the cleaning roll 22 and the charging roll 12 is applied to the bearing hole of the charging roll 12.

  Therefore, when the cleaning roll 22 is present, a large part of the load applied to the charging roll 12 is received from the cleaning roll 22 and the photosensitive drum 11, and the application of the load becomes a substantially equally distributed load. Therefore, unlike the case where there is no cleaning roll 22 that receives a concentrated load on the bearing portion, the shaft deflection of the charging roll 12 becomes as small as its own weight, so even if the crown amount is small or not, a substantially uniform nip is formed. It becomes possible to form.

  On the other hand, in order to keep the contact state between the photosensitive drum 11 and the charging roll 12 and between the charging roll 12 and the cleaning roll 22 in a good and uniform nip, both rolls have a certain thickness, for example, about 2 to 3 mm. An elastic layer is required.

  In order to make the outer diameter ≦ Φ12 or so, the core material diameter should be about Φ4-6 or less, but with such a thin core material, for example, Φ4 core material, When the axial length is about 300 mm, when the pressure is applied with a load of about 1 kg, the cleaning roll 22 side may bend about 0.5 mm at the central portion even if the strength is secured by using a stainless alloy such as SUS303. is there.

  If the core material is bent in this way, the pressure contact state of the cleaning roll 22 changes between the central portion and the end portion, and the central portion may float in a remarkable case. In this case, since the force with which the cleaning roll 22 presses the charging roll 12 is closer to the end concentrated load than the uniform distribution load, it is difficult to form a uniform nip between the charging roll 12 and the photosensitive drum 11 as described above. Become.

On the other hand, by giving the cleaning roll 22 a crown corresponding to the deflection of the shaft, the nip state between the charging roll 12 and the cleaning roll 22 can be made substantially uniform, and as described above, the photosensitive drum 11. Also, the nip of the charging roll 22 can be made substantially uniform.
<Pressure balance 2>
FIG. 7 shows a balance of forces applied to the photosensitive drum, the charging roll, and the cleaning roll according to the second embodiment of the present invention.

  In this configuration, the cleaning roll 22 and the charging roll 12 are respectively held by different bearing members and pressed by separate spring members.

  The charging roll 12 and the cleaning roll 22 are held by separate bearings 33 and 36, respectively. Spring members 35 and 37 are attached to the respective bearings as pressing members, and are configured to urge the charging roll 12 and the cleaning roll 22 toward the photosensitive drum 11.

  Further, the bearing 33 of the charging roll 12 has a guide portion 31A for restricting the moving direction thereof, and the regulating portion 31B provided on the housing 39 tilts the bearing 33 in the process direction and the longitudinal direction of the charging roll shaft. Is preventing. Further, the bearing member of the cleaning roll 22 is provided with a through hole 36a that is sufficiently larger than the core material 12a of the charging roll 12 so that the core material 12a passes therethrough. This prevents the bearing 36 of the cleaning roll 22 from being greatly inclined in the process direction or the charging roll shaft longitudinal direction.

  Further, the spring member 37 that presses the cleaning roll 22 has a load such that good cleaning property of the charging roll can be obtained by the cleaning roll 22, for example, 100 gf to 600 gf on one side, preferably 250 gf to 500 gf on one side, more preferably 350 gf to 500 gf on one side. Selected to be granted.

  Further, the spring roll 35 that presses the charging roll 12 is provided with a cleaning roll so as to make up for the shortage of the charging roll 12 only by pressing the charging roll 12 against the photosensitive drum 11 due to the action of the spring member 37 for pressing the cleaning roll 22. It is selected so that a load of 50 gf to 300 gf on one side is applied in a range weaker than the spring member 37 for 22 pressing.

  In the following examples, the cleaning roll pressing compression spring means used is 400 gf on one side and the charging roll pressing compression spring is 70 gf on one side.

  In the above configuration, the nip load between the charging roll 12 and the photosensitive drum 11 is the reaction force of the cleaning roll 22 + charging roll pressing member-charging roll 12 self-weight as shown in FIG. Therefore, the necessary nip load can be distributed to the cleaning roll 22 pressing member and the charging roll 12 pressing member.

  As shown in FIGS. 7 and 11, the charging roll 12 and the cleaning roll 22 are supported by bearings 33 and 36. Here, first, Fb is the force by which the bearing 33 pushes the charging roll 12 with the spring member 35, Fc is the force with which the bearing 36 pushes the cleaning roll 22 with the spring member 37, Mg acts on the charging roll 12, and Mg acts on the cleaning roll 22. The gravity is mg, the reaction force that the charging roll 12 receives from the photosensitive drum 11 is Nb, and the force that the charging roll 12 pushes the cleaning roll 22 (reaction force that is received from the cleaning roll 22) is Nc.

At this time, the force acting on the charging roll 12 is 2Fb + Nc = Nb + Mg
So,
Nb = 2Fb + Nc-Mg
It is. For the cleaning roll 22, 2Fc = Nc + mg
Therefore, the balance of force between the charging roll 12 and the cleaning roll 22 is 2Fb + 2Fc = Nb + (M + m) g.
It becomes.

  Here, while the load by the spring member 35 that presses the charging roll 12 acts as an end concentrated load, the load by the spring member 37 that presses the cleaning roll 22 acts on the charging roll 12 as a reaction force of the cleaning roll 22. Since it acts, it will be added as a substantially equally distributed load.

  Therefore, by setting the load distribution of both the pressing members as the spring member 37 >> the spring member 35, it is possible to suppress the bending of the charging roll 12, and it is possible to reduce the charging roll 12 to a minimum or a crown amount of 0. It is possible to form a substantially uniform charging nip.

On the other hand, since the cleaning roll 22 is supported at the end portion, the shaft is greatly bent, but a crown amount corresponding to the amount of bending is provided, so that a substantially uniform cleaning nip can be realized.
<Pressure balance 3>
FIG. 8 shows a balance of forces applied to the photosensitive drum, the charging roll, the cleaning roll, and the auxiliary roll according to the third embodiment of the present invention.

  In this example, in addition to the charging roll 12 and the cleaning roll 22, a pressing roll 40 is provided as a member that presses the cleaning roll 22.

  As the pressing roll 40, iron, copper, brass, stainless steel, aluminum, nickel or the like is used. In addition, materials other than metals can be used as long as they have moderate rigidity. For example, resin molded products in which fillers such as glass particles and carbon fibers are dispersed, ceramics, and the like can also be used.

  Moreover, the outer diameter is changing about the longitudinal direction of the axis | shaft similarly to the cleaning roll 22 shown in FIG.4 (c). That is, the pressing roll 40 is formed in a crown shape whose central part (intermediate part, intermediate part) is thicker than both end parts, and the outer diameter of the central part is d1 compared to the outer diameters of both end parts. Only getting bigger.

  That is, when the outer diameter of both ends is D1, the outer diameter of the central portion is D1 + d1. In the present invention, the pressing roll 40 made of SUS303 alloy having a central outer diameter of 6 mm and an end outer diameter D1 of 5.5 mm is used.

  Further, as the bearing holes (through holes) 38a, 38b, 38c of the respective rolls provided in the bearing 38, the bearing holes 38a, 38c for the charging roll 12 and the pressing roll 40 are set to 0 to 0 from the outer diameters of the respective core members. It has a circular shape with a large inner diameter of about 0.1 mm, and the bearing hole 34b for the cleaning roll 22 has a long hole shape.

  In addition to this, in consideration of the outer diameter variation of the cleaning roll 22, the cleaning roll 22 is not separated from the charging roll 12 / pressing roll 40 even if the cleaning roll 22 is about 0.5 mm smaller than the predetermined outer diameter ( Cleaning roll 22 outer diameter + charging roll 12 radius + pressing roll 40)-(distance between centers of 34a / 34c) is set to 1 to 2 mm.

  A spring member 34 is attached to a part of the bearing 38 as a pressing member, and the charging roll 12, the cleaning roll 22, and the pressing roll 40 are integrally biased to the photosensitive drum 11. The load of the spring member 34 is adjusted so that the charging roll 12 contacts the photosensitive drum 11 with an appropriate pressure contact force, and is selected so that, for example, a load of 300 gf to 700 gf can be applied per side.

  Here, first, the force that the bearing 38 pushes the charging roll 12 with the spring member 34 is Fb, the force that the bearing 38 pushes the cleaning roll 22 is Fc, the force that the bearing 38 pushes the pressing roll 40 is Fa, and the gravity that acts on the charging roll 12 Mg, gravity acting on the cleaning roll 22 in mg, gravity acting on the pressing roll 40 μg, reaction force that the charging roll 12 receives from the photosensitive drum 11 is Nb, and the charging roll 12 pushes the cleaning roll 22 (cleaning roll 22 Nc, and the force that the pressing roll 40 pushes the cleaning roll 22 (the reaction force that the cleaning roll 22 receives from the pressing roll 40) is Na.

At this time, the force acting on the charging roll 12 is 2Fb + Nc = Nb + Mg
For the cleaning roll 22, 2Fc + Na = Nc + mg
For the pressing roll 40, 2Fa = Na + μg
It is. The bearing 32, the charging roll 12, the cleaning roll 22, and the auxiliary roll are 2F = Nb + (M + m + μ) g
Therefore, the balance of the above three forces is 2Fc = Nc-Na + mg
= (Nb + Mg-2Fb)-(2Fa- [mu] g) + mg
= (2F- (M + m + μ) g + Mg-2Fb) -2Fa + (M + m) g
It becomes. As a result, Fb = F−Fa−Fc
≒ F-Fa
It can be seen that it is.

  As described above, since the bearing portion of the cleaning roll 22 has a long hole shape, the force Fc that the cleaning roll 22 receives from the bearing member 38 is substantially 0, and the surface load is received from the charging roll 12 and the pressing roll 22. become.

On the other hand, since the pressing roll 40 is end-supported, the shaft is greatly bent, but a crown amount corresponding to the amount of bending is provided, so that a substantially uniform nip can be realized. Therefore, the surface load exerted on the cleaning roll 22 by the pressing roll 40 can be made to be substantially equally distributed. As a result, it is possible to form a substantially uniform nip without providing the crown amount on the cleaning roll 22, and furthermore, a substantially uniform charging nip can be obtained simply by attaching a very small or zero crown amount to the charging roll 12. It is possible to form.
<Nip width evaluation method>
Next, a method for evaluating the nip width between the charging roll and the photosensitive drum will be described.

  As shown in FIG. 9, the nip width evaluation device 43 includes the φ30 photosensitive drum 11, the charging roll 12 shown in FIG. 4, and the cleaning roll 22. The cleaning roll 22 and the charging roll 12 are fixed by a bearing 32. The bearing 32 is urged toward the photosensitive drum 11 by a spring member 34, whereby the charging roll 12 is pressed against the photosensitive drum 11.

  In the nip width evaluation device 43, the positional relationship (particularly in the vertical direction) of the photosensitive drum 11, the charging roll 12, and the cleaning roll 22 is substantially the same as that used in an actual image forming apparatus. Furthermore, the press roll 40 is provided regarding 3rd Embodiment.

  Further, as an electrical state, the base material of the photosensitive drum 11 is grounded, and the charging roll 12 is supplied with an AC bias (a peak to peak voltage is 2.5 kV in a low temperature and low humidity environment, high temperature and high humidity) from a high voltage power source 31. In the environment, a DC bias (-700 V) superimposed with 1.8 kV) can be applied. Here, the cleaning roll 22 is electrically floated, but the same bias as that of the charging roll 12 may be applied. The measurement environment was evaluated in a low temperature and low humidity environment of 10 ° C. and 15% RH and a high temperature and high humidity environment of 30 ° C. and 90% RH.

  Here, the bearing 32 and its configuration will be described. As a material for the bearing 32, resin members such as polycarbonate, acrylic, nylon (PA), polyphenylene oxide, polyethylene (PE), polyacetal (POM), etc. can be used in addition to the treated steel plate and stainless steel alloy. However, at least the bearing holes 32a and 32b that are in direct contact with the charging roll 12 and the cleaning roll 22 are made of a member having good slidability, such as nylon, high-sliding polyacetal, high-density polyethylene, or a ball bearing. It is desirable to use Further, it is possible to supply power to the charging roll 12 through the bearing 32 by using a ball bearing having a conductive high sliding resin or conductive grease. In the present invention, Tenac-C TFC64 manufactured by Asahi Kasei Kogyo Co., Ltd., which is a conductive high sliding resin, was used.

  In the above configuration and conditions, the nip width was measured as follows. First, a resin bearing is selected so that the amount of biting between the cleaning roll 22 and the charging roll 12 becomes a predetermined value, and the charging roll 12 is pressed against the photosensitive drum 11 by using a spring member 34 that applies a predetermined load. It was. In this state, the output of the high voltage power supply 31 is started, and the output of the high voltage power supply 31 is stopped when 15 minutes have passed.

  The nip width distribution was measured by removing the photosensitive drum from the apparatus, and measuring the width of the discharge mark generated at the portion in contact with the charging roll 12 with a caliper every 40 mm from the end.

  In this evaluation experiment, the cleaning roll 22 having an end outer diameter D1 of 10 mm was used. At this time, for example, a dimension of 0.5 mm can be adopted as the crown amount d1. That is, the central portion of the cleaning roll 22 is 10.5 mm, which is 0.5 mm thicker than both ends. In the third embodiment and the conventional example, the cleaning roll 22 having an end outer diameter D1 of 10 mm and a crown amount d1 of substantially 0 is used.

  In addition, in 3rd Embodiment, the press roll 40 which consists of SUS303 alloy whose center part outer diameter is 6 mm and whose edge part outer diameter D1 is 5.5 mm was used.

 The experiment was conducted in a high temperature and high humidity environment (30 ° C./90%) and a low temperature and low humidity environment (10 ° C./10%). In addition, in order to compare the influence of the variation in the outer diameter of the cleaning roll 22, there are three types of outer diameter cleaning in which the average outer diameter (= (both ends + center) / 3) is 10.3 mm / 10.0 mm / 9.7 mm. A roll 22 was prepared and a comparative experiment was performed.

  FIG. 13 shows a conventional method, FIG. 14 shows an experimental result of the first embodiment, FIG. 15 shows a second embodiment, and FIG. 16 shows an experimental result of the third embodiment.

As shown in FIGS. 13 to 16, as a result of the nip width measurement under the above conditions, the nip width variation due to environmental conditions and the cleaning roll 22 of both the first to third embodiments compared to the conventional example. It was found that there was little variation in nip width due to variation in outer diameter. It was also found that the third embodiment is the most excellent in nip width variation due to environmental conditions.
<Others>
In addition, this invention is not limited to said embodiment.

  For example, in the above embodiment, the method of manufacturing the droplet discharge head is not limited to this, but the present invention is not limited to this method, and may be applied to other types of products as long as it is necessary to process a fine hole with a taper angle. Good.

1 is a schematic diagram illustrating an image forming apparatus according to the present invention. 1 is a schematic diagram illustrating an image forming apparatus according to the present invention. 1 is a schematic diagram illustrating an image forming apparatus according to the present invention. It is a figure which shows the charging roll and cleaning roll which concern on this invention. It is a figure which shows the pressing force of the cleaning roll and charging roll which concern on this invention. It is a figure which shows the force balance of each roll which concerns on 1st Embodiment of this invention. It is a figure which shows the force balance of each roll which concerns on 2nd Embodiment of this invention. It is a figure which shows the force balance of each roll which concerns on 3rd Embodiment of this invention. It is a figure which shows the nip width evaluation apparatus of the charging roll which concerns on this invention. It is a figure which shows the bearing part of each roll which concerns on 1st Embodiment of this invention. It is a figure which shows the bearing part of each roll which concerns on 2nd Embodiment of this invention. It is a figure which shows the bearing part of each roll which concerns on 3rd Embodiment of this invention. It is a figure which shows the nip width of the conventional charging roll and a photoreceptor drum. It is a figure which shows the nip width of the charging roll which concerns on 1st Embodiment of this invention, and a photoconductive drum. It is a figure which shows the nip width of the charging roll which concerns on 2nd Embodiment of this invention, and a photoreceptor drum. It is a figure which shows the nip width of the charging roll and photoconductor drum which concerns on 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Photosensitive drum 12 Charging roll 22 Cleaning roll 32 Bearing 34 Spring member 40 Press roll

Claims (5)

An image carrier that forms an image on the surface;
A charging roll that rotates following the image carrier;
A cleaning roll that contacts and cleans the surface of the charging roll and presses the charging roll against the image carrier;
The image forming apparatus according to claim 1, wherein the cleaning roll is a roll member having a shape in which the diameters of the central portion in the length direction and the both end portions are different. The pressure distribution of the cleaning roll to the charging roll is defined such that the nip width between the charging roll and the image carrier is substantially constant in the length direction. The image forming apparatus described. The cleaning roll and the charging roll are supported by a pair of bearing members so that the distance between the axes is constant, and the cleaning roll and the charging roll are integrally pressed against the image carrier. The image forming apparatus according to claim 1. First pressing means for pressing the cleaning roll against the charging roll with a substantially constant load;
A second pressing means for pressing the charging roll against the image carrier with a substantially constant load smaller than the first pressing means;
The image forming apparatus according to claim 1, further comprising: An image carrier that forms an image on the surface;
A charging roll that rotates following the image carrier;
A cleaning roll that contacts the charging roll and cleans the surface;
A cleaning roll pressing member that contacts the surface of the cleaning roll and presses the charging roll and the cleaning roll against the image carrier drum;
The image forming apparatus according to claim 1, wherein the cleaning roll pressing member is a crown-shaped roll member having a central portion in the length direction that is thicker than both end portions.

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