JP2016145947A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing a transfer residual toner amount on an image carrier, in a second transfer mode for transferring a toner image from the image carrier to a transfer body.SOLUTION: An image forming apparatus includes an image carrier 31, toner image forming means 1 which forms the toner image on the image carrier, a transfer body 41 which comes into contact with the surface of the image carrier, to form a transfer nip, and transfer electric field forming means 39 which applies a transfer bias to between the image carrier and the transfer body, to form a transfer electric field. The image forming apparatus has a first transfer mode for transferring the toner image formed on the image carrier to a recording medium in the transfer nip and the second transfer mode which has a transfer condition different from that of the first transfer mode and is for transferring the toner image formed on the image carrier to the transfer body in the transfer nip.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, there has been known an image forming apparatus in which a toner image of each color formed on a photoconductor is primarily transferred onto an intermediate transfer belt and then secondarily transferred onto a recording medium.

  In the image forming apparatus described in Patent Document 1, the intermediate transfer belt is rotatably stretched by a plurality of stretching members. A toner image is primarily transferred from the photosensitive member to the intermediate transfer belt at a primary transfer nip formed by contacting the photosensitive member and the intermediate transfer belt. A sheet, which is a recording medium on which a toner image is secondarily transferred from the intermediate transfer belt, is carried on a secondary transfer belt that is rotatably stretched by a plurality of tension members, and the intermediate transfer belt and the secondary transfer belt are connected to each other. It is conveyed to a secondary transfer nip formed in contact therewith. In the secondary transfer nip, a transfer electric field is formed by applying a secondary transfer bias between the intermediate transfer belt and the secondary transfer belt by a power source. By the action of the transfer electric field, the toner on the intermediate transfer belt is formed. The image is secondarily transferred onto the paper at the secondary transfer nip.

  In this image forming apparatus, a toner pattern is formed on a portion corresponding to the space between the sheets on the intermediate transfer belt, and the toner pattern formed between the sheets is transferred from the intermediate transfer belt to the secondary transfer belt at the secondary transfer nip. To do. The toner pattern transferred onto the secondary transfer belt is detected by the toner image detection unit, and the image forming conditions are corrected based on the detection result detected by the toner image detection unit.

  As a result of intensive studies by the inventors of the present application, the amount of residual toner remaining on the intermediate transfer belt after transfer has increased too much during the belt transfer in which the toner pattern is transferred from the intermediate transfer belt to the secondary transfer belt. It turns out that there is a case. As described above, if the amount of residual toner on the intermediate transfer belt becomes excessive during belt transfer, the cleaning load of the cleaning device that cleans the intermediate transfer belt increases, resulting in a problem of defective cleaning. The image forming apparatus configured to transfer the refresh toner pattern formed on the intermediate transfer belt via the photoconductor to refresh the toner in the developing device from the intermediate transfer belt to the secondary transfer belt is also described above. The same problem occurs.

  In order to solve the above problems, according to the present invention, in an image forming apparatus, an image carrier, a toner image forming unit that forms a toner image on the image carrier, and a surface of the image carrier are transferred in contact with the image carrier. A transfer body that forms a nip; and transfer electric field forming means that forms a transfer electric field by applying a transfer bias between the image carrier and the transfer body, and is formed on the image carrier. A first transfer mode in which a toner image is transferred to a recording medium at the transfer nip, and a toner image formed on the image carrier having different transfer conditions from the first transfer mode are transferred to the transfer body at the transfer nip. And a second transfer mode for transferring.

  As described above, according to the present invention, in the second transfer mode in which the toner image is transferred from the image carrier to the transfer body, there is an excellent effect that the amount of residual toner on the image carrier can be reduced.

The figure which shows the secondary transfer rate to a paper and a secondary transfer belt. 1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 3 is an enlarged configuration diagram illustrating an enlarged image forming unit for K in a printer. FIG. 3 is an enlarged cross-sectional view partially showing a cross section of an intermediate transfer belt of the printer. FIG. 3 is an enlarged plan view showing a partially enlarged intermediate transfer belt. FIG. 3 is an enlarged perspective view illustrating an image quality adjustment toner pattern formed on a secondary transfer belt. 6 is a time chart when toner pattern for image quality adjustment of each color is detected and toner pattern interval measurement is performed. FIG. 5 is a schematic diagram illustrating an example of a shape of a refresh toner pattern. FIG. 10 is a schematic diagram illustrating another example of the shape of the refresh toner pattern. 6 is a graph showing the results of evaluating the amount of residual toner in a refresh toner pattern made up of a halftone toner image and a refresh toner pattern made up of a solid toner image by changing the environment. The figure which shows the secondary transfer rate to a paper and a secondary transfer belt. FIG. 6 is a diagram illustrating a secondary transfer rate of a toner pattern for density control in a low temperature and low humidity environment (LL environment). FIG. 6 is a diagram illustrating a secondary transfer rate of a toner pattern for density control in a normal temperature and normal humidity environment (MM environment). FIG. 6 is a diagram illustrating a secondary transfer rate of a toner pattern for density control in a high temperature and high humidity environment (HH environment).

[Embodiment 1]
Hereinafter, an embodiment of an electrophotographic color printer (hereinafter simply referred to as a printer) will be described as an image forming apparatus to which the present invention is applied. First, a basic configuration of the printer according to the embodiment will be described. FIG. 2 is a schematic configuration diagram illustrating the printer according to the embodiment. In the drawing, the printer according to the embodiment includes four toner image forming units 1Y, 1M, 1C, and 1 for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. It has 1K. Also provided are a transfer unit 30, an optical writing unit 80, a fixing device 90, a feeding cassette 100, a registration roller pair 101, and the like.

  The four toner image forming units 1Y, 1M, 1C, and 1K use Y, M, C, and K toners of different colors as image forming materials, but the other configurations are the same, and when the lifetime is reached. Exchanged. Taking a toner image forming unit 1K for forming a K toner image as an example, this includes, as shown in FIG. 3, a drum-shaped photosensitive member 2K as a latent image carrier, a drum cleaning device 3K, a charge eliminating device, a charging device. A device 6K, a developing device 8K, and the like are provided. These devices are held by a common holding body and integrally attached to and detached from the printer main body, so that they can be exchanged at the same time.

  The photoreceptor 2K has an organic photosensitive layer formed on the surface of a drum base, and is driven to rotate clockwise in the figure by a driving means. The charging device 6K generates a discharge between the charging roller 7K and the photosensitive member 2K while bringing the charging roller 7K to which a charging bias is applied into contact with or in proximity to the photosensitive member 2K, thereby making the surface of the photosensitive member 2K uniform. Charge like this. In the embodiment, the toner is uniformly charged to the same negative polarity as the normal charging polarity of the toner. Here, the normal charging polarity of the toner refers to the charging polarity of the toner in the developer in the developing device 8. As the charging bias, a bias in which an AC bias is superimposed on a DC bias is employed. The charging roller 7K is formed by coating a metal cored bar with a conductive elastic layer made of a conductive elastic material. Instead of a method in which a charging member such as a charging roller is brought into contact with or close to the photoreceptor 2K, a method using a charging charger may be adopted.

  The uniformly charged surface of the photosensitive member 2K is optically scanned by a laser beam emitted from an optical writing unit, which will be described later, and carries an electrostatic latent image for K. The electrostatic latent image for K is developed by the developing device 8K using K toner to become a K toner image. Then, primary transfer is performed on an intermediate transfer belt 31 described later.

  The drum cleaning device 3K removes the transfer residual toner adhering to the surface of the photoreceptor 2K after the primary transfer process (primary transfer nip described later). It includes a cleaning brush roller 4K that is driven to rotate, a cleaning blade 5K that abuts the free end of the cleaning brush roller 4K in a cantilevered state, and the like. The transfer residual toner is scraped off from the surface of the photoreceptor 2K by the rotating cleaning brush roller 4K, and the transfer residual toner is scraped off from the surface of the photoreceptor 2K by the cleaning blade.

  The static eliminator neutralizes the residual charge on the photoreceptor 2K after being cleaned by the drum cleaning device 3K. By this charge removal, the surface of the photoreceptor 2K is initialized and prepared for the next image formation.

  The developing device 8K includes a developing unit 12K that includes a developing roll 9K that is a developer carrier, and a developer transport unit 13K that stirs and transports the K developer. The developer transport unit 13K includes a first transport chamber that houses the first screw member 10K and a second transport chamber that houses the second screw member 11K. Each of the screw members includes a rotary shaft member whose both ends in the axial direction are rotatably supported by bearings, and a spiral blade projecting in a spiral manner on the peripheral surface thereof.

  The first transfer chamber containing the first screw member 10K and the second transfer chamber containing the second screw member 11K are partitioned by a partition wall, but both ends of the partition wall in the screw axial direction. A communication port for communicating the two transfer chambers is formed at each location. The first screw member 10K conveys the K developer held in the spiral blade from the back side to the front side in the direction orthogonal to the paper surface in the drawing while stirring in the rotation direction with the rotational drive. To do. Since the first screw member 10K and a later-described developing roll 9K are arranged in parallel so as to face each other, the conveying direction of the K developer at this time is also a direction along the rotation axis direction of the developing roll 9K. . Then, the first screw member 10K supplies K developer along the axial direction to the surface of the developing roll 9K.

  After the K developer transported to the vicinity of the front end of the first screw member 10K in the drawing passes through the communication opening provided in the vicinity of the front end of the partition wall in the drawing and enters the second transport chamber. The second screw member 11K is held in the spiral blade. And with the rotational drive of the 2nd screw member 11K, it is conveyed toward the back | inner side from the near side in a figure, stirring in a rotation direction.

  In the second transfer chamber, a toner concentration sensor is provided on the lower wall of the casing, and detects the K toner concentration of the K developer in the second transfer chamber. As the K toner density sensor, a sensor composed of a magnetic permeability sensor is used. Since the magnetic permeability of the K developer containing K toner and magnetic carrier has a correlation with the K toner concentration, the magnetic permeability sensor detects the K toner concentration.

  The printer is provided with Y, M, C, and K toner replenishing means for individually replenishing Y, M, C, and K toners in the second storage chamber of the developing device for Y, M, C, and K, respectively. It has been. The printer control unit stores Vtref for Y, M, C, and K, which are target values of output voltage values from the Y, M, C, and K toner density detection sensors, in the RAM. When the difference between the output voltage value from the Y, M, C, K toner density detection sensor and the Vtref for Y, M, C, K exceeds a predetermined value, the Y, M, C, K toner is detected for the time corresponding to the difference. M, C, K toner supply means is driven. As a result, Y, M, C, and K toners are replenished into the second transfer chamber of the developing device for Y, M, C, and K.

  The developing roll 9K accommodated in the developing unit 12K faces the first screw member 10K and also faces the photoreceptor 2K through an opening provided in the casing. The developing roll 9K includes a cylindrical developing sleeve made of a nonmagnetic pipe that is rotationally driven, and a magnet roller that is fixed inside the developing roll 9K so as not to rotate with the sleeve. Then, the K developer supplied from the first screw member 10K is carried on the sleeve surface by the magnetic force generated by the magnet roller, and is conveyed to the developing region facing the photoreceptor 2K as the sleeve rotates.

  A developing bias having the same polarity as the toner and having an absolute value larger than the potential of the electrostatic latent image on the photosensitive member 2K and smaller than the uniform charging potential of the photosensitive member 2K is applied to the developing sleeve. ing. As a result, a developing potential for electrostatically moving the K toner on the developing sleeve toward the electrostatic latent image acts between the developing sleeve and the electrostatic latent image on the photoreceptor 2K. Further, a non-developing potential that moves K toner on the developing sleeve toward the sleeve surface acts between the developing sleeve and the background portion of the photoreceptor 2K. By the action of the developing potential and the non-developing potential, the K toner on the developing sleeve is selectively transferred to the electrostatic latent image on the photoreceptor 2K, and the electrostatic latent image is developed into the K toner image.

  In FIG. 2, the Y, M, and C toner image forming units 1Y, 1M, and 1C are also Y, M, and C on the photoreceptors 2Y, 2M, and 2C in the same manner as the K toner image forming unit 1K. A toner image is formed. Above the toner image forming units 1Y, 1M, 1C, and 1K, an optical writing unit 80 serving as a latent image writing unit is disposed. The optical writing unit 80 optically scans the photoreceptors 2Y, 2M, 2C, and 2K with laser light emitted from a laser diode based on image information transmitted from an external device such as a personal computer. By this optical scanning, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 2Y, 2M, 2C, and 2K. The optical writing unit 80 irradiates the photosensitive member through a plurality of optical lenses and mirrors while polarizing the laser light L emitted from the light source in the main scanning direction by a polygon mirror rotated by a polygon motor. It is. You may employ | adopt what performs optical writing by the LED light emitted from several LED of the LED array.

  Below the toner image forming units 1Y, 1M, 1C, and 1K, a transfer unit 30 is disposed as a transfer device that moves the endless intermediate transfer belt 31 endlessly in the counterclockwise direction in the drawing. Yes. The transfer unit 30 includes a drive roller 32, a secondary transfer counter roller 33, a cleaning backup roller 34, four primary transfer rollers 35Y, 35M, 35C, and 35K in addition to the intermediate transfer belt 31 that is an image carrier. Yes. Further, it also has a belt cleaning device 37 and the like.

  The intermediate transfer belt 31 is stretched by a driving roller 32, a secondary transfer counter roller 33, a cleaning backup roller 34, and four primary transfer rollers 35Y, 35M, 35C, and 35K disposed inside the loop. Then, it is moved endlessly in the same direction by the rotational force of the driving roller 32 that is driven to rotate counterclockwise in the figure by the driving means.

  The four primary transfer rollers 35Y, 35M, 35C, and 35K sandwich the intermediate transfer belt 31 that is moved endlessly between the photoreceptors 2Y, 2M, 2C, and 2K. As a result, primary transfer nips for Y, M, C, and K in which the front surface of the intermediate transfer belt 31 and the photoreceptors 2Y, 2M, 2C, and 2K abut are formed. A primary transfer bias is applied to the primary transfer rollers 35Y, 35M, 35C, and 35K by a primary transfer power source. As a result, a transfer electric field is formed between the Y, M, C, and K toner images on the photoreceptors 2Y, 2M, 2C, and 2K and the primary transfer rollers 35Y, 5M, 5C, and 5K. The Y toner formed on the surface of the Y photoconductor enters the Y primary transfer nip as the photoconductor 2Y rotates. Then, the image is primarily transferred from the photoreceptor 2Y to the intermediate transfer belt 31 by the action of the transfer electric field and nip pressure. The intermediate transfer belt 31 on which the Y toner image has been primarily transferred in this way then passes sequentially through the primary transfer nips for M, C, and K. Then, the M, C, and K toner images on the photoreceptors 2M, 2C, and 2K are sequentially superimposed on the Y toner image and primarily transferred. A four-color superimposed toner image is formed on the intermediate transfer belt 31 by the primary transfer of the superposition. In place of the primary transfer rollers 35Y, 35M, 35C, and 35K, a transfer charger, a transfer brush, or the like may be employed.

  Below the transfer unit 30, a sheet conveying unit 38 including a secondary transfer roller 36, a secondary transfer belt 41, and the like is disposed. The endless secondary transfer belt 41 is stretched by a plurality of rollers such as the secondary transfer roller 36 disposed on the inner side of the loop, and is rotated clockwise in the drawing by the rotational drive of the secondary transfer roller 36. Can be rotated. Then, a secondary transfer nip is formed by the secondary transfer roller 36 in contact with a region where the intermediate transfer belt 31 is wound around the secondary transfer counter roller 33 in the circumferential direction. That is, the secondary transfer counter roller 33 of the transfer unit 30 and the secondary transfer roller 36 of the sheet conveying unit 38 sandwich the intermediate transfer belt 31 and the secondary transfer belt 41 between each other. As a result, a secondary transfer nip is formed in which the front surface of the intermediate transfer belt 31 and the front surface of the secondary transfer belt 41 as a transfer body abut. The secondary transfer roller 36 disposed in the loop of the secondary transfer belt 41 is grounded. On the other hand, a secondary transfer bias obtained by superimposing a DC bias and an AC bias is applied to the secondary transfer counter roller 33 disposed in the loop of the intermediate transfer belt 31 by a secondary transfer power source 39. As a result, secondary transfer in which negative polarity toner is electrostatically moved from the secondary transfer counter roller 33 side to the secondary transfer roller 36 side between the secondary transfer counter roller 33 and the secondary transfer roller 36. An electric field is formed. In addition, it is good also as a secondary transfer bias only by DC bias, without superimposing AC bias.

  Below the sheet conveying unit 38, a feeding cassette 100 that stores a plurality of sheets P in a bundle of sheets is disposed. In the feeding cassette 100, a sheet feeding roller 100a is brought into contact with the uppermost sheet P of the sheet bundle, and the sheet P is directed toward the feeding path by being rotationally driven at a predetermined timing. Send it out. A registration roller pair 101 is disposed near the end of the feeding path. The registration roller pair 101 stops the rotation of both rollers as soon as the sheet P fed from the feeding cassette 100 is sandwiched between the rollers. Then, rotation driving is resumed at a timing at which the sandwiched paper P can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 31 in the secondary transfer nip, and the paper P is sent out toward the secondary transfer nip.

  The four-color superimposed toner image on the intermediate transfer belt 31 brought into intimate contact with the paper P at the secondary transfer nip is secondarily transferred onto the paper P by the action of the secondary transfer electric field and nip pressure to form a full-color toner image. Become. The sheet P having the full-color toner image formed on the surface in this manner is carried and conveyed by the secondary transfer belt 41 and passes through the secondary transfer nip, and is separated from the intermediate transfer belt 31 by curvature. Further, the curvature is separated from the secondary transfer belt 41 by the curvature of the separation roller 42 around which the secondary transfer belt 41 is wound. Further, by carrying and transporting the paper P on the secondary transfer belt 41, the paper P having a low rigidity such as a thin paper does not cause wrinkles or cause a jam due to a poor transport, so that the paper P can be stabilized. Can pass through the secondary transfer nip.

  Untransferred toner that has not been transferred to the paper P adheres to the intermediate transfer belt 31 after passing through the secondary transfer nip. This is cleaned from the belt surface by a belt cleaning device 37 in contact with the front surface of the intermediate transfer belt 31. A cleaning backup roller 34 disposed inside the loop of the intermediate transfer belt 31 backs up the cleaning of the belt by the belt cleaning device 37 from the inside of the loop.

  A fixing device 90 is disposed downstream of the secondary transfer nip in the sheet conveyance direction. The fixing device 90 forms a fixing nip with a fixing roller 91 containing a heat source such as a halogen lamp and a pressure roller 92 that rotates while contacting with the fixing roller 91 with a predetermined pressure. The sheet P fed into the fixing device 90 is sandwiched between the fixing nips in a posture in which the unfixed toner image carrying surface is in close contact with the fixing roller 91. Then, the toner in the toner image is softened by the influence of heating and pressurization, and the full color image is fixed. The paper P discharged from the fixing device 90 passes through a post-fixing conveyance path and is then discharged outside the apparatus.

  When a monochrome image is formed, the printer according to the embodiment changes the posture of the support plate that supports the primary transfer rollers 35Y, 35M, and 35C for the Y, M, and C in the transfer unit 30 by driving a solenoid or the like. Let As a result, the primary transfer rollers 35Y, 35M, 35C for Y, M, C are moved away from the photoreceptors 2Y, 2M, 2C, and the front surface of the intermediate transfer belt 31 is separated from the photoreceptors 2Y, M, C. Let In this way, only the black toner image forming unit 1K out of the four toner image forming units 1Y, 1M, 1C, and 1K in a state where the intermediate transfer belt 31 is in contact with only the black photoconductor 2K. Is driven to form a K toner image on the black photoreceptor 2K. The present invention can be applied not only to an image forming apparatus that forms a color image but also to an image forming apparatus that forms only a monochrome image.

  FIG. 4 is an enlarged sectional view partially showing a transverse section of the intermediate transfer belt 31. The intermediate transfer belt 31 includes an endless belt-like base layer 31a made of a material having a certain degree of flexibility and high rigidity, and an elastic layer made of an elastic material excellent in flexibility laminated on the front surface thereof. 31b. Particles 31c are dispersed in the elastic layer 31b, and these particles 31c are densely packed in the belt surface direction as shown in FIG. 5 with a part of the particles 31c protruding from the surface of the elastic layer 31b. Are lined up. A plurality of irregularities are formed on the belt surface by the plurality of particles 31c.

  Examples of the material of the base layer 31a include a resin in which an electrical resistance adjusting material made of a filler or an additive for adjusting the electrical resistance is dispersed. From the viewpoint of flame retardancy, the resin is preferably a fluorine-based resin such as PVDF (polyvinylidene fluoride) or ETFE (ethylene / tetrafluoroethylene copolymer), a polyimide resin, or a polyamide-imide resin. . Further, from the viewpoint of mechanical strength (high elasticity) and heat resistance, a polyimide resin or a polyamideimide resin is particularly preferable.

  Examples of the electrical resistance adjusting material dispersed in the resin include metal oxides, carbon black, ionic conductive agents, and conductive polymer materials. Examples of the metal oxide include zinc oxide, tin oxide, titanium oxide, zirconium oxide, aluminum oxide, and silicon oxide. In order to improve the dispersibility, the metal oxide previously subjected to surface treatment may be used. Examples of carbon black include ketjen black, furnace black, acetylene black, thermal black, and gas black. Examples of the ionic conductive agent include tetraalkyl ammonium salts, trialkyl benzyl ammonium salts, alkyl sulfonates, and alkyl benzene sulfonates. Alkyl sulfate, glycerin fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid alcohol ester, alkyl betaine, lithium perchlorate and the like may be used. A mixture of two or more of these ionic conductive agents may be used. The electrical resistance adjusting material to which the present invention can be applied is not limited to those exemplified so far.

For the coating liquid that is the precursor of the base layer 31a (in which the electrical resistance adjusting material is dispersed in the liquid resin before curing), a dispersion aid, a reinforcing material, a lubricant, and a heat conducting material are used as necessary. An antioxidant or the like may be added. Intermediate transfer amount of the electric resistance adjusting material contained in the base layer 31a of the belt 31 is preferably 1 at the surface resistivity ^{× 10 8 ~1 × 10 13 [} Ω / □], 1 × 10 6 ~1 × volume resistivity The amount is 10 ¹² [Ω · cm]. However, from the viewpoint of mechanical strength, it is necessary to select and add an amount in a range where the molded film is brittle and does not easily break. In other words, electrical properties (surface resistance and volume resistance) and mechanical strength using a coating liquid in which the blending ratio of resin components (polyimide resin precursor, polyamideimide resin precursor, etc.) and an electrical resistance adjusting material is adjusted appropriately. It is preferable to manufacture and use a seamless belt with a good balance. In the case of carbon black, the content of the electrical resistance adjusting material is preferably 10 to 25 [wt%], more preferably 15 to 20 [wt%] of the total solid content in the coating liquid. Further, the content in the case of a metal oxide is preferably 150 [wt%] of the total solid content in the coating liquid, more preferably 10 to 30 [wt%]. If the content is less than the above-mentioned range, a sufficient effect cannot be obtained. If the content is more than the above-mentioned range, the mechanical strength of the intermediate transfer belt 31 (seamless belt) is remarkably lowered. Absent.

  The thickness of the base layer 31a is not particularly limited and may be appropriately selected depending on the situation, but is preferably 30 [μm] to 150 [μm], and more preferably 40 [μm] to 120 [μm]. 50 [μm] to 80 [μm] is particularly preferable. If the thickness of the base layer 31a is less than 30 [μm], the belt is likely to tear due to cracks, and if it exceeds 150 [μm], the belt may be broken by bending. On the other hand, when the thickness of the base layer 31a is within the particularly preferable range described above, it is advantageous in terms of durability.

  In order to improve the belt running stability, it is preferable to reduce the layer thickness unevenness of the base layer 31a as much as possible. The method for adjusting the thickness of the base layer 31a is not particularly limited, and can be appropriately selected depending on the situation. For example, measurement with a contact type or eddy current type film thickness meter or a method of measuring a cross section of the film with a scanning electron microscope (SEM) can be mentioned.

  As described above, the elastic layer 31b of the intermediate transfer belt 31 has a concavo-convex shape formed by a plurality of dispersed particles 31c on the surface. Examples of the elastic material for forming the elastic layer 31b include general-purpose resins, elastomers, and rubbers. In particular, an elastic material excellent in flexibility (elasticity) is preferably used, and an elastomer material or a rubber material is preferable. Examples of the elastomer material include polyester, polyamide, polyether, polyurethane, polyolefin, polystyrene, polyacryl, polydiene, and silicone-modified polycarbonate. A thermoplastic elastomer such as a fluorinated copolymer may be used. Examples of the thermosetting resin include polyurethane, silicone-modified epoxy, and silicone-modified acrylic resins.

  Examples of the rubber material include isoprene rubber, styrene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, butyl rubber, silicone rubber, chloroprene rubber, and acrylic rubber. Furthermore, chlorosulfonated polyethylene, fluorine rubber, urethane rubber, hydrin rubber and the like can also be exemplified. From the materials exemplified so far, it is possible to appropriately select a material capable of obtaining desired performance. In particular, it is preferable to select a material that is as soft as possible in order to follow the surface unevenness of a recording sheet having an uneven surface, such as a leather paper. Further, since the particles 31c are dispersed, a thermosetting material is preferable to a thermoplastic material. This is because the thermosetting material has excellent adhesion to the resin particles and can be reliably fixed by the effect of the functional group contributing to the curing reaction. Vulcanized rubber is also a preferred material for the same reason.

  Among the elastic materials constituting the elastic layer 31b, acrylic rubber is most preferable from the viewpoints of ozone resistance, flexibility, adhesion to particles, imparting flame retardancy, environmental stability, and the like. The acrylic rubber may be generally commercially available and is not limited to a specific product. However, among various crosslinking systems (epoxy groups, active chlorine groups, carboxyl groups) of acrylic rubber, those having a carboxyl group crosslinking system are superior in terms of rubber physical properties (particularly compression set) and processability. It is preferable to select a crosslinking type. As the crosslinking agent used for the carboxyl group-based acrylic rubber, an amine compound is preferable, and a polyvalent amine compound is most preferable. Specific examples of such amine compounds include aliphatic polyvalent amine crosslinking agents and aromatic polyvalent amine crosslinking agents. Further, examples of the aliphatic polyvalent amine cross-linking agent include hexamethylene diamine, hexamethylene diamine carbamate, N, N′-dicinnamylidene-1,6-hexane diamine and the like. Examples of the aromatic polyvalent amine crosslinking agent include 4,4′-methylenedianiline, m-phenylenediamine, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4 ′-(m- And phenylene diisopropylidene) dianiline. 4,4 '-(p-phenylenediisopropylidene) dianiline, 2,2'-bis [4- (4-aminophenoxy) phenyl] propane, 4,4'-diaminobenzanilide and the like may be used. Furthermore, 4,4′-bis (4-aminophenoxy) biphenyl, m-xylylenediamine, p-xylylenediamine, 1,3,5-benzenetriamine, 1,3,5-benzenetriaminomethyl, etc. Good.

  The proper range of the amount of the crosslinking agent is preferably 0.05 to 20 parts by weight, and more preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the acrylic rubber. When the blending amount of the crosslinking agent is too small, crosslinking is not sufficiently performed, so that it is difficult to maintain the shape of the crosslinked product. On the other hand, when there is too much content, a crosslinked material will become hard too much and the elasticity etc. as crosslinked rubber will be impaired.

  The acrylic rubber used for the elastic layer 31b may be blended with a crosslinking accelerator for the purpose of promoting the crosslinking reaction of the crosslinking agent described above. The type of the crosslinking accelerator is not particularly limited, but it is preferable that the crosslinking accelerator can be used in combination with the polyvalent amine crosslinking agent described above. Examples of such crosslinking accelerators include guanidine compounds, imidazole compounds, quaternary onium salts, tertiary phosphine compounds, alkali metal salts of weak acids, and the like. Examples of the guanidine compound include 1,3-diphenylguanidine, 1,3-diortolylguanidine and the like. Examples of the imidazole compound include 2-methylimidazole and 2-phenylimidazole. Examples of the quaternary onium salt include tetra n-butylammonium bromide and octadecyltri-n-butylammonium bromide. Examples of the polyvalent tertiary amine compound include triethylenediamine and 1,8-diaza-bicyclo [5.4.0] undecene-7 (DBU). Examples of the tertiary phosphine compound include triphenylphosphine and tri-p-tolylphosphine. Examples of the alkali metal salt of a weak acid include inorganic weak acid salts such as sodium or potassium phosphates and carbonates, and organic weak acid salts such as stearates and laurates.

  An appropriate range of the amount of the crosslinking accelerator used is preferably 0.1 to 20 parts by weight, more preferably 0.3 to 10 parts by weight per 100 parts by weight of the acrylic rubber. When there are too many crosslinking accelerators, the crosslinking rate may become too fast at the time of crosslinking, the bloom of the crosslinking accelerator on the surface of the crosslinked product may occur, or the crosslinked product may become too hard. On the other hand, when there are too few crosslinking accelerators, the tensile strength of a crosslinked material may fall remarkably, and the elongation change or tensile strength change after a heat load may be too large.

  In preparing the acrylic rubber, an appropriate mixing method such as roll mixing, Banbury mixing, screw mixing, and solution mixing can be employed. The order of blending is not particularly limited, but after sufficiently mixing components that are not easily reacted or decomposed by heat, as a component that is easily reacted by heat or a component that is easily decomposed, for example, a crosslinking agent is used at a temperature at which reaction or decomposition does not occur. What is necessary is just to mix in a short time.

  Acrylic rubber can be made into a crosslinked product by heating. A preferable heating temperature is 130 [° C.] to 220 [° C.], and more preferably 140 [° C.] to 200 [° C.]. Moreover, a preferable crosslinking time is 30 seconds to 5 hours. As a heating method, a method used for crosslinking of rubber such as press heating, steam heating, oven heating, hot air heating and the like may be appropriately selected. Further, after cross-linking once, post-cross-linking may be performed in order to surely cross-link to the inside of the cross-linked product. The post-crosslinking time varies depending on the heating method, crosslinking temperature, shape, etc., but is preferably 1 to 48 hours. About the heating method and heating temperature at the time of post-crosslinking, it is possible to select suitably. For the selected material, appropriate materials such as an electrical resistance adjusting agent for adjusting electrical characteristics, a flame retardant for obtaining flame retardancy, and an antioxidant, a reinforcing agent, a filler, a crosslinking accelerator, etc., as necessary. You may make it contain. Furthermore, the various materials already described can be used as an electric resistance adjusting agent for adjusting electric characteristics. However, since carbon black, metal oxide, and the like impair flexibility, it is preferable to reduce the amount used, and it is also effective to use an ionic conductive agent or a conductive polymer. Moreover, you may use them together.

  It is preferable to add 0.01 to 3 parts of various perchlorates and ionic liquids to 100 parts by weight of rubber. When the addition amount of the ionic conductive agent is 0.01 parts or less, the effect of reducing the resistivity cannot be obtained. Further, if the addition amount is 3 parts or more, there is a high possibility that the conductive agent will bloom or bleed onto the belt surface.

Regarding the addition amount of the electrical resistance adjusting material, the resistance value of the elastic layer 31b is 1 × 10 ⁸ to 1 × 10 ¹³ [Ω / □] in terms of surface resistance and 1 × 10 ⁶ to 1 × 10 ¹² [Ω in terms of volume resistance. -It is preferable to adjust so that it may be in the range of cm]. Further, in order to obtain a high toner transfer property to a concavo-convex sheet as required for a recent electrophotographic image forming apparatus, the micro rubber hardness of the elastic layer 31b in a 23 [° C.] 50 [%] RH environment. It is preferable to adjust the flexibility so that the value is 35 or less. In so-called microhardness measurements such as Martens hardness and Vickers hardness, the deformation performance of the entire belt cannot be evaluated because only the hardness in a shallow region in the bulk direction of the measurement site, that is, a very limited region near the surface is measured. For this reason, for example, when a flexible material is used for the outermost surface of the intermediate transfer belt 31 having a low deformation performance, the microhardness value is lowered. Such an intermediate transfer belt 31 has low deformation performance, that is, poor followability to the concavo-convex sheet. As a result, the transfer performance to the concavo-convex sheet required for the recent image forming apparatus cannot be sufficiently exhibited. End up. Therefore, it is preferable to evaluate the flexibility of the intermediate transfer belt 31 by measuring the micro rubber hardness that can evaluate the deformation performance of the entire intermediate transfer belt 31.

  The layer thickness of the elastic layer 31b is preferably 200 [μm] to 2 [mm], and more preferably 400 [μm] to 1000 [μm]. When the layer thickness is smaller than 200 [μm], the followability to the surface irregularities of the recording sheet and the effect of reducing the transfer pressure are lowered, which is not preferable. If the layer thickness is larger than 2 [mm], the elastic layer 31b is easily bent due to its own weight, and the running performance becomes unstable, or the belt is cracked by wrapping around the roller that stretches the belt. It is not preferable because it is easy to make. In addition, as a measuring method of layer thickness, the method of measuring by observing a cross section with a scanning microscope (SEM) can be illustrated.

  The particles 31c dispersed in the elastic material of the elastic layer 31b have an average particle diameter of 100 [μm] or less, a true spherical shape, insoluble in an organic solvent, and 3 [%] thermal decomposition. Resin particles having a temperature of 200 [° C.] or higher are used. Although there is no restriction | limiting in particular in the resin material of particle | grains 31c, An acrylic resin, a melamine resin, a polyamide resin, a polyester resin, a silicone resin, a fluororesin, rubber | gum etc. can be illustrated. The base surface of the particles made of these resin materials may be surface treated with a different material. A hard resin may be coated on the surface of spherical base particles made of rubber. Moreover, as a base particle, you may use a hollow thing and a porous thing. For example, as the particles 31c, particles having a charging performance opposite to the normal charging polarity of the toner can be used. In this printer, the particles are made of a positively charged melamine resin. In such a configuration, the charge of the particles 31c cancels the transfer bias having a large negative factor, and the occurrence of a phenomenon in which the secondary transfer current is concentrated between the particles is suppressed, thereby further reducing the injection amount of the reverse charge into the toner. Can do.

  Among the resin materials exemplified so far, silicone resin particles are most preferable from the viewpoint of excellent lubricity, releasability with respect to toner, abrasion resistance, and the like. Particles obtained by finishing a resin material into a spherical shape by a polymerization method or the like are preferable, and particles closer to a true sphere are more preferable. Moreover, as the particles 31c, it is desirable to use particles having a volume average particle diameter of 1.0 [μm] to 5.0 [μm] and monodispersed particles. The monodisperse particles are not particles having a single particle size but particles having a very sharp particle size distribution. Specifically, the particles have a distribution width of ± (average particle size × 0.5 [μm]) or less. When the particle size of the particles 31c is less than 1.0 [μm], the effect of promoting the transfer performance by the particles 31c cannot be sufficiently obtained. On the other hand, if the particle size is larger than 5.0 [μm], the gap between the particles is increased and the belt surface roughness is increased, so that the toner cannot be transferred satisfactorily. It becomes easy to generate the 31 defective cleaning. Furthermore, since the particles 31c made of a resin material are generally highly insulating, if the particle size is too large, the charges of the particles 31c tend to cause image disturbance due to the accumulation of charges during continuous printing.

  As the particles 31c, specially synthesized particles or commercially available products may be used. By applying the particles 31c directly to the elastic layer 31b and leveling, the particles can be easily and uniformly aligned. By doing in this way, the overlap of the particles 31c in the belt thickness direction can be almost eliminated. The cross-sectional diameter of the plurality of particles 31c in the surface direction of the elastic layer 31b is desirably as uniform as possible, and specifically, the distribution width is ± (average particle diameter × 0.5 [μm]) or less. Is preferred. For this reason, it is preferable to use a powder having a small particle size distribution as the powder of the particles 31c. However, if a method that realizes selectively applying only the particles 31c having a specific particle size to the surface of the elastic layer 31b is employed. It is also possible to use a powder having a relatively large particle size distribution. The timing at which the particles 31c are applied to the surface of the elastic layer 31b is not particularly limited, and may be any before or after crosslinking of the elastic material of the elastic layer 31b.

  In the surface direction of the elastic layer 31b in which the particles 31c are dispersed, the projected area ratio between the portion where the particles 31c are present and the portion where the surface of the elastic layer 31b is exposed is that the particles 31c exist. It is desirable that the projected area ratio of the existing portion be 60% or more. If it is less than 60 [%], the chances of direct contact between the toner and the solid surface of the elastic layer 31b are increased, and good toner transferability cannot be obtained, or the toner cleaning performance from the belt surface is reduced. Or reduce the filming resistance of the belt surface. It is also possible to use an intermediate transfer belt 31 in which the particles 31c are not dispersed in the elastic layer 31b.

  In the printer according to the present embodiment, the optical sensor 20 is provided so as to face the surface of the secondary transfer belt 41, and the secondary transfer belt 41 is disposed downstream of the optical sensor 20 in the movement direction of the secondary transfer belt. A cleaning blade 60 for cleaning the surface is provided. Further, a lubricant application roller 70 for applying a lubricant 71 to the surface of the secondary transfer belt 41 is disposed downstream of the cleaning blade 60 in the secondary transfer belt surface movement direction.

  The image quality adjusting toner pattern formed on the surface of the photosensitive member 2 is primarily transferred onto the intermediate transfer belt 31 and is transferred from the intermediate transfer belt 31 at a timing such as between sheets where the paper P does not exist in the secondary transfer portion. The image is transferred to the next transfer belt 41. Then, the image density (toner adhesion amount) ID of the toner pattern transferred onto the secondary transfer belt 41 on the surface of the secondary transfer belt 41 is detected using the optical sensor 20. The image quality adjustment toner pattern that has passed through the surface of the secondary transfer belt 41 facing the optical sensor 20 is removed from the secondary transfer belt 41 by the cleaning blade 60. After the image quality adjustment toner pattern is removed by the cleaning blade 60 in this way, the lubricant 71 is applied to the surface of the secondary transfer belt 41 by the lubricant application roller 70.

  Here, image quality adjustment control (process control) will be described. In image quality adjustment control, a test pattern is created, and image density control and displacement control are performed based on the result of detecting the image density and image forming position of the test pattern. In the image density control, for example, a toner adhesion amount (image density) of a density control toner pattern (a kind of image quality adjustment toner pattern) obtained by developing a predetermined pattern latent image is detected. Then, in accordance with the detection result of the toner adhesion amount, setting values such as the toner concentration in the developer in the developing device 8, the writing condition (exposure power, etc.) of the optical writing unit 80, the charging bias and the developing bias are changed. To do. In the misregistration control, for example, the latent image writing timing of each color toner image is adjusted by the detection timing of the misregistration control toner pattern (a kind of toner pattern for adjusting image quality).

  In general, image quality adjustment control (process control) is performed in a non-image forming operation period other than an image forming operation period such as when a predetermined number of images are formed before or after the start of a print job (image forming operation) when the power is turned on. Done. However, in order to further stabilize the image quality, the image quality adjustment is performed between the recording sheets, which are non-image areas between the image area (the image portion transferred to one recording sheet) and the image area, even during the image forming operation period. An image pattern may be created and detected to implement image quality adjustment control.

  The density control toner pattern is difficult to detect on the photoreceptor 2 due to the installation space of the image density detection sensor when the diameter of the photoreceptor 2 is small, but there is a problem on the secondary transfer belt 41. Can be detected. On the other hand, with respect to the toner pattern for misregistration control, it is necessary to observe the misregistration between the color toner images due to the variation in the distance between the photoconductors or the misregistration due to the writing timing of each color latent image. In this embodiment, since the transfer of the toner image on which the positional deviation has occurred on the intermediate transfer belt 31 is received on the secondary transfer belt 41, the positional deviation between the color toner images can be observed. For this reason, in this embodiment, both the density control toner pattern and the positional deviation control toner pattern can be detected on the secondary transfer belt 41 by the optical sensor 20.

  Further, as the image forming operation of a low image area continues, the amount of old toner that remains in the developing device 8 for a long time increases, so the amount of deteriorated toner with deteriorated toner charging characteristics and the like increases, and the developing ability decreases. This causes a decrease in transferability and leads to deterioration in image quality. In order to prevent such deteriorated toner from staying in the developing device 8, the toner is forcibly discharged from the developing device 8 to a non-image area corresponding to an interval between images (between sheets) at a predetermined timing. The refresh mode which is toner forced consumption control is executed. New toner is supplied to the developing device 8 whose toner density has been reduced by the forced discharge of the toner, whereby the deteriorated toner in the developing device 8 is replaced with new toner.

  When the refresh mode is executed, a refresh toner pattern (toner consumption pattern) is created in a non-image area corresponding to an interval between images (between recording sheets) on the photoreceptor 2, and a developing device is used when forming the refresh toner pattern. 8 consumes toner. The refresh toner pattern thus formed is transferred from the photoreceptor 2 to the intermediate transfer belt 31, further transferred from the intermediate transfer belt 31 to the secondary transfer belt 41, and then on the secondary transfer belt 41 by the cleaning blade 60. Removed from.

  FIG. 6 is an enlarged perspective view illustrating the image quality adjusting toner pattern 400 of each color formed on the secondary transfer belt 41. FIG. 7 is a timing chart when the image quality adjustment toner pattern 400 is detected and the toner pattern interval is measured. In the printer according to the present embodiment, the toner images are individually formed by the toner image forming units 1Y, 1M, 1C, and 1K for each color, and then the toner images for each color are sequentially superimposed on the intermediate transfer belt 31. For this reason, if the toner images of the respective colors are misaligned, the toner images superimposed on the intermediate transfer belt 31 may be misaligned, and the image quality may be deteriorated.

  Color misregistration correction performed to improve such color misregistration is performed prior to the image forming operation. For example, it is performed at the time of startup of the image forming apparatus (immediately after the main power is turned on by turning on the main power switch) or at the time of recovery (immediately after the return from the energy saving mode for power saving to the standby mode in which the printing operation is possible). The formation of the image quality adjustment toner pattern 400 and the correction amount calculation based on the image quality adjustment toner pattern 400 are performed as a series of operations. This series of operations is also preferably performed when a predetermined temperature change is detected, when an elapse of a predetermined time is detected, or when a predetermined number of sheets are printed. Further, when the predetermined number of sheets is set by the temperature, the timer or the counter, the image quality adjusting toner pattern 400 is formed between the sheets P between the sheets P without stopping the printing operation.

Next, calculation of the color misregistration amount due to regular reflection light will be described. First, the horizontal line toner patterns 400Y ₁ , 400M ₁ , 400C ₁ , and 400K ₁ of the respective colors, which are the image quality adjustment toner patterns 400 formed on the photoreceptors 2Y, 2M, 2C, and 2K, are transferred to the surface of the intermediate transfer belt 31 in the direction of surface movement. To transfer to a different position. Similarly, the shaded toner patterns 400Y ₂ , 400M ₂ , 400C ₂ , and 400K ₂ of the respective colors, which are the image quality adjustment toner patterns 400 formed on the photoreceptors 2Y, 2M, 2C, and 2K, are moved on the surface of the intermediate transfer belt 31. Transfer to different positions in the direction. After that, as shown in FIG. 6, the image quality adjusting toner pattern 400 transferred to the intermediate transfer belt 31 is transferred to the secondary transfer belt 41, and the optical sensor 20 (optical sensors 20a, 20b, 20c) uses the secondary transfer belt. 41 detects the image quality adjustment toner pattern 400.

For example, each time interval between the detection signal of the horizontal line toner pattern 400K ₁ of a specific color, here black, and the detection signals of the horizontal line toner patterns 400Y ₁ , 400M ₁ , and 400C ₁ of other colors Y, M, and C Measure. By controlling the sub-scanning position (circumferential position) of the laser beam irradiated from the optical writing unit 80 shown in FIG. Make the time difference the target relative time difference. From the black K image forming position on the secondary transfer belt 41, the image forming positions are adjusted so as to be the target pitch intervals of the other colors M, C, and Y. As shown in FIG. 7, the registration positions in the sub-scanning direction, which is the secondary transfer belt surface moving direction y, are aligned by the horizontal line toner patterns 400Y ₁ , 400M ₁ , 400C ₁ , 400K ₁ . The registration alignment in the main scanning direction x, which is the belt width direction orthogonal to the secondary transfer belt surface movement direction, is performed based on the time interval difference between the horizontal line toner pattern and the diagonal line toner pattern.

In the above example, it has described a case where image quality adjustment toner pattern 400 (horizontal toner pattern 400 ₁ and the hatched toner pattern 400 ₂₎ is formed once on the secondary transfer belt 41 is not limited thereto. Actually, an error at the time of measurement occurs due to a mechanical speed fluctuation factor. Therefore, a similar image quality adjusting toner pattern 400 is formed on the secondary transfer belt 41 a plurality of times in the sub scanning direction. In the same manner as described above, the registration adjustment value is calculated, and the average value thereof is calculated, thereby reducing the mechanical periodicity error.

  As shown in FIG. 6, the image quality adjusting toner patterns 400 are formed on the secondary transfer belt 41 at three locations in the main scanning direction x. The two image quality adjustment toner patterns 400 formed at both ends in the main scanning direction on the secondary transfer belt 41 are formed at both ends in the main scanning direction of the writing area. The image quality adjustment toner pattern 400 formed at the central portion in the main scanning direction, which is the remaining one portion on the secondary transfer belt 41, is formed at the central portion in the main scanning direction of the writing area. Here, the “writing area” is a range in which the toner image can be transferred onto the paper P. In the setting of the adjustment value, using the three image quality adjustment toner patterns 400 in the writing area, in addition to the registration adjustment value in the main scanning direction x and the sub-scanning direction y, the skew adjustment value of the scanning line, the scanning It is possible to determine an adjustment value for the width.

Each of the optical sensors 20a, 20b, and 20c is provided with a light emitting element and a light receiving element, and light emitted from the light emitting element is regularly reflected by the secondary transfer belt 41 to reach the light receiving element. If there is an image quality adjustment toner pattern 400 on the secondary transfer belt 41, the amount of light received by the light receiving element changes, and a detection signal corresponding to the image quality adjustment toner pattern 400 is output as the output of the optical sensor 20 as shown in FIG. Is obtained. This detection signal is compared with the threshold level, and a pulse output waveform when the toner pattern is detected is output as shown in FIG. Then, the time is converted from the count number obtained by counting the number of clocks from START to the pulse at the time of toner pattern detection in the figure, and time T1, time T2, time T3, and time T4 from START are obtained. As a central location at the toner pattern detected from the result, for example, the horizontal line toner pattern _{400K 1, TK = (T1 +} T2) / 2 is obtained, the horizontal toner pattern _{400C 1, TC = (T3 +} T4) / 2 value can get. Similarly, horizontal line toner patterns 400M ₁ , 400Y ₁ and oblique line toner patterns 400Y ₂ , 400M ₂ , 400C ₂ , 400K ₂ are also calculated. Then, the patch interval Pc1 = (TC-TK) of the horizontal line toner pattern 400 K ₁ and horizontal toner pattern 400C ₁ shown in FIG. 6 is calculated. Similar to this calculation method, patch intervals Pm1, Py, Pc2, Pm2, and Py2 are also calculated.

  FIG. 1 is a diagram showing the secondary transfer rate to the paper P and the secondary transfer belt 41. The measurement environment for the secondary transfer rate is a normal temperature and normal humidity environment (MM environment) in which the temperature is 23 [° C.] and the relative humidity is 50 [%]. Then, the secondary transfer current with respect to the secondary transfer current is transferred in the belt transfer mode in which the one-color solid toner image and the two-color superimposed toner image are transferred from the intermediate transfer belt 31 to the secondary transfer belt 41 and in the paper transfer mode in which the toner image is transferred to the paper P. The rate is plotted.

  As shown in FIG. 1, in the paper transfer mode, the secondary transfer current I1 is such that the secondary transfer rate of the two-color superimposed toner image having the larger toner amount among the one-color solid toner image and the two-color superimposed toner image is the highest. Is set. On the other hand, the secondary transfer current I2 that maximizes the secondary transfer rate during belt transfer is different from the secondary transfer current I1 in the paper transfer mode, and the secondary transfer current I2 during belt transfer is the paper transfer mode. It can be seen that the absolute value is smaller than the mode secondary transfer current I1.

  The secondary transfer rate with respect to the secondary transfer current differs between the sheet transfer mode in which the transfer is performed from the intermediate transfer belt 31 to the sheet P and the belt transfer in which the transfer is performed from the intermediate transfer belt 31 to the secondary transfer belt 41. This is because the resistance during transfer changes depending on the presence or absence of the paper P. For this reason, if the secondary transfer current I1 is set so that the secondary transfer rate in the paper transfer mode is high, the current flowing through the secondary transfer nip during belt transfer becomes excessive, and the secondary transfer current during belt transfer compared to the paper transfer mode. Next transfer rate decreases. In addition, since the secondary transfer rate curve is a region that changes sharply, the transfer rate varies greatly with changes in the use environment and changes in the deterioration state of the developer. When the secondary transfer rate fluctuates, the secondary transfer rate of the image quality adjustment pattern, the density control pattern, the refresh toner pattern, etc. transferred from the intermediate transfer belt 31 to the secondary transfer belt 41 becomes low. The amount of residual toner on the intermediate transfer belt 31 increases. For this reason, the cleaning load of the belt cleaning device 37 that cleans the intermediate transfer belt 31 becomes large, and there is a possibility that defective cleaning may occur.

  In the printer according to this embodiment, a sheet transfer mode in which a toner image is transferred from the intermediate transfer belt 31 to the sheet P and a transfer condition different from the sheet transfer mode are transferred from the intermediate transfer belt 31 to the secondary transfer belt 41. And a belt transfer mode for transferring a toner image. As the transfer condition, the absolute value of the secondary transfer current I2 in the belt transfer mode is made smaller than the absolute value of the secondary transfer current I1 in the sheet transfer mode as shown in FIG. In FIG. 1, the secondary transfer current I1 in the sheet transfer mode is set to −105 [μA], and the secondary transfer current I2 in the belt transfer mode is set to −93 [μA]. As a result, the secondary transfer current I2 in a region where the secondary transfer rate is high and stable is used to transfer the image quality adjustment toner pattern, the density control toner pattern, the refresh toner pattern, and the like from the intermediate transfer belt 31 to the secondary transfer belt 41. Can be transferred onto. In the belt transfer mode, as can be seen from FIG. 1, the secondary transfer current I2 has a higher secondary transfer rate than the secondary transfer current I1, and accordingly, the amount of residual toner on the intermediate transfer belt 31 is reduced accordingly. can do. Therefore, the cleaning load of the belt cleaning device 37 is reduced, and the occurrence of defective cleaning can be suppressed.

  The set value of the secondary transfer bias that becomes the secondary transfer current I2 in the belt transfer mode is 70 with respect to the set value of the secondary transfer bias that becomes the secondary transfer current I1 in the paper transfer mode. It is good to set it to the magnitude | size of [%] or more and less than 100 [%]. More preferably, the size is set to about 80 [%].

  Further, when the temperature and humidity environment in the printer changes, the resistance of the paper P, the intermediate transfer belt 31, the secondary transfer belt 41, etc. changes, so the secondary transfer current I1 in the paper transfer mode and the secondary in the belt transfer mode. The transfer current I2 is changed depending on the temperature and humidity environment. Table 1 shows secondary transfer currents I1 and I2 in the sheet transfer mode and the belt transfer mode in a low temperature and low humidity environment (LL environment), a normal temperature and normal humidity environment (MM environment), and a high temperature and high humidity environment (HH environment), respectively. An example of the set value is shown.

  Each temperature and humidity environment has a temperature and relative humidity of 10 [° C.] 15 [%] in a low temperature and low humidity environment (LL environment) and 23 [° C.] 50 [%] in a normal temperature and normal humidity environment (MM environment). In this case, the high temperature and high humidity environment (HH environment) is 27 [° C.] 80 [%]. In the MM environment and the HH environment, a superimposed bias obtained by superimposing a DC bias and an AC bias is applied to the secondary transfer counter roller 33 as the secondary transfer bias, and the set values of the secondary transfer currents I1 and I2 are two. This is the output value of the DC component of the next transfer bias. On the other hand, in the LL environment, the AC bias is not output as the secondary transfer bias, and only the DC bias is applied to the secondary transfer counter roller 33, and the set values of the secondary transfer currents I1 and I2 are the output values of the DC bias. is there.

  Thus, by changing the secondary transfer current I1 in the paper transfer mode and the secondary transfer current I2 in the belt transfer mode according to the temperature and humidity environment, a good transfer rate is always obtained regardless of the temperature and humidity environment. Can be obtained.

[Embodiment 2]
A second embodiment (hereinafter referred to as a second embodiment) of an image forming apparatus to which the present invention is applied will be described. Note that the basic configuration of the printer that is the image forming apparatus according to the second embodiment is the same as the configuration of the printer according to the first embodiment, and a description thereof will be omitted.

  Also in the printer according to the present embodiment, a refresh mode for refreshing the developer in the developing device 8 can be executed as in the printer according to the first embodiment. In this refresh mode, toner that discharges toner from the developing device 8 to the non-image area of the photoreceptor 2 at a constant timing so that old toner does not stay in the developing device 8 and forcibly consumes the toner in the developing device 8. Implement forced consumption control. Then, after the toner is discharged from the developing device 8, toner supply control for supplying new toner to the developing device 8 in which the toner density is lowered is performed. By executing such a refresh mode, the toner in the developing device 8 is refreshed to improve the image quality.

  The refresh mode is performed, for example, when image formation with an image area ratio of 2.5 [%] or less is performed. Then, a refresh toner pattern (toner consumption pattern) is formed at the interval between papers or at the end of the job so that the same amount of toner is consumed as when the image formation with an image area ratio of 2.5 [%] is performed. . The refresh toner pattern formed in the non-image forming area corresponding to the space between the sheets of the photoreceptor 2 is primarily transferred from the photoreceptor 2 to the intermediate transfer belt 31, and then secondary from the intermediate transfer belt 31 to the secondary transfer belt 41. It is transferred and removed by the cleaning blade 60.

  Here, if the transfer rate of the refresh toner pattern from the intermediate transfer belt 31 to the secondary transfer belt 41 is low, the residual transfer toner remaining on the intermediate transfer belt 31 increases, and the cleaning load of the belt cleaning device 37 increases. . As a result of intensive studies by the inventors of the present application, when the toner image is transferred from the intermediate transfer belt 31 to the secondary transfer belt 41, the transfer rate of the halftone toner image is higher than the transfer rate of the solid pattern toner image. It turned out to be worse. The toner image transferred from the intermediate transfer belt 31 to the secondary transfer belt 41 includes a density control toner pattern, a positional deviation control toner pattern, a refresh toner pattern, and the like. Among them, the toner of the refresh toner pattern The amount is the largest. Therefore, when the refresh toner pattern is formed with a halftone toner image, the cleaning load becomes more significant.

  Therefore, in the printer according to the present embodiment, the refresh toner pattern is formed with a solid pattern toner image. As a result, the transfer rate of the refresh toner pattern from the intermediate transfer belt 31 to the secondary transfer belt 41 is improved as compared with the case where the refresh toner pattern is formed as a halftone toner image, and the transfer residue remaining on the intermediate transfer belt 31 is increased. Toner can be reduced. Therefore, the transfer residual toner input to the belt cleaning device 37 is reduced, and accordingly, the cleaning load of the belt cleaning device 37 can be reduced.

  Table 2 shows the transfer rate of the halftone toner image and the solid toner image and the amount of residual toner.

  The image area ratio of the halftone toner image is 50 [%], and the image area ratio of the solid toner image is 100 [%]. In the table, “one color” is a single color toner image, “two color superposition” is a superposition of two color toner images, “three color superposition” is a superposition of three color toner images, “4-color superposition” indicates a case where four-color toner images are superposed and formed on the intermediate transfer belt 31.

  As can be seen from Table 2, the transfer rate of the solid toner image is higher than that of the halftone toner image in any of the cases of “one color”, “two color overlap”, “three color overlap”, and “four color overlap”. It can be seen that the amount of toner remaining on the transfer belt 31 decreases. The two-color superimposed halftone toner image and the single-color solid toner image have the same image area ratio of 100%, but the single-color solid toner image has a transfer rate that is higher than the two-color superimposed halftone toner image. High and the amount of toner remaining on the intermediate transfer belt 31 is small. Similarly, the four-color stacked halftone toner image and the two-color stacked solid toner image have the same image area ratio of 200%, but the two-color stacked solid toner image is the four-color stacked halftone toner image. The transfer rate is higher than that, and the amount of toner remaining on the intermediate transfer belt 31 is small. Accordingly, even when the image area ratio is the same, the amount of residual toner on the intermediate transfer belt 31 is smaller in the solid toner image than in the case of superimposing the halftone toner images, and thus the cleaning load of the belt cleaning device 37 is reduced. can do.

  Table 3 shows the number of toner drop occurrences when the refresh toner pattern is formed with a halftone toner image and with a solid toner image.

  As can be seen from Table 3, when the refresh toner pattern is formed with a halftone toner image, the transfer rate is poor as described above, and the amount of residual toner on the intermediate transfer belt 31 increases and is input to the belt cleaning device 37. The amount of toner is increased. For this reason, the toner once collected by the belt cleaning device 37 is dropped on the intermediate transfer belt 31. On the other hand, when the refresh toner pattern is formed as a solid toner image, the transfer rate is good as described above, the amount of residual toner on the intermediate transfer belt 31 is reduced, and the amount of toner input to the belt cleaning device 37 is reduced. . Therefore, the toner once collected by the belt cleaning device 37 does not fall on the intermediate transfer belt 31 and no toner is dropped.

  Next, the shape of the refresh toner pattern formed between the papers will be described. When each of the four refresh toner patterns of Y, M, C, and K is formed so as not to overlap by shifting the position in the intermediate transfer belt moving direction, the refresh toner patterns of all four colors are accommodated. It is necessary to increase the width in the moving direction of the intermediate transfer belt. For this reason, productivity at the time of continuous image formation is lowered. On the other hand, by superimposing all four color refresh toner patterns at the same location, it is possible to form a four color superposition refresh toner pattern between papers without increasing the width of the intermediate transfer belt movement direction between the papers. it can. However, in the case where the refresh toner pattern is formed as a solid toner image, if the refresh toner patterns of all four colors are overlapped, the toner amount is too large and the transfer rate is lowered, and the amount of residual toner on the intermediate transfer belt 31 is increased. End up.

  For this reason, in the printer according to the present embodiment, refresh toner patterns made up of solid toner images formed between paper sheets are superposed up to a maximum of two colors. As a result, the width of the intermediate transfer belt between the papers in the moving direction is increased and the productivity during continuous image formation is suppressed, while the transfer rate is reduced and the amount of residual toner on the intermediate transfer belt 31 is increased. Can be suppressed.

  FIG. 8 is a schematic diagram illustrating an example of the shape of the refresh toner pattern. FIG. 8 shows the shape of the refresh toner pattern of each color when the three-color refresh toner patterns of Y, M, and C are formed between sheets. FIG. 8 shows the shape of the refresh toner pattern for each color that is formed between the sheets when the amount of toner discharged for refreshing the developer is larger than that of the developing devices 8M and 8C. .

  First, a Y-color refresh toner pattern is formed on the intermediate transfer belt 31. Then, an M color refresh toner pattern and a C color refresh toner pattern are formed on the Y color refresh toner pattern side by side in the intermediate transfer belt width direction orthogonal to the intermediate transfer belt surface movement direction. Thereby, it is possible to suppress an increase in the width of the intermediate transfer belt surface movement direction between sheets, and it is possible to suppress a decrease in productivity at the time of continuous image formation.

  Also, from Table 2, it is possible to overlap two colors of Y color and M color, or Y color and C color, compared to the case where C color is further formed on M color formed on Y color and three colors are superimposed. Since the transfer rate is higher when two colors are superimposed on the color, the amount of toner remaining on the intermediate transfer belt 31 can be reduced. Therefore, when the three-color refresh toner pattern is formed between the sheets, it is preferable to form each color refresh toner pattern so that the refresh toner patterns overlap up to two colors as shown in FIG.

  FIG. 9 is a schematic diagram illustrating another example of the shape of the refresh toner pattern. In FIG. 9, as in FIG. 8, the refresh toner pattern for each color formed between sheets when the amount of toner discharged for refreshing the developer is larger than that of the developing devices 8M and 8C. The shape is shown.

  Here, in order to form the refresh toner patterns of M color and C color side by side on the intermediate transfer belt 31 in the belt width direction, the intermediate transfer belt width direction (photosensitive member axis line) on the surface of the photosensitive members 2M and 2C is used. (Direction) It will be formed on one side of the center. Therefore, the drum cleaning device 3 scrapes the surface of the photoreceptor on the side where the refresh toner pattern is formed and the side where the refresh toner pattern is not formed on the surface of the photoreceptor 2M, 2C in the width direction of the intermediate transfer belt (photoreceptor axial direction). However, problems such as uneven wear may occur.

  Therefore, in FIG. 9, the M color refresh toner pattern and the C color refresh toner pattern are formed side by side in the intermediate transfer belt surface movement direction on the Y color refresh toner pattern formed on the intermediate transfer belt 31. As a result, when the refresh toner pattern is formed only on one side of the intermediate transfer belt width direction (photosensitive member axial direction) on the surface of the photosensitive members 2M and 2C, the surface of the photosensitive member is unevenly worn. It can be suppressed from occurring.

  Also in the printer according to the present embodiment, as in the printer according to the first embodiment, the absolute value of the secondary transfer bias in the belt transfer mode in the refresh mode is smaller than the absolute value of the secondary transfer bias in the paper transfer mode. Control may be performed. At that time, it is preferable to change the secondary transfer current I1 in the sheet transfer mode and the secondary transfer current I2 in the belt transfer mode according to the temperature and humidity environment as shown in Table 1 of the first embodiment. Thus, by changing the secondary transfer current I1 in the paper transfer mode and the secondary transfer current I2 in the belt transfer mode according to the temperature and humidity environment, a good transfer rate is always obtained regardless of the temperature and humidity environment. Can be obtained.

  FIG. 10 shows the result of evaluating the amount of residual toner in the refresh toner pattern composed of a halftone toner image and the refresh toner pattern composed of a solid toner image by changing the temperature and humidity environment. As for the temperature and humidity environment, the temperature and relative humidity are 10 [° C.] 15 [%] in the low temperature and low humidity environment (LL environment), 23 [° C.] 50 [%] in the normal temperature and normal humidity environment (MM environment), and the high temperature and high humidity, respectively. This is a case where the wet environment (HH environment) is 27 [° C.] 80 [%]. Further, ΔID in the figure is a difference in image density between a region where the transfer residual toner remains on the intermediate transfer belt 31 and a region where there is no transfer residual toner. Therefore, the closer the ΔID is to 0, the less the transfer residual toner on the intermediate transfer belt 31.

  As shown in FIG. 10, in any temperature and humidity environment, ΔID is smaller when the refresh toner pattern is formed with a solid toner image than when the halftone toner image is formed, and there is less residual toner on the intermediate transfer belt 31. I understand that Further, the secondary transfer current in the belt transfer mode is made smaller in absolute value than the paper transfer mode, so that the secondary transfer rate of the refresh toner pattern in the belt transfer mode can be suppressed from decreasing. As a result, ΔID becomes smaller, and the amount of residual toner on the intermediate transfer belt 31 can be further reduced. Therefore, in the refresh toner mode, the transfer residual toner input to the belt cleaning device 37 is reduced and the cleaning load is reduced, so that it is possible to suppress the occurrence of abnormal images due to poor cleaning or toner dropping. Also, by setting the secondary transfer currents I1 and I2 for the paper transfer mode and belt transfer mode (in the refresh mode) according to the temperature and humidity environment, a good secondary transfer rate is ensured regardless of the temperature and humidity environment. can do.

[Embodiment 3]
A third embodiment (hereinafter referred to as a third embodiment) of an image forming apparatus to which the present invention is applied will be described. Note that the basic configuration of the printer that is the image forming apparatus according to the third embodiment is the same as the configuration of the printer according to the first embodiment, and a description thereof will be omitted.

  FIG. 11 is a diagram showing the secondary transfer rate to the paper P and the secondary transfer belt 41. From FIG. 11, in the paper transfer mode, the secondary transfer current I1 is such that the secondary transfer rate of the two-color superimposed toner image having the larger toner amount among the one-color solid toner image and the two-color superimposed toner image is the highest. Is set. On the other hand, the secondary transfer current I2 that gives the highest secondary transfer rate during belt transfer of a single color solid toner image is different from the secondary transfer current I1 in the paper transfer mode, and the secondary transfer current I2 during belt transfer. Is smaller in absolute value than the secondary transfer current I1 in the sheet transfer mode.

  The secondary transfer rate with respect to the secondary transfer current differs between the sheet transfer mode in which the transfer is performed from the intermediate transfer belt 31 to the sheet P and the belt transfer in which the transfer is performed from the intermediate transfer belt 31 to the secondary transfer belt 41. This is because the resistance during transfer changes depending on the presence or absence of the paper P. For this reason, if the secondary transfer current I1 is set so that the secondary transfer rate in the paper transfer mode is high, the current flowing through the secondary transfer nip during belt transfer becomes excessive, and the secondary transfer current during belt transfer compared to the paper transfer mode. Next transfer rate decreases. In addition, since the secondary transfer rate curve is an area where the curve changes sharply, the secondary transfer rate fluctuates greatly with respect to changes in the use environment and changes in the deterioration state of the developer. As the secondary transfer rate fluctuates, the image density of the density control toner pattern transferred from the intermediate transfer belt 31 to the secondary transfer belt 41 varies, and image density control, which is image quality adjustment control (process control), is performed. The accuracy deteriorates and the image density fluctuation is likely to occur.

  Therefore, in this embodiment, as shown in FIG. 11, the absolute value of the secondary transfer current I2 in the belt transfer mode in the image density control is made smaller than the absolute value of the secondary transfer current I1 in the paper transfer mode. Thus, the density control toner pattern can be transferred from the intermediate transfer belt 31 to the secondary transfer belt 41 with the secondary transfer current I2 in a region where the secondary transfer rate is high and stable. Accordingly, the variation in image density of the density control toner pattern transferred onto the secondary transfer belt 41 can be suppressed, and the accuracy of the image density control executed based on the detection result of the density control toner pattern by the optical sensor 20. Can be increased. Further, as can be seen from FIG. 11, in the belt transfer mode, the secondary transfer current I2 has a higher secondary transfer rate than the secondary transfer current I1, and accordingly, the transfer residual toner on the intermediate transfer belt 31 is reduced accordingly. can do. Therefore, the transfer residual toner input to the belt cleaning device 37 is reduced, and the cleaning load is reduced. Therefore, it is possible to suppress the occurrence of abnormal images due to poor cleaning or toner drop.

  FIG. 12 is a diagram illustrating the secondary transfer rate of the toner pattern for density control in a low temperature and low humidity environment (LL environment). FIG. 13 is a diagram illustrating the secondary transfer rate of the toner pattern for density control in a normal temperature and normal humidity environment (MM environment). FIG. 14 is a diagram showing the secondary transfer rate of the toner pattern for density control in a high temperature and high humidity environment (HH environment). FIGS. 12, 13, and 14 show the results of measuring the secondary transfer rate of the toner pattern for density control while changing the experimental environment. In the experimental environment, the temperature and relative humidity are 10 [° C.] 15 [%] in a low temperature and low humidity environment (LL environment), 23 [° C.] 50 [%] in a normal temperature and normal humidity environment (MM environment), and high temperature and high humidity. This is a case where the environment (HH environment) is 27 [° C.] 80 [%]. As the toner pattern for density control of each color, a monochrome solid image is used for Y, M, and C colors, and a monochrome halftone image is used for K color. In the present embodiment, based on the image density detection result of the density control toner pattern, the setting values such as the toner density in the developer of the developing device 8, the writing condition of the optical writing unit 80, the charging bias and the developing bias are changed. Image density adjustment control is performed.

  Table 4 shows the paper transfer mode and the belt transfer mode (during image density control) in a low temperature and low humidity environment (LL environment), a normal temperature and normal humidity environment (MM environment), and a high temperature and high humidity environment (HH environment). An example of set values of the next transfer currents I1 and I2 is shown.

  In the MM environment and the HH environment, a superimposed bias obtained by superimposing a DC bias and an AC bias is applied to the secondary transfer counter roller 33 as the secondary transfer bias, and the set values of the secondary transfer currents I1 and I2 are two. This is the output value of the DC component of the next transfer bias. On the other hand, in the LL environment, the AC bias is not output as the secondary transfer bias, and only the DC bias is applied to the secondary transfer counter roller 33, and the set values of the secondary transfer currents I1 and I2 are the output values of the DC bias. is there.

  As shown in FIGS. 12, 13, and 14, the absolute value of the secondary transfer current I2 in the belt transfer mode is the absolute value of the secondary transfer current I1 in the paper transfer mode in any temperature and humidity environment. By making it smaller than this, the secondary transfer rate of the toner pattern for density control increases. In particular, the K color tends to be in an overtransfer state because the toner charge amount is lower than the other colors, and the absolute value of the secondary transfer current I2 in the belt transfer mode (at the time of image density control) is the second value in the paper transfer mode. By making it smaller than the absolute value of the next transfer current I1, the secondary transfer rate is greatly improved over other colors.

  In addition, as shown in Table 6, by setting the secondary transfer currents I1 and I2 in the paper transfer mode and the belt transfer mode (during image density control) according to each temperature and humidity environment, it is favorable regardless of the temperature and humidity environment. A secondary transfer rate can be secured. Therefore, the accuracy of image density control can be increased.

[Embodiment 4]
A fourth embodiment (hereinafter referred to as a fourth embodiment) of an image forming apparatus to which the present invention is applied will be described. Note that the basic configuration of the printer that is the image forming apparatus according to the fourth embodiment is the same as the configuration of the printer according to the first embodiment, and a description thereof will be omitted.

  Based on the detection result of the color misregistration correction toner pattern, which is a toner pattern for controlling the misregistration of each color (image quality adjustment toner pattern) by the optical sensor 20, the color misregistration that is the misregistration between the toner images of the respective colors is corrected. However, the following problems may occur. That is, the falling or rising gradient of the sensor output of the optical sensor 20 which is a reflection type optical sensor is a point where light from the edge of the color misregistration correction toner pattern occupying the entire light receiving region of the light receiving element is received. This occurs because the area ratio changes every moment. Therefore, if the secondary transfer rate varies for each color misregistration correction toner pattern and the toner adhesion amount of each color misregistration correction toner pattern is different, the amount of light received by detecting the edge portion of the color misregistration correction toner pattern is different. The gradient will also be different. For this reason, variations occur in the time until the sensor output of the optical sensor 20 reaches the threshold level, and the position of each color misregistration correction toner pattern cannot be detected accurately, resulting in color misregistration.

  Therefore, in this embodiment, the absolute value of the secondary transfer current I2 in the belt transfer mode at the time of color misregistration correction is made smaller than the absolute value of the secondary transfer current I1 in the paper transfer mode. As a result, the color misregistration correction toner pattern can be transferred from the intermediate transfer belt 31 to the secondary transfer belt 41 with the secondary transfer current I2 in a region where the secondary transfer rate is high and stable. Therefore, the variation in the toner adhesion amount of the color misregistration correction toner pattern transferred onto the secondary transfer belt 41 is reduced, and the shape reproducibility at the edge portion of the color misregistration correction toner pattern of each color is improved. Therefore, the accuracy of the sensor output timing of the color misregistration correction toner pattern is improved, and variations in sensor output can be suppressed. Therefore, the position of the color misregistration correction toner pattern can be accurately detected by the optical sensor 20, and the color misregistration of the multiple color superimposed toner image can be sufficiently reduced.

  Also in this embodiment, in the belt transfer mode at the time of color misregistration correction, the secondary transfer current I2 has a higher secondary transfer rate than the secondary transfer current I1, and accordingly, the transfer on the intermediate transfer belt 31 is accordingly performed. Residual toner can be reduced. Therefore, the transfer residual toner input to the belt cleaning device 37 is reduced, and the cleaning load is reduced. Therefore, it is possible to suppress the occurrence of abnormal images due to poor cleaning or toner drop.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
In the image forming apparatus, an image carrier such as an intermediate transfer belt 31; a toner image forming unit such as a toner image forming unit 1 that forms a toner image on the image carrier; and a surface of the image carrier. Transfer field forming means such as a secondary transfer power source 39 that forms a transfer electric field by applying a transfer bias between the transfer body such as the secondary transfer belt 41 that forms a transfer nip and the image carrier and the transfer body. A first transfer mode such as a sheet transfer mode for transferring a toner image formed on the image carrier to a recording medium such as a sheet P at the transfer nip, and the first transfer mode and transfer conditions. And a second transfer mode such as a belt transfer mode in which a toner image formed on the image carrier is transferred to the transfer body at the transfer nip.
In (Aspect A), the transfer conditions are different between the first transfer mode and the second transfer mode, so that, on the image carrier after transfer in the second transfer mode, as described in the above embodiment. The amount of transfer residual toner remaining in the toner can be reduced.
(Aspect B)
In (Aspect A), the absolute value of the transfer bias in the second transfer mode is made smaller than the absolute value of the transfer bias in the first transfer mode.
In the first transfer mode in which the toner image is transferred from the image carrier to the paper and the second transfer mode in which the toner image is transferred from the image carrier to the transfer body, depending on whether or not there is a recording medium such as paper in the transfer nip. Resistance during transfer changes. Therefore, if the transfer bias in the second transfer mode is the same as the transfer bias that increases the transfer rate in the first transfer mode, the transfer current flowing through the transfer nip becomes excessive, and the transfer rate may decrease.
In (Aspect B), since the absolute value of the transfer bias in the second transfer mode is made smaller than the absolute value of the transfer bias in the first transfer mode, the transfer current flowing through the transfer nip in the second transfer mode is excessive. Can be suppressed. Thereby, the transfer rate in the second transfer mode can be increased as compared with the case where the transfer current flowing through the transfer nip becomes excessive. Therefore, the amount of transfer residual toner remaining on the image carrier after transfer in the second transfer mode can be reduced accordingly.
(Aspect C)
In (Aspect B), the transfer bias in the second transfer mode is set to a magnitude of 70 [%] or more and less than 100 [%] with respect to the transfer bias in the first transfer mode. According to this, as described in the above embodiment, a good transfer rate can be ensured in the second transfer mode.
(Aspect D)
In (Aspect B) or (Aspect C), the transfer bias in the second transfer mode is changed according to a temperature and humidity environment. According to this, as described in the above embodiment, it is possible to ensure a good transfer rate in the second transfer mode regardless of changes in the temperature and humidity environment.
(Aspect E)
In any one of (Aspect A) to (Aspect D), the image forming apparatus includes toner image detection means such as an optical sensor 20 that detects a toner image on the transfer body, and is used for density control formed by the toner image formation means. Image density adjustment control such as image density control for detecting a toner image for image density adjustment such as a toner pattern by the toner image detecting means and adjusting the image density based on the detection result of the toner image detecting means can be executed. In addition, when the image density adjustment control is executed, the toner image for image density adjustment is transferred from the image carrier to the transfer body in the second transfer mode. According to this, as described in the above embodiment, the accuracy of the image density adjustment control can be improved.
(Aspect F)
Any one of (Aspect A) to (Aspect D) includes a toner image detection unit such as an optical sensor 20 that detects a toner image on the transfer body, and a color misregistration correction formed by the toner image formation unit. Color misregistration correction control for detecting a color misregistration correction toner image such as a toner pattern by the toner image detecting unit and correcting the color misregistration based on a detection result of the toner image detecting unit is possible. When the shift correction control is executed, the toner image for color shift correction is transferred from the image carrier to the transfer body in the second transfer mode. According to this, as described in the above embodiment, the accuracy of color misregistration correction control can be increased.
(Aspect G)
In any one of (Aspect A) to (Aspect D), when a predetermined toner forced consumption control execution condition is satisfied, the toner included in the toner image forming unit is forcibly consumed in the second transfer mode. A solid toner image is formed on the image carrier. According to this, as described in the above-described embodiment, when the toner of the toner image forming unit is forcibly consumed, the transfer to the transfer member is more than when the halftone toner image is formed on the image carrier. The transfer rate can be increased.
(Aspect H)
In (Aspect G), a plurality of the toner image forming units are provided, and the solid toner image formed on the image carrier in the second transfer mode is a toner image formed by each of the two toner image forming units. Are superimposed on the image carrier or formed by one toner image forming unit. According to this, as described in the above embodiment, it is possible to prevent the transfer rate from decreasing and the amount of residual toner on the image carrier from increasing.
(Aspect I)
(Aspect H) includes three or more toner image forming units that form toner images using toners of different colors, and in the second transfer mode, the one color The remaining two-color solid toner images smaller than the solid toner image are arranged side by side in a direction orthogonal to the image carrier surface movement direction. According to this, as described in the above embodiment, the transfer rate is reduced and the amount of residual toner on the image carrier is increased while suppressing the reduction in productivity during continuous image formation. Can be suppressed.
(Aspect J)
(Aspect H) includes three or more toner image forming units that form toner images using toners of different colors, and in the second transfer mode, the one color The remaining two-color solid toner images smaller than the solid toner image are arranged in the moving direction of the image carrier surface. According to this, as described in the above embodiment, the transfer rate is reduced and the amount of residual toner on the image carrier is increased while suppressing the reduction in productivity during continuous image formation. Can be suppressed. Further, uneven wear of the surface of the photoreceptor provided in the toner image forming unit can be suppressed.
(Aspect K)
In any one of (Aspect A) to (Aspect J), the image carrier is a belt member having elasticity. According to this, as described in the above embodiment, the transferability of the toner image to the surface uneven sheet can be improved.
(Aspect L)
In any one of (Aspect A) to (Aspect J), the image carrier is a belt member having a multilayer structure including a plurality of layers, and the plurality of layers are formed on a base layer such as a base layer 31a and the base layer. And an elastic layer such as the formed elastic layer 31b. According to this, as described in the above embodiment, it is possible to improve the transferability of the toner image with respect to the recording medium having an uneven surface shape.
(Aspect M)
In (Aspect L), particles such as a plurality of particles 31c are dispersed on the surface of the elastic layer. According to this, as described in the above embodiment, it is possible to improve the transfer efficiency by enhancing the toner releasability from the surface of the image carrier. Further, the separation property of the recording medium from the image carrier can be improved.
(Aspect N)
In (Aspect M), particles having a charging performance opposite to the normal charging polarity of the toner are used as the particles. According to this, as described in the above embodiment, the amount of reverse charge injected into the toner can be further reduced.
(Aspect O)
In any one of (Aspect A) to (Aspect N), the transfer body is a belt member that is rotatably provided by a plurality of stretching members. According to this, as described in the above embodiment, the recording medium can be carried on the transfer body and the recording medium can be conveyed to the transfer nip. Can be suppressed.

DESCRIPTION OF SYMBOLS 1 Toner image formation unit 2 Photoconductor 3 Drum cleaning apparatus 4 Cleaning brush roller 5 Cleaning blade 6 Charging apparatus 7 Charging roller 8 Developing apparatus 9 Developing roll 10 Screw member 11 Screw member 12 Developing part 13 Developer conveyance part 20 Optical sensor 30 Transfer Unit 31 Intermediate transfer belt 31a Base layer 31b Elastic layer 31c Particles 32 Drive roller 33 Secondary transfer counter roller 34 Cleaning backup roller 35 Primary transfer roller 36 Secondary transfer roller 37 Belt cleaning device 38 Sheet transport unit 39 Secondary transfer power supply 41 Secondary transfer Transfer belt 42 Separating roller 60 Cleaning blade 70 Lubricant application roller 71 Lubricant 80 Optical writing unit 90 Fixing device 91 Fixing roller 92 Pressure roller 100 Feed cassette G 100a Paper feed roller 101 Registration roller pair 400 Toner pattern for image quality adjustment

Japanese Patent No. 5533002

Claims (15)

An image carrier;
Toner image forming means for forming a toner image on the image carrier;
A transfer body that forms a transfer nip in contact with the surface of the image carrier;
A transfer electric field forming unit that forms a transfer electric field by applying a transfer bias between the image carrier and the transfer member;
A first transfer mode for transferring a toner image formed on the image carrier to a recording medium at the transfer nip;
An image forming apparatus comprising: a second transfer mode in which a toner image formed on the image carrier having different transfer conditions from the first transfer mode is transferred to the transfer body at the transfer nip. The image forming apparatus according to claim 1.
An image forming apparatus according to claim 1, wherein the transfer condition is such that an absolute value of the transfer bias in the second transfer mode is smaller than an absolute value of the transfer bias in the first transfer mode. The image forming apparatus according to claim 2.
The image forming apparatus, wherein the transfer bias in the second transfer mode is set to a magnitude of 70% or more and less than 100% with respect to the transfer bias in the first transfer mode. The image forming apparatus according to claim 2 or 3,
An image forming apparatus, wherein the transfer bias in the second transfer mode is changed according to a temperature and humidity environment. The image forming apparatus according to any one of claims 1 to 4,
A toner image detecting means for detecting a toner image on the transfer body;
Image density adjustment control for detecting an image density adjusting toner image formed by the toner image forming means by the toner image detecting means and adjusting the image density based on the detection result of the toner image detecting means can be executed. ,
An image forming apparatus, wherein the image density adjustment toner image is transferred from the image carrier to the transfer body in the second transfer mode when the image density adjustment control is executed. The image forming apparatus according to any one of claims 1 to 4,
A toner image detecting means for detecting a toner image on the transfer body;
Color misregistration correction control for detecting a color misregistration correction toner image formed by the toner image forming unit by the toner image detecting unit and correcting the color misregistration based on the detection result of the toner image detecting unit can be executed. ,
An image forming apparatus that transfers the color misregistration correction toner image from the image carrier to the transfer body in the second transfer mode when the color misregistration correction control is executed. The image forming apparatus according to any one of claims 1 to 4,
When a predetermined toner forced consumption control execution condition is satisfied, a solid toner image for forcibly consuming the toner included in the toner image forming unit is formed on the image carrier in the second transfer mode. An image forming apparatus. The image forming apparatus according to claim 7.
A plurality of toner image forming means;
The solid toner image formed on the image carrier in the second transfer mode is formed by superimposing toner images formed by the two toner image forming units on the image carrier, or one toner image. An image forming apparatus formed by a forming unit. The image forming apparatus according to claim 8.
Having three or more toner image forming means for forming toner images using toners of different colors;
In the second transfer mode, the remaining two-color solid toner images smaller than the one-color solid toner image are formed side by side in a direction orthogonal to the image carrier surface movement direction on the one-color solid toner image. Image forming apparatus. The image forming apparatus according to claim 8.
Having three or more toner image forming means for forming toner images using toners of different colors;
An image forming apparatus, wherein in the second transfer mode, the remaining two-color solid toner images smaller than the one-color solid toner image are arranged side by side in the image carrier surface movement direction on the one-color solid toner image. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the image carrier is a belt member having elasticity. The image forming apparatus according to claim 1,
The image carrier is a multilayer belt member having a plurality of layers,
The image forming apparatus, wherein the plurality of layers includes a base layer and an elastic layer formed on the base layer. The image forming apparatus according to claim 12.
An image forming apparatus, wherein a plurality of particles are dispersed on a surface of the elastic layer. The image forming apparatus according to claim 13.
An image forming apparatus comprising: a particle having a charging performance opposite to a normal charging polarity of toner. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the transfer body is a belt member rotatably provided by a plurality of stretching members.

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