JP2010060705A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of double-sided printing, which makes productivity compatible with high image quality without decreasing printing speed. <P>SOLUTION: The image forming apparatus includes: a first image carrying unit 20 in which a first image carrying belt 21 is allowed to carry a first image formed by a first image forming unit 80 (Y, C, M and K); a second image carrying unit 30 in which a second image carrying belt 31 is allowed to carry a second image formed by a second image forming unit 81 (Y, C, M and K); first and second transfer means 28 and 34 which transfer the first and the second images carried by the first and the second image carrying units to both sides of a recording medium P; a recording medium conveyance path 43A which includes conveying means 42A and 45 for supplying and conveying the recording medium to space between the first and the second transfer means; and a thermal fixing device 60 which fixes the image transferred to both sides of the recording medium. The first and the second image carrying belts 21 and 31 have an elastic layer of 50 to 500 μ, and the first and the second transfer means transfer toner having a different sign to front and back surfaces of the recording medium P simultaneously. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for transferring a toner image formed on an image carrier onto both surfaces of a recording medium such as transfer paper and fixing the transferred toner image.

  Conventionally, as a method for recording an image on both front and back sides of a transfer paper as a transfer medium, a method in which the transfer paper once passed through a fixing device is reversed and toner is transferred again to another side of the transfer paper and fixed. Has been used. However, in this method, the transfer paper is changed in the transport direction, and once the transfer paper is heated and pressurized through the fixing device, the transfer paper is curled. Have.

  As a method for solving such a problem, for example, Patent Document 1 proposes an image forming apparatus that fixes a toner image on both sides of a transfer sheet and then fixes the image at once. More specifically, after the first image formed on the image carrier is transferred to the first image carrier belt by the first transfer means, the second image carrier belt disposed opposite to the first image carrier belt. The image is transferred by the second transfer means. Next, the second image formed on the same image carrier is transferred to the first image carrier belt by the first transfer means. The second image is transferred from the first image carrier belt, and the first image is transferred from the second image carrier belt to the transfer paper, thereby printing on both sides of the transfer paper.

Japanese Patent No. 4031923

  In the image forming apparatus capable of double-sided printing described in Patent Document 1, the first and second images to be transferred onto both sides of the transfer paper are formed by a common image carrier, and the first image is temporarily set to the second image. Since it is necessary to transfer the image onto the image bearing belt, not only the productivity of printing decreases, but also the number of times of transfer of the first image increases, which causes image deterioration. This difference in the number of transfers between the first and second images appears as a difference in image quality on both sides of the transfer paper. Further, the transfer image quality is affected by the characteristics of the toner used, that is, the average circularity of the toner, the shape factor of the toner, the relationship between the volume average particle diameter Dv and the number average particle diameter Dn of the toner, etc. In order to obtain the toner, consideration must be given to the characteristics of the toner.

  An object of the present invention is to provide an image forming apparatus capable of double-sided printing that achieves both productivity and high image quality without reducing the printing speed.

  In order to achieve the above object, the image forming apparatus according to the present invention can support the first image formed by the first image forming unit using a developer on the first image bearing belt. A first image carrying unit; a second image carrying unit capable of carrying a second image formed by the second image forming unit using a developer on a second image carrying belt; The first and second transfer means for transferring the first and second images carried by the first and second image carrying units onto both sides of the recording medium, and the recording medium between the first and second transfer means. A recording medium conveyance path including conveyance means for supplying and conveying; and a heat fixing device for fixing the first and second images transferred on both sides of the recording medium, the first image carrying belt and the second image. Each of the carrying belts has an elastic layer of 50 μm to 500 μm, and the first and second transfer means Thus, toners having different signs are simultaneously transferred onto both sides of the recording medium.

  An image forming apparatus according to the present invention includes a first image carrying unit capable of carrying a first image formed by a first image forming unit using a developer on a first image carrying belt. A second image carrying unit capable of carrying a second image formed by the second image forming unit using a developer on the second image carrying belt, and first and second image carrying Transport for supplying and transporting the recording medium between the first and second transfer means for transferring the first image and the second image carried by the unit to both surfaces of the recording medium, and the first and second transfer means A recording medium conveyance path including means, and a heat fixing device for fixing the first and second images transferred on both sides of the recording medium. The first image bearing belt and the second image bearing belt are 50 μm to 500 μm. The second image formed by the second image forming unit is It is characterized in that after being carried on the image carrying belt, the polarity is changed by the polarity changing means before transferring by the second transferring means, and simultaneously transferred onto the front and back of the recording medium by the second transferring means.

  In the image forming apparatus according to the present invention, the first image carrying belt and the second image carrying belt have polyimide as a base, and an elastic layer is provided on the base.

  In the image forming apparatus according to the present invention, the polarity conversion by the polarity conversion unit is performed in a non-contact manner.

  An image forming apparatus according to the present invention includes a first image carrying unit capable of carrying a first image formed by a first image forming unit using a developer on a first image carrying belt; A second image carrying unit capable of carrying a second image formed by the second image forming unit using a developer on a second image carrying belt; and first and second image carrying units The first and second transfer means for simultaneously transferring the first image and the second image carried on the recording medium to both sides of the recording medium, and the conveyance for supplying and conveying the recording medium between the first and second transfer means A recording medium conveyance path including means, a heat fixing device for fixing the first and second images transferred on both sides of the recording medium, and the first image carrier unit or the second image fixing device according to the operation information of the device. It has a control means for controlling the operation of the image carrier unit.

  In the image forming apparatus according to the present invention, the operation information is abnormality information of the first image carrying unit and the second image forming unit, and the abnormality information is the first image carrying unit and the second image. The toner used for the forming unit has run out.

  In the image forming apparatus according to the present invention, the developer includes toner, the toner has an average circularity of 0.90 to 0.99, a toner shape factor SF-1 of 120 to 180, and a shape factor SF−. 2 is 120 to 190, and Dv / Dn is 1.05 to 1.30, where Dv is the volume average particle diameter of the toner and Dn is the number average particle diameter of the toner.

  According to the present invention, the first and second image forming units for forming the first image and the second image, and the first and second image holding belts that hold the images formed by these units on the first and second image holding belts, respectively. Since the image bearing unit and the first and second transfer means for transferring the first and second images carried on the first and second image bearing units onto both sides of the recording medium are provided, There is no need to transfer one image to another belt, and the first image and the second transfer count are equal. For this reason, it is possible to increase the productivity of printing without decreasing the printing speed and to improve the image quality of the double-sided printed matter by eliminating the cause of image deterioration.

  Further, the first image carrying belt and the second image carrying belt each have an elastic layer of 50 μm to 500 μm, and toners having different signs are simultaneously transferred to both surfaces of the recording medium in the first and second transfer means. However, the toner can be transferred at a time by changing the polarity of one of the toners, and further, a high-quality double-sided image can be obtained even on a recording medium having a rough surface due to the elastic layer acting on the irregularities of the recording medium. .

  According to the present invention, the first image bearing belt and the second image bearing belt each have an elastic layer of 50 μm to 500 μm, and the second image formed by the second image forming unit is converted into the second image. After being carried on the carrying belt, the polarity is changed by the polarity changing means before transferring by the second transferring means, and the second transferring means is simultaneously transferred to the front and back of the recording medium, so that the polarity of one toner image is different. As a result, transfer can be performed at a time, and a high-quality double-sided image can be obtained even on a recording medium having a rough surface with the belt conforming to the irregularities of the recording medium by the action of the elastic layer.

  According to the present invention, since the polarity conversion by the polarity conversion means is performed in a non-contact manner, the transferred image is not disturbed, so that a higher quality image can be obtained.

  According to the present invention, since the operation of the first image carrying unit or the second image carrying unit is controlled according to the operation information of the apparatus, the downtime can be reduced and the printing productivity can be further increased. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The image forming apparatus shown in FIG. 1 includes a first image carrier belt 21 that moves endlessly in the direction of an arrow at the top, with a recording medium conveyance path 43A disposed substantially horizontally as a boundary, inside the apparatus main body 100. The first image carrier unit 20 is provided at the lower part thereof, and the second image carrier unit 30 provided with the second image carrier belt 31 that moves endlessly in the direction of the arrow is provided respectively. Four first image forming units 80Y, 80C, 80M, and 80K are provided on the upper tension surface of the first image carrier belt 21, and four first image forming units 80Y, 80C, 80M, and 80K are provided on the inclined tension surface of the second image carrier belt 31. Second image forming units 81Y, 81C, 81M, 81K are respectively provided. Y, C, M, and K along the code numbers of the first and second image forming units correspond to the colors of the toner to be handled, Y is yellow, C is cyan, M is magenta, K Means black. Y, C have the same meaning for the photosensitive member 1 as an image carrier that is provided in the first and second image forming units and rotates together with the first image carrier belt 21 and the second image carrier belt 31. , M, K. The photoreceptors 1Y to 1K are arranged at the same interval, and at least at the time of image formation, a part of the stretched portion between the image bearing belts 21 and 31 is in contact with each other. This contacting surface is called an image receiving surface, and the mutual positional relationship is shown in FIG.

  Although the toner colors to be handled are different, the configurations of the first image forming units 80Y, 80C, 80M, and 80K are the same. Therefore, the configuration of the first image forming unit 80 will be described as a representative with reference to FIG. During the operation of the image forming apparatus, a scorotron charger (charging means) is provided around the cylindrical photosensitive member 1 rotatably supported by a drive source (not shown) so as to rotate in the direction of the arrow according to an electrostatic photographic process. (Hereinafter referred to as “charging charger”) 3, an image forming member such as an exposure device 4, a developing device 5, a cleaning device 2 and a photostatic device Q, a potential sensor S1, and an image sensor S2.

  The photoreceptor 1 is obtained by forming an organic photosensitive layer (OPC), which is a photoconductive substance, on the surface of an aluminum cylinder having a diameter of about 30 to 120 mm, for example. A photoreceptor having an amorphous silicon (a-Si) layer formed on the surface of an aluminum cylinder can also be used. A belt-like photoreceptor can also be employed. The cleaning device 2 includes a cleaning brush 2a, a cleaning blade 2b, and a recovery member 2c, and has a function of removing and recovering foreign matters such as toner remaining on the surface of the photoreceptor.

  The exposure device 4 scans light corresponding to image data for each color on the surface of each photoconductor 1 that has been uniformly charged by the charging charger 3 to form an electrostatic latent image. The exposure apparatus 4 in the illustrated example is an exposure apparatus that includes an LED (light emitting diode) array and an imaging element as light emitting elements, but uses a laser light source, a polygon mirror, etc., and beam light modulated according to image data to be formed. It is also possible to employ a laser scanning type exposure apparatus based on the above. As the charging means, in addition to the charging charger 3, a type that is brought into contact with the surface of the photoreceptor 1, for example, a charging roller can be adopted.

  The development in this embodiment is a development system that employs a two-component developer composed of toner and carrier. The electrostatic latent image for each color formed on the surface of each photosensitive member 1 by a laser beam with respect to the negatively charged photosensitive member 1 is developed with toner of a predetermined color having the same polarity (negative polarity) as the charged polarity of the photosensitive member. And become a visible image. So-called reversal development is performed.

  When each color toner of yellow (Y), cyan (C), magenta (M), and black (K) is consumed by the developing device 5 that handles each color, the magnetic toner detection means 5e provided in the developing device 5 Detected and supplied to each developing device 5 from a toner cartridge 86 provided in the toner cartridge housing portion 85 mounted on the apparatus main body 100 shown in FIG.

  As this supply means, a system using a known MONO pump can be adopted. According to this method, there are few restrictions on the installation locations of the toner cartridges 86 for the respective colors, which is advantageous for space allocation inside the apparatus main body. Further, since toner can be replenished in a timely manner, it is not necessary to provide a large toner storage space in each developing device 5, and the developing device 5 can be downsized.

  The developing device 5 includes a screw 5c and a screw 5d for stirring and conveying the toner and the carrier. When the developing device 5 is mounted on the apparatus main body 100, one end of the toner replenishing means is connected to a part of the screw 5d. The toner is supplied to the developing roller 5a rotating in the direction of the arrow by the screw 5c, but the thickness on the surface of the developing roller 5a is regulated to a predetermined thickness by the blade 5b. The developing roller 5a is a cylinder made of stainless steel or aluminum, and is supported by the frame of the developing device 5 so as to be rotatable and a distance from the photosensitive member 1 is properly secured, and a predetermined line of magnetic force is formed inside. A magnet is provided.

  In this embodiment, the toner used has an average circularity of 0.90 to 0.99, a shape factor SF-1 of 120 to 180, a shape factor SF-2 of 120 to 190, and a volume average particle diameter Dv / number average. The particle diameter Dn is 1.05 to 1.3 μm. The carrier has a volume average particle size of about 25 to 60 μm. The basis for these numbers will be described later.

  As for the second image forming units 81Y to 81K used in the second image carrier unit 30, the second image forming unit 81 will be described as a representative with reference to FIG. The second image forming unit 81 shown in FIG. 5 has the same constituent members as the first image forming unit 80, but the rotational direction of the photoreceptor 1 is different from that of FIG. However, they are mutually shaped with respect to the y-axis passing through the rotation axis 1a of the photosensitive member 1 indicated by an arrow in the drawing. This shape is an important matter although it is related to the arrangement of image forming members provided around the photoreceptor 1. In other words, the first image forming units 80Y to 80K can be combined with a coupling unit with the image forming apparatus, for example, a coupling unit with a driving unit, an electrical connection unit, a toner supply unit, and a toner discharge unit. The second image forming units 81Y to 81K can be compatible. Therefore, it is not necessary to separately manufacture the developing device, the cleaning device, and the parts for the first image forming unit 80 and the second image forming unit 81, and the efficiency in manufacturing parts and managing parts is high. Reduction is achieved.

  As a first condition that can be used in the first image carrier unit 20 and the second image carrier unit 30 in the form of an axis object with the first and second image forming units 80 and 81 as the center of the y axis, photosensitive is used. The peripheral surface on which the member for image formation is not provided around the body 1 is secured, that is, a wide range where the image bearing belt can contact is secured. The second condition is that the arrangement angle of the first image carrier belt 21 and the second image carrier belt 31 is appropriate.

  The above first condition and second condition will be described with reference to FIGS. 4 and 5, the image carrier belt 21 or the image carrier belt 31 can be installed between the arrows A1 and A2. That is, the A1 side indicates that the developing device 5 can be installed, and the A2 side indicates that the image bearing belt can be installed in a range where the image bearing belt does not contact the cleaning device 2. The inclusion of the second image carrier belt 31 in FIG. 4 shows an image carrier belt on which the target image forming unit can be arranged with respect to the y axis including the rotation shaft 1 a of the photoreceptor 1.

  If the image forming unit 80 is turned upside down with respect to an axis orthogonal to the y-axis and used as the image forming unit 81, there is an influence of earth gravity. At least in the developing device 5, the toner is agitated and the developing roller 5a is moved. The toner replenishment conditions are different and must be optimized, and it is impossible to share parts.

  As shown in FIG. 2, as the positional relationship between the image receiving surface 210 of the first image bearing belt 21 and the image receiving surface 310 of the second image bearing belt 31, the angle α exceeds 180 degrees and is 270 degrees, preferably 210 degrees. As the image forming unit 80, the first image carrier belt 21 may have the form shown in FIG. 4 and the second image carrier belt 31 may have the form shown in FIG. In other words, as described above, it is possible to avoid an image forming unit that makes it impossible to share parts.

  In this embodiment, as shown in FIG. 2, since the recording medium conveyance path 43A can be secured almost horizontally and linearly above the second image forming unit 81, the conveyance / reliability of the paper P as the recording medium can be secured. And the unity of the entire image forming apparatus is good.

  In particular, since the first image carrying belt 21 is stretched in the horizontal direction and is flattened, and the second image carrying belt 31 is stretched in the vertical direction to be long and inclined, the recording medium conveyance path 43A is used as a boundary. The space in the height direction of the second image carrier belt 31 increases below, but as shown in FIG. 1, the sheet feeders 40 a to 40 d having the same height as that occupied by the second image carrier belt 31. Can be installed side by side. Thus, a paper feeding device capable of storing a large amount of paper P can be installed, and the paper feeding surface on the upper surface of the paper feeding device 40a and the recording medium conveyance path 43A can be made substantially the same height. Sex can be secured.

  As described above, in the present embodiment, the image forming unit 80 and the image forming unit 81 can realize the arrangement of the components necessary for image formation around the photoreceptor 1 and the arrangement of the image bearing belt, that is, the second condition. It has a lot in common and is very advantageous in terms of manufacturing.

  A first image carrying belt 21 supported by a plurality of rollers 23, 24, 25, 26 (two), 27, 28, and 29 shown in FIG. It is provided below the photoconductors 1Y, 1C, 1M, and 1K at 80K. The image bearing belt 21 is endless, and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. Further, on the inner peripheral portion of the first image carrying belt 21, a primary transfer roller 22 constituting a primary transfer portion is provided so as to face the photoreceptors 1Y, 1C, 1M, and 1K, respectively.

  A cleaning device 20 </ b> A is provided on the outer periphery of the first image carrying belt 21 at a position facing the roller 23. The cleaning device 20 </ b> A wipes off unnecessary toner remaining on the surface of the first image carrying belt 21 and foreign matters such as paper dust. The members related to the image carrier belt 21 are integrally configured as the first image carrier unit 20 and can be attached to and detached from the apparatus main body 100.

  The second image carrier belt 31 that is supported by a plurality of rollers 33, 34, 35, 36 (two), 37, 38 and travels in the direction of the arrow is a photosensitive member 1Y in the second image forming units 81Y to 81K. It is provided to face 1C, 1M, and 1K. The image carrying belt 31 is endless and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. A primary transfer roller 32 constituting a primary transfer portion is provided on the inner peripheral portion of the image carrying belt 31 so as to face the photoreceptors 1Y, 1C, 1M, and 1K.

A cleaning device 30 </ b> A is provided on the outer periphery of the second image bearing belt 31 at a position facing the roller 33. The cleaning device 30 </ b> A wipes away unnecessary toner remaining on the surface of the image bearing belt 31 and foreign matters such as paper dust. Members related to the image carrier belt 31 are integrally formed as the second image carrier unit 30 and can be attached to and detached from the apparatus main body 100.
(Image carrier belt configuration and materials)
As shown in FIG. 3, the first and second image bearing belts 21 and 31 are formed on resin substrates having a thickness of 50 to 100 μm, for example, substrates 21a and 31a made of polyimide, and substrates 21a and 31a. A belt provided with rubber elastic layers 21b and 31b as an elastic layer of 50 to 500 μm, and a toner image to be a first image and a second image carried by each photoconductor 1 is transferred to a primary transfer roller 22, 32 has a resistance value that enables electrostatic transfer to the belt surface by a bias applied to the belt 32. The volume resistance value is a resistance adjusted to about 10 ⁶ to 10 ¹² Ωcm.

  In this embodiment, since color images are formed by superimposing toner images of Y, M, C, and K, the expansion and contraction of each image carrier belt affects the color misregistration of the image, the image expansion, and the like. Become. Accordingly, the inventor of the present application has selected and adopted polyimide, which is a material having excellent mechanical strength, and has particularly low expansion and contraction, as the material for the bases 21a and 31a of each image carrier belt.

  The reason for providing the rubber elastic layers 21b and 31b on the bases 21a and 31a is to improve the paper type compatibility characteristic, and in particular to improve the image quality for the paper P having poor surface properties. In general, the concave portion of the paper P is inferior in transfer because there is no contact between the toner (belt) and the paper P. By providing such rubber elastic layers 21b and 31b, the image bearing belts 21 and 31 become uneven on the paper P. Therefore, the image can be transferred even in the concave portion, and high image quality can be achieved.

The rubber elastic layers 21b and 31b include elastic rubber, elastomers such as butyl rubber, fluorine rubber, acrylic rubber, EPDM, NBR, acrylonitrile-butadiene-styrene rubber natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, Ethylene-propylene rubber, ethylene-propylene terpolymer, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, urethane rubber, syndiotactic 1,2-polybutadiene, epichlorohydrin rubber, ricone rubber, fluorine rubber, polysulfide rubber , Polynorbornene rubber, hydrogenated nitrile rubber, thermoplastic elastomer (eg polystyrene, polyolefin, polyvinyl chloride, polyurethane, polyamide, polyurea, polyester, fluorine It is possible to use one kind or two kinds or more selected from the group consisting of fat-based) or the like. However, it is a matter of course that the thickness of the rubber elastic layers 21b and 31b depends on the hardness of the elastic layer, but if it is too thick, the surface will expand and contract and the surface layer will crack. It becomes easy to do. Further, since the amount of expansion / contraction increases, it is not preferable that the image is too thick (approximately 500 μm or more) due to the expansion / contraction of the image. If it is too thin (approximately 50 μm or less), the effect as an elastic belt cannot be obtained.

  The appropriate range of the hardness of the rubber elastic layers 21b and 31b is 10 ≦ HS ≦ 60 ° (JIS-A) because the optimum hardness differs depending on the belt layer thickness. Those having a hardness of less than 10 ° JIS-A are very difficult to mold with high dimensional accuracy. This is due to the fact that it is susceptible to shrinkage and expansion during molding. When softening, it is a general method to contain an oil component in the base material, but it has a drawback that it is oozed out when continuously operated in a pressurized state. As a result, it has been found that each photosensitive member in contact with the surfaces of the first and second image bearing belts 21 and 31 serving as an intermediate transfer member is contaminated to cause horizontal band unevenness. On the other hand, those having a hardness of 60 ° JIS-A or higher can be molded with high accuracy and the amount of oil that does not contain or contain oil can be reduced. However, the effect of the elastic body cannot be obtained.

There are no particular restrictions on the conductive agent for adjusting the resistance value. For example, carbon black, graphite, metal powder such as aluminum or nickel, tin oxide, titanium oxide, antimony oxide, indium oxide, potassium titanate, antimony oxide-tin oxide composite Examples thereof include conductive metal oxides such as oxide (ATO) and indium oxide-tin oxide composite oxide (ITO). The conductive metal oxide may be coated with insulating fine particles such as barium sulfate, magnesium silicate, and calcium carbonate. Of course, the conductive agent is not limited thereto. Belt detent ribs for stabilizing the running of the belt are provided on one side or both ends of the belt.
(Regarding the configuration of the primary transfer roller)
As one embodiment, the primary transfer rollers 22 and 32 are obtained by coating the surface of a metal roller serving as a core metal with a conductive rubber material, and applying a primary transfer bias to a core metal portion from a power source (not shown). Is done. In the conductive rubber material, carbon is dispersed in urethane rubber, and the resistance is adjusted to a volume resistance of about 10 ⁵ Ωcm.

  In this embodiment, monochrome printing with black (K) toner alone is also possible. In such a case, there are photosensitive members that are not used. That is, not only the unused photoreceptors 1Y, 1C, 1M or the developing device 5 are operated, but also a mechanism for keeping these unused photoreceptors and the image bearing belt 21 or the image bearing belt 31 in a non-contact state. In this embodiment, an internal frame (not shown) that supports the roller 26 and the primary transfer roller 22 is provided, is supported so as to be rotatable around a certain point, and moves away from the photoreceptors 1Y, 1C, and 1M. By rotating in the direction, only the photosensitive member 1K comes into contact with the image bearing belt 21 or the image bearing belt 31 and the image forming process is executed, so that a monochrome image with black toner can be created. Thus, avoiding contact between the photoconductor and the image bearing belts 21 and 31 when not in use is advantageous in terms of improving the life of the photoconductor.

A first secondary transfer roller 28 serving as a secondary transfer portion is disposed on the inner periphery of the first image carrying belt 21. The secondary transfer roller 28 is made of a metal roller serving as a core metal and is coated with conductive rubber, and a secondary transfer bias is applied to the core metal part from a power source (not shown). Carbon is dispersed in the conductive rubber, and the volume resistance is adjusted to about 10 ⁷ Ωcm. In the present embodiment, the first transfer roller 28 is applied with a secondary transfer bias while passing the paper P between the first image carrier belt 21 and the second image carrier belt 31, so that the first A toner image to be a first image carried by the image carrying belt 21 is transferred onto the surface of the paper P.

  A second secondary transfer roller 34 serving as a secondary transfer portion is disposed on the inner periphery of the second image carrying belt 31. A metal roller is used as the second secondary transfer roller 34, and the sheet P is passed between the first image carrying belt 21 and the second image carrying belt 31, while the first secondary transfer roller 28. A toner image to be a second image carried by the second image carrying belt 31 is transferred to the back surface of the paper P by applying a bias.

  The toner used in this embodiment has a negative polarity. By applying a negative transfer bias to the first secondary transfer roller 28, the toner on the first image carrying belt 21 is repulsively transferred to the paper P. Is done. At this time, the toner on the second image carrying belt 31 is formed by the second image forming unit (81Y, C, M, K) and carried on the second image carrying belt 31, and then the secondary transfer roller. The polarity is converted from the minus pole to the plus pole by the polarity converting means 47 constituted by the transfer charger arranged before 34. Therefore, the toner on the second image bearing belt 31 is sucked and transferred to the paper P by the bias of the first secondary transfer roller 28. By using positive polarity toner in the second image forming unit (81Y, C, M, K) from the beginning, the toner image is transferred onto both sides of the paper P without using the polarity conversion means 47. Also good.

  The polarity conversion by the polarity conversion means 47 is carried out after the second image formed by the second image forming unit (81Y, C, M, K) is carried on the second image carrying bell 31 and then the polarity conversion means 47. This is achieved by applying positive ions to the surface. That is, in this embodiment, the polarity conversion by the polarity conversion means 47 is performed in a non-contact state with respect to the second image carrier belt 31.

  On the right side of the apparatus body 100. A paper feeding device 40 that accommodates the paper P is provided. The paper feeding device 40 includes a paper feeding device (tray) 40a storing a large amount of paper P in a plurality of stages, for example, an upper stage, and three lower paper feeding cassettes 40b, 40c, and 40d below the paper surface on the right side ( It is arranged on the operation surface side so that it can be pulled out. Among the sheets P stored in the sheet feed tray 40a and the sheet cassettes 40b, 40c, and 40d, the uppermost sheet P is selectively fed and separated by the corresponding sheet feeding / separating means 41A to 41D. Thus, only one sheet is reliably sent to the recording medium conveyance path 43B and the recording medium conveyance path 43A by the plurality of conveyance roller pairs 42B.

  In the recording medium conveyance path 43A, the secondary transfer rollers 28 and 34 take a feeding timing for feeding the paper P to the secondary transfer position disposed opposite to each other via the image bearing belts 21 and 31, and therefore, a pair of A registration roller 45 is provided. In the recording medium conveyance path 43B, a jogger 44 for setting the position perpendicular to the conveyance direction of the paper P to a normal position is provided. The jogger 44 includes a guide member that moves from both sides toward the edge of the paper P in the conveyance direction of the paper P, and the guide presses the paper P for a moment from both sides of the paper P that is running. Align with the position of. The sheet P is conveyed from the registration roller pair 45 toward the secondary transfer position.

A sheet P can be supplied to a recording medium conveyance path 43 </ b> C having a conveyance roller pair 42 </ b> C provided in the sheet feeding device 40 from another sheet feeding device 300 that can be installed upstream in the conveyance direction. The upper sheet feed surface of the sheet feed tray 40a is arranged so that the uppermost sheet P of the sheet feed tray 40a is fed and then conveyed straight without being bent. Therefore, even thick paper and highly rigid paperboard can be reliably fed. In addition, it is convenient to adopt an air paper feed comprising a vacuum mechanism so that the paper feed tray 40a can reliably feed paper P having various characteristics. Although not shown in the drawing, sensors for detecting the paper P are arranged at important points of the recording medium conveyance path 43A and the recording medium conveyance path 43C, and serve as triggers for various signals based on the presence of the paper P. . An original reading device 200 is provided above the paper feeding device 40. On the extension of the recording medium conveyance path 43A, on the downstream side of the secondary transfer portion by the secondary transfer rollers 28 and 34 in the paper conveyance direction, A fixing device 60 and a recording medium transfer means 50 are provided. The recording medium transport means 50 is for transporting the paper P that has passed through the secondary transfer portion while maintaining a flat state to the fixing nip in the fixing device 60. The recording medium transfer means 50 is supported by a plurality of rollers 52, 53, 54, 55, 56 and is disposed endlessly moving in the direction of the arrow, and is disposed outside the conveyance belt 51 so as to face the roller 55. A cleaning device 50 </ b> A, a suction charger 57 for sucking the paper P so as to face the roller 56, and a static elimination / separation charger 58 facing the roller 57 are provided. The traveling speed of the conveyance belt 51 is matched with the traveling speed of the paper P in the fixing device 60.

  The fixing device 60 fixes the toner image secondarily transferred to the paper P by the secondary transfer unit to the paper P by heat and pressure. The fixing device 60 includes a roller type having a roller member provided with a heater inside which constitutes a fixing nip arranged opposite to each other, a belt fixing device for running a belt heated by heating means, and a heating method. A fixing device using induction heating can be used as appropriate. In order to make the hue and glossiness of the images on both sides of the paper the same, the material, hardness, surface property, etc. of the fixing roller and the fixing belt that are in contact with both sides of the paper P are the same up and down. Further, the fixing device 60 controls the fixing conditions based on full-color and monochrome images, or single-sided or double-sided, and is controlled by the control unit 95 so that the optimal fixing conditions are obtained according to the type of the paper P.

  A cooling roller pair 70 serving as a cooling unit having a cooling function is provided on the downstream side of the fixing device 60 in the paper conveyance direction to cool the paper P after the fixing and stabilize the unstable toner state at an early stage. Is arranged. As the roller member constituting the cooling roller pair 70, a heat pipe structure roller having a heat radiating portion can be adopted. The paper P cooled by the cooling roller pair 70 is discharged and stacked by a paper discharge roller pair 71 on a paper discharge stack portion 75 provided on the left side of the apparatus main body 100. The discharge stacking unit 75 employs a mechanism in which a receiving member moves up and down according to a stack level by an elevator mechanism (not shown) so that a large amount of sheets can be stacked. It is also possible to pass the paper P after fixing through the paper discharge stack unit 75 toward another post-processing apparatus. Another post-processing apparatus is an apparatus for bookbinding such as punching, cutting, folding, and binding.

  The toner cartridges 86Y, 86C, 86M, and 86K for each color in which unused toner is stored are stored in a storage space 85 formed in the upper portion of the apparatus main body 100 in a detachable manner. The toner cartridges 86Y, 86C, 86M, and 86K are configured to supply toner to each developing device as required by a toner transport unit (not shown). In the configuration of this embodiment, the toner cartridge is common to the upper and lower image forming units 80 and 81, but may be separated. The toner cartridge 86K for black toner, which is highly consumed, can be set to have a particularly large capacity. The storage space 85 protrudes upward from the planar upper surface of the apparatus main body 100 and is disposed on the back side when viewed from the operation direction. For this reason, since a plane portion is secured on the near side of the upper surface of the apparatus main body 100, it can be used as a work table.

  The operation provided on the upper surface of the apparatus main body 100 and the display unit 90 are provided with a keyboard (not shown) and the like, and conditions for image formation can be input, and the state of the apparatus is displayed on the display unit. Exchange of information with the image forming apparatus is facilitated.

  The waste toner storage portion 87 provided inside the apparatus main body 100 is connected to the cleaning device 2 of the image forming units 80 and 81, the cleaning devices 20A and 30A of the image bearing belts, and the cleaning device 50A of the conveyance belt 51 through a collection path (not shown). It is connected and configured to collect and store foreign matters such as waste toner and paper dust all at once. In the present embodiment, since the large waste toner storage portion 87 is provided, it is not necessary to provide the cleaning device (2, 20A, 20B, 50A) with a large capacity waste toner storage portion, and each cleaning device can be reduced in size. The operability of waste toner disposal is also good. A full sensor (not shown) is used to issue a warning such as toner disposal in the waste toner storage unit 87 or container replacement. A control device 95 is provided inside the apparatus main body 100. The control device 95 is composed of a well-known computer, and controls the operation of each drive source, unit, etc. inside the apparatus main body 100. Reference numeral 96 denotes a power supply device connected to an external power supply.

  The apparatus main body 100 is provided with a fan 98 as a countermeasure against the high temperature inside the apparatus main body due to heat from the fixing device 60 and heat generated from the electrical device. The function of the fan 98 prevents deterioration of the function due to the heat of the internal member. The fan 98 is also coupled to the heat radiating portion of the cooling roller pair 70 to ensure the cooling effect of the cooling roller pair 70. The apparatus main body 100 achieves simultaneous double-sided printing by the first image forming unit 80 and the second image forming unit 81, but troubles such as failure of one of the units and running out of toner occur. In such a case, the control means 95 detects the state and uses the normal unit, so that it is not necessary to rest the apparatus and single-sided printing is possible.

That is, in this embodiment, the control means 95 has a function of controlling the operation of the first image carrier unit 80 or the second image carrier unit 90 in accordance with the operation information of the apparatus. The operation information of the apparatus referred to here is abnormality information of the first image carrying unit 80 and the second image forming unit 81, and the abnormality information is the first image carrying unit and the second image forming unit. The toner used in is out of toner or in a failure state. Toner out is provided with a sensor (not shown) in the toner cartridge 86, and the control means 95 determines that the signal is output to the control means 95 or is detected by the toner detection means 5e. If it is determined that the toner has run out, the image forming operation is executed on the unused unit side. For a failure of one unit, a failure diagnosis sensor (not shown) is provided in each unit, the control unit 95 executes failure determination from the output signal of the sensor, and an unused unit to use a unit that does not output a failure signal. Causes the image forming operation to be executed.
(Single-sided recording operation)
An operation during single-sided recording in which a full-color image is formed on one side of the paper P in the above configuration will be described. There are basically two types of single-sided recording methods that can be selected. One of the two methods is a method of directly transferring an image carried on the first image carrying belt 21 onto one side of the paper P, and the other method is carried on the second image carrying belt 31. In this method, the image is directly transferred to one side of the paper P. In the present embodiment, due to the configuration of the apparatus main body 100, when the image carried on the first image carrying belt 21 is directly transferred to one side of the paper P, the image is placed on the upper surface of the paper P and the second image carrying is carried. When the image carried on the belt 31 is directly transferred to one side of the paper P, the image is formed on the lower surface of the paper P. In the case where the data to be recorded is a plurality of pages, it is convenient to control the image forming order so that the pages are aligned on the paper discharge stack unit 75. An explanation will be given of a method in which an image is carried on the first image carrying belt 21 and then transferred onto the paper P so that the image order is recorded in order from the image data of the last page.

  When the image forming apparatus is operated, the photoreceptors 1Y, 1C, 1M, and 1K in the first image carrying belt 21 and the first image forming units 80Y to 80K rotate. At the same time, the second image carrier belt 31 rotates. However, the photoreceptors 1Y, 1C, 1M, and 1K in the second image forming units 81Y to 81K are separated from the second image carrier belt 31 and are not rotated. Is done. First, image formation by the image forming unit 80Y is started. By the operation of the exposure device 4 composed of an LED (light emitting diode) array and an imaging element, light corresponding to image data for yellow emitted from the LED is irradiated onto the surface of the photoreceptor 1Y uniformly charged by the charging charger 3. Thus, an electrostatic latent image is formed.

  This electrostatic latent image is developed with yellow toner by the developing roller 5a to become a visible image, and is electrostatically applied on the first image carrying belt 21 that moves in synchronization with the photoreceptor 1Y by the transfer action of the primary transfer roller 22. Primary transfer. Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner on the photosensitive members 1C, 1M, and 1K.

  As a result, yellow, cyan, magenta, and black color toner images are carried on the first image carrying belt 21 as sequentially overlapping full-color toner images, and move together with the first image carrying belt 21 in the direction of the arrow. Is done.

  At the same time, the paper P used for recording is fed out from the paper feed tray 40a or the paper feed cassettes 40b to 40d in the paper feed device 40 by one of the paper feed / separation means 41A to 41D for feeding the paper P. The pair 42B and 42C are conveyed to the recording medium conveyance path 43C. Before the leading edge of the paper P is not picked up by the registration roller pair 45, the jogger 44 operates to push both sides of the paper P from both the upstream and downstream sides with respect to the conveyance direction of the paper P. Horizontal alignment is achieved. At this time, the registration roller pair 45 is stationary, and the leading edge of the paper P is stationary while entering the nip of the registration roller pair 45, but the position of the image on the first image carrier belt 21 is normal. Thus, the registration roller pair 45 is rotated at a timing to convey the paper P to the secondary transfer portion (secondary transfer region).

  The full-color toner image on the first image carrying belt 21 is transferred to the upper surface of the paper P conveyed in synchronization with the first image carrying belt 21 by receiving a transfer action by the secondary transfer roller 28. The secondary transfer bias applied to the secondary transfer roller 28 has a negative polarity that is the same polarity as the charging polarity of the toner.

  Thereafter, the surface of the first image carrying belt 21 is cleaned by the belt cleaning device 20A. Further, foreign matters such as toner remaining on the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K in the first image forming units 80Y to 80K that have finished the primary transfer are removed by the cleaning brush 2a and the cleaning blade 2b of the cleaning device 2. It is removed from the surface of each photoconductor. The surface of each photoconductor is subjected to a discharging operation of residual potential by the discharging device Q to prepare for the next image formation / transfer process. The removed foreign matter such as toner is sent to the collecting unit 87 by the collecting unit 2c. Sensors S1 and S2 detect whether the surface potential after exposure on the surface of the photoconductor and the concentration of toner attached to the surface of the photoconductor after the development process are appropriate, and appropriately set image forming conditions. Information is output to the control means 95 for control.

  The paper P onto which the toner image that has been superposed and carried on the image carrying belt 21 is transferred is transferred toward the fixing device 60 by the carrying belt 51 of the carrying device 50. The surface of the transfer belt 51 is charged in advance by an adsorption charger 57 for the paper P so that the paper P can be reliably transferred together with the transport belt 51. The neutralization / separation charger 58 operates to neutralize the paper so that the paper P is separated from the transport belt 51 and is reliably sent to the fixing device 60.

  When the toners of the respective colors superimposed on the paper P reach the fixing device 60, they are subjected to a fixing action by heat, and are melted and mixed to completely form a color image. Since toner is contained only on one side (upper surface) of the paper, less heat energy is required for fixing compared to double-sided recording with toner on both sides. Further, the control means 95 optimally controls the power used by the fixing device 60 according to the image. Until the fixed toner is completely fixed on the paper, it is rubbed with a guide member or the like during conveyance, and an image is lost or distorted. In order to prevent this problem, the cooling roller pair 70 as a cooling unit is operated to cool the toner and the paper P. Thereafter, the paper is discharged by the paper discharge roller 71 onto the paper discharge stack 75 with the image surface facing upward. In the paper discharge stack 75, the image forming order is programmed so that the recorded matter of young pages is stacked so as to be sequentially stacked on top of each other. Since the paper discharge stack section 75 is configured to descend as the number of paper P to be discharged increases, the paper P can be stacked in an orderly and reliable manner, and the page order is not disturbed. Instead of directly stacking the recorded paper P on the paper discharge stack section 75, it is possible to carry out a punching process or to transport it to a post-processing device such as a sorter, a collator, a binding device or a folding device.

  In another method of forming an image on one side of the paper P, image formation is performed in order from the image data of young pages in order not to form images in the first image forming units 80Y to 80K. However, since it is basically the same as the one-side recording process described above, details are omitted.

In this embodiment, if any one of the first image forming units 80Y to 80K fails or the toner runs out during the image formation by the method carried on the first image carrying belt 21, the control means 95 controls the second image forming units 81 </ b> Y to 81 </ b> 81 so as to switch to the method of supporting the second image bearing belt 31. Therefore, it is not necessary to stop the image forming operation for maintenance work or toner replacement, so that continuous image recording is possible, downtime can be reduced, and printing productivity can be increased.
(Operation during double-sided recording)
Next, the operation during double-sided recording in which images are formed on both sides of the paper P will be described. When a start signal is input to the image forming apparatus, a toner image for each color sequentially formed by the first image forming units 80Y, 80C, 80M, and 80K described in the single-sided recording operation is transferred to the first image carrier. The toner images for the respective colors sequentially formed by the second image forming units 81Y, 81C, 81M, 81K are substantially in parallel with the step of sequentially transferring the images to the belt 21 and carrying them as the first images. A step of carrying out primary transfer sequentially onto the support belt 31 and supporting it as a second image is performed. Then, in order for the first image and the second image to coincide with each other at the leading end in the transport direction of the paper P, the formation of the second image is started after the start of the formation of the first image. Further, since the sheet P is stopped and retransmitted by the registration roller pair 45, the sheet P is fed in consideration of the time and aligned by the jogger 44. The registration roller pair 45 conveys the paper P to the secondary transfer unit at a timing. Here, a transfer bias having a negative polarity is applied to the transfer roller 28, and the full color previously carried on the one side (upper surface in the drawing) of the paper P from the first image carrying belt 21 and on the second image carrying belt 31. The second image is converted into a positive polarity by the polarity conversion device 47 and transferred to one side (lower surface) of the paper P at a time.

  The paper P on which the full color toner images are transferred on both sides in this way is transported to the fixing device 60 by the transport belt 51. The sheet is separated from the conveying belt 51 by an AC bias applied to the charge eliminating / separating charger 58 and transferred to the fixing device 60. The paper P on which the full color toner images are transferred on both sides is subjected to fixing processing by heat of the fixing device 60, and the toner images on both sides of the paper are melted, mixed and fixed. The sheet P is subsequently cooled by passing through the cooling roller pair 70 and is discharged onto the discharge stack unit 75 by the discharge roller 71.

  When double-sided recording is performed on a plurality of pages of paper P, when the image forming order is controlled so that the image of a young page becomes the bottom surface and is stacked on the paper discharge stack section 75, the top and bottom surfaces are reversed. The recorded material is one page in order from the top, two pages on the back, three pages on the second sheet, four pages on the back, and the page order is aligned. Such control of the image forming order and control such as increasing the power input to the fixing device 60 from that during single-sided recording are executed by the control means 95.

  In this embodiment, an example in which full-color recording is executed regarding single-sided recording and double-sided recording operations has been described, but monochrome recording using only black toner is also possible.

  Thus, according to the present embodiment, the first and second image bearing units 20 and 30 that carry the first image and the second image on the first and second image bearing belts 21 and 31, respectively, Since the first and second transfer means 28 and 34 for transferring the first and second images carried on the first and second image carrying units 20 and 30 onto both sides of the paper P are provided, There is no need to transfer the first image to another belt, and the first image and the second transfer count are equal. For this reason, the reduction in printing speed is eliminated and the productivity of printing can be improved, and the cause of image deterioration is eliminated, so that it is possible to improve the image quality of the double-sided printed matter.

  The first image carrying belt 21 and the second image carrying belt 31 have elastic layers 21b and 31b of 50 μm to 500 μm, respectively, and toners having different signs are simultaneously applied to the first and second transfer units 28 and 32. Since the transfer is performed on both sides of the paper P, the transfer can be performed at one time because the polarity of one of the toners is different. Further, the elastic layers 21b and 31b cause the belts to become familiar with the irregularities of the paper P, resulting in rough surfaces. A high-quality double-sided image can be performed on the paper P as well.

  According to this embodiment, the first image carrier belt 21 and the second image carrier belt 31 have the elastic layers 21b and 31b of 50 μm to 500 μm, respectively, and the second image formed by the second image forming unit is displayed. After being carried on the second image carrying belt 31, the polarity is converted by the polarity converting means 47 before the transfer by the second transfer means 32, and the simultaneous toner images are transferred onto the front and back of the paper in the second transfer means 32. As a result, the toner image can be transferred at one time because the polarity of one of the toner images is different. Further, the belts are adapted to the irregularities of the recording medium by the action of the elastic layers 21b and 31b, and the paper P is rough. High-quality double-sided images can be created.

  According to this embodiment, since the polarity conversion by the polarity conversion means 47 is performed in a non-contact manner, the transferred image is not disturbed, so that a higher quality double-sided image can be obtained.

Next, the characteristics of the toner will be described.
(Toner circularity and circularity distribution)
In this embodiment, the circularity of the toner is one of parameters representing the shape of the toner. It is important for the toner in this embodiment to have a specific shape and distribution of the shape. With an irregularly shaped toner having an average circularity of less than 0.90 and far from a spherical shape, satisfactory transferability and High-quality images without dust cannot be obtained. As a method for measuring the shape, an optical detection band method is suitable in which a suspension containing particles is passed through an imaging unit detection band on a flat plate, and a particle image is optically detected and analyzed by a CCD camera. Toner having an average circularity of 0.90 to 0.99, which is a value obtained by dividing the perimeter of an equivalent circle having the same projected area obtained by this method by the perimeter of the actual particle, has high reproducibility with an appropriate density reproducibility. It was found to be effective in forming a clear image. More preferably, the particles having an average circularity of 0.93 to 0.97 and a circularity of less than 0.94 are 10% or less. Further, when the average circularity exceeds 0.99, in a system employing blade cleaning or the like, poor cleaning occurs on the photosensitive member 1 and each of the image bearing belts 21 and 31 and stains on the image. It becomes a cause. For example, when outputting an image with a low image area ratio, there is little transfer residual toner and cleaning defects do not become a problem. However, when outputting an image with a high image area ratio such as a color photographic image, a paper feed failure is further caused. If an untransferred image remains on the photoconductor 1 or the like, a cleaning failure is likely to occur. If the above-mentioned cleaning failures occur frequently, further, if a contact-type charging roller is used as a charging device for charging the photoreceptor 1, the device or the like is contaminated, and the original charging ability can be exhibited. It will disappear. From this point of view, a toner having an average circularity of 0.90 to 0.99, preferably an average circularity of 0.93 to 0.97 and particles having a circularity of less than 0.94 of 10% or less is used. Is preferred.
(Measurement method of toner circularity)
The average circularity of the toner can be measured by a flow type particle image analyzer FPIA-2100 (manufactured by Toa Medical Electronics Co., Ltd.). As a specific measuring method, 0.1 to 0.5 ml of a surfactant, preferably alkylbenzene sulfonate is added as a dispersant to 100 to 150 ml of water from which impure solids have been removed in advance, and further measurement is performed. Add about 0.1-0.5g of sample. The suspension in which the sample is dispersed is obtained by performing dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes and measuring the shape and distribution of the toner with the above apparatus at a dispersion concentration of 3000 to 10,000 / μl. .
(Toner shape factors SF-1 and SF-2)
The toner according to the present feature is characterized in that the shape factor SF-1 is 120 to 180 and the shape factor SF-2 is 120 to 190. The shape factor SF-1 here is a value (parameter) indicating the ratio of the roundness of the shape of the spherical substance, as shown in FIG. 6, and is an elliptical shape formed by projecting the spherical substance on a two-dimensional plane. It is represented by a value obtained by dividing the square of the maximum length of the figure MXLNG by the figure area AREA and multiplying by 100π / 4.
That is, the shape factor SF-1 is expressed by the following equation:
SF-1 = {(MXLNG) ² / AREA} × (100π / 4)
Is defined by
When the value of SF-1 is 100, the shape of the substance becomes a true sphere, and as the value of SF-1 increases, the shape of the substance becomes indefinite.

As shown in FIG. 7, the shape factor SF-2 is a numerical value indicating the ratio of the unevenness of the shape of the substance, and the square of the perimeter PERI of the figure formed by projecting the substance on the two-dimensional plane is represented by the figure area AREA. It is expressed as a value when divided and multiplied by 100 / 4π.
That is, the shape factor SF-2 is expressed by the following equation:
SF-2 = {(PERI) ² / AREA} × (100 / 4π).
When the value of SF-2 is 100, there is no unevenness on the surface of the substance, and as the value of SF-2 increases, the unevenness on the surface of the substance becomes more prominent.

  In this embodiment, a FE-SEM (S-800) manufactured by Hitachi, Ltd. is used, and a toner image is randomly sampled 100 times, and the image information is introduced into an image analysis apparatus (LUSEX3) manufactured by Nireco Corporation for analysis. , Calculated from the above equation.

  The inventors of the present invention have clarified that the transfer efficiency increases when the toner shape approaches the spherical shape as much as possible (both SF-1 and SF-2 approach 100). This is because there is only point contact between the toner particles and the thing (toner particles, image carrier, etc.) in contact with the toner particles due to the shape effect. This is probably because the attracting force (mirror force) is weakened and is easily affected by the transfer electric field.

  On the other hand, when the shape of the toner approaches a spherical shape, it is disadvantageous for mechanical cleaning (such as blade cleaning). As described above, this is because the toner fluidity is increased and the adsorbing force (mirroring force) to the image carrier is weakened so that the toner easily passes through a slight gap between the cleaning member and the image carrier. End up. Therefore, from the viewpoint of cleaning properties, the shape of the toner is somewhat deformed (in the direction in which the value of SF-1 is larger than 100) or uneven (in the direction in which the value of SF-2 is larger than 100) to some extent. It is preferable to have done.

In this embodiment, Dv represents the volume average particle diameter (μm) of the toner, and Dn represents the number average particle diameter (μm) of the toner. The toner used in this embodiment is characterized in that Dv / Dn is 1.05 to 1.30. Dv / Dn is one of the parameters representing the toner particle size distribution.
(Dv / Dn (ratio of volume average particle diameter / number average particle diameter))
The volume average particle diameter (Dv) of the toner is 4 to 8 μm, and the ratio (Dv / Dn) to the number average particle diameter (Dn) is 1.05 to 1.30, preferably 1.10 to 1.25. Some dry toners have the following advantages because the toner particle size distribution is narrow.

  1. A stable image can be formed at all times because a phenomenon such as selective development on the toner particle size surface (toner particles having a (suitable) toner particle size corresponding to the image pattern are selectively developed) hardly occurs. Can do.

  2. When a toner recycling system is provided, a large amount of small-sized toner particles that are difficult to transfer are recycled in quantity. However, since the toner particle size distribution is originally narrow, it is difficult to receive the above-described effects. A stable image can always be formed.

  3. In the two-component developer, even if the toner balance for a long time is performed, the fluctuation of the toner particle diameter in the developer is reduced, and good and stable developability can be obtained even in the long-term stirring in the developing device.

  4). Even when used as a one-component developer, even if the balance of the toner is performed, the fluctuation of the toner particle diameter is reduced, the filming of the toner on the developing roller, and a blade for thinning the toner The toner was not fused to a member such as the above, and good and stable developability and an image were obtained even in the long-term use (stirring) of the developing device.

  In general, it is said that the smaller the particle size of the toner, the more advantageous it is to obtain a high-resolution and high-quality image, but it is disadvantageous for transferability and cleaning properties. is there. Further, when the volume average particle diameter is smaller than the range of the present embodiment, in the case of the two-component developer, the toner is fused to the surface of the carrier during long-term stirring in the developing device 5, and the charging ability of the carrier is reduced. When used as a developer, toner filming on the developing roller and toner fusion to a member such as a blade for thinning the toner are likely to occur. In addition, these phenomena are the same for the toner having a fine powder content higher than the range of the present embodiment.

Conversely, when the toner particle diameter is larger than the range of this embodiment, it becomes difficult to obtain a high-resolution and high-quality image, and when the toner balance in the developer is performed, In many cases, the variation of the particle size becomes large. It was also clarified that the same applies when the volume average particle diameter / number average particle diameter is larger than 1.30. Further, when the volume average particle size / number average particle size is smaller than 1.05, there are preferable aspects from the viewpoint of stabilizing the behavior of the toner and uniformizing the charge amount, but the fine line portion is developed with small size particles. On the other hand, since it becomes difficult to separate the functions depending on the toner particle size, such as developing a solid image centering on large-size particles, it is not preferable.
(Measurement method related to toner particle size)
Examples of the measuring device for the particle size distribution of toner particles by the Coulter counter method include Coulter Counter TA-II and Coulter Multisizer II (both manufactured by Coulter). The measurement method is described below.

  First, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of an aqueous electrolytic solution. Here, the electrolytic solution is a solution prepared by preparing a 1% NaCl aqueous solution using primary sodium chloride. For example, ISOTON-II (manufactured by Coulter) can be used. Here, 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the measurement device is used to measure the volume and number of toner particles or toner using a 100 μm aperture as an aperture. Volume distribution and number distribution are calculated. From the obtained distribution, the volume average particle diameter (Dv) and the number average particle diameter (Dn) of the toner can be obtained.

  As channels, 2.00 to less than 2.52 μm; 2.52 to less than 3.17 μm; 3.17 to less than 4.00 μm; 4.00 to less than 5.04 μm; 5.04 to less than 6.35 μm; 6 Less than 35 to 8.00 μm; less than 8.00 to less than 10.08 μm; less than 10.08 to less than 12.70 μm; less than 12.70 to less than 16.00 μm; less than 16.00 to less than 20.20 μm; Uses 13 channels of less than 40 μm; 25.40 to less than 32.00 μm; 32.00 to less than 40.30 μm, and targets particles having a particle size of 2.00 μm to less than 40.30 μm.

1 is a schematic central sectional view showing an internal configuration of an image forming apparatus capable of duplex printing to which the present invention is applied. FIG. 2 is a simplified diagram showing an arrangement of image carrier belts in FIG. 1. It is sectional drawing which shows the structure of an image carrier belt. It is an enlarged view which shows one main part for image formation. It is an enlarged view showing the other main part for image formation. FIG. 7 is an enlarged view for explaining a toner shape factor SF-1. FIG. 6 is an enlarged view for explaining a toner shape factor SF-2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 1st image carrying unit 21 1st image carrying belt 21a Base | substrate 21b Elastic layer 28 1st transfer means 30 2nd image carrying unit 31 2nd image carrying belt 31a Base | substrate 31b Elastic layer 34 2nd transfer means 42A, 45 Conveying means 43A Recording medium conveying path 47 Polarity converting means 60 Heat fixing device 80 (Y, C, M, K) First image forming unit 81 (Y, C, M, K) Second image forming unit 95 Control means P Recording medium

Claims (11)

A first image carrying unit capable of carrying a first image formed by the first image forming unit using a developer on a first image carrying belt;
A second image carrying unit capable of carrying a second image formed by the second image forming unit using a developer on the second image carrying belt;
First and second transfer means for transferring the first and second images carried by the first and second image carrying units to both sides of the recording medium;
A recording medium conveyance path including conveyance means for supplying and conveying the recording medium between the first and second transfer means;
An image forming apparatus comprising a heat fixing device for fixing the first and second images transferred on both sides of the recording medium,
The first image bearing belt and the second image bearing belt each have an elastic layer of 50 μm to 500 μm,
An image forming apparatus, wherein the first and second transfer units simultaneously transfer toners having different signs onto both sides of the recording medium.   2. The image forming apparatus according to claim 1, wherein the first image carrying belt and the second image carrying belt have polyimide as a base and the elastic layer is provided on the base. A first image carrying unit capable of carrying a first image formed by the first image forming unit using a developer on a first image carrying belt;
A second image carrying unit capable of carrying a second image formed by the second image forming unit using a developer on the second image carrying belt;
First and second transfer means for transferring the first image and the second image carried by the first and second image carrying units to both surfaces of the recording medium;
A recording medium conveying path including conveying means for supplying and conveying the recording medium between the first and second transfer means;
An image forming apparatus comprising a heat fixing device for fixing the first and second images transferred on both sides of the recording medium,
The first image bearing belt and the second image bearing belt each have an elastic layer of 50 μm to 500 μm,
After the second image formed by the second image forming unit is carried on the second image carrying belt, the polarity is converted by the polarity conversion unit before transfer by the second transfer unit, and the second image forming unit An image forming apparatus wherein transfer is performed simultaneously on the front and back of a recording medium in a transfer means.   4. The image forming apparatus according to claim 3, wherein the first image carrying belt and the second image carrying belt have polyimide as a base, and the elastic layer is provided on the base.   4. The image forming apparatus according to claim 3, wherein the polarity conversion by the polarity conversion means is performed in a non-contact manner. A first image carrying unit capable of carrying a first image formed by the first image forming unit using a developer on a first image carrying belt;
A second image carrying unit capable of carrying a second image formed by the second image forming unit using a developer on the second image carrying belt;
First and second transfer means for simultaneously transferring the first image and the second image carried by the first and second image carrying units to both surfaces of a recording medium;
A recording medium conveyance path including conveyance means for supplying and conveying the recording medium between the first and second transfer means;
An image forming apparatus comprising a heat fixing device for fixing the first and second images transferred on both sides of the recording medium,
An image forming apparatus comprising control means for controlling the operation of the first image carrying unit or the second image carrying unit in accordance with operation information of the apparatus.   7. The image forming apparatus according to claim 6, wherein the operation information is abnormality information of the first image carrying unit and the second image forming unit.   8. The image forming apparatus according to claim 7, wherein the abnormality information is out of toner used for the first image carrying unit and the second image forming unit.   The image forming apparatus according to claim 1, wherein the developer includes a toner, and the average circularity of the toner is 0.90 to 0.99.   9. The developer according to claim 1, wherein the developer includes a toner, and the toner has a shape factor SF-1 of 120 to 180 and a shape factor SF-2 of 120 to 190. Image forming apparatus.   2. The developer according to claim 1, wherein the developer has a toner, and Dv / Dn is 1.05 to 1.30, where Dv is a volume average particle diameter of the toner and Dn is a number average particle diameter of the toner. Or an image forming apparatus according to any one of items 8 to 8;

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